Accelerated Traffic Load Testing of Expansion Joints for the Self-anchored Suspension Section of the New San Francisco–Oakland Bay Bridge East Span
A relatively unique opportunity was recently identified for accelerated traffic load testing of a new bridge expansion joint design. This study was part of the construction of the new East Span of the San Francisco–Oakland Bay Bridge and assessed whether these new Caltrans seismic expansion joints (which were designed to function in harmony with the bridge decks in the event of a high-magnitude earthquake) linking the Self-anchored Span with the Transition and Skyway spans would withstand truck traffic loading. A test structure incorporating one of the full-scale joints was constructed close to the actual bridge and tested with the California Department of Transportation / University of California Pavement Research Center Heavy Vehicle Simulator in a series of phases. A total of 1.36 million load repetitions, equating to about 46 million equivalent standard axle loads, were applied in seven phases during the three-month test. On completion of this testing, no structural damage was recorded by any of the Linear Variable Differential Transducers or strain gauges installed on the steel plates, steel frames, bolts, or washers. There was also no visible damage on any of these components. Excessive overloading with a 150 kN halfaxle load in the last phase of the test caused some damage to the Trelleborg unit of the joint. This included abrasion, tearing, shoving and permanent deformation of the rubber inserts, and deformation and shearing of one of the steel supports directly under the wheel load. Based on the results of this limited testing, it was concluded that the Caltrans seismic expansion joint would perform adequately under typical Bay Bridge traffic. The distress observed to the Trelleborg unit under the high loads in the last phase of testing is unlikely to occur under normal traffic. However, the Trelleborg unit was found to be the weakest point of the expansion joint, as expected. On the actual bridge structure, these units will require periodic maintenance and replacement in line with manufacturer’s specifications. The findings from this study indicate that the Caltrans seismic expansion joint tested would be appropriate for typical Bay Bridge traffic. No seismic or structural testing was undertaken on the seismic expansion joint as part of this study and no recommendations toward its seismic or structural performance are made. Ride quality, skid resistance, and tire noise studies were carried out by Caltrans in a separate study and are reported on in separate Caltrans reports.