Analysis Of Elasto-plastic Seismic Responses And Failure Modes Of Three-centered Cylindrical Reticulated Shells

Three-centered cylindrical reticulated shell is commonly used as a kind of large span structures. Analysis on dynamic behaviors is the main basis of reticulated shells’ performance-based aseismic measures and design methods under fortification intensity and rear earthquake. But the related research is relatively weark. Systematic analysis and research about reticulated shells’ elasto-plastic dynamic response characterstics under fortification intensitiy earthquake and rear earthquake is made, by taking15three-centered cylindrical reticulated shells with different span, different length, different supports and different thickness as the investigation objects. Meanwhile, the failure mode and its influential factors are studied.The main study contents and conclusions are as follows:(1) Not only the geometrical and material nonlinearity of the steel bars, but also the stiffness degradation of whole structure caused by bar buckling should be taken into consideration during the process of elasto-plastic time-history analysis of lattice structure. The effect of bar buckling is considered by non-proportional subdividing the beam elements and introducing1/450initial imperfection in bars; and the results compared to the codes shows that the proposed method is efficient.(2) The cross-section size of bars in the15shell models is determined by the full stress design under non-seismic load cases. The load transfer path, self-vibration characteristics and dynamic responses under frequent-occurred earthquake of reticulated shells are checked. Research shows that, the sections of models which are designed under non-seismic conditions rarely need adjustment because of frequently occurred earthquake checking.(3) The elasto-plastic dynamic behaviors of reticulated shells subjected to7and8degree fortification intensity earthquake and rare earthquake are analyzed by considering material and geometrical nonlinearities as well as member buckling. The distribution of plastic bars and magnitude of plastic strain are counted after analyzing. The result indicates that the change of length, span and thickness of structure will sharply influence the dynamic performance of structure. Under fortification intensity earthquake and rare earthquake, failures may happen to a cylindrical reticulated shells only checked by frequent-occurred earthquake. The weak region mainly locates in the area about1/4span away from support lines. The time interval from the first appearance of plastic strain appear in weak region to the failure of structure is very short.(4) The dynamic stability of cylindrical reticulated shell is studied by adopting the B-R criterion. In addition, the ultimate bearing capacity and failure mode of reticulated shell are investigated by using three earthquake waves and harmonic actions with different frequencies. The result reveal that, the failure mode of three-centered cylindrical reticulated shell is typical dynamic instability. The amplitude of critical failure load is associated with the frequency of the load. If the frequency of harmonic action is in the structure’s resonance region, the ultimate bearing capacity is low. Otherwise, the capacity is large. The buckling of the bars which located in the weak region have a significant impact on the ultimate bearing capacity of three-centered cylindrical reticulated shell subjected to dynamic actions. The bearing capacity of the structure will be overestimated when only taking into acount of the bar-elements’ idealized elasto-plastic model which has unfavorable impacts on the engineering.