Implications of the embedded through-section technique for improving the resilience and sustainability of existing reinforced concrete infrastructure

结构缺陷混凝土基础设施的强度增强是具有相当经济和战略重要性的应用，特别是在桥梁的情况下。据估计，仅在联合王国，战略公路网上就有大约10 000座桥梁，地方公路上有150 000座桥梁，其中相当多的桥梁需要加固或更换。评估和加强这些结构的估计费用超过40亿英镑。其他国家，例如美国，也面临同样的挑战，因此强调了这一问题的全球重要性。在过去的二十年里，纤维增强聚合物（FRP）加固已被接受为现有钢筋混凝土（RC）结构的加固系统。FRP加固系统的使用是有利的，因为它们具有优异的机械和耐久性。广泛的研究已经导致批准的FRP抗弯加固方法的钢筋混凝土结构。与此相反，FRP抗剪加固钢筋混凝土结构尚未完全理解。迄今为止，FRP抗剪加固系统已被应用于现有的钢筋混凝土结构主要是作为外部粘结（EB）或近表面安装（NSM）钢筋。为了使用这些系统，必须能够接近各个梁腹板的两侧。然而，在一些实际情况下，很难提供这样的访问。此外，需要费力且耗时的表面或凹槽制备，以确保混凝土与EB或NSM系统之间分别具有足够的粘结力。此外，除非提供适当的锚固，EB和NSM系统从混凝土中剥离的应力水平为FRP筋的极限强度的20%至30%。嵌入式贯穿截面（ETS）技术是最近开发的现有RC结构的抗剪加固方法。在这种方法中，垂直孔钻从拱腹向上的现有钢筋混凝土梁的剪切跨度。然后将高粘度环氧树脂注入钻孔中，并将FRP筋嵌入到位。ETS技术比EB或NSM系统提供更高的强化效果。ETS技术的其他优点包括更高的防火和防破坏能力，更少的环氧树脂消耗量，不需要进入顶板或耗时的表面preparation.Research调查与ETS FRP筋加固钢筋混凝土梁的抗剪性能受到限制。迄今为止测试的所有梁的有效深度小于400毫米。这是不具有代表性的几个实际情况下，钢筋混凝土桥梁梁有显着更高的有效深度。此外，影响加固梁的结构行为的其他参数的效果，如剪跨有效深度（a/d）比和FRP筋类型，还没有得到充分的研究。正确理解上述参数对加固性能的影响对于ETS技术的最佳利用至关重要。本项目将通过实验和数值计算，研究a/d和FRP筋类型对ETS FRP筋加固的实际尺寸RC梁剪切性能的影响。实验和数值技术的结合将确保一个综合的建模方法，这将不可避免地导致更好地了解加强的行为。实验结果将用于检查当前设计标准的准确性，并在需要时改进其预测。从该项目中获得的见解将使FRP加固的利用能够提高现有RC基础设施的可持续性和弹性。在这项工作中所包含的概念将巩固我们对FRP加固混凝土结构的行为的理解，从而在混凝土建筑的其他领域的各种平行的影响。

The strength enhancement of structurally deficient concrete infrastructure is an application of considerable economic and strategic importance, particularly in the case of bridges. In the United Kingdom alone, it has been estimated that there are approximately 10,000 bridges on the strategic road network and 150,000 bridges on local roads, of which a considerable number need strengthening or replacement. The estimated cost of assessing and strengthening such structures is in excess of £4 billion. Other countries, e.g. the United States, are faced with the same challenge, so emphasising the global significance of the issue.During the past two decades, fibre reinforced polymer (FRP) reinforcement has gained acceptance as strengthening systems for existing reinforced concrete (RC) structures. The use of FRP strengthening systems is advantageous due to their excellent mechanical and durability properties. Extensive research has resulted in approved FRP flexural strengthening methods for RC structures. In contrast, FRP shear strengthening of RC structures is not yet fully understood.To date, FRP shear strengthening systems for existing RC structures have primarily been applied as externally bonded (EB) or near-surface mounted (NSM) reinforcement. In order to utilise these systems, both sides of individual beam webs must be accessible. However, it is difficult to provide such an access in several practical situations. Moreover, laborious and time-consuming surface or groove preparation is required to ensure adequate bond between the concrete and the EB or NSM systems respectively. Furthermore, unless proper anchorage is provided, both the EB and NSM systems debond from the concrete at a stress level of 20% to 30% of the ultimate strength of the FRP reinforcement.The embedded through-section (ETS) technique is a recently developed shear strengthening method for existing RC structures. In this method, vertical holes are drilled upwards from the soffit in the shear spans of existing RC beams. High viscosity epoxy resin is then injected into the drilled holes and FRP bars are embedded into place. The ETS technique provides higher strengthening effectiveness than that provided by the EB or NSM systems. Other advantages of the ETS technique include higher protection against fire and vandalism, less epoxy consumption, and no need for access to the top slab or time-consuming surface preparation.Research investigating the shear behaviour of RC beams strengthened with ETS FRP bars has been limited. All beams tested to date had effective depths of less than 400 mm. This is unrepresentative of several practical situations where RC bridge beams have significantly higher effective depths. Moreover, the effect of other parameters that influence the structural behaviour of the strengthened beams, such as the shear span to effective depth (a/d) ratio and FRP bar type, has not been sufficiently investigated. A proper understanding of the effect of the above-mentioned parameters on the strengthened behaviour is vital for the best utilisation of the ETS technique.This project will investigate, experimentally and numerically, the effect of a/d and FRP bar type on the behaviour of realistically sized RC beams strengthened in shear with ETS FRP bars. The combination of experiments and numerical techniques will ensure an integrated modelling approach that will inevitably lead to a better understanding of the strengthened behaviour. The experimental results will be used to check the accuracy of current design standards and improve their predictions where needed. The insight gained from this project will enable the utilisation of FRP reinforcement for improving the sustainability and resilience of existing RC infrastructure. The concepts encompassed in this work will underpin our understanding of the behaviour of FRP-strengthened concrete structures and thus have parallel implications in a variety of other areas of concrete construction.