The use of modal superposition in nonlinear dynamics

This paper describes the application of the modal superposition method to the calculation of the nonlinear dynamic response of structures. Although this method has often been used in the analysis of linear response, it was seldom been applied in nonlinear problems. The reasons for this are obvious and seem to be quite valid, but the examples considered herein indicate that modal superposition may be a more useful computational tool than has heretofore been imagined. Four different problems are considered in this paper: a three dimensional cable stayed bridge, a double layered three dimensional cable network, an unstiffened suspension bridge, and a three dimensional elastic-plastic frame. The problems are chosen to exemplify both the strengths and weaknesses of the modal superposition method.