Experimental Study On Fire(Post-fire) Behaviours Of Concrete Continuous Two-way Slabs

At present,the fire behavior of the simply supported slabs and the restrained slabs were investigated by many researchers.However,the influence of the position and number of the heated spans on the mechanical performance of the(post-fire)concrete continuous two-way slabs should be further studied.Therefore,it is necessary to investigate the mechanical performance of the continuous concrete slabs in fire or after fire.The details are as follows:(1)To study the influence of the number and position of the heated spans on the fire behavior of the concrete continuous slab,a total of fire continuous three-span slabs were tested under single compartment fire,two-compartment fires and threecompartment fires.The measurements involve furnace temperatures,the concrete and steel temperature,vertical and horizontal displacements,restraint forces,cracks and failure modes.The present results were compared with those reported in the literature.Results show that the fire behavior of the continuous slabs depend on the number and position of the heated spans.The concrete and steel temperatures of the slabs were dependent on the furnace temperature.The downward deflection of the heated edge spans often appeared,and its deflection gradually increased with increasing temperature.The heated middle spans may experience upward or downward deflctions,and its deflection trend was dependent on fire scenario of the concrete slab.The cracks pendicular to the edge appeared on the bottom surface of the heated spans,and shortspan cracks appeared on the top surface of the heated spans as well as the internal supports.(2)Based on ABAQUS software and concrete plastic damage model,the numericalanalyses were conducted to predict the temperature,the deflection,the equivalent plastic tensile strain,the moment,the axial force and the tested slabs.In addition,the parameter analysis was carried out to investigate the load level,thickness,the reinforcement ratio and arrangement on the fire behavior of the concrete continuous slabs.Results show that the maximum equivalent plastic tensile strains mainly concentrated near to the internal supports(top surface)and on the outer edges(bottom surface),and the axial forces in the continuous slab were compressive during the fire test.Increasing thickness and reinforcement ratio were beneficial to enhancing the fire resistance of the concrete continuous slabs.(3)The mechanical performance of five post-fire continuous RC slabs and one reference slab was investigated,including cracks,deflection,concrete and reinforcement strains and failure modes.Meanwhile,based on the statistical results,the constitutive model of concrete and reinforcement after high temperature was proposed.The residual load carrying capacity of the test slab was calculated and compared by the yield line theory,tensile membrane theory and punching theory.Results show that different from the yield line failure mode of the slab at ambient temperature,the failure mode of each span in the post-fire slab depends on the position and number of the heated spans,concrete spalling,the maximum temperature of concrete and steel,and thus the local or overall punching failure may occur.In addition,l/50 can be used as the failure criterion to determine the residual ultimate bearing capacity of the post fire slab.Compared with the edge span,the middle span of the post fire slab has better ductility due to the constraints of adjacent spans.The steel strain difference method(bending failure)and the American ACI code(punching failure)can be used to determine the residual ultimate bearing capacity of the post fire slab.This dissertation has 83 figures,14 tables and 149 references.