Study On Asymmetric Restoring Force Model And Parameter Identification Technique Of Corroded Reinforced Concrete Columns

Reinforced concrete (RC) column is one of the most important load bearing members of bridge, building and other engineering structures. Subjected to corrosive environmental actions such as concrete carbonation or chloride ion ingress, the RC column often degraded due to steel bar corrosion after a certain service time. Steel bar corrosion may not only reduce the effective cross-sectional area of both longitudinal and transverse reinforcements, but also can reduce the seismic bearing capacity, ductility and energy dissipation capacity of RC columns due to cracking or spalling of concrete cover induced by steel bar corrosion. The corroded RC column under cyclic loading often exhibits some typical hysteretic characteristics, such as stiffness degradation, strength degradation, pinching effect and asymmetric behavior, due to the influence of concrete cover cracking, bond-slip between steel bar and concrete as well as non-uniform corrosion of steel bar. Therefore, it is quite important for the seismic performance evaluation of the corroded RC columns to establish an efficient asymmetric restoring force model which can comprehensively describe the above typical hysteretic characteristics of the corroded RC columns. Thus, the aim of this thesis is to develop an efficient asymmetric restoring force model of corroded RC columns as well as methods for parameter sensitivity analysis and parameter identification. The main contents of this thesis include:(1) Based on the traditional symmetric Bouc-Wen-Baber-Noori (BWBN) model, an efficient asymmetric BWBN model was established by introducing an non-symmetric shape parameter into the differential relationship between the nonlinear relative displacement and nonlinear hysteretic displacement, which can consider the typical hysteretic behaviors of the corroded RC columns. The proposed asymmetric BWBN model provides a fundamental basis for the parameter sensitivity analysis and parameter identification of the corroded RC columns.(2) Based on the experimental data of the pseudo static test of the corroded RC columns, the parameters sensitivity analysis of the asymmetric BWBN model was carried out by both the local parameters sensitivity analysis method (e.g., One-factor-at-a-time method) and the global parameters sensitivity analysis method (e.g., Sobol method). As a result, both the local and global sensitivity indices of the asymmetric BWBN model were determined, which provides a criterion to select the important model parameters to be identified of the asymmetric BWBN model.(3) Based on the differential evolution (DE) algorithm, an effective parameter identification technique for the asymmetric BWBN model was proposed. Then the asymmetric BWBN model parameters of the corroded column were identified based on the experimental data of the pseudo static test of eight corroded RC columns, which can further be used to evaluate the seismic performance of corroded RC columns.