Shear strength analysis of slabs without transverse reinforcement under concentrated loads according to ABNT NBR 6118:2014

Abstract Concentrated loads in slabs without transverse reinforcement, usual in highway bridges, result in the horizontal spreading of the shear force towards the supports, situation in which not all the slab width contributes in the shear strength. Based on this, the analytical models of shear strength and punching capacity in slabs may not be suitable to deal with this loading. Since this topic is not widely discussed in the national technical literature, the paper aims to present contributions to these analyses with a focus on the accuracy level of the shear strength analytical models recommended by ABNT NBR 6118:2014. Therefore, the models available in the Brazilian code were applied to an experimental database with 118 test results and the results obtained by the Brazilian and European codes were compared. The results demonstrated that, as presented in the Brazilian code, shear strength model in one-way slabs can lead to unsafe resistance predictions while the punching capacity model can lead to very conservative predictions. From the analysis, it is concluded that considering the reduction of the shear force, in the case of loads distributed in small areas close to the support in slabs, and the use of more suitable procedures to define the effective width, it is possible to improve the level of accuracy of relations between experimental and theoretical values, but this still leads to high percentages of unsafe predictions of resistance (> 40%).摘要：无横向配筋的板内集中荷载常见于公路桥梁，此类荷载会使剪力向支座方向水平扩散，此时并非全板宽均可参与抗剪强度贡献。基于该工况特性，现有板件抗剪强度与冲切承载力的解析模型或不适用于此类荷载情形。由于该主题在巴西国内技术文献中尚未得到广泛探讨，本文旨在针对此类分析展开研究，重点聚焦ABNT NBR 6118:2014推荐的抗剪强度解析模型的精度水平。据此，本文将巴西规范中收录的模型应用于包含118组试验数据的试验数据库，并对比了巴西规范与欧洲规范的计算结果。研究结果表明，按照巴西规范的规定，单向板的抗剪强度模型可能得出不安全的承载力预测结果，而冲切承载力模型则会给出过于保守的预测值。经分析可得，针对板件支座附近小范围分布荷载的工况，若考虑剪力折减并采用更合理的有效宽度确定方法，可提升试验值与理论值之间关联关系的精度，但此类修正仍会导致较高比例的不安全承载力预测（占比超40%）。