Analysis On Dynamic Behaviors Of Double-layer Spherical Reticulated Shells Under Fortification Intensity Earthquake

Analysis on dynamic behaviors is the main basis of reticulated shell’s seismic design and performance-based aseismic measures in fortification intensity earthquake. But the related research is still in the blank stage. Systematic analysis and research about double-layer reticulated spherical shell’s elasto-plastic dynamic response characteristics and influence factors under fortification intensity earthquake is made. And a performance-based design procedure under moderate earthquake is applied to large-span structures by increasing structural steel consumptions to avoid complicated repairing. The main improvement on existing research: the collaborative work of the lattice shell and substructure is considered; The constitution of the lattice shell takes into account the influence of geometric nonlinearity and material nonlinearity. A three-direction artificial earthquake wave generated according to the code response spectrum is adopted.The main study contents and conclusions are as follows:(1) The seismic responses characteristics under frequently occurred earthquake of double-layer reticulated spherical shells with full-stress design are investigated. Research shows that, the sections of25models which are designed under non-seismic load cases rarely need adjustment because of frequently occurred earthquake checking.(2) The elasto-plastic response characteristics of double-layer reticulated spherical shells under fortification intensity earthquake and influence of the main structural factors is analyzed. The small-(36m) and medium-(60m) span shells can easily meet the seismic design demand that structures are not allowed to damage during frequently occurred earthquake. And amount of plastic members occur in large-span(90m、120m) double-layer spherical reticulated shells under7and8degree fortification intensity earthquake. When the stiffness of substructure is weak, plastic members occur in the inner annular region near the center of shell which is dominated and the region near the abutment. When the stiffness of substructure is strong, plastic members only occur in the inner annular region near the center of shell.(3) The cross sections of shell’s members are designated to be satisfied with the check for the fortification intensity earthquake. The results reveal that the structural steel consumption increases very limitedly even though the member cross sections of shell models are checked according to the performance level of "elastic design under fortification intensity earthquakes". Meanwhile, the fortification requirements of "repairable under moderate earthquake is also satisfied. (4) For those models satisfied with the check for fortification intensity earthquake, their elasto-plastic dynamic responses under seldom occurred earthquake are also calculated based on time-history analysis. Research shows that obviously plastic members only occur in large-span shells under8degree seldom-occurred earthquake, and "no collapsing under seldom occurred earthquake" are also satisfied. Span、 intensity and symmetry of substructure are three major factors influencing the elasto-plastic dynamic behaviors of the reticulated shells. The negative influence of asymmetry of substructure is dominated under high intensity earthquake.(5) For the small-and medium-span shell models, the difference between two design methods of substructure considered and non-substructure considered only cause imperceptible changes of structural steel consumption, but the difference of dynamic responses under seldom occurred earthquake is rarely, and the shells with two design methods can satisfy the fortification requirement of "no collapsing under seldom occurred earthquake".