Energy dissipation in fiber-polymer composites adhesive joints under cyclic loading

Sustainable development has emerged as a paramount consideration in various fields of industry, including construction, to preserve the environment and its finite resources. Lightweight structures, such as fiber-polymer composite structures, address both sustainability and earthquake resistance concerns. Despite their reduced weight, which lowers seismic input energy, the inherent brittleness of composite structures limits their energy dissipation capacity. To overcome this challenge, the concept of pseudo-ductility has been leveraged, focusing on enhancing energy dissipation within beam-column connections. The capability of pseudo-ductile adhesives to dissipate inelastic energy through mechanisms such as viscoelastic friction, plasticity, or damage substantiates them as a potential solution to the concerns on seismic performance of composite structures' connections. The performance of pseudo-ductile adhesive and bolted double-lap joints composed of pultruded glass composite profiles were experimentally investigated and compared. The effects of applied displacement rates on the behavior of the pseudo-ductile adhesive and configurations of bolted joints were studied through monotonic and cyclic experiments. The adhesive joints showed significantly higher energy dissipation than bolted joints at lower displacement rates while maintaining similar or greater strength under monotonic loading. A phenomenological model comprised of two parallel Maxwell units, one conventional-linear, and one extended-nonlinear, was developed. The model captured effectively pre- and post-yield monotonic and cyclic responses of pseudo-ductile adhesive double lap joints under various displacement rates. The developed phenomenological model's advantage over other constitutive models lies in its fewer parameters and computational efficiency.Seismic forces might induce variable strain rates in the form of torsional moments in the joint area. Therefore, a novel angle joint configuration was designed, with a bolt positioned at the geometric centroid of the joint area that permitted relative rotation while restricting relative displacements, leading to pure torsion in the adhesive layer. The angle joints were then subjected to various rates of monotonic displacement-controlled loadings. It was observed that with an increase in the range of strain rates, the ultimate strength of the experimented angle joints increased while their energy dissipation capacity and failure rotation decreased. An analytical model was introduced to predict the torsional behavior of pseudo-ductile adhesive joints using a bilinear material behavior. The analytical model effectively predicted angle joints' torsional behavior. In conclusion, this thesis provides insight into the mechanical behavior of a pseudo-ductile adhesive in composite joints and their energy dissipation capacity. The developed phenomenological model can serve as a useful tool for future engineers and researchers to design and analyze adhesively bonded composite joints, taking into consideration the complex and highly nonlinear cyclic behavior of the pseudo-ductile adhesive. Furthermore, the novel angle joint configuration designed in this study contributes to a better understanding of the effects of variable strain rates on the behavior of pseudo-ductile adhesive joints, expanding the scope of potential applications and enhancing the seismic performance of composite structures.