Strength and stiffness of adhesively bonded GFRP beam-column moment resisting connections

For the first time, the feasibility of adhesively bonded connections in FRP frame structures is explored as an alternative to bolted connections. Eight full-scale GFRP beam-column connections are tested and their failure mode, strength and rotational stiffness are investigated. A single pultruded GFRP I-profile is used for the two members. In four of the specimens the beam and the column are connected by epoxy adhesive and GFRP seat angles, similar to the so-called “standard bolted connection”. In the remaining four specimens, the seat angles are supplemented by additional GFRP angles and stiffeners to strengthen the column flange and web. The beam-column assembly forms an inverted L-shape frame, with the column being fixed at the bottom and attached to the beam near the top. The beam, acting as a cantilever, is loaded by a point load near its free end, which subjects the connection to bending and shear. The current standard connection failed by debonding within the column flange while the improved/strengthened connection failed within the adhesive or at the adhesive-column flange interface. The test results reveal that both the standard and improved connection can have at least the same strength as the corresponding bolted connection, irrespective of whether GFRP or steel bolts are used to make the connection. Hence, the current restrictions against the use of adhesive beam-column connections in GFRP frame structures may be unjustified. In making this comparison, the observed failure load of each connection is normalized by the ultimate moment capacity of the GFRP profile in the beam-column assembly.