Anchorage systems to reduce the loss of pre-stress in stress-laminated timber bridges

Stress-laminated timber (SLT) decks consist of a number of planks, boards or glulam elements, placed edgewise, side by side, in which holes are pre-drilled at regular intervals along the longitudinal axis. High-strength bars are then inserted into the holes and pre-tensioned. The pretensioning of the bars introduces compressive stresses in the transverse direction of the deck. One of the main problems with SLT decks has been the loss of tension in the pre-stressed bars, which leads to a reduction in the structural efficiency of the deck. A phenomenon of this kind is mainly caused either by local indentation of the wood at the anchorage system and/or by long-term effects. This paper describes the results of laboratory tests and numerical simulations conducted on SLT reinforced in the anchorage zones by means of self-tapping screws. The loss of tension in the prestressed bars has been recorded both instantaneously and after a few months in a climate chamber where they were exposed to moisture variation