Development of a novel beam-to-column connection system for pultruded GFRP tubular profiles

Despite the increasing use of pultruded glass fibre reinforced polymer (GFRP) profiles in civil engineering structural applications, most common beam-to-column connection systems still mimic those used in steel frame structures, not accounting for the inherent differences of mechanical properties between the GFRP and steel. Therefore, due to the low transverse modulus and strength of GFRP profiles, these connection systems have several limitations in terms of stiffness and load carrying capacity. This paper presents the development of an innovative beam-to-column bolted connection system for GFRP tubular profiles comprising tailor-made steel connection parts that are positioned inside the GFRP sections. The experimental investigations first included double-lap tests to characterize the behaviour of bolted connections between GFRP and steel plates. Next, tests were performed on full-scale beam-to-column connections using the novel connection system, in which the following configurations were assessed: (i) one bolt per web (W1), (ii) two bolts per flange and short edge distance (F2), (iii) two bolts per flange and long edge distance (F2S), and (iv) four bolts per flange (F4). Results showed that the stiffness of the connection system is mainly influenced by the number of bolt rows, while the strength depends on the bolt edge distance - the maximum stiffness and strength were provided by configurations F4 and F2S, respectively. Moreover, with these configurations it was possible to obtain a pseudo-ductile failure behaviour. The stiffness of each connection type was estimated with reasonable accuracy using the “component method”. On the other hand, estimates of the failure load using the same method and the available design guides were non-conservative and presented poor correlation with the test results, suggesting the occurrence of mechanisms more complex than those considered to estimate the loads. Therefore, numerical models were developed to estimate the stress resultants in the bolts, which allowed to predict the strength of the connection series.