WoodST: An Advanced Modelling Tool for Fire Safety Analysis of Timber Structures

Significance 

The urge to develop green and sustainable building structures has seen an increase in the use of wood products in the building and construction industry. Being classified as a combustible material, stringent fire safety measures are typically prescribed for timber structures. The analysis of timber connections under fire conditions remains however a significant challenge to engineers and researchers. Among the available constitutive models for wood materials simulation, finite element models are unsuitable for accurate prediction of thermomechanical behaviors and failure modes, that play a critical role in the fire safety of timber structures.

Recently, Dr. Zhiyong Chen, Dr. Christian Dagenais, and Dr. Chun Ni from FPInnovations which is a Canadian not-for-profit R&D private organization which spans the pulp and paper industry, forest operations, wood products, and bio-sourced products developed a temperature-dependent constitutive model, WoodST, for numerical simulations of wood-based materials and connections exposed to fire. The model is a combination of several mechanics sub-models: orthotropic linear elasticity, extended Yamada-Sun strength criteria, thermomechanical relationships, strain-based damage and hardening evolution, plastic flow and hardening law. The simulation objectives included the prediction of failure modes, load-displacement and time-displacement relationships. The research was conducted in collaboration with Dr. Steven Kuan from the British Columbia Institute of Technology and is currently published in Journal of Structural Engineering.

In their work, the research team modelled the structural performance of a laminated veneer lumber (LVL) beam, and a glulam bolted connection under forces and fire to validate the feasibility of the developed model. In comparison with the results of the experimental tests, the model was observed to reasonably simulate the thermal and mechanical behaviors of the LVL beam and glulam connection exposed to fire. The predicted time to failure lied within 10% of the actual failure time, an indication that the model could be accurately used to predict failure time given the nature of the fire event. For the LVL beam and glulam bolted connection, the heat transfer models provided a right prediction of the residual wood dimensions comparable to the experiment results.

The sub-models, in particular, play a significant role in the success of the developed model. For instance, the extended Yamada-Sun strength criteria are useful in determining whether the materials yield or fail in any directions, a strained-based damage evolution describes the softening of the brittle failure due to tension or shear. In contrast, multilinear reduction models describe the influence of fire on the mechanical behaviors of the materials. Further validation of the model, e.g. I-joists and wood-frame floors, has been made since its development, but more validation on timber connections with various types of fasteners and wood products would be necessary.

In a nutshell, the study presented a temperature-dependent plastic-damage constitutive model for simulating the structural performance of timber materials and connections under forces and fire. The obtained results compared well with the results of the experimental tests. The model was, notably, demonstrated to be capable of simulating the thermomechanical responses of LVL beam and glulam connection with only 10% difference. In a statement to Advances in Engineering, the authors highlighted their findings will help researchers and engineers to study in further details, the thermomechanical behavior and fire resistance of wood-based materials and connections.

WoodST: An Advanced Modelling Tool for Fire Safety Analysis of Timber Structures - Advances in Engineering

About the author

Dr. Zhiyong Chen is a scientist in the Building Systems group at FPInnovations where his main research topics are advanced multidisciplinary numerical simulation, mechanics-based analytical modelling, seismic performance, resilient/low-damage structures, fire resistance, and hygrothermal analysis. He is the author of numerous journal/conference papers, books/chapters, standards, and research reports on the structural performance of timber components, connections, and systems under various actions, e.g. earthquakes and fire. He serves as a referee for more than twenty international journals and conferences. Moreover, he is actively involved in technical task groups of timber design standards, e.g. CSA O86. Finally, he is an external graduate faculty and faculty associate at University of Maine.

About the author

Dr. Christian Dagenais is a Lead Scientist and Project Leader in the Building Systems group at FPInnovations where his main research topics are fire resistance, reaction to fire, performance-based fire design, fire modelling and fire safety engineering. He participated in many performance-based design allowing to build timber buildings that would have otherwise been required to be of noncombustible construction. He is the author of numerous technical publications and research reports on fire performance of timber elements and buildings. Moreover, he is actively involved in several technical committees on fire tests, fire safety engineering and timber design, such as ULC, ASTM and CSA. He is currently the ISO TC 92 Fire Safety Canadian Mirror Committee Chair and Head of Canadian delegation at its sub-committee SC4 responsible for developing international standards on fire safety engineering. He participates in many overseas standardization activities, namely the United States, Australia, China and Japan. Finally, he is an invited professor at Université Laval where he teaches a full course on fire safety in buildings and supervise graduate students. Christian is a member of OIQ and SFPE.

About the author

Dr. Chun Ni received Bachelor and Master Degrees from the Department of Civil Engineering, Tongji University, Shanghai in 1985 and 1988, respectively. He received Ph.D. degree from the Faculty of Forestry and Environmental Management, University of New Brunswick in 1997.

Dr. Ni joined Forintek Canada Corp in 1997 and is now a principal research scientist of Advanced Building System in FPInnovations, a national research organisation that provides technical and marketing support for Canadian forest industries. He is in charge of FPInnovations’ China Code and Standard program.

Dr. Ni is a member of Canadian code committee CSA O86 – Engineering Design in Wood, Part 9 Lateral Load Task Group of National Building Code of Canada, and the Objective Based Codes for Wood Frame Constructions. Since 2000, he has been actively involved in various Chinese code and standard committee work on wood products and wood building systems. He is one of the key players in developing design provisions for wood frame construction in the Chinese timber design codes.

References

Chen, Z., Ni, C., Dagenais, C., & Kuan, S. (2020). WoodST: A Temperature-Dependent Plastic-Damage Constitutive Model Used for Numerical Simulation of Wood-Based Materials and Connections. Journal of Structural Engineering, 146(3), 04019225.

Go To Journal of Structural Engineering

Dagenais, C., and Chen, Z. (2020). Expanding Wood Use Towards 2025: Part 1 – Calculating Fire Resistance of Wood-Frame Floor Elements. FPInnovations Project (No.301013618) Report, Quebec City, Canada.

Dagenais, C. and Chen, Z. (2019). ÉVALUATION DE LA RÉSISTANCE AU FEU DES POUTRELLES DE BOIS EN I (Evaluation of the Fire Resistance of Wood I-Beams). FPInnovations Project (No. 301013016) Report, Quebec City, Canada.

Chen, Z., Ni, C., and Dagenais, C. (2018). Advanced Wood-Based Solutions for Mid-Rise and High-Rise Construction: Modelling of Timber Connections under Force and Fire. FPInnovations Project (No. 301012203) Report, Vancouver, Canada.

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