Seismic Performance Of Masonry Infilled RC Frame Structures With Openings

Masonry infilled reinforced concrete(RC)frame is widely applied to construct multi-story buildings in China and all over the world.Due to the need of lighting and using function,door and window openings are commonly found on the infill walls.The poor performance of the masonry infilled RC frames in the previous earthquakes indicate that the influence of infill wall on the RC frames was non-negligible.Furthermore the existence of openings made the damage of the infill wall more complicated.The interaction and cooperative work between infill wall and RC frame influenced the mechanical behavior and failure mechanism of the structure.Door and window openings altered the force-transferring of infill wall and influenced the seismic performance of infilled frame significantly.However infill walls are regarded as non-structural element by engineers in structural seismic design and analysis.Thus,the contribution and effect of infill wall during the earthquake response are neglected.So studying the seismic performance of infilled RC frame with opening and finding a reasonable analytical model to assess the influence of infill wall with opening on the frame structure,becomes a significant research topic.In this study,the seismic performance of masonry infilled RC frames with openings was studied through full-scale quasi-static experiments and detailed finite element technique.The detailed finite element model was established and verified by the experimental results.Parameters analyses were conducted and a simplified analytical procedure for the equivalent inclined strut considering the infill wall with openings was proposed.The main contents of this study are as followings:(1)Two full-scale single-story single-bay masonry infilled RC frames with opening were established,with different aspect ratios for the wall.Infill walls were constructed with hollow block units made of ceramsite concrete.A bare frame and a solid masonry infilled specimen were treated as two reference specimens.Quasi-static tests were conducted on the specimens under cyclic loadings.The failure mode and the lateral load-displacement hysteresis curves were discussed for specimens.The stiffness,lateral resistance capacity,ductility,energy dissipation and equivalent damping of specimens were compared to study the seismic performance of masonry infilled RC frame with opening.(2)The constitutive relation on the cracks in the extended finite element method and interface element were studied,considering the progressive degradation of elastic stiffness and the reversible geometric dilatation of crack interface for quasi brittle materials under reversed cyclic load.Based on FEAP software,the constitutive relation was added to extended finite element analytical procedure for masonry infilled RC frame.The effectiveness of the constitutive relation to simulate crack interface was verified by simulating the available experimental tests about the cracks of quasi brittle material.Detailed finite element model for infilled RC frames with openings was established.Full-scale experiment in this study and the reduced scale experiment in literature were simulated.The comparison between the analytical and experimental results verified the detailed finite element model.(3)Using the detailed finite element model for masonry infilled RC frame,the effect of opening size,opening position,opening configuration,opening aspect ratio,wall aspect ratio,wall slenderness ratio and masonry strength on the seismic performance(stiffness,load resistance capacity,failure mode,etc)of infilled RC frames with openings were studied.(4)Calculation formulae of reduction factor for the stiffness and peak load of infill wall with openings were proposed.Comparison with the available formulae in literatures verified the effectiveness of the formulae in this study.A simplified analytical procedure for the equivalent inclined strut considering the infill wall with openings was proposed and verified by comparison with the full-scale experimental results and detailed finite element analytical results.Using the proposed simplified analytical model,the influence of infill arrangement and openings on the seismic performance of multi-storey multi-bay RC frames was studied.