An investigation is underway into the cause of longitudinal cracks that have appeared in the precast-concrete girders installed for the aerial guideway of the Silver Line rail project in northern Virginia.
The cracks, some of which are several feet long, were discovered in the top flange of the 96-in.-high, 125- to 150-ft-long girders shortly after they were erected at Dulles International Airport in April by Capital Rail Constructors (CRC), a joint venture of Clark Construction Group LLC and Kiewit Infrastructure South. The JV is constructing the 11.4-mile, $2.778-billion project for the Metropolitan Washington Airports Authority (MWAA).
The 75-ton girders were designed by Parsons Transportation Group, CRC’s lead designer, and fabricated by Coastal Precast Systems, Chesapeake, Va.
According to MWAA, eight of 108 girders initially fabricated for the project had been delivered and installed before the cracks’ appearance led the agency to halt erection work on April 27. CRC inspected the girders at Coastal’s yard; then, upon arrival at the jobsite, CRC and MWAA also inspected them. The ends of the girders were fastened to separate trailers, with the middle sections unsupported for the approximately 220-mile trip between Chesapeake and Dulles.
Charles Stark, MWAA project executive, says a longitudinal top-flange crack appeared to be repairable but grew once the girder’s stiffening travel strand was detensioned.
“That leads us to believe … the cracks may be due to localized stresses during transport, [which] would subject the girder to stresses it wouldn’t see when installed in a structure,” says Stark.
The girders also contained small transverse cracks in the top flange and its “armpit” transition to the column. Stark thinks these cracks are a result of the curing process. While the columns and lower flanges are free of cracks, “our goal, of course, is for the girders to have no cracks at all,” he says.
Parsons and forensic structural-engineering consultant Pivot Engineers, Austin, Texas, are leading CRC's investigation. MWAA has retained a Parsons Brinckerhoff-AECOM joint venture to perform an independent analysis of the girder design. Girder fabrication also has been halted, pending the outcome of the investigation.
MWAA says the erected girders remain in place; however, following the conclusion of the investigation, the girders will be removed and not used for the project. CRC will pay all repair costs, including, if necessary, recasting the girders.
Stark is hopeful the answers and a path forward will be revealed within the next few weeks.
“We have 50 to 60 days of float in the girder-erection operation before it affects the critical path,” he says. “I’m confident we’ll get it resolved.”
A delay would mark another setback for the second phase of the 23.1-mile, $5.76-billion transit line, which is already 13 months behind schedule and now slated for a 2019 completion. MWAA attributes the delays to the design's more than 150 modifications in phase two, many of which paralleled design changes made in the latter stages of the 11.7-mile first phase. That Silver Line segment began operation in July 2014, six months late and $226 million over budget.
Work continues on other facets of the new rail line, including installation of drilled shafts and columns for the aerial guideway, as well as, later this month, the expected start of excavation for the station that will serve the airport terminal.