Dynamic Failure Analysis And Experimental Study On The Reticulated Shell Under Strong Earthquake And Impact

In recent years, because of the influence of various human factors or geological disasters, the accidents of buildings with serious damage occur frequently. If important large-span reticulated shells such as regional landmark buildings are damaged by some unintentional injuries such as great earthquakes and collision, it will not only cause great losses of life and property, but also have profound political influence. The fundamental task of structural design is to ensure the safety of structures, and preventing structural collapse is the baseline of ensuring structural safety. Making a collapse analysis and taking some measures to prevent dynamic collapse for long-span reticulated shells gathering large crowds will gradually become an important content of structure design.The accidents causing the damage of building are either the earthquakes in nature or emergency collisions. Taking the spherical reticulated shells, including two forms of single-layer and double-layer reticulated shells, as the objects, this paper makes an analysis of dynamic response and the failure mode under the great earthquake and impact load, simulates the process of dynamic collapse and reveals the collapse mechanism with the method of combining numerical modeling and experimental research. Major contents are as follows:(1) Based on the numerical modeling of structural collapse, nonlinear explicit dynamic program LS-DYNA is applied for the platform of numerical modeling. The related technologies and its difficulties of numerical modeling are analyzed and the elastoplastic damage constitutive model of steel was used by handling subroutine before self-documenting. The calculation process of dynamic collapse of spherical reticulated shells on the basis of IDA method is established and the judgment criteria of collapse based on the energy conservation have been proposed.(2) Based on the dynamic analysis of single-layer spherical reticulated shell, failure modes of reticulated shell under strong earthquake are defined. The paper studies the dynamic response and failure characteristics of single-layer reticulated shell under earthquake, mainly simulates the whole process of structural collapse and reveals the collapse mechanism from the perspective of production and extension of dent. In addition, the paper also analyzes the factors affecting the ultimate bearing capacity of reticulated shell such as rise-span ratio, roof load and supporting structure, makes a dynamic collapse analysis under unsymmetrical load distribution and makes an analysis of dynamic process of vierendeel double-layer reticulated shell.(3) The paper puts forward that adding perforating double-steel tube Buckling-Restrained Braces(BRBs) in the reticulated shell is an energy damping device and analyzes the energy dissipation. In addition, the paper puts forward the arrangement way of BRB on the single-layer and double-layer reticulated shell, analyzes the damping effects and makes a comparative analysis of the ultimate bearing capacity of reticulated shell with and without BRBs. The results show that the shell with BRBs has a good damping effect, and can improve the ultimate bearing capacity of the reticulated shell.(4) The paper verifies the failure mode of single-layer reticulated shell under unsymmetrical load distribution by scale model shaking table test. The results show that the unsymmetrical load distribution will reduce the ultimate bearing capacity of the reticulated shell. In the design process, we should fully consider unsymmetrical load impact on dynamic stability of the reticulated shell.(5) The paper studies the impact load with bigger quality and slower speed such as rockfall, analyzes the impact load, establishes the numerical model of reticulated shell under impact, defines the failure modes of reticulated Shell under impact, analyzes the dynamic response characteristics of every failure model and researches the failure mechanism. And the paper also analyzes the dynamic response when the reticulated shell is impacted by two nodes or three nodes and researches the dynamic collapsed mechanism of the reticulated shell under the impact of three nodes. The results show that as for the single node’s impact, the failure mode is slightly damaged, local dent and local punching failure. When both of the quality and speed is small, the impact energy is small and the bar has a slight damage; only when the speed is bigger can local punching failure occur and only when the quality is bigger and the speed is moderate can local dent occur. The dynamic failure mechanism of shell under the impact of two nodes or three nodes is that the formation, extension and linking together of local dent finally lead to dynamic collapse.(6) The paper carries out the impact tests on the reticulated shell of scaled model, tests on different nodes of reticulated shell by the impacted body with different qualities, analyzes the dynamic stress, dynamic displacement and acceleration supporting, makes a comparative analysis on the FEM results, researches the dynamic response characteristics of reticulated shell and verifies the failure model of local dent of reticulated shell under the low-velocity impact. The results show that the response of impact area is significantly greater than other area and the response of main ribs node is greater than the other response, which proves that the stress wave produced by the impact spread along the direction of impact and the energy attenuation is faster when spreading along the circular. The response impact by different points is different, the vertex and middle ribs node is the most adverse impact point.