International Concrete Abstracts Portal

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.

The plate bonding technique has been known and established in Europe for more than 20 years. Up to the present time, however, it has only been used in some specific applications. This is mainly due to the lack of an integral system approach. The increasing demand for strengthening, repair, and rehabilitation measures, especially in the field of the maintenance of structures, and the seismic upgrading or the change in use of structures ask for structural reliability and cost effectiveness. Both can be met with a new system approach for the plate bonding technique focusing on the requirements of engineering based design fundamentals; increase in ductility and strength, provided with permanent pressure applied to the steel plate; safe and easy handling on jobsite with adequate application system; overall quality control and assurance; integration of other plate/strip materials; and extension of the system to other subground material (masonry, wood, steel). A new system for the end anchorage of the bonded steel plates has led to a pronounced increase in ductility of the overall structural system so that the stringent requirements for structural elements used in engineering design can be met in full. A new design procedure is in development, based on extensive laboratory tests and preliminary field tests, as well as on finite element calculations. The new design procedure is fully in length with current developments in reinforced concrete design.

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.

Although some test data are available on the behavior of reinforced concrete beams with bonded plates in shear, there is still considerable lack of information on the effectiveness of such plates in resisting shear forces. This paper presents the results of the first stage of a comprehensive study to evaluate the role and mechanism of strengthening in shear when bonded steel plates are used either at the tension face or in the webs. The major variable in this study was the shear span-effective depth ratio, which is the critical parameter for shear failures; two different geometries of web plates were used. The effect of these bonded plates on deformations, cracking, failure loads, and mode of failure are presented and discussed. Bonded plates at the tension face enhanced the flexural stiffness of the original beams which were weak in shear, but their influence in enhancing shear behavior was minimal. Bonded web plates, on the other hand, were very effective in upgrading the structural behavior in shear. However, the latter were unable to reach their full load capacity due to shear cracking in the unreinforced part of the webs and the consequent debonding of the web plates.

This paper shows the application of a new technique called the plate bonding technique to repair damaged structures. The good results obtained show the ability of this technique to solve different structural problems and demonstrated its validity and flexibility from a technical and economic point of view. To have good results, it is necessary to begin with knowledge of the causes of deterioration; therefore, this paper deals with the four main groups of testing methods to analyze these deficiencies. Two examples of research and tests analyzing the applied technique are included which confirm its validity.