AbstractIt is widely accepted that the seismic retrofitting of nonseismically detailed reinforced concrete beam-column joints (BCJs) in reinforced concrete (RC) frame buildings is an urgent necessity due to its high vulnerability and potential consequences in seismic events. As a result, considerable effort has already been put into developing efficient and practical retrofitting solutions for such BCJs. Most of the existing techniques, however, are based on either passive confinement techniques, for example, fiber reinforced polymer (FRP) wrappings, or involve a considerable joint enlargement, which, in many cases, is undesirable. In this study a new technique of retrofitting BCJs is proposed by employing a more effective method of confinement (i.e., active confinement), utilizing the shape recovery feature of shape memory alloys (SMAs). To evaluate the performance of the proposed retrofitting scheme, experimental tests were conducted on full-scale BCJ specimens. The efficacy of the proposed retrofitting scheme is evaluated in terms of enhancement in strength, ductility, energy dissipation capacity, damage reduction in the specimens, and ease of application. The results from this study suggest that the proposed retrofitting scheme could be effectively used in achieving the full capacity of the joints corresponding to beam yielding and consequently enhances the energy dissipation capacity of the system significantly. The test results demonstrated that the proposed retrofitting scheme performs excellently in reducing the joint shear strain (core damage) (to almost zero or negligible) and also in retaining the full axial load carrying capacity of the column, even at very large drift values. The proposed retrofitted scheme could also be conveniently used in cases where the capacity ratio of column-to-beam needs to be improved.Practical ApplicationsThis paper presents a novel retrofitting technique for beam-column joints of a reinforced concrete frame buildings. Beam-column joints that are either falling short of the minimum recommended strength to withstand medium to strong earthquakes or requiring an upgrade due to a change in use or class could be retrofitted using this technique. This proposed retrofitting scheme consists of two main components: (1) precast concrete attachments that are first attached to the column section near the joint region, and (2) shape memory alloy wire that is wound over the precast concrete attachment. The proposed scheme employs the unique material property of shape memory alloy wire. Shape memory alloy wire is a class of smart materials that have several unique material properties, including the shape memory effect used in this technique. The process requires heating of shape memory alloy wires to about 200–300°C. Heating shape memory alloy wires causes them to shorten due to shape memory effect and thus results in an inward pressure in the confined region. The inward pressure applied by the shape memory alloy wire spiral together with the supplementary stiffness provided by the precast concrete attachment makes the overall joint considerably stronger and ductile. The proposed technique could be easily used in retrofitting the external beam-column joints—the most critical ones. Moreover, it has a potential to be used in conjunction with other conventional materials, such as steel or fiber reinforced polymer, to reduce the overall cost of the retrofitting.

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