Study On The Bearing Capacity Of Regular Hexagonal Honeycomb Composite Beams Before And After Fir

Honeycomb composite beam is a new type of composite structure developed from the basis of solid web composite beam,which has the double advantages of honeycomb steel beam and solid web composite beam.Honeycomb steel beams are widely used in high-rise buildings because of the open holes in the web,which not only can save steel,but also the holes are convenient for crossing pipelines and can save effective height.In recent years,the frequent occurrence of fires has led to the increasingly prominent problem of fire in building structures.High temperature has obvious influence on the bearing capacity of honeycomb composite beams,so the bearing capacity of honeycomb composite beams after fire needs to be properly evaluated.At present,there is a gap in the research on the bearing performance of honeycomb composite beams after fire at home and abroad.The hexagonal hole is the more widely used opening form of honeycomb composite beam.In this thesis,the damage morphology of the carried out fire resistance test of the full-scale hexagonal open cellular composite beam is compared and analyzed,and the bearing performance of the full-scale hexagonal open cellular composite beam before and after fire is studied experimentally and simulated numerically,considering the influence of different opening rates,based on the results of experimental research and finite element numerical analysis,the damage morphology of the honeycomb composite beam Based on the results of the experimental study and FEM numerical analysis,the damage morphology of the honeycomb composite beam is studied and the calculation formula of the load carrying capacity of the hexagonal open cellular composite beam before and after the fire is proposed.The main research conclusions of this thesis are as follows:(1)The foot-span hexagonal open cellular composite beam with simple support at both ends was mainly deformed in vertical deflection after 60 min of heating,and the deformation of the cellular steel beam and concrete slab were consistent,while the web and lower flange at the hole at the end of the beam showed slight buckling and slight end-slab separation at the end of the cellular composite beam.The cracks at the top of the concrete slab of the composite beam were mainly composed of longitudinal cracks distributed above the steel beam in the slab and eight diagonal cracks above the supports at both ends.(2)After 60 min of heating,the vertical deflection deformation in the span of the specimen with 70% open cellular composite beam is larger than that of the specimen with 60%open cellular composite beam,and the deformation recovery ability of the specimen with larger open cellular composite beam is relatively poor after natural cooling at high temperature.Therefore,the larger the perforation rate of hexagonal open cellular composite beams,the larger the vertical deflection deformation and the more obvious the damage characteristics.(3)After the fire,the hexagonal open cellular composite beam undergoes four stages:widening of the original cracks,new cracks in the concrete,crack development,and damage of the specimen under load.The difference lies in the slight buckling of the steel beam at the L1 loading position and the severe bulging of the web between the holes at the L2 loading position,which indicates that the larger the opening rate of the honeycomb composite beam,the more the web of the steel beam is weakened,the more the web bearing capacity and stiffness are reduced,and the web between the holes is more likely to buckle.(4)The opening rate is an important factor affecting the load-bearing performance of post-fire hexagonal open cellular composite beams.Reducing the opening rate can effectively improve the flexural performance,ultimate load-bearing capacity and deformation capacity of the specimens after yielding of the post-fire hexagonal open cellular composite beams.(5)Under the load,the damage of the square hexagonal open cellular composite beams before and after the fire went through the elastic phase,the elasto-plastic working phase and the bearing capacity reduction phase,showing the bending damage characteristics.However,the concrete strength of the specimens degraded after the fire,and the load that the concrete could bear at loading was smaller than the total load that the specimens could bear,which made the load level at the time of cracking of the specimens relatively low.(6)Using ABAQUS finite element software,analytical models were created for the specimens of the ortho-hexagonal open cellular composite beams at room temperature and after being subjected to fire,respectively.By comparing the FEA results with the experimental results,the accuracy and reliability of the FEA models were demonstrated,which laid the foundation for further study of the load-bearing performance of the honeycomb composite beams.(7)Based on the experimental study and numerical simulation results,the calculation method of the residual bearing capacity of the hexagonal open cellular composite beam before and after the fire is proposed,and the errors between the calculation results and the experimental results are within the allowed range,which indicates that the calculation method can be used for the calculation of the residual bearing capacity of the hexagonal open cellular composite beam before and after the fire.