025 - Structural fire engineering with engineered timber with Felix Wiesner

In Episode 18  we have touched on the important topic of fire performance of engineered wood and its wide use in the modern built environment. Today,  we follow up on this subject with Dr Felix Wiesner from the University of Queensland. We leave the (important) topic of compartment fire dynamics and focus on what happens inside the wood in the fire. And there is much more going on than I have initially thought... The transport of moisture, weakening bonds at the glue line and connections, complex thermodynamics of char layers... I will be honest - this is not an easy episode. But that is how it is supposed to be. Because this topic is not easy. You cannot proxy all of these considerations with simple fire resistance. You cannot pretend these issues do not exist.

So the next time someone writes on LinkedIn that "wood in fire is stronger than steel" please send them a link to this episode, with a comment that it is not that simple...

You should definitely follow Felix on Twitter, where you can learn a lot about timber in fire and be updated with the progress on the National Centre for Timber Durability and Design Life.

To arm you up with some resources, please check Felixs' PhD Thesis on "Structural behaviour of cross-laminated timber elements in fires".

In terms of papers interesting ones to read on the structural reductions in the cooling phase are: 

• Wiesner et al, Structural capacity in fire of laminated timber elements in compartments with exposed timber surfaces – for a theoretical consideration of the problem based on real temperatures. The predictions of capacity loss for the glulam column are from tests that were done for a real building.
•  Wiesner et al, Structural Capacity of One-Way Spanning Large-Scale Cross-Laminated Timber Slabs in Standard and Natural Fires where they've validated the model from the paper above in follow up tests by CERIB
• And they have also checked the recovery potential of heated stiffness loss in the following paper (which originated from my PhD). There was no recovery! There was a big dependency on the adhesive type and ply thickness in the loss in structural capacity, which was kind of the whole theme of the PhD - Wiesner, Deeny, and Bisby, Influence of ply configuration and adhesive type on cross-laminated timber in flexure at elevated temperatures

 In terms of testing of structural wall elements, there is the following paper, which kind of then kickstarted a lot of Felixs' PhD research. He says "I was very fortunate to have worked with great Masters students on this and other projects" Wiesner, Randmael, Wang, Bisby, and Hadden Structural response of cross-laminated timber compression elements exposed to fire)

 Also, if your listeners are interested in outcomes from sitting hours in front of a Universal Test machine and waiting for the wood to heat up to specified temperatures before crushing it then they might be interested in the following paper:  (Wiesner, Thomson and Bisby, The effect of adhesive type and ply number on the compressive strength retention of CLT at elevated temperatures). Again we found that adhesive is an important factor in determining failure temperatures in CLT. Also a big difference between transient and steady-sta

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