THE CONCRETE BRIDGE MAGAZINE

SPRING 2017

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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PROJECT ANTLERS BRIDGE by Jason Lynch, California Department of Transportation In Northern California, Interstate 5 follows a historical route through the Sacramento River Canyon, and the new Antlers Bridge is one of its significant structures. The 1942-ft-long bridge crosses Shasta Lake, near the community of Lakehead, on a new alignment to replace an aging truss. For the California Department of Transportation (Caltrans), the $131 million project improves a critical link for the movement of people and goods in the West. For the general contractor, it presented a host of challenges, requiring innovation and flexibility. Replacement Needed The structure replaces a narrow steel deck truss built during the construction of Shasta Dam in 1941. Its active structural-steel fatigue cracks and a deteriorating deck made the existing bridge an annual drain on the state’s maintenance resources. The approach highway lacked shoulders and had a steep, tightly curved alignment that could drive like a luge run. New Design Seeking to improve safety and reduce long-term costs, the state realigned the roadway and opted for the durability and ease of maintenance of a cast-inplace, prestressed concrete box-girder bridge. The height of the bridge and the challenging site access discouraged Cal i fornia’s typical fal sework construction, driving the project to the balanced-cantilever, segmental method. Designers located the piers to miss the greatest depth of the lake and a recreational hot spot fronting the Antlers public boat ramp. The result was a bridge with five continuous spans and a 591-ft-long main span. Symmetry in the layout and the boxgirder dimensions helped to economize on equipment and formwork costs. The design followed the AASHTO LRFD Bridge Design Specifications, supplemented by project-specific criteria. For bridge trivia buffs, the effort holds the inconsequential distinction of being the last California bridge designed in metric units and among the first using the load-and-resistance-factor design method. Design Challenges Caltrans’s Seismic Design Criteria requires ductility and resilience of all California bridges, particularly for operationally important structures. With a two-lane detour more than 100 miles long, this lifeline structure needs to perform. But performance would come (cont. next page) PROFILE ANTLERS BRIDGE / LAKEHEAD, CALIFORNIA BRIDGE DESIGN ENGINEER: California Department of Transportation (Caltrans), Sacramento, Calif. PRIME CONTRACTOR: Tutor-Saliba Corp., Sylmar, Calif. POST-TENSIONING CONTRACTOR AND FORM TRAVELERS: Schwager-Davis Inc., San Jose, Calif. CONTRACTOR’S ENGINEER: Finley Engineering Group, Tallahassee, Fla.

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