An improved equivalent force control algorithm for hybrid seismic testing of nonlinear systems

The equivalent force control (EFC) algorithm is a hybrid seismic testing method based on both an implicit integration algorithm and force feedback control. As it performs the computation of the numerical substructure with a fixed sampling number and some evaluations are not necessary, the EFC method is believed to be time-consuming for seismic testing of nonlinear systems with complicated numerical substructure model. In order to tackle this problem, the EFC method with varying sampling number (vEFC) has been conceived. The analysis of the vEFC method has shown that 2 traditional pseudodynamic testing (PDT) variants on the basis of implicit time integration schemes and numerical iteration, that is, the IPDT1 method and the IPDT2 method, can be recovered from the vEFC method. Moreover, the advantages of the vEFC method, such as fast response rate and compensation for control errors and possible slippage, are demonstrated.