Analysis of reinforced concrete bridge with circular pier subjected to earthquake

Abstract

Structural engineers and designers have a great responsibility for incorporating seismic design into reinforced concrete (RC) structures, particular RC bridges, in order to minimise damages and loss of life during an earthquake event. Extensive research has been conducted to develop robust seismic design procedures for RC bridges. Recent research has indicated that among several displacement-based design methods developed, the direct displacement-based design (DDBD) method has become one of the most reliable methods for designing the RC bridge under earthquake conditions. Due to the uncertainty in the estimation of the yield displacement and target displacement, further developments are needed to fill those gaps in the development of the robust DDBD method. Therefore, those research gaps are addressed in this PhD research. In this PhD research, a comprehensive 3D FEM for analysis of RC bridge with circular pier subjected to the earthquake has been developed. The FEM can be used for the fullscale modelling of RC bridge and assess the earthquake resistance of RC bridge with a circular pier. The 3D FEM considers the full interaction between circular RC bridge pier, deck, and steel reinforcement. The developed FEM can accurately predict the structural responses of the RC bridge with circular pier subjected to an earthquake in terms of displacement, strain, and damage. In this 3D FEM, the concrete damage plasticity (CDP) material model is considered to capture the nonlinear behaviour of concrete. A bilinear stress-strain relationship is adopted for reinforcing steel. Also, a full implementation of damage parameters is considered where compressive and tensile damage parameters for unconfined and confined concrete are taken into account to accurately capture the damage of the circular RC bridge pier and bridge subjected to an earthquake. Also, an analytical model has been developed for predicting the yield displacement of circular RC bridge piers for the DDBD method in this PhD project. The model is based on the improved yield curvature estimation by introducing new essential parameters, including concrete strength, longitudinal reinforcement ratio, and axial load ratio. The model incorporates a modified plastic hinge region with equivalent curvature distribution for strain penetration length to predict the yield displacement of the RC bridge pier. A series of RC bridge piers previously tested under cyclic loading (pushover tests) are selected to validate the proposed model. The yield displacement is estimated through the force–displacement response and is compared with the proposed model. A series of validation subjected to a seismic loading are conducted to evaluate the proposed model of yield displacement. Extensive parametric studies are conducted to evaluate the influence of several parameters on the prediction of the yield displacement of RC bridge pier. In this PhD research, a new model has been developed for predicting the damage-control target displacement of circular RC bridge piers for the DDBD method. The proposed model is based on the damage-control limit states, where new expressions are introduced in the model. Existing damage-control concrete compression strain and new expressions of damage-control reinforcement tensile strain are considered in this model, along with the modified plastic hinge length, modified strain penetration length, and yield displacement. The model improves the estimation of damage-control target displacement, mainly for the circular RC bridge pier. Also, the FEM is employed to validate the proposed model. The developed model has been validated using a series of RC bridge piers tested under cyclic loading (pushover tests). A series of validations are conducted using the RC bridge pier, which it is subjected to different earthquake conditions and simulated by the validated FEM. A parametric study is conducted to evaluate the influences of concrete strength and reinforcement ratio on the prediction of damagecontrol target displacement of the RC bridge pier. Finally, a comprehensive study to assess the behaviour of multi-span RC bridge with a circular pier (designed based on EC8 and DDBD methods) under different earthquake conditions is conducted. Therefore, the 3D FEM developed is used to predict the behaviour of two RC bridges designed using EC8 and DDBD methods. The FE modelling results are used to investigate the seismic performance of the two RC bridges under five different earthquakes. The results indicated that the bridge designed based on EC8 suffered higher maximum displacement and more significant damages compared to the bridge designed by the DDBD method under different earthquakes. This reveals some weaknesses of the current EC8 design method.