Investigation of Element Size Effect on the Nonlinear Behavior of Flanged Shear Walls

Completion and development of reliable analytical models using finite element method could help investigation and prediction of the actual structure response results. Analysis of each model in finite element software needs meshing, in which computer results are dependent specifically to geometry and dimensions of the elements, called "mesh dependence". Finding a strategy for independency of the results to meshing is tangible. For the mentioned purpose and also to investigate the role of finite elements meshing in flanged shear walls, finite element software was used. Different meshings of shear walls (tested by Vecchio and Palermo) were analyzed and studied. The results of analyses with different meshs showed different ultimate strengthes and lateral displacementes. Different shapes of mesh create various results, which are indicated in the finite element model. By increasing of the size of mesh, the final force was increased and the lateral displacement was decreased, which presents a rigid model. On the other hand, by decreasing of the dimension of mesh, a stiff model was seen. So, it is a need to create well proses to analyze and evaluate the flanged section of shear walls with finite element model. Getting suitable accuracy of finite element model, the mentioned concrete shear wall (vecchio and Palermo) was modeled by ANSYS. 3D SOLID65 element was employed for modeling of shear wall structures. This element is capable of cracking in tension and crushing in compression. In concrete applications, for instance, the solid capability of the element may be used to model the concrete while the rebar capability is available for modeling of reinforcement behavior. After calibration, optimum forms and dimensions are recommended. As an illustration, an idea was presented, by which flanged shear wall could be analyzed more carefully in ultimate strength and ductility. This analysis showed that the results of squared mesh are closer to the fact. For example, this type of meshing 6% error in ultimate strength and ductility in accordance to lab Specimen, presented the closer responses. Furthermore, investigation on the optimum size of the mesh showed that if the mesh has the same size of the thickness of the connecting element (Shear Wall Web), the results will have very high accuracy. For instance, squared meshes with same dimension of meshes equal to web thickness, rather than those with half dimension of that led to 1% of lateral resistance, which is closer to experimental test. It is possible that web thickness is 150 mm, thereby, we can use mesh sizes of 150mm, 75mm or 50mm. However, in order to obtain ultimate loads accurately, the mesh size of 150mm seems reasonable. Square meshes have four degrees of freedom. If the size of square is chosen to be the same as the web thickness, nodal forces induced in the web would be proportionate. For thischallenge, a flanged section reinforced concrete shear wall tested was selected to confirm the web thickness square theory. This shear wall was modeled by finite element program. The results of analysis showed accuracy in the investigated theory. In this study, the web thikness square theory has indicated 8% error in ultimate strength.