| HRB600 steel bar is a new type of high-strength steel bar,which has the characteristics of good ductility,high strength and excellent welding performance.It has been widely used in practical engineering abroad,but the main steel bar used in my country is still ordinary strength steel bar.For HRB600 steel bar and There are only a few research results on the mechanical properties of its concrete structures,and no scholars have been involved in the research on the fire resistance of its concrete structures.Fire is still one of the serious disasters faced by building structures.Therefore,it is urgent to carry out research on the fire resistance of HRB600 steel bars and their concrete structures,and to have an in-depth understanding of the mechanical properties of HRB600 steel bars and their concrete structures after fire.And practical significance.For this reason,this paper carried out the uniaxial tensile test of HRB600 steel bar after high temperature and the bending performance test of HRB600 reinforced concrete beam,and analyzed the influence of different temperature on the mechanical properties of HRB600 steel bar and its concrete beam.The main research contents of this paper are as follows:(1)The uniaxial tensile test was carried out on the three strength grades of steel bars(HRB400,HRB500 and HRB600)after experiencing different high temperatures.The stress-strain curves of the three steel bars after high temperature were measured,and the yield strength and ultimate strength were analyzed.Modulus of elasticity and elongation and other mechanical properties change with different temperatures.The results show that when the temperature is less than 500℃,the mechanical properties of the three types of steel bars have no significant changes;when the temperature is greater than 600℃,the yield strength and ultimate strength of the three steel bar strength grades decrease sharply,while the elongation rate increases sharply.The modulus of elasticity decreases slightly with the increase of temperature.Finally,this paper conducts regression analysis on the test data,and puts forward the formulas for calculating the elastic modulus,yield strength,ultimate strength and maximum elongation of HRB600 steel bars after different temperatures.(2)Four plain concrete beams were subjected to fire tests on three sides,and the changes of temperature at different positions of the concrete beam section with time and the damage of the concrete beams after experiencing different high temperatures were studied.The results show that the color of the concrete beam changes from gray-blue to gray-white after experiencing high temperature;the higher the temperature experienced,the larger the crack width of the concrete beam;with the increase of the constant temperature time,the maximum temperature of each measuring point in the beam continues to increase,But the growth rate has slowed down compared with that in the heating process,and the temperature difference has gradually decreased.(3)Four HRB600 reinforced concrete beams subjected to different high temperatures and one HRB600 reinforced concrete beam at room temperature were subjected to bending tests.The bending performance of HRB600 reinforced concrete beams after different high temperatures was studied,and the beam’s performance was analyzed.Crack development,deflection,flexural capacity and failure mode.The results show that as the temperature increases,the number of cracks in the beam and the height of the cracks decrease.The ultimate bearing capacity of the beam after200℃,400℃ and 600℃ is not much different from the ultimate bearing capacity at room temperature;the ultimate bearing capacity of the beam after 800℃ decreases by 12.5% compared with room temperature,and the initial stiffness is significantly reduced.(4)Using ABAQUS software to numerically simulate the flexural performance of HRB600 reinforced concrete beams after high temperature.The simulation results are in good agreement with the test results.The load-deflection curve obtained by the numerical simulation is basically consistent with the curve obtained from the test.The bearing capacity is relatively close to the test value. |
