Investigation On Fire Behavior Of Steel Cables Based On Large-Space Building Fire Model

The steel cable is one of the core components of the large space building structure.In the fire environment,material degradation,high temperature creep and other factors often lead to the decrease of its mechanical performance.The steel cable is more likely to be damaged than the normal temperature,and may further cause the continuous collapse of the structure.The existing research on the fire resistance of steel cables is mainly based on the ISO834 standard heating conditions,which is not suitable for the large space building application scenarios where the steel cables are located.At present,the research on the fire resistance of large space building structures and their components in China is still in its infancy,and there is a lack of relevant norms and research results to guide the fire safety design in engineering practice.Therefore,it is necessary to analyze the working mechanism of steel cables in large space building fires,study the relevant influencing factors and influencing laws of the fire resistance limit of steel cables,and focus on the protection effect of fire protection measures on steel cables,so as to provide relevant basis for future fire resistance performance evaluation and fire protection design of steel cables.Based on this,this paper uses numerical analysis and theoretical analysis methods to study the fire resistance of steel strands and closed cables commonly used in engineering practice based on large space building fire model.The main research contents and conclusions are as follows :(1)The finite element analysis software Abaqus is used to establish the refined temperature field model and thermal-mechanical coupling model of steel strand cable and closed cable respectively.The thermal and thermal properties of the material are reasonably selected in the modeling process,and the cavity radiation and high temperature creep of the steel cable in the heat transfer process are considered.Based on the comparative analysis of the numerical results and the existing experimental results,the rationality and effectiveness of the finite element numerical model are verified.(2)The thermal-mechanical coupling numerical model of steel strand cable and closed cable under the condition of large space building fire heating is established.The heat transfer mechanism of the steel cable during the heating process is studied,and the similarities and differences between the steel strand cable and the closed cable during the heating process are compared.The results show that the steel strand cable and the closed cable have similar failure development process,similar failure characteristics and internal force redistribution process under the condition of large space building fire heating.In addition,the temperature field of the steel strand is higher than that of the closed cable,and the fire resistance limit of the closed cable is higher than that of the steel strand.(3)The parametric numerical analysis of the factors affecting the fire resistance limit of steel strands is carried out,including the fire heating model of large space buildings,nonuniformity of fire,fire location,load ratio,span and fire protection layer factors.The results show that the influence of fire model parameters on the fire resistance limit of large space buildings is as follows : fire source power,cable position height,large space building area,fire source growth type;the fire location of steel strand will affect the influence of fire nonuniformity and span on the fire resistance limit.The fire protection layer can significantly improve the fire resistance of the steel cable.Compared with the closed cable,the fire protection layer has a more obvious effect on the improvement of the steel strand cable.(4)Based on the theory of heat transfer and considering the radiation effect of the cavity,a simplified model for calculating the temperature field of the closed cable under four-sided fire conditions is proposed.The finite difference method is used to derive the boundary node of the closed cable.The explicit discrete calculation formula of the temperature field of the internal node and the mixed boundary point is derived,and the calculation results of the theoretical derivation formula are compared with the experimental results and the finite element calculation results.The results show that the theoretical calculation formula can better fit the test results and the finite element calculation results,and can effectively calculate the heating history of each element node in the steel cable section.