Experimental Study On Seismic Collapse-resistance Performance And Failure Mechanism Of Rc Frame Columns

Reinforced Concrete(RC)frame column is not only a lateral resistance member,but also a vertical load-bearing member,so it plays a very important part in the RC frame structures against earthquake-induced collapse.The failure criterion for RC columns should be selected reasonably in order to get the reliable result during the collapse-resistance performance evaluation of RC frame structures under strong earthquakes.In the experimental study on seismic performance of RC frame columns,it is generally used as the failure criterion of the component that the lateral load bearing capacity drops to 85% of the peak value.This means the actual remaining bearing and deformation capacity beyond this state is totally ignored.Such failure criterion will lead to too conservative results when applied to the collapse-resistance performance evaluation of RC frame structures under strong earthquakes.In this thesis,six full-scale RC frame columns designed according to the current codes are studied by quasi-static test firstly.The test focuses on the degradation rate of lateral load bearing capacity,the maintenance capacity of vertical bearing capacity and the micro-damage phenomena of concrete and reinforcing bar materials in the later stage of large deformation.Based on the experiment research,a more reasonable failure criterion of RC frame columns in structural seismic collapse analysis is proposed.Then,combined with the finite element numerical simulation,the relationship between ultimate drift ratio and relevant design parameters for RC frame columns controlled by bending failure mode that can be applied to earthquake-induced collapse analysis of RC frame structures is proposed.The main research contents and achievements are as follows:(1)The quasi-static tests of six RC column specimens were completed.The seismic performance and failure mechanism of RC columns were analyzed from the following aspects: failure process and failure mode,lateral load bearing capacity-displacement hysteresis curve,moment-rotation relationship at root section,deformation capacity,stiffness degradation and energy dissipation capacity.The effects of different axial pressure ratios and loading systems on the above results were also investigated.According to the experimental study and the test data of RC frame columns at very large deformation state presented by some other researchers,the criterion for judging whether the RC column fails under strong earthquake is proposed.This failure criterion relates the macroscopic phenomenon that the lateral load bearing capacity drops sharply and the stable vertical bearing capacity was lost to the microscopic phenomenon that the concrete edge in the core area of column crushes causing rapid buckling of the longitudinal bars.(2)According to the conclusions of experimental research,the numerical analysis model which can consider the buckling effect of compressed longitudinal bars and adopted appropriate constitutive model of concrete confined by stirrups was established based on the general finite element software MSC.Marc.The quasi-static tests of six RC columns were simulated using this numerical analysis model,which shows the validity of the numerical model.(3)Based on the above numerical analysis model,the parametric analyses of axial compression ratio and stirrup characteristic value were conducted.The results show that the ultimate drift ratio of the RC column based on the failure criterion proposed is generally larger than that based on the traditional criterion.Furtherly,the relationship between ultimate drift ratio and stirrup characteristic value and axial compression ratio is proposed for RC frame column controlled by bending failure mode,which provides a useful reference for researchers to accurately evaluate the collapse-resistance performance of RC frame structures under strong earthquakes.