Experimental investigation of retrofitting and structural repairing of foundation-column joints without transverse reinforcement

Field investigations conducted after earthquakes in Türkiye, which is located within an active seismic zone, have revealed that insufficient confinement in the column–foundation joint region is a widespread construction defect. This study focuses on the performance of column–foundation joints without transverse reinforcement under cyclic quasi-static loading, with particular emphasis on damage mechanisms, repair strategies, and strengthening techniques. To simulate seismic effects, four full-scale test specimens were subjected to a constant axial load combined with quasi-static cyclic lateral loading. The reference specimen was detailed in accordance with the Turkish Building Earthquake Code (TBEC 2018), while the other specimens were intentionally constructed without transverse reinforcement in the column–foundation joint region. One of these specimens was repaired using carbon fiber reinforced polymer (CFRP) wrapping after initial damage, one of the undamaged specimen was strengthened with steel angle profiles. Experimental results indicated that the specimen TK-3, repaired with CFRP, exhibited the highest levels of ductility, deformation capacity, and energy dissipation. In contrast, the unreinforced specimen TK-2 demonstrated the poorest performance. The specimen TK-4, strengthened with steel angles, showed improved strength and stiffness but comparatively limited ductility. These findings demonstrate that CFRP wrapping is an effective technique for restoring and enhancing the structural performance of deficient joints, while steel angle strengthening offers a practical alternative for retrofitting poorly detailed regions. Overall, the study underscores the significance of adequate confinement in the column–foundation joint and provides applicable strategies for the repair and strengthening of existing structures that may be subjected to seismic loading.