Local and global integrative retrofitting of reinforced concrete frames using in-plane buckling steel braces

Abstract

Two large-scale, single-storey, single-bay reinforced concrete (RC) moment frames, designed as per an outdated seismic code to represent a typical framing detail of a four-storey building, have been tested under displacement-controlled quasi-static loading protocol as per ACI 374.1-05. The RC frames include a plinth beam with brick infill underneath, a slab monolithically cast with the top beam and provision for applying axial load to the column to simulate real construction scenario. One of the frames has been tested as a bare frame, and the second one has been retrofitted with conventional steel braces designed to undergo in-plane buckling. The size of the brace has been selected based on the result of a nonlinear time history analysis of representative low- to mid-rise open-ground storey RC buildings. Post-installed chemical anchors have been utilized to connect the steel braces to the narrow RC frame members following the outcomes of an experimental investigation by the same authors. Local-level retrofitting by steel jacketing using adhesives has been designed and utilized on columns and beams to achieve the desired seismic response. The seismic performance of the retrofitted frame has been compared with the bare frame in terms of strength, stiffness, ductility, energy dissipation and hysteretic damping. The tests provide insight into the role of the plinth beam, effect of RC slab on the strong-column weak-beam aspect and the achievement of the desirable hinge mechanism through a precise design and detailing of global and local level retrofitting technique.