Hybrid simulation is an innovative method that combines an analysis model of a structural system with physical tests of one or more substructures. The analysis model is typically a finite element analysis (FEA) model that outputs displacements applied to the physical substructure using a control system operated in displacement control. For stiff specimens, the displacement commands can be so small that the control system has difficulty imposing the command displacements accurately. To do hybrid simulation with a stiff specimen, force control is desirable. Cascade control, which features two layers of closed loop control, is proposed to address this issue. The inner control loop has force control mode that provides accurate control for hybrid tests with stiff specimens. The outer control loop is in displacement control mode for accepting displacement commands from an FEA model. The effectiveness of the cascade control method in conducting hybrid simulation of stiff test specimens was evaluated with three sets of tests. For each set of tests, the results of both cascade control and displacement control methods were compared. The three test cases covered a wide range of variation from specimen size, test equipment, model type (2-D vs. 3-D), experimental element type (beam-column vs. truss), and test speed (slowdown 10 times in Test Case 1 and 2 versus 100 times in Test Case 3). In all cases, cascade control proved to be an effective method for conducting hybrid simulation with a stiff specimen.

混合仿真是一种创新方法，它将结构系统的分析模型与一个或多个子结构的物理测试相结合。分析模型通常是有限元分析（FEA）模型，其使用在位移控制中操作的控制系统输出施加到物理子结构的位移。对于刚性样本，位移命令可能非常小，以至于控制系统难以准确地施加命令位移。为了对刚性样本进行混合模拟，需要力控制。为了解决这个问题，提出了具有两层闭环控制的级联控制。内部控制回路具有力控制模式，可为刚性样本的混合测试提供精确控制。外控制环处于位移控制模式，用于接受来自有限元分析模型的位移命令。通过三组试验评估了级联控制方法在刚性试件混合模拟中的有效性。对于每组测试，都比较了串级控制和位移控制方法的结果。这三个测试用例涵盖了样本尺寸、测试设备、模型类型（2-D 与 3-D）、实验元件类型（梁柱与桁架）和测试速度（减速 10 倍）等各种变化。测试用例 1 和 2 与测试用例 3 中的 100 次相比）。在所有情况下，级联控制被证明是用刚性样本进行混合模拟的有效方法。