Wikipedia - Benutzerbeiträge [de]

Black Castle (County Wicklow)

2008-06-23T15:22:42Z

Ferdiaob: Reverted 1 edit by 62.77.166.81; Yes but the article you link to references the island, not the country which is what the sentence references. (TW)

{{dablink|This article is about the town in Ireland. For the county, see [[County Wicklow]].}}
{{Infobox Irish Place|
name = Wicklow |
gaeilge = Cill Mhantáin |
crest image = |
motto = |
map image = Ireland map County Wicklow Magnified.png |
pin coords = left: 90px; top: 63px |
north coord = 52.9779 |
west coord = 6.033 |
irish grid = T312940 |
area = |
elevation = 69 m |
province = [[Leinster]] |
county = [[County Wicklow]] |
town pop = 6,930 |
rural pop = 3,140 |
census yr = 2006 |
web = www.wicklow.ie |
|}}
'''Wicklow''' ({{Irish place name|Cill Mhantáin|Church of the Toothless One}}) is the county seat of [[County Wicklow]] in [[Republic of Ireland|Ireland]]. Located south of the capital [[Dublin]] on the east coast of the island, it has a population of 10,070<ref>[http://www.cso.ie/census/documents/census2006_Table_7_and_12.pdf Population CSO 2006]</ref> according to the 2006 census.

The town lies off the [[N11 road|N11]] [[Roads in Ireland#National Primary Routes|route]] between Dublin and [[Wexford]]. Wicklow is also connected to the [[Rail transport in Ireland|rail network]] with Dublin commuter services now extending to the town. Additional services connect with [[Arklow]], Wexford and [[Rosslare]], a main ferry port. There is also a commercial port, mainly importing timber.

== History ==
Local history contends that the town of Wicklow was founded by the [[Vikings]], probably around [[870|870 AD]]. The name 'Wicklow' comes from ''Vikinglow'', meaning ''Meadow of the Vikings'', or more likely ''Wykynlo'', meaning ''Viking Loch''. However, given the town's natural harbour and rich agricultural surrounds, it is not surprising that the area was an established settlement prior to the 9th century.<ref name=aa>{{cite book
| title = The illustrated road book of Ireland
| publisher = [[Automobile Association]]
| year = 1970}}</ref>

The origin of the [[Irish language|Irish]] name ''Cill Mhantáin'' has an interesting folklore of its own. [[Saint Patrick]] is said to have attempted to land on Travailahawk beach, to the south of the harbour. Hostile locals attacked the landing party causing one of the Saint's party to lose his front teeth. Manntach (toothless one), as he became known was undeterred and returned to the town, eventually founding a church. Hence ''Cill Mhantáin'', meaning ''Church of the Toothless One''. There is however no evidence, material or written, that such a local holy man ever existed, and the name ''Cill Mhantáin'' could in theory be assigned as a toponym, suggesting a chapel overlooking the rather gap-toothed topographical shape of the local harbour.{{Fact|date=February 2007}}

The English-language 'Wicklow' placename bears no relation to the original Irish ''Cill Mhantáin'' (''Church of Mantáin''). The [[Normans]], who came to dominate the area, preferred the non-[[Goidelic languages|Gaelic]] placename. The Norman influence can still be seen today in some of the town's place and family names.

After the Norman invasion, Wicklow was granted to Maurice FitzGerald who set about building the 'Black Castle', a land-facing fortification that lies ruined on the coast immediately south of the harbour.

The surrounding County of Wicklow is rich in [[bronze age]] monuments. The oldest existing settlement in the town is the [[Franciscan]] Abbey, located at the west end of Main Street, within the gardens of the local [[Roman Catholic]] parish grounds.

Other notable buildings include the [[Town Hall]] and the [[Gaol]], built in [[1702]] and recently renovated as a heritage centre and tourist attraction. The East Breakwater, arguably the most important building in the town, was built in the early 1880s by Wicklow Harbour Commissioners. The architect was William George Strype and the builder was John Jackson of Westminster. The North Groyne was completed by about 1909 - John Pansing was the designer and Louis Nott of Bristol the builder. The Gaol was a place of [[execution]] up to the end of the 19th century and it was here that [[Billy Byrne]], a leader of the [[1798 rebellion]], met his end in [[1799]]. He is commemorated by a statue in the town square. The gaol closed in 1924 and is today a
tourist attraction with living displays and exhibits.<ref>{{cite book
| title = Illustrated guide to Ireland
| author = S Shepherd et al
| publisher = [[Reader's Digest]]
| year = 1992}}</ref>

At Fitzwilliam Square in the centre of Wicklow town is an obelisk commemorating the career of [[Robert Halpin|Captain Robert Halpin]], commander of the telegraph cable ship [[SS Great Eastern|Great Eastern]] who was born in Wicklow in 1836.<ref name=aa/>

[[Image:IMGWicklowHarbour 4256w.jpg|400px|thumb| Wicklow Harbour]]

== Geography ==
Wicklow town forms a rough semicircle around Wicklow harbour. To the immediate North lies 'The Murrough', a popular grassy walking area beside the sea, and the eastern coastal strip. The land rises into rolling hills to the West. The dominant feature to the south is the rocky headlands of Bride's Head and '[[Wicklow Head]]', the easternmost mainland point of the Republic of Ireland.

== A changing town ==
Since 1995, the town has undergone significant change and expansion reflecting the simultaneous growth in the Irish economy. Considerable residential development has taken place to the southwest of the town along Marlton Road (L29A). More recently, housing developments have been concentrated to the northwest of the town towards the neighbouring village of [[Rathnew]]. The completion of the [[Ashford, County Wicklow|Ashford]]/[[Rathnew]] bypass in [[2004]] has meant that Wicklow is now linked to the capital, Dublin, lying 42km to the north, by [[N11 road|dual carriageway or motorway]]. These factors have led to a steady growth in population of Wicklow and its surrounding townlands while its importance as a commuter town to Dublin increases.

==References==
{{reflist}}

==Bibliography==
* Cleary, J and O'Brien, A (2001) ''Wicklow Harbour: A History'', Wicklow Harbour Commissioners

==See also==
*[[County Wicklow]]
*[[List of towns in the Republic of Ireland]]

==External links==
*[http://www.visitwicklow.ie/towns/wicklow_town/index.htm Wicklow at Wicklow County Tourism]
*[http://www.wicklowchamber.ie/ Wicklow Chamber of Commerce]
*[http://www.wicklow.com/walk/ History of Wicklow Town in MP3 format]

{{County Wicklow}}

[[Category:Towns and villages in County Wicklow]]
[[Category:Port cities and towns in the Republic of Ireland]]
[[Category:County Wicklow]]
[[Category:Lifeboats in the Republic of Ireland]]

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Roscommon Castle

2008-06-23T15:21:44Z

Ferdiaob: Reverted good faith edits by 62.77.166.81; Yes but the article you link to references the island, not the country which is what the sentence references. (TW)

{{otheruses2|Roscommon}}

{{Infobox Irish Place|
name = Roscommon |
gaeilge = Ros Comáin |
crest image = Logo-contea-Roscommon.png |
motto = Constans Hiberniae Cor |
map image = Ireland map County Roscommon Magnified.png |
pin coords = left: 60px; top: 70px |
north coord = 53.6333 | west coord = 8.1833 | irish grid = M879648 |
area = 2463 sq km |
elevation = 80 m |
province = [[Connacht]] |
county = [[County Roscommon]] |
town pop = <br />4,489 | rural pop = 4,168|
census yr = 2002 and Prelim. Census 2006|
web = |
|}}
'''Roscommon''' ({{lang-ga|Ros Comáin}}) is the [[county town]] of [[County Roscommon]] in the [[Republic of Ireland]].

==History==
The name Roscommon is derived from [[St. Coman]], who built a monastery there in the fifth century. The woods near the monastery became known as St. Coman's Wood, or Ros Comáin in Irish. This was later anglicised to Roscommon.

This attractive and busy [[market town]] once had a [[executioner|hangwoman]] called Lady Betty – as well as a [[Dominican Order|Dominican]] [[Friary]], founded in [[1253]] by Felim O'Connor, King of [[Connacht]] (see [[Abbeys and priories in the Republic of Ireland]]). [[Roscommon Castle]], built in [[1269]], is an [[Normans|Anglo-Norman]] fortress. Roscommon is situated 145 km (90 mi) west of [[Dublin]] and 75 km (47 mi) east of [[Galway]] and 32 km (20 mi) west of [[Athlone]].

==Amenities==
[[Image:Ros_Comáin_1.jpg|280px|left|thumb|Bank of Ireland Roscommon. (Formerly the Harrison Hall), 4 May 2005.]]
Roscommon Golf Club was founded in 1904, the course, set in parklands filled with mature sycamore, beech, whitethorn trees and ash trees, was extended to eighteen holes in 1996 and now measures 6,390 metres (6,900 yards).<ref>{{cite web | title= Roscommon Golf Course | work=GolfMaster | url=http://www.golfmaster.ie/showdetail.asp?type=crs&id=265 | accessdate=18/09/07}}</ref> Dr [[Douglas Hyde]] park Roscommon is an important [[GAA]] venue in Ireland and is home to the county footballers and Roscommon Gaels club. A horse racing course is situated approximately 1.6 km (1 mi) from the town centre, the track itself is an oblong right-handed track 2 km (1.25 mi) in length, the course has stabling for up to 95 horses. Roscommon has a leisure centre which opened early 2002 and has a 25m deck level pool with a learner swimming pool and spectator gallery and fully equipped gymnasium, situated next to the swimming pool is St Comans handball club established in 1930 which has produced many All-Ireland winning handballers. Moate park approximately 1.6 km (1 mi) from the town centre is a woodland area covering several miles and is popular with walkers.

==Transport==
[[Roscommon railway station]] opened on [[13 February]] [[1860]].<ref>{{cite web | title=Roscommon station | work=Railscot - Irish Railways | url=http://www.railscot.co.uk/Ireland/Irish_railways.pdf | accessdate=2007-09-2007}}</ref> Roscommon is situated near the major road networks in Ireland. Regular bus services to other major towns can be taken from Roscommon square.

==See also==

*[[List of towns in the Republic of Ireland]]
*[[Market Houses in the Republic of Ireland]]
*[[Lord Roscommon]]

==External links==
*[http://www.newadvent.org/cathen/13190a.htm Roscommon] - [[Catholic Encyclopedia]] article
*[http://www.bandsinireland.com Roscommon Bands]

==References==
{{reflist}}

{{coord|53.6333|-8.1833|region:IE_type:city|display=title}}

[[Category:Towns and villages in County Roscommon]]
[[Category:Horse racing venues in the Republic of Ireland]]
[[Category:County towns in the Republic of Ireland]]

{{Roscommon-geo-stub}}

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Mike Crapo

2008-01-17T14:33:15Z

Ferdiaob: Reverted 2 edits by 216.56.5.2 identified as vandalism to last revision by VoABot II. (TW)

{{Infobox Senator
| name = Mike Crapo
| nationality = American
| image name = Mike Crapo official photo.jpg
| jr/sr=Junior Senator
| state=[[Idaho]]
| party = [[Republican Party (United States)|Republican]]
| term_start = [[January 6]], [[1999]]
| alongside = Larry Craig
| preceded = [[Dirk Kempthorne]]
| succeeded = [[Incumbent]] ([[2011]])
| date of birth = {{birth date and age|1951|05|20}}
| place of birth = {{flagicon|Idaho}} [[Idaho Falls, Idaho|Idaho Falls]], [[Idaho]]
| dead = alive
| date of death =
| place of death =
| spouse = Susan Crapo
| profession=[[Attorney]]
| religion = [[The Church of Jesus Christ of Latter-day Saints]]
| state2=Idaho
| district2=[[Idaho's 2nd congressional district|2nd]]
| term_start2 = [[January 5]], [[1993]]
| term_end2 = [[January 6]], [[1999]]
| preceded2=[[Richard H. Stallings]]
| succeeded2=[[Mike Simpson]]
| signature =
}}

'''Michael Dean "Mike" Crapo''' (pronounced "Cray-poe") (born [[May 20]], [[1951]]) is the junior [[United States Senate|United States Senator]] from Idaho. He is a member of the [[Republican Party (United States)|Republican Party]].

==Education and early career==
Crapo was born in [[Idaho Falls, Idaho|Idaho Falls]], [[Idaho]] to Melba Olsen and George Lavelle Crapo.<ref>http://freepages.genealogy.rootsweb.com/~battle/senators/crapo.htm</ref> He is distantly related to [[Henry Howland Crapo]], who served as [[Governor of Michigan]] from 1865 to 1869, and [[William Crapo Durant]], Henry's grandson, who founded [[General Motors]]. Mike Crapo and Henry Crapo are first cousins, five times removed, as Henry's father, Jesse Crapo, and Mike's great-great-great grandfather, Charles Crapo, were brothers. Crapo earned a [[Bachelor of Arts|B.A.]] from [[Brigham Young University]] in 1973 and [[Juris Doctor|J.D.]] from the [[Harvard Law School]] in 1977. He served for one year as clerk to Judge [[James M. Carter]], [[United States Court of Appeals]], [[Ninth Circuit]] and then returned to Idaho to become a lawyer. While practicing law in [[Idaho Falls, Idaho]] in the 1980s, he was active in the Republican Party's campaigns for seats in the state legislature.

Crapo was elected to the state senate in 1984. He was a member of the state senate from 1985 until 1992, serving as Senate President Pro Tempore from 1988 to 1992, when he was elected to the [[United States House of Representatives]]. He was a member of the House from 1993 until 1999, being re-elected in 1994 and 1996.

He married Susan Diane Hasleton in June [[1974]]; the couple has five children: Michelle, Brian, Stephanie, Lara and Paul.

==US Senate==
Crapo was elected to the United States Senate in [[U.S. Senate election, 1998|1998]], gaining the seat of Republican [[Dirk Kempthorne]], who ran for governor and was elected to that position. In his Senate bid, as in his House campaigns, his campaign signs had a [[macron]] placed over the "a" in his name ("Cray-poe") to hint at the correct pronunciation.

Crapo was re-elected in [[U.S. Senate election, 2004|2004]] with 99% of the vote, with the other 1% going to write-in candidates. He was the only Senate candidate in 2004 to run unopposed on the ballot. Some Republicans want him to be appointed to a high position in the Senate Republican leadership because his seat is considered one of the 'safest' in the entire Senate. Senator [[Harry Reid]], then the Democratic [[Senate Minority Leader]] of [[Nevada]], also suggested Crapo be considered for the vacancy on the [[United States Supreme Court]] occasioned by Justice [[Sandra Day O'Connor|Sandra Day O'Connor's]] retirement announcement.

