Research On Simplified Calculation Model And Real-Time Dynamic Hybrid Testing For Frame Structure In Open Systems

Structures are always built on sites,result in the open systems with soilstructure interaction,which affects the natural vibration frequency,damping and seismic response of the structure.The structural dynamic characteristics in open systems can be defined as the frequencies,amplitudes attenuation and the relative displacements among structural degrees,when the structure is disturbed at its equilibrium position and vibrates without any external force.Since there are large amounts of soil modes in the numerical calculation model for open system,to establish the calculation method for structural modes and simplify the seismic response analysis for open system,the frame structures were analyzed based on theoretical analysis and shaking table test.The main contents and achievements are as follows:(1)Calculation methods for dynamic characteristics of the structure in open systems1)In order to calculate natural frequencies,mode shapes and modal damping ratios including the influence of radiation damping for the frame structure in open systems,an impulse-load-based modal analysis method was proposed.In the method,the finite element model of soil-structure interaction system is excitated by the impulse load to obtain the dynamic response,so the dynamic characteristics can be obtained by modal identification method.On this basis,the convergence of dynamic characteristics by the proposed method with the increase of soil region was studied.2)In order to identify structural related modes and quantify the effect of radiation damping on structural modal damping ratio in soil-structure interaction systems,a complex-modal-based identification method was proposed.In this method,the complex modal eigenvalues and eigenvectors of the soil-structure finite element model,including the influence of radiation damping and material damping,are calculated by state space method;then the local complex modal mass ratio is developed to identify the structural related modes,thus the modal damping ratios with the effect of radiation damping can be obtained.It was verified that the modal damping ratios by complex modal analysis method for the finite element model with viscoelastic artificial boundary included the effect of radiation damping,when compared with the impulse-load-based modal analysis method.The effects of radiation damping,structural material damping and soil material damping on the modal damping ratios were discussed based on complexmodal-based identification method.(2)Simplified calculation model and seismic response calculation method of equivalent rigid foundation structure considering soil-structure interaction1)In order to analysis the factors that influence the structural dynamic characteristics considering soil-structure interaction,foundation width,structure height,structure mass,structure stiffness,soil wave velocity and soil density were studied for the structures with single-degree of freedom.The approximate calculation formulas for natural frequency and damping ratio were obtained.Based on the effective mode mass,the multi-degrees of freedom structure was equivalent to multiple single degree of freedom structures.On this basis,a calculation model of equivalent rigid foundation structure considering soilstructure interaction was proposed based on the principle of equivalence of natural frequencies and modal damping ratios.2)The soil-structure interaction system and simplified calculation model are non-proportionally damped systems,in order to improve the efficiency of seismic response analysis for such systems,a complex mode superposition method based on real modes was proposed.The complex eigenvalues and modes are represented by the linear combination of real modes through the modal perturbation method.Thus the solution of forced vibration can be expressed by the real modes.On this basis,the calculation accuracy and efficiency of the proposed method for the dynamic characteristics and seismic responses analysis were discussed.Meantime,the rationality of the simplified calculation model was verified by comparing with the results of the direct finite element method.(3)Real-time dynamic hybrid testing and the verification of simplified calculation model for frame structure in open systems1)Since the conventional shaking table test is difficult to simulate the radiation damping of elastic half-space,a real-time dynamic hybrid testing method based on pulse load was proposed.In this method,the structure was fixed on the shaking table as physical substructure,and the semi-infinite site was simulated as numerical substructure,so the free vibration of the structure considering the soil structure interaction was excitated by applying pulse load on the soil-structure connection point.Then,the time-domain identification method based on the empirical wavelet transform(EWT)and Hilbert transform was established.The real-time dynamic hybrid testing of frame structure under different site conditions were carried out.Meanwhile,the rationality of the test method and calculation method for dynamic characteristics in open system were verified by comparing with the test and numerical results.2)The conventional shaking table test under rigid foundation and real-time dynamic hybrid test of soil-structure interaction system were carried out with three earthquake waves.Then,the influence of soil-structure interaction on structural seismic responses was studied.On this basis,the accuracy of the simplified calculation model of equivalent rigid foundation structure for seismic response analysis was verified by comparing with the test results.