Research On Seismic Performance Of Existing Reinforced Concrete Shear Wall Structure Retrofitting

As a principal structural component to resist lateral force, the reinforced concrete shear wall, which can provide much larger lateral stiffness to resist most of horizontal loads, is widely used in hide-rise buildings. In the past 30 years, an amount of reinforced concrete shear wall structures were built based on a series of Chinese specifications issued in 1974. However, due to changes of demands and functions, a part of existing shear wall structures needs retrofitting. Apparently, seismic performance of the structure after retrofitting is very essential for the safety. In other words, the structure after retrofitting should satisfy the seismic fortification criterion"no damage under frequent earthquake, repairable under moderate earthquake, and no collapse under severe earthquake". The purpose of this paper is to establish a seismic performance evaluation method of existing reinforced concrete shear wall structures, including the following aspects:1) Based on different constructional details of a series of Chinese codes issued in 1974 and current Chinese codes, ten shear wall models are designed for low cyclic loading tests. Primary parameters are details and openings. The mechanical and seismic behavior such as failure modes of specimens, load-strain relationships, strain distribution of wall sections, characteristic points of cracking, yielding, limit state and failure, load-displacement hysteretic curves, stiffness degradation curves, energy dissipation capacity are analyzed.2) Based on experimental results mentioned above, considering the effect of parameters including design criterions, axial compression ratios and openings, the seismic performance of specimens such as failure modes, bearing capacity, ductility performance, stiffness degradation and energy dissipation capacity is analyzed. In addition, the performance of shear wall before and after retrofitting is compared.3) Based on test results, the finite-element analysis (FEA) is carried out using the nonlinear analysis platform OpenSEES by introducing a kind of fiber element model -- Multiple Vertical Line Element Model (MVLEM). Comparison between FEA and Test results verified that the finite-element models and parameters are reasonable and reliable. Furthermore, parameters including spring members, vertical and horizontal divisions are analyzed. As a result, a practical recommendation is provided.4) According to the performance-based seismic design method, a seismic evaluation method of existing buildings is put forward. Also design equations under frequent earthquake, moderate earthquake and severe earthquake are presented. Furthermore, performance objectives of structures and different structural components under different seismic fortification criterions are summarized.5) The method proposed in this paper has been applied to seismic evaluation analysis for retrofitting a hide-rise shear wall structure. The seismic performance of original and retrofitted structure, the requirement of the method and current Chinese codes is compared. Also the finite element analysis for original and altered single shear wall is carried out. Eventually, seismic evaluation method of shear wall structures reconstructing is proved to be reliable and feasible.