In the 110th Congress, Crapo currently serves on the following Senate Committees: Agriculture; Banking, Housing and Urban Development; Budget; and Finance. He co-chairs the Senate Nuclear Caucus, the Canada-U.S. Interparliamentary Group (IPG); the COPD (Chronic Obstructive Pulmonary Disease) Caucus, which he also founded; and the Congressional Sportsmen's Caucus.

==Environmental record==
{{cleanup-sect|date=December 2007}} 
Idaho has a high proportion of public lands (approximately 64%), and as such Crapo's environmental record has come under scrutiny. He has introduced S. 700, legislation to update and improve conservation incentives for landowners to protect endangered and threatened species through tax benefits. The legislation is supported by a broad array of prominent environmental advocacy organizations and outdoor recreationists; a listing of those groups is available at http://crapo.senate.gov/issues/cresa/support_letters.cfm. This bipartisan, widely-supported legislation has twice been approved by the Senate Finance Committee.

Two environmental initiatives Crapo has sponsored or promoted continue that collaborative approach. He sponsored a local working group partnership in Owyhee County, Idaho, to protect and preserve sensitive ecological and riverine areas in the county while ensuring the cooperation of landowners and grazers in the area. The Owyhee Initiative working group brings together local tribal members, ranchers, recreators, land managers, environmentalists, and county leaders and the process has been endorsed by editorials in local papers, including the Boise-based [[Idaho Statesman]] newspaper. Another collaboration promoted by Crapo is the Elk Cooperative, a loose working group of tribal members, wildlife officials, and recreators to identify plans that preserve stable populations of elk in North-central Idaho.

An effort to assist small communities confronting environmental problems is another project Crapo has undertaken. Project SEARCH (Special Environmental Assistance for the Regulation of Communities and Habitat) has been approved in several Congresses, most recently authorized in the 2002 Farm Bill. It provides grants to small communities, to assist rural communities throughout the country with planning and engineering grants for environmental infrastructure projects necessary to meet the requirements of water and wastewater regulations.

Crapo partnered with the Environmental Protection Agency to provide funding and technical assistance to the Coeur d'Alene Basin Planning Commission, a partnership of state, local, community, and federal officials charged with implementing restoration of formerly-contaminated Superfund areas in the Silver Valley of North Idaho.

However, in 2006, Crapo was given the lowest possible score (0%) by the [[League of Conservation Voters]] for his voting record in the Senate. This followed his score of 5% in 2005 to bring his lifetime score down to 4%. The LCV uses selected set of votes to determine the scoring for its yearly rating. Reasons for the low score include his votes for offshore drilling, for [[Arctic National Wildlife Refuge|arctic refuge]] drilling, against funding to help "low-income families insulate and weatherize their homes", against funding for the environment and natural resources, against independent review of [[Army Corps of Engineers]] projects, and for having the Army Corps of Engineers review themselves.<ref>{{cite web | url=http://www.lcv.org/images/client/pdfs/LCV_2006_Scorecard_final.pdf | title=National Environmental Scorecard | publisher=[[League of Conservation Voters]] | date=[[2006]] | accessdate=2007-09-03}}</ref>

==Personal life==
Crapo was diagnosed with [[prostate cancer]] in 1999 and underwent a radical prostectomy in January 2000. While he had a full recovery and was declared cancer-free at that time, prostate cancer recurred in 2005, and he underwent a series of radiation treatments. His experience led him to become active in advocating for early detection tests for cancer and other treatable diseases.

Crapo is an [[Eagle Scout (Boy Scouts of America)|Eagle Scout]], awarded in 1966, and was awarded the [[Distinguished Eagle Scout Award]] (DESA) in 2000. He is a member of [[The Church of Jesus Christ of Latter-day Saints]].

==Electoral history==

{| class="wikitable" style="margin:0.5em ; font-size:95%"
|+ {{ushr|Idaho|2|}}: Results 1992–1996<ref name="clerkresults">{{cite web |url=http://clerk.house.gov/member_info/electionInfo/index.html |title=Election Statistics |accessdate=2007-08-08 |publisher=Office of the Clerk of the House of Representatives }}</ref>
!|Year
!
!|Democrat
!|Votes
!|Pct
!
!|Republican
!|Votes
!|Pct
!
!|3rd Party
!|Party
!|Votes
!|Pct
!
!|3rd Party
!|Party
!|Votes
!|Pct
!
|-
|[[U.S. House election, 1992|1992]]
|
|{{Party shading/Democratic}} |{{nowrap|J. D. Williams}}
|{{Party shading/Democratic}} align="right" |81,450
|{{Party shading/Democratic}} |35%
|
|{{Party shading/Republican}} |'''Mike Crapo'''
|{{Party shading/Republican}} align="right" |139,783
|{{Party shading/Republican}} |61%
|
|{{Party shading/Independent}} |Steven L. Kauer
|{{Party shading/Independent}} |[[Independent (politician)|Independent]]
|{{Party shading/Independent}} align="right" |4,917
|{{Party shading/Independent}} align="right" |2%
|
|{{Party shading/Independent}} |David William Mansfield
|{{Party shading/Independent}} |[[Independent (politician)|Independent]]
|{{Party shading/Independent}} align="right" |3,807
|{{Party shading/Independent}} align="right" |2%
|
|-
|[[U.S. House election, 1994|1994]]
|
|{{Party shading/Democratic}} |{{nowrap|Penny Fletcher}}
|{{Party shading/Democratic}} align="right" |47,936
|{{Party shading/Democratic}} |25%
|
|{{Party shading/Republican}} |'''Mike Crapo'''
|{{Party shading/Republican}} align="right" |143,593
|{{Party shading/Republican}} |75%
|
|
|
|
|
|
|
|
|
|
|
|-
|[[U.S. House election, 1996|1996]]
|
|{{Party shading/Democratic}} |{{nowrap|John D. Seidl}}
|{{Party shading/Democratic}} align="right" |67,625
|{{Party shading/Democratic}} |29%
|
|{{Party shading/Republican}} |'''Mike Crapo'''
|{{Party shading/Republican}} align="right" |157,646
|{{Party shading/Republican}} |69%
|
|{{Party shading/Independent}} |John Butler
|{{Party shading/Independent}} |[[Natural Law Party (United States)|Natural Law]]
|{{Party shading/Independent}} align="right" |3,977
|{{Party shading/Independent}} align="right" |2%
|
|
|
|
|
|
{{end box}}

{| class="wikitable" style="margin:0.5em ; font-size:95%"
|+ [[List of United States Senators from Idaho|Idaho Senator (Class III)]] results: 1998–2004<ref name="clerkresults">{{cite web |url=http://clerk.house.gov/member_info/electionInfo/index.html |title=Election Statistics |accessdate=2007-08-08 |publisher=Office of the Clerk of the House of Representatives }}</ref>
!|Year
!
!|Democrat
!|Votes
!|Pct
!
!|Republican
!|Votes
!|Pct
!
!|3rd Party
!|Party
!|Votes
!|Pct
!
|-
|[[U.S. Senate election, 1998|1998]]
|
|{{Party shading/Democratic}} |[[Bill Mauk]]
|{{Party shading/Democratic}} align="right" |107,375
|{{Party shading/Democratic}} |28%
|
|{{Party shading/Republican}} |'''[[Mike Crapo]]'''
|{{Party shading/Republican}} align="right" |262,966
|{{Party shading/Republican}} |70%
|
|{{Party shading/Independent}} |George J. Mansfeld
|{{Party shading/Independent}} |[[Natural Law Party (United States)|Natural Law]]
|{{Party shading/Independent}} align="right" |7,833
|{{Party shading/Independent}} align="right" |2%
|
|-
|[[U.S. Senate election, 2004|2004]]
|
|{{Party shading/Democratic}} |''(no candidate)''
|{{Party shading/Democratic}} align="right" |
|{{Party shading/Democratic}} |
|
|{{Party shading/Republican}} |'''[[Mike Crapo]]'''
|{{Party shading/Republican}} align="right" |499,796
|{{Party shading/Republican}} |99%
|
|{{Party shading/Independent}} |[[Scott McClure|Scott F. McClure]]
|{{Party shading/Independent}} |Write-in
|{{Party shading/Independent}} align="right" |4,136
|{{Party shading/Independent}} align="right" |1%
|
{{end box}}

==Footnotes==
{{reflist}}

== External links ==
*[http://crapo.senate.gov/ United States Senator Mike Crapo], Senate site
{{CongLinks | congbio = c000880 | fec = S8ID00027 | opensecrets = N00006267 | votesmart = H1002103 | ontheissuespath = Senate/Michael_Crapo.htm}}
{{s-start}}
{{s-par|us-hs}}
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| state=Idaho
| district=2
| before=[[Richard H. Stallings]]
| years=1993 – 1999
| after=[[Mike Simpson]]}}
{{s-par|us-sen}}
{{U.S. Senator box
| before=[[Dirk Kempthorne]]
| state=Idaho
| class=3
| start=1999
| alongside=[[Larry Craig]]}}
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{{DEFAULTSORT:Crapo, Mike}}
[[Category:1951 births]]
[[Category:Living people]]
[[Category:Idaho lawyers]]
[[Category:Idaho State Senators]]
[[Category:Members of the United States House of Representatives from Idaho]]
[[Category:United States Senators from Idaho]]
[[Category:Harvard Law School alumni]]
[[Category:Brigham Young University alumni]]
[[Category:American Latter Day Saints]]

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[[Category:Distinguished Eagle Scouts]]

Bau des World Trade Centers

2007-07-10T00:52:36Z

Ferdiaob: /* References */ minor reformat

{{for|the post-9/11 rebuilding and ongoing construction at the World Trade Center site|World Trade Center site}}
[[Image:World trade center new york city construction flickr.png|thumb|right|250px|View of the World Trade Center's construction from across the [[Hudson river]]]]
The '''building of the [[World Trade Center]]''' started as a post-[[World War II]] [[urban renewal]] project, spearheaded by [[David Rockefeller]], to help revitalize [[Lower Manhattan]]. The project was developed by the [[Port Authority of New York and New Jersey]], which hired architect [[Minoru Yamasaki]] who came up with the specific idea for twin towers. After extensive negotiations, the [[New Jersey]] and [[New York|New York State]] governments, which oversee the Port Authority, agreed to support the World Trade Center project at the [[Radio Row]] site on the lower-west side of [[Manhattan]]. To make the agreement acceptable to New Jersey, the Port Authority agreed to take over the bankrupt Hudson & Manhattan Railroad (renamed as [[Port Authority Trans-Hudson|PATH]]), which brought commuters from New Jersey to the Lower Manhattan site.

The towers were designed as framed tube structures, which provided tenants with open floor plans, uninterrupted by columns or walls. This was accomplished using numerous, closely-spaced perimeter columns to provide much of the strength to the structure, along with gravity load shared with the core columns. The [[elevator]] system, which made use of [[sky lobby|sky lobbies]] and a system of express and local elevators, allowed substantial floor space to be freed up for use as office space by making the structural core smaller. The design and construction of the World Trade Center twin towers involved many other innovative techniques, such as the [[slurry wall]] for digging the [[Foundation (architecture)|foundation]], and [[wind tunnel]] experiments. Construction of the World Trade Center's North Tower began in August 1968, and the South Tower in 1969. Extensive use of prefabricated components helped to speed up the construction process. The first tenants moved into the North Tower in December 1970 and into the South Tower in January 1972. Four other, low-level buildings were constructed as part of the World Trade Center in the 1970s, and a [[7 World Trade Center|seventh]] building was constructed in the mid-1980s.

==Planning==
In 1942, [[Austin J. Tobin]] became the Executive Director of the [[Port Authority of New York and New Jersey|Port Authority]], beginning a 30-year career during which he would oversee the planning and development of the World Trade Center.<ref name="Doig-chap1">{{cite book |last=Doig |first=Jameson W. |title=Empire on the Hudson |year=2001 |publisher=Columbia University Press |chapter=Chapter 1}}</ref> The concept of establishing a "[[World Trade Center (disambiguation)|world trade center]]" was conceived during the post-[[World War II]] period, when the [[United States]] thrived economically and international trade was increasing. In 1946, the [[New York State Legislature]] passed a bill that called for a "world trade center" to be established.<ref name="nyt-07061946">{{cite news |title=Dewey Picks Board for Trade Center |publisher=The New York Times |date=July 6, 1946}}</ref> The World Trade Corporation was set up and a board appointed by New York Governor [[Thomas E. Dewey]] to develop plans for the project.<ref name="nyt-07061946"/> Architect [[John Eberson]] and his son Drew devised a plan that included 21 buildings over a ten-block area, at an estimated cost of $150 million.<ref>{{cite news |title=Plans are Tabled for Trade Center |author=Crisman, Charles B. |publisher=The New York Times |date=November 10, 1946}}</ref> In 1949, the World Trade Corporation was dissolved by the New York State Legislature, and plans for a "world trade center" were put on hold.<ref>{{cite news |title=Lets Port Group Disband, State Senate for Dissolution of World Trade Corporation |publisher=The New York Times |date=March 11, 1949}}</ref>
===Original plans===
[[Image:East-side-wtc.png|thumb|right|300px|Architect's model for the proposed World Trade Center on the East River]]
During the post-war period, economic growth was concentrated in [[Midtown Manhattan]], in part stimulated by the [[Rockefeller Center]], which was developed in the 1930s. Meanwhile, Lower Manhattan was left out of the [[Boom and bust|economic boom]]. One exception was the construction of [[One Chase Manhattan Plaza]] in the [[Financial District, Manhattan|Financial District]], by [[David Rockefeller]], who led [[urban renewal]] efforts in Lower Manhattan.<ref name="Gillespie-chap1">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |chapter=Chapter 1 |publisher=Rutgers University Press}}</ref> In 1958, Rockefeller established the Downtown-Lower Manhattan Association (DLMA), which commissioned [[Skidmore, Owings and Merrill]] to draw up plans for revitalizing [[Lower Manhattan]]. The plans, made public in 1960, called for a World Trade Center to be built on a 13 [[acre]] (5.25 [[Hectare|ha]]) site along the [[East River]], from [[Old Slip]] to [[Fulton Street (Manhattan)|Fulton Street]] and between [[Water Street (Manhattan)|Water Street]] and [[South Street (Manhattan)|South Street]].<ref name="Levinson">{{cite book|last=Levinson |first=Leonard Louis| title=Wall Street| year=1961| publisher=Ziff Davis Publishing| location=New York| page=346}}</ref><ref name="nyt-01271960">{{cite news |title=A World Center of Trade Mapped Off Wall Street |date=January 27, 1960 |publisher=The New York Times |author=Grutzner, Charles}}</ref> The complex would include a 900 [[Foot (unit of length)|foot]] (275 [[Metre|m]]) long [[Convention center|exhibition hall]], and a 50-70 story building, with some of its upper floors used as a hotel.<ref>{{cite book |title=Men of Steel: The Story of the Family That Built the World Trade Center |author=Koch, Karl III |publisher=Three Rivers Press |year=2002 |pages=p. 173}}</ref> Other amenities would include a theater, shops, and restaurants.<ref name="dlma-plan">{{cite news |title=Text of Trade Center Report by the Downtown-Lower Manhattan Association |publisher= The New York Times |date=January 27, 1960}}</ref> The plan also called for a new [[securities]] exchange building, which Downtown-Lower Manhattan Association hoped would house the [[New York Stock Exchange]].<ref name="nyt-01271960"/>

