Experimental And Theoretical Study On Crack Widths Of Full Scale Reinforced Concrete Beams With HRB500 Bars

HRB500 bar is a new hot rolled ribbed bar with hi-strength and strong ductility, which has been used widely in foreign countries. At present, this kind of steel bar has been taken in by Steel for the reinforcement of concrete—Part 2:Hot rolled ribbed bars (GB 1499.2-2007), and it will be listed in the modifying Chinese Code for design of concrete structures. However, there are not enough experiments to support the properties of HRB500 reinforced concrete members, including ultimate bearing capacity, cracks, deflection. The study can provide theoretic and testing bases for the application of HRB500 bar.Based on the flexural performance experiment of three full scale beams with HRB500 bars and one beam with HRB335 bars, the paper evaluates the applicability of the current standard formula about flexural cracks, deflection and the ultimate bearing capacity in Code for design of concrete structures (GB 50010-2002). The results indicate that the performance of flexural members reinforced with HRB500 bars has the same performance of the common reinforced concrete members, and the beams with HRB500 bars have good bearing performance and present ductile failure. The bearing capacity of the flexural members with HRB500 bars can be calculated by the formula for cross-section in the current standard, which is safe enough when f y = 430MPa.The crack behaviors under the state of serviceability are mainly studied in this paper. The average crack spacings and maximum crack widths of the members with HRB500 bars are less than the calculated values, and all of the maximum crack widths exceed the allowable crack width. The HRB500 bars'strength will not be used sufficiently if the maximum crack widths of these members just meet standard requirements. Therefore, it's suggested that the allowable crack width should be broadened and the checking computation to the crack width should be strengthened. All the deflections under the state of serviceability don't exceed the allowable value of deflection. The deflections of the members with HRB500 bars are close to the allowable value of deflection, while to the members with HRB335 bars are far less than it. Therefore, it should stick to check the deflection of the concrete beams with high-strength bars.The influence of dρte and concrete cover thickness on crack width is analyzed in this paper. A formula of the maximum crack width is given, which is based on a reasonable crack model.