Publication
Bending-active represents a structural typology whose geometry is based on the elastic deformation of initially straight members that, in the case of beams, is known as elastica. This configuration involves applying horizontal displacements to a sliding support, causing a beam to be bent into an arched shape. Previous research has primarily focused on small-scale temporary applications, investigating the form-finding process and stability of these structures, but overlooking material strength, which is essential for real-scale applications and structural design. Concerning permanent bending-active structures, using fiber-polymer composites involves complex viscoelastic responses that have not yet been thoroughly investigated. Furthermore, a validated design methodology and evaluation of influencing parameters are also needed for a safe design. This research explores, experimentally and numerically, the structural response of fiber-polymer composite elastica beams under short- and long-term loading conditions and the application limits of composites for permanent large-scale bending-active structures. Series of short-term and long-term experiments were conducted on medium-scale elastica beams, consisting of pultruded glass fiber-polymer composite profiles, commonly used in real-scale structures. Furthermore, a strain-based failure criterion and a design methodology tailored to permanent elastica beams were developed and validated through experimental results. Considering the structural response under short-term loading conditions, i.e., applying symmetric/asymmetric point load to elastica beam, the results revealed that steeper beams experience material failure, while shallower ones exhibit snap-through buckling. Material failure initiates on the tensile side of the beams, with cracks initiating at locations of maximum curvature. Moreover, higher bending degrees and symmetric loading result in higher maximum loads. Considering the structural response under long-term loading conditions, i.e., under combined bending-compression stresses, the results demonstrated that viscoelastic responses are based on an interaction of stress relaxation and creep with their effects increased with increasing bending degree and time of exposure to sustained strains and stresses. The imposed horizontal displacement to one of the supports to maintain the bent beam shape induced sustained bending stresses into the beam. Beneficial relaxation of these stresses occurred, predicted to reach 12% during a targeted 50-year design service life. The possibility of the curved beam to exhibit in-plane deformations under sustained stresses enabled creep to occur simultaneously. While creep deformations remained insignificant, progressive creep rupture occurred at highest bending degrees, exhibiting sequential creep rupture in the outer combined fiber mat layers, delamination, crack opening and final fiber failure. Creep rupture can be prevented by postponing crack initiation be