Stability bracing of steel trusses using timber roof elements
Rehman, Ahtesham ur (2025)
2025
Master's Programme in Civil Engineering
Rakennetun ympäristön tiedekunta - Faculty of Built Environment
Hyväksymispäivämäärä
2025-06-16
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202505266177
https://urn.fi/URN:NBN:fi:tuni-202505266177
Tiivistelmä
Lateral bracing must possess sufficient stiffness and strength to prevent buckling in steel compression members, especially within truss systems. Traditionally, steel elements provide this bracing; however, this thesis investigates the use of timber roof elements as lateral braces for steel trusses, offering a potentially more economical and sustainable alternative. The main goal of this study is to evaluate various lateral bracing design methods for steel truss top chord compression members, analyse their theoretical basis and effectiveness, and recommend the most appropriate design approach when simplified methods prove non-conservative. The research focuses on calculating brace force and stiffness for hybrid bracing systems for truss compression members.
A comprehensive literature review examines both ideal and real compression members with initial imperfections. Several design approaches, including Winter’s method, the 2% rule, AISC 360 provisions, EN 1993-1-1 (steel Eurocode), and EN 1995-1-1 (timber Eurocode), are critically assessed for their suitability in hybrid systems. A key aspect of the study is comparing EN 1993-1-1 and EN 1995-1-1, noting their differences in bracing design. Notably, EN 1993-1-1 considers the full member length for buckling, while EN 1995-1-1 treats each bay length (or twice the bay length) independently.
The analysis indicates that Eurocode 3 (EN 1993-1-1) and Eurocode 5 (EN 1995-1-1) for Laminated Veneer Lumber (LVL) yield brace force values close to the actual calculated brace force of approximately 14.89 kN. Conversely, Eurocode 5 for solid timber and AISC 360 predict slightly higher, more conservative brace forces and stiffness values, with both providing very similar results. Thus, for safer design of steel truss connections with timber roof elements, this thesis recommends applying either Eurocode 5 (solid timber) or AISC 360 methods, which explicitly consider brace stiffness and strength to ensure lateral stability and buckling resistance in hybrid systems.
Overall, this thesis aims to provide clear design guidance for engineers working with steel-timber hybrid structures, proposing refined methods to ensure safe, efficient, and code-compliant bracing of steel trusses using timber roof elements.
A comprehensive literature review examines both ideal and real compression members with initial imperfections. Several design approaches, including Winter’s method, the 2% rule, AISC 360 provisions, EN 1993-1-1 (steel Eurocode), and EN 1995-1-1 (timber Eurocode), are critically assessed for their suitability in hybrid systems. A key aspect of the study is comparing EN 1993-1-1 and EN 1995-1-1, noting their differences in bracing design. Notably, EN 1993-1-1 considers the full member length for buckling, while EN 1995-1-1 treats each bay length (or twice the bay length) independently.
The analysis indicates that Eurocode 3 (EN 1993-1-1) and Eurocode 5 (EN 1995-1-1) for Laminated Veneer Lumber (LVL) yield brace force values close to the actual calculated brace force of approximately 14.89 kN. Conversely, Eurocode 5 for solid timber and AISC 360 predict slightly higher, more conservative brace forces and stiffness values, with both providing very similar results. Thus, for safer design of steel truss connections with timber roof elements, this thesis recommends applying either Eurocode 5 (solid timber) or AISC 360 methods, which explicitly consider brace stiffness and strength to ensure lateral stability and buckling resistance in hybrid systems.
Overall, this thesis aims to provide clear design guidance for engineers working with steel-timber hybrid structures, proposing refined methods to ensure safe, efficient, and code-compliant bracing of steel trusses using timber roof elements.