Nonlinear Seismic Response Analysis Of Frame Structure Based On Effects Of Masonry Infill Walls

So far as Human construction industry developed, the reinforced concrete frame structure has gradually becomed one of the most widely used forms of the structure.The prominent features of it are more economical cost, wide range of applications, very flexible architectural layout, good ductility, strong deformation capacity, able to resist strong earthquake, etc.It is an ideal seismic structural system. As a non-structural components in the structure, filled wall can not afford to load and play a supportive role, just as the role of envelope and partitions.But the earthquake resistance impact of the infilled wall to frame structure is still very important. Although domestic and foreign scholars have already done some research in this regard, basically at a preliminary stage, still have a lot of research to complete.Currently during the seismic calculation of infilled frame structure, the role of the infilled wall is to be considered by reducing the system's natural period. "Technical specification for concrete high-rise building" clearly defined after the addition of infilled walls, the reduction coefficient of structural natural period is designated as 0.6～0.7 and when carrying out the analysis of Internal force, designers only consider the stiffness of major structural components and regardless of the stiffness of infilled walls. Clearly such a provision is limited. The addition of infilled wall increases overall stiffness of the structure floor and makes the story drift and the overall displacement of structure to be smaller than calculated. In structural design, because the distribution of structure's level force without considering the impact of infilled wall, which may lead to frame structure with infilled wall and net framework assigned to the same earthquake.Moreover, the arrangement of infilled wall is always arbitrary. In 5.12 Wenchuan earthquake,the frame structure with reasonable arrangement of infilled wall,its main part was well preserved, damage was concentrated in the wall or a number of subsidiary structure; the frame structure with unreasonable arrangement of infilled wall, the main part damaged seriously and most have collapsed;what's more if the infilled wall is arranged unreasonably,it will result in the mass centre of building does not coincide with the rigidity of it.It is visible that in the current seismic design,the impact of infilled wall to structural stiffness and period is not considered reasonably and adequatly,only to be reduced by multiplying by the coefficient.Also the number of filled wall and different locations both effect structure's natural period significantly,these are not proposed specifically in the specification.Therefore,based on the influence of infilled wall,it is very important to do in-depth nonlinear earthquake response analysis on frame structure.In this paper a frame structure is selected as an example which was in some secondary school of wenchuan county, Wale model is selected to simulate the role of the infilled wall and ABAQUS finite element software is used to establish the computational model.Through respectively inputing 6 ground motions inclouding EL centro and Wenchuan Wolong etc, different nonlinear earthquake response analysis about net framework,ground weak and completely filled these three models are done in turn. Under earthquake the layer displacement,story drift,floor acceleration and drift angle of the three models are studied,by contrasting the results, the following conclusions are obtained:When adding the infilled wall,the stiffness of the structure increases and period of it decreases.We compare the deta from actual analyzes of this paper with the coefficient provised in specification,find out the reduction coefficient(0.6~0.7) provised in specification is not comprehensive. Such a calculation makes the earthquake can not be fully considered and causes the structural design unsafe. Therefore, based on this analysis,when arrangement of infilled wall is broader and more uniform,we modify the reduction coefficient.By comparing the displacement time history of three models,we obtain that the displacement and story drift of completely filled structure are smaller than those of pure frame structure.It is can be seen that when arrangement of infilled wall is continuous,uniform and reasonable,the lateral stiffness of overall structure is larger, limits the deformation of the structural layers to a certain extent.When inputing the Wenchuan Wolong ground motion, the maximum story drift of completely filled structure is 1/90, compared with the pure frame structure, the overall seismic capacity of the structure increased significantly,which show that the infilled wall has a beneficial effect on the anti-seismic behavior.Under the fuction of earthquake, due to the addition of infilled wall, the story drift of upper structure decreases,but because of the functional requirements of the underlying structure,people will reduce the number of infilled wall to expand the space,which causes the vertical arrangement of the infilled wall is not continuous,thus the stiffness of the underlying structure caprices and weak layers are formed. When inputing the Wenchuan Wolong ground motion, the maximum story drift of the ground weak structure is 1/63, compared with that of the pure frame structure(1/126), the maximum story drift angle increases obviously and this structure can be destroyed easily.It is visible that when arrangement of infilled wall is discontinuous and unreasonable, it has an adverse effect on the anti-seismic behavior.In the design of infilled frame structure,we cann't ideally consider the original structure as the pure structure.If the role of the infilled wall cann't be considered fully, greater error may be caused. For example, the displacement of many structures will be larger than the maximum specification allowed,we only can make up for this defect by increasing the cross-sectional area of components or increasing the strength of the materials which are used, obviously it is unreasonable in the practical projects, on the one hand the costs will be increased, on the other hand the structure weight will be increased too,which will result in a further increase on the fuction of earthquake. Therefore, in the structural design,we should take full account of the Strengths and weaknesses about the infilled wall to structural seismic capacity, through the aid calculation and taking effective strengthen measures to make the calculation model of the structure is identical with the actual stress state.