Finite Element Analysis On Post-fire Seismic Performance Of SRC Column-RC Beam Joints

With the development of building technology,structure tends to be getting higher and increasingly complicated,the traditional reinforced concrete structure can not meet the actual needs anymore.Because of the characteristics,such as high bearing capacity,high rigidity,good seismic performance and small component cross section,steel reinforced concrete structures(SRC)can be widely used in high-rise buildings.Otherwise,there are intensive staffs and a lot of fire hazards in high-rise building result in frequent fire safety problems,the fire resistance of structure and mechanical properties after the fire is particularly important to ensure the safety of personnel and to avoid the loss of property.At present,the evaluation,strengthening and reinforcement of the structure after fire lack of sufficient theoretical basis because of short of the research on the seismic performance of the steel reinforced concrete composite structure after fire.In this paper,the hysteretic behavior and its influencing factors of SRC column-RC beam joints after fire are analyzed by finite element method.The research results can provide theoretical support for the evaluation and reinforcement work of post-fire structure.The hysteretic behavior of SRC column-RC beam joints after fire is analyzed by using the large-scale general finite element analysis software ABAQUS in this paper.In order to verify the accuracy of finite element model,test specimens were simulated firstly.The results of numerical calculation which are temperature field and hysteretic performance were compared with that of experiment,and they are basically consistent.Based on the validity of the numerical model,the parameters that affect the hysteresis performance of the joints after fire were analyzed,which were heating time,axial compression ratio of column,concrete strength and steel ratio of column section.The results show that:(1)As the concrete has a hot inertness,there is a hysteresis of the changes of internal temperature in the component,which result in the slower heating rate and the lower peak temperature while the distance from the fire surface is farther;(2)The heating time is one of the main factors that affect the hysteretic behavior of SRC column-RC beam joints after fire.With the prolonging of heating time,the bearing capacity,stiffness,energy dissipation capacity,ductility and other performance indexes of the nodes are decreased seriously.When the heating time reaches 120 min,the decrease of the performance parameters of the joints is obviously increased.Relative to the non-fire node,the bearing capacity decreased by 46.8% and stiffness decreased by 25.9%;(3)The axial compression ratio of the column has little effect on the hysteretic behavior of SRC column-RC beam joints after fire under the failure pattern of concrete crashing at theend of beam;(4)The concrete strength grade has a great influence on the hysteretic performance of the joints after fire.With the concrete strength grade increases,the bearing capacity of nodes increases obviously,and the increase of stiffness is smaller than that of bearing capacity.And the ductility and energy dissipation capacity of joints decrease;(5)The bearing capacity,stiffness and energy dissipation capacity of the post-fire SRC column-RC beam joints are increased in different degrees with the increasing of the steel ratio of column,but the ductility coefficient of the joints decreases.According to the results of numerical analysis of hysteretic behavior of SRC column-RC beam joints after fire,the post-fire bearing capacity formula of joints under the failure mode of concrete crashing at the end of beam is put forward.The calculated results are in good agreement with the results of finite element analysis.The results of this study can provide the basis for the evaluation,strengthening and reinforcement work of post-fire SRC column-RC beam joints.At the same time,it can offer reference for later research.