A shear panel dampers consisting of stiffeners and a panel surrounding four flanges are used as aseismic dampers for buildings in Japan. Cracks can easily form in a shear panel damper when the panel undergoes shear buckling during cyclic loading caused by a severe earthquake. The damper's plastic deformation capacity can be enhanced by installing several vertical and horizontal stiffeners on the panel. Plastic deformation capacity means the amplitude of cyclic deformation angle under which the damper's strength keeps its designed yield strength. Overall shear buckling of the panel causes sudden deterioration of the damper's strength. Hence, overall shear buckling in a panel must be prevented to ensure that the shear panel damper maintains its yield strength up to an assumed deformation angle. Chusilp and Usami proposed an optimum stiffener flexural rigidity ratio, which defines the stiffener's sectional properties in which subpanels divided by stiffeners reach shear buckling before the panel undergoes overall shear buckling. However, the terms of the Fourier series in the Rayleigh-Ritz method were 6x6, and the accuracy of the plate buckling coefficient is not satisfactory. The torsional rigidity of the stiffener is not taken into account in the analysis. Application conditions are restricted so that the vertical and horizontal stiffeners must be the same. Hence, we derived an equation for the shear buckling eigen value problem considering the effect of the stiffener's torsional rigidity from the principle of virtual work. Then, the optimum stiffener flexural rigidity ratio was calculated by the regula-falsi method using various combination numbers of vertical and horizontal stiffeners. Then, the required sectional properties of the stiffener are clarified for a shear panel damper.
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