Fire Performance Of Concrete-Filled Steel Tubular(CFST) Members And K-joints Protected With Intumescent Coating

The concrete-filled steel tubular(CFST)structure might be threatened by fire disaster during service.The intumescent fire coating(IFC)for steel structures offers numerous benefits including lightweight,thin thickness,convenient construction,ease of maintenance,efficient thermal insulation,and aesthetic appearance,which has a good application prospect in the fire safety design for CFST structures.However,previous research on the fire performance of IFC protected CFST members is still rare,and there is almost no reported study on the fire performance of the CFST K-joints.Therefore,combined with experimental study and theoretical analysis,fourfold research is carried out in this dissertation as follows:1.A series of temperature field tests are carried out on twenty CFST specimens and four hollow steel tubular specimens under fire.All the specimens are protected with IFC,with a maximum section diameter of 1300 mm.The temperature rise characteristics under fire of the CFST sections and its governing parameters are analysed.The mechanism of combined effects between the expanded coating,steel tube,and core concrete under fire is clarified.Based on the analysis of the measured temperature rise curves of steel tube and the foaming reaction process of expanded coating,a calculation model of the equivalent thermal conductivity of IFC applied to CFST members is established,which effectively improved the finite element analysis of the temperature field for CFST sections protected with IFC.2.A series of fire tests are carried out on nine eccentrically loaded CFST specimens.All the specimens are protected with IFC,with a maximum load ratio of 0.61.The performance of cooperation work between the expanded coating and CFST members under the coupled effects of high temperature and load is analyzed.The applicability of IFC in CFST members required with high fire rating is affirmed.The finite element model is established,and the fire performance of straight CFST members and tapered CFST members is revealed.Based on systematic parametric study,a practical calculation method for the fire safety of CFST members protected with IFC is proposed.3.A series of fire tests are carried out on five CFST K-joints and one hollow steel tubular K-joint.The main parameters in the tests include the load ratio,dry film thickness,whether to employ the coupled conditions of sustained load and chloride corrosion.The bond behavior between the expanded coating and K-joint is analyzed,and the applicability of IFC in CFST K-joints for fire safety design is affirmed.The criteria to determine the fire resistance limit state of K-joint are defined,and the fire rating,failure modes,temperature rise characteristics and development of deformation are obtained.4.Considering the coupled effects of sustained load and chloride corrosion,a finite element model for the fire performance of IFC protected CFST K-joint is established and verified.The fire performance of CFST K-joints is studied,and the mechanism of mixed effects between hollow steel tubular brace and CFST chord under fire is clarified.Based on the statistical analysis of parametric study,a practical calculation method for fire safety design of CFST K-joints under the coupled effects of sustained load and chloride corrosion is proposed,which can provide reference for relevant engineering practice and formulation of technical standards.