| Steel fibres improve the tensile and flexural properties,ductility and durability of normal concrete.It makes normal concrete have a better impact and fatigue resistance.Steel fibre reinforced concrete has been widely used in various fields of civil engineering and achieved good technical and economic and social and environmental benefits.With the acceleration of modernization,building fires occur frequently.It not only caused huge economic and property losses,but also damaged the overall bearing capacity of the structure,reduced the safety level of the structure,caused a collapse in serious cases,and even threatened people’s lives.A fire sprinkler is the most important way to put out fires.There are few studies on the bond performance of steel reinforcement and steel fiber reinforced concrete after high temperature water jet cooling at home and abroad.This paper conducted a central pull-out test to provide theoretical and test data for the study of the bond performance of steel reinforcement and steel fiber reinforced concrete after high temperature water jet cooling.It is of reference for fire protection design and rehabilitation work carried out after the disaster.The main researches of this paper are as follows:(1)In this paper,24 normal concrete specimens and 72 steel fibre reinforced concrete specimens were subjected to high temperature water jet cooling test and central pullout test with the reinforcement diameter(12mm,14 mm,16mm),temperature(20℃,200℃,400℃,600℃)and the fraction of steel fibre by volume(0%,0.5%,1.0%,1.5%)as parameters.The apparent changes in the specimens after high temperature water jet cooling was observed and recorded.The temperature development trend of the specimens at the center of the bond zone was studied.The relationship between the damaged morphology of the specimens and the three parameters was analyzed.(2)The bond—slip curves under various working conditions were plotted by the data obtained from the central drawing test.The effects of temperature,the fraction of steel fibre by volume and reinforcement diameter on the ultimate bond strength were investigated.The research results showed that under the same conditions of reinforcement diameter and the fraction of steel fibre by volume,the ultimate bond strength was reduced to different degrees with the increase in temperature.Steel fibre reinforced concrete had a smaller reduction in ultimate bond strength than normal concrete.Under the same condition of reinforcement diameter and temperature,the ultimate bond strength increased with the increase in the fraction of steel fibre by volume,and the higher the temperature,the more significant the steel fibre reinforcing effect.Under the same condition of the fraction of steel fibre by volume and temperature,with the increase of reinforcement diameter,the relative rib height and relative rib spacing showed a decreasing trend,and the steel occlusion area and the ultimate bond strength decreased.(3)The calculation formula of the ultimate bond strength of steel reinforcement and steel fibre reinforced concrete after high temperature water jet cooling was developed by considering the influence of the fraction of steel fibre by volume and temperature on the ultimate bond strength of steel fibre reinforced concrete.(4)A suitable model of the bond—slip intrinsic relationship between steel reinforcement and concrete has been selected.The bond—slip constitutive relationship between steel reinforcement and steel fiber reinforced concrete after high temperature water jet cooling was developed by modifying the parameters in the model,considering the effects of temperature and fraction of steel fibre by volume.(5)Finite element simulation of high temperature water jet cooling test and center pullout test of steel fibre concrete specimens was carried out by ABAQUS software.The temperature distribution characteristics inside the specimen during the high temperature water jet cooling process and the development trend were analyzed.The stress distribution in the bonded area of steel reinforcement and steel fibre reinforced concrete was studied to provide a basis for the detailed analysis of the bond—slip of steel reinforcement and steel fibre reinforced concrete. |
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