Experimental Study On Fire Resistance Of Honeycomb Composite Beams Restrained At Beam End

Honeycomb composite beam is a new type of composite structure based on the traditional composite beam,which designs the steel beam web with different shapes to meet the requirements of saving steel,reducing floor height and convenient pipeline laying.It is suitable for long-span structures or multi-storey buildings.At present,there are few researches on the fire resistance of honeycomb composite beams at home and abroad,and there is a gap in the research on fire resistance of honeycomb composite beams restrained at the end of the beam.Therefore,this thesis studies the fire resistance of six honeycomb composite beams with different hole shapes（round holes and regular hexagonal holes）,different beam end constraints（hinged joints and rigid joints）and different slab thicknesses（100mm and 120mm）,and analyzes the temperature distribution,displacement and failure patterns of honeycomb composite beams in the whole process of fire.The main conclusions of this thesis are as follows:（1）At the beginning of the heating stage,the transverse and oblique cracks with water stains first appeared on the end slab surface of the honeycomb composite beam,and the cracks gradually extended and expanded in the heating stage.In the middle of the heating stage,the surface of the honeycomb composite beam appeared water stains,water bays,and water vapor in turn.In the later stage of the heating stage,the water stains on the slab surface of the honeycomb composite beam gradually dried and disappeared,the vertical flexure deformation and the inclination of the slab were obvious.In the cooling stage,the original oblique cracks and transverse cracks at the end of the honeycomb composite beam and slab basically disappear,and the new oblique cracks are opposite to the development direction of the original oblique cracks.After stopping the heating,several longitudinal cracks are formed on the upper slab of the honeycomb steel beam,and the cracks are further formed,extended and expanded in the cooling stage.（2）The existence of beam end constraint makes the crack at the end of the slab more complex and the damage more serious.Under the condition of the same hole shape and slab thickness,the plate inclination of rigid-jointed constrained honeycomb composite beams is smaller than that of hinged constrained honeycomb composite beams.（3）The existence of beam end constraint leads to serious local buckling of the web and lower flange at the end of the steel beam,and the local buckling of the lower flange is mainly located at the first opening at the end of the beam.The web between holes forms buckling deformation in varying degrees,and the web between holes at the end is "S" shaped deformation,the web between the middle holes is deformed in the shape of "C".The overall torsional deformation of the honeycomb steel beam in the tension area,and the torsion angle of the lower flange of the hexagonal hole honeycomb steel beam is larger than that of the round hole honeycomb steel beam.The beam end joint after the fire is seriously damaged,the welds of the upper and lower flange of the rigid joint are broken in varying degrees.The corner web of the hexagonal hole nearest to the beam end of the L6 honeycomb composite beam is cracked.（4）The temperature distribution of honeycomb composite beams with round holes and regular hexagonal holes is basically the same,and there is little difference between the web between holes and the web at the edge of holes in honeycomb steel beams.（5）Under the condition of the same beam end constraint and slab thickness,the mid-span vertical deflection of the honeycomb composite beams with round holes and regular hexagonal holes is basically the same,indicating that the hole shape has little influence on the bearing performance of the honeycomb composite beams.The slab thickness has little effect on the bearing performance of honeycomb composite beams under high temperature.After heating up for 30 min to 40 min,the mid-span vertical deflection of rigid confined composite honeycomb beams is larger than that of hinged confined composite honeycomb beams.Compared with hinged composite beams,the recovery ratio of rigid beam is smaller,and the recovery ratio of regular hexagonal beam is smaller than that of round beam.（6）At the beginning of heating stage,the rapidly increasing axial pressure of honeycomb composite beams is an important reason for local buckling of web and flange of steel beams.The expansion of beam end of rigid confined composite honeycomb beam is obviously larger than that of hinged confined composite honeycomb beam.The axial pressure of honeycomb composite beams increases first and then decreases in the heating stage.（7）The thermal-mechanical coupling analysis of the beam end confined honeycomb composite beam was carried out by ABAQUS,and the temperature-time curve and the mid-span vertical displacements time curve were obtained.It was found that the numerical simulation results were in good agreement with the experimental results,which verified the correctness and validity of the finite element model.