The Seismic Responses Analysis Of RC Frame Including Bond-Slip

At present time,the post seismic performance of reinforced concrete frame is represented by the member's relative nonlinear deformation capability under extreme lateral loads, namely the energy inputed by the ground motion ,is dissipated by the steady cyclic deformation on the base of ensuring necessary bearing capacity. In the important dissipation framework of beam hinge and beam-column hinge ,nonlinear deformation concentrative appear by the zone of beam-column joints and bottom end of ground floor columns(as zone of beam end hinge and column end hinge) .The deformations at hinge zone is composed of two parts:①flexure deformation ;②the end rotations caused by bond-slip.For reinforced concrete structures subjected to moderate to large earthquakes, capturing the structural response and associated damage require accurate modeling of localized inelastic deformations occurring at the member end regions .The cause that reinforcement and concrete can work in together is the bond effects between them .Researchers have established dfifferent analytical means to simulate the bond-slip. Nonlinear rotational springs have been used at the end of beam-column elements to include the member end rotation due to bond-slip effects, but the monotomic properties of the rotational springs are typically edtablished using empirical methods, and its shortage in considering the affects between variable axial load and bond-slip .So the new methods based on fiber-based analytical method must solve that problems.A significant effort has been invested to model the bond slip of beam bars anchored into building mid-joints while studies on the bond slip effects of longitudinal bars into footings and frame side joints ,or how bond slip affect the local and global response considering three parts (as bottom end of columns, middle joints and side joints)bond slip of frame at the same time are very scarce .In the fiber-based method, a zero-length section element that can individually considering bond slip effects, combined at the end of the member, can solve above-mentioned problems. At first, the ability of this proposed model to capture the bond-slip effects was calibrated by comparing the simulated results with experiments ,then the method is introduced into a plain frame to evaluate how the bond slip of different parts affect the global and local seismic responses.The critical contents and conclusions :①Based on the calibration of column , the ability is calibrated by evaluating how the concrete model in two elements affects the simulation results, and comparing the simulated flexural rotation and fixed end rotation due to bar slippage of a reinforced concrete column with the corresponding experimental results, respectively .By comparing simulation results and experiments of two cantilever beam ,which is conformed in load and anchorage conditions , the suitbility and accuration of the model is calibrated .The text carry out the simulation of middle joints of the frame , as two points loading mode transform in one point by a additional rigid frame . A stress–slip model that can represent the cyclic bond slip anchored in middle joints is used ,because the difference in loading and anchorage conditions between middle joints and side joints,bottom columns.②The validated modeling bond-slip method is transformed in plain frame. Based on a multilayer RC frame.carrying out five times simulations: without bond slip ,considering bottom columns bond slip only,considering middle joints bond slip,considering middle and side joints bond slip,considering bottom columns and joints bond slip ,evaluating the different bond slip how to affects the seismic response individually.The critical conclusions by compariton:1)Only considering bottom bond slip can magnify the global reponses and beam end rotations of the first to third floor , reduce the flexure rotations of bottom end columns.2)When only considering middle joints bond slip ,the max top displacement is magnified. The beam end flexural rotations diminish, which connects with middle joints ,but when appending the corresponding bond slip rotation ,it familiar with without bond slip, so the bond slip just change the composition of deformations.3)When considering the middle and side joints bond slip ,the top displacement is magnified more than only considering middle joints bond slip, but the range is diminished. The beam end flexural rotations is reduced ,the compostion of deformations is changed .4)The top displacement is manified more than others when considering bottom columns and joints bond slip. It is same to considering joints bond slip that the beam end flexural rotations is reduced,bond slip effects change the compositions of deformations.Whether columns or beam,the hysterical relationship of bending moment-flexural rotation have the same characteristic:comparing with without bond slip,the peak bearing capacity is reduced ,the max flexural rotations diminish; when appending the corresponding bond slip rotation ,it familiar with without bond slip, so the bond slip just change the composition of deformations,as pure flexural deformation transform to flexure and bond slip . the intension degradation of bending moment-flexural rotation is severe.③The validated modeling bond-slip method is transformed in 3D frame. By comparing of results between without bond-slip and with bond-slip, the bond-slip how to affect the global and local response of the 3D frame is found.The critical conclusions:When the bond-slip is included in the analysis, the frame also appear column-beam hinge character, but the quantity of column hinge is more than beam hinge , the rotation of column is large than beam hinge. The top displacements of X and Y directions is amplified when including bond-slip. The quantity of hinges is familiar with without bond-slip, the rotation of 1st story columns is reduced,but the rotation of 2nd story columns is augmented.For all ,on the base of fiber-based model,the method that combining a zero-length section element to individually simulating bond slip effects can caputuring the response of the member, by quantifying the affects of bond slip to members and structures, can more accurately evaluate the composition ratios of the member, improve the precision of fiber-based model.