|FACADE FEAR Convention center's varied skin so unnerved bidders that it was built on the basis of time and materials. (Photos courtesy of Clark Construction)|
The $833.9-million Washington Convention Center nearing completion in the nation's capital could contain two Washington Monuments laid end to end. It could also hold six football fields or four Boeing 747 jetliners. The more than 2.3-million-sq-ft building, one of the 10 largest in the U.S., has 16 acres of roof. It contains more than 40,000 tons of steel in 250 trusses and columns. It has roughly 600,000 sq ft of facade, more than 8 acres of masonry walls, and enough piping to run around the Washington Mall 15 times.
"Everything about the convention center is supersized," says Mark J. Tamaro, project manager for the local structural engineer of record, James Madison Cutts Consulting Structural Engineers Inc.
Everything is supersized except the job's schedule. In a rush to get revenue flowing in, the Washington Convention Center Authority compressed the timetable from five to four years.
Much like oil and water, supersizing and fast-tracking don't mix easily. "I've never had to juggle as many critical activities at the same time," says Ronald D. Strompf, a vice president of Clark Construction Group Inc., Bethesda, Md., and senior project superintendent for Clark/Smoot, the at-risk construction management joint venture of Clark and Sherman R. Smoot Corp., Falls Church, Va. Strompf, a 25-year Clark veteran, says the job caught him off-guard. "No one could have anticipated this in advance," he says.
ENDS TO MIDDLE Work proceeded from the ends toward the middle. Shear walls line up to help brace perimeter slurry wall. |
(Photo courtesy of Mark Tamaro)
Click photo for larger image.
There have been more than 12,600 requests for information and 5,000 submittals. "We were getting volumes of drawings," says Strompf. "It was difficult keeping up with the flow of information."
To tame the beast, Strompf holds daily early morning meetings with his supervisors, which include at least nine superintendents and five assistants within a staff of 60. Members of the design team, which set up shop at the site, join in at 8:30 a.m. Walk-throughs follow, also with designers, to take care of problems. "We didn't want paperwork to stop the job," he adds, "so we would generate the RFI after the walk-through, to confirm what was discussed."
Tracking information was also a monumental task for architect TVS-D&P-Mariani. The joint venture consists of Thompson Ventulett Stainback & Associates, Atlanta; and Devrouax & Purnell Architects Planners and Mariani Architects Engineers, both local. The design team peaked in 2000 at more than 100, including engineering consultants.
To handle the data, the architect set up a digital tracking system. Everything is stamped so it can be retrieved as needed, says Karim S. Najjar, the architect's construction administrator.
Najjar uses an alphabet soup of terms to help with communication. One that had its debut on the job is the RFE--a request for explanation also known as a reverse RFI.
The architect has issued only 100 RFEs. "Clark did not like [the system]," says Najjar, so it was only partially implemented.
"It was important [to Najjar], not us," says Strompf.
Some subcontractors answered RFEs. It often depended on whether there was a feeling "we were documenting a screw-up," says Najjar, who sees a big future for the RFE. "The A-E is always held accountable by the contractor," he says. "We would like to hold the contractor accountable."
Another device is the submittal modification request, used to make a minor adjustment to an approved shop drawing without having to resubmit the entire drawing. There are 400 SMRs on the job. "Clark loved them," says Najjar, because they saved time.
Then there are the 600 AECs--architect-engineer clarifications--which are design changes after bidding. To date, there are 149 CDRs, or construction deficiency reports, with only a dozen unresolved. That's "phenomenal" for a job of "this size and speed," says Strompf.
The CM generated about 3,250 change event notifications, which alert the owner to possible cost changes. The CENs translated into 462 change orders. That amounts to about 5% of the construction budget. The figure is within the industry norm, says Najjar.
The center is financed by $507 million in bonds backed by revenue from hotel and restaurant taxes and the existing convention center. There is also $70 million from federal and city grants, $30 million from contracts with vendors and $11 million from the authority's operating budget for administrative costs and about $200 million on interest earnings.
|REAL ESTATE The basement contains 40% of the volume. In plan, the convention center looks like two linked buildings. (Photos courtesy of Mark Tamaro)|
The original budget, in 1998, was estimated at $714 million. The number has increased several times, most recently last month. Allen Y. Lew, managing director of operations for the public owner, the Washington Convention Center Authority, attributes the increase to basing the original figure on an incomplete design. That was done to get the required U.S. congressional approval for the project, he says.
Lew attributes the latest bump up in price, from $799.5 million about a year earlier, to increased costs associated with mechanical, electrical, fireproofing work and the curtain wall support. In addition, the owner is spending more money to expedite construction. Lew also says more money was needed for design changes, to resolve field coordination issues and to meet requirements of the city.
There is $839.5 million budgeted for the project and an additional $90 million in reserves. The CM's guaranteed maximum price has risen to $606 million from $500.6 million. Click here to view layout
Room to grow. In the early 1990s, the district decided its existing convention center, which had opened only a decade earlier, was obsolete. It had no room to expand, only 30-ft ceilings and a shortage of meeting rooms.
The new, six-block building straddles a residential area to the north and a commercial area to the south. Roof heights vary from 40 to 130 ft and 40% of the volume is below grade. The basement measures roughly 1,450 x 400 ft and spreads under the street grid. It has 473,000 sq ft of contiguous exhibit space.
