Experimental Study On Bearing Capacity Of Large Prestressed Concrete Roof Sheathing After Natural Cooling Of Fire

Building fires are one of the more frequent disasters today.Therefore,research on the fire resistance of building structures has become one of the research hotspots in the field of disaster prevention and mitigation.Due to its large span and thin thickness,prestressed concrete roof slabs of industrial buildings are seriously degraded after fire,and the durability is seriously reduced.Because there is relatively little research on large prestressed concrete roof slabs after fire,this paper will study the bearing capacity of prestressed concrete roof slabs subjected to fire and natural cooling,and provide effective evaluation of bearing performance of industrial buildings after disasters.in accordance with.In this paper,the large-scale fire simulation test system is used to carry out the fire test of prestressed concrete roof slab,observe the test phenomenon,analyze the actual distribution law of temperature field in the process of temperature rise and fall of prestressed concrete roof slab,and measure and analyze the deflection.After natural cooling,the roof panel was tested for bearing capacity and deterioration,and compared with the water-cooled prestressed concrete roof slab.The main research contents and conclusions of this thesis are as follows:(1)During the fire in the prestressed concrete roof slab,it is found that when the furnace temperature curve peaks,the appearance of the temperature peak of the concrete measuring point will be relatively delayed.When the furnace temperature reaches the peak value,the temperature of the concrete surface is peaked,the heat is transmitted from near to far,and the temperature of the concrete point farther away from the fire surface will reach the peak value;the farther the measuring point is from the fire surface,the peak value The more obvious the hysteresis.(2)After the fire stress of the prestressed concrete roof slab,it was found that only the 30 mm thick plate surface was also damaged to varying degrees.Since the bottom surface of the plate is directly exposed to fire during the fire,under the action of high temperature,the concrete is pulled at the interface between the top surface of the plate and the primary and secondary ribs,and the crack occurs.The longer the fire is applied,the more obvious the depression is,and the more the crack and the width of the crack The bigger it is.(3)Analysis of the fire effect on prestressed concrete roof slabs: During the heating and natural cooling of prestressed concrete roof slabs,the concrete surface of the roof is subjected to high temperature due to the fire surface,that is,the prestressed concrete The roof panel is cracked by the surface layer of the fire surface and cracks.(4)Research and analysis show that in the process of heating and natural cooling,the prestressed concrete roof slab has undergone the process of recovering from the first arch,and then recovering after flexing,due to the effect of prestressing,the roof panel The main rib locally has a normal crack that is wide and narrow.(5)Research and analysis show that the load-carrying capacity of prestressed concrete roof slabs is reduced after fire,and the longer the fire-fighting time,the more the load-bearing capacity of the roof slab decreases;the fire is 30 minutes,45 minutes,60 minutes.After natural cooling,the bearing capacity loss is within 5%,and the carrying capacity of 1.5%,2.3%,and 4.4% is lost.When the fire is applied for 75 minutes,the load-carrying capacity of the prestressed concrete roof slab is significantly reduced,reducing the load carrying capacity by about 15%.(6)Research and analysis show that the fire effect makes the stiffness of the prestressed concrete roof slab slightly lower,and the longer the fire action time,the more obvious the stiffness reduction.(7)Through the research and analysis of prestressed concrete roof slabs with different cooling modes,the bending stiffness of prestressed concrete slabs after cooling by natural cooling method is generally slightly smaller than that of prestressed concrete slabs after cooling by cooling method.Bending stiffness;the load-carrying capacity of prestressed concrete roof slabs cooled by watering cooling is slightly lower than that of prestressed concrete slabs after natural cooling.