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MATERIALS 49
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lower than tests. Eurocode 5, Swedish, AWC TR10, and CSA current charring models remain slightly conservative, residual
O86 maintained mean values close to unity, demonstrating strength predictions may be non-conservative for extended
reliable and balanced performance. exposure durations.
For CLT elements, residual strengths showed extensive In contrast, CLT demonstrated a more complex and less
scatter ranging from 10 percent to 70 percent depending on predictable thermal response, as evidenced by the increased
lamella configuration, adhesive performance, and degree of scatter and bias observed across experimental datasets.

delamination. Swedish, AWC TR10, and CSA O86 standards Cross-lamination, adhesive softening, and inter-layer interfaces
all overestimated the mean residual strength, with mean promoted delamination, intermittently exposing previously
normalised values ranging from 1.36 to 1.61. uncharred layers to renewed heating and accelerating effective
The corresponding standard deviation approached 100 charring beyond code-based assumptions.
percent for all standards, highlighting the substantial variability The adhesive-dependent behaviour provides a critical
of predictions compared with Glulam outcomes. explanation for the observed divergence between experimental
Residual stiffness predictions for Glulam beams showed results and code predictions. CLT panels bonded with thermosetting
considerable scatter when compared with experimental data, adhesives generally exhibited limited delamination and more
indicating inconsistency in predicting post-fire stiffness retention. stable char development, while panels manufactured with

AS/NZS 1720.4 consistently underpredicted residual stiffness, heat-softening adhesives experienced earlier bond degradation,
while Eurocode 5, Swedish, AWC TR10, and CSA O86 tended increased delamination frequency, and accelerated charring.
to overestimate stiffness recovery. When comparing international standards, Eurocode 5 and
Standard deviations across all codes ranged between 40 CSA O86 provided the closest agreement with experimental
percent and 90 percent, indicating that residual stiffness was charring rates for Glulam, whereas AWC TR10 and AS/NZS
more sensitive to localised charring, adhesive degradation, and 1720.4 were consistently more conservative.
moisture-induced softening than residual strength. For CLT, however, none of the evaluated standards adequately

For CLT elements, residual stiffness ranged from 10 percent captured the magnitude or variability of the observed charring
to 50 percent of initial stiffness, with greater scatter than behaviour, reinforcing the need for time-dependent, adhesive-
Glulam due to composite layer configuration and interlaminar sensitive, or interface-aware correction factors.
adhesive behaviour.
All standards overestimated stiffness retention, with mean
normalised values ranging from 1.46 to 1.65. The standard Nicolerose25
deviation exceeded 200 percent across all standards, highlighting
extreme variability and poor correlation with test data.
The results demonstrate clear and systematically distinct

behavioural differences between Glulam and CLT when exposed
to fire. Glulam specimens exhibited steady and predictable
charring behaviour, consistent with the assumptions embedded
in international standards.
Although measured charring rates were marginally lower
than design values, the experimentally observed ZSL was often
thicker than assumed in most codes. This indicates that while