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MATERIALS 47
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laminated timber beams to address research gaps related to min for small-scale specimens.
the limited understanding of loaded beam behaviour, internal The ZSL thickness ranged between 6 and 25 mm, and
temperature distribution, and post-fire stiffness degradation. loaded specimens retained approximately 20 to 25 percent of
The mean charring rates were 0.70 mm/min for non-load their initial stiffness after exposure.
bearing beams and 0.71 mm/min for the load-bearing beam. Experimental investigations on Glulam and CLT elements
The load-bearing beam retained 22 percent of its initial flexural reveal distinct behavioural characteristics under fire exposure.

stiffness after 120 minutes of fire exposure. For Glulam, experimental findings generally validate the steady-
The study concluded that GLT beams maintained structural state charring and residual strength assumptions adopted in
integrity under fire but that AS/NZS provisions were overly international fire design standards.
conservative. In contrast, CLT elements exhibit more complex fire behaviour
Lineham et al. conducted experimental tests on CLT due to cross-laminated layering and adhesive-dependent
beams under four-point bending with simultaneous sustained delamination. Adhesive degradation and delamination remain
mechanical loading and intense radiant heating following the the dominant contributors to accelerated charring and reduced
ISO 834 standard fire curve. post-fire stiffness.
The results showed that the assumption of a constant 7 mm The literature review consistently highlights the need for

ZSL thickness is invalid for non-standard heating exposures. time-dependent and scale-adjusted predictive models that
The findings highlight the need to replace the ZSL concept with incorporate adhesive thermal resistance, layer separation, and
more detailed thermo-mechanical cross-sectional analyses that variable ZSL evolution.
properly account for the structural effects of real fire exposures.
Xing et al. investigated the fire resistance and ZSL thickness Comparative Analysis
of CLT floor elements to address research gaps regarding ZSL A comprehensive evaluation of the charring rates of Glulam
variability, charred layer shedding, and the influence of natural and CLT elements under standard fire exposure was

versus standard fire conditions. conducted, comparing experimental results with predictions
The mean charring rate under ISO 834 fire exposure was from internationally recognised standards.
0.69 mm/min, slightly higher than the 0.65 mm/min specified by For Glulam, most international standards produced charring
Eurocode 5, whereas under natural fire, the rate exceeded 1.0
mm/min due to faster heating and higher peak temperatures.
The ZSL thickness ranged from 5 to 34 mm, depending
on lamella configuration, fire type, and char layer shedding,
contrasting with the constant 7 mm assumption in international Flickr
codes.

Bai et al. investigated the scaling effects on the fire
resistance of CLT floors to address gaps in understanding size-
dependent charring behaviour, ZSL development, and residual
thermo-mechanical performance under standard fire exposure.
Results showed that smaller specimens exhibited faster
charring due to reduced thermal inertia, with mean charring
rates increasing from 0.63 mm/min for full-scale to 1.10 mm/