Analysis Of Bend-torsion Buckling Of Steel Beam And Free Vbration Frequencies Of Cracked Beam Under High Temperatures

The material properties of the steel degenerate with temperature increased. Internal forceredistribution and obvious deformation will be appeared in the steel structure. The integralload capacity weakens sharply. Even totally collapse or damage will be happened due to a fire.So it is important to build a reasonable fire resisting method. It is meaningful to analysis theinternal force variation against temperature, especially through theoretical analysis.The flexural torsional buckling of steel beams in high temperature is discussed in thispaper. The aspects that were studied in this research are as follows:1. The elastic flexural torsional buckling of steel beams are analysised in hightemperature ranging from20℃to300℃considering the influence of high temperature onmaterial properties. The critical buckling moment equations of simply supported, fixed endedand cantilever beams considering the deformation before buckling are also provided.2. The buckling critical moment and the corresponding coefficient equations of beamswith constant and varying cross-sections under transverse uniform or concentrated loads aredriven in high temperature ranging from20℃to300℃.3. The critical buckling moments of steel beams against temperature are analysisedthrough an example. It is can be known from the example that influence of the section formand load point on elastic buckling critical moment in high temperature are observably. Thedowntrend and magnitude of the critical buckling moment against temperature of the twoinfluencing factors are analogously.4. The flexural torsional and critical buckling moments of simplely supported steelbeams against temperature are analysised based on elastic-plastic theory. The elastic-plasticcritical buckling moment equations are provided. The elastic-plastic critical bucklingmoments of steel beams against temperature are analysised through an example. The verticaldeformations of steel beam at different fire burning moments are simulated by ANSYS.5. The vibration frequencies of simply supported beam with cracks is analysisedconsidering the influence of temperature on material properties. The free vibration frequencyequation of simply supported beam with cracks in high temperature is provided. The vibration frequency variations of a simply supported steel beam and a aluminum alloy beam withcracks against temperature are obtained through numerical simulation. A series of conclusioncan be obtained. Material Young’s modulus decrease with temperature increased, the decreaseof material elasticity modulus will result in the decrease of natural frequency. Deeper crackbring more significant drop of natural frequency against temperature, the influence of crackon natural frequency is small when the crack is near the support. The relational expression ofnatural frequency and Young’s modulus of the simply supported beam is also obtained.