David Rockefeller suggested that the Port Authority would be a logical choice for taking on the project.<ref name="nyt-01271960"/> Rockefeller argued that the Trade Center would provide great benefits in facilitating and increasing volume of international commerce coming through the Port of New York.<ref name="dlma-plan"/> Given the importance of [[New York City]] in global commerce, Port Authority director Austin J. Tobin remarked that the proposed project should be ''the'' World Trade Center, and not just ''a'' "world trade center".<ref>{{cite news |title=Tobin Says Proposed Center Should Be World's Best |publisher=The New York Times |date=May 5, 1960}}</ref> After a year-long review of the proposal, the Port Authority formally backed the project on [[March 11]], [[1961]].<ref>{{cite news |title=355 Million World Trade Center Backed by Port Authority Study |publisher=The New York Times |date=March 12, 1961}}</ref>

===Agreement===
[[Image:Wtc locator map.png|thumb|right|300px|Location of World Trade Center and originally proposed site]]
The State of New York and New Jersey also needed to approve the project, given their control and oversight role of the Port Authority. Objections to the plan came from [[New Jersey]] Governor [[Robert B. Meyner]], who resented that [[New York]] would be getting this $335 million project.<ref name="Gillespie-chap1"/> Meanwhile, ridership on New Jersey's [[Hudson and Manhattan Railroad]] (H&M) had declined substantially from a high of 113 million riders in 1927 to 26 million in 1958, after new automobile tunnels and bridges opened across the [[Hudson River]].<ref>{{cite book |title=Rails Under the Mighty Hudson |author=Cudahy, Brian J. |publisher=Fordham University Press |year=2002 |pages=p. 56}}</ref> Towards the end of 1961, negotiations with outgoing New Jersey Governor Meyner regarding the World Trade Center project reached a stalemate. In December 1961, Tobin met with newly elected New Jersey Governor [[Richard J. Hughes]], and made a proposal to shift the World Trade Center project to a west side site where the [[Hudson Terminal]] was located.<ref name="nyt-1961dec29">{{cite news |title=Port Unit Backs Linking of H&M and Other Lines |author=Grutzner, Charles |publisher=The New York Times |date=December 29, 1961}}</ref> In acquiring the Hudson & Manhattan Railroad, the Port Authority would also acquire the Hudson Terminal and other buildings which were deemed obsolete.<ref name="nyt-1961dec29"/> On [[January 22]], [[1962]], the two states reached an agreement to allow the Port Authority to take over the railroad and to build the World Trade Center on Manhattan's lower west side.<ref>{{cite news |title=2 States Agree on Hudson Tubes and Trade Center |author=Wright, George Cable |date=January 23, 1962 |publisher=The New York Times}}</ref> The shift in location for the World Trade Center to a site more convenient to New Jersey, together with Port Authority acquisition of the H&M Railroad, brought New Jersey to agreement in support of the World Trade Center project.

===Controversy===
Even once the agreement between the states of New Jersey, New York, and the Port Authority was finalized, the World Trade Center plan faced continued controversy. The site for the World Trade Center was the location of [[Radio Row]], which was home to hundreds of commercial and industrial tenants, property owners, small businesses, and approximately 100 residents.<ref name="Gillespie-chap1"/> The World Trade Center plans involved evicting these business owners, some of whom fiercely protested the forced relocation.<ref name="Gillespie-chap1"/> In June 1962, a group representing approximately 325 shops and 1,000 other affected small businesses filed an [[injunction]], challenging the Port Authority's power of [[eminent domain]].<ref>{{cite news |title=Injunction Asked on Trade Center |date=June 27, 1962 |publisher=The New York Times |author=Clark, Alfred E.}}</ref> The dispute with local business owners worked its way through the court system, up to the [[New York Court of Appeals|New York State Court of Appeals]], which in April 1963 upheld the Port Authority's right of eminent domain, saying that the project had a "public purpose".<ref>{{cite news |title=World Trade Center Here Upheld by Appeals Court |author=Crowell, Paul |publisher=The New York Times |date=April 5, 1963}}</ref><ref>{{cite news |title=Merchants Ask Supreme Court to Bar Big Trade Center Here |publisher=The New York Times / Associated Press |date=August 26, 1963}}</ref> On [[November 12]], [[1963]], the [[United States Supreme Court]] refused to accept the case.<ref name="nyt-1963nov13">{{cite news |title=High Court Plea is Lost by Foes of Trade Center |author=Arnold, Martin |publisher=The New York Times |date=November 13, 1963}}</ref><ref>[http://caselaw.lp.findlaw.com/scripts/getcase.pl?navby=CASE&court=US&vol=375&page=78 375 US. 4] - ''Courtesy Sandwich Shop, Inc., et al. v. Port of New York Authority''</ref> Under the state law, the Port Authority was required to assist business owners in relocating, though many business owners regarded what the Port Authority offered as inadequate.<ref name="nyt-1963nov13"/><ref>{{cite news |title=Port Body Raises Relocation Aid |author=Apple, Jr. R.W. |publisher=The New York Times |date=November 16, 1963}}</ref> Questions continued while the World Trade Center was constructed, as to whether the Port Authority really ought to take on the project, described by some as a "mistaken social priority".<ref>{{cite news |title=Kheel Urges Port Authority to Sell Trade Center |date=November 12, 1969 |publisher=The New York Times}}</ref>

Private [[real estate]] developers and members of the Real Estate Board of New York also expressed concerns about this much "subsidized" office space going on the open market, competing with the private sector when there was already a glut of vacancies.<ref name="Gillespie-chap1"/><ref>{{cite news |title=New Fight Begun on Trade Center |author=Knowles, Clayton |date=February 14, 1964 |publisher=The New York Times}}</ref> An especially vocal critic was Lawrence A. Wien, owner of the [[Empire State Building]], which would lose its title of [[List of tallest buildings and structures in the world|tallest building in the world]].<ref name="Gillespie-chap1"/><ref>{{cite news |title=Critics Impugned on Trade Center |author=Ennis, Thomas W. |date=February 15, 1964 |publisher=The New York Times}}</ref> Wien organized a group of builders into a group called the "Committee for a Reasonable World Trade Center" which demanded the project be scaled down.<ref>{{cite news |title=All Major Builders are Said to Oppose Trade Center Plan |author=Knowles, Clayton |date=March 9, 1964 |publisher=The New York Times}}</ref>

In January 1964, the Port Authority inked a deal with the State of New York to locate government offices at the World Trade Center.<ref>{{cite news |title=State Will Rent at Trade Center |author=Sibley, John |publisher=The New York Times |date=January 14, 1964}}</ref> The Port Authority began signing up some commercial tenants in the Spring and Summer of 1964, including several banks.<ref>{{cite news |title=4th Bank Signed by Trade Center |date=July 14, 1964 |publisher=The New York Times}}</ref> In 1965, the Port Authority signed up the [[United States Customs Service]] as a tenant.<ref>{{cite news |title=Customs to Move to Trade Center |author=Fowler, Glenn |date=July 7, 1965 |publisher=The New York Times}}</ref>

A final obstacle for the Port Authority was getting approval from New York City Mayor [[John Lindsay]] and the [[New York City Council]]. They raised concerns about the limited extent that the Port Authority involved the city in the negotiations and deliberations. Negotiations between The City of New York and the Port Authority were centered on tax issues. A final agreement was made on [[August 3]], [[1966]], that the Port Authority would make annual payments to the city in lieu of taxes, for the portion of the World Trade Center leased to private tenants.<ref>{{cite news |title=City Ends Fight with Port Body on Trade Center |author=Smith, Terence |date=August 4, 1966 |publisher=The New York Times}}</ref> In subsequent years, the payments would rise as the overall [[Property tax|real estate tax]] rate rise.<ref>{{cite news |title=Mayor Signs Pact on Trade Center |author=Smith, Terence |publisher=The New York Times |date=January 26, 1967}}</ref>

==Design==
On [[September 20]], [[1962]], the Port Authority announced the selection of [[Minoru Yamasaki]] as lead architect, and [[Emery Roth|Emery Roth & Sons]] as associate architects.<ref>{{cite news |title=Architect Named for Trade Center |author=Esterow, Milton |date=September 21, 1962 |publisher=The New York Times}}</ref> Originally, Yamasaki came back to the Port Authority with the concept of twin towers, but with each building only 80 stories tall. Yamasaki remarked that the "obvious alternative, a group of several large buildings, would have looked like a housing project".<ref name="nyt-1964jan19a">{{cite news |title=A New Era Heralded |author=Huxtable, Ada Louise |publisher=The New York Times |date=January 19, 1964}}</ref>
[[Image:World Trade Center Building Design with Floor and Elevator Arrangment.svg|thumb|250px|A typical floor layout and elevator arrangement of the WTC towers.]]
To meet the Port Authority's requirement to build 10 million [[Square foot|square feet]] (930,000 m²) of office space, the buildings would each need to be 110 stories tall. A major limiting factor in building heights were elevators. The taller the building, the more [[elevator]]s are needed to service the building and more space-consuming elevator banks.<ref>{{cite news |title=Biggest Buildings Herald New Era |author=Huxtable, Ada Louise |date=January 26, 1964 |publisher=The New York Times}}</ref> Yamasaki and the engineers decided to use a new system with sky lobbies, which are floors where people can switch from a large capacity, express [[elevator]] that goes only to the sky lobbies to a local elevator that goes to each floor in a section. The local elevators were stacked on top of each other, within the same elevator shaft. Located on the 44th and 78th floors of each tower, the sky lobbies enabled the elevators to be used efficiently, while also increasing the amount of usable space on each floor from 62 to 75 percent by reducing the number of required elevator shafts.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 9 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> The World Trade Center towers were the second [[supertall]] buildings to use sky lobbies, after the [[John Hancock Center]] in [[Chicago]].<ref>{{cite web |url= http://www.otis.com/otis150/section/1,2344,ARC3066_CLI1_RES1_SEC5,00.html|publisher=[[Otis Elevator Company]]|title= Otis History: The World Trade Center|accessdate=2006-12-07}}</ref> This system was inspired by the [[New York City Subway]] system, whose lines include local stations where local trains stop and express stations where all trains stop.<ref name="gillespie-p76">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 76}}</ref>
[[Image:Wtc_model_at_skyscraper_museum.jpg|thumb|left|185px|Original architectural and engineering model]]
Yamasaki's design for the World Trade Center was unveiled to the public on [[January 18]], [[1964]], with an eight-foot model.<ref name="nyt-1964jan19a"/> The towers had a square plan, approximately 207 feet (63 m) in dimension on each side.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 7 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> The buildings were designed with narrow office windows, only 18 [[inch]]es (45 [[Centimetre|cm]]) wide, which reflected on Yamasaki's [[Acrophobia|fear of heights]] and desire to make building occupants feel secure.<ref name="pekala">{{cite news |title=Profile of a lost landmark; World Trade Center |publisher=Journal of Property Management |date=November 1, 2001 |author=Pekala, Nancy}}</ref> Yamasaki's design called for the building facades to be sheathed in aluminum-alloy.<ref name="nyt-1966may29">{{cite news |title=Who's Afraid of the Big Bad Buildings |author=Huxtable, Ada Louise |date=May 29, 1966 |publisher=The New York Times}}</ref> In all, the World Trade Center complex contained six buildings within the 16 acre (6.5 ha) [[City_block#Superblock|superblock]].

