Serviceability Design of Long-Span Timber Beams Considering Semi-Rigid Beam-Column Connections

The increasing adoption of engineered timber systems in long-span construction has intensified the need for accurate prediction and control of mid-span deflections at the serviceability limit state (SLS). Conventional timber design practice typically assumes idealised pinned supports in deflection calculations, neglecting the partial rotational restraint provided by real beam-column connections. This simplification often results in overly conservative designs, inefficient material use, and underutilisation of structural capacity. Addressing this gap, this thesis investigates the influence of semi-rigid connection stiffness on the deflection behaviour of long-span timber beams and develops a validated, design-oriented framework that explicitly incorporates realistic end connection behaviour. The research is structured into three interrelated phases. The first phase comprises a parametric analytical study examining the sensitivity of beam deflection to end connection rigidity across 39 LVL and glulam beam sections with spans ranging from 4 to 12 m. The results demonstrate that incorporating connection stiffness in deflection calculation has a pronounced influence on beam design, particularly for spans exceeding 6 m, where deflection governs the design. Even moderate end fixity significantly improves compliance with SLS criteria, highlighting the limitations of conventional pinned-support assumptions. In the second phase, component-level experimental investigations are conducted on both conventional dowelled (bolted) LVL-to-post connections and an innovative top-and-seat angled steel connection. Fourteen bolted and sixteen angled connection configurations are tested under monotonic loading to characterise their moment-rotation behaviour, initial stiffness, moment capacity, and failure modes. The results show that even simple bolted connections exhibit measurable semi-rigid behaviour, while the angled connections provide substantially higher rotational stiffness with stable and ductile failure mechanisms. Analytical models based on the component method are developed to predict initial stiffness and ultimate moment capacity, alongside nonlinear models that accurately reproduce full moment-rotation responses. The final phase integrates the experimentally derived connection stiffness values into beam-level deflection analysis using the moment-area method, with end supports modelled as rotational springs. Mid-span deflections are evaluated under uniformly distributed and central point loads. The results confirm that incorporating realistic connection stiffness reduces mid-span deflections by approximately 20–35% for spans between 6 and 12 m, compared with pinned assumptions. Furthermore, accounting for semi-rigid behaviour enables substantial reductions in required beam section modulus, reaching up to 67–85% for spans of 6-8 m. A modified deflection equation incorporating a restraint coefficient 〖(c〗_d) linked to connection stiffness and span length is proposed and validated, showing perfect agreement with analytical predictions. Practitioner-oriented charts and c_d-factors are also developed to facilitate direct implementation of the proposed framework in routine design. Overall, this thesis demonstrates that recognising and modelling semi-rigid connection behaviour leads to more accurate, efficient, and economical serviceability design of long-span timber beams. The proposed analytical framework, validated deflection equations, and practical design tools provide a clear and systematic link between connection-level behaviour and beam-level performance, offering a foundation for improved design guidance and future code development in timber engineering.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2026

Author dc:creator

• Patowary, Mohammed Ziauddin

Statement dc:rights

• embargoed access
• CC BY 4.0

Licence

• http://purl.org/coar/access_right/c_f1cf
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

en

Identifier

https://doi.org/10.26190/unsworks/32383

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/108011