Page 48 - FDMAsia Mar/Apr 2026

46 MATERIALS MAR/APR 2026 FDM ASIA | www.fdmasia.com

Getty Images closely with the rates adopted in Eurocode 5 but calibrated to
reflect Canadian timber properties and manufacturing standards.
To account for the strength reduction in the heated wood
beyond the char front, CSA O86 introduces a ZSL that is
subtracted from the residual section, with a thickness of 7
mm for exposures of 20 minutes or longer.

Fire Testing & Behaviour
Understanding the fire performance of mass timber elements
such as Glulam and CLT is fundamental to ensuring structural
safety and advancing the reliability of design standards.
by a coordinated framework comprising the International Fire testing provides critical data on charring progression,
Building Code, the National Design Specification for Wood temperature distribution, delamination behaviour, and residual
Construction, and the American Wood Council Technical mechanical performance, enabling validation of theoretical
Report No. 10 (TR10). models and regulatory provisions.

Unlike Eurocode 5 and AS/NZS 1720.4, AWC TR10 explicitly This section presents a consolidated review of experimental
includes CLT fire design guidance, accounting for adhesive investigations on Glulam and CLT elements exposed to standard
type, delamination behaviour, and charring rate variations fire conditions.
among engineered timber products. In this study, a total of six Glulam and CLT element
The report advances the modelling of timber behaviour fire experiments were reviewed, providing the experimental
under fire exposure by introducing a nonlinear charring rate foundation for evaluating and comparing the predictive accuracy
approach, which differs from the linear charring assumptions of international fire design standards.

used in other international standards. Darmon and Lalu conducted fire testing of a simply supported
For structural analysis, AWC TR10 recommends using an Glulam beam subjected to fire on three sides following the
effective char depth to represent the weakened layer adjacent ISO 834 standard fire curve.
to the char front, defined as 1.2 times the calculated char The test results revealed that the ZSL exceeded the
depth, thereby incorporating a 20 percent allowance for the commonly adopted value, suggesting that the Eurocode 5
heated zone with reduced strength and stiffness. method may be non-conservative and requires revision.
In Canada, the fire design of timber structures is primarily Fahrni et al. conducted six fire resistance tests at the SP
governed by CSA O86, which provides the national framework fire laboratory in Stockholm, using a model-scale furnace and
for the structural design and fire performance evaluation of four-point bending tests.

timber members. The average notional charring rate of six test specimens
Annex B of CSA O86 provides analytical procedures for was found to be 0.73 mm/min, aligning with the 0.7 mm/min
determining the charring depth, ZSL, and effective residual rate specified in Eurocode 5.
cross-section for solid timber, Glulam, and CLT members From four fire tests on Glulam beams under bending stress,
exposed to standard fire conditions. an average ZSL thickness of 6.4 mm was identified, aligning
The one-dimensional and notional charring rates are with Eurocode 5's 7 mm ZSL thickness.
prescribed based on the material type and application, aligning Navaratnam et al. investigated the fire resistance of glued