Reduction of Steel Usage in Timber Structures through Wooden Reinforcement Applications in Connections

Abstract

Timber structures increasingly rely on steel components to ensure sufficient load-bearing capacity in joints subjected to compression perpendicular to the grain. While effective, this practice conflicts with ambitions to reduce material complexity and improve circularity in timber construction. Wooden dowels, particularly when densified, offer a fully timber-based alternative, but their structural behaviour and design applicability are not yet sufficiently understood or codified.This thesis investigates the mechanical behaviour of timber elements reinforced with wooden dowels under compression perpendicular to the grain, with a focus on column--beam--column connections. A finite element modelling framework is developed to capture stress redistribution, local crushing, contact behaviour, and interaction effects between timber and reinforcement. The numerical model is validated against reference behaviour and used in a parametric study to assess the influence of dowel geometry, layout, and interaction on system-level response. In parallel, an analytical model is derived to estimate reinforcement contributions based on simplified load-transfer assumptions and is evaluated against numerical results.The results show that wooden dowel reinforcement can enhance stiffness and load-bearing capacity, but the effective contribution of individual dowels at system level is significantly lower than their isolated capacity. Load transfer is governed by non-uniform stress mobilisation along the dowel length, with partial side interaction and a relatively large contribution from dowel tip bearing. As a result, local timber crushing beneath the dowel tip governs the global response. Analytical design approaches provide conservative lower-bound estimates but are sensitive to assumptions regarding load-transfer mechanisms.A case study application demonstrates how the developed models can be used to assess steel reduction potential in practice and highlights the need for additional numerical verification when applying timber-based reinforcement strategies. The findings contribute to a better mechanical understanding of wooden dowel reinforcement and provide a basis for future experimental validation and design-oriented development within the framework of Eurocode 5.