The World Trade Center design brought criticism of its aesthetics from the [[American Institute of Architects]] and other groups.<ref>{{cite news |title=Marring City's Skyline |author=Steese, Edward |date=March 10, 1964 |publisher=The New York Times}}</ref><ref name="nyt-1966may29"/> [[Lewis Mumford]], author of ''[[The City in History]]'' and other works on [[urban planning]], criticized the project and described it and other new skyscrapers as "just glass-and-metal filing cabinets".<ref>{{cite news |title=Mumford Finds City Strangled By Excess of Cars and People |author=Whitman, Alden |publisher=The New York Times |date=March 22, 1967}}</ref> [[Television]] broadcasters raised concerns that the World Trade Center twin towers would cause interference in television reception for viewers in the [[New York metropolitan area|New York City area]].<ref>{{cite news |title=TV Group Objects to Trade Towers |author=Schumach, Murray |date=February 20, 1966 |publisher=The New York Times}}</ref> In response to these concerns, the Port Authority offered to provide new television transmission facilities at the World Trade Center.<ref>{{cite news |title=TV Mast Offered on Trade Center |date=February 24, 1966 |publisher=The New York Times}}</ref> The [[Linnaean Society]] of the [[American Museum of Natural History]] also opposed the Trade Center project, citing hazards the buildings would impose on [[Bird migration|migrating bird]]s.<ref>{{cite news |title=Big Trade Center Called Bird Trap |author=Knowles, Clayton |publisher=The New York Times |date=March 16, 1967}}</ref>

The structural engineering firm, Skilling, Helle, Christiansen, [[Leslie Robertson|Robertson]], worked to implement Yamasaki's design, developing the tube-frame structural system used in the buildings. The Port Authority's Engineering Department served as foundation engineers, Joseph R. Loring & Associates as [[electrical engineering|electrical engineers]], and Jaros, Baum & Bolles as [[mechanical engineering|mechanical engineers]]. [[Tishman Reality & Construction|Tishman Realty & Construction Company]] was the [[general contractor]] on the World Trade Center project. Guy F. Tozzoli, director of the World Trade Department at the Port Authority, and the Port Authority's Chief Engineer, Rino M. Monti, oversaw the project.<ref>{{cite book |author=National Construction Safety Team |url=http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf |format =PDF | title=Final Report on the Collapse of the World Trade Center Towers |publisher=NIST |chapter=Chapter 1 |date=September 2005 |pages=p. 1}}</ref>

===Structural design===
As an interstate agency, the Port Authority was not subject to local laws and regulations of the City of New York, including [[building code]]s. Nonetheless, the Port Authority required architects and structural engineers to follow the New York City building codes. At the time when the World Trade Center was planned, new building codes were being devised to replace the 1938 version that was in place. The structural engineers ended up following draft versions of the new 1968 building codes which incorporated "advanced techniques" in [[building design]].<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. xxxviii |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref>

The World Trade Center towers included many [[structural engineering]] innovations in [[skyscraper design and construction]], which allowed the buildings to reach new heights and become the [[List of tallest buildings in the world|tallest]] in the world. Traditionally, [[skyscraper]]s used a skeleton of [[column]]s distributed throughout the interior to support building loads, with interior columns disrupting the floor space. The tube-frame concept was a major innovation, allowing open floor plans and more rentable space. The buildings used high-strength, load bearing perimeter [[steel]] columns called [[truss#Vierendeel truss|Vierendeel trusses]], that were spaced closely together to form a strong, rigid wall structure. There were 59 perimeter columns, narrowly spaced on each side of the buildings. These were designed to provide support for virtually all lateral loads (such as wind loads) and to share the gravity loads with the core columns.<ref>{{cite book |author=National Construction Safety Team |url=http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf |title=Final Report on the Collapse of the World Trade Center Towers |publisher=NIST |format =PDF |date=September 2005 |chapter=Chapter 1 |pages=p. 6}}</ref>
[[Image:Nistncstar1-1-fig2-4.png|thumb|right|Typical WTC architectural floor plan]]
The perimeter structure was constructed with extensive use of prefabricated modular pieces, which consisted of three columns, three stories tall, connected together by [[wikt:spandrel|spandrel]] plates. The perimeter columns had a square cross section, 14 inches (36 cm) on a side, and were constructed of welded steel plate.<ref name="NIST-chapter1">{{cite book |author=National Construction Safety Team |url=http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf |format =PDF |title=Final Report on the Collapse of the World Trade Center Towers |publisher=NIST |date=September 2005}}</ref> The thickness of the plates and grade of [[structural steel]] varied over the height of the tower, ranging from 36,000 to 100,000 pounds per square inch<ref>[[A36 steel]] has a nominal [[Yield (engineering)|yield strength]] of 36,000 to 100,000 pounds per square inch.</ref> (260 to 670 MPa). The strength of the steel and thickness of the steel plates decreased with height because they were required to support lesser amounts of building mass on higher floors.<ref name="NIST-chapter1"/> The tube-frame design required 40 percent less structural steel than conventional building designs.<ref name="steel">{{cite journal |author=American Iron and Steel Institute |title=The World Trade Center - New York City |journal=Contemporary Steel Design |volume=1(4) |year=1964 |publisher=American Iron and Steel Institute}}</ref> From floor #7 to the ground level and down to the foundation, the columns were spaced 10 feet (3 m) apart.<ref>{{cite book |author=National Construction Safety Team |url=http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf |format =PDF |title=Final Report on the Collapse of the World Trade Center Towers |publisher=NIST |date=September 2005 |pages=p. 10}}</ref> All columns were founded on [[bedrock]], which unlike Midtown Manhattan, where the bedrock is shallow, is at 65–85 feet (20–26 m) below the surface.<ref>{{cite journal |url=http://www.nae.edu/nae/bridgecom.nsf/weblinks/CGOZ-58NLJ9?OpenDocument |title=World Trade Center "Bathtub": From Genesis to Armageddon |journal=Bridges |author=Tamaro, George J. |date=Spring 2002 |volume=32(1)}}</ref>

The spandrel plates were welded to the columns to create the modular pieces off-site at the fabrication shop.<ref>{{cite book |author=National Construction Safety Team |url=http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf |format =PDF |title=Final Report on the Collapse of the World Trade Center Towers |publisher=NIST |date=September 2005 |pages=p. 8}}</ref> The modular pieces were typically 52 inches (1.3 m) deep, and extended for two full floors and half of two more floors.<ref name="NIST-chapter1"/> Adjacent modules were bolted together, with the splices occurring at mid-span of the columns and spandrels. The spandrel plates were located at each floor, and served to transmit [[shear stress]] between columns, thus allowing them to work together in resisting lateral loads. The joints between modules were staggered vertically, so the column splices between adjacent modules were not at the same floor.<ref name="NIST-chapter1"/>

The building's core housed the [[elevator]] and utility shafts, restrooms, three stairwells, and other support spaces. The core of each tower was a rectangular area 87 by 135 feet (27 by 41 m), and contained 47 steel columns running from the bedrock to the top of the tower.<ref name="NIST-chapter1"/> The columns tapered with height, and consisted of welded box-sections at lower floors and rolled wide-flange sections at upper floors. The core in 1 WTC was oriented with the long axis east to west, while that of 2 WTC was oriented north to south. All of the elevators were located in the core. Each building had three stairwells that were also located in the core, except on the [[mechanical floor]]s where they were located outside of the structural core.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 8 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref>
[[Image:Wtc floor truss system.png|thumb|left|Schematic of composite floor truss system]]
The large, column-free space between the perimeter and core was bridged by pre-fabricated floor trusses. The floors supported their own weight, as well as [[live loads]], provided lateral stability to the exterior walls, and distributed wind loads among the exterior walls. The floors consisted of 4 inch (10 cm) thick lightweight [[concrete]] slabs laid on a fluted steel deck. A grid of lightweight bridging trusses and main trusses supported the floors. The trusses had a span of 60 feet (18.2 m) in the long-span areas and 35 feet (11 m) in the short span area.<ref name="NIST-chapter1"/> The trusses connected to the perimeter at alternate columns, and were therefore on 6 foot 8 inch (2.03 m) centers. The top chords of the trusses were bolted to seats welded to the spandrels on the exterior side and a channel welded to the core columns on the interior side. The floors were connected to the perimeter spandrel plates with [[Viscoelasticity|viscoelastic]] dampers, which helped reduce the amount of sway felt by building occupants. The trusses supported a 4 inch thick (10 cm) lightweight concrete floor slab, with shear connections for composite action.<ref name="NIST-chapter1"/>

Hat [[trusses]] (or "outrigger truss") located from the 107th floor to the top of the buildings were designed to support a tall communications [[Antenna (radio)|antenna]] on top of each building.<ref name="NIST-chapter1"/> Only 1 WTC (north tower) actually had an antenna fitted, which was added in 1978.<ref>{{cite web |url=http://www.pbs.org/wgbh/amex/newyork/sfeature/sf_building.html |title=New York: A Documentary Film - The Center of the World (Construction Footage) |publisher = Port Authority / PBS |accessdate=2007-05-16}}</ref> The truss system consisted of six trusses along the long axis of core and four along the short axis. This truss system allowed some load redistribution between the perimeter and core columns and supported the transmission tower.

===Wind effects===
The tube frame design using steel core and perimeter columns protected with sprayed-on fire resistant material created a relatively lightweight structure that would sway more in response to the wind, compared to traditional structures such as the [[Empire State Building]] that have thick, heavy [[masonry]] for fireproofing of steel structural elements.<ref>{{cite book |title=City in the Sky |author=Glanz, James and Eric Lipton |pages=p. 138 |publisher=Times Books |year=2003}}</ref> During the design process, [[wind tunnel]] tests were done at [[Colorado State University]] and at the [[National Physical Laboratory, UK|National Physical Laboratory]] in the [[United Kingdom|U.K.]] to establish design wind pressures that the World Trade Center towers could be subjected to and structural response to those forces.<ref>{{cite book |title=Design and Construction of Structural Systems (NCSTAR 1-1A) |publisher=National Institute of Standards and Technology |pages=p. 65 |author=Fanella, David A., Arnaldo T. Derecho, S.K. Ghosh |date=September 2005}}</ref> Experiments were also done to evaluate how much sway occupants could tolerate. Subjects were recruited for "free eye exams", while the real purpose of the experiment was to subject them to simulated building sway and find out how much they could comfortably tolerate.<ref>{{cite book |title=City in the Sky |author=Glanz, James and Eric Lipton |pages=p. 139-144 |publisher=Times Books |year=2003}}</ref> Many subjects did not respond well, experiencing [[dizziness]] and other ill effects. The chief engineer [[Leslie Robertson]] worked with Canadian engineer Alan G. Davenport to develop viscoelastic [[Damping|dampers]] to absorb some of the sway. These viscoelastic dampers, used throughout the structures at the joints between floor trusses and perimeter columns, along with some other structural modifications reduced the building sway to an acceptable level.<ref>{{cite book |title=City in the Sky |author=Glanz, James and Eric Lipton |pages=p. 160-167 |publisher=Times Books |year=2003}}</ref>

===Fire protection===
[[Fireproofing|Sprayed-fire resistant material]]s (SFRMs) were used to protect some structural steel elements in the towers, including all floor trusses and beams.<ref name="NCSTAR 1-1-p8">{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 8 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> [[Gypsum]] [[wallboard]] in combination with SFRMs, or in some cases gypsum wallboard alone, was used to protect core columns.<ref name="NCSTAR 1-1-p8"/> [[Vermiculite]] plaster was used on the interior-side and SFRMs on the other three sides of the perimeter columns for fire protection.<ref name="NCSTAR 1-1-p8"/> The 1968 New York City building codes were more lenient in some aspects of fire protection, such as allowing three exit stairwells in the World Trade Center towers, instead of six as required under older building codes.<ref name="NCSTAR 1-1-p153">{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 153 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref>

The 1968 New York City building codes did not require [[Fire sprinkler|sprinkler]]s for [[high-rise]] buildings, except for underground spaces. In accordance with building codes, sprinklers were originally installed only in the underground parking structures of the World Trade Center.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 162 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> Following a major fire in February 1975, the Port Authority decided to start installing sprinklers throughout the buildings. By 1993, nearly all of Tower 2 [South Tower], and 85% of Tower 1 had sprinklers installed,<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 163 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> and the entire complex was retrofitted by 2001.<ref>{{cite book |title=Active Fire Protection Systems (NCSTAR 1-4) |publisher=National Institute of Standards and Technology |pages=p. 14 |author=Evans, David D., Richard D. Peacock, Erica D. Kuligowski, W. Stuart Dols, William L. Grosshandler |date=September 2005}}</ref>

==Construction==
In March 1965, the Port Authority began acquiring property at the World Trade Center site.<ref>{{cite news |title=Port Agency Buys Downtown Tract |author=Ingraham, Joseph C. |date=March 29, 1965 |publisher=The New York Times}}</ref> The Ajax Wrecking and Lumber Corporation was hired to do the [[demolition]] work, which began on [[March 21]], [[1966]] to clear the site for construction of the World Trade Center.<ref name="gillespie-p61">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 61}}</ref>

[[Groundbreaking]] was on [[August 5]], [[1966]], marking the beginning of construction of the World Trade Center's foundations.<ref>{{cite news |title=Jackhammers Bite Pavement to Start Trade Center Job |date=August 6, 1966 |publisher=The New York Times}}</ref> The site of the World Trade Center was located on landfill, with the bedrock located 65 feet (20 m) below.<ref name="iglauer">{{cite news |url=http://www.newyorker.com/archive/content/articles/010924fr_archive02 |title=The Biggest Foundation |author=Iglauer, Edith |date=November 4 1972 |publisher=The New Yorker}}</ref> In order to construct the World Trade Center, it was necessary to build the "bathtub", with the [[slurry wall]] along the [[West Street]] side of the site, to keep water from the Hudson River out. The slurry method involves digging a [[trench]], and as [[excavation]] proceeds, filling the space with a "slurry" mixture, comprised of [[bentonite]] which plugs holes and keeps water out. When the trench was dug out, a steel cage was inserted, with concrete poured in, forcing the "slurry" out. The "slurry" method was devised by Port Authority chief engineer, John M. Kyle, Jr. Towards the end of 1966, work began on building the [[slurry wall]], led by [[Montreal]]-based Icanda, a subsidiary of an Italian engineering firm, Impresa Costruzioni Opere Specializzate (I.C.O.S.).<ref name="gillespie-p68">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 68}}</ref> It took fourteen months for the slurry wall to be completed, which was necessary before excavation of material from the interior of the site could begin.<ref name="gillespie-p68"/> The original [[Downtown Hudson Tubes|Hudson Tubes]], which carried PATH trains into Hudson Terminal, remained in service as elevated [[tunnel]]s until 1971 when a new [[World Trade Center (PATH station)|PATH station]] was built.<ref>{{cite news |author=Carroll, Maurice |title=A Section of the Hudson Tubes is Turned into Elevated Tunnel |date=December 30, 1968 |publisher=The New York Times}}</ref>
[[Image:Wtc panynj 1973.jpg|thumb|right|200px|World Trade Center in 1973]]
[[Construction|Construction work]] began on the North Tower in August 1968 with construction beginning on the South Tower by January 1969.<ref name="pbstimeline">{{cite web |url=http://www.pbs.org/wgbh/amex/newyork/timeline/index.html |title=Timeline: World Trade Center chronology |publisher=PBS - American Experience |accessdate=2007-05-15}}</ref> In January 1967, $74 million in contracts were awarded to the [[PACCAR|Pacific Car and Foundry Company]], [[Laclede Steel Company]], [[U.S. Steel|Granite City Steel Company]], and [[Karl Koch Steel Consulting|Karl Koch Erecting Company]] to supply [[steel]] for the project.<ref name="nyt-1967jan24">{{cite news |title=Contracts Totaling $74,079,000 Awarded for the Trade Center |publisher=The New York Times |date=January 24, 1967}}</ref> The Port Authority chose to use many different steel suppliers, bidding on smaller portions of steel, rather than buy larger amounts from a single source such as [[Bethlehem Steel]] or [[U.S. Steel]] as a cost-saving measure.<ref name="gillespie-p83">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 83}}</ref> Karl Koch was also hired to do all the work of erecting the steel, and a contract for work on the aluminum facade was awarded to the [[Alcoa|Aluminum Company of America]].<ref name="nyt-1967jan24"/> [[Tishman Realty & Construction]] was hired in February 1967 to oversee construction of the project.<ref>{{cite news |title=Trade Center Job To Go To Tishman |author=Kihss, Peter |publisher=The New York Times |date=February 27, 1967}}</ref>

