Shaking Table Substructure Testing Considering Complex Dynamic Boundary Conditions

Shaking table test is a real method to simulate seismic excitation,but it is often limited by scaling effect so that it is difficult to accurately reproduce local damage of the structure.In recent years,the hybrid testing technology can flexibly select part of the structure concerned for physical test and the rest for numerical simulation,so it can simulate the seismic response of large-scale engineering structures and solve the problem of scaling effect caused by too small scale in shaking table testing.The hybrid testing using shaking table for loading is called as shaking table subtructure testing(STST).The main problem of STST lies in the realization of boundary conditions.On the one hand,it is reflected on the realization of boundary between shaking table and physical substructure.On the other hand,how to realize the dynamic force boundary condition between physical substructure and numerical substructure.The two kinds of STST platform in this paper are proposed and establised to study the two types of boundary conditions,respectively.The major studies are focused on high-precision reproducing method of shaking table for wide frequency acceleration signal and the realization method of the complex dynamic force boundary condition on physical substructure.The corresponding control algorithm and loading device are developed to solve these problems.Finally,a hybrid flexible controller is developed to provide a support platform for the control of those algorithms and hardwares.The content of this paper is summarized as follows:(1)Establish and control of wide-frequency double-layer shaking table system:Aiming at solving the low frequency response of large-scale shaking table,which is difficult to meet the broadband excitation requirements of major projects,a double-layer shaking table system(DLST)is developed,and the offline iterative control method(OIC)is proposed to effectively broaden the working frequency band of the shaking table.The numerical simulation model of DLST is established to verify the effectiveness of OIC for DLST.The effect of the structural nonlinear effect and different mass ratios of two shaking table on the stability of DLST are analyze.An experimental system is built to fully verify the feasibility of DLST and OIC for large-scale shaking table to improve broadband waveform reproduction performance.(2)Substructure testing based on shaking table boundary coordination: An experimental platform based on shaking table boundary coordination is firsly built,whose hardware system,control framework and compensation strategy are introduced with details.An equivalent shear model considering rotation effect was proposed,and the difference between different simplified dynamic models was analyzed to achieve efficient coordination between numerical substructure and physical substructure.As for wind turbine tower under complex environment,the substructure test considering multidisaster coupling effect is carried out on this platform,The feasibility of multi disaster coupling effect test using this platform based on shaking table boundary coordination is verified as well as the effectiveness of the proposed multi-stage adjustable frequency tuned mass damper for wind-induced vibration control.(3)The theory study of substructure testing based on dynamic boundary force coordination: The major structural damaged due to strong earthquake are comcentrated on the bottom of structure.this study proposed a substructure testing framework technology that chooses lower part of whole structure as the object of study,in which bending shear dynamic loading strategy and error-response negative-feedback compensation method(ENC)are put forward to solve the problem of multi-dimensional dynamic loading and stability problem caused by error propagation,respectively.The correctness of the proposed theory and the feasibility of multi-disaster coupling effect test using dynamic boundary coordination device(BCD)are verified by numerical simulation.(4)Loading device for substructure testing based on dynamic boundary force coordination: Based on the requirements of numerical and physical dynamic boundary coordination in substructure test,a multi degree of freedom dynamic boundary coordination device is developed to realize the dynamic loading of bending moment and shear force by the parallel arrangement scheme of double-layer shakers.An enhanced three parameter control method(ETVC)is proposed to drive the boundary coordination device,and a shaking table hybrid substructure platform is built to test the effectiveness of ETVC and ENC,the ability of the dynamic boundary coordination device to realize complex boundary conditions is fully verified by STST of four-story frame test.(5)A flexible control platform for hybrid test: Aiming at the difficulty of building a complex hybrid test platform,A flexible control platform for hybrid test is developed by designing a flexible controller with modular concept,rich control and acquisition ports,which can drive multiple dynamic loading devices at the same time and establish a complex substructure hybrid test system;The control software system adopts the masterslave scheme with the basic instruction set to ensure the basic control and has the basic control logic framework to facilitate the secondary development,can realize the independent design of inner loop control and outer loop control,which greatly facilitates the construction of complex hybrid test system and solves the problem of synchronous control of multiple dynamic loading system.The function of the proposed flexible controller is verified by experiments.