Pre-earthquake and post-earthquake retrofitting of poorly detailed exterior RC beam-to-column joints

• Specimens K1 and SM1 exhibited pullout failure of the beam bars from the joint.
• Anchorage improvement should not be underestimated during the retrofit process.
• SL1 and SK1 performed very satisfactorily with respect to the original specimen.
• The columns and joint region of SL1 and SK1 remained intact at the end of the test.
• The formulation successfully predicted the observed capacity of SL1 and SK1.

In the present study the effectiveness of a proposed scheme for the retrofitting of substandard exterior reinforced concrete (RC) beam-to-column joints was experimentally and analytically investigated. The joint sub-assemblages were poorly detailed, representing structural members of old RC buildings, designed prior to the 1970s. Thus, the columns of the specimens had sparse transverse reinforcement, the beam-column joint region was unconfined and the longitudinal reinforcement of the adjacent beam had straight anchorage of insufficient length in the joint. The retrofitting technique proposed herein combines the improvement of the beam longitudinal reinforcing bars’ anchorage in the joint, by using extension bars and steel plates and the RC jacketing of the columns and the joint region. The strengthened specimens conform to the standards of modern design codes for RC structures. To evaluate the effectiveness of the proposed retrofitting scheme the lateral performance of one pre-earthquake and one post-earthquake retrofitted specimen was compared to that of an original, control specimen and that of a retrofitted one only by RC jacketing. The experimental results revealed a substantial improvement of the overall seismic behaviour of the sub-assemblages retrofitted according to the proposed technique, with respect to the lateral performance of the control specimen. Moreover, the specimen retrofitted only by RC jacketing showed poor seismic performance under the incremental displacement amplitudes of the lateral loading and developed a failure mode dominated by bond-slip, similar to that of the control specimen.

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