Modal Nonlinear Static Analysis of Structures Based on Story Shears

In this paper a modal pushover procedure is presented in which distribution of lateral forces is calculated using the story shears. The shear force of each story is determined using its relative interstory displacement and stiffness in each mode of vibration utilizing spectral analysis relations. To retain simplicity of the procedure, like the common pushover procedures, the initial elastic dynamic characteristics of buildings are used for spectral analysis throughout. A combination rule for modal story shears is proposed that keeps the signs of responses. Therefore, the computed lateral loads contain effects of the desired number of modes and the nonlinear static analysis is performed in a single stage accounting for effects of higher modes. The lateral displacements, story shears and cumulative plastic hinge rotations are compared with the results of the conventional and modal pushover analysis and with the result of the exact nonlinear dynamic analysis. The comparative study establishes good accuracy of the proposed method as an alternative modal pushover procedure.