Seismic performance of unbonded elastomeric bearings on bridges : an experimental and parametric study

Domaniç, Kemal Arman
Elastomeric bearings were used in a majority of bridges completed in Turkey. Usually, the connection between bearings and the structure were established only by means of friction. Vertical excitation can contribute to a significant damage in such cases, especially at bearing locations, as indeed was the case in the recent 1999 İzmit Earthquake. In Turkish seismic design practice, a common friction coefficient of 0.20 is frequently used. The aim of this study is to look into the values suggested by specifications for friction coefficient between bearings and steel girders through experiments and to explore dynamic and static shear behavior of unbonded bearings. An actual bridge, spanning 12 m with a concrete deck of 3.5 m width over 3 steel I-girders is constructed on a shake table with a hydraulic actuator capable of delivering a user supplied displacement history. Bearing responses under seismic loadings were measured. Due to a very high friction coefficient, bonded and unbonded bearings exhibited similar seismic performance. Results of shake table and static friction tests performed on unbonded bearings indicated that use of a friction coefficient of 0.20 in seismic analysis can be unconservatively low to determine substructure forces and may significantly overestimate seismic displacement demands. Such low values should not be used in seismic design unless indicated otherwise by test data. A comprehensive parametric study was performed and a conservative trendline of deck displacements as a function of acceleration coefficients is presented with a procedure to estimate maximum bearing shear forces for the investigated cases.
Citation Formats
K. A. Domaniç, “Seismic performance of unbonded elastomeric bearings on bridges : an experimental and parametric study,” Ph.D. - Doctoral Program, Middle East Technical University, 2015.