THE CONCRETE BRIDGE MAGAZINE

SPRING 2010

ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

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states are still hesitant to consider them. Cable-stayed designs also must fight their reputation. "They're often considered 'landmark' designs, which equates to being fancy—which means expensive." In fact, the concept was developed in post-war Germany to exploit material efficiencies. "The market for stays and stay hardware is robust, and increasingly competitive, which can create a very cost- effective and efficient design, especially for spans longer than 500 ft. This has added advantages where slightly longer spans can help mitigate impacts to a sensitive environment." Owners Demand Speed Owners are studying options more closely as designs are proven in the field and costs are reconsidered. They also are demanding one other element: faster construction. "Speed has taken a huge leap forward," Hall says. In part, the design-build delivery approach has been a factor. "Design-build teams have proven the process can be sped up and demonstrates that schedules can be compressed," he explains. "Now, owners are seeing that high-quality bridges can be safely constructed a lot quicker than they realized—and they want that compressed time." That expectation leaves little room for maneuvering. "It's reaching a point of equilibrium, where the push for speed has begun to obscure potential cost efficiencies," he notes. "There is a sweet spot between cost and speed that has to be acknowledged, and squeezing too tightly can have an impact on cost that isn't worth the time gained. It's a judgment call on each project." The motivation to finish bridges quickly is easy to understand, he adds. Much of America's aging infrastructure— built in the 1950s with a 50-year life span—is reaching the end of its service life. But swapping old for new can be difficult with communities built around these access points. "Bridges, especially concrete ones, have shown a lot of resilience to date, but you can squeeze out extra service life for only so long." New Designs Tested IBT is currently testing a technology in Massachusetts, where the 248-ft-long Randolph Department of Conservation and Recreation (DCR) Access Road channel bridge is being designed with precast concrete components to replace a four-span steel girder structure. The short-span bridge features two large edge girders that will serve as the roadway barriers, reducing material and increasing vertical clearance. The bridge's total depth will be 5 ft 4 in., including barriers. "It offers an opportunity for a quick replacement on a small span by bringing in a few precast concrete components and assembling them quickly on site," he explains. New concrete technologies are aiding new designs. "Concrete is both science and art," Hall says. "More and more is being done to improve its capabilities." For instance, significant efforts are underway to enhance performance of concrete decks by expanding and refining concrete properties to create more durable structures with lower concrete permeability. "The condition of decks is the most visible aspect of the bridge's condition to users, and it's the first part to go because of the wear and exposure," he says. "Modifications to the mix designs can really aid that aspect and provide better concrete products." Self-consolidating concrete also is producing new solutions and its use will continue to grow, he adds. Hall expects more concrete technologies to arrive in the future. "Concrete segmental bridge projects have seen a lot of success," he notes. "The DOTs and bridge owners are still building their level of comfort with the capabilities of segmental construction as more are built and a record of their service life grows. We believe precast segmental designs still have a lot of potential for expanding even further." "There is still a lot of opportunity to innovate and explore new design and construction options," Hall says. "We honestly didn't know for certain how true that would be when we started out 10 years ago. But we found there are definitely ways to take bridge concepts to the next generation so that owners benefit, time is saved, and projects are delivered at a lower cost." 'There is a sweet spot between cost and speed that has to be acknowledged.' The DCR Access Road over Route 24 Bridge in Randolph, Mass., now underway, uses two large edge girders as roadway barriers, reducing materials and increasing vertical clearance. The low profile adds 2.5 ft to the vertical clearance without altering the approach grade. 'There is still a lot of opportunity to innovate and explore new design and construction options.' ASPIRE , Spring 2010 | 11 Focus_IBT_spr10-1.indd 11 4/30/14 10:52 AM

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