Dynamic Analysis of Multibay Multistory Frames

A computer program has been developed to analyze steel frames with or without shear walls which are subjected either to blast loads or to earthquake motions. Equivalent rotational springs are used at the ends of each member to account for the influence of axial load, the inelastic behavior (including the strain-hardening effect) of the member and joint distortion. Estimating the axial load and the point of inflection for each member, the relationship between the moment, M, and the relaxation angle, ΔΘ, of the rotational spring is calculated. The M-ΔΘ relationship may be modified to account for the presence of a semirigid joint or to include the shear distortion of the connection. Slope deflection equations are developed for members attached with rotational springs and are combined to construct a stiffness matrix for the complete frame. The dynamic equations are solved, changing the stiffness matrix so that it is compatible with the deteriorated structure at every instant of the motion. Examples illustrate the procedure.