Inelastic Analysis of Multistory Multibay Frames

An incremental load procedure is presented for determining the elasto-plastic behavior of plane rectangular rigid frames from the unloaded state to the ultimate carrying capacity. The procedure utilizes the displacement method of analysis and includes the effects of joint displacement, strain reversal, axial force, and spread of the inelastic zones in the members. The numerical procedure was programmed to study bending and bifurcation failures of fixed base portal and multibay, multistory frames under proportional and nonproportional loading. On the basis of the frames studied the inclusion of joint displacements in the analysis had a significant effect on the computed value of the ultimate carrying capacity of the structure. The studies indicated that the value for the determinant of the stiffness matrix approaches zero at the ultimate carrying capacity regardless of whether the frame fails by bifurcation or by bending, elastically or inelastically.