Extensive use of [[prefabrication|prefabricated]] parts for the perimeter framing and floor truss systems helped speed up the construction process and reduce costs, while providing greater [[quality control]].<ref name="steel"/> Steel components were freighted into a [[Penn Central Transportation|Penn Central]] yard in [[Jersey City, New Jersey|Jersey City]]. From there, they were brought in early morning hours through the [[Holland Tunnel]] to the construction site, and lifted into place by a [[Crane (machine)|crane]].<ref>{{cite news |title=Trade Center is Doing Everything Big |publisher=The New York Times |date=June 6, 1969 |author=Kaufman, Micheal T.}}</ref> Larger pieces were brought to the construction site by [[tugboat]]s.<ref name="gillespie-p88">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 88}}</ref> A special type of crane, suitable for constructing such tall buildings, that used [[hydraulics]] to lift components and provided its own power was used in construction of the World Trade Center. The Favco Standard 2700 Crane, manufactured by Favelle Mort Ltd. of [[New South Wales]], [[Australia]] was informally called a "[[kangaroo]] crane".<ref name="gillespie-p92">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 92-94}}</ref>

In 1970, tugboat workers went on [[Strike action|strike]], halting the transport of material to the construction site.<ref>{{cite news |title=300 Tugboats Idle as Men Walk Out for Doubled Wage |author=McFadden, Robert D. |date=February 2, 1970 |publisher=The New York Times}}</ref> The Port Authority attempted other means of transporting material, including via [[helicopter]]. When this method was tried, the helicopter lost its load of steel into the [[Kill Van Kull]].<ref name="gillespie-p91">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 91}}</ref> Some other mishaps occurred during the construction process, including disruption of [[telephone]] service in Lower Manhattan when telephone cables were crushed by [[pile driver]]s.<ref>{{cite news |author=Carroll, Maurice |title=Phones Disrupted by a Pile Driver |date=March 19, 1969 |publisher=The New York Times}}</ref> On [[March 16]], [[1970]], a [[propane]] gas explosion injured six workers, when a truck hit a propane tank.<ref>{{cite news |title=Propane Blast Hits Trade Center |author=Van Gelder, Lawrence |date=March 17, 1970 |publisher=The New York Times}}</ref> In all, 60 workers were killed in construction accidents while the World Trade Center was being built.<ref>{{cite web |url=http://www.pbs.org/americarebuilds/engineering/engineering_qfacts.html |title=America Rebuilds: Quick Facts |publisher=PBS |accessdate=2007-05-15}}</ref>

Construction of 1 World Trade Center (North Tower) was completed on [[December 23]], [[1970]], with 2 World Trade Center (South Tower) completed on [[July 19]], [[1971]].<ref name="pbstimeline"/> First tenants moved into the North Tower in December 1970, and into the South Tower in January 1972.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. xxxvi |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> The buildings were dedicated on [[April 4]], [[1973]], with Tobin, who resigned the year before, absent from the ceremonies.<ref name="Darton-chap6">Darton, Eric (1999) ''Divided We Stand: A Biography of New York's World Trade Center'', Chapter 6, Basic Books.</ref>

Building the World Trade Center involved excavating 1.2 million [[cubic yard]]s (917,000 [[Cubic metre|m³]]) of material.<ref name="gillespie-p71">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 71}}</ref> Rather than transporting this material at great costs out to sea or to landfills in [[New Jersey]], the fill material was used to expand the [[Manhattan]] shoreline across [[West Street]].<ref name="gillespie-p71"/> Work to demolish the [[pier]]s began on [[January 5]], [[1967]], including Pier 7 to Pier 11 which were all constructed around 1910.<ref>{{cite news |title=Demolition Begun on 5 City Piers |author=Horne, George |publisher=The New York Times |date=January 5, 1967}}</ref> The demolition work moved forward, despite conflicts between [[David Rockefeller]], Governor [[Nelson Rockefeller]], and Mayor [[John Lindsay]] regarding plans for Battery Park City.<ref>{{cite news |title=Conflicts Stall Landfill Plans |author=Roberts, Steven V. |publisher=The New York Times |date=January 17, 1967}}</ref> Landfill material from the [[World Trade Center]] was used to add land, and a cellular [[cofferdam]] was constructed to retain the material.<ref name="iglauer">{{cite news |url=http://www.newyorker.com/archive/content/articles/010924fr_archive02 |title=The Biggest Foundation |author=Iglauer, Edith |date=November 4 1972 |publisher=The New Yorker}}</ref> The result was a 700 foot (210 m) extension into the [[Hudson River]], running six blocks or 1,484 feet (450 m).<ref name="gillespie-p71"/> This land was a "gift" to New York City, allowing more [[tax]]-generating developments in [[Battery Park City, Manhattan|Battery Park City]].<ref>{{cite news |title=New York Gets $90 Million Worth of Land for Nothing |publisher=Engineering News Record |date=April 18, 1968}}</ref>

The original estimates put forth by the Port Authority had the costs for construction of the World Trade Center at $350 million — an optimistic figure.<ref name="gillespie-p70">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 70}}</ref> In December 1966, the Port Authority announced increased cost estimates, bringing the estimated total to $575 million.<ref name="gillespie-p69">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 69}}</ref> This announcement brought criticism of the project from private real estate developers, the [[New York Times]], and others in New York City.<ref>{{cite news |title=Questions on the Trade Center |publisher=The New York Times |date=December 24, 1966}}</ref> The critics charged that the Port Authority figure was unrealistically low estimate, and they estimated the project would end up costing $750 million.<ref>{{cite news |title=Estimate Raised for Trade Center |author=Phillips, McCandlish |date=December 29, 1966 |publisher=The New York Times}}</ref> When the World Trade Center twin towers were completed, the total costs to the Port Authority had reached $900 million.<ref name="Cudahy">Cudahy, Brian J. (2002) ''Rails Under the Mighty Hudson: The Story of the Hudson Tubes, the Pennsy Tunnels, and Manhattan Transfer'', Chapter 3, Fordham University Press.</ref> The project was financed through [[Tax exemption|tax-exempt]] [[Bond (finance)|bond]]s issued by the Port Authority.<ref>{{cite news |author=Allan, John H. |title=Bonds: Port of New York Authority to Raise $100-Million |date=February 28, 1968 |publisher=The New York Times}}</ref>

==Other buildings==
The World Trade Center complex included four other, smaller buildings constructed during the 1970s. 3 World Trade Center was a 22-story building, which was home to the [[Marriott World Trade Center]]. It was designed by [[Skidmore, Owings and Merrill]] in 1978-79.<ref>{{cite book |author=McAllister, Therese, Johnathan Barnett, John Gross, Ronald Hamburger, Jon Magnusson |chapter=WTC3 |title=World Trade Center Building Performance Study |publisher=FEMA |date=May 2002}}</ref> [[4 World Trade Center]], [[5 World Trade Center]], and [[6 World Trade Center]] were all 8-9 story buildings that were designed by the same team as the Twin Towers, including Minoru Yamasaki, Emery Roth & Sons, and Skilling, Helle, Christiansen, Robertson.<ref>{{cite book |author=McAllister, Therese, Johnathan Barnett, John Gross, Ronald Hamburger, Jon Magnusson |chapter=WTC4, 5, and 6 |title=World Trade Center Building Performance Study |publisher=FEMA |date=May 2002}}</ref> A seventh building ([[7 World Trade Center]]) was built in the mid-1980s, just to the north of the main World Trade Center site. The 47-story building was designed by Emery, Roth & Sons, and constructed on top of a [[Con Edison]] power [[substation]].<ref>{{cite book |author=McAllister, Therese, Johnathan Barnett, John Gross, Ronald Hamburger, Jon Magnusson |chapter=WTC7 |title=World Trade Center Building Performance Study |publisher=FEMA |date=May 2002}}</ref>

==Modifications==
Over time, numerous structural modifications were made to suit the needs of tenants in the Twin Towers. Modifications were made in accordance with the Port Authority's ''Tenant Alteration Review Manual'' and were reviewed by the Port Authority to ensure the changes did not compromise structural integrity of the buildings. Oftentimes, openings were cut in the floors to allow new [[stairway]]s to be built to connect tenant floors. Some steel beams in the core were reinforced and strengthened to accommodated heavy live loads, such as large amounts of heavy files that tenants had on their floors.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. xliv |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref>

Repairs to structural elements on the lower levels of 1 WTC [North Tower] were made following the [[1993 World Trade Center bombing]]. The greatest damage occurred on levels B1 and B2, with significant structural damage also on level B3.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. xlv |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> Primary structural columns were not damaged, but secondary steel members experienced some damage.<ref>{{cite web |url=http://www.interfire.org/res_file/pdf/Tr-076.pdf |format =PDF |title=Experiences of the Chief Engineer of the Port Authority |author=Fasullo, Eugene |publisher=United States Fire Administration |accessdate=2007-05-15}}</ref> Floors that were blown out needed to be repaired, to restore the structural support they provided to columns.<ref>{{cite web |url=http://www.interfire.org/res_file/pdf/Tr-076.pdf |format =PDF |title=The World Trade Center Complex |author=Port Authority Risk Management Staff |publisher=United States Fire Administration |accessdate=2007-05-15}}</ref> The slurry wall was in peril following the bombing and loss of the floor slabs which provided lateral support to counteract pressure from Hudson River water on the other side.<ref name="ennala">{{cite journal |author=Ramabhushanam, Ennala and Marjorie Lynch |title=Structural Assessment of Bomb Damage for World Trade Center |journal=Journal of Performance of Constructed Facilities |volume=8(4) |pages=229-242}}</ref> The [[refrigeration]] plant on sublevel B5, which provided [[air conditioning]] to the entire World Trade Center complex, was heavily damaged and replaced with a temporary system for the summer of 1993.<ref name="ennala"/> The [[fire alarm]] system for both towers needed to be replaced, after critical wiring and signaling in the original system was destroyed in the 1993 bombing. Installation of the new system took years to complete, and replacement of some components was still underway at the time of the [[September 11, 2001 attacks]].<ref>{{cite book |title=Active Fire Protection Systems (NCSTAR 1-4) |publisher=National Institute of Standards and Technology |pages=p. 44 |author=Evans, David D., Richard D. Peacock, Erica D. Kuligowski, W. Stuart Dols, William L. Grosshandler |date=September 2005}}</ref>

==See also==
* [[Collapse of the World Trade Center]]
* [[Freedom Tower]]
* [[150 Greenwich Street]]
* [[175 Greenwich Street]]
* [[200 Greenwich Street]]

==References==
<div class="references-small" style="-moz-column-count: 2; column-count: 2;">
<references/>
</div>

==External links==
* [http://www.pbs.org/wgbh/amex/newyork/sfeature/sf_building.html New York: A Documentary Film - The Center of the World] - ''Building the World Trade Center'', an 18-minute film, with construction footage, produced by the Port Authority in 1983
* [http://www.skyscraper.org/WHAT%27S_UP/WTC_DOSSIER/wtc.htm World Trade Center] - Skyscraper Museum
* {{Cite web
| title = Corus in construction - Systems evolution
| accessdate = 2007-05-14
| url = http://corusconstruction.com/en/reference/teaching_resources/architectural_studio_reference/design/tall_building_designs/systems_evolution/
}}
* [http://wtc.nist.gov/ NIST and the World Trade Center]
* [http://www.ericdarton.net/ New York's World Trade Center - A Living Archive] - by author, Eric Darton
* [http://www.antiqueradio.com/Sep02_RadioRow_Steinhardt.html The Death of New York's Radio Row], by Syd Steinhard - Downtown Express

{{WTC navigation}}
{{Featured article}}
[[Category:World Trade Center]]

Bau des World Trade Centers

2007-07-10T00:51:27Z

Ferdiaob: /* References */ minor reformat

{{for|the post-9/11 rebuilding and ongoing construction at the World Trade Center site|World Trade Center site}}
[[Image:World trade center new york city construction flickr.png|thumb|right|250px|View of the World Trade Center's construction from across the [[Hudson river]]]]
The '''building of the [[World Trade Center]]''' started as a post-[[World War II]] [[urban renewal]] project, spearheaded by [[David Rockefeller]], to help revitalize [[Lower Manhattan]]. The project was developed by the [[Port Authority of New York and New Jersey]], which hired architect [[Minoru Yamasaki]] who came up with the specific idea for twin towers. After extensive negotiations, the [[New Jersey]] and [[New York|New York State]] governments, which oversee the Port Authority, agreed to support the World Trade Center project at the [[Radio Row]] site on the lower-west side of [[Manhattan]]. To make the agreement acceptable to New Jersey, the Port Authority agreed to take over the bankrupt Hudson & Manhattan Railroad (renamed as [[Port Authority Trans-Hudson|PATH]]), which brought commuters from New Jersey to the Lower Manhattan site.

The towers were designed as framed tube structures, which provided tenants with open floor plans, uninterrupted by columns or walls. This was accomplished using numerous, closely-spaced perimeter columns to provide much of the strength to the structure, along with gravity load shared with the core columns. The [[elevator]] system, which made use of [[sky lobby|sky lobbies]] and a system of express and local elevators, allowed substantial floor space to be freed up for use as office space by making the structural core smaller. The design and construction of the World Trade Center twin towers involved many other innovative techniques, such as the [[slurry wall]] for digging the [[Foundation (architecture)|foundation]], and [[wind tunnel]] experiments. Construction of the World Trade Center's North Tower began in August 1968, and the South Tower in 1969. Extensive use of prefabricated components helped to speed up the construction process. The first tenants moved into the North Tower in December 1970 and into the South Tower in January 1972. Four other, low-level buildings were constructed as part of the World Trade Center in the 1970s, and a [[7 World Trade Center|seventh]] building was constructed in the mid-1980s.

