برآورد ضریب مقاومت افزون سازه های مسلح به دیوارهای برشی فولادی

Steel plate shear walls are very effective lateral load resisting systems which have high lateral stiffness and high ductility capacity at the same time. Although there are valuable experimental data available for such systems, most of the current seismic codes (including Iran’s Standard NO. 2800) provide none or limited design provisions for such structural systems. One of the important seismic performance parameters of the structures is “over-strength factor” which is implicitly or explicitly part of seismic design base shear formulation. Most of the available data on this factor are obtained from experimental research and therefore results are limited to low-rise structures and/or with reduced scaled structures/specimens. The main objective in this research is to assess the over-strength factor for the steel plate shear walls. A closed-form-solution is proposed for obtaining this factor based on a plate-frame interaction. This formulation is on the basis of the assumption that steel plate yields first and then the frame undergoes into the inelastic range. Therefore, an important factor that controls the amount of overstrength in an steel plate shear wall panel is the ratio of the steel plate yield displacement to the that of the steel frame. The lower this ratio is the higher the overstrength factor would be. The results of four experiments from four different universities accross the world were considered. The results also include the geometric and material properties of the specimens as well as their hystresis behaviors under cyclic loading. From the hystresis loops one can obtain experimental overstrength factors. It was found that the over-strength factors obtained by this proposed method are in line with available experimental results obtained from these four tests. It was also found that as the steel plate thickness decreases, the overstrength factor increases. Also, as yield stress of the steel plare decreases, the overstrength factor increases. In other words, the softer the steel plate /panel becomes, the better the chance of the redistribuition of internal forces would be and therefore the higher the overstrength factor would become. Two sets of results and/or comparisons are made in this study. First for the purpose of vrification of the proposed closed form solution, one of the test specimens were extended and it was shown that for the certain condition of that the test the proposed formulation matched the experimental results however if the plate thickness were to increase the overstrength factor would drastically decreases. The second set of results were for steel plate/panels with real sizes and not small lab sizes. It was shown that for such moderate and realistic steel panel sizes and thicknesses the overstrength factor comes out to be about 1.3. In addition, an square like panel has the highest overstrength factor compared to a rectangle ones.