The Mechanical Analysis For World Trade Center's Collapse In 9.11

The world trade center's collapse in 9.11 has received the attention of researchers at home and abroad because of its important engineering background.There were many analysis about it ,but most of them researched it on the view of exploding or combusting, and there were few research in China.This article demonstrates the reason from the view of limit analysis firstly. We suppose there will be three plastic hinges in the structure during the building's breaking down, and apply the method of statics to calculate the limit static load of the building's collapse, then we make it contact with the impact impulse between the upper-floor and the lower-floor, and conclude the dependence relation between the possibility of the building's collapse and the rigid impact time.At the same time ,we used The Lagrange Dynamic Equation to figure out the structure's locomotive state after the upper-floor's colliding, and gave the minimum impacting momentum for WTC's collapse.At last ,we introduced the Exploding equivalent weight > the Dead radius^ the Wealth damnify radius and so on, and forecasted the future for tall buildings to design against disaster.