Strut and Tie Models with elastic reinforcement

本研究的目的是研究钢筋混凝土结构中弹性配筋不连续区域(d区)的变形和承载性能。由于耐久性和耐久性在建筑业中的重要性日益重要，无腐蚀性纤维增强聚合物加固(FRP加固)越来越受到人们的关注。为了充分发挥这种线弹性加固的潜力，全面了解这种加固截面的受力性能是必不可少的。STM方法将高度不确定的d区域的复杂内力分布理想化为自由理想桁架。它是建立在塑性下限定理的基础上的，根据该定理，假设弹塑性或刚塑性材料的行为，任何可以指定稳定的静态允许应力状态的载荷都不高于轴承载荷。由于应力和变形的解耦，可以假定STM中的倾角是恒定的，而不考虑载荷。这样就满足了稳定平衡的要求。在依赖于应变的材料行为(线弹性增强)的情况下，力产生应变。这会导致节点区的旋转，从而导致STM内的力的增长。因此，无法达到所需的稳定应力状态。为了确保稳定的平衡，需要验证STM内旋转的兼容性。应变不能引起倾角的变化。严格地说，这也适用于RC横截面。在现实中，钢表现出应变硬化，而混凝土在更大的应变下表现出应变软化。根据文献，限制混凝土的强度和巧妙地选择内部承载系统(STM)是为了确保假设的应力分布仍然可以发生。对STM转动能力的评估不仅可以将STM方法推广到弹性钢筋混凝土截面，同时还可以缩小现有的钢筋混凝土-型钢混凝土的定义差距。其思想是将相关节点复杂的承载机理简化为利用几何储备和多轴应力状态。用离散压缩节点的水平应力场锥化来描述旋转能力是一种很有前途的方法。通过将受压支柱的合力向外移动，可以在不改变倾角的情况下吸收应变。通过几组不同节点几何形状的实验，验证了该方法的有效性。

The object of the research project is the investigation of the deformational and loadbearing behavior of elastically reinforced discontinuous regions (d-regions) in reinforced concrete (RC) structures. It aims to provide a qualified statement about the applicability of the method of strut and tie models (STM) for these types of RC-structures.Due to the growing significance of sustainability and durability in construction industry, there is an increasing interest in noncorrosive fiber-reinforced-polymer-reinforcement (FRP-reinforcement). In order to fully exploit the potential of this linear elastic reinforcement, a comprehensive understanding of the loadbearing behavior of such reinforced cross-sections is essential. Herein lies the relevance of the evoked project.The STM method idealizes the complex internal force distribution of the highly indeterminate d-regions into a free ideal truss. It is based on the lower bound theorem of plasticity, according to which, assuming elastic-ideal plastic or rigid-plastic material behavior, any load for which a stable statically permissible state of stress can be specified is not higher than the bearing load. Due to the decoupling of stresses and distortions, the angles of inclination in the STM can be assumed to be constant regardless of the load. The requirement for a stable equilibrium is thus fulfilled.In the case of strain-dependent material behavior (linear elastic reinforcement), forces generate strains. These cause rotation in the nodal zones, which results in a growth of the forces within the STM. Therefore, the required stable stress state cannot be achieved. In order to ensure a stable equilibrium, the compatibility of the rotation within the STM need to be verified. The strains must not cause a change of the inclination angles.Strictly speaking, this also applies to RC cross-sections. In reality, Steel exhibits strain-hardening whereas concrete presents strain-softening at larger strains. According to the literature, limiting the strength of concrete and the "skillful" choice of the internal load-bearing system (STMs) is intended to ensure that the assumed stress distribution can still occur. An assessment of the rotational capacity of the STM not only allows the extension of the STM method to elastically reinforced concrete cross-sections, but also closes the existing definition gap for steel RC-concrete at the same time. The idea is to reduce the complex load bearing mechanisms of the relevant nodes to the utilization of geometric reserves and multi-axial stress states. The description of the rotational capacity by tapering the horizontal stress fields in the discrete compression nodes is a promising approach. By shifting the resultant force of the compression struts outwards, strains can be absorbed without changing the angle of inclination. Validation of this approach is carried out in several series of experiments with different nodal geometries.