SP-165 The ACI Technical Session "Repair and Strengthening with Adhesive Bonded Plates" was held in Washington, D C on March 15-16, 1992. The papers presented at the technical session and the additional papers included in this special publication provide the first comprehensive publication of information on this subject in the United States. The papers cover research, design, construction methods, and case histories. The research described includes not only theoretical analysis and short-term experimental programs but also test programs that involve long-term outdoor exposure. research in the use of fiber reinforced plastic plates instead of the more commonly used steel plates is also described. The design papers illustrate practical engineering approaches and include details of anchoring plates, effect of plate dimensions, adhesive performance, and temperature limitations. Construction methods described include preparation of the plates, application of adhesive, and installation of the plates. The case histories provide a broad and historical view of the use of adhesive bonded plates to strengthen buildings and civil engineering structures.

An experimental investigation was carried out on a total of 72 simply supported open sandwich beams in flexure under two symmetrical point loads. The beams were reinforced with 1.5 mm thick grit-blasted steel plates bonded to the concrete with a suitable epoxy resin adhesive. The major parameters investigated include the duration of exposure and the amount of sustained load. The results of these tests are presented and discussed in this paper. Test results indicate that for the type of adhesive selected, use of a double layer of adhesive in which the first layer has been allowed to harden for 24 hours before application of the second provides adequate bond strength under sustained loading up to 5 years of outdoor exposure. A steel surface which has been thoroughly degreased and metal grit-blasted appears to be a suitable preparation for the open sandwich beams.

Although strengthening by bonded steel plates, where adhesive is used to bond the steel plates to the structural members, has been established for more than two decades, it was not until recently that this strengthening technique has been used in Singapore. A number of reinforced concrete structures have been successfully strengthened using this technique over the last three years. This paper describes this strengthening technique with particular reference to the material selection and design considerations, as well as the strengthening and construction methodologies. A case study on one of the structures strengthened is also presented. The structural members strengthened include bonding of steel plates to beams to increase flexural as well as shear capacities and encasing columns to prevent buckling and increased load carrying capacity.

In this paper, a closed-form solution is obtained for partially plated beams. Linear elastic behavior is assumed for beam, plate, and adhesive. The behavior of the adhesive is idealized using the Roberts and Haji-Kazemi model. A system of differential equations is obtained and finally solved by detecting the distribution of shearing stresses through the adhesive layer. All other beam resultants are obtained via equations of equilibrium. The approach has suggested a simple experimental device that enables the user to evaluate the stiffness parameters of the adhesive layer. Finally, the response of the model is compared with numerical solutions by finite element model and the experimental results obtained for flexural tests on partially plated beams. A good agreement is observed.

Repair and strengthening of concrete structures by external reinforcement with steel plates affords the manufacturer of concrete adhesives an attractive new and potentially large opportunity for his products. In this application, bond lines are generally thicker and environmental effects more pronounced than in more traditional uses of such adhesives. In plate bonding, the adhesive becomes an integral part of the reinforcement system and must be capable of transferring stresses without lasting hysteresis effects. High modulus epoxy adhesives with high heat deflection temperatures (HDT) have been shown to have the necessary creep resistance and shear strength. In plate bonding, the internal steel surface is not protected against corrosion by the alkalinity of concrete. Corrosion resistant primers were found either to lack bond strength at high temperature or to enhance a reaction between the freshly prepared metal surface and the hardener component of the epoxy adhesives, which led to the use of unprimed steel plates. Unfilled, low viscosity resins appear to have better barrier properties against corrosion than filled pastes. Treatment of freshly prepared steel surfaces with certain silanes appears to retard flash rust formation as claimed in the literature.