Analysis On Dynamic Effect Of Progressive Collapse Of Grid Structure

The progressive collapse refers to the phenomenon in which an initial local damage of structure elements caused by abnormal loads leads to a disproportional collapse of the structure. In terms of long-span structures such as grid structure, the progressive collapse would bring serious social influence and economic losses. In this thesis, this article will analysis the dynamic effect of two grid structures with different supporting forms which were damaged,mainly from following aspects:SECTION I:Using the method of transiently unloads the equivalent load to simulate the instantaneous dynamic effect of damaged members. Obtaining the failure time and loading time and condition analysis. The results show that the loading time can be taken for 50 times the natural vibration period, the failure can be taken for 0.01 seconds and the analysis is suggested to take for the actual working condition.SECTION II: For the different supporting forms of grid structure, analysing the dynamic magnification factor of damaged chord member and web member,which has the biggest stress, including its value and distribution. The results show that the dynamic magnification factor is associated with the plastic development degree of the structure. dynamic magnification factor of members in plastic period is bigger when the plastic development degree is higher; When the structure doesn’t reach the plastic or its’ plastic development degree is lower, the dynamic magnification factor is associated with its internal force undertaking in the remainder structure, and its damping. the fixed end also effects the distribution of it.SECTION III:From the analysis, get the progressive collapse performance and characteristic of grid structure in different supporting forms with damaged member. Then putting forward some suggestions based on the analysis to prevent the occurrence of progressive collapse of structure.