Research On Fire Resistance Of Regular Hexagonal Cell Honeycomb Composite Beams

The castellated composite beam is a modern composite beam that can work as a whole by setting shear connectors between the castellated steel beam and the concrete slab to resist the lifting and relative slippage at the interface.The castellated composite beam has holes on the steel beam web.In addition to the advantages of steel-concrete composite beams,the web holes are convenient for pipelines to get through,which can effectively reduce the height of the floor structure and save steel.Castellated composite beams are widely used in industrial plants,office buildings and parking lots in practical projects,and are also used in the reinforcement and reconstruction of old buildings and factories.The frequency of fire in buildings is high,and the elevated temperature leads to the deterioration of the mechanical properties of materials and the reduction of the bearing capacity of components.It is of great significance to study the fire resistance of castellated composite beams for reducing the damage of the structure in the fire,avoiding the casualties caused by the overall collapse of the structure in the fire,and reducing the repair cost of the structure after the fire.The existing research on the fire resistance of castellated composite beams is mostly finite element simulation analysis,and there are few fire resistance tests.The test objects are mostly castellated composite beams coated with fireproof coating and scaled castellated composite beams.Take into account this,this thesis conducts an experimental study on the fire resistance of three full-scale hexagon castellated composite beams simply supported at both ends under normal service loads,with a total temperature rise of 120 min,considering the opening ratio and whether to add stiffeners.The temperature field distribution,displacement change and failure characteristics of castellated composite beams under different parameters were explored.Through the combination of experimental research and finite element simulation analysis,the following main conclusions are drawn:（1）The castellated composite beam with regular hexagonal holes simply supported at both ends suffered bending failure as a whole after heating up for 120 minutes.The web of the steel beam was partially buckled,and the hole corners of the web were torn.The cracks on the top of the concrete slab are mainly composed of longitudinal cracks distributed above the studs in the slab and "eight"-shaped diagonal cracks above the supports at both ends,and the bottom of the concrete slab bursts in a large area.During the test,the horizontal displacements of the three specimens all reached their peaks at the 80 th minute during the heating process.（2）The temperature of each measuring point in the same measuring point group is relatively secure within 0min-10 min of the hexagon castellated composite beams.The temperature of the web is greater than of the upper flange.There is an obvious temperature gradient between the steel beam and the concrete slab.The maximum temperature difference can reach 200 C.There is an obvious heat exchange phenomenon between the concrete slab and the upper flange of the steel beam,the two constrain each other’s deformation.（3）Under the condition that other parameters remains unchanged.The opening ratio of the hexagonal castellated composite beam and whether to add stiffeners has little effect on its temperature field distribution under fire.（4）Under the condition that other parameters remain unchanged,whether to add stiffeners has little effect on the vertical deflection of the specimen from 0min to 78 min,and there is a large difference in the vertical deflection of the two specimens after the 78 th minute of heating.The addition of stiffeners can enhance the local stability of the lower web under fire.Compared with the castellated composite beam without stiffeners,the ability to resist deformation is improved by 7.26%.（5）Compared with the castellated composite beam with an opening rate of 60%,the castellated composite beam with an opening rate of 70% has a greater degree of weakening on the web.With extra parameters unchanged,reducing the porosity of the castellated composite beam from 70% to 60% increases its resistance to deformation by 13.53%.（6）The ABAQUS finite element simulation analysis of the simply supported hexagon castellated composite beam is carried out.The model used in this thesis can better simulate the behavior of castellated composite beams with unusual opening ratios and stiffeners under fire.The temperature field distribution and deformation verify the correctness of the finite element simulation analysis.The model can serve as a reference for the finite element simulation analysis of the fire resistance of hexagon castellated composite beams.