Design Approach to Predict Post-Tensioning Losses in Post-Tensioned Timber Frames

Abstract

Since 21, twelve post-tensioned timber (Pres-Lam) buildings have been constructed throughout the world. The technology relies on unbonded post-tensioning tendons to provide moment capacity to beam-column, wall-foundation, or column-foundation connections. Supplemental energy dissipation can be introduced by mild steel bars or replaceable damping devices when designing buildings for high seismic risk areas. Creep within the timber elements leads to losses in post-tensioning force over time. The amount of post-tensioning loss depends on the members’ geometry, environmental service conditions, and the initial moisture content of wood. This paper presents a design approach for estimating, via hand calculations, the amount of post-tensioning loss expected for the most common design configurations.