Enhancing seismic resilience of reinforced concrete external beam column connection by employing an innovative prestressing method

Beam column joint is often treated as seismic vulnerable structural component in a reinforced concrete (RC) building. Due to vital importance of beam column joints; special attention shall be given for its structural design. This necessitates improving joint shear strength in a simple and efficient way. External beam column joints were prestressed in a non-conventional way with high tensile wires for the intended purpose. It overcomes the shortcomings of the non-seismic design. Six shear deficient RC external beam-column joints (BCJs) were examined under reversed cyclic loading. Five samples were prestressed with the planned technique and one specimen was kept as a reference. Anchorage zone was specially designed for the post tensioning work. The prestressing force for these five test specimens was varied for studying their behavior under the reversed cyclic loading. The principle of “strong column-weak beam” was implemented while deciding the cross sections of the connecting members. Depending on the bending strength of the connecting members, degree of prestressing was decided. During the test process it was noted that, prestressing wires experienced stress reversals alternately during up and down motion of beam; whereas the joint region acted like a pinned connection. It was observed that, force required for initial deflection of each prestressed specimen was higher than the control specimen. It increases substantially with the rise in the level of prestressing; at the same time, it limits the deflection. A brittle mode of shear failure was identified in reference beam column joint specimen, whereas in prestressed beam column joints, prestressing wires failed first and the concrete in later stage. In addition to this, the energy dissipation capacity, load–deflection capacity, ductility ratio and stiffness deterioration of all the test specimens was examined; where significant improvements were observed in prestressed samples as compared to control specimen. It was noted that, the prestressing greatly enhances the shear resistance of deficient external BCJ.