Ductile design of glued-laminated timber beams

Ductility is a fundamental component in the design of robust structures. For timber structures, the unfavorable material characteristics pose particular problems to its realization. Two approaches for improving the post elastic behavior of glued-laminated timber beams have been investigated by testing and numerical analysis. The first is based on forming mixed beams with suitably assembled lamellae of different strength class; in the second, steel reinforcement is used. Satisfactory results have been obtained mixing laminations of different grade, whether from a single or from different species, as long as the strengths of the lamellae are well differentiated. Steel reinforced timber beams require taking special provisions in order to develop a ductile bending behavior, because material irregularities induce brittle failure of wood in tension before the steel bars may yield. Positive results were obtained specifically preventing local failure modes, by releasing tension stresses in wood, by inserting small-diameter steel screws, or with a suitably balanced distribution of steel area. Steel reinforcement seemed once more capable of providing a simple and reliable solution.