Experimental Study On Fire Resistance Of Simply Supported On Four Sides Of Reinforced Concrete Composite Slab

Among all kinds of disasters,fire is one of the most frequent disasters.Building fire has become one of the main disasters threatening the safety of buildings.When fire occurs,the floor bears the function of preventing fire from breaking and preventing the fire from spreading upward.As one of the most seriously damaged components,the fire resistance of floor is an important research topic in the field of building fire safety.At present,the prefabricated structure is being strongly advocated in our country,and the reinforced truss concrete composite slab is the most widely used component in the prefabricated building.Up to now,there is no research on fire resistance of reinforced truss concrete composite slab in fire at home and abroad.For the first time in this paper Experimental study on fire resistance of reinforced truss concrete composite slab is carried out.Under the ISO834 standard heating curve,real fire test of four simply supported reinforced truss concrete composite plates is carried out.By analyzing the failure characteristics of the test slab under the coupling of high temperature and load,the cracking of the floor slab,the distribution of temperature field inside the concrete,and the law of deformation inside and outside the plane,the following conclusions are drawn:(1)Under the action of high temperature and load coupling,except for the small horizontal cracks at the corner of the composite plate,there is no phenomenon of the breakaway between the prefabricated layer and the post-cast-in-situ composite layer,and the deflection of the plate does not show a sudden anomaly during the whole combustion process.Therefore,the laminated slab with steel truss can work together with the prefabricated layer under the action of fire,and the steel truss is the main structural measure to ensure the superimposed layer and the prefabricated layer to work together.(2)When the reinforced concrete simply supported composite slab is affected by fire,the temperature of the place directly affected by fire in the furnace is high,while the temperature of the plate located around the supporting part is relatively low,thus forming a low temperature circumferential zone along the circumference of the plate.The thermal expansion of the plate in the high temperature region results in the tensile stress in the circumferential zone around the low temperature.With the increase of burning time,the properties of the material in the high temperature zone change,the bottom concrete falls off,and the damage is serious,while the damage in the circumferential zone of the low temperature is relatively light.The stress system of the slab is changed,and the floor slab is similar to the surrounding side beam.The circumferential circumferential zone around the slab is the edge beam,and the edge beam will be produced under the load.Torque,the maximum torque in the four corners of the plate,due to the effect of torque will also produce tensile stress,when the above two cases of tensile stress over the tensile limit strength of concrete will appear cracks,torque cracks should be inclined cracks,Therefore,vertical cracks occur in the side span of the plate,and oblique cracks occur at both ends of the plate.(3)When the composite plate with reinforced truss is subjected to fire,the temperature of the fire surface of the composite plate is much higher than that of the top surface of the plate,so that the temperature distribution in the plate is not uniform,and the temperature gradient will cause the thermal stress.Because the joint of laminated slab is at the junction of prefabricated slab and post-pouring layer,the bond strength is low,so the longitudinal crack of the floor is formed at the joint,and the reinforcement truss acts as a bolt bolt in the prefabricated layer and the composite layer.The shear stress between the prefabricated layer and the superimposed layer due to the temperature gradient,in addition to the joint plane,some of which need to be transmitted by the steel truss,so in the post-pouring superimposed layer along the steel truss section.After stress concentration,the thermal conductivity of steel bar is better,the temperature of concrete is high and the mechanical property of concrete is decreased greatly at the position of steel truss on the top of slab,so tensile cracks appear above the steel bar of truss.(4)Under the action of fire,the concrete burst at the bottom joint is more serious,which shows that the concrete at the joint of the test plate is weak,and the steel bar under stress at the joint joint adopts the way of lap connection,and the bond force will be reduced after the crack.This is unfavorable to the stress of the laminated plate.(5)The different thickness of post-pouring layer and the number of prefabricated panels have little effect on the temperature field distribution of the composite slab.(6)Under the coupling effect of high-temperature and load,the deflection of laminated plate will be partially restored when the temperature decreases after combustion because of the change of material properties.The results show that the deformation recovery degree is higher when the thickness of post-sprue layer of test plate is larger,and the effect of pre-made board splicing number on the recovery deformation of post-fire plate is very small.(7)Under the action of high temperature,the laminated plate will form a through crack at the junction of the joint seam,the floor slab is burned through to reach the fire resistance limit,so that the junction point of the joint seam is the weak part of the laminated plate,and the thickness of the post-pouring layer is short.(8)the number of splicing of the laminate has no obvious effect on the fire resistance of the plate.