Study On Three-Dimensional Seismic Isolation Effect Of Double Layer Cylindrical Shell With Lower Supporting Structure

With the development of society and economics,a variety of large span space structures emerge one after another.As a major form of large span space structure,double layer cylindrical shell is widely applied in industrial and civil architecture.There is a popular belief that the double layer latticed structure has better earthquake bearing capacity and the research should emphasize in single layer latticed structure,which makes the study about earthquake response pattern of double layer cylindrical shell is less and the study about double layer cylindrical shell with lower supporting structure is rare.However,two double layer cylindrical shell structures,known as Lushan Middle School Gymnasium and Lushan Gymnasium,was destroyed in a 7.0-magnitude earthquake in Lushan County,Sichuan Province on the year of 2013.These two structures were designed and built based on the new Code for Seismic Design of Buildings(GB 50010-2010)after the world-shocked Wenchuan earthquake.The failure of these two structures clarified the lack of study on seismic response pattern of double layer cylindrical shell with lower supporting structure and the need of further of the failure pattern of such structures.In order to have an adequate study of the seismic response pattern of double layer cylindrical shell with lower supporting structure and the isolation effect of the threedimensional isolation support,this paper conducted a series of earthquake simulation shaking table test and FEM parametric simulation analysis based on typical structure form,which reveals the seismic response pattern and isolation effect of the structures with different design parameters.The major research contents are summarized as below:1.Shaking Table Contrast Test of Double Layer Cylindrical Shell with Lower Supporting Structure with/without Isolation SupportA reduced scale double layer cylindrical shell with lower supporting structure model was designed and built on the earthquake simulation shaking table.With the input of stepwise seismic load,the dynamic response data of structures under different load pattern were collected and the failure pattern of double layer cylindrical shell was observed.Then a new model with three-dimensional isolation supports installed between the lower supporting structure and the double layer cylindrical shell was loaded with same loading mode.The dynamic response data of isolated structure was collected and the deformation of isolation support was observed.It is revealed by the collected data that the dynamic amplification effect caused by lower supporting structure is the main reason of the failure of double layer cylindrical shell and the three-dimensional isolation support could reduce the dynamic amplification effect efficiently under different loading conditions.2.Numerical Simulation of Test Model Based on ABAQUSBased on the design data of test model,a series of numerical dynamic history simulation was carried out based on the FEM software ABAQUS.The comparison between the simulated data and test data verify the correctness of the FEM model and give a solid foundation for further full-scale parametric numerical simulation of double layer cylindrical shell with lower supporting structure.Meanwhile,by the comparison of the vibration mode between isolated and non-isolated structures,the isolation mechanism is revealed to be the extension of the natural period of vibration of isolated structure so that the structure could keep away from the predominant period of seismic wave.The deformation of structure in first three modes is the monolithic translation,which could avoid self-deformation failure of double layer cylindrical shell.3.Parametric Numerical Analysis of Double Layer Cylindrical Shell with Lower Supporting StructureBased on the Numerical simulation of test data,a series of parametric numerical simulations of full-scale double layer cylindrical shell with lower supporting structure were carried out.The dynamic response pattern and limit seismic load of structures with different height and cross section of lower supporting structure and different length-width ratio,rise-span ratio,and roof load of double layer cylindrical shell were obtained and compared with the data obtained from isolated structures.The simulated results revealed that the limit seismic load of double layer cylindrical shell with lower supporting structure is less than the load of structures without lower supporting structure for the dynamic amplification effect,torsion effect,wave filtering effect caused by lower supporting structure.The higher the lower supporting structure,the less the limit seismic load,and the dynamic response will increase and the limit seismic load decrease if the cross section of lower support structure is oversize or undersize.The limit seismic load will decrease if the length width ratio is oversize or undersize,and the rise span ratio changes the limit seismic load by the change of vertical load bearing capacity.Meanwhile,the greater the roof load,the greater the dynamic response,the less the limit seismic load.For structures with different parameters,three-dimensional isolation support shows universal isolation capacity.With the increase of the dynamic load,the isolation effect becomes better.The position of isolation support changes the isolation effect significantly for the isolation effect for lower supporting structure of interlayer isolation support is limited while the isolation effect of base isolation support is better for both of the lower supporting structure and double layer cylindrical shell.