==Planning==
In 1942, [[Austin J. Tobin]] became the Executive Director of the [[Port Authority of New York and New Jersey|Port Authority]], beginning a 30-year career during which he would oversee the planning and development of the World Trade Center.<ref name="Doig-chap1">{{cite book |last=Doig |first=Jameson W. |title=Empire on the Hudson |year=2001 |publisher=Columbia University Press |chapter=Chapter 1}}</ref> The concept of establishing a "[[World Trade Center (disambiguation)|world trade center]]" was conceived during the post-[[World War II]] period, when the [[United States]] thrived economically and international trade was increasing. In 1946, the [[New York State Legislature]] passed a bill that called for a "world trade center" to be established.<ref name="nyt-07061946">{{cite news |title=Dewey Picks Board for Trade Center |publisher=The New York Times |date=July 6, 1946}}</ref> The World Trade Corporation was set up and a board appointed by New York Governor [[Thomas E. Dewey]] to develop plans for the project.<ref name="nyt-07061946"/> Architect [[John Eberson]] and his son Drew devised a plan that included 21 buildings over a ten-block area, at an estimated cost of $150 million.<ref>{{cite news |title=Plans are Tabled for Trade Center |author=Crisman, Charles B. |publisher=The New York Times |date=November 10, 1946}}</ref> In 1949, the World Trade Corporation was dissolved by the New York State Legislature, and plans for a "world trade center" were put on hold.<ref>{{cite news |title=Lets Port Group Disband, State Senate for Dissolution of World Trade Corporation |publisher=The New York Times |date=March 11, 1949}}</ref>
===Original plans===
[[Image:East-side-wtc.png|thumb|right|300px|Architect's model for the proposed World Trade Center on the East River]]
During the post-war period, economic growth was concentrated in [[Midtown Manhattan]], in part stimulated by the [[Rockefeller Center]], which was developed in the 1930s. Meanwhile, Lower Manhattan was left out of the [[Boom and bust|economic boom]]. One exception was the construction of [[One Chase Manhattan Plaza]] in the [[Financial District, Manhattan|Financial District]], by [[David Rockefeller]], who led [[urban renewal]] efforts in Lower Manhattan.<ref name="Gillespie-chap1">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |chapter=Chapter 1 |publisher=Rutgers University Press}}</ref> In 1958, Rockefeller established the Downtown-Lower Manhattan Association (DLMA), which commissioned [[Skidmore, Owings and Merrill]] to draw up plans for revitalizing [[Lower Manhattan]]. The plans, made public in 1960, called for a World Trade Center to be built on a 13 [[acre]] (5.25 [[Hectare|ha]]) site along the [[East River]], from [[Old Slip]] to [[Fulton Street (Manhattan)|Fulton Street]] and between [[Water Street (Manhattan)|Water Street]] and [[South Street (Manhattan)|South Street]].<ref name="Levinson">{{cite book|last=Levinson |first=Leonard Louis| title=Wall Street| year=1961| publisher=Ziff Davis Publishing| location=New York| page=346}}</ref><ref name="nyt-01271960">{{cite news |title=A World Center of Trade Mapped Off Wall Street |date=January 27, 1960 |publisher=The New York Times |author=Grutzner, Charles}}</ref> The complex would include a 900 [[Foot (unit of length)|foot]] (275 [[Metre|m]]) long [[Convention center|exhibition hall]], and a 50-70 story building, with some of its upper floors used as a hotel.<ref>{{cite book |title=Men of Steel: The Story of the Family That Built the World Trade Center |author=Koch, Karl III |publisher=Three Rivers Press |year=2002 |pages=p. 173}}</ref> Other amenities would include a theater, shops, and restaurants.<ref name="dlma-plan">{{cite news |title=Text of Trade Center Report by the Downtown-Lower Manhattan Association |publisher= The New York Times |date=January 27, 1960}}</ref> The plan also called for a new [[securities]] exchange building, which Downtown-Lower Manhattan Association hoped would house the [[New York Stock Exchange]].<ref name="nyt-01271960"/>

David Rockefeller suggested that the Port Authority would be a logical choice for taking on the project.<ref name="nyt-01271960"/> Rockefeller argued that the Trade Center would provide great benefits in facilitating and increasing volume of international commerce coming through the Port of New York.<ref name="dlma-plan"/> Given the importance of [[New York City]] in global commerce, Port Authority director Austin J. Tobin remarked that the proposed project should be ''the'' World Trade Center, and not just ''a'' "world trade center".<ref>{{cite news |title=Tobin Says Proposed Center Should Be World's Best |publisher=The New York Times |date=May 5, 1960}}</ref> After a year-long review of the proposal, the Port Authority formally backed the project on [[March 11]], [[1961]].<ref>{{cite news |title=355 Million World Trade Center Backed by Port Authority Study |publisher=The New York Times |date=March 12, 1961}}</ref>

===Agreement===
[[Image:Wtc locator map.png|thumb|right|300px|Location of World Trade Center and originally proposed site]]
The State of New York and New Jersey also needed to approve the project, given their control and oversight role of the Port Authority. Objections to the plan came from [[New Jersey]] Governor [[Robert B. Meyner]], who resented that [[New York]] would be getting this $335 million project.<ref name="Gillespie-chap1"/> Meanwhile, ridership on New Jersey's [[Hudson and Manhattan Railroad]] (H&M) had declined substantially from a high of 113 million riders in 1927 to 26 million in 1958, after new automobile tunnels and bridges opened across the [[Hudson River]].<ref>{{cite book |title=Rails Under the Mighty Hudson |author=Cudahy, Brian J. |publisher=Fordham University Press |year=2002 |pages=p. 56}}</ref> Towards the end of 1961, negotiations with outgoing New Jersey Governor Meyner regarding the World Trade Center project reached a stalemate. In December 1961, Tobin met with newly elected New Jersey Governor [[Richard J. Hughes]], and made a proposal to shift the World Trade Center project to a west side site where the [[Hudson Terminal]] was located.<ref name="nyt-1961dec29">{{cite news |title=Port Unit Backs Linking of H&M and Other Lines |author=Grutzner, Charles |publisher=The New York Times |date=December 29, 1961}}</ref> In acquiring the Hudson & Manhattan Railroad, the Port Authority would also acquire the Hudson Terminal and other buildings which were deemed obsolete.<ref name="nyt-1961dec29"/> On [[January 22]], [[1962]], the two states reached an agreement to allow the Port Authority to take over the railroad and to build the World Trade Center on Manhattan's lower west side.<ref>{{cite news |title=2 States Agree on Hudson Tubes and Trade Center |author=Wright, George Cable |date=January 23, 1962 |publisher=The New York Times}}</ref> The shift in location for the World Trade Center to a site more convenient to New Jersey, together with Port Authority acquisition of the H&M Railroad, brought New Jersey to agreement in support of the World Trade Center project.

===Controversy===
Even once the agreement between the states of New Jersey, New York, and the Port Authority was finalized, the World Trade Center plan faced continued controversy. The site for the World Trade Center was the location of [[Radio Row]], which was home to hundreds of commercial and industrial tenants, property owners, small businesses, and approximately 100 residents.<ref name="Gillespie-chap1"/> The World Trade Center plans involved evicting these business owners, some of whom fiercely protested the forced relocation.<ref name="Gillespie-chap1"/> In June 1962, a group representing approximately 325 shops and 1,000 other affected small businesses filed an [[injunction]], challenging the Port Authority's power of [[eminent domain]].<ref>{{cite news |title=Injunction Asked on Trade Center |date=June 27, 1962 |publisher=The New York Times |author=Clark, Alfred E.}}</ref> The dispute with local business owners worked its way through the court system, up to the [[New York Court of Appeals|New York State Court of Appeals]], which in April 1963 upheld the Port Authority's right of eminent domain, saying that the project had a "public purpose".<ref>{{cite news |title=World Trade Center Here Upheld by Appeals Court |author=Crowell, Paul |publisher=The New York Times |date=April 5, 1963}}</ref><ref>{{cite news |title=Merchants Ask Supreme Court to Bar Big Trade Center Here |publisher=The New York Times / Associated Press |date=August 26, 1963}}</ref> On [[November 12]], [[1963]], the [[United States Supreme Court]] refused to accept the case.<ref name="nyt-1963nov13">{{cite news |title=High Court Plea is Lost by Foes of Trade Center |author=Arnold, Martin |publisher=The New York Times |date=November 13, 1963}}</ref><ref>[http://caselaw.lp.findlaw.com/scripts/getcase.pl?navby=CASE&court=US&vol=375&page=78 375 US. 4] - ''Courtesy Sandwich Shop, Inc., et al. v. Port of New York Authority''</ref> Under the state law, the Port Authority was required to assist business owners in relocating, though many business owners regarded what the Port Authority offered as inadequate.<ref name="nyt-1963nov13"/><ref>{{cite news |title=Port Body Raises Relocation Aid |author=Apple, Jr. R.W. |publisher=The New York Times |date=November 16, 1963}}</ref> Questions continued while the World Trade Center was constructed, as to whether the Port Authority really ought to take on the project, described by some as a "mistaken social priority".<ref>{{cite news |title=Kheel Urges Port Authority to Sell Trade Center |date=November 12, 1969 |publisher=The New York Times}}</ref>

Private [[real estate]] developers and members of the Real Estate Board of New York also expressed concerns about this much "subsidized" office space going on the open market, competing with the private sector when there was already a glut of vacancies.<ref name="Gillespie-chap1"/><ref>{{cite news |title=New Fight Begun on Trade Center |author=Knowles, Clayton |date=February 14, 1964 |publisher=The New York Times}}</ref> An especially vocal critic was Lawrence A. Wien, owner of the [[Empire State Building]], which would lose its title of [[List of tallest buildings and structures in the world|tallest building in the world]].<ref name="Gillespie-chap1"/><ref>{{cite news |title=Critics Impugned on Trade Center |author=Ennis, Thomas W. |date=February 15, 1964 |publisher=The New York Times}}</ref> Wien organized a group of builders into a group called the "Committee for a Reasonable World Trade Center" which demanded the project be scaled down.<ref>{{cite news |title=All Major Builders are Said to Oppose Trade Center Plan |author=Knowles, Clayton |date=March 9, 1964 |publisher=The New York Times}}</ref>

In January 1964, the Port Authority inked a deal with the State of New York to locate government offices at the World Trade Center.<ref>{{cite news |title=State Will Rent at Trade Center |author=Sibley, John |publisher=The New York Times |date=January 14, 1964}}</ref> The Port Authority began signing up some commercial tenants in the Spring and Summer of 1964, including several banks.<ref>{{cite news |title=4th Bank Signed by Trade Center |date=July 14, 1964 |publisher=The New York Times}}</ref> In 1965, the Port Authority signed up the [[United States Customs Service]] as a tenant.<ref>{{cite news |title=Customs to Move to Trade Center |author=Fowler, Glenn |date=July 7, 1965 |publisher=The New York Times}}</ref>

A final obstacle for the Port Authority was getting approval from New York City Mayor [[John Lindsay]] and the [[New York City Council]]. They raised concerns about the limited extent that the Port Authority involved the city in the negotiations and deliberations. Negotiations between The City of New York and the Port Authority were centered on tax issues. A final agreement was made on [[August 3]], [[1966]], that the Port Authority would make annual payments to the city in lieu of taxes, for the portion of the World Trade Center leased to private tenants.<ref>{{cite news |title=City Ends Fight with Port Body on Trade Center |author=Smith, Terence |date=August 4, 1966 |publisher=The New York Times}}</ref> In subsequent years, the payments would rise as the overall [[Property tax|real estate tax]] rate rise.<ref>{{cite news |title=Mayor Signs Pact on Trade Center |author=Smith, Terence |publisher=The New York Times |date=January 26, 1967}}</ref>

==Design==
On [[September 20]], [[1962]], the Port Authority announced the selection of [[Minoru Yamasaki]] as lead architect, and [[Emery Roth|Emery Roth & Sons]] as associate architects.<ref>{{cite news |title=Architect Named for Trade Center |author=Esterow, Milton |date=September 21, 1962 |publisher=The New York Times}}</ref> Originally, Yamasaki came back to the Port Authority with the concept of twin towers, but with each building only 80 stories tall. Yamasaki remarked that the "obvious alternative, a group of several large buildings, would have looked like a housing project".<ref name="nyt-1964jan19a">{{cite news |title=A New Era Heralded |author=Huxtable, Ada Louise |publisher=The New York Times |date=January 19, 1964}}</ref>
[[Image:World Trade Center Building Design with Floor and Elevator Arrangment.svg|thumb|250px|A typical floor layout and elevator arrangement of the WTC towers.]]
To meet the Port Authority's requirement to build 10 million [[Square foot|square feet]] (930,000 m²) of office space, the buildings would each need to be 110 stories tall. A major limiting factor in building heights were elevators. The taller the building, the more [[elevator]]s are needed to service the building and more space-consuming elevator banks.<ref>{{cite news |title=Biggest Buildings Herald New Era |author=Huxtable, Ada Louise |date=January 26, 1964 |publisher=The New York Times}}</ref> Yamasaki and the engineers decided to use a new system with sky lobbies, which are floors where people can switch from a large capacity, express [[elevator]] that goes only to the sky lobbies to a local elevator that goes to each floor in a section. The local elevators were stacked on top of each other, within the same elevator shaft. Located on the 44th and 78th floors of each tower, the sky lobbies enabled the elevators to be used efficiently, while also increasing the amount of usable space on each floor from 62 to 75 percent by reducing the number of required elevator shafts.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 9 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> The World Trade Center towers were the second [[supertall]] buildings to use sky lobbies, after the [[John Hancock Center]] in [[Chicago]].<ref>{{cite web |url= http://www.otis.com/otis150/section/1,2344,ARC3066_CLI1_RES1_SEC5,00.html|publisher=[[Otis Elevator Company]]|title= Otis History: The World Trade Center|accessdate=2006-12-07}}</ref> This system was inspired by the [[New York City Subway]] system, whose lines include local stations where local trains stop and express stations where all trains stop.<ref name="gillespie-p76">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 76}}</ref>
[[Image:Wtc_model_at_skyscraper_museum.jpg|thumb|left|185px|Original architectural and engineering model]]
Yamasaki's design for the World Trade Center was unveiled to the public on [[January 18]], [[1964]], with an eight-foot model.<ref name="nyt-1964jan19a"/> The towers had a square plan, approximately 207 feet (63 m) in dimension on each side.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 7 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> The buildings were designed with narrow office windows, only 18 [[inch]]es (45 [[Centimetre|cm]]) wide, which reflected on Yamasaki's [[Acrophobia|fear of heights]] and desire to make building occupants feel secure.<ref name="pekala">{{cite news |title=Profile of a lost landmark; World Trade Center |publisher=Journal of Property Management |date=November 1, 2001 |author=Pekala, Nancy}}</ref> Yamasaki's design called for the building facades to be sheathed in aluminum-alloy.<ref name="nyt-1966may29">{{cite news |title=Who's Afraid of the Big Bad Buildings |author=Huxtable, Ada Louise |date=May 29, 1966 |publisher=The New York Times}}</ref> In all, the World Trade Center complex contained six buildings within the 16 acre (6.5 ha) [[City_block#Superblock|superblock]].

