Post-tensioned Bridge Shows Excellent Performance Following Shake Table Testing at UB
The bridge deck, as well as each pier, consists of precast concrete segments post-tensioned together with unbonded high strength steel tendons.
Recent years have witnessed a growing interest in Accelerated Bridge Construction (ABC) techniques primarily due to the advantages of rapid construction and high quality control that they offer. A representative application of ABC is related to the use of precast segments post-tensioned together by internal or external tendons, forming the bridge’s superstructure and substructure. Despite the apparent advantages of the segmental bridge construction method, concerns have been raised among the engineering design community regarding the performance of these systems under intense earthquake shaking.
To address these concerns, a large scale (~1:2.4) bridge model was designed and constructed according to Accelerated Bridge Construction (ABC) techniques. The 70-ton, 60 ft. precast concrete segmental bridge specimen is a single span system with both of its supports overhanging at equal lengths. The bridge seismic design, which is based on current bridge design codes, incorporated several innovative concepts such as the use of unbonded internal tendons for the piers and the superstructure, consideration of vertical seismic loading and hybrid sliding-rocking segmental joints (joints that respond with sliding or rocking) for both the superstructure and the piers.
Testing was conducted using the two shake tables in the Structural Engineering and Earthquake Simulation Laboratory (SEESL) at the University at Buffalo, in May 2010. Over a three-week period, the bridge was subjected to nearly 150 simulated earthquake ground motions. The tests gradually increased in intensity, with varying levels of longitudinal, transverse, and vertical motion representing different seismic hazard levels. Apart from using synchronous excitations for the two shake tables, asynchronous motions were also simulated in order to explore the effect of seismic waves reaching the bridge’s supports with a time lag.
Between seismic tests, white-noise system identification tests were conducted to monitor the progress of damage throughout the bridge structure. Particularly, the final test replicated a maximum considered earthquake (MCE), and resulted in only minor spalling on the segments, but no damage to the superstructure.
Rendering of the test specimen.
The test results indicated that this design would perform well in a severe earthquake, primarily due to the post-tensioning, which allowed the test bridge to re-center itself after the shaking. In addition, the hybrid sliding-rocking joints that controlled the amplitude of the seismic forces applied to the bridge provided an excellent way to dissipate the seismic energy.
The research program is sponsored by the Federal Highway Administration, as part of MCEER’s Highway Project. MCEER investigators Amjad Aref and Andre Filiatrault are the principal investigators, and Petros Sideris, Ph.D. student and MyrtoAnagnostopoulou, SEESL Structural Engineer, all from the Department of Civil, Structural and Environmental Engineering at the University at Buffalo, comprise the project team.
The FHWA will use the data collected to begin developing standards to ensure the best performance from ABC in seismically active areas.
For more information, visit the Accelerated Bridge Construction Project Page.