Actively controlled temperature induction to strengthen reinforced concrete structures

许多现有的钢筋混凝土结构需要加强。这样做的典型动机是针对增加的负载进行升级，例如由于交通或由于额外的服务负载而发生在桥梁上的负载。附加加固的关键问题和基本限制是，如果没有临时提升或预应力，它对自重无效。因此，只有服务荷载按比例分配给现有结构和新放置的加固。这对于自重通常高达70%左右的钢筋混凝土结构尤其有害。在此，提出了一种全新的方法来解决这一问题，即在局部温度感应过程中安装附加钢筋。这种方法对梁和板都有效。它以快速硬化高性能混凝土（HPC）为复合材料在槽内插入额外的钢筋，从而补充现有的钢筋，从而提高了弯曲承载能力。其核心思想是通过系统加热，将现有的预应变诱导到额外的钢筋上，从而使两者的应变平衡。然后，两种增强筋作为一个真正的单元一起作用，增加了承重能力和限制裂缝宽度。局部的热量输入必须严格限制在预拉伸和快速硬化所需的槽内。相比之下，总截面的加热将减少额外钢筋的拉伸，因此是不可取的。因此，归纳需要精确的时间和空间控制。在该项目中，温度感应在建模（数字孪生）和相应的实验之间以通用和交互的方式开发。这是在规模（实验）和方法扩展（模型建立）方面连续进行的。建模从数学系统、致动器和传感器位置的描述开始，并由此发展热固化及其热-机械耦合的控制和优化。结果是一个基于模型的顺序控制概念，具有一个能够实现瞬态温度和应变曲线的观测器。在材料层面确定了必要的热参数，并对复合材料的快速硬化和蠕变进行了实验研究。在构件层面，确定了热垫和红外散热器的净温度输入，并研究了热-机械耦合，以实现必要的预应变和减少不必要的二次裂纹。最后，将模型与实验相结合，形成一个仪器完备的大型验证样机。为此，典型的钢筋混凝土板应加强以承受其使用荷载的两倍。在这个演示器上，所有的开发都是按比例实施和评估的。

Many existing reinforced concrete structures need to be strengthened. The typical motivation for this is an upgrade against increased loads such as those that occur on bridges due to traffic or on buildings due to additional service loads.The key issue and fundamental limitation of additional reinforcement is that it is not effective for self-weight without temporary lifting or pre-stressing. Thus, only service loads are proportionately distributed to the existing structure and the newly placed reinforcement. This is in particular detrimental with respect to reinforced concrete structures, in which the self-weight usually amounts up to around 70%.Here, a completely new method is proposed to solve this problem, namely installing of additional reinforcement during local temperature induction. This method works for both, beams and plates. It increases the bending load bearing capacity by additional reinforcement inserted into slots with fast hardening high-performance concrete (HPC) as a composite and thus supplements the existing reinforcement.The core idea is to induce the pre-strain of the existing to the additional reinforcement by systematic heating, and thus to equalize both strains. Then, the two reinforcements act together as a real unit regarding both, increased load-bearing capacity and limited crack widths. Locally, the heat input must be strictly limited to the slots where it is necessary for pre-stretching and rapid hardening of the HPC. By contrast, heating of the total cross-section would reduce the stretching of the additional reinforcement and is hence undesirable. Induction therefore requires precise temporal and spatial control. In the project, temperature induction is developed in a generic and interactive way between modelling (digital twin) and corresponding experiments. This is performed consecutively with respect to size scale (experiment) and methodological extension (model building). Modelling starts from the description of the mathematical system and the actuator as well as sensor placements and develops the control and optimization of the thermal curing and its thermo-mechanical coupling from this. Outcome is a model-based concept of sequential control with an observer that is able to realize transient temperature and strain profiles. On material level necessary thermal parameters are identified while rapid hardening of HPC and creeping of the composite is investigated experimentally. On component level, the net temperature input from thermal mats and infrared radiators is determined and the thermo-mechanical coupling is investigated to achieve the necessary pre-strain and to reduce undesired secondary cracks. Finally, model and experiment are combined to a fully instrumented large-scale demonstrator. For this purpose, a typical reinforced concrete slab shall be strengthened to carry twice its service load. On this demonstrator all developments are implemented and evaluated true to scale.