Theoretical Research On High Falsework System To Resist Progressive Collapse

ABSTRACT:Recently the accidents of high falsework system occur frequently. Investigations of the accidents indicate that the failures of falsework are caused by overall collapse. There is no place for builders to escape after the collapse, which causes serious personnel dead and injured. And it’s hard to set up rescue channel to rescue the wounded personnel under the collapsed parts. To improve reliability and safety, a new way to build the high falsework system is urgently needed. Patent (ZL 201410324086.3,2014) puts forward a new kind of high falsework system to resist progressive collapse. It’s composed of single-function structure system and dual-function structure system. The whole system will work together on normal conditions (first stage, for short). While the single-function structure system fails on abnormal conditions, the dual-function structure system will work alone(second stage, for short) to resist progressive collapse of the whole system. By research on the above-mentioned high falsework system through theoretical analyses, the main research contents of this paper are as follows:(1) Considering the differences of the "two stages" in structure, loads and function, the target reliability indexes of the "two stages" are discussed and determined in the paper.(2) Combine with the target reliability indexes of "two stages" and finite element analysis, both the ultimate capacity and the steel quantity are considered in the research on appropriate constructional measures and tubes of the above-mentioned high falsework system.The conclusions are as follows:(1) For the first stage, the failure model is considered as brittle failure on Safety Level Ⅲ and the target reliability index is determined as 3.2 which is the same as the existing standards. For the second stage, according to the reliability index obtained by load code of China and the United States, the target reliability index is determined as 1.65 which is from appropriate adjustments of the safety level of falsework system.(2) Finite element analysis indicates that the most appropriate constructional measure include both vertical braces and horizontal restraints. This conclusion provides the theoretical basis for the above-mentioned patent.(3) It’s recommended that the tubes use 048.3×3.6 in the single-function structure symtem and vertical tubes use Φ76.1×3.6 while the others use Φ48.3×3.6 in the dual-function structure system. Both the ultimate capacity and the steel quantity have certain superiority with this constructional measure. And the single-function structure system will fail first when the falsework reaches the ultimate capacity in the first stage while the dual-function structure system can work alone to resist progressive collapse of the whole system in the second stage with the structural measures.