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Timber structures Fire safety

Structural capacity during the developed and decay phases is typically demonstrated by calculating the amount of timber charring that has occurred and the remaining load-carrying capacity of the timber elements. A typically assumed charring rate is 0.65mm/min, although it varies depending on: • material • geometry • fire exposure • fire protection treatment applied. CLT is known to char non-linearly. As the char layer penetrates the material, the lamina may spall off, exposing the virgin material underneath sooner than anticipated.

Figure 10: Charring of NLT ceiling subject to heat flux. Source: Entuitive

Figure 8: Charring of a CLT wall panel subject to heat flux. Source: Entuitive

Figure 9: Charring of CLT: the effect of delamination on char penetration. Source: Entuitive

Nail-laminated timber (NLT) chars linearly due to the vertical alignment of laminae. However, there is an opportunity for the sides of laminae to char if the connection is not robust and the cross-flow upwards is prevented.

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Timber 2019 Industry Yearbook

Charring of longitudinal members (beams and columns) is slightly different. The heat transfer is no longer one-dimensional and can act on all sides of the member. This results in corner rounding.

Figure 11: Corner rounding of beams and columns. Source: Entuitive

Fire engineers must demonstrate that the timber structure has a sufficient loadbearing capacity for the duration of the fire, taking into account the portion of the material lost to charring. In long-span floors, the size of members is likely

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Timber 2019 Industry Yearbook  

The annual publication of the Timber Research and Development Association (TRADA) includes topical and technical features on all aspects of...

Timber 2019 Industry Yearbook  

The annual publication of the Timber Research and Development Association (TRADA) includes topical and technical features on all aspects of...

Profile for trada
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