Study On Influence Of Masonry Infills On Seismic Response Of Reinforced Concrete Frames

Reinforced concrete frame(RC)structure is one of the most widely used structural forms,most important public buildings such as schools and hospitals are RC frame structure.However,seismic damage investigation indicated that the frame structures with masonry infills is often unable to realize the failure mechanism of “strong column-weak beam” and “strong shear-weak flexure” under the strong earthquakes,which went against the ductility design conception.Infills are regarded as architectural elements in design.But there is a complex interaction between the infills and frames,its influence on the seismic performance of structure cannot be ignored.In this paper,the seismic behavior of RC frame structures is analyzed and studied by experiments and finite element analysis.The main researches are as follows:(1)In order to study the effect of infills on seismic performance of RC frames,this paper presents a low cyclic loading tests of RC frames.RC frames include a control specimen,frame with full-filled infills,frame with large window opening infills,and frame with eccentric door opening infills.Based on the test data,the cracks of specimens,hysteretic loops,characteristic displacement and load,flexural moments of columns,column shear force,energy dissipation capacity and joint shear force were analyzed.Tests results indicated that the carrying capacity,initial stiffness,the energy dissipation capacity and the joint shear force were influenced significantly by infills.This effect reduced with the increase area of openings.(2)Four RC frame specimens were established by ABAQUS.The skeleton cure,characteristic load and stress cloud chart of the finite element model and the test model were compared an analysed.The reliability of finite element analysis results was verified as the basis of variable parameter analysis.(3)A more comprehensive variable parameter analysis is carried out for the RC frame structure with infills.The strength ratio of infills to frame,the thichness of infills,location of door openings,area of window openings and the height to longth ratio of infills were studied by FEM.The analysis results indicated that in the case of “weak frame strong infill”,small wall thickness and large ratio of height to width of infills,the effect of infills was more obvious.The specimens with centric opening have greater carrying capacity,strut effect decreased with increasing of opening areas.(4)Based on the FEM analysis results,the maximum equivalent strut width of each model was calculated.The calculated results were compared with the existing equivalent strut width formulas.The applicability of different equivalent strut width formula to the masonry infills with different parameters was analyzed according to the infills without openings and the infills with openings.