Seismic retrofit of external concrete beam-column joints reinforced by plain bars using steel angles prestressed by cross ties

A method for seismic retrofit of beam-column joints, designed without seismic considerations and reinforced by plain bars, is examined. The method, already applied to connections reinforced by deformed bars, has been modified for joints with plain bars. Retrofit of these relatively old connections needs special attention due to the weak steel concrete bond, let alone the lack of seismic consideration in design. In this method, steel angles are placed on the faces of beam-column intersections and are externally fixed by prestressed cross-ties. Five half-scale specimens were tested under cyclic load: two control specimens under two levels of axial load, and three retrofitted specimens with varying dimensions of angles, different number and prestressing rate of cross ties, with and without stiffener plates in the angles. The tests show significant improvement of the retrofitted specimens in terms of protecting the joint region against large deformation, showing more ductile response and higher hysteresis energy capacity, as well as moderate strength improvement. The tests show that the specimen with the minimum level of retrofit, which had the smallest angle, minimum number of cross ties, and lowest rate of prestressing, with no stiffeners, has performed well. Accordingly, the corresponding retrofit measures may be recommended for similar cases. (C) 2017 Elsevier Ltd. All rights reserved.