Cyclic response of exterior reinforced concrete beam-column joints reinforced with headed bars - Experimental investigation

In seismic design, the locations of beam plastic hinge regions should be predetermined because they require special detailing. In structural moment resisting frames, beam plastic hinges designed for seismic forces usually develop at the face of the column. Formation of a plastic hinge at the face of a column results in yielding of reinforcing bars at the face of the column, as well as into the beam-column joint. Yielding of the reinforcing bars in the beam-column joint results in bond deterioration between the reinforcing bars and the surrounding concrete. If not well-detailed, joint deterioration may result in serious strength and stiffness degradation in the joint region. Relocating plastic hinges in beams moves the plastic mechanism away from the column face. In practice, this has been done by bending some of the longitudinal bars at a predetermined plastic hinge location or increasing the depth of the beam cross section at the face of the column. Both details are not very practical. This paper presents results of an experimental investigation of a practical solution for relocating potential beam plastic hinge regions by the use of headed bars. Four large-scale beam-column subassemblages, with and without headed bars, were tested under quasistatic cyclic lateral loads/displacements. Results of the test specimens suggest that straight-headed bars are very effective in relocating beam potential plastic hinge regions.