The Effect Of Floor Slab And Infill Walls On The Seismic Behavior Of Reinfroced Concrete Frames

Reinforced concrete frame with infilled walls and cast-in-situ beam-platessystem can be recognised as a structure form which have been widely used in thedomestic building construction. There are a number frames with a toypical seismicdamage in Wenchuan Earthquake, while the failure mode with a “strong columnweak beam” mechanism occurred rarely which have not match the anticipation ofcivil engineers. This may due to the reason that the effects of floor slab and infilledwalls on the seismic behavior of frame structures have been ignored during theprocess of design.In order to investigate the effects of floor slab and inflilled walls on the seismicbehavior of frame structures, the reason on the effects of “strong column weakbeam” mechanism also need to be analyzed. The main work can be summarised asfollows:(1) The effects of floor slab and infilled walls on stiffness of frame structure,vibration period, seismic internal force, story drift, plastic hinges and any otherfactors can not be ignored, need to be paid attention during the process of structuredesign.(2) Based on the unchanged mass distribution of frame structure, a modellingof pure frame and frame with floor slab have been set up, to investigate the lineartime history analysis under frequent earthquake and non-linear time history analysisunder rare earthquake. It was found that the floor slab make the structure as a whole,while the flexural rigidity and capacity of the frame have been enhanced. The duereason for the occurred “strong column weak beam” mechanism is the stiffnesseffect of the cast-in-situ beam-plates. In general, the floor slab have a negativeinfluence on seismic behavior because it may make the plastic hinge occur easily,and it should be enhanced in structure design.(3) A finite element (FE) modelling of two span frame structure was developed to analyze different influence factors. Considering the factors of slab thickness andthe bay, a formula of stiffness amplification coefficient was proposed for centerbeam and edge beam.(4) Another modelling of frame with infilled walls and cast-in-situ beam-platessystem, and even frame with nothing in bottome but fullfilled walls at upper weredeveloped for linear and non-linear time history analysis. It can be found that theexist of infilled walls have influence on the failure mode of structure, then theuneven setting of infilled walls can form weak layer in the frame and lead a yieldmechanism of layer. The effects of the infilled walls on seismic behavior of framestructure need to be fully considered to improve the stiffness and capacity ofcolumns.(5) Combined with seismic damage of frame in Wenchuan Earthquake, failuremode of the infilled walls have been analyzed. Based on the analysis of the differentfactors, three kinds of strengthening methord to the frame structure with weakness inbottom layer were developed according to tentative specification of buildingstructure aseismatic design in Fujian Province. From the comparison, suitablestrengthening methord can be adapt which based on the consideration of actualsituation in engineering practice.