Seismic upgrade of interior beam-column subassemblages with high-performance fiber-reinforced concrete jackets

Simulated seismic load tests on reinforced concrete gravity load-designed (GLD) reinforced concrete frames with interior beam-column (B-C) joints of nonoptimal reinforcing details to resist earthquake are described. The interior B-C joint lacked transverse reinforcement, column lap-splices, and continuous bottom beam reinforcement. In this investigation, ten 1/3-scale interior B-C sub-assemblages were subjected to reversed cyclic loading under no axial column load or Under low levels of axial load. The joints of these subassemblages were typical in geometry and reinforcement detailing to an interior B-C subassemblage of a prototype Jordanian building frame designed before 1970 only for gravity loads. Some of these subassemblages were tested after strengthening using a 25 nun-thick jacket of high-performance fiber-reinforced concrete (HPFRC) all around the joint-column regions. The test results indicated that the seismic behavior of upgraded specimens was improved substantially compared with reference ones; higher load levels were attained, larger energy dissipation was observed, and slower stiffness degradation was also noted. The upgraded B-C subassemblages failed as a result of plastic hinges in the beams, whereas excessive damage to joint region of the reference specimen led to failure. Within the range of the a-vial loads used in this study. the jackets containing hooked steel fibers (HSF) provided a better confinement and more ductility to the joint region compared with the jackets containing brass-coated steel fibers (BCS).