Abstract:To improve computational efficiency, constrained mode synthesis method is discussed and a linear space consists of displacement vectors calculated by different mode cut-off numbers is defined. A function is also defined and verified to be a norm of this linear space mathematically. Then adopt the maximum value of that norm as the potential energy criterion. The relationship between potential energy criterion and mode cut-off number is derived. Consequently, the mode cut-off criterion based on potential energy criterion is proposed. In addition, the situation of adopting mechanical energy as the criterion of constrained mode synthesis method is considered. It is proved that mechanical energy is not a monotonic function towards mode cut-off number, so it is not suitable for constrained mode synthesis method. Finally, the proposed potential energy criterion is applied to seismic analysis of soil and multi-story buildings interaction system and the results are compared with method without mode synthesis. It shows that the proposed mode cut-off criterion based on potential energy criterion is effective while that based on mechanical energy criterion which generally used in superposition method is not suitable for constrained mode synthesis method.