Research On Fire Resistance Of Honeycomb Composite Beams With Circular Holes

As a kind of fabricated component,honeycomb composite beam is developed from traditional composite beam.It has the advantages of high bearing capacity,light weight,large stiffness,good seismic performance and simple construction.The circular hole honeycomb composite beam is composed of circular hole honeycomb steel beam and concrete slab connected as a whole through studs.The circular hole honeycomb steel beam is directly cut through hot-rolled H-section steel from the factory or misplaced into holes after cutting.At present,honeycomb composite beams have been widely used in high-rise,super high-rise and long-span structures.The proportion of building fire in such structures is increasing year by year,and the proportion of casualties is high.Therefore,it is necessary to study their fire resistance performance.At present,many scholars have studied the mechanical properties of honeycomb composite beams at room temperature,while the research on the fire resistance of honeycomb composite beams mainly focuses on finite element simulation analysis and scale fire test.Based on this,considering the two parameters of opening rate and whether to set stiffeners,this thesis carries out full-scale fire test and finite element simulation analysis on three simply supported circular hole honeycomb composite beams,and studies the effects of different parameters on the temperature field distribution,displacement change and failure characteristics of honeycomb composite beams.The main conclusions are as follows:（1）The overall deflection deformation of the honeycomb composite beam occurs during the heating process,and the honeycomb steel beam and the concrete slab can work together well.The opening of the honeycomb steel beam web reduces the strength and stiffness of the web around the hole,and the torsional buckling of the web and the lower flange at the hole at the beam end occurs;In the process of heating up,a small number of longitudinal cracks and transverse cracks with similar spacing appear on the concrete slab surface of the composite beam.About 40 minutes after the ceasefire,the transverse cracks basically disappear,leaving only white marks,while about 4 longitudinal cracks appear on the concrete slab surface at the edge of the upper flange of the honeycomb steel beam and at the stud,of which the cracks at the stud are more obvious;The end plate separation phenomenon appears at the beam end of honeycomb composite beam,the vertical crack appears at the concrete slab side at the beam end,the " 八 " shaped inclined crack appears on the slab surface,and the concrete burst phenomenon occurs at the long side of the bottom of the concrete slab.（2）When the other parameters of the honeycomb composite beam are the same,the two parameters of the opening rate and whether to set stiffeners have basically no effect on the temperature field distribution of the honeycomb composite beam,but have a significant effect on its displacement development,failure characteristics and deformation recovery ability.The larger the opening rate of the honeycomb composite beam,the greater the vertical displacement,the more obvious the failure characteristics,and the deformation recovery ability of the honeycomb composite beam with smaller opening rate is stronger;Stiffeners can effectively resist the deflection deformation and torsional buckling of honeycomb composite beams,but have little effect on their deformation recovery ability.（3）There is an obvious temperature gradient along the section height of the concrete slab.The closer the concrete slab is to the fire surface,the higher the temperature is,and the faster the temperature changes;The reinforcement in the slab is not directly exposed to fire,and only in contact with the concrete slab,and its temperature is basically the same as that of the surrounding concrete,while the stud is in contact with the honeycomb steel beam,which is subject to the heat transfer of the steel beam,so that the temperature of the lower part of the stud and the surrounding concrete is higher;When the concrete slab is about 100 ℃,the temperature platform is generated due to the heat carried away by the evaporation of water in the slab,and the closer it is to the bottom of the concrete slab,the greater the impact.（4）Due to the opening of the web,the fire area of the honeycomb composite beam increases,the temperature at the web of the honeycomb steel beam rises fastest,and the temperature of the steel beam and the web is basically the same,while the upper flange transmits the temperature to the concrete slab,resulting in an obvious temperature gradient with the web and lower flange;There is thermal inertia in the concrete slab.During the whole test process,there is an obvious temperature gradient between the concrete slab and the honeycomb steel beam.They affect each other’s temperature field distribution and restrict each other’s deformation.（5）The model of simply supported circular hole honeycomb composite beam is established through the finite element software ABAQUS.The thermal mechanical coupling analysis of honeycomb composite beam is carried out with the opening rate and whether stiffeners are set as parameters,and the effects of different parameters on its fire resistance are studied.Comparing the simulation results with the test results,it is found that this model can well reflect the temperature field distribution,displacement development and failure characteristics of the test components.