Thermally controlled prestressing of bonded steel lamellae for the strengthening of slab structures using the example of reinforced concrete bridges

转让项目是基于研究项目“主动控制温度感应加固钢筋混凝土结构”（项目编号458161128），该项目自2021年底开始运行。该转移项目涉及钢筋混凝土板结构的后续加固，采用粘钢层，通过控制回火进行预应力。其目的是将控温诱导的基本方法付诸实践。这将在Schwerte（德国北威州）的一座真实的板桥上进行原型应用。来自混凝土结构和数字工艺工程领域的研究人员正在与三个实际合作伙伴合作，即一家建筑公司，负责开发钢结构应用技术，Straßen. NRW作为桥梁的所有者和控制专家，从建筑当局的角度来看，以及一家粘合剂制造商，用于将车身结构中已知的热粘合技术转移到老化的混凝土表面上。与基础工程相比，受弯钢筋的加固方法已由原来的内置钢筋槽改为外置钢筋板。此外，该方法还从梁结构扩展到板结构。该方法正在从实验室推广到环境条件下的应用，并按比例扩大到真实的建筑尺寸。该项目的目的是确定合适的粘合剂类型和配置，开发和实施稳健的温度控制概念，并在现实条件下验证该方法。为此，实验研究和基于模型的分析将与尺寸规模和复杂性的连续增加相结合。他们最终在现场的桥梁上联合原型实施。在申请过程中会遇到一些特殊的挑战。为此，必须配置相互作用的、部分竞争的温度参数、粘合剂层厚度和热处理持续时间。同时，粘合剂层中的蠕变损失必须量化，在温度控制中进行补偿并最小化。对于坚固的加固，必须考虑真实世界的边界条件，例如退化的表面和环境温度或湿度变化带来的环境影响。对于钢薄板的最终锚固，追求温度沿薄板长度沿着分级的想法。因此，温度按计划朝向薄板的端部降低，并且随之降低对混凝土的剪切应力，使得在施加外力时不会发生不希望的混凝土剥落。同时，在薄板的中心保持完全预应力。从控制的角度来看，必须确定用于温度控制的适当传感器放置和热感应或附加冷却的位置。

The transfer project is based on the research project "Actively controlled temperature induction to strengthen reinforced concrete structures" (project number 458161128), which has been running since the end of 2021. The transfer project deals with the subsequent strengthening of reinforced concrete slab structures with bonded steel lamellae, which are prestressed with controlled tempering. The aim of the transfer is to put the basic mthod of controlled temperature induction into practice. This will be carried out up to prototypical application on a real slab bridge in Schwerte (NRW, Germany). Researchers from the fields of concrete structures and digital process engineering are working together with three practical partners, namely a construction company for the development of the application technology for the steel lamellae, Straßen.NRW as the owner of the bridge and controlling expert from the point of view of a construction authority, and an adhesive manufacturer for the transfer of the hot bonding technology known from car body construction to use on aged concrete surfaces. In contrast to the basic project, the method of bending reinforcement is now transferred from internal bar reinforcement inserted into slots to externally applied steel lamellae. In addition, the method is expanded from beam to plate structures. The method is being extended from the laboratory to application under ambient conditions and scaled up to real building dimensions. The aims of the project are to identify suitable adhesive types and configurations, to develop and implement a robust temperature control concept, and to verify the method under real-world conditions. For this, experimental investigations and model-based analyses are to be combined with successive increases in size scale and complexity. They culminate in the joint prototypical implementation on the bridge on site. Special challenges arise in the application process. For this purpose, the interacting, partly competing, parameters of temperatures, adhesive layer thickness and duration of heat treatment have to be configured. At the same time, creep losses in the adhesive layer have to be quantified, compensated for in the temperature control and minimized. Real-world boundary conditions, such as degraded surfaces and ambient influences from changing ambient temperatures or humidity, must be considered for robust reinforcement. For the final anchoring of the steel lamellae, the idea of temperature grading along the lamella length is pursued. The temperature is thereby reduced as planned towards the end of the lamella, and with it the shear stresses to the concrete, so that no unwanted concrete spalling occurs at the external force application. At the same time, full prestressing is maintained in the center of the lamella. From the control point of view, suitable sensor placements and locations of heat induction or additive cooling for temperature control must be determined.