source:
http://enr.ecnext.com/coms2/article_nebuar081015
WTC Hub’s Complex Design Overhauled for Constructibility 10/15/2008
By Nadine M. Post The most visible way the Port Authority of New York & New Jersey is trying to get a grip on the 16-acre World Trade Center redevelopment is through the simplification of Santiago Calatrava’s WTC Transportation Hub. To to keep the hub on its revised-upward $3.2-billion budget while retaining the architect-engineer’s “iconic” look, the port authority has eliminated the flapping wings of the steel hub, which is shaped like a dove. In the hub’s underground hall to the west, the Vierendeel trusses to support the arched concrete ceiling are gone.
Port Authority of NY & NJ
World Trade Center work fraught with delays, overruns.
The original design, budgeted at $2.2 billion, had “construction and engineering complexity that increased schedule, cost and constructibility risk,” says the port authority in its 70-page report, “A Roadmap Forward,” released on Oct. 2. Delays would have snowballed onto other WTC projects, such as Memorial Plaza, says the report.
In the redesign by the hub’s local Downtown Design Partnership, bolted steel plate girders supported by columns replace Vierendeels. The conventional approach reduces steel tonnage by 15%, sim-plifies fabrication and erection and eliminates field welding, says the report. Conventional framing allows the existing PATH subway station roof to remain in place during construction and reduces PATH track outages.
For the steel dove, the new approach, which eliminates operable roof arches that would open and close the wings, also simplifies engineering and construction. In addition, wing length has been shortened on one side. The redesign cuts the number of structural connections between wing elements from five to one, says the port authority.
Means and methods have also been revamped. Originally, the hub was going to be built from the bottom up. Roof work was to have been staged and would have meant that the Memorial Plaza atop the buried hall, which is part of the National Sept. 11 Memorial, would not have been finished until 2013. To open it as planned by Sept. 11, 2011, the hub’s local construction manager-general contractor, Phoenix Constructors Joint Venture, will build the hub using a top-down approach.
“The deckover approach incorporated in the new design means that we will build the roof first, thus prioritizing the completion of Memorial Plaza,” says the port authority. The solution will cost $75 million extra because of lost productivity and the need for a temporary deck, says the report.
Instead of going out to bid for a CM-GC for remaining work, Phoenix will remain. “An open bid process would only increase project risk through the uncertainty of contracting resources in the marketplace at this time, and the challenge of coordinating many different contractors... new to the site and the project,” says the report.
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But the port authority is revamping its relationship with Phoenix, a joint venture of Slattery Skanska, Fluor Corp., Granite Construction Northeast and Bovis Lend Lease. Under the new plan, Phoenix, which was working on a time and materials basis, will commit to working on a lump-sum, fixed-price basis. “This will result in cost certainty... better budget control and will also create improved incentives for the Phoenix team to perform efficiently,” says the report, available on
www.wtcprogress.com. “We now have a single point of accountability.” The port authority hopes to open the hub in mid-2014 instead of late 2009.