The World Trade Center design brought criticism of its aesthetics from the [[American Institute of Architects]] and other groups.<ref>{{cite news |title=Marring City's Skyline |author=Steese, Edward |date=March 10, 1964 |publisher=The New York Times}}</ref><ref name="nyt-1966may29"/> [[Lewis Mumford]], author of ''[[The City in History]]'' and other works on [[urban planning]], criticized the project and described it and other new skyscrapers as "just glass-and-metal filing cabinets".<ref>{{cite news |title=Mumford Finds City Strangled By Excess of Cars and People |author=Whitman, Alden |publisher=The New York Times |date=March 22, 1967}}</ref> [[Television]] broadcasters raised concerns that the World Trade Center twin towers would cause interference in television reception for viewers in the [[New York metropolitan area|New York City area]].<ref>{{cite news |title=TV Group Objects to Trade Towers |author=Schumach, Murray |date=February 20, 1966 |publisher=The New York Times}}</ref> In response to these concerns, the Port Authority offered to provide new television transmission facilities at the World Trade Center.<ref>{{cite news |title=TV Mast Offered on Trade Center |date=February 24, 1966 |publisher=The New York Times}}</ref> The [[Linnaean Society]] of the [[American Museum of Natural History]] also opposed the Trade Center project, citing hazards the buildings would impose on [[Bird migration|migrating bird]]s.<ref>{{cite news |title=Big Trade Center Called Bird Trap |author=Knowles, Clayton |publisher=The New York Times |date=March 16, 1967}}</ref>

The structural engineering firm, Skilling, Helle, Christiansen, [[Leslie Robertson|Robertson]], worked to implement Yamasaki's design, developing the tube-frame structural system used in the buildings. The Port Authority's Engineering Department served as foundation engineers, Joseph R. Loring & Associates as [[electrical engineering|electrical engineers]], and Jaros, Baum & Bolles as [[mechanical engineering|mechanical engineers]]. [[Tishman Reality & Construction|Tishman Realty & Construction Company]] was the [[general contractor]] on the World Trade Center project. Guy F. Tozzoli, director of the World Trade Department at the Port Authority, and the Port Authority's Chief Engineer, Rino M. Monti, oversaw the project.<ref>{{cite book |author=National Construction Safety Team |url=http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf |format =PDF | title=Final Report on the Collapse of the World Trade Center Towers |publisher=NIST |chapter=Chapter 1 |date=September 2005 |pages=p. 1}}</ref>

===Structural design===
As an interstate agency, the Port Authority was not subject to local laws and regulations of the City of New York, including [[building code]]s. Nonetheless, the Port Authority required architects and structural engineers to follow the New York City building codes. At the time when the World Trade Center was planned, new building codes were being devised to replace the 1938 version that was in place. The structural engineers ended up following draft versions of the new 1968 building codes which incorporated "advanced techniques" in [[building design]].<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. xxxviii |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref>

The World Trade Center towers included many [[structural engineering]] innovations in [[skyscraper design and construction]], which allowed the buildings to reach new heights and become the [[List of tallest buildings in the world|tallest]] in the world. Traditionally, [[skyscraper]]s used a skeleton of [[column]]s distributed throughout the interior to support building loads, with interior columns disrupting the floor space. The tube-frame concept was a major innovation, allowing open floor plans and more rentable space. The buildings used high-strength, load bearing perimeter [[steel]] columns called [[truss#Vierendeel truss|Vierendeel trusses]], that were spaced closely together to form a strong, rigid wall structure. There were 59 perimeter columns, narrowly spaced on each side of the buildings. These were designed to provide support for virtually all lateral loads (such as wind loads) and to share the gravity loads with the core columns.<ref>{{cite book |author=National Construction Safety Team |url=http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf |title=Final Report on the Collapse of the World Trade Center Towers |publisher=NIST |format =PDF |date=September 2005 |chapter=Chapter 1 |pages=p. 6}}</ref>
[[Image:Nistncstar1-1-fig2-4.png|thumb|right|Typical WTC architectural floor plan]]
The perimeter structure was constructed with extensive use of prefabricated modular pieces, which consisted of three columns, three stories tall, connected together by [[wikt:spandrel|spandrel]] plates. The perimeter columns had a square cross section, 14 inches (36 cm) on a side, and were constructed of welded steel plate.<ref name="NIST-chapter1">{{cite book |author=National Construction Safety Team |url=http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf |format =PDF |title=Final Report on the Collapse of the World Trade Center Towers |publisher=NIST |date=September 2005}}</ref> The thickness of the plates and grade of [[structural steel]] varied over the height of the tower, ranging from 36,000 to 100,000 pounds per square inch<ref>[[A36 steel]] has a nominal [[Yield (engineering)|yield strength]] of 36,000 to 100,000 pounds per square inch.</ref> (260 to 670 MPa). The strength of the steel and thickness of the steel plates decreased with height because they were required to support lesser amounts of building mass on higher floors.<ref name="NIST-chapter1"/> The tube-frame design required 40 percent less structural steel than conventional building designs.<ref name="steel">{{cite journal |author=American Iron and Steel Institute |title=The World Trade Center - New York City |journal=Contemporary Steel Design |volume=1(4) |year=1964 |publisher=American Iron and Steel Institute}}</ref> From floor #7 to the ground level and down to the foundation, the columns were spaced 10 feet (3 m) apart.<ref>{{cite book |author=National Construction Safety Team |url=http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf |format =PDF |title=Final Report on the Collapse of the World Trade Center Towers |publisher=NIST |date=September 2005 |pages=p. 10}}</ref> All columns were founded on [[bedrock]], which unlike Midtown Manhattan, where the bedrock is shallow, is at 65–85 feet (20–26 m) below the surface.<ref>{{cite journal |url=http://www.nae.edu/nae/bridgecom.nsf/weblinks/CGOZ-58NLJ9?OpenDocument |title=World Trade Center "Bathtub": From Genesis to Armageddon |journal=Bridges |author=Tamaro, George J. |date=Spring 2002 |volume=32(1)}}</ref>

The spandrel plates were welded to the columns to create the modular pieces off-site at the fabrication shop.<ref>{{cite book |author=National Construction Safety Team |url=http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf |format =PDF |title=Final Report on the Collapse of the World Trade Center Towers |publisher=NIST |date=September 2005 |pages=p. 8}}</ref> The modular pieces were typically 52 inches (1.3 m) deep, and extended for two full floors and half of two more floors.<ref name="NIST-chapter1"/> Adjacent modules were bolted together, with the splices occurring at mid-span of the columns and spandrels. The spandrel plates were located at each floor, and served to transmit [[shear stress]] between columns, thus allowing them to work together in resisting lateral loads. The joints between modules were staggered vertically, so the column splices between adjacent modules were not at the same floor.<ref name="NIST-chapter1"/>

The building's core housed the [[elevator]] and utility shafts, restrooms, three stairwells, and other support spaces. The core of each tower was a rectangular area 87 by 135 feet (27 by 41 m), and contained 47 steel columns running from the bedrock to the top of the tower.<ref name="NIST-chapter1"/> The columns tapered with height, and consisted of welded box-sections at lower floors and rolled wide-flange sections at upper floors. The core in 1 WTC was oriented with the long axis east to west, while that of 2 WTC was oriented north to south. All of the elevators were located in the core. Each building had three stairwells that were also located in the core, except on the [[mechanical floor]]s where they were located outside of the structural core.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 8 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref>
[[Image:Wtc floor truss system.png|thumb|left|Schematic of composite floor truss system]]
The large, column-free space between the perimeter and core was bridged by pre-fabricated floor trusses. The floors supported their own weight, as well as [[live loads]], provided lateral stability to the exterior walls, and distributed wind loads among the exterior walls. The floors consisted of 4 inch (10 cm) thick lightweight [[concrete]] slabs laid on a fluted steel deck. A grid of lightweight bridging trusses and main trusses supported the floors. The trusses had a span of 60 feet (18.2 m) in the long-span areas and 35 feet (11 m) in the short span area.<ref name="NIST-chapter1"/> The trusses connected to the perimeter at alternate columns, and were therefore on 6 foot 8 inch (2.03 m) centers. The top chords of the trusses were bolted to seats welded to the spandrels on the exterior side and a channel welded to the core columns on the interior side. The floors were connected to the perimeter spandrel plates with [[Viscoelasticity|viscoelastic]] dampers, which helped reduce the amount of sway felt by building occupants. The trusses supported a 4 inch thick (10 cm) lightweight concrete floor slab, with shear connections for composite action.<ref name="NIST-chapter1"/>

Hat [[trusses]] (or "outrigger truss") located from the 107th floor to the top of the buildings were designed to support a tall communications [[Antenna (radio)|antenna]] on top of each building.<ref name="NIST-chapter1"/> Only 1 WTC (north tower) actually had an antenna fitted, which was added in 1978.<ref>{{cite web |url=http://www.pbs.org/wgbh/amex/newyork/sfeature/sf_building.html |title=New York: A Documentary Film - The Center of the World (Construction Footage) |publisher = Port Authority / PBS |accessdate=2007-05-16}}</ref> The truss system consisted of six trusses along the long axis of core and four along the short axis. This truss system allowed some load redistribution between the perimeter and core columns and supported the transmission tower.

===Wind effects===
The tube frame design using steel core and perimeter columns protected with sprayed-on fire resistant material created a relatively lightweight structure that would sway more in response to the wind, compared to traditional structures such as the [[Empire State Building]] that have thick, heavy [[masonry]] for fireproofing of steel structural elements.<ref>{{cite book |title=City in the Sky |author=Glanz, James and Eric Lipton |pages=p. 138 |publisher=Times Books |year=2003}}</ref> During the design process, [[wind tunnel]] tests were done at [[Colorado State University]] and at the [[National Physical Laboratory, UK|National Physical Laboratory]] in the [[United Kingdom|U.K.]] to establish design wind pressures that the World Trade Center towers could be subjected to and structural response to those forces.<ref>{{cite book |title=Design and Construction of Structural Systems (NCSTAR 1-1A) |publisher=National Institute of Standards and Technology |pages=p. 65 |author=Fanella, David A., Arnaldo T. Derecho, S.K. Ghosh |date=September 2005}}</ref> Experiments were also done to evaluate how much sway occupants could tolerate. Subjects were recruited for "free eye exams", while the real purpose of the experiment was to subject them to simulated building sway and find out how much they could comfortably tolerate.<ref>{{cite book |title=City in the Sky |author=Glanz, James and Eric Lipton |pages=p. 139-144 |publisher=Times Books |year=2003}}</ref> Many subjects did not respond well, experiencing [[dizziness]] and other ill effects. The chief engineer [[Leslie Robertson]] worked with Canadian engineer Alan G. Davenport to develop viscoelastic [[Damping|dampers]] to absorb some of the sway. These viscoelastic dampers, used throughout the structures at the joints between floor trusses and perimeter columns, along with some other structural modifications reduced the building sway to an acceptable level.<ref>{{cite book |title=City in the Sky |author=Glanz, James and Eric Lipton |pages=p. 160-167 |publisher=Times Books |year=2003}}</ref>

===Fire protection===
[[Fireproofing|Sprayed-fire resistant material]]s (SFRMs) were used to protect some structural steel elements in the towers, including all floor trusses and beams.<ref name="NCSTAR 1-1-p8">{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 8 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> [[Gypsum]] [[wallboard]] in combination with SFRMs, or in some cases gypsum wallboard alone, was used to protect core columns.<ref name="NCSTAR 1-1-p8"/> [[Vermiculite]] plaster was used on the interior-side and SFRMs on the other three sides of the perimeter columns for fire protection.<ref name="NCSTAR 1-1-p8"/> The 1968 New York City building codes were more lenient in some aspects of fire protection, such as allowing three exit stairwells in the World Trade Center towers, instead of six as required under older building codes.<ref name="NCSTAR 1-1-p153">{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 153 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref>

The 1968 New York City building codes did not require [[Fire sprinkler|sprinkler]]s for [[high-rise]] buildings, except for underground spaces. In accordance with building codes, sprinklers were originally installed only in the underground parking structures of the World Trade Center.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 162 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> Following a major fire in February 1975, the Port Authority decided to start installing sprinklers throughout the buildings. By 1993, nearly all of Tower 2 [South Tower], and 85% of Tower 1 had sprinklers installed,<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. 163 |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> and the entire complex was retrofitted by 2001.<ref>{{cite book |title=Active Fire Protection Systems (NCSTAR 1-4) |publisher=National Institute of Standards and Technology |pages=p. 14 |author=Evans, David D., Richard D. Peacock, Erica D. Kuligowski, W. Stuart Dols, William L. Grosshandler |date=September 2005}}</ref>

==Construction==
In March 1965, the Port Authority began acquiring property at the World Trade Center site.<ref>{{cite news |title=Port Agency Buys Downtown Tract |author=Ingraham, Joseph C. |date=March 29, 1965 |publisher=The New York Times}}</ref> The Ajax Wrecking and Lumber Corporation was hired to do the [[demolition]] work, which began on [[March 21]], [[1966]] to clear the site for construction of the World Trade Center.<ref name="gillespie-p61">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 61}}</ref>

