Experimental Study On Fire Resistance Of One-way Simply Supported Laminated Slabs

Laminated plate is a new practical assembly-monolithic floor,which is widely used in the domestic market.Laminated board has been widely used owing to achieving the construction of industrialization,designing standardization,installation mechanization,manufacturing industrialization,the construction is not affected by the weather,construction speed and can save a large number of templates and many other advantages in the new building and reinforcement projects.In all kinds of disasters,fire is a very high frequency of disasters,building fire is a threat to building safety,one of the main disasters,in the fire,the floor bears the fire cut off and prevents the fire from the spread of the role of fire in the largest extent,most damage by the most serious components.Therefore,the fire resistance performance of floor slab is an important research subject in the field of building fire safety.At present,the research on the fire resistance of laminated plate is not deep.Based on the engineering practice,the paper studies the fire behavior of the laminated slab with steel truss and the stress performance after the fire,mainly carries on the following research work:(1)To study the distribution and development law of the section temperature field in the process of fire.(2)To study the failure form,maximum deflection and the mechanical performance of the composite interface of the laminated plate in fire test.(3)To study the mechanical properties of laminated plates after 90min fire,and the residual bearing capacity of laminated plates after fire.Through this experimental study,the main conclusions are as follows:(1)Setting the laminated simple supporting plate of the steel truss,the tensile strength of rebar and concrete will be reduced after high temperature,at the same time,the bottom concrete falls off after high temperature,which leads to the damage of the specimen,the section is weakened,the crack resistance is reduced,and the vertical crack occurs under the action of the bending moment and the temperature stress.In addition,when the specimen is subjected to high temperature,not only the material strength is reduced,but also the bond between the steel bar and the concrete will decrease,and the elastic modulus of the steel bar will be reduced,therefore,the crack is more obvious under the coupling of load-temperature.The oblique crack on the plate is the result of the interaction of shear force and temperature stress produced by external load.The fire behavior of the laminated plates with steel truss under load-temperature coupling is basically the same as that of the general pouring plate.(2)The laminated plate of the steel truss is arranged under the coupling of load-temperature,because of the temperature stress produced by the temperature gradient,the small horizontal crack is produced near the plate end bearing and the cross-joint surface,but it does not produce the penetrating crack along the joint surface,the precast layer and the laminated layer still work together,which shows that the steel truss plays a key role.The steel truss is an important measure to ensure the joint work of precast and post pouring layers in the composite slab fire.(3)The distribution of the temperature field in the plate is the same as that of the whole slab when the laminated plate of the steel truss is set up by the fire.The distribution of temperature field in different post-pouring layer is basically the same,and the thickness of the post-pouring layer has no effect on the temperature field distribution.(4)When the thickness of the precast layer is certain,the external load is the same,the thickness of the laminated layer is about large(the greater the thickness of the floor),the longer the fire resistance limit of the plate.(5)Under the coupling of load-temperature,the composite plate has a large deformation due to the poor performance of the material and the decrease of stiffness.The specimen achieved the fire resistance limit,the temperature reduced,deformation basically can not be restored.A specimen that has not reached the refractory limit can be recovered in most cases when the fire occurs.(6)The laminated plate of the steel truss,the damage form of the plate under the load is basically the same as that of the laminated plate without the fire,and the vertical crack is produced under the load,and the concrete is damaged by the pressure loss.There is no complete detachment between the precast layer and the back-pouring laminated layer.(7)When the thickness of the laminated layer is larger,whether the laminated plate after the fire or the laminated board which is not affected by the fire,in the load test,the horizontal cracks are produced in the laminated surface,but the precast layer and the back-pouring laminated layer are not completely detached,and the precast layer and the back-pouring laminated layer can still work together.The steel truss is the key technical measure to ensure the normal use of the laminated plate,even if the fire effect is not considered,the steel truss should be set at room temperature.(8)The residual carrying capacity of the laminated plate which reaches 90min by the fire time can still reach more than 80%,and the thicker the thickness of the back-pouring layer is,the larger the residual bearing capacity of the laminated plate after fire.(9)After the component is subjected to fire,the mechanical properties of concrete and rebar are affected to a certain extent,which results in the stiffness of the component being reduced,and under the same load,the deflection of the component under fire is larger than that of the fire-less member.(10)Whether the laminated plate after the fire,or the laminated plate without fire,there is a large deflection,which shows that the steel truss can improve the deformation ability of the plate.