A simulation method was studied to calculate the vibration response during seismic excitation of a group of hexagonal bars installed in a restraint. Since impact phenomena take place between adjacent bars, or between a bar and a restraint, nonlinear force caused by the impact should be considered in the response calculation. The simulation method is a combination of the mode superposition method and the pseudo external force method. Time integration is carried out using the method proposed by Nigam. The nonlinear forces at the next time step can be determined through matrix calculation by introducing influence coefficient matrices which express the influence of impact forces on intersections at impact points. In this report, the influence coefficient matrices are expanded for hexagonal bars in a two-dimensional arrangement, by taking the impact direction of each impact point into consideration. In order to verify the above method, the calculated results were compared with experimental ones. The two results for maximum impact force were similar.
