Instability And Bending Behavior Analysis Of Circular Arch Under High Temperature Of Fire

The arch structure is a thrust structure with an arc axis.Under the vertical load,the bearing generates horizontal thrust,and the curved arch axis converts bending moment generated by external load is transformed into axial pressure,which has high bearing efficiency.It has been widely used in engineering practice.Steel structures are widely used due to their high material strength and good ductility and the stability of arch structure is a classical mechanical problem,including in-plane stability with sufficient out-of-place support and out-of-plane stability with no out-of-plane support or insufficient support.For arch structures,the ultimate bearing capacity involves both strength and stability.The failure mode should be determined and its criterion should be given in the analysis of arch instability and bending behavior.The ultimate bearing capacity of steel arche is significantly reduced under high temperature of fire.Once the arch structure is damaged in high-rise and long-span buildings,the safety of people's life and property will be seriously threatened.Therefore,it is of great economic and social significance to study the instability and bending behavior of arch under high temperature.In this paper,the problems of in-plane deformation and strength of the arch,the out-of-plane bending and torsion instability of arch and the jumping instability of the shallow arch under fire and high temperature are analyzed.The main research contents are as follows:Firstly,through the finite element convergence test,the appropriate unit type and unit quantity are determined,and a reasonable finite element calculation model is established.Secondly,the feasibility of the rese arch method and the correctness of the finite element calculation model are verified by comparing with the existing arch tests.Finally,the plasticity and thermal expansion effects of materials under fire and high temperature are analyzed todetermine the failure mode of arch under the situation,and a large number of parameters are analyzed according to the factors that affect the failure mode and critical temperature of arch.The results show that:(1)For the in-plane deformation behavior of arch,the bending failure of arch is dominant under the combined action of static load and fire.With the increase of load ratio,the final temperature of the structure gradually decreases.Under different end constraints,the fire resistance of fixed arch is the strongest while the fire resistance of hinged arch is the weakest.When the span ratio is small,the limit temperature of the arch increases with the increase of the span ratio.(2)Under the combined action of static load and fire,the buckling behavior of arch out-of-plane is dominated by flexural-torsional buckling.With the increase of load,the critical temperature of the arch structure decreases gradually.When the load ratio is small,with the rise-span ratio increasing,the critical failure temperature of arch increases first and then decreases.Under different constraints,the fire resistance of fixed arch is the weakest,and that of hinged arch is the strongest.(3)Under the combined action of static load and fire,shallow circular arch has two failure modes,namely bending failure and jumping instability.When the load ratio increases gradually in the range of 0.1-0.9,the critical temperature of the structure gradually decreases and decreases basically linearly.When the load ratio approaches to 1,the slight load increases and the critical temperature changes sharply.Under different end constraints,the fire resistance of fixed arch is the strongest while the fire resistance of hinged arch is the weakest.The critical temperature varies monotonically with the geometric parameters of the structure.