Experimental and reliability assessment of fire resistance of glue laminated timber beams

Abstract

Glue-laminated timber (GLT) is an engineered wood product widely used in mass timber construction for its strong structural and fire-resistant properties. However, the fire performance of GLT varies significantly due to the natural and uncertain phenomena (moisture, exposure time, isotropic, homogenous properties, etc.) of fire and timber. This makes it difficult to predict the fire behaviour of the GLT structural elements. To ensure building safety, it is crucial to assess GLT's fire behaviour and post-fire structural integrity during the design stages. This study conducted the experimental tests of GLT beams (280 mm × 560 mm) without loading (1.4 m) and under a four-point bending load (5.4 m). Tests identified thermal behaviour and charring rates of GLT beam. Then, the residual stiffness of the GLT beam was calculated, and the charring rates of the beams were compared with Australian and European standards. Reliability analysis was conducted for beams for a fire exposure of 120 min, considering the charring rates observed through the analysis and simulating the fire insulations. Results show that the charring rate of GLT made with spruce pine timber varied between 0.43 and 0.81 mm/min, with a mean rate of 0.7 mm/min, aligning with both Australian and European standards. However, considering timber density and moisture content, the charring rates in Australian standards were conservative. The study also found that structural capacity significantly degrades under fire, with a 22 % reduction in flexural stiffness after 120 min of exposure. Additionally, GLT beams can safely function for 30 min under 75 % of their design moment capacity and for 60 min under 50 % capacity.

Keywords

Fire test / Thermal behaviour / GLT beam / Charring rate / Residual stiffness / Deflection under fire

Relevance to resilience

This article investigates the performance of glulam timber beams under fire loads, focusing on their structural behaviour and safety. Experimental results are validated numerically, accounting for uncertainties in material properties and fire dynamics. A reliability-based assessment provides critical insights for post-fire downtime, resilience, and recovery planning. The findings support multi-hazard design frameworks that address both fire and earthquake risks, contributing to safer and more robust infrastructure.

Funding statement

This work was funded by the 2022-2023 Fellowship of the Coalition for Disaster Resilient Infrastructure (CDRI), 210927702. The authors also acknowledge the funding support from Ronnie & Koh Consultants Pte Ltd, 573972 Singapore.

Data availability

The datasets generated during and/or analysed during the current study are not publicly available due to privacy. but are available from the corresponding author upon request.

CRediT authorship contribution statement

Satheeskumar Navaratnam: Writing - original draft, Methodology, Investigation, Formal analysis, Conceptualization. Thisari Munmulla: Writing - original draft, Formal analysis, Data curation, Conceptualization. Pathmanthan Rajeev: Writing - review & editing, Supervision, Conceptualization. Thusiyanthan Ponnampalam: Project administration, Methodology, Investigation. Solomon Tesfamariam: Writing - review & editing, Supervision, Conceptualization.

Declaration of competing interest

The authors declare there are no conflicts of interest in this research.

Acknowledgement

The authors acknowledge the Coalition for Disaster Resilient Infrastructure (CDRI), Ronnie & Koh Consultants Pte Ltd, 573972 Singapore and RMIT University for their support in terms of financial, and other research facilities.

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