The influence of the frequency content of ground motion on the nonlinear dynamic response and seismic vulnerability of historical masonry towers

Abstract

Observations made on the response of historical masonry towers during past earthquakes indicate that in addition to the intensity of the ground shaking, the frequency content of shaking also affects the seismic performance of these monuments. To evaluate this phenomenon, the influence of the mean period of the ground motion (Tm), as a frequency content indicator, on the seismic behavior of the towers is assessed. To this end, first, the vulnerability of four towers with different aspect ratios and vibration periods (Ts) are evaluated by means of the Incremental Dynamic Analysis (IDA). For this purpose, 37 ground motion records, corresponding to the stations located in sites with different types of soil, are utilized. The nonlinear time history analyzes of the towers are carried out using the OPENSEES software by means of an Equivalent Beam Element with fiber sections. In order to investigate the effects of the frequency content of the ground motion on the seismic response of the towers, for every tower, the variation of the PGA of the ground motion and the induced internal force in the tower at the point of failure are plotted against the period ratio (Tm/Ts). According to the analysis results, it is found that the failure PGA increases as the period ratio becomes smaller. It is also noted that the induced shear in the tower exhibits a similar trend.