Study On Fire Resistance Of Single And Bidirectional Concrete Slabs For Underground Structures

With the rapid development of economic construction in our country,some cases of building fire up,the occurrence of fire to the people’s life and property safety brought great harm,now for underground building fireproof performance study is less,and the underground building when the fire rescue and evacuation more difficult,so the fire protection design requirements will be higher,in order to protect the safety of the people’s life and property,It is necessary to systematically study the fire resistance of underground reinforced concrete structures.In reinforced concrete building structure fire resistance at home and abroad research situation,foreign code for fire protection design of buildings and code for fire protection design of buildings in our country still exists many differences,which for reinforced concrete slab,the differences in refractory limit regulations,the code for fire protection in our country in the condition of components under different fire resistance design also is not very precise.In this paper,the finite element software ABAQUS is used to calculate the fire resistance performance of reinforced concrete simply-supported one-way slabs,continuous one-way slabs and simply-supported two-way slabs,and determine the influence rules of span height ratio,load ratio,protective layer thickness and other factors.First determine the mechanical properties of steel and concrete and the thermal performance parameters,and then determine the temperature field of plate,the temperature field is defined as a predefined fields in the form of the force applied to the plate model,then in the analysis of slab under the action of uniformly distributed load deformation situation,to observe the deflection of plate changes as a result,reveals the influence law of fire resistance.For simply supported one-way plate,the span of reinforced concrete simply supported one-way plate is taken as 3m,and the thickness of the one-way plate is changed to 200 mm,150mm,100 mm and 80 mm respectively,that is,the span height ratio is 15,20,30 and 37.5respectively,and the protective layer is taken as 15 mm,20mm and 25 mm.The influence law of0.2-0.9 times load ratio on fire resistance of reinforced concrete simple supported one-way slabs,a total of 96 working conditions.The relationship between reasonable span height ratio and load ratio of simply supported one-way slabs with different protective layers is revealed under different fire resistance limits.For the continuous one-way plate calculation is to take the span of reinforced concrete continuous one-way plate is 3m,the extension length of the two ends of the plate is 2m,change the thickness of the one-way plate,the thickness of the plate is 200 mm,150mm,100 mm,80mm,that is,the span height ratio is 15,20,30,37.5,the protective layer is 15 mm,20mm,25 mm,The influences of load ratios 0.2,0.3,0.4,0.5,0.7,0.9 on the fire resistance performance of reinforced concrete continuous one-way slabs were determined.The relationship between reasonable protective layer thickness,span height ratio and load ratio meeting the fire resistance limit requirements was determined.There were a total of 51 working conditions.For the calculation of simply supported two-way plate is to take the side length of reinforced concrete simply supported two-way plate is 3m,change the thickness of two-way plate,plate thickness is 200 mm,150mm,100 mm,80mm respectively,that is,the span height ratio is 15,20,30,37.5,the protective layer is 15 mm,20mm,25 mm,The influences of load ratios of 0.3,0.5,0.7 and 0.9 on the fire resistance of reinforced concrete simply-supported bidirectional slabs are investigated under 48 working conditions.Deflection and deformation diagrams of simply supported bidirectional slabs under different types were obtained by simulation calculation,and the relationship between reasonable protective layer thickness,span height ratio and load ratio satisfying the fire resistance limit condition was also obtained.However,the fire resistance requirements of reinforced concrete unidirectional slabs and bidirectional slabs for underground structures are not specified in Code for Building Fire Protection Design.The influence of span height ratio,load ratio and protective layer thickness on the fire resistance of reinforced concrete slabs is studied,and the basis of quick identification of fire resistance limit of unidirectional slabs and bidirectional slabs is put forward.The relevant research contents and methods can provide reference for the fire resistance design of reinforced concrete slabs.There are certain differences between this paper and other researchers in studying the influence of load ratio.Most researchers study the load ratio when the load changes,but the reinforcement remains unchanged,which is not from the design perspective.In this paper,the ratio of reinforcement and load change with the change of load ratio,which is considered from the perspective of design and application,and is closer to the engineering practice.The research on the fire resistance of reinforced concrete unidirectional slabs and bidirectional slabs under high temperature environment should be introduced to provide methods and references for the research of different reinforced concrete members under high temperature.