Research On Stiffness Property Of Shear Wall Considering The Inelasticity

Reinforced concrete structural members almost have gradually exhibited theirinelastic properties which are increasingly evident since the very moment whenconcrete starts to crack in tension. Therefore, the elastic analytical results of them arenot adequate to reflect the deformation and the internal force of the structure actuallyonce these components successively get into the state that concrete starts to crack intension. This is a significant impact which bothers the design and analysis forreinforced concrete structures. Definitely, the optimal choice is to conduct inelasticstatic and dynamic analyses in order to involve the inelastic properties of structuralcomponents and elements mentioned before, but these analyses are difficult to carryout. Hence, we hope to utilize the elastic analytical program (including the plane tothree-dimensional analysis) to consider the nonlinear properties of reinforcedstructures.Early in the1980s, the method which the original elastic stiffness is replace by thesecant stiffness for various types of components subjected to different forces andutilizing elastic analytical program to consider inelastic behaviors of reinforcedconcrete structures was proposed. Possible utilization of this method to use theequivalent secant stiffness involves these following situations of structural analysis:1)structural static elastic analysis utilizing equivalent secant stiffness of components(including the second order effect analysis);2) structural static push-over analysisutilizing equivalent secant stiffness of components (including the second order effectanalysis);3) structural dynamic time-history analysis utilizing equivalent secantstiffness of components.Although significant developments of the quantification of the equivalent stiffnessof structural components have been made by the academia in deferent countries inrecent years, and additionally, there has been adequate research for the quantificationof the stiffness reduction coefficient for beams and columns currently, thequantification of the stiffness reduction coefficient for shear wall-columns still remainsan vast array of problems to be researched further. Because of this, this paper mainlyconcentrates on the reasonable quantification of the stiffness reduction coefficient forshear walls and the analysis and research on some unresolved problems. The researchfindings that are of limited importance are as follows: ①Integrating the main characteristics of the force analysis of shear walls, theproblem of stiffness reduction for shear walls is further considered utilizingPERFORM-3D software, the three-dimension nonlinear analysis program, as theanalytical measure. The observation results of comparison tests confirm that it isfeasible to utilize the shear wall element in PERFORM-3D to simulate the behavior ofshear walls before they yield and in a given deformation range after they yield.②This paper tries to apply the equivalent secant stiffness in the structuraldynamic time-history analysis, i.e. verifying whether structural nonlinear dynamictime-history analysis can be equated to the dynamic elastic response (i.e. equivalentlinear method with modified stiffness). This attempt is full of risk for the reason thatthe workload is large and hence the conclusions we draw may not be of positivesignificance. Here in this paper, the PERFORM3D soft ware is applied to design aframe-tube structure model according to the state-of–the-art structural codes and toconduct the nonlinear dynamic response analysis with the input of five ground motionsof the rarely met level in the X-axis. And the ETABS software is applied to build theequivalent elastic model utilizing the stiffness reduction coefficient for eachcomponent and also to conduct the linear elastic time-history analysis with the input offive ground motions of the rarely met level in the X-axis. Then we compare the resultsfrom these two methods and conclude that: when the stiffness reduction coefficient forbeams is set as0.4, that coefficient for columns is set as0.6and for shear walls it is0.7,the tendency of the top displacement time-history curve of the equivalent elastic modelis generally similar to that of the elastic-plastic model and the partially precisemaximum top displacement of the real structure can be assessed, but it is difficult toreflect the low how the stiffness and especially the interior forces of the structurechange in the ultimate state.③In order to provide effective data for the academic project carried out byChongqing University and Chinese Southwest Architecture Design Institutecorporately, this paper conducts a tentative research on the range of on the base ofwalls and provides the number of floors for the fortified base region according to bothChinese codes and the0.2f_c ’ method proposed by American code (i.e. ACI318-08[8])on the background of former computing cases. We find that the acquired number offloors for the fortified base region proposed by ACI318-08[8]utilizing the0.2f’cprinciple is relatively larger in comparison with that number according to Chinesecodes, and that the fortified base regions for structures with various heights are generally the same according to Chinese codes while the American0.2f_c ’methodproposes different numbers of floors which require special boundary elements based onvarious structural characteristics. Therefore, we can draw on the American0.2f_c ’method to check our decision for complicated situations in order to enhance theflexibility of the engineering design.