Shaking Table Substructure Experimental And Numerical Studies Of Equipment-steel Frame-soil System

In buildings,equipment and other non-structural components play important roles in the normal functioning of buildings and relief efforts after earthquakes.Moreover,failure of non-structural components usually causes huge economic losses and safety hazards.Recent research on earthquake engineering has paid increasing attention to the equipment-structure(ES)system.Existing research on seismic performance of ES system is mostly based on the assumption of rigid ground.Considering that soil-structure interaction may have an adverse effect on the structure or the equipment inside it under some circumstances,it is more reasonable to analyze the seismic performance of the equipment-structure-soil(ESS)entire system.As the complexity of the system has restricted research involving the interaction between the three parts,there is an urgent need for appropriate experimental techniques and analytical methods for investigating the seismic response of ESS systems.Based on the branch modal substructure approach,this study proposed a seismic testing method applicable to ESS systems which called shaking table substructure testing(STST).This method treats the ES subsystem in steel frame buildings as an experimental substructure and soil as a numerical substructure.The steel frame structure is selected for structural type,so the steel frame is replaced by structure for clear and unified description.The two substructures went through shaking table testing together for comprehensive evaluation of the entire system’s seismic performance.To demonstrate its reliability,STST was conducted on an ES subsystem on rigid ground,which is regarded as a special test case of the ESS system.Given that the behavior of soil during strong earthquakes is not entirely nonlinear,a locally nonlinear soil model was used as the numerical substructure in STST to account for the nonlinear effect of soil after examining its feasibility.Later,STST was used to research the seismic performance of an equipment-high rise structure(HRS)-soil system,in order to expand its applications.The major work done in this study and relevant results are summarized below:(1)This study proposed a seismic testing method applicable to the ESS system,called STST,and then illustrated how to derive the computational formula for the complex system needed in STST.The equation of motion for the ESS system was derived through the branch modal substructure approach.The equation obtained features clear concepts and convenient operations and can be applied to STST after transformation.Some key issues involved in constructing a STST system,such as real-time communication,control method,and numerical computation,were addressed.Real-time numerical control was used in combination with real-time physical control for compensating control of the shaking table.This allows for efficient tracking and control of the shaking table with desired accuracy.(2)A reduced-scale model of ESS system was constructed based on the concept of similarity.An experimental model was created for the ES subsystem based on the design parameters,while the soil was simulated with a numerical model based on the principle of predominant period similarity.In order to achieve a real-time testing process,the soil model was analyzed using RITZ vectors and then truncated to a proper number of dominant modes based on the principle of potential energy truncation.In addition,the study verified that it is reasonable to use the soil model as a numerical substructure after reducing its number of degrees of freedom,which offers a feasible way for a complex soil model to participate in STST.STST was successfully applied to an ES subsystem and an ESS system.And STST of ES subsystem can be regarded as a special case of the ESS system.The results from the testing on the ES subsystem were compared with those from the entire system in order to examine the reliability of the STST derived from branch modal substructure method.(3)The equation of motion for the locally nonlinear soil model was derived for using as the numerical substructure in STST,through a combination of the branch modal substructure and linear-nonlinear hybrid constraint modal substructure approaches.Then a method called interactive numerical computation was proposed as a way to examine the feasibility of using a locally nonlinear soil model as the numerical substructure in STST.In this method,experimental substructure and numerical substructure models were created by different software to simulate the STST process.Besides,a computational module for simulating the response of locally nonlinear soil in STST was developed using SIMULINK,thereby solving the difficulties in computing and software development associated with the need to take into account soil’s nonlinearity.(4)In light of the size difference between a large equipment-HRS-soil system and its small scale model,the main part of the equipment-HRS subsystem were treated as an experimental building substructure,while the rest was treated as a numerical building substructure and the soil model as an independent numerical substructure.The entire system was subjected to STST and more detailed data could be obtained.The difficulty in modeling equipment-HRS subsystem should be solved in this testing process.Equipment was modeled as a secondary substructure in the analysis which had the characteristics such as model building simply,conveniently and flexible.The results of whole finite element model were compared with the results of interactive numerical computation based on the formula derived for the equipment-HRS-soil system in order to confirm the feasibility of the testing method.(5)A case study of the system composed of equipment,high-rise steel frame structure and soil was conducted.The equipment was simulated with a simplified model with a single degree of freedom.The structure was a 13-story,4-span steel frame structure.Two types of soil were analyzed separately: Class II ground and Class III ground.The time histories of dynamic responses in the equipment-HRS subsystem on rigid ground and the equipment-HRS-soil system were obtained by interactive numerical computation.Furthermore,the study also revealed how soil type and changes in the equipment’s frequency ratio,mass ratio,damping ratio,and location influence the seismic responses of the equipment and HRS.