Nonlinear dynamic analysis of frames eased on semi-rigid technique

This paper presents a method for nonlinear dynamic analysis of frames with material and geometric nonlinearities and nonlinear connections, which is based on the semi-rigid technique. The plastic hinge that accounts for the material nonlinearity is modelled as a pseudo-semi-rigid connection at the element end. The stiffness matrix of a frame member with material and geometric nonlinearities is expressed as the sum of products of the standard stiffness matrix and the geometric stiffness matrix of the member with their corresponding correction matrices. The plastic rotation history can be calculated directly or in an approximate indirect way. The method presented is efficient in computation and it needs no additional connection elements, which makes it convenient for incorporation into existing linear dynamic analysis programmes. A portal frame and a five-storey frame are used to verify and illustrate the applicability of the method.