Seismic Response Analysis Of Large-scale Truss String Structure Under Multi-support Excitation

As a self-balanced prestressed spatial structure with high-efficiency force-transferring mechanism,truss string structure has smaller horizontal thrust to foundations under vertical loads,and is safe and stable with lower steel usage,because of which it is widely used in space structures such as large storage,exhibition center and gymnasium in recent years.Our country is characterized by complicated geologic structure,and the seismic activity has the characteristics of wide distribution,high intensity and high frequency.The dynamic characteristics of truss string structure are complex and truss string structure is influenced greatly by spatial variation of seismic motions in the earthquakes,so studying the seismic behavior of truss string structure under multi-support excitation has become an important subject in the research field of spatial structure.Aiming at these problems above,based on travelling wave method,on the engineering background of cylindrical truss-string coal shed structure,the research includes three parts:rules of seismic response of truss string structure under multi-support excitation for frequent earthquakes,seismic action effect adjustment coefficients of truss string structure considering multi-support excitation effect in Shanghai area,weak section distribution of truss string structure under rare earthquakes,and details are as follows.Firstly,uniform excitation and multi-support excitation time-history analyses under frequent earthquakes were performed for nine common size large-scale truss string structures.The multi-support excitation’s impact on seismic responses of truss string structure and relations between multi-support excitation effect with regard to structural span,structural length,length-span ratio,seismic wave direction,apparent wave velocity and seismic wave type were obtained by comparing the results of multi-support excitation and uniform excitation time-history analyses.The study shows that multi-support excitation has a great impact on the upper truss,but the impact on cables and struts can be neglected generally;There exists correlations between upper truss multi-support excitation effect and structural scale parameters;Differences in structural style along seismic wave direction lead to the result that the seismic wave direction has a great impact on multi-support excitation effect of upper truss;The impact of the apparent wave velocity on multi-support excitation effect is achieved by changing vibration phase difference among supports;The upper truss is influenced in different degree by multi-support excitation action under different seismic waves.Secondly,the suggested seismic action effect adjustment coefficients of primary truss chords and linking truss chords were given in order to consider multi-support excitation effect in the process of designing such truss string structure in Shanghai area.The study shows that seismic action effect adjustment coefficients of primary truss chords lie between 1.3～1.55 according to the structural span.Multi-support excitation affects linking truss chords drammatically,and coefficients of linking truss chords lie between 2.0～7.2 according to their locations in the structure.Thirdly,based on plastic hinge theory,uniform excitation and multi-support excitation time-history analyses under rare earthquakes were performed,and seismic behavior was investigated and weak sections of truss string structure were found.The study shows that truss string structure has good seismic behavior but exists weak sections.The weak sections mainly include lower chords of primary truss connecting to supports,linking truss chords intersecting directly to primary truss,and linking truss chords near the supports.Besides,this paper proposes strengthening plans aiming at weak sections and the numerical simulation results validated the effectiveness of plans.The results can provide references for seismic design of truss string structure.