THE HYSTERETIC CHARACTERISTIC WITH P-Δ EFFECT AND INFLUENCE ON THE COLLAPSE RESISTANCE CAPACITY OF STRUCTURE UNDER EARTHQUAKES

The P-Delta effect is one of the crucial reasons to cause structural collapse under strong earthquake excitations. The seismic response characteristic with consideration of P-Delta effect is discussed firstly in this paper. The numerical examples indicate that the stiffness of the structure decreases with the backbone curve demostrating a significant negative slope under large ductility. A simplified trilinear curve including the elastic range, the yield range and the softening range is used to simulate the characteristic of the backbone curve of the structure. Preliminary analysis shows that the steel structure with full hysteretic loop has more tendence to collapse compared to reinforced concrete structure, which dissipates less energy during excitations. In order to investigate this phenomenon, the hysteretic characteristics of different hysteretic models, including the nonlinear elastic model, the full elasto-plastic model and the Clough model, all with a negative post-yield stiffness to present the P-A effect, are discussed. The influence of hysteretic characteristic on the collapse resistance capacity of the structure is researched by a seris of IDA analysis. The results show that the displacement is more likely to concentrate to one particular side for the full elasto-plastic model with plump hysteretic loops, which results in a relatively lower capacity of collapse resistance, while the vibrations of the nonlinear elastic model and Clough model with whole or part pinching is more symmetrical, and the capacity of collapse resistance is better. It demonstrates that the collapse resistance capacity is not only related to the energy dissipation capacity of structure.