| As we all know,laminated boards have been widely used in new construction projects and have achieved good economic benefits,while pre-stressed laminated boards have superior overall performance,mechanical properties and crack resistance compared with ordinary laminated boards.At present,a lot of researches have been done on the mechanical properties of ordinary laminated plates at normal temperature and high temperature at home and abroad,and fruitful results have been obtained,but the behavior of pre-stressed laminated plates under high temperature is still limited.In this paper,12 pre-stressed composite plates with different thicknesses of laminated layers were designed.The fire resistance tests were carried out on 9 laminated plates.Three of the laminated plates were subjected to fire test to fire endurance,and three laminated plates were cooled by fire for 60 minutes.In the static loading test,the three composite plates were subjected to a static loading test after being cooled for 40 minutes,and the other three laminated plates were subjected to a static load test without fire.The fire behavior of the composite panel under the coupling of fire and load and the mechanical mechanism and residual bearing capacity after fire were studied by experiments.Through analysis,the following main conclusions are obtained:(1)Under the action of load and fire coupling,the stress performance of the pre-stressed composite plate will change,vertical cracks will be generated in the span of the plate,oblique cracks will be generated at both ends of the test piece,the deflection of the plate will increase,and the rigidity will decrease.(2)When the pre-stressed laminated plate is subjected to fire,a temperature gradient will be formed along the cross-section height of the test piece,which will generate temperature stress and generate shear stress at the joint surface.Shear stress will also occur under the external load,and the two will interact to produce horizontal cracks on the laminated surface.Since the temperature shear stress generated by the bonding surface is mainly related to the temperature gradient and is not proportional to the burning time,the laminated layer is not completely separated,and the test piece still has a certain overall working performance.Reinforced trusses also play an important role in ensuring the integrity of the specimen when it is exposed to fire.(3)Under the action of fire,the bond strength between the steel and the concrete will be reduced.Because the pre-stressed steel bars are in a high stress state,the reinforced tendons are generated along the longitudinal steel bars,and the bond failure occurs.(4)The thickness of the laminated layer has little effect on the temperature field distribution of the board during fire.(5)The pre-stressed laminated plate is loaded with fire after the fire,and the prefabricated layer and the laminated layer will be completely separated and disengaged,but the laminated plate still has certain working performance,but the force mechanism of the plate changes and is transformed by the bent member.For the truss structure,the laminated layer is a compression flange,so the steel truss has an important influence on the fire resistance of the pre-stressed laminate.(6)The bearing capacity of the pre-stressed laminated plate will be reduced after being fired,and the longer the fire is,the greater the reduction.For pre-stressed laminates with a protective layer thickness of 20 millimeter,the residual bearing capacity can reach 80% or more after being exposed to fire for 60 minute.(7)The fire resistance limit of the pre-stressed laminated plate is not only related to the thickness of the protective layer of the pre-stressed steel bar,but also related to the thickness of the floor slab.For the thickness of the protective layer of 20 millimeter,the thickness of the prefabricated layer is 40 millimeter,and the thickness of the laminated layer is not less than 70 millimeter.Plywood,its fire resistance can reach more than 2 hours. |
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