Fire Performance Of The Special-Shaped CFST Column And Frame Structures

Combining the advantages of special-shaped columns and steel-concrete composite structures,the special-shaped concrete-filled steel tubular(CFST)columns demonstrate excellent performance in loading carrying capacity,seismic capacity,and production convenience.In addition,the application of the special-shaped CFST columns can avoiding the exposure of the indoor column corner and improve the interior space utilization.In the past few years,great efforts have been devoted to investigating the mechanical behavior of the special-shaped CFST columns at ambient temperature.However,the special-shaped CFST columns are commonly applied to residential and office buildings,in which the occurrence frequency of fire is higher.There have been few studies concerning the special-shaped CFST columns’ fire behaviors.Therefore,it’s necessary to explore their fire performance.Based on the fire tests and numerical simulation,the fire performance of the special-shaped CFST columns and the frame structure was investigated.The study conducted is as follows:(1)Twelve equal-limb special-shaped CFST columns were designed and tested under the eccentric compression and the ISO-834 standard fire.The temperature distribution and axial displacement of specimens were measured,and the failure mode and fire resistance of specimens were obtained.The effects of the cross section shape,stiffener type,load eccentricity,and load angle on the fire resistance of the special-shaped CFST columns were discussed.(2)The thermo-mechanical coupling models were established using the software ABAQUS and the finite element(FE)models were verified by the test results.The Python programming language was applied to develop a modeling of batch process system to improve the computational efficiency of the parametric analysis,in which4016 FE runs were developed.The considered parameters contain load ratio,slenderness ratio,column limb width,column limb depth-to-width ratio,load eccentricity ratio,steel ratio,material strength,and load angle.Based on the parametric analysis,the simplified calculation approach for the fire resistance of special-shaped CFST columns is designed.(3)Four equal-limb special-shaped CFST columns with fire protection layer were designed and tested under the eccentric compression and the ISO-834 standard fire.The effects of the cross section shape and the thickness of fireproof coating on the fire resistance of the special-shaped columns were investigated.Based on the test results,the FE model was developed and the parametric study was conducted on the fire performance of special-shaped CFST columns with different thickness fireproof coating.Then,the design method for predicting the thickness of the fire protection layer was proposed.(4)The FE model of the special-shaped CFST column to U-shaped steel-concrete beam frame whose joint is connected by the vertical stiffener was developed.The work mechanism of the frame structure in a fire were studied.Then,the parametric analysis was carried out to investigate the influences of different design parameters on the fire resistance of the frame.The fire design method of the frame column was proposed by comparing the fire resistance of the frame columns and pin-ended columns.