Structural Behavior of Longitudinally Posttensioned Timber Beams under Serviceability Gravity Loading

The scope of this paper is to quantify the advantages of using unbonded longitudinal post-tensioning for long-span timber beams. This sustainable system can be a suitable alternative to more traditional pre-stressed concrete and (non-pre-stressed) glulam or LVL solutions. Unbonded post-tensioning provides enhanced performance at serviceability limit state conditions, the ability to control deflections, and an increase in flexural strength. An experimental campaign limited to serviceability limit states for gravity loads was carried out at the University of Canterbury, New Zealand. In particular, two different static configurations were tested (simply supported and statically indeterminate beams) with different tendon profile configurations (straight and draped), internal and external to the beam section. A semi-analytical iterative procedure for the solution of the geometrical nonlinear problem of unbonded post-tensioning was implemented in order to capture and predict the experimental behavior. The experimental and numerical results confirm the enhanced deflection performance of the longitudinally post-tensioned beams with respect to traditional timber beams, especially when external draped tendons are used.