EBR Strengthening Technique for Concrete, Long-Term Behaviour and Historical Survey

Abstract

Epoxy bonded steel plates (externally bonded reinforcemen: EBR) for the strengthening of concrete structures were introduced to the construction industry in the late 1960s, and the use of fibre reinforced polymers (FRPs) was introduced in the 1990s, which means that these techniques have already been used in construction for 50 and 25 years, respectively. In the first part of the paper, a historical survey of the development and introduction of these strengthening techniques into the construction industry are presented. The monitoring of such applications in construction is very important and gives more confidence to this strengthening technique. Therefore, in the second part of the paper, two long-term monitoring campaigns over an extraordinarily long duration will be presented. Firstly, a 47-year monitoring campaign on a concrete beam with an epoxy bonded steel plate and, secondly, a 20-year monitoring campaign on a road bridge with epoxy bonded CFRP (carbon fibre reinforced polymers) strips are described. The paper is an expanded version of the paper presented at the SMAR2017 Conference.Keywords: externally bonded reinforcement; EBR; strengthening of reinforced concrete; epoxy adhesive; bond; steel; CFRP; long-term behaviour Historical Survey of Development of EBR Technique Research on EBR SteelThe first ideas on strengthening of concrete with epoxy bonded steel plates were presented in the 1960s by L'Hermite et al. Figure 1 showing the principle idea of applying a steel plate to a concrete beam with an adhesive (tole d'acier: steel plate and colle: adhesive). The first applications on a highway bridge and in a building followed in 1966-1967 [3]. Bresson [2] presented in the year 1971 the derivation of the differential equation of bond behaviour of EBR and its elastic solution. Afterwards, other researchers worked on that topic-for example, Johnson et al. [4] presented in 1981 a research study on sixteen tests on plated reinforced concrete members subjected to bending, shear and axial tension, in order to study the influence of geometric parameters on the maximum tensile strain that can be developed in a mild steel plate before breakdown of the adhesive layer or failure of the concrete member. No failures occurred in the epoxy adhesive, and strains exceeding yield could be developed in the plates. Furthermore, Dussek [5] described results of tests on plate-reinforced beams, discussed a design method and presented strengthening projects where steel plates were applied on several bridges in UK. A timeline of the developments discussed is displayed in Figure 2.In the 1970s and 1980s, besides the investigations mentioned above, research on the performance and on a better understanding on the epoxy bonded steel plates was also performed at Empa in City,

The Gradient Anchorage Method for Prestressed CFRP Strips: from the Development to the Strengthening of an 18 M Long Bridge Girder

“…-A feasible setup for on-site GA applications was developed in cooperation with the S&P Clever Reinforcement Company AG (Seewen, Switzerland) and Empa. -It has been demonstrated that environmental conditions, such as humidity, temperature and FT cycle can affect the performance of the GA and, in combination with high CFRP prestresses and/or high sustained loading, are critical for their long-term behavior. Therefore, similar recommendations such as the one proposed by (Czaderski and Meier, 2018) for unstressed CFRP can be applied to RC elements strengthened using the GA method. The most important are:…”

“…The use of composite materials for structural strengthening is nowadays considered a practical and ordinary solution to increase load-carrying capacity and extend the life of reinforced concrete structures. As a result of more than two decades of international research and pioneering applications (Czaderski and Meier 2018), it is possible to deliver strengthening solutions based on the use of FRP with a good level of safety. The advantages are well known; composite materials used for structural strengthening, such as, for example, Carbon Fiber Reinforced Polymers (CFRP) have excellent mechanical properties, i.e., a high ultimate tensile strength and modulus of elasticity.…”

Discussion on the Reinforcement of Reinforced Concrete Slab Structures

“…A. CFRP patches: Externally bonded reinforcement (EBR) appeared in the 1980s [27]. In the last decades, fiber reinforced polymer (FRP) materials have been increasingly proposed to strengthen RC structures [28].…”

Experimental and Analytical Investigations of the Use of Groove-Epoxy Anchorage System for Shear Strengthening of RC Beams Using CFRP Laminates

“…Strengthening of the deteriorated structures, using externally bonded reinforcement (EBR) materials became one of the most widely used strengthening methods as given by several comprehensive reviews and surveys [ 1 , 2 , 3 , 4 , 5 , 6 ]. During the last three decades, carbon fiber reinforced polymer (CFRP) composites have become the material of choice that has been used widely for flexure and shear strengthening in the construction industry.…”