Additionally, this ratio decreased at higher stress levels. The ratio of maximum to average crack width was observed to be slightly less than that commonly associated with conventional 414 MPa (60 ksi) reinforcing steel. These results were confirmed by comparison to available experimental data. The results were relatively insensitive to changes in reinforcing ratio. Reinforcing ratio p = 0.01 or higher, regardless of reinforcing grade, the crack width and crack spacing will be similar.īased on this study, it can be concluded that through reinforcing bar stresses of 496 MPa (72 ksi), average crack widths remain below 0.43 mm (0.017 in.) for cases having p < 0.02 and for all but the largest bars considered. 7 Measured crack widths with longitudinal reinforcing bar stress forflexural beams (1 MPa = 145 psi 1 mm = 0.03937 in. In all cases considered, for reinforcing ratios p = 0.01 and higher, cracks form at bar stresses below 482 MPa (70 ksi). As the reinforcing ratio becomes larger, cracking remains distributed but crack widths may be expected to be more uniform since cracking stresses vary very little. Whereas for typical reinforcing ratios (0.01 and 0.015), cracking occurs in a more progressive manner and is better distributed, and hence some variation in crack width along the member should be expected. As the reinforcing ratio falls, the behavior becomes dominated by a small number of large cracks. 2011).īased on a parametric study on crack widths, it is shown that crack development and spacing are affected by bar sizeĪnd the effective concrete area surrounding the reinforcement. A limitation on service-level stresses of f < 414 MPa (60 ksi) is recommended this is consistent with a related recommendation thatf < 689 Mpa (100 Ksi) (Shahrooz et al. Table 2 Details of flexural beam specimens F1-F6 (Shahrooz et al. This conservativeness allows present specifications to be extended to the anticipated higher service level stresses associated with the use of high strength reinforcing steel. (19 mm)] in the lowermost layer thus, crack control reinforcing would be considered excellent for these beams.Ĭonsidering the measured crack widths in this experimental study, it appears that the existing equations are inherently conservative. It is noted that all 305 mm (12 in.) wide beams had four bars [#5 (15.9 mm) or #6 Crack width is largely unaffected by the reinforcing ratio within the range considered. Indeed, with the exception of beam F2, maximum crack widths also fall below this threshold through bar stresses of 496 MPa (72 ksi). 7 clearly show that at rational service load levels f < 496 MPa 72 ksi), average crack widths are all below the present AASHTO de facto limit of 0.43 mm (0.017 in.). Predicted crack widths from parametric study. In this case, the bond stress distribution along the length of the reinforcement corresponding to the tension force will be in a new form in which the angle of the descending branch, a, decreases (in Fig. A limitation on service-level stresses off L1. Additionally, based on the results of available flexural tests, crack widths at service load levels were evaluated and found to be within presently accepted limits for highway bridge structures, and were predictable using current AASHTO provisions. A parametric study investigating crack widths and patterns in reinforced concrete prisms is presented in order to establish limits to the service-load steel stress and strain. Consequently, the service-load steel strains are greater affecting cracking behavior. (Received January 29, 2013, Accepted August 16, 2013)Ībstract: A major difference between high-strength reinforcing steel and conventional steel in concrete is that the service-load steel stress is expected to be greater. International Journal of Concrete Structures and Materials Vol.7, No.4, pp.253-264, December 2013 DOI 10.1007/s4006-z ISSN 1976-0485 / elSSN 2234-1315Ĭrack Opening Behavior of Concrete Reinforced with High StrengthĪmir Soltani1^*, Kent A.
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