Damage Constitutive Model Of Concrete Under Complex Loading And Seismic Damage Analysis Of Reinforced Concrete Bridges

As one of the important transportation infrastructures, seismic performance of bridges has been paid more attention by researchers and engineers around the world. The seismic response analysis of the bridge structures is the most effective method of evaluating the seismic performance of the bridge structures. With the deveoplement and mature of continuous damage mechanics (CDM), the theory has been introduced into the field of the nonlinear seismic response analysis of RC structures as a new tool, in order to accurately simulate the damage process including strength and stiffness degradation of concrete under cyclic loading. In the present thesis, the multi-axial and uni-axial damage models for concrete are applied into the solid model and beam-column model of RC structures, separately. Taking the general purpose FEA software ABAQUS as a platform, the seismic performance analysis of RC bridge structures has been carried out. The main results and conclusions are as follows:(1)Faria-Oliver damage model for concrete is an easy and effective damage model, and the model is very applicable to the seismic performance evaluation of the large scale RC structures. On the base of the Faria-Oliver model for concrete, a modification has been introduced in order to describle the unilateral effect of concrete more properly. Furthermore, the rate dependency is taken into account, so that strain rate effect of concrete is able to be considered in the seismic response analysis. Then, based on the general purpose FEA software ABAQUS,user material subroutines UMAT and VUMAT have been coded according to the modified Faria-Oliver damage model, and this provides an effective tool for the seismic response and damage analysis of large scale RC bridge structures.(2)Fiber beam-column element is an efficient and accurate beam-column element model. In order to perform the seismic damage analysis of the RC bridge piers and whole bridges using the beam-column elements, A uniaxial version of the modified Faria-Oliver model has been proposed and the two modifications to the original Menegotto-Pinto model by Filippou et al and Sakai, Kawashima, respectively are incorporated into a new modified Menegotto- Pinto model, Moreover, Based on the fiber beam column elements associated with the uni-axial material models, the seismic response analysis of RC bridge piers have been performed.(3)Using the elastoplastic damage model and fiber beam column model, the damage analysis of short piers, high piers and whole bridges with high piers are performed respectively.The results indicate that the damage zone of the short piers is located at the bottom of the piers, while the high piers tent to have the multi-location damage, and the more slender the high piers are, the stronger the trend of the muti-location damage is.(4)There are many long and large continous rigid frame bridges with high piers located in the western area of China. The seismic behavior of these bridges is very complex. Therefore, it is nessary that using a refined model and performing a detailed analysis. Based on the rate dependant elastoplastic damage model for concrete, the seismic response analysis of a continous rigid frame bridge with high piers has been conducted under the multi-support excitation and uniform excitation. The result shows that the displacement time history is not sensitive to the strain rate effect but the damage distribution and evolution is relatively sensitive to the strain rate effect; the travelling wave effect has a significant influence on the seismic displacement and damage and the influence trends are complex.