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.
Issue link: http://www.aspiremagazinebyengineers.com/i/306855
A project team of five U.S. government agencies, lead by the Central Federal Lands Highway Division of the Federal H i g h w a y A d m i n i s t r a t i o n ( C F L H D ) collaborated to develop a highway bypass to the existing U.S. Highway 93 over the Hoover Dam. The existing highway route over the dam mixed the throng of tourists for whom the dam is a destination with heavy highway traffic and commercial trucking. The blend of these two created hazards and hardships for both, and served as a bottleneck for commerce along this major north-south route. Project Development A consortium of firms working under the moniker of HST (HDR, Sverdrup, and T.Y. Lin International) teamed with specialty sub-consultants and CFLHD to deliver the final design for 1.6 km (1 mile)* of approach roadway in Arizona, 3.5 km (2.2 miles) of roadway in Nevada, and a major 610-m (2000-ft) -long Colorado River crossing about 450 m (1475 ft) downstream of the historic Hoover Dam. Bridge Type Screening Process With the selection of an alignment so close to Hoover Dam, the new bridge will be a prominent feature within the Hoover Dam Historic District, sharing the view-shed with one of the most famous engineering landmarks in the United States. The environmental document set a design goal to minimize the height of the new bridge crossing on the horizon when viewed from both the dam and Lake Mead. The State Historic Preservation Officers for both Nevada and Arizona— both members of the Design Advisory P a n e l — e m p h a s i z e d t h e n e e d t o complement and not compete with the architecture of the dam. ____________ * The Mike O'Callaghan–Pat Tillman Memorial Bridge at Hoover Dam was designed using SI units. Conversions are included for the benefit of the reader. CFLHD took full advantage of prior studies and public processes to focus on the alternatives that met all the design objectives. As a result of this screening process, the type study proceeded with only deck arch options. Major Design Features The final design went through an evolution of form dictated by the engineering demands on the structure to arrive at the twin rib-framed structure. At the outset of design it was assumed that earthquake loading would control the lateral design of the bridge. A project specific probabilistic seismic hazards analysis was conducted in order to assess the range of ground motion associated with return periods appropriate for design. A 1000-year return period was selected resulting in a design basis peak ground acceleration of 0.2g. Wind was also a major environmental loading condition from the outset of design. During the preliminary design phase, a site wind study was conducted to correlate the wind speeds at the bridge site with those at the Las Vegas Airport in the valley. With this correlation, the long- term statistics from the airport were used to develop site wind speeds for design. As profile MIKE O'CALLAGHAN–PAT TILLMAN MEMORIAL BRIDGE (HOOVER DAM BYPASS, COLORADO RIVER BRIDGE) / BOULDER CITY, NEVADA BRIDGE DESIGN ENGINEER: T.Y. Lin International, Olympia, Wash., in collaboration with HDR Engineering, Omaha, Neb. CONSTRUCTION ENGINEERS: OPAC, San Francisco, Calif., and McNary Bergeron, Denver, Colo. PROJECT DELIVERY: Central Federal Lands Highway Division, Federal Highway Administration, Denver, Colo. PRIME CONTRACTOR: Obayashi PSM, JV; San Francisco, Calif. CONCRETE SUPPLIER: Casino Redi-Mix, Las Vegas, Nev. POST-TENSIONING CONTRACTOR: Schwager-Davis, San Jose, Calif. BRIDGE BEARINGS: R.J. Watson, Buffalo, N.Y. The Mike O'Callaghan–Pat Tillman Memorial Bridge at Hoover Dam set to open Fall 2010 HOOVER DAM BYPASS by David Goodyear, T.Y. Lin International The 1060-ft-span twin rib arch of the Mike O'Callaghan–Pat Tillman Memorial Bridge spanning the Colorado River near the Hoover Dam. Photos: Central Federal Lands Highway Division, Federal Highway Administration. 16 | ASPIRE , Spring 2010 P R O J E C T Colorado River_spr10-1.indd 16 4/30/14 10:58 AM