The Seismic Vulnerability Analysis Of The High-strength Reinforced Concrete Frame Structure

From the historical records of earthquakes occurrence,strong earthquakes often cause damage or destroy to buildings in different degrees and bring huge economic losses to people.Most of structure types of public buildings and facilities such as office buildings and schools are frame structures.Once these public buildings are severely damaged,will cause a large number of casualties.Therefore,it is of great significance to study the seismic vulnerability of the frame structures for earthquake prevention and disaster reduction.Some scholars have studied the influence of the stirrup strength,the stirrup rate,the axial compression ratio,the longitudinal reinforcement ratio and the spacing of the stirrup on the seismic performance of the beam-column members,but there is still a lack of research on the seismic vulnerability of the high-strength reinforced concrete frame structure under the earthquake action.The reinforcement areas of beams and columns of concrete frame structure,with high strength steel of HRB400,HRB500 and HRB600 as the longitudinal reinforced bar of the beams and columns and HPB300 as the stirrup,in the fortification intensity region 9(0.4g),8(0.2g),7(0.1g)and 6(0.05g),was calculated by equal strength substitution.In this paper,the finite element analysis models of frame structure were established by SAP2000,the structure analysis software,and 13 seismic waves,which are in line with the Ⅱclass site,were selected from the PEER database according to the 8 point principles of the American ATC-63 report.The maximum inter-layer displacement angle was chosen as the structural damage index and the seismic wave intensity index was the acceleration spectrum corresponding to the basic period of the structure with the damping ratio of 5%and the IDA curves of each model were drawn.The finite data were processed to reduce data discreteness and obtain the maximum inter-layer displacement angle and the seismic wave intensity corresponding to different behavior points by using 16%,50%and 84%three percentile curves,and fitted by using the least square method,numerically to obtain the probabilistic demand model and failure probability formula for each model.Finally,the seismic vulnerability curves.of each model were obtained and the structure collapse margin ratio was calculated.By analyzing the variation rule of IDA curves,seismic vulnerability curves and the structure collapse margin ratio,the following conclusions were obtained:(1)The overall trend of the IDA curves is that the larger the seismic wave intensity,the greater the dispersion.But,the larger the high steel strength,the smaller the IDA curves divergence in the same seismic intensity range and all IDA curves can be classified into 3 categories:softening type,transition softening type and hardening type.(2)When the collapse limit state is reached,the maximum inter-layer displacement angles of the HRB500 and HRB600 grade reinforced concrete frames are respectively increased by 12.5%and 17.5%compared with that of the HRB400 grade reinforced concrete frame.(3)When the increase of the steel strength under the same fortification intensity region,the structure collapse margin ratio increases and the structure collapse probability decreases.(4)In the same fortification intensity region and limit state,when the structure is 100%failure,the higher the steel strength,the greater the seismic wave intensity.It is proved that the reinforced concrete frame with HRB600 is obviously better than that of the configuration with HRB400 and HRB500 high strength reinforced concrete frame in resisting earthquake damage.