At grade, the center is divided into north, middle and south buildings by two cross streets. The south building, which contains the lobby, meeting rooms, and prefunction space for a 52,000-sq-ft ballroom with up to 48-ft ceilings, is connected to the rest by a pedestrian bridge. The other two buildings have a 230,000-sq-ft contiguous exhibit space on the second level.
Foundations consist of spread footings under columns and interior shear walls. A continuous 45-ft-deep slurry wall, designed by Mueser Rutledge Consulting Engineers, New York City, forms the basement perimeter. Instead of floor diaphragms, the slurry wall is laterally braced by horizontal steel compression struts, 115 ft long, which extend inward to shear walls. Each strut was jacked with more than 4 million lb of force to eliminate wall movement when loads from earth pressure were transferred from temporary tiebacks to the shear walls.
The building's frame is mostly 50-ksi steel with composite metal decking. Typical 90-ft-sq bays are supported by trusses up to 14 ft deep and built-up column sections. Exhibit floors are designed for 350 psf of live load. Upper exhibit hall roof trusses, 10 ft apart, are arched and span 180 ft. Ballroom bowstring trusses also span 180 ft and are 20 ft deep.
The entire facade required separate backup support, mostly steel tubular structure, due to tall floor-to-floor heights. At the south end, the curtain wall is supported by architecturally exposed trusses that span vertically up to 55 ft.
From the groundbreaking on March 8, 1999, the "construction cart" was often on the verge of getting ahead of the "design horse." To keep pace with the schedule, the first structural bid package went out in August 1999, nearly a year before the architecture was substantially complete.
The strategy was to build from the ends toward the middle. "The sheer quantities of materials removed from the site and brought onto the site created a logistics nightmare," says Strompf. "We met with subs every day to sequence deliveries."
To allow excavation under Ninth Street, running north to south on the site's western edge, workers temporarily had to relocate the street down the site's center. Eventually, workers built a grade viaduct over the Ninth Street excavation to reinstate the street. Eighth Street was closed permanently.
|UP FOR GOOD After batch of trusses were lost at sea, replacements collapsed. (Photo courtesy of Mark Tamaro)|
The excavation, touted as the biggest new-building excavation in the western hemisphere, went well, reports Strompf. So did slurry wall construction.
The next major challenge was to sequence the erection of structural steel, which took place over 15 months, ending in October 2001. The CM divided the work into two sequences, beginning with concurrent steel erection in north and south buildings. North building crews then moved into the middle building.
|(Photo by Tom Ichniowski for ENR)|
The job was so big that Havens Steel Global Steel Solutions, Kansas City, Mo., which held a $110-million-plus steel contract, had steel fabricated in seven places--including China, Russia and Korea. Heavy truss members were fabricated in Seoul and shipped around the Panama Canal to Baltimore, where they were trucked to the site.
Overboard. Steel work did not go smoothly. Things first went awry in the fall of 2000, halfway through steel erection. A ship loaded with some twenty, 14-ft-deep roof trusses lost power at sea when a bearing blew out of its engine. Then, bad weather hit. Eventually, a decision was made to throw cargo overboard, say sources. The freighter's insurance paid for refabrication. To save the eight-week shipping time, the work was done in the U.S.
That was only the first mishap. In April 2001, several hours after crews from Derr Steel Erection Co., Euless, Texas, had erected a roof truss and left for the day, the truss tipped over, knocking down 13 others. No one was hurt. Investigations concluded the collapse had been caused by high winds combined with inadequate temporary bracing (ENR 5/21/01 p. 20).
Fourteen trusses were lost. That was the bad news. The good news was that the collapse involved many of the trusses just refabricated in the U.S., so detailing had already been redone. Project insurance covered the cost of the second refabrication--also in the U.S. During that time, the erector, using crawler cranes, pushed southward, bypassing the affected area. During refabrication, Derr installed two tower cranes to re-erect the trusses. The crawlers would have had inadequate reach.
Despite the difficulties, Derr finished up steel erection pretty much on time, according to the structural engineer.
Construction of the south building was done in a horseshoe fashion from the east side to the south and then west. That "allowed us to get to the skin system sooner," says Strompf, which the CM knew was going to be time-consuming.
Najjar claims the articulated skin, which contains eight systems including curtain wall, precast concrete, limestone and two glazing systems, has a more complex profile than any other convention center facade. No one wanted to bid it lump sum, so it was executed on the basis of time and materials.
Facade work was done from mid-2001 through last year. Field coordination of the trades was intense, especially because base building architecture was not yet complete. The backup steel was literally modified to accept the skin as it was built.
Now, the scramble is on to get the building to substantial completion by March 31. The CM has added four supers and assistant supers, for a total of 22 supervisors. A composite crew of 50 is picking up loose ends relating to mechanical, electrical, sheet metal and drywall work. A second shift and more day shift workers should help meet the end date.
No punchlist activities have begun yet, says Najjar, though the architect and CM made a list of facade items either missing, incomplete or damaged. The consensus is that aesthetic punchlisting will have to occur after the building is open. Testing and operation of all life safety systems will have to occur prior to March 31, to ensure that a certificate of occupancy is issued, says Najjar.
Looking back over the project's tugs of war, structural engineer Tamaro says that most fights have been resolved. "Surprisingly," he adds, "we are coming out without too many scars."