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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The bridge clear span length of 204 ft warranted a structure depth of about 10 ft using the guide depth-to-span ratio of 0.05 for a simply-supported bulb- tee girder structure. The girders should ideally have had a depth of about 9 ft. However due to the weight limitations, 8-ft-deep girders were used instead. The use of a shallower girder resulted in reducing the spacing between girders to support the design loads. Shallower girders required a concrete compressive strength of 8500 psi (at 5 6 d a y s ) . T h e c o n c re t e s t re n g t h requirement of 8000 psi (at 56 days) for the closure pours was higher as well. Achieving this strength is typically not a problem. However, the structure is located at an elevation of 6500 ft above sea level in a freeze-thaw environment so there was the additional requirement for 6% (±1.5%) air entrainment. Air entrainment reduces the strength of high strength concrete. While it was not an easy task, both the committed precast concrete manufacturer and the general contractor managed to provide the required concrete for the girders and closure pours. The individual girder segments were pretensioned for transportation. The assembled spliced girders were post- tensioned in two stages. The first stage of post-tensioning took place after the closure concrete achieved the required strength at the staging area. During the first stage, four of the six ducts per girder were stressed to 2330 kips total. Final stressing took place once the girders were on the abutments and securely braced. The final force was 3560 kips per girder. End diaphragms and intermediate diaphragms were cast after stressing was complete. __________ Jose Higareda is a senior bridge engineer with the California Department of Transportation, Sacramento, Calif. For more information on this or other projects, visit www.aspirebridge.org. Cranes were positioned over abutments and lifted the girders from trailers that were pulled across the temporary haul road. A special tractor and trailer were required to transport the girders from the staging area to the bridge site through several sharp turns. Caltrans felt it was essential to consult with the precast concrete industry early on to study the construction challenges. An assembled spliced girder is shown being driven over Abutment 1. The temporary haul road crosses the uphill end of the abutments to allow delivery of materials including the assembled girders. Note the braced forms and bridge over the forms. Once girders were delivered, the road was removed and the full abutment unearthed. The temporary haul road crosses the uphill end of the abutments to allow delivery of materials including the assembled girders. 22 | ASPIRE , Spring 2010 Angeles Crest Bridge_spr10.indd 22 4/30/14 11:02 AM

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