Development of upgradation schemes for gravity load designed beam–column sub-assemblage under cyclic loading

In this paper, it is attempted to upgrade the poor gravity load designed (‘GLD’) exterior beam–column sub-assemblage for improving the seismic performance. Three different upgradation schemes have been proposed for ‘GLD’ sub-assemblage under seismic loading. In all three schemes, shear upgradation was carried out by using GFRP wrapping, and joint region was upgraded by using steel plate jacketing with through–through steel bolts. For flexural upgradation, CFRP fiber and laminates were respectively used in first two schemes. Third upgradation scheme was similar to that proposed in the first scheme but limited to the D-region (disturbed region) only. Before implementing the upgradation schemes, proper surface treatment on original specimens were carried out. First, the original ‘GLD’ and target ‘ductile’ sub-assemblages were experimentally investigated under reserve cyclic loading. Thereafter, the upgraded sub-assemblages were investigated under same cyclic load history as that was opted for ‘GLD’ one. Specimen details considered, materials used, execution procedure for upgradation adopted and experimental investigation carried out are discussed in step by step. It was observed from the investigation that the ‘GLD’ specimen seized to function under reserve loading and the lack in proper anchorage of beam bottom reinforcement formed a huge crack at the joint face. Under reverse cyclic loading, it was found that the upgraded specimens showed a considerable improvement in seismic performance. Further, the CFRP laminate based upgraded specimen showed better performance over the CFRP fiber based one and the plastic hinge could be successfully shifted from the joint zone to a predefined location.

► Three different upgradation schemes proposed for GLD beam–column joints using FRP and steel plate.
► Flexural- and shear- strengthening were carried out using CFRP GFRP respectively.
► Confinement of joint zone was ensured by steel plate with through–through bolts.
► Performance of all three specimens was comparable to that obtained from ‘Ductile’ specimen.
► Shift in plastic hinge to beam is achieved in two of the upgradation schemes proposed in this study.