Force Characteristic Analysis And Criteria Of The Key Components Of Steel Frame Under High Temperature(Fire)

Steel structure has been widely used in construction of various kinds of infrastructure due to its merits of light weight, high strength and good flexibility, etc. However, the fire resistance of steel structure is relatively poor with respect to the reinforced concrete structure and masonry structure. In particular, the elastic modulus decrease significantly as the temperature increases. The poor fire resistance of steel structure will lead to failure under fire conditions. A simple method, based on the stress analysis of the key steel frame components under high temperature, is put forward to assess the key components.The main work of this paper can be categorized into three aspects. First, we summarize the representative works on this topic and analyze the steel structure’s performance under high temperature, figuring out how to choose proper parameters for analysis. Second, by static analysis of vital components at room temperature, we derive the average stress of beams; through quantitative comparison, we find the maximum of column members’ average stress appears at the bottom of column, while for beam members, the maximum appears at the bottom edge of beam. As such, we determine the bottom of column and bottom edge of beam as the key component, which could generate significantly insecure impacts to the remaining structure. We then use the finite element analysis software ANSYS to model the process and perform thermal coupling analysis on the temperature field, further determining the key component. Third, we systemically study the stress of the key components under high temperature by adopting material nonlinearity, geometric nonlinearity and ANSYS. By tracking the temperature change(using the ISO834 temperature-time curve) in simulated fire environments, we utilize the three-dimensional thermal coupling unit of ANSYS to calculate the temperature stress and analyze the mechanical properties.By the above analysis, we summarize our key findings as follows. First, the vital component of steel frame structure lies in its bottom of the column, undertaking the major stress; it will produce the greatest impact to surrounding components if damaged. Second, we suggest paying special attention to fire protection of the vital component, using refractory structures like reinforced concrete and steel concrete column. Last, steel beam only has slight influence on the performance of fire resistance, thus can be cared less in fire protection.Conclusions are achieved through stress analysis of vital components of steel frame. These conclusions can be used for further fire resistance research of steel structure.