Experimental Study on the Load Bearing Behaviour of Textile Reinforced Concrete under Uniaxial Compression – Phase II: Influence of Lateral Compression and Tension

申请人的调查表明，纺织格栅对纺织钢筋混凝土(TRC)受压性能的影响是不可忽视的。除了纺织品的影响，测试表明，即使是手工层压的制造过程，也会对试件的最大强度产生负面影响。此外，层向加载方向对混凝土强度有显著影响。对于TRC试件，未加固试件的各向异性性能更强。在这里，纺织平面取向的变化甚至会导致不同的破坏模式。如果纺织品平行于加载方向对齐，则会发生脆性破坏。另一方面，纺织品与加载方向垂直对齐将产生相当大的延展性。这些差异可能是由于两种对立的机制造成的。一方面，纺织品起到了不连续的作用，因为它们不能传递任何垂直于其纵向的压应力。这会导致试件中的应力场发生变化。这些扰动会对混凝土产生额外的拉应力，从而导致加速破坏。另一方面，纺织品产生侧向约束，在加载过程中稳定试件。这些机制控制着材料的行为和失效模式，特别是当纺织品垂直于加载方向对齐的时候。不同参数的变化，如层间距、纱线直径、网目大小或使用相互错开的纺织层，都表明了不同的影响因素对TRC在压缩下的材料性能。所有试验的结果是，单一参数对强度和各向异性的影响随着层间距的增加而减小。有待解决的是将所得结果转化为实际构件的问题。解决方案的第一步是在项目的第二阶段，通过研究TRC在压缩-压缩和压缩-拉伸载荷下的双向材料性能来进行，因为在大多数结构构件中，存在多轴应力状态，例如在梁上，暴露在剪切或扭转载荷下。计划试验应主要考察以下参数的影响：纺织增强材料的种类、制造工艺和不同的应力比。单轴和双向试验的结果被认为是数值材料模型对大型混凝土构件(如梁或柱)进行虚拟参数研究的基础。数值计算的目的是减少对这种混凝土构件的试验次数，这些试验相当复杂和昂贵，但对于在第三个资金期验证工程模型是必要的。

Investigations of the applicant show that the influence of textile grids on the load-bearing behaviour of textile reinforced concrete (TRC) under compression is not negligible. In addition to the impact of textiles, the tests showed that even the manufacturing process by manual lamination affects the specimen’s maximum strength negatively in regard to casted ones. Furthermore, the orientation of the layers to the loading direction has a significant influence on the concrete strength. The anisotropic material behaviour of unreinforced specimens, which were manufactured layer by layer, is even stronger for TRC specimens. Here, the variation of the orientation of the textile plane leads even to different failure modes. If the textiles are aligned parallel to the loading direction, a brittle failure occurs. On the other hand, a perpendicular alignment of the textiles to the loading direction will cause a quite ductile behaviour. These differences are probably due to two opposing mechanisms. On the one hand, the textiles act as a discontinuity, because they cannot transfer any compressive stresses perpendicular to their longitudinal direction. This causes diversions in the stress field in the specimen. These disturbances induce additional tensile stresses into the concrete, which lead to an accelerated failure. On the other hand, the textiles cause a lateral constraint, and stabilize the specimens during the loading process. These mechanisms dominate material behaviour and failure mode especially if the textiles are aligned perpendicular to the loading direction. The variation of different parameters, like layer spacing, yarn diameter, mesh size or the use of textile layers located offset from each other showed the various impact factors on the material behaviour of TRC under compression. A result of all tests is that the influence of the single parameters on the strength and the anisotropy decreases with a taller layer spacing.What is open is the question of the transferability of the findings of the obtained results to practical components. A first step towards the solution is to be carried out in the second phase of the project by investigating the biaxial material behaviour of TRC under compression-compression and compression-tension loads, because in most of the structural members, there is a multiaxial stress state, e.g. at beams, which are exposed to shear or torsional loads. The planed tests should mainly investigate the impact of the following parameters: kind of textile reinforcement, manufacturing process and different stress ratios. The results of the uni- and biaxial tests are supposed to be a basis for a numerical material model to conduct virtual parameter studies on large-scale concrete members, like beams or columns. The goal of the numerical calculations is to reduce the number of test on such concrete members, which are quite complex and expensive, but necessary for validation of an engineering model in a 3rd funding period.