The Experimental Study On The Mechanical Properties Of HRB500 Reinforced Concrete Beams At Normal Temprature And High Temperature

Reinforced concrete frame structure in the event of a fire,as a major component of reinforced concrete beams under,its internal formation temperature field changes over time,the temperature effect of the concrete section strength of varying degrees of decline,the capacity is reduced,thus influence on the performance of the structure of the support,the increase of reinforcement ratio is helpful to improve the bearing performance.It is necessary to study the mechanical properties of reinforced concrete beams in order to prevent local damage and repair after the fire.Therefore,in this paper,the reinforcement ratio and the fire time as the main influence factors,design the nine root specimen,namely eight grade HRB500 reinforced concrete reinforcement beam and one grade HRB400 steel bar is used to contrast,the research content is as follows:(1)Under the normal temperature of HRB level 500 reinforced concrete optimum reinforcement mechanics mechanism of static test and ordinary reinforced concrete specimen basic same,by contrast,reinforcement ratio lower specimen being bending moment is small steel yield,namely premature damage.The higher ratio of the specimens is the opposite of this.The feasibility of the calculation value of the theoretical formula in the specification of concrete structure design(GB50010-2010)is verified.(2)The temperature of each measurement point in the high temperature sample rises with the rise of furnace temperature,and the whole change law is basically the same.Each measuring point heating rate at 100?,temperature-time curve turning points and with the measuring point height increase gradually shift to the right,and the water molecules in the 100? heat absorption and evaporation results in the decrease of heating rate transient.(3)The longer the fire time,the more serious the damage.Specimens after high temperature,the two points of the most obvious,followed by the bottom of the concrete surface color is white,the crack distribution,local position with honeycomb appeared accompanied by the phenomenon such as concrete,crack.The appearance of this phenomenon is developed from the bottom surface and gradually decreases,and the obvious stratified distribution is seen through the side,which is consistent with the temperature value of the measurement points.(4)After the high temperature effect,the bending moment-deflection curve is significantly different from that of normal temperature,and there is no turning point when the concrete first cracks,entering the fracture work section directly.Due to the temperature crack,the whole process of the experiment is a typical two stage,i.e.The fracture work section and the failure stage after the steel reinforcement yield.(5)Static load failure test shows that the high temperature has obvious influence on the bearing capacity of the specimen,and the carrying capacity of the specimens after the high temperature decreases significantly compared with the normal temperature.Due to the thermal inertia of concrete,the time of fire is nonlinear with the decrease of bearing capacity,and the bearing capacity decreases gradually as the time of fire continues.The average decrease amplitude of the ultimate bearing capacity was 44.47% and 49.0% respectively from 2h to 2.5h.(6)After high temperature test environment,same level HRB500 reinforced concrete specimens of the same reinforcement ratio compared with the contrast of using grade HRB400 reinforced,the bending moments,such as the deflection value is small,show level configuration HRB500 reinforced specimen can enhance flexural rigidity.The remaining carrying capacity of the latter is only 81.9% of the former,indicating the configuration of HRB500 reinforced concrete specimens with strong resistance to fire performance and high residual bearing capacity.(7)Control the single influence factor,that is,compare and analyze the static load failure test with the same ratio of the reinforcement rate,the different high temperature time,the same high temperature time and different reinforcement rate.Reinforcement ratio of the same specimen,after high temperature,its deflection change rate increased,the same deflection deformation under the external load is larger,the length of fire also makes the deflection deformation,show that high temperature bending stiffness reduction.In the same time of fire,the test pieces with higher reinforcement rate have less deflection value under the same bending moment,and have similar mechanical properties with normal temperature specimens.(8)Room temperature specimens bearing capacity calculation method and the principle and the basic similar,after high temperature of specimen ultimate bearing capacity calculation combined in this paper,the single side by the fire,to effectively reduce concrete cross section,and based on the concept of bond stress temperature reduction factor,put forward considering bond-slip performance of reinforced concrete theoretical calculation formula of attenuation.The formula is also applicable to the calculation of bearing capacity at normal temperature and high temperature,and verifies the feasibility of this formula in the actual experiment,which provides theoretical basis for further experimental research.