For work on the superstructure, crews have set four of the 10 pairs of 125-ft-long by 32-ft-wide girder assemblies. “The first arch segments pinned into a 4-feet-deep vertical plate of the arch on each side,” Roebuck says. “Making sure everything was oriented correctly was challenging.” Each arch will have 98 cables connecting the bridge deck to the arch above it, with an array of 49 cables coming down on either side. Crews have hung two cables, and full cable erection will begin later this year, after removing falsework to finish the pedestrian deckway, Roebuck says. The McDermott bridge project is the most visible part of the $798-million Dallas Horseshoe project, which will replace the I-30 and I-35E bridges spanning the Trinity River floodway. It also will reconstruct the I-30 “Mixmaster” interchange—the most congested interchange in north Texas—and update roadway geometry to create a more easily navigable horseshoe configuration. The project includes the widening of I-30 and I-35E to provide 13 driving lanes and 10 shoulder lanes at the river crossing.

“The main reason for the project is to replace some very old bridges that are costing more to maintain each year,” says Ceason Clemens, project manager for the Texas Dept. of Transportation. The project includes removing 26 bridges and building 43 new ones. Some 460,000 vehicles travel through the project on a weekday. Design-build will deliver the project “in half the time it would take Texas DOT to deliver a project of this complexity through our traditional design-bid-build method,” Clemens says. TxDOT also is aiming to reduce longterm maintenance costs by using precastconcrete girders. “Pegasus Link is using spliced concrete girders for the main spans across the Trinity River. Most of [the main spans] are about 250 feet in length,” Clemens says. While the highway segment of the McDermott bridge is pure design-build, the Calatrava bridge segment is not, says Bob Stevens, project director at PLC. “Texas DOT and the city of Dallas have an agreement for the city to fund [the bridge] and Texas DOT to build the bridge,” he explains. Calatrava has a contract with Huitt- Zollars, Dallas, for the detailed design, and Charlie Quade is the engineer of record.

“The two [firms] at the extreme ends of the contract chain are American Bridge, the steel erector, and Huitt-Zollars, the sub for Calatrava. So, in the chain of contracts, the two separated the most through contracts were the two that needed each other the most,” Stevens says. To allow for smooth communication between American Bridge and Huit-Zollars on technical details of the structural steel, PLC created a weekly technical work group, he says. “Early teleconferencing between me, PLC, TxDOT, Huitt-Zollars, Tampa Steel, Tensor Engineering and the city of Dallas allowed us to resolve issues quickly,” Roebuck recalls. “Mr. Calatrava [who lives and works in Zurich] did not participate in those conferences, but his rep helped to resolve detailing and fabrication issues by working through [3D] design drawings to help resolve or clarify issues.” Fabrication The unique geometry makes it challenging to fabricate and construct the steel arch and girder segments, Roebuck says, adding, “The midpoint of the arch is octagonal-shaped near the concrete abutment it bifurcates into where it connects with the abutment.” To verify the geometry of the steel segments, Florida-based Tampa Steel assembled and bolted at least four segments in the shop to verify the geometry. “They checked that everything was in tolerance, and American Bridge sent down a surveyor to verify the geometry. Tolerances are tight,” Roebuck says. Construction of the concrete abutment was a unique process that used bright-blue formwork that looks as if it were something out of “Star Wars,” says PLC’s Stevens. “One set of custom-made forms were used four times to construct the abutments,” he says.

“They are such a unique shape—[they are] not conventional pieces of formwork that would typically be reused multiple times,” he says. “At least Calatrava gave us that [chance to duplicate the segments],” he quipped. The concept, developed by LaPlace, La.-based Aluma Systems, was to fabricate steel in a way that allowed the formation of four identical concrete monoliths in sequence within a single steel formwork system. Aside from the technical challenges of designing slender arches with complex geometry, “much work focused on the design of the bridge lighting so that the structures maintain their signature status on the Dallas skyline at nighttime as well as during the day,” Calatrava says.