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
Heavy runoff along with sliding debris overwhelmed drainage systems and caused major damage to the roadway along scenic Route 2 northeast of the city of Los Angeles within the Angeles National Forest. Much of the damage occurred during the spring thaws of 2006 and 2007. Tr a n s p o r t a t i o n o ff i c i a l s w i t h t h e California Department of Transportation (Caltrans) looked for economical and more durable repairs for the route. At the Angeles Crest Bridge 1 location where the roadway was washed out, they were faced with limited practical solutions. From the onset, the steep and loose terrain made it difficult to perform adequate subsurface investigations. Geologists were confined to work within the reach of their drill rig and from where the roadway was sturdy enough to support the equipment. Several alternatives were considered but ultimately, Caltrans opted to use 208-ft-long spliced precast, prestressed concrete girders to bridge the gap in the roadway. The girders were shipped to the site in three segments and spliced together on the ground near the bridge location. This avoided the need to construct temporary bents on the unstable slope in order to splice the girders in place. The long-span girders allowed the structure to bypass the area of geotechnical uncertainty. The abutments were placed away from known fracture planes in the rock and were founded on stable ground. The intent was also to create a gap between the structure and the natural chute of sliding debris allowing the debris to slide under the structure. The single-span, simply-supported structure provides the added benefit of not having intermediate supports that could transmit earth loads to the structure during a seismic event. This is important given that the bridge location is situated in a high seismic area (peak ground acceleration of 0.7g and maximum credible earthquake of 8.0). Engineers needed only to confine the structure laterally at the abutments and provide sufficient seat length to prevent the girders from being dislodged. Construction Logistics Caltrans felt it was essential to consult with the precast concrete industry early on to study the construction challenges that this type of structure presented. The industry was represented by the Precast/Prestressed Concrete Manufacturers Association of California (PCMAC) who provided assistance with feasibility studies. Two of the chief concerns were the transportation and erection of the girders. The girders spliced and fully loaded with rigging weigh nearly 180 tons each. PCMAC confirmed that erection was feasible if cranes could be staged at each abutment. It was determined that to install the girders, a 500-ton-capacity hydraulic crane at 91% margin and a 330-ton-capacity conventional crane at 88% margin would be required. It was not, however, feasible for either crane to reach across from one abutment to the other while lifting one end of a girder. The swing radius for the cranes had to remain as short as profile ANGELES CREST BRIDGE 1 / LOS ANGELES COUNTY, CALIFORNIA BRIDGE DESIGN ENGINEER : California Department of Transportation, Sacramento, Calif. PRIME CONTRACTOR: Griffith Company, Brea, Calif. PRECASTER: Pomeroy, Perris, Calif., a PCI-certified producer CONCRETE SUPPLIER: Cornerstone Materials, Palmdale, Calif. AWARDS: PCI 2009 Design Award for Best Bridge Project (Spans More than 150 ft) by Jose Higareda, California Department of Transportation ANGELES CREST BRIDGE 1 Searching for a practical solution The Angeles Crest Bridge 1 northeast of the city of Los Angeles within the Angeles National Forest. Photos: Caltrans. The girders were shipped to the site in three segments and spliced together on the ground. 20 | ASPIRE , Spring 2010 Angeles Crest Bridge_spr10.indd 20 4/30/14 11:02 AM