Numerical Analysis For Behavior Of Composite Portal Frames With Steel Box-columns In Fire

The steel structure is increasingly widely used in architecture engineering for its character of plasticity and toughness, high strength-to-weight ratio, short period of construction and recycling convenience,however,its disability of fire-endurance is becoming outstanding. Presently, in domestic and foreign the steel structure research of fire-resistance performance based on members is gradually transformed on structures in order to consider the complex influence of entirety of structure. Frame columns is restricted to uniformly in fire and the others,unevenly in fire,are researched on the basis of members so that its failure pattern is flexural-torsional buckling. The circumstance of frame columns,constructed close to wall(or fire-protection wall),with three faces exposed in fire is common. Full-scale test of frames in fire is restricted for its high price,complicated work and inconvenience of fire distribution.Based on the problems of fire-resistance study shown above, the analysis model of composite portal frame with steel-box columns three faced in fire was established by means of ANSYS12.0 FEM. Firstly,on the basis of the thermal-transfer principle,it simulated the ISO fire and then the thermal-structure coupled analysis was carried out.It demonstrated that the frame failed in the typical mode of symmetrical in-plane buckling with plastic hinges located in the steel columns, simultaneouly, the influence on failure pattern and fire endurance of frames,caused by the initial slope of columns,its cross section types and fire conditions in joints, was discussed. Otherwise,parametric analyses of fire endurance of frames,such as load ratio, span of beam and slenderness ratio of columns, were conducted so as to provide references for the design offire-resistance of frames.