Seismic Performance of Substandard Reinforced Concrete Roof T-joints Retrofitted with Prestressed Steel Plates

Abstract This study proposes an innovative and practical retrofitting method for reinforced concrete (RC) roof T-joints with substandard structural details. Retrofitting was performed by assembling steel plates with threaded rods on the roof T-joints, which have typically only been applied to exterior-roof beam–column joints (BCJs). The aim of the retrofitting method was to fully utilize the capability of the column to dissipate seismic energy while limiting the shear demand in the joint panel zone. Four roof T-joint sub-assemblage specimens were constructed and tested using a reverse cyclic loading test. One control specimen and three retrofitted specimens were used with variations in the initial prestressing force, epoxy adhesive, and haunch availability. The effects of the retrofitting variants on the test results, such as the crack patterns, failure mode, and hysteresis behavior, were analyzed. A significant increase in the maximum lateral strength by an average of approximately 138% was observed after applying the proposed retrofitting method. Moreover, when the haunch was removed, the specimen retrofitted with a high initial prestressing force dissipated the most cyclic energy, which was at least seven times that of the control specimen. This considerable seismic performance was achieved when the column was designed with appropriate deformability to develop flexural strength without being hindered by joint shear failure or the short-column effect. Thus, this study makes a notable contribution to the development of seismic retrofitting technology, particularly for BCJs at the roof levels of RC buildings.