Reliability Research On Limit State Of Reinforced Concrete Beams With HRB500 Bundled Steel Bars

With the high-rise,large-span construction in China's construction more and more,in the force of the concentrated parts due to reinforcement are more intensive,and usually use the bundled bars in these area.The state in the Code for design of concrete structures to promote the use of high-strength steel as a bearing force reinforced.The flexural bearing capacity,the crack width and the deflection of the reinforced concrete beams are affected by the high-strength steel and the bundled bars,and then affecting the reliability of the beams.Therefore,this paper will focus on the bearing capacity limit state and the serviceability limit state of the reinforced concrete beams with HRB500 bundled steel bars.In this paper,the experimental data of bending bearing capacity,crack width and deflection are collected and analyzed,and the change of bending bearing capacity,crack width and deflection of reinforced concrete beams with bundled bars are analyzed statistically.The working load,the model of calculation,the geometric size and material property will be treated as random variables,the sensitivity coefficients of each random variable are obtained by means of the checking point method,and the random variables are quantitatively analyzed according to the size of the sensitivity coefficient,and preliminary judgment the size of the influence by the bundled bars and the high-strength steel on the random variables.Then,the reliability index of the structural under different influence of random variables is calculated by means of the checkpoint method.The influence of the random variables on the structural reliability and the influence of the HRB500 steel bars and the bundled bars on the structural reliability are analyzed concretely.The conclusions are as follows:(1)In the study of the reliability of bundled bars in reinforced concrete beam based on the flexural bearing capacity limited state,the results show that: compared with ordinary steel,HRB500 bars has little effect on the reliability.And the bundled bars have a negative effect on the reliability of the flexural bearing capacity limited stated of the reinforced concrete beams,and the adverse effects of the bundled bars should be taken into account when calculating the flexural bearing capacity.(2)In the sensitivity study of the beam based on the maximum crack width and the deflection,the results show that: the influence of the load ratio on the reliability indexof the crack width and the deflection is the largest,and the load ratio plays a decisive role in the reliability index of the crack width and the deflection.The influence of the calculation model uncertainty coefficient is the second.The influence of the concrete strength grade,the thickness of the concrete protective layer,the crack limit,the deflection limit is small.(3)In the study of the reliability of the beam based on the maximum crack width and the deflection,the results show that: the reliability index of the beam with the bundled bars is higher than that of the ordinary beam,and reinforced concrete beams with bundled bars according to China's current Code for design of concrete structures of the maximum crack width and deflection calculation formula.