NUMERICAL INVESTIGATION ON STRUCTURAL BEHAVIOR OF SQUARE STEEL TUBE CONFINED REINFORCED CONCRETE COLUMNS UNDER FIRE LOADING

Abstract

Occurrence of fire inside the building is an unexpected phenomenon which can cause damage to the property and loss of human life. The response of the structural members under fire should be properly studied to minimize the damage caused by fire. Steel tube confined (STC) reinforced concrete column is a type of special composite member which resembles CFST column but with discontinuous outer steel tube. This thesis aims to investigate the structural behavior of SSTC reinforced concrete columns exposed to fire from one, two, three and four sides respectively using non-linear finite element software (ANSYS 19.2) considering cross section size and load ratio as main parameters. In this thesis 30 models of which 1 CSTC reinforced concrete column for calibration, 28 SSTC reinforced concrete columns and 1 CFST column for comparison were modeled and analyzed. The result of the axial displacement-time curve, temperature distribution and failure mode of the CSTC reinforced concrete column model were verified against experimental results and further parametric studies were done to investigate the effect of parameters on axial displacement- time curves, lateral deformations and temperature distributions through cross sections. From this investigation, it was found that both cross-section size and load ratio have significant effect on the axial displacement curve and lateral deformation in all scenarios. For instance, the axial displacement rates were increased by 38.4%, 50.023%, 65.297% and 74.829% when the cross-section size was decreased from 400mmx400mm to 300mmx300mm for SSTC reinforced concrete columns when exposed to fire from one, two, three and all sides. In all the cases higher cross section has higher fire resistance and minimum axial deformation. Additionally, SSTC reinforced concrete columns with only one side exposed to fire had higher fire resistance compared to the SSTC reinforced concrete columns with two, three and all sides were exposed to fire. The effect of load ratio on the axial displacement was very significant when the columns were exposed to fire on all sides and for higher load ratios (>0.4). Therefore the rate of axial displacement and fire resistance of the SSTC reinforced concrete columns were much diminished at higher load ratios. The temperature of the cross section decreases as we go from the face (steel tube) to internal section. The SSTC reinforced concrete columns have much higher fire resistance relative to CFST column due to the contribution of the embedded reinforcing bars. For the same load ratio and cross section the axial displacement of CFST column was increased by 63.56%.