Exterior beam-to-column bolted connections between GFRP I-shaped pultruded profiles using stainless steel cleats. Part 1: Experimental study

Abstract

Beam-to-column connections are very relevant in the design of glass fibre reinforced polymer (GFRP) structures, since they can (i) govern the load capacity and robustness, presenting brittle failure modes, and (ii) reduce the deflections of GFRP flexural members. This paper presents a study about the mechanical behaviour of exterior beam-to-column connections between I-shaped pultruded GFRP profiles using stainless steel cleats. The main objective was to develop a connection system with non-corrodible auxiliary parts and improved ductility, by exploiting the stainless steel properties. For that, full-scale tests were performed to investigate (i) the monotonic response of nine different connection series, and (ii) the cyclic response of four of those series. The series differed in the number of bolts/rods (one or two bolt rows), cleat thickness (3, 6 and 8 mm), position of the cleats (flange or web) and use of column reinforcements, materialized by stainless steel rods and plates connecting the cleats to the columns’ back flange. All series that did not include such reinforcements presented tensile rupture at the columns’ web-flange junction at a very initial stage of the monotonic and cyclic tests, limiting the connections’ strength, ductility and capacity to dissipate energy. In the reinforced series, where this failure mode was avoided, the stiffness, strength, ductility and energy dissipation was highly influenced by the cleats thickness and bolts row number. The series that presented the best overall mechanical behaviour comprised 6 mm thick flange cleats, each with two bolt rows, and column reinforcements; in this series, the intermediate thickness of the cleats provided the best balance between the initial stiffness and non-linear deformation capacity, delaying GFRP local failure and allowing to mobilize the stainless steel ductility — this connection presented the highest strength and energy dissipation capacity. In addition to the experimental study presented herein, Part 2 (Martins et al., 2021) presents predictions of the stiffness and strength of the reinforced connection series using analytical and numerical methods.