Seismic performance of bridges with different pier heights. Longitudinal analysis of an existing bridge

Abstract

This paper is dedicated to the study of the seismic performance of an existing long reinforced concrete (RC) bridge localized in a region of moderate seismicity. The bridge is 440 m long with 6 spans and piers with very different heights, 3 of which are monolithically connected to the deck. To understand the roles of the different pier sizes in the overall behavior several analyses were carried out in the longitudinal direction: (i) linear dynamic approach; (ii) non-linear static approach and (iii) non-linear dynamic approach. The aim of the linear elastic analysis was to obtain the design for the ultimate limit state considering the largest value of the ductility factor for the piers. No safety verification was made for the other loads. The linear analysis was made for a region with a seismic action similar to Lisbon with a EC-8 response spectrum. N2 method was used to check the design, concentrating the attention on pier 4, the smallest and the more critical element. Minimum and maximum values of reinforcement were adopted for all other piers. Using non-linear static analyses, sensitivity was performed to check the influence of steel quantities in the overall behavior of the bridge. For the non-linear dynamic approach a series of strong motion records compatible with the EC-8 spectrum were generated. Various combinations of amount of steel reinforcement for flexural efforts in piers were studied with the objective of optimizing the cost-performance. Comparisons between static non-linear N2 method and non-linear dynamic analysis were made to confirm the validity of the former method in the case under analysis, where the period of vibration is quite high.