Research On Fire Resistance Of Steel Fiber Reinforced Concrete Slab

In response to the cracking defects of concrete,many researchers in the field of civil engineering have proposed methods to improve the tensile strength and toughness of concrete,among which the method of incorporating steel fibers in concrete is generally accepted both at home and abroad.Steel fibers have the effect of hindering the expansion of micro cracks and macro cracks in concrete,thus enhancing the properties of ordinary concrete to resist bending,tension,impact damage and fatigue,as well as durability,making the performance of concrete greatly improved.As a result,steel fiber reinforced concrete(SFRC)is increasingly receiving more and more attention,and with the depth of research,it is also more often used in hydraulic engineering,structural elements,road,airport and bridge retaining surfaces.In today’s world of various types of disasters,building fires are still the most frequent and one of the most widely affected disasters,causing huge losses to society and people.Therefore,the research on the fire resistance of engineering structures has become urgent.At present,there are few studies on the fire resistance of SFRC slabs at home and abroad.Based on the above background,this thesis conducts an experimental study and finite element simulation analysis on the fire resistance of SFRC slabs to reveal their behavioral responses and damage modes under the action of fire.In addition,based on the parametric analysis,a suitable theory applicable to the fire resistance performance of SFRC slabs is obtained.A large number of mechanical properties tests of steel and steel fiber reinforced concrete materials at room temperature were conducted to obtain the mechanical properties parameters of the materials at room temperature.Based on the available domestic and foreign research results on the mechanical properties and thermophysical properties of steel and steel fiber reinforced concrete at elevated temperature,various parameters suitable for the study of the fire resistance of SFRC slabs were determined.Based on the analysis of the mechanical properties of materials at room temperature and elevated temperature,experimental studies were conducted on the room temperature bearing capacity of one SFRC slab and the fire resistance of nine SFRC slabs.The effects of slab thickness,steel fiber content and load ratio on the fire resistance of SFRC slabs were mainly investigated to reveal the behavioral response of each specimen under fire,and the test results such as temperature-time curve,vertical displacement-time curve and damage mode of each specimen were obtained.The test results demonstrated that:(1)The thickness of SFRC slabs has a great influence on the fire resistance of specimens,and the specimens have better fire resistance when the thickness of specimens increases under the same conditions.(2)The load ratio n has a significant influence on the fire resistance of SFRC slabs.The larger the load ratio n,the smaller the fire resistance limit of the specimen and the faster the deformation rate.(3)During the fire test,all specimens showed bending and shear damage mode,the middle of the specimen was bent obviously,and the side of the specimen showed shear damage phenomenon.(4)After the test,each specimen produced a certain amount of rebound deformation.Based on the software ABAQUS,a finite element analysis model of SFRC slab was built to numerically simulate the fire resistance performance of each specimen.The results of temperature-time curve at different parts along the thickness direction,mid-span vertical displacement-time curve and critical temperature of each specimen were obtained.The finite element results were analyzed and compared with the test results,thus verifying the accuracy of the finite element analysis model.Based on the validated finite element analysis model,a parametric analysis of nine factors(load ratio n,SFRC thickness h_c,steel beam flange thickness t_f,steel beam web thickness t_w,steel beam height h_s,steel beam width b_s,shear connection degreeη,steel fiber volume content V_f and concrete compressive strength grade)affecting the fire resistance of steel fiber concrete slabs was carried out.The analysis results indicate that:(1)Load ratio n and slab thickness h_care the key factors affecting the fire resistance of SFRC slab.The smaller the load ratio n or the larger the thickness h_c,the higher the fire resistance limit and critical temperature of SFRC slab.(2)The steel beam width b_s,steel fiber volume content V_f and concrete compressive strength grade have some influence on the ultimate bearing capacity of SFRC slab at room temperature.But under the condition that other parameters such as load ratio n remain unchanged,the influence of steel beam width b_s,steel fiber volume content V_f and concrete compressive strength grade on the fire resistance performance of SFRC slab is small.(3)The effects of changes in steel beam flange thickness t_f,steel beam web thickness t_w,steel beam height h_s and shear connection degreeηon the fire resistance of steel fiber concrete slabs are small.(4)There is a coupling effect between the load ratio n and the slab thickness h_c on the fire resistance limit and critical temperature of SFRC slab.Based on the parametric analysis results,the fire resistance calculation method of steel fiber concrete slab is proposed through analytical research and numerical fitting.(1)The temperature calculation formula for different parts along the thickness direction inside the SFRC slabs at elevated temperatures is obtained,and the formula calculation results are analyzed and compared with the test results to validate the reliability.(2)The formula for calculating the fire resistance limit of SFRC slab considering the two key factors of load ratio n and slab thickness h_c is obtained,and the accuracy of the formula is verified.(3)The load carrying capacity method applicable to the critical temperature calculation of SFRC slabs is proposed,and the calculated results are compared with the finite element results.(4)An empirical equation for the critical temperature of SFRC slabs considering two key factors,load ratio n and slab thickness h_c,is established,and the high fitting accuracy of the empirical equation is verified.The research analysis in this paper provides an important reference for the subsequent research on the fire resistance of SFRC slabs.