Numerous studies have shown that adding steel fibers to the concrete mixture improves both the shear strength and ductility of reinforced concrete beams. Most current shear design formulations for steel fiber reinforced concrete beams are empirically based and their predictions provide acceptable results when compared with tests results, but only in limited ranges of the parameters involved. On the other hand, many shear theoretical models suggested in the literature are derived by extending previous formulations for conventional reinforced concrete beams, just introducing the stresses transferred across the critical shear crack. Since the effects of steel fibers on the others shear resisting mechanisms are not accounted for, “adjusting” empirical factors must be used to fit the experimental results. There is, therefore, the need for developing mechanical models capable to rationally account for the effects of steel fibers on the global shear strength and on each shear resisting mechanisms. In this paper, the previously derived and validated Multi Action Shear Model for RC elements is extended to steel fiber reinforced concrete beams without stirrups. The effects of steel fibers on each resisting mechanism have been identified and incorporated in the formulation of each shear component and in the Multi-Action Shear Model equilibrium equations. The residual tensile stresses of fibrous concrete, obtained through a simple formulation, has been used to: capture the enhancement of the compression chord contribution; the shear transferred by bridging effect of the fibres along the critical shear crack and by dowel action. The proposed model is shown to properly estimate the shear resistance of a large set of available test data, being able to account for most influencing parameters, like fibers types and amounts, concrete strength, longitudinal reinforcement ratios and beam geometry.

中文翻译：

---

无箍筋钢纤维混凝土 (SFRC) 梁抗剪强度的力学模型

大量研究表明，在混凝土混合物中加入钢纤维可提高钢筋混凝土梁的抗剪强度和延性。目前大多数钢纤维混凝土梁的剪切设计公式都是基于经验的，与测试结果相比，它们的预测提供了可接受的结果，但仅限于所涉及的参数范围有限。另一方面，文献中提出的许多剪切理论模型是通过扩展传统钢筋混凝土梁的先前公式推导出来的，只是引入了跨临界剪切裂缝传递的应力。由于钢纤维对其他抗剪机制的影响没有考虑在内，因此必须使用“调整”经验因素来拟合实验结果。因此，有 需要开发能够合理解释钢纤维对整体剪切强度和每种抗剪机制的影响的机械模型。在本文中，先前推导出和验证的 RC 元件多作用剪切模型扩展到没有箍筋的钢纤维混凝土梁。钢纤维对每种抗力机制的影响已被确定并纳入每个剪切分量的公式和多作用剪切模型平衡方程中。通过简单的公式获得的纤维混凝土的残余拉应力已被用于： 捕捉压缩弦贡献的增强；通过纤维沿临界剪切裂纹的桥接效应和销钉作用传递的剪切力。