Abstract
Abstract This article presents an analysis of NBR6118:2014 models used to determine the one-way shear strength in reinforced concrete members without transversal reinforcement. The study compares model predictions with 751 experimental results, taken from the 2015 ACI-DAfStb database and from Quach. Model errors are quantified. Mean values observed are around unity, indicating models with no bias, but coefficients of variation are large. Model error trends are identified with respect to cross-section depth and longitudinal reinforcement rate. In elements with low rate of longitudinal reinforcement and/or large cross-section depths, the normative models provide results with low safety. This shows the need for revision of the normative models. By means of non-linear regression analysis, two correction terms are proposed to consider the longitudinal reinforcement rate and the size effect (decrease in shear strength with increase in section depth). With the proposed corrections, the observed trends are eliminated, and the design equation becomes more accurate with respect to cross-section shear.
Highlights
Designing procedures provided by regulatory codes must be safe, correct in concept, simple to understand, and should not increase design and construction costs unnecessarily
The scientific community does not fully understand all the mechanisms and parameters that govern the problem of shear strength on reinforced concrete members, which incurs in many design codes using empirical equations in their provisions, including the Brazilian code (NBR 6118:2014)
To verify the model’s safety, this paper presented a comparison between model predictions of NBR6118:2014 [16] for one-way shear strength of reinforced concrete members without transversal reinforcement and experimental results compiled from the ACI-DAfStb database [19] and Quach [20], through the analysis of model error variable
Summary
Designing procedures provided by regulatory codes must be safe, correct in concept, simple to understand, and should not increase design and construction costs unnecessarily. The significant amount of research in this topic in the last decades, is evident Such studies allowed a better understanding of the different mechanisms of shear transfer in concrete, as follows [1], [2]: (a) shear transfer at the crack interface, as a result of the resistance to the sliding of the sections, due to the roughness of cracked concrete and aggregate interlock (Va); (b) dowelling action, related to the shear resistance of the longitudinal reinforcement crossing the crack (Vd); (c) arc effect, when the compressed chord inclines towards the support, absorbing part of shear strength and decreasing the traction in the web (Vc); (d) residual tensile stresses after cracking the concrete, transferred directly through the cracks (Vt). Brazilian code (NBR 6118/2014) [16] and EUROCODE 2/2004 [17], use purely empirical formulations to determine the contribution of shear transfer mechanisms [18]
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