Seismic Performance of Precast Segmental Bridges
Accelerated Bridge Construction Test Unit under Seismic Loading
3D rendering of bridge specimen
Longitudinal view of bridge specimen
Transverse view of bridge specimen
Recent years have witnessed growing interest in Accelerated Bridge Construction (ABC) both in the United States and Europe mainly due to the advantages of rapid construction and high quality control that it offers. A representative application of the ABC is related to the adoption 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 arisen amongst the engineering design community regarding the performance of such systems under intense earthquake shaking.
Test Structure & Experiment Setup
A 1/2.4 scale single span bridge specimen is underway on the adjacent re-locatable shake tables of the SEESL Laboratory at the University at Buffalo. Following the principles of the ABC techniques, the deck of the bridge specimen is a single-cell box girder that consists of eight segments; whereas each pier consists of five segments of hollow square cross-section. Both the superstructure and substructure segments are post-tensioned together using internal unbonded tendons. A cap beam of trapezoidal cross-section provides the support of the superstructure on each pier, whereas the anchorage of the piers on the shake tables is achieved through a foundation concrete block mounted on each shake table. Once the specimen has been mounted on the shake table, sand bags are placed and tied on top of each deck segment to simulate the additional load due to surfacing, railings, etc.
The bridge design, which is based on current bridge design codes, has incorporated several innovative concepts such as the use of unbonded internal tendons, consideration of vertical seismic loading and simple friction-type connections defined by direct contact of adjacent segments for both the deck and the piers.
The test model will be subjected to a suite of ground motions from the FEMA P695 Far-Field Ground Motion Ensemble, appropriately scaled to match three desired seismic hazard levels. The data collected during testing are expected to provide information on the behavior of segment-to-segment joint opening, frictional properties of the deck-to-cap beam interface, behavior of the internal unbonded tendons, as well as the ductility capacity and self-centering capabilities of the precast segmental bridge system.