System ductility and redundancy of FRP beam structures with ductile adhesive joints

This paper reports on a structural concept for engineering structures composed of FRP components to provide system ductility that compensates for the lack of material ductility inherent to FRP materials. The concept includes the use of redundant structural systems and ductile or flexible adhesive joints. To demonstrate the feasibility of the proposed concept, quasi-static experiments on pultruded GFRP beams were performed. The two-span beams were connected with flexible adhesive joints at the middle support. The flexible joints from highly non-linear adhesives provided a favorable redistribution of the internal and external forces in the statically indeterminate system compared to single-span and continuous beams, which were also examined. In the case of adhesive joint failure, structural collapse was prevented because of system redundancy. Due to the stiffness-governed design of the GFRP beams, the stresses in the flexible adhesive joints were small and creep deformations in the joints could be controlled.