Strengthening of Exterior Beam-Column Junction

Abstract

Beam-column junction plays a very important role in moment resisting framed structures, when it is subjected to seismic loading. Amongst all the junctions, exterior junctions are considered as the most critical due to asymmetric loading under seismic action. Fiber Reinforced Polymer Composites (FRPC) have become popular for civil engineering applications, especially in structural upgradation due to their good engineering properties. FRPC wraps are successfully employed as external confinement for improving the strength and ductility of existing concrete beam column joints. The present study is focused on the mechanical response of exterior beam column junction wrapped with GFRP and CFRP material. To study the behavior of external beam-column junction wrapped with GFRP and CFRP, 20 half scale specimens are prepared having cross section of 150mm x 200mm for beam and 200mm x 200mm for column. Reinforcement for these specimens is divided in to two major categories, i.e. Non-ductile and Ductile. From these two categories, GFRP and CFRP sheets are wrapped on the non-ductile specimen in four different patterns and results are compared with the non-ductile control specimen, and ductile specimen, respectively. Thus in totality two non-ductile, two ductile, eight GFRP wrapped specimen and eight CFRP wrapped specimen are included in present study. Static loading is applied at the tip of the beam and considering displacement is measured. A 300 kN axial load is applied to the column with fixed boundary conditions. The structural response has been measured in terms of displacement, load at tip of the beam and strain at the joint. LVDT and load cell are used to measure displacement and load, respectively. Electronic and mechanical strain gauges are used to evaluate strain induced at different locations for the beam-column junction. By compiling the results, maximum displacement under corresponding load, energy absorption capacity, ductility, failure pattern and stiffness have been calculated for beam column junction. From the failure of beam column joint it is clearly shown that the crack is moved from junction to the end of the beam. The percentage increment in ultimate failure load is ranging from 14% to 67%. In GFRP and CFRP wrapped specimen as the no of layers of L wrap increase, the ultimate capacity of beam column joint is increased but the ultimate capacity increment is not in linear relationship with the no of L wrapped layers. Overall the GFRP wrapped specimen with pattern 3 the combination of L wrap and U wrap shows better result in terms of ultimate load while the CFRP wrapped specimen with pattern 1 shows better result in terms of Energy absorption capacity, Ductility and stiffness.