Problems in Building and Manipulating Large Stiffness Matrices

Large computer systems have enhanced the use of finite element methods to build structural stiffness matrices with many degrees of freedom. The building and manipulating of these matrices as required for dynamic analyses presents many difficult problems. Often these problems are encountered by the analyst during final phases of a project. When this happens, schedules are missed and costly computer reruns are required. The purpose of this paper is to focus attention on more common problem areas and to suggest methods of solutions to these difficulties. Problem areas that are discussed include: (1) determination of correct input parameters for structural analysis computer programs, (2) reduction of unconstrained structural stiffness matrices, (3) reordering and rearranging structural stiffness matrices, (4) assemblage of matrices by stiffness coupling techniques, (5) methods of checking unconstrained stiffness matrices, and (6) eigenvalue solutions for determining resonant frequencies and mode shapes of structural systems.