On failure modes and design of multi-bolted FRP plate in structural joints

Technical recommendations for design of all FRP structures are by now available and recognized. Inside this frame, the design of all FRP bolted connections with steel bolts has a not negligible position due to its importance in application, especially when bolted connection have, or could have, a significant role in term of bearing capacity and hierarchy between structural parts. The design strength formula for bolted FRP connections proposed in European and national normative and guidelines - define different approaches in function of the numbering of bolts, the geometrical characteristics and typology of each joint and action, that could be out or in plane. Nevertheless, the specific case of multi-bolted (MB) or high-multi-bolted (HMB) FRP plate used in structural joints has been not yet clearly faced, nor from experimental and numerical approach, nor for failure mode. Besides also the strength design approach becomes complex in presence of MB connections. By the way, this research try to investigate specifically this point starting from recent experimental based results dedicated to the structural performance of MB and HMB FRP plates used in connections, and in comparing them with expected ultimate strengths and available design formula. In comparing available formula with experimental outputs - and in verifying their reliability/compatibility - the proposed investigation shows also some thought onto the potential oversize/undersize of this kind of structural joints. The research is exclusively dedicated to the MB FRP plates produced by pultrusion process and used in joints subjected to only in plane action.