Seismic Performance Analysis Of Multi-age R.C. Structures

Recently, frequent destructive earthquakes struck the whole world, causing severe damage to buildings and infrastructures, great economic losses, and casualties, and urban engineering structures with higher population and wealth densities are the main hazard-affected bodies in earthquakes. China is a country prone to earthquakes with large amount and sizes of cities, so the anti-seismic design of urban engineering structures are very important, with existing structures as its key and weakness for their low seismic design levels, insufficient structural measures and years of usage. So in this paper, taken multi-age R.C. structures as object, the following content are discussed:Firstly, four factors that influence seismic capabilities of multi-age R.C. structures are summarized based on Wenchuan earthquake reconnaissance and Chinese seismic building codes, which are seismic design level, structural measures, structural material property, and environmental effect.Secondly, based on these factors and an existing macroscopic joint model, a simplified joint model considering shear failure of joints and bar-slippage behavior is proposed, with which a new modeling method for global seismic analyses is presented in Opensees, and validated with two R.C. frame experiments to be a general solution for low-ductile R.C. frame structures.Thirdly, sensitivity analysis of the factors that influence seismic capabilities is conducted under member level, with the results of which, as well as the modeling method mentioned above, the seismic performance of R.C. structures built in different periods are analysed. The results show their differences in ductility, energy dissipation and seismic failure modes, and the failure mode of existing structures tend to be brittle.Finally, two typical multi-age structures are selected to study their realistic seismic capabilities and failure modes. One is a R.C. frame structure in Dujiangyan city with severe damage in Wenchuan Earthquake, and the other is an inner frame-supported masonry structure based on an in-situ impact test in Dalian. The simulated results of the former one agree well with the typical earthquake damage observed in Wenchuan earthquake, with which the proposed modeling method is proved to be reliable.Based on the previous research, the paper concludes that seismic capabilities of existing structures are weaker than those of current ones, but are all satisfied with the current code under severe earthquakes. When structures suffer earthquake severer than design seismic intensity, seismic capabilities of existing structures are much weaker than those of current ones, showing as poor energy dissipation capacities, low ductilities, weak collapse-resistance capacities, and brittle falure modes. In addition, the results also show that inner frame-supported masonry buildings have poor seismic capabilities and weak story-the first story, indicating they should not be built in areas prone to earthquakes.