Study On The Dynamic Performance Of Multilayer Long-span Steel Grid Structure

As one of the most important resource elements for urban development,construction land should be made full use of.The employment of multistory buildings to replace traditional ones of single story with long span is the most effective measure to increase the utilization of industrial and public facility land.Space steel grid structure,with steel Vierendeel Sandwich Plates(hereafter,refer as VSPs)as floor slabs and grid walls as lateral force resisting systems,is a new structural system of great technical and economic benefit in multistory buildings with long span.Compared with the general frame structure,the spatial steel grid structure has the characteristics of large span-height ratio,low vertical natural frequency and significant spatial stress effect.Under normal use and accidental action,the response of such structure is quite different from that of the traditional one.Firstly,the relevant literature was reviewed and analyzed.The focus of the literature is mainly on the forms of multistory and long-span floors,the static performance of the spatial steel grid structure,analysis methods and evaluation standards of human force on floors,seismic analysis methods of long-span structures and so on.The study shows that the spatial steel grid structure is a promising structure form of great application in multistory industrial and public buildings with long span.It bears the advantage of profound study on the static performance while it also lacks in research on the dynamic performance,which has become a restriction of its popularization.Following methods as testing method,numerical method,analytic method and their combination are adopted to conduct modal analyses of long-span steel VSPs.Numerical models of different scales are studied to identify the influence that natural frequency has posed on calculation results,and the influences of different structural parameters on the natural frequency of steel VSPs are also taken into consideration.The theoretical calculation formula of vertical fundamental frequency of steel VSPs is put forward,and it is verified by using numerical method.The formula can greatly help to simplify the calculation of fundamental frequency in the preliminary model design phase.Numerical method is used to study the characteristics of the vibration response of human force on the floor slabs with steel VSPs,and thus the method to assess comfort is put forward.Time-domain analysis is employed to study the characteristics of the acceleration response of long-span steel VSPs under the load of human force.The influence of structural damping,load parameters and structural parameters on the response of floor is also studied in the process.The study shows that the distribution of peak acceleration of long-span steel VSPs under human force is funnel-shaped,that is,responses at the center is extreme and there is rapid attenuation to the periphery.In the light of such characteristic,the method to assess comfort is proposed based on comfort assurance rate,which helps to avoid the problem of being too conservative of the traditional assessment.The experimental method and numerical method are used together to study the hysteretic behavior of joints in the space steel grid structure.Based on the stress characteristics of shear connectors in the steel SVPs,pseudo static test device is designed for cyclic loading experiments,and numerical models are compared and analyzed after the experiment.The strength,stiffness,ductility and energy dissipation of shear connectors and Vierendeel beam-column joints are analyzed by adopting numerical method.The influence of geometric parameters of joints on dynamic performance is taken into consideration in the analysis.Based on the requirements for the seismic conceptual design “joints can never be too strong”,design suggestions for joint structure are put forward.The numerical method is used to study the seismic behavior of space steel grid structure.The influence of different scale numerical models on the hysteretic behavior of shear connectors is analyzed and results show that the calculations of the multiscale models are accurate but with low calculation efficiency.Results also show that frame model can bring high calculation efficiency,but it is impossible to accurately simulate the mechanical properties of joints without stiffeners.In view of the characteristics of shear connectors without stiffeners,a semi-rigid joint model of spring hinge is proposed.The Seismic Time-history Response of a single Vierendeel beam-column frame is analyzed by using numerical method.The calculation efficiency and accuracy of shell element model,multi-scale model and semi-rigid joint model are discussed in the analysis.The availability of the semi-rigid joint model of spring hinge is verified.The static elastoplastic analysis of space steel grid structure is carried out and it is proved that the space steel grid structure has formed four anti-seismic defense lines with good ductility during strong earthquakes.In addition,through calculation and analysis,the increasing coefficients of the elastic-plastic story drift are obtained.In a word,the study focused on the dynamic performance of space steel grid structure under the limit state of normal use and bearing capacity.The response mechanism of the structure under the dynamic action is depicted,numerical analysis models are established,theoretical calculation method is raised,and finally design suggestions are given in the paper.