Research On Mechanical Behaviors Of The Dog Bone-cellular Frame Composite Slim Beam And The Joint

Composite slim beam with deep deck is a new type of composite members by encasing I-steel beam in profiled sheet-concrete slab.Compared with T-composite beam,it has the advantages of light weight,good fire resistance and lower floor eight.However,the existing research mainly focus on the simple or continuous composite slim beam embedded with solid I-steel beam,which is not consistent with the actual situation of composite slim beam bearing the loads of structure as frame beam.Besides,it brings difficulties to the laying of pipelines in buildings.Therefore,a new type of dog bone-cellular composite slim beam is proposed in this paper,and the mechanical performances of its frame beam and joint are studied.The main research contents and conclusions are as follows:(1)Models of frame composite slim beam with deep deck and joint of concrete filled square steel tube-composite slim beam are established using the finite element software ABAQUS.Their mechanical performances under static and cyclic loading are simulated and compared with the experimental results in order to verify the accuracy of finite element modeling method and analysis results.(2)The bending performances of dog bone-cellular frame composite slim beam are analyzed under one-way static loading.The results show that dog bone-cellular frame composite slim beam has an about 5.6% reduction in the ultimate bearing capacity compared with solid frame composite slim beam but shows better deformation ability.In addition,the depth of the weakened zone have great influences on the bearing capacity of the frame composite slim beam and it is advised to be controlled below 26% of the flange width.The perforating ratio of web plate and the length of the weakened zone have influences on the bearing capacity in some degree.The former is suggested to be controlled between 35% and 50%,and the latter is within 75% of the steel beam height.The concrete in the ribbed slab and the starting position of the weakened zone have little influences on the bearing capacity.(3)Three finite element models of dog bone-cellular composite slim beam joint,cellular composite slim beam joint and dog bone-cellular bare steel joint are established and their mechanical performances under static and cyclic loading are analyzed.The results indicate that under static loading,the contribution of concrete floor to stiffness and bearing capacity of dog bone-cellular composite slim beam joint can not be ignored.Compared with the cellular composite slim beam joint,the elastic stiffness of dog bone-cellular composite slim beam joint changes little,and its peak bearing capacity decreases by about 10%.Under cyclic loading,the bearing capacity,ductility and energy dissipation performance of the two types of composite joints are better than the bare steel joints.Compared with the cellular composite slim beam joint,the deformation and energy dissipation performances of the dog bone-cellular composite slim beam joint become better.(4)The influence of different design parameters on the mechanical performance of dog bone-cellular composite slim beam joint under cyclic loading is studied by controlling the single variable.The results show that the depth of weakened zone has great effect on formation position of plastic hinge and bearing capacity of the joint.It is recommended to control the depth of weakened zone between 14%～26% of flange width.By increasing the longitudinal reinforcement ratio,the bearing capacity and ductility of the joint are improved,but the energy dissipation becomes worse.It is suggested to control the longitudinal reinforcement ratio between 1.33% and 2.60%.The increasement of floor thickness has negative effects on the deformation and energy dissipation.It is advised that the floor thickness should be within 80 mm.The incresement of the length of the weakened zone has little effect on its bearing capacity and energy dissipation.,and it is advised to be controlled between 45%～75% of the steel beam height.With the distance from the starting point of the weakened zone to the flange of column increasing,the joint gets higher bearing capacity and deformation performance,but its energy dissipation becomes worse.And it is recommended to be controlled between 55%～85% of the width of steel beam bottom flange.