BRIDGE ABUTMENT INTERACTION UNDER SEISMIC LOADING André R. Barbosa, Manuel A. G. Silva Civil Engineering Department Univ. Nova de Lisboa, 2829-516 Caparica, Portugal Abstract: Abutments may undergo significant damage of difficult repair due to earthquakes. Simultaneous consideration of all intervening factors is difficult to achieve at present and simplified models that integrate most representative features are required. The study illustrates a simplified methodology for considering non-linear aspects and interaction abutment- superstructure for a bridge actually built and examines the influence of some parameters on the response. 1. Seismic damages in abutments Damages on bridges and abutments due to earthquakes have shown the need to consider the abutment–embankment participation on the response, unlike previous practice. Abutments may undergo significant damage of difficult repair due to earthquakes especially when the bridges have integral type abutments; however, seat type abutments may also experience damage once the gap between superstructure and abutments backwall closes during an earthquake. This mode of failure may result in unacceptable post event repair cost and lifelines downtime, and should be avoided. For seat abutments, this may be accomplished by providing gaps that are wide enough or by inserting fluid dampers or locking devices to limit the relative motion of bridge sections under transient motion. However, as shown in the next series of figures, extensive, serious damages in both integral and seat type abutments have been reported. Fig. 1-a) shows the failure of an abutment of Mouken Bridge due to the Chichi earthquake (Taiwan, September.1999) and b) the damages caused to one of the abutments at the Moss Landing bridge due to liquefaction (Loma Prieta, October.1989). Fig. 2-a) shows a failed support bent at one abutment of a bridge in Highway 8A East of Bhachau (Bhuj, India, January. 2001), and Fig 2-b diagonal cracking at bridge on road Moquegua-Tacna (Atico, Peru, June.2001). The result of longitudinal impact between deck and abutment is shown in Fig. 3-a) while b) illustrates wall cracking caused by the transversal motion of the backfill soil of an abutment in a Californian bridge (Northridge, January.1994). These and similar failures motivated a large experimental program at The Network for Earthquake Engineering Simulation (NEES) where the behavior of 4-span bridges including abutments and foundations was examined. The studies comprised static and dynamic tests that were performed on the shaking table at the Englekirk Center of UCSD, Fig.4 (http://nees.unr.edu/4- spanbridges/ ). Fig. 1- a) Mouken Bridge(Taiwan, September.1999); b) Moss Landing. U.S.G.S. (Loma Prieta, October.1989) The dynamic response of bridges may be affected by the interaction with foundation, abutments and embankments. Werner et al. (1987, 1990), Wilson and Tan (1990a,b). Goel (1997), and, Goel and Chopra (1997) showed that the response was, indeed, influenced by the abutments, soil nonlinearities and SSI. The influence of SSI was also addressed by Zhang and Makris (2002) and Price (1997) who studied the peak spectral values for the abutments and the transversal frequency of In Proceedings of 2nd International Conference on Structural Condition Assessment, Monitoring and Improvement Changsha, China, 19-21 November 2007