[[Groundbreaking]] was on [[August 5]], [[1966]], marking the beginning of construction of the World Trade Center's foundations.<ref>{{cite news |title=Jackhammers Bite Pavement to Start Trade Center Job |date=August 6, 1966 |publisher=The New York Times}}</ref> The site of the World Trade Center was located on landfill, with the bedrock located 65 feet (20 m) below.<ref name="iglauer">{{cite news |url=http://www.newyorker.com/archive/content/articles/010924fr_archive02 |title=The Biggest Foundation |author=Iglauer, Edith |date=November 4 1972 |publisher=The New Yorker}}</ref> In order to construct the World Trade Center, it was necessary to build the "bathtub", with the [[slurry wall]] along the [[West Street]] side of the site, to keep water from the Hudson River out. The slurry method involves digging a [[trench]], and as [[excavation]] proceeds, filling the space with a "slurry" mixture, comprised of [[bentonite]] which plugs holes and keeps water out. When the trench was dug out, a steel cage was inserted, with concrete poured in, forcing the "slurry" out. The "slurry" method was devised by Port Authority chief engineer, John M. Kyle, Jr. Towards the end of 1966, work began on building the [[slurry wall]], led by [[Montreal]]-based Icanda, a subsidiary of an Italian engineering firm, Impresa Costruzioni Opere Specializzate (I.C.O.S.).<ref name="gillespie-p68">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 68}}</ref> It took fourteen months for the slurry wall to be completed, which was necessary before excavation of material from the interior of the site could begin.<ref name="gillespie-p68"/> The original [[Downtown Hudson Tubes|Hudson Tubes]], which carried PATH trains into Hudson Terminal, remained in service as elevated [[tunnel]]s until 1971 when a new [[World Trade Center (PATH station)|PATH station]] was built.<ref>{{cite news |author=Carroll, Maurice |title=A Section of the Hudson Tubes is Turned into Elevated Tunnel |date=December 30, 1968 |publisher=The New York Times}}</ref>
[[Image:Wtc panynj 1973.jpg|thumb|right|200px|World Trade Center in 1973]]
[[Construction|Construction work]] began on the North Tower in August 1968 with construction beginning on the South Tower by January 1969.<ref name="pbstimeline">{{cite web |url=http://www.pbs.org/wgbh/amex/newyork/timeline/index.html |title=Timeline: World Trade Center chronology |publisher=PBS - American Experience |accessdate=2007-05-15}}</ref> In January 1967, $74 million in contracts were awarded to the [[PACCAR|Pacific Car and Foundry Company]], [[Laclede Steel Company]], [[U.S. Steel|Granite City Steel Company]], and [[Karl Koch Steel Consulting|Karl Koch Erecting Company]] to supply [[steel]] for the project.<ref name="nyt-1967jan24">{{cite news |title=Contracts Totaling $74,079,000 Awarded for the Trade Center |publisher=The New York Times |date=January 24, 1967}}</ref> The Port Authority chose to use many different steel suppliers, bidding on smaller portions of steel, rather than buy larger amounts from a single source such as [[Bethlehem Steel]] or [[U.S. Steel]] as a cost-saving measure.<ref name="gillespie-p83">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 83}}</ref> Karl Koch was also hired to do all the work of erecting the steel, and a contract for work on the aluminum facade was awarded to the [[Alcoa|Aluminum Company of America]].<ref name="nyt-1967jan24"/> [[Tishman Realty & Construction]] was hired in February 1967 to oversee construction of the project.<ref>{{cite news |title=Trade Center Job To Go To Tishman |author=Kihss, Peter |publisher=The New York Times |date=February 27, 1967}}</ref>

Extensive use of [[prefabrication|prefabricated]] parts for the perimeter framing and floor truss systems helped speed up the construction process and reduce costs, while providing greater [[quality control]].<ref name="steel"/> Steel components were freighted into a [[Penn Central Transportation|Penn Central]] yard in [[Jersey City, New Jersey|Jersey City]]. From there, they were brought in early morning hours through the [[Holland Tunnel]] to the construction site, and lifted into place by a [[Crane (machine)|crane]].<ref>{{cite news |title=Trade Center is Doing Everything Big |publisher=The New York Times |date=June 6, 1969 |author=Kaufman, Micheal T.}}</ref> Larger pieces were brought to the construction site by [[tugboat]]s.<ref name="gillespie-p88">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 88}}</ref> A special type of crane, suitable for constructing such tall buildings, that used [[hydraulics]] to lift components and provided its own power was used in construction of the World Trade Center. The Favco Standard 2700 Crane, manufactured by Favelle Mort Ltd. of [[New South Wales]], [[Australia]] was informally called a "[[kangaroo]] crane".<ref name="gillespie-p92">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 92-94}}</ref>

In 1970, tugboat workers went on [[Strike action|strike]], halting the transport of material to the construction site.<ref>{{cite news |title=300 Tugboats Idle as Men Walk Out for Doubled Wage |author=McFadden, Robert D. |date=February 2, 1970 |publisher=The New York Times}}</ref> The Port Authority attempted other means of transporting material, including via [[helicopter]]. When this method was tried, the helicopter lost its load of steel into the [[Kill Van Kull]].<ref name="gillespie-p91">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 91}}</ref> Some other mishaps occurred during the construction process, including disruption of [[telephone]] service in Lower Manhattan when telephone cables were crushed by [[pile driver]]s.<ref>{{cite news |author=Carroll, Maurice |title=Phones Disrupted by a Pile Driver |date=March 19, 1969 |publisher=The New York Times}}</ref> On [[March 16]], [[1970]], a [[propane]] gas explosion injured six workers, when a truck hit a propane tank.<ref>{{cite news |title=Propane Blast Hits Trade Center |author=Van Gelder, Lawrence |date=March 17, 1970 |publisher=The New York Times}}</ref> In all, 60 workers were killed in construction accidents while the World Trade Center was being built.<ref>{{cite web |url=http://www.pbs.org/americarebuilds/engineering/engineering_qfacts.html |title=America Rebuilds: Quick Facts |publisher=PBS |accessdate=2007-05-15}}</ref>

Construction of 1 World Trade Center (North Tower) was completed on [[December 23]], [[1970]], with 2 World Trade Center (South Tower) completed on [[July 19]], [[1971]].<ref name="pbstimeline"/> First tenants moved into the North Tower in December 1970, and into the South Tower in January 1972.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. xxxvi |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> The buildings were dedicated on [[April 4]], [[1973]], with Tobin, who resigned the year before, absent from the ceremonies.<ref name="Darton-chap6">Darton, Eric (1999) ''Divided We Stand: A Biography of New York's World Trade Center'', Chapter 6, Basic Books.</ref>

Building the World Trade Center involved excavating 1.2 million [[cubic yard]]s (917,000 [[Cubic metre|m³]]) of material.<ref name="gillespie-p71">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 71}}</ref> Rather than transporting this material at great costs out to sea or to landfills in [[New Jersey]], the fill material was used to expand the [[Manhattan]] shoreline across [[West Street]].<ref name="gillespie-p71"/> Work to demolish the [[pier]]s began on [[January 5]], [[1967]], including Pier 7 to Pier 11 which were all constructed around 1910.<ref>{{cite news |title=Demolition Begun on 5 City Piers |author=Horne, George |publisher=The New York Times |date=January 5, 1967}}</ref> The demolition work moved forward, despite conflicts between [[David Rockefeller]], Governor [[Nelson Rockefeller]], and Mayor [[John Lindsay]] regarding plans for Battery Park City.<ref>{{cite news |title=Conflicts Stall Landfill Plans |author=Roberts, Steven V. |publisher=The New York Times |date=January 17, 1967}}</ref> Landfill material from the [[World Trade Center]] was used to add land, and a cellular [[cofferdam]] was constructed to retain the material.<ref name="iglauer">{{cite news |url=http://www.newyorker.com/archive/content/articles/010924fr_archive02 |title=The Biggest Foundation |author=Iglauer, Edith |date=November 4 1972 |publisher=The New Yorker}}</ref> The result was a 700 foot (210 m) extension into the [[Hudson River]], running six blocks or 1,484 feet (450 m).<ref name="gillespie-p71"/> This land was a "gift" to New York City, allowing more [[tax]]-generating developments in [[Battery Park City, Manhattan|Battery Park City]].<ref>{{cite news |title=New York Gets $90 Million Worth of Land for Nothing |publisher=Engineering News Record |date=April 18, 1968}}</ref>

The original estimates put forth by the Port Authority had the costs for construction of the World Trade Center at $350 million — an optimistic figure.<ref name="gillespie-p70">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 70}}</ref> In December 1966, the Port Authority announced increased cost estimates, bringing the estimated total to $575 million.<ref name="gillespie-p69">{{cite book |author=Gillespie, Angus K. |year=1999 |title=Twin Towers: The Life of New York City's World Trade Center |publisher=Rutgers University Press |pages=p. 69}}</ref> This announcement brought criticism of the project from private real estate developers, the [[New York Times]], and others in New York City.<ref>{{cite news |title=Questions on the Trade Center |publisher=The New York Times |date=December 24, 1966}}</ref> The critics charged that the Port Authority figure was unrealistically low estimate, and they estimated the project would end up costing $750 million.<ref>{{cite news |title=Estimate Raised for Trade Center |author=Phillips, McCandlish |date=December 29, 1966 |publisher=The New York Times}}</ref> When the World Trade Center twin towers were completed, the total costs to the Port Authority had reached $900 million.<ref name="Cudahy">Cudahy, Brian J. (2002) ''Rails Under the Mighty Hudson: The Story of the Hudson Tubes, the Pennsy Tunnels, and Manhattan Transfer'', Chapter 3, Fordham University Press.</ref> The project was financed through [[Tax exemption|tax-exempt]] [[Bond (finance)|bond]]s issued by the Port Authority.<ref>{{cite news |author=Allan, John H. |title=Bonds: Port of New York Authority to Raise $100-Million |date=February 28, 1968 |publisher=The New York Times}}</ref>

==Other buildings==
The World Trade Center complex included four other, smaller buildings constructed during the 1970s. 3 World Trade Center was a 22-story building, which was home to the [[Marriott World Trade Center]]. It was designed by [[Skidmore, Owings and Merrill]] in 1978-79.<ref>{{cite book |author=McAllister, Therese, Johnathan Barnett, John Gross, Ronald Hamburger, Jon Magnusson |chapter=WTC3 |title=World Trade Center Building Performance Study |publisher=FEMA |date=May 2002}}</ref> [[4 World Trade Center]], [[5 World Trade Center]], and [[6 World Trade Center]] were all 8-9 story buildings that were designed by the same team as the Twin Towers, including Minoru Yamasaki, Emery Roth & Sons, and Skilling, Helle, Christiansen, Robertson.<ref>{{cite book |author=McAllister, Therese, Johnathan Barnett, John Gross, Ronald Hamburger, Jon Magnusson |chapter=WTC4, 5, and 6 |title=World Trade Center Building Performance Study |publisher=FEMA |date=May 2002}}</ref> A seventh building ([[7 World Trade Center]]) was built in the mid-1980s, just to the north of the main World Trade Center site. The 47-story building was designed by Emery, Roth & Sons, and constructed on top of a [[Con Edison]] power [[substation]].<ref>{{cite book |author=McAllister, Therese, Johnathan Barnett, John Gross, Ronald Hamburger, Jon Magnusson |chapter=WTC7 |title=World Trade Center Building Performance Study |publisher=FEMA |date=May 2002}}</ref>

==Modifications==
Over time, numerous structural modifications were made to suit the needs of tenants in the Twin Towers. Modifications were made in accordance with the Port Authority's ''Tenant Alteration Review Manual'' and were reviewed by the Port Authority to ensure the changes did not compromise structural integrity of the buildings. Oftentimes, openings were cut in the floors to allow new [[stairway]]s to be built to connect tenant floors. Some steel beams in the core were reinforced and strengthened to accommodated heavy live loads, such as large amounts of heavy files that tenants had on their floors.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. xliv |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref>

Repairs to structural elements on the lower levels of 1 WTC [North Tower] were made following the [[1993 World Trade Center bombing]]. The greatest damage occurred on levels B1 and B2, with significant structural damage also on level B3.<ref>{{cite book |title=Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1) |publisher=National Institute of Standards and Technology |pages=p. xlv |author=Lew, H.S., Richard W. Bukowski, Nicholas J. Carino |date=September 2005}}</ref> Primary structural columns were not damaged, but secondary steel members experienced some damage.<ref>{{cite web |url=http://www.interfire.org/res_file/pdf/Tr-076.pdf |format =PDF |title=Experiences of the Chief Engineer of the Port Authority |author=Fasullo, Eugene |publisher=United States Fire Administration |accessdate=2007-05-15}}</ref> Floors that were blown out needed to be repaired, to restore the structural support they provided to columns.<ref>{{cite web |url=http://www.interfire.org/res_file/pdf/Tr-076.pdf |format =PDF |title=The World Trade Center Complex |author=Port Authority Risk Management Staff |publisher=United States Fire Administration |accessdate=2007-05-15}}</ref> The slurry wall was in peril following the bombing and loss of the floor slabs which provided lateral support to counteract pressure from Hudson River water on the other side.<ref name="ennala">{{cite journal |author=Ramabhushanam, Ennala and Marjorie Lynch |title=Structural Assessment of Bomb Damage for World Trade Center |journal=Journal of Performance of Constructed Facilities |volume=8(4) |pages=229-242}}</ref> The [[refrigeration]] plant on sublevel B5, which provided [[air conditioning]] to the entire World Trade Center complex, was heavily damaged and replaced with a temporary system for the summer of 1993.<ref name="ennala"/> The [[fire alarm]] system for both towers needed to be replaced, after critical wiring and signaling in the original system was destroyed in the 1993 bombing. Installation of the new system took years to complete, and replacement of some components was still underway at the time of the [[September 11, 2001 attacks]].<ref>{{cite book |title=Active Fire Protection Systems (NCSTAR 1-4) |publisher=National Institute of Standards and Technology |pages=p. 44 |author=Evans, David D., Richard D. Peacock, Erica D. Kuligowski, W. Stuart Dols, William L. Grosshandler |date=September 2005}}</ref>

==See also==
* [[Collapse of the World Trade Center]]
* [[Freedom Tower]]
* [[150 Greenwich Street]]
* [[175 Greenwich Street]]
* [[200 Greenwich Street]]

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==External links==
* [http://www.pbs.org/wgbh/amex/newyork/sfeature/sf_building.html New York: A Documentary Film - The Center of the World] - ''Building the World Trade Center'', an 18-minute film, with construction footage, produced by the Port Authority in 1983
* [http://www.skyscraper.org/WHAT%27S_UP/WTC_DOSSIER/wtc.htm World Trade Center] - Skyscraper Museum
* {{Cite web
| title = Corus in construction - Systems evolution
| accessdate = 2007-05-14
| url = http://corusconstruction.com/en/reference/teaching_resources/architectural_studio_reference/design/tall_building_designs/systems_evolution/
}}
* [http://wtc.nist.gov/ NIST and the World Trade Center]
* [http://www.ericdarton.net/ New York's World Trade Center - A Living Archive] - by author, Eric Darton
* [http://www.antiqueradio.com/Sep02_RadioRow_Steinhardt.html The Death of New York's Radio Row], by Syd Steinhard - Downtown Express

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