Home » Second Calatrava Trinity Span Crossing Floodplain in Dallas
Despite nail biting over predictions of 20-mph winds, crews on Aug. 22 erected the 200-ton center segment of the eastbound steel arch on the Margaret McDermott Bridge in Dallas. The lift went pretty smoothly, and the winds stayed within 15 mph, says Adam Roebuck, project manager at American Bridge. “Winds of 20 miles per hour would have pushed the limit of what was allowable,” he recalls. “There were no structural concerns, but we had a 312-ft-long arch segment hanging 280 feet that would catch the wind like a big sail.” American Bridge is a sub for Pegasus Link Constructors, a Fluor-Balfour Beatty partnership that is lead contractor for the $113-million project, which comprises two 18-ft-wide pedestrian and bicycle crossings designed by Spanish architect and structural engineer Santiago Calatrava. The white, 1,125-ft-long twin arch bridges that will rise 274 ft above the deck will flank the new eastbound and westbound I-30 frontage roads. The four-year project is scheduled for completion in summer 2017. Helping to keep the job on track are penalties of $100,000 per hour if the contractor closes too many lanes for too long during peak hours.
This bridge is the second such Calatrava structure to grace the Trinity River floodplain in downtown Dallas. The Margaret Hunt Hill Bridge, a 40-story arch and curving-cable structure, is three miles northwest of the McDermott bridge. Both bridges are part of the Trinity River Corridor project, which is helping to realize Calatrava’s ambitious idea of transforming the neglected Trinity River floodplain into a green parkway, served by a new transportation node. Erection of the eastbound bridge arch began in January 2015 and consisted of 11 separate lifts, Calatrava noted via email. “The largest arch element was the central segment, which measured 312½ feet long and weighed approximately 200 tons.” Beginning in July, seven individual arch sections of the bridge were assembled. “We had eight [temporary] falsework towers supporting the arch up through the center portion as we erected the segments,” Roebuck says. “The middle two falsework towers supported strand-jack equipment to lift the center arch into place.” The erection required four strand jacks, with two working in unison at each end of the arch. “To raise the crane picking point above the center of gravity—over the end of the field splices, off the center arch pick—we pinned a custom-designed lift frame on each side,” Roebuck says. Strand jacks were then connected into that pick frame to perform the highly orchestrated heavy-metal ballet. “We started [the erection] at 11 p.m. and had the arch substantially in position by 4 a.m., with minor adjustments by 5 a.m.” the following day, Roebuck says. “It went relatively smoothly. We wanted to limit [this operation] to 15-mph winds, and everything held within that limit,” he says. “Once we got the new arch into position, there was ¾ inches of clearance at each end of the field splices, and we were able to use a vertical jacking system to lower the previously erected arch to close the gap between the existing arch and the new arch.”