Strut and Tie Models with elastic reinforcement

带弹性加固的支柱和拉杆模型

• 批准号: 495079204
• 负责人: Professor Dr.-Ing. Mike Schlaich
• 金额: --
• 依托单位: Fachgebiet Entwerfen und Konstruieren - Massivbau
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/495079204?language=en
• 关键词: Strut; Tie; Models; elastic; reinforcement

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.

研究项目的目的是研究钢筋混凝土（RC）结构中弹性增强不连续区域（d区）的变形和承载行为。它的目的是提供一个关于支撑和拉杆模型（STM）方法对这些类型的rc结构的适用性的合格声明。由于可持续性和耐久性在建筑工业中的重要性日益增加，人们对无腐蚀性纤维增强聚合物增强材料（frp增强材料）的兴趣越来越大。为了充分利用这种线弹性钢筋的潜力，全面了解这种钢筋截面的承载行为是必不可少的。这就是被唤起的项目的相关性。STM方法将高度不确定的d区复杂内力分布理想化为一个自由的理想桁架。它基于塑性下界定理，根据该定理，假设材料具有弹理想塑性或刚塑性的特性，任何可以规定其稳定的静容许应力状态的载荷都不高于承载载荷。由于应力和变形的解耦，无论载荷如何，STM的倾角都可以假设为恒定的。这样就满足了对稳定平衡的要求。在应变依赖的材料行为（线弹性钢筋）的情况下，力产生应变。这些引起节点区域的旋转，从而导致STM内力的增长。因此，不能达到所要求的稳定应力状态。为了保证稳定的平衡，需要验证STM内旋转的兼容性。应变不能引起倾角的变化。严格来说，这也适用于RC截面。实际上，钢表现为应变硬化，而混凝土在较大应变下表现为应变软化。根据文献，限制混凝土的强度和“熟练”选择内部承重系统（STMs）是为了确保假设的应力分布仍然可以发生。对STM旋转能力的评估不仅允许将STM方法扩展到弹性钢筋混凝土截面，同时也缩小了钢rc混凝土的现有定义差距。其思想是将相关节点的复杂承载机制简化为利用几何储备和多轴应力状态。通过对离散压缩节点的水平应力场逐渐变细来描述旋转能力是一种很有前途的方法。通过向外移动压缩杆的合力，可以在不改变倾斜角度的情况下吸收应变。通过一系列不同节点几何形状的实验验证了该方法的有效性。