Study On Impact Comparability Rule And Impact Resistance Of Kiewitt-lamella Single Layer Reticulated Shells

Reticulated shells are wildly applied for large landmark buildings, their researches under earthquakes and wind loads have been relatively mature. However, such structures suffer not only conventional loads, but also short-term powerful loads such as explosion, impact and etc. After 9/11, to prevent terrorist attacks, researches of dynamic response for various structures have been carried out, most of the researches are focus on frame structures, only few about reticulated shells. In this paper, Kiewitt-Lamella single-layer Reticulated Shell, which is applied wildly in recent years, is selected as research object. By using theoretical analysis and numerical simulation, a systematic study about its comparability rule under impact is carried out. Failure law and failure mechanism are obtained by large number analysis of examples. Finally, defence suggestion which has engineering application values is given. The main contents are shown as follows.(1) On the basis of LS-DYNA, finite element models are established to compare with theoretical solutions and two cases of the test results. It is showed that numerical solutions are in good agreement with the theoretical and experimental one, indicating that the finite element analysis method is reliable.(2) Based on the dimensional analysis, the comparability rule for reticulated shells subjected to vertex impact was derived. The scaling requirement of velocity was corrected to consider the effect of strain rate. By using numerical examples, the accuracy of the corrected model is verified. On this basis, the effects of geometric deviation and gravity are taken into account respectively. For geometric deviation, impact velocity is corrected further by adding one variable of geometric deviation; for gravity, two methods are introduced to satisfy the comparability rule: prepare material specially or add extra mass. Results show that the corrected models can accurately predict the dynamic responses of prototype under different velocities, prediction error of non-corrected models is large, and with the geometric scale smaller, the higher strain rate, the greater prediction error, so the non-corrected models cannot be used for engineering practice.(3) Summary four response modes of Kiewitt-Lamella single-layer reticulated shell under impact loads, analyze the failure mechanism for each mode, study their failure law through a mass of case analysis. The criticality of reticulated shell and minimum impact kinetic energy are defined to compare impact resistance of different reticulated shells. Compare dynamic responses of different kind of impact conditionsand different parameters of reticulated shell, so the parameters that have better impact resistance are obtained. It is showed that impactor with high-speed and small mass is more dangerous for structure when the kinetic energy remains unchanged; the most dangerous situation is impacting the middle nodes of reticulated shell from outside to inside; the impact resistance is better when combinations of grids is inner Kiewitt type and outer Lamella type; improving the yield strength of steel and increasing cross section areas of bars are benefit to enhance the impact resistance performance of structures.(4) On the basis of the above parameters analysis, several defence suggestions are proposed aiming at resisting criticality of structure. In the stage of design, using light roofing materials and increasing dividing frequency appropriately can enhance the impact resistance of structures. In the stage of strengthening, partly increasing bar sections and entirely improving the steel yield stress if cost allowed, can achieve a better protection. The proposed methods in this paper have high reference value for practical engineering.