| Kiewitt-Lamella single layer reticulated shells,which are grid structures composed of inner Kiewitt and outer Lamella grids,solve the deficiencies of the single grid structures effectively and now have become research and application focus in the field of spatial structures.In recent years,due to the frequent occurrence of terrorist attacks,plane crashes and other accidents,the probability of occurrence of impact is increasing,however,the dynamic research of this kind of structures under impact is relatively few at present.Therefore,the dynamic response,failure modes and dynamic stability of Kiewitt-Lamella single layer reticulated shells under impact are investigated in this dissertation.The main contents are as follows:(1)A finite element method for dynamic analysis of reticulated shells under impact based on ANSYS/LS-DYNA is proposed and its applicability is verified theoretically and experimentally,based on which the dynamic analysis models of Kiewitt-Lamella single layer reticulated shells under impact are established.The results show that the errors between the numerical simulation results and the theoretical calculation values as well as the experimental results in the previous literatures are small,indicating that finite element method for dynamic analysis of reticulated shells under impact proposed in this dissertation is reliable.When the structure considering the effect of roof slabs is under impact,calculation accuracy and efficiency should be comprehensively considered and it is suggested that the number of equal segments on each side of the roof slabs should be 4.(2)The dynamic responses of Kiewitt-Lamella single layer reticulated shells with and without roof slabs under impact are compared and the impact response modes of the former are studied emphatically.The collapse coefficient D is put forward as the evaluation index of impact resistance of the structure and the parameter analysis is carried out to summarize the failure law.The researches show that there are 5 impact response modes of the structures considering the effect of roof slabs,which are no failure,local dent,large-scale dent,global collapse and punching failure.The existence of roof slabs increases the stiffness of the structure,changes its impact response mode,and the collapse coefficient D of the structure considering the effect of roof slabs is relatively small.In engineering practice,the role of roof slabs should be considered in the analysis of the impact resistance of this kind of structures.When the apex of the structure is impacted vertically,ring ratio of Kiewitt to Lamella and the change of member section under the premise of approximately constant steel consumption have little influence on the impact resistance of Kiewitt-Lamella single layer reticulated shells considering the effect of roof slabs,and the impact resistance of Kiewitt single layer reticulated shells is better than that of the former.When the structure is under normal impact,the impact resistance of the node in the middle part of the structure is better,and the closer the impact node is to the support,the worse the impact resistance of the structure is.(3)A criterion for determining the dynamic stability of reticulated shells under impact based on the change rate of energy is proposed and its correctness is verified to analyze and determine the impact dynamic stability of Kiewitt-Lamella single layer reticulated shells without considering the effect of roof slabs.The critical impact energy is given as the evaluation index of the impact dynamic stability of the structure and parameter analysis is carried out to summarize the law of impact dynamic stability of structure.The analysis results show that the traditional B-R criterion cannot strictly and effectively distinguish and screen the real dynamic instability of structure.When the apex of the structure is impacted vertically,the larger the rise-span ratio of the structure is,the better performance of the impact dynamic stability of it is.When the rise-span ratio increases from 1/5 to 1/4,the improvement effect of the performance of the impact dynamic stability of the structure is the most significant.In engineering practice,it is suggested that the upper limit of rise-span ratio of this kind of structure should be 1/4.For the Kiewitt-Lamella single layer reticulated shells,changing the ring ratio of Kiewitt to Lamella has little influence on the performance of the impact dynamic stability of the structure,however,the grid form has a great influence on that,and the performance of the impact dynamic stability of the Kiewitt single layer reticulated shells is better than that of the former.The greater the roof load is,the worse the performance of the impact dynamic stability of the structure is.In practical engineering,it is suggested to use light roof to improve the performance of the impact dynamic stability of the structure. |
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