Estudo comparativo de modelos de cisalhamento para elementos de concreto armado com seções circulares cheias e vazadas

Abstract

In the design of reinforced concrete structures, the analysis of shear strength is an essential step to ensure the safety and durability of the structure. Although most of the technical standards, such as NBR 6118 (2023), provide models for evaluation of the shear strength of rectangular cross-sections, specific guidelines for the cases of circular cross-sections, widely used in engineering applications, in general, are not reported. To overcome this gap, some international codes and standards use simplified methods based on those developed for rectangular crosssections, introducing adequacy parameters to define fictitious dimensions, such as, effective depth 𝑑 and the width 𝑏௪. Different theoretical approaches and experimental works are available in the literature aiming to evaluate the individual contributions of concrete and transversal reinforcements to the shear strength of elements with circular cross-sections. However, a consensual conclusion on the best model for evaluating such contributions does not exist yet. In this context, the present work aimed to analyze the performance of existing models for predicting the shear strength of reinforced concrete elements with solid and hollow circular cross-sections, subjected to simple bending and flexo-compression. Additionally, the performance of both circular and spiral stirrups for such cross-sections was also assessed. For this end, a bibliographical review of existing prediction models was carried out, followed by the construction of a large database from 291 tested specimens available in the literature, for comparative analysis between theoretical and experimental values. Electronic spreadsheets were used to automate the calculations of the selected models. A descriptive statistical analysis was conducted, covering measures of central tendency, variability, and error metrics. Graphic representations, such as box plots and radar charts, were employed for result visualization. Normality and hypothesis tests were applied to evaluate the statistical significance and adequacy of the models to the experimental data. Based on the statistical analyses, it is observed that, in general, the theoretical results presented non-negligible discrepancies in relation to the experimental data, although the predictions of some models showed good adherence in relation to the experimental results. Also, it is worth noting that, even though most of the models exhibited conservative results, some of them provided unsafe shear strength values. In summary, there is a need to carry out more theoretical and experimental studies aiming at a more accurate representation of the shear strength behavior of circular reinforced concrete sections, improving the design guidelines for those structural elements and contributing to scientific and practical discussions in the corresponding field of knowledge.