Research On The Collapse Process Of Steel Structure In Different Fire Scenes

The steel structures are widely used in modem building structures due to the impetus of our country to develop steel structure buildings. However, the progressive collapse of high-rise steel structures have attracted more and more attention by researchers from all over the world since this phenomenon is more and more frequent under the accident(such as fire, explosion, etc.). Steel structure has many advantage properties such as good ductility, strong plastic deformation capacity and so on. However, the poor fire-resistance ability is the most significant weakness of the steel structures. The progressive collapse will occur in a very short time and severe damage will happen due to its mechanical property such as strength and elastic modulus decrease severely in high temperature.This paper first describes the research results and the design method of progressive collapse of steel structure under fire at home and abroad and analyses the fire development process and mechanical properties and physical properties of steel structure under fire condition. And then simulates the whole process of the structure in the standard temperature curve from the beginning of fire to the entire collapse using the finite element analysis method and considering the effect of geometric nonlinearity, material nonlinearity, status-changing nonlinearity to the model. The main contents of this paper can be summarized as follows:(1) This paper uses the whole process analysis method of progressive collapse of steel structure under fire and simulates the temperature field of high-rise steel structure in fire room within 0.5 hours through establishing relative numerical model and studies on failure mechanism of progressive collapse of steel structure by imitating the failure process of component under this temperature field.(2) Under the different fire room location circumstances this paper compares the bearing performance and deformation performance of every fire room under progressive collapse. Then finds which are the key areas and protect them.(3) Some measures of high-rise steel structures to resist progressive collapse and the advantages and disadvantages of these measures are proposed to be improved in the practical engineering.The main conclusions are as follows:1) It is concluded that the temperature distribution, change and destruction of steel structure in fire scenes, and the temperature rises rapidly in the early period in fire through the whole process stimulation method. It is also analyzed that after the first ten minutes, the process of temperature rising slows down. However, because of rapid temperature rising in the first ten minutes, there are continuous collapses caused by damaged components.2) Through the comparative analysis of destruction in fire of bottom, middle and top-floor in a building, it is concluded that the destruction in bottom-floor has the most influential impact on the whole construction. At the same time, the middle-floor needs enough protective measures because it tends to be destructed at first once catches fire.3) Through the analysis of engineering projects and rooms in different floors in fire, it is concluded that corner posts tend to be destructed before other posts. Therefore, there should be reinforced measures in the fireproof design of corner posts to make them work well.4) If the middle-floor catches fire, girder will be destructed at first because it can’t stand the deformation in fire. After destruction of girder, post will be destructed in higher temperature.5) When several rooms in the same floor catch fire, fire pillars will lose efficiency at first due to too many components in fire. Several rooms in fire at the same time will be easier to collapse than a single room.6) If rooms in different floors catch fire at the same time, fire pillars in the same position but different floors will influence each other and lead to severe deformation. In this situation, the components will be easier to collapse than a single room.The conclusions of this context are important to prevent steel construction from collapsing.