Crack spacing has been identified as an important parameter in predicting the crack widths in reinforced concrete (RC) structures. An experimental program has been conducted to investigate the crack spacings when reinforced concrete beams are subjected to both axial tension and flexure. The stochastic nature of cracking behavior makes the experimental program complicated. A large sample size of the crack spacing data was recorded, in order to give a statistical overview. Recent studies in the literature were used to verify the experimental results. The existing crack spacing prediction models have been developed based on different theoretical approaches, namely bond-slip, no-slip, and combined approaches. In this study, Eurocode 2, Model Code 2010, Japanese Code, Eurocode 2 with German Annex and Beeby's crack spacing models were selected, as they represent each theoretical approach. Experimental results of this study and from selected literature were compared with the aforementioned prediction models. Japanese Code gave better predictions for axial tensile tests. For the four-point bending test, all the calculation models gave good agreement with the results, except for Eurocode 2 with German Annex.
Cracks due to the service load in the reinforced concrete structures are controlled at the design stage, by limiting the calculated crack width. Widely used crack width calculation models (Eurocode 2 and Model code 2010), estimates the crack width by multiplying the crack spacing with the mean strain difference of concrete and reinforcement. Concrete cover thickness and the ratio of diameter to reinforcement area to effective tensile area of concrete (∅/ρp,ef) are the two main crack spacing governing parameters in the aforementioned models. The existing models are mostly applicable when concrete cover thickness is within the specified limit. For example, Model Code 2010 model limits the concrete cover thickness to 75 mm. In order to identify the influence of aforementioned two governing parameters on crack spacing, the results of recent experiments have been considered. According to some recent studies, it is found that the concrete cover thickness has a significant influence and the ∅/ρp,ef parameter has a negligible effect on crack spacing. To investigate the reasons why the ∅/ρp,ef parameter has a negligible effect on crack spacing, the involvement of bond properties is needed to study. Some authors have specified that the large diameter bars consist of higher bond force per unit surface area than the small diameter bars, due to the high rib area. Due to this reason, the similar bond behavior could be identified, from low number of large bar diameters and high number of small diameter bars. A literature review has been carried out to study the bond behavior on specimens subjected to pure tension. With the facts and available data, it is further verified that the ∅/ρp,ef parameter has a negligible influence and concrete cover thickness has a significant effect on crack spacing.
Crack spacing is a governing parameter in widely used crack width calculation models. Axial tensile experiments are conducted to examine the crack spacing behavior of reinforced concrete specimens with multiple reinforcement bars. To reduce the time, cost, and labor of the experiments, nonlinear finite element simulations are widely used. In this study, 3D non‐linear finite element simulation models have been developed with the smeared cracking approach to predict the average crack spacings. These models are calibrated and validated using both the experiment conducted by the authors and an experiment given in the literature. The governing crack spacing parameters have been identified as concrete cover thickness and clear distance between tensile bars. After conducting a series of 3D nonlinear finite element method simulations with the calibrated model, an equation is developed to predict the average crack spacings using multiple linear regression analysis. The validity of the proposed crack spacing equation has been checked with 18 recent experimental results in the literature. The proposed crack spacing equation gives a good agreement with the results of these experiments.
Widely used crack width calculation models and allowable crack width limits have changed from time to time and differ from region to region. It can be identified that some crack width calculation models consist with limitations for parameters like cover thickness. The current Norwegian requirement for cover thickness is larger than these limitations. The applicability of existing crack width calculation models and the allowable crack width limits must be verified for structures with large cover thickness. The background of crack width calculation models in Eurocode, Model Code 2010, Japanese code, American code and British code have been examined. By comparing the experimental crack widths with the predictions of the aforementioned models, the existing codes can be identified as requiring modification. Considering the durability aspect, it can be identified a long-term study proving that the allowable crack width can be increased with the increase in cover thickness. When considering the aesthetic aspect, the authors suggest categorizing the structures based on their prestige level and deciding the allowable crack widths accordingly. The paper proposes potential solutions for future research on how to improve both crack width calculation methods and allowable crack width limits to be used effectively in structures with large cover thickness.
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