Effect of Frequency Content of Near-Fault Ground Motions on Seismic Performance of Reinforced-Concrete Bridge Piers

Seismic performance evaluation of bridges requires the use of natural recorded ground motions or artificially produced records to be used in non-linear time history analysis. Due to the complexity related to energy dissipation characteristics of bridges and dynamic characteristics of earthquakes, the quality and adequacy of inelastic dynamic analysis results are highly dependent on the universality of selected seismic records, numerical modeling of the bridge, and material behavior. These factors unveil the need to consider appropriate criteria in earthquake records selection and to assess the damage potential to connect seismic loading and structural response more than ever. Based on the seismic-response studies of bridge piers, it is well known that among the other factors, the earthquake frequency content increases structural damage. Hence, in this paper, earthquake frequency content is considered as the main factor which affects inelastic response of reinforced concrete (RC) bridge piers. Different methods are presented to determine the earthquake frequency content, and the best method is selected to determine the frequency content. Using the selected method, the frequency content of seven selected records was determined based on the respective index. The influence of this index was also examined on seismic performance of RC bridge piers as well as formation process of plastic hinges. The results showed that due to different characteristics of earthquakes, plastic hinge patterns, which are derived from seismic excitation, indicate the changes among earthquake records. Results also showed that an earthquake with high frequency content causes extended length of plastic hinges at the base of the piers. For earthquakes which have been scaled to the same peak ground acceleration, low frequency content forms long plastic hinges.