Experimental Study On Fire Resistance Of Multi-span Steel Truss Prestressed Composite Panels

The steel truss prestressed composite slab is a new type of integrally assembled floor slab composed of a steel truss prestressed prefabricated bottom plate and a post-cast concrete layer.The advantages of simplicity,efficiency and template saving are widely used in domestic prefabricated buildings.At present,there have been systematic results in the research on the mechanical properties of steel truss prestressed concrete composite panels at room temperature,but the research on their mechanical properties under the action of fire and high temperature,especially considering that the floor slabs in the structure are subjected to fire as a continuous member.The results have not yet been reported.In this thesis,considering the actual constraints of the floor in the structure and combined with laboratory conditions,the fire resistance performance test and analysis of the steel truss prestressed concrete continuous laminated slabs with different thickness of the laminated layer in two spans are carried out under the action of fire high temperature and load coupling.The research results provide an important reference for the fire-resistant design of steel truss prestressed concrete composite slabs and the damage assessment and reinforcement of such slabs after fire.The research results have certain engineering application value.This thesis introduces the fire resistance test of four steel truss prestressed concrete composite slabs with different stack thicknesses under the conditions of single-span fire and double-span fire respectively.The main conclusions are as follows:（1）Multi-span steel truss prestressed laminated slab,due to the high concrete strength of the precast layer,the low bonding strength of the laminated surface,the deformation is restricted by the support,the prestressed tendons make the concrete pre-compressed and other factors,the prefabricated layer in the event of fire.will produce a severe burst.（2）When the multi-span steel truss prestressed laminated plate is subjected to fire,due to the temperature stress generated by the temperature gradient,a crack perpendicular to the plate span will occur at the cross-section of the negative bending moment reinforcement bar of the intermediate support,and the crack runs through the entire post-casting The appearance of cracks will change the distribution law of the internal force of the connecting plate under the load.（3）Under the action of temperature-load coupling,shear stress will be generated at the superimposed surface of the laminated plate,which will cause shear failure and separation at the superimposed surface,resulting in horizontal cracks.（4）The multi-span steel truss prestressed laminated plate is subjected to the high temperature of fire.Although the laminated surface is damaged by bonding and produces horizontal cracks,and the bottom of the plate is seriously damaged,it still has good working performance,indicating that the steel truss and the laminated plate have two The anchoring of the reserved beard bars at the end in the cast-in-place concrete at the end plays a key role in the integrity of the laminated slab.Therefore,in order to improve the fire resistance of the slab,a steel truss should be properly installed,and it is recommended that the steel truss be anchored into the support.（5）Under the action of fire high temperature-load coupling,the multi-span steel truss prestressed composite slab will lead to the deterioration of the material mechanical properties of concrete and prestressed tendons,resulting in the degradation of the overall stiffness of the composite slab,the reduction of the bearing capacity,and the vertical deformation of the intermediate support.Due to the cracks in the plate span,the laminated plate has a large deflection deformation.The smaller the thickness of the post-cast laminated layer,the more serious the relative damage of the plate’s mechanical properties and the worse the fire resistance.（6）Because the prefabricated layer at the bottom of the slab bursts and falls off,the floor slab becomes thinner,the thermal insulation performance of the slab with the thinner post-cast layer is seriously reduced,and the temperature of the slab top rises rapidly,reaching the fire resistance limit.The fire resistance rating of the 60 mm laminated plate with the post-cast layer is 90 min,and the fire resistance of the 80 mm laminated plate with the post-cast layer is 130 min.Therefore,it is recommended that the thickness of the post-cast layer should not be less than60 mm.（7）The fire behavior of the multi-span steel truss prestressed composite slab is basically the same as that of the single-span fire and the multi-span fire,but the deformation of the multispan fire and the single-span fire is larger than that of the single-span fire under the fire-load coupling.