Calculation method for crack width of reinforced UHPC flexural components
Qiu Minghong1,2 Shao Xudong1,2 Hu Weiye1,3 Zhao Xudong1,2 Wang Yan1,2
1. College of Civil Engineering, Hunan University, Changsha 410082, China;
2. Hunan Province Key Laboratory of Wind and Bridge Engineering, Changsha 410082, China；
3. Zhejiang Provincial Institute of Communications Planning,Design and Rosearch Co.,Ltd.,Hangzhou 310013,China
In order to establish the method for calculating the crack width of reinforced UHPC flexural components, the four-point bending tests on six beams of reinforced UHPC were carried out, and the development and distribution of cracks in the test beams were investigated. Based on the experiments, the applicability of crack width formula in the existing design specification to predicting the crack width of reinforced UHPC flexural components was evaluated. In addition, the calculation method of rebar's stress in the reinforced UHPC flexural members considering the contribution of tensile strength of UHPC as well as the prediction formula for crack width of UHPC were proposed. Furthermore, the applicability of the proposed crack width formula was verified by97 sets of effective crack width results from 16 UHPC beams in China. The results showed that: ① When the surface crack width of UHPC beam was less than 0.25mm, the crack width appeared to propagate linearly, the number of cracks continuously increased, and the spacing of cracksgradually decreased; when the crack width exceeded 0.25mm, however, the crack width rapidly increased so that the main crack was formed, the number of cracks remained basically unchanged, and the crack spacing tended to be stable. Additionally, the cracks in UHPC beams were narrow and densely distributed, and with the multiple-cracking behavior. ② For the crack width of reinforced UHPC flexural components, quite large deviations between the test results and calculated results by referring to the code of GB 50102010 and CECS 38—2004. ③ Based on the material properties of UHPC, a calculation method for the rebar's stress in the cracked section of the UHPC flexural members, which considers the UHPC tensile behavior and can predict the rebar's stress in the cracked section very well, was proposed. ④ Based on the test results and analysis, the average crack spacing, the uniformity coefficient of steel strain and the characteristic coefficient of the component specified in the code of GB 50010—2010 were modified, and the formula for calculating the crack width of UHPC flexural members was given. The calculated results from the modified formula agreed well with the experimental results, exhibiting smaller deviations when comparing to the predicted results from French UHPC code. ⑤ The average value for the ratios of the predicted crack width to the experimental crack width from the experimental database on the crack width of UHPC was 099, and its standard deviation was 0.19, indicating the good applicability of the proposed formula. Therefore, the proposed calculation method for crack width can be referred to by the UHPC structural design code.
