079 - Timber columns failure in the decay phase with Thomas Gernay and Jochen Zehfuss

WEBVTT

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<v Wojciech Wegrzynski>Hello, everybody.

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<v Wojciech Wegrzynski>You're welcome to the fire science show.

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<v Wojciech Wegrzynski>And other episodes related to timber.

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<v Wojciech Wegrzynski>So I guess that's getting everyone excited.

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<v Wojciech Wegrzynski>I usually see.

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<v Wojciech Wegrzynski>More interest in timber'y episodes than any other type of topic in, in fire science.

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<v Wojciech Wegrzynski>I really wonder why, why is that?

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<v Wojciech Wegrzynski>I guess it's one of the most exciting things that happen around and one of the least well understood problems in fire science for people outside of our core group of fire science engineers.

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<v Wojciech Wegrzynski>And, My today's guests have certainly stirred the attention to the problem and the issues and some features of it.

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<v Wojciech Wegrzynski>For sure.

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<v Wojciech Wegrzynski>Uh, with their post on LinkedIn, that went absolutely crazy.

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<v Wojciech Wegrzynski>They've posted a video of a collapse of a column under loads.

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<v Wojciech Wegrzynski>The column was heated for fairly short amount of time, like 15 minutes, and then left all alone.

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<v Wojciech Wegrzynski>Still.

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<v Wojciech Wegrzynski>Underload.

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<v Wojciech Wegrzynski>And after 90 or so minutes, it just cracked.

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<v Wojciech Wegrzynski>And that was one of the.

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<v Wojciech Wegrzynski>Shoulders.

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<v Wojciech Wegrzynski>And the easiest visual.

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<v Wojciech Wegrzynski>Representations of what the threat looks like.

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<v Wojciech Wegrzynski>The fact that fire has ended doesn't mean.

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<v Wojciech Wegrzynski>the, the structural performance is from now unhindered by the consequences of the fire.

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<v Wojciech Wegrzynski>The fact that you have completely different material that behaves completely different.

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<v Wojciech Wegrzynski>At certain temperatures at certain.

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<v Wojciech Wegrzynski>Points of heat transfer into the element.

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<v Wojciech Wegrzynski>That's beautiful.

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<v Wojciech Wegrzynski>fire science.

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<v Wojciech Wegrzynski>Absolutely beautiful.

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<v Wojciech Wegrzynski>So I, after I saw this poster, I had to invite them immediately to the podcast episode to discuss the decay face collapse and all the stuff around that.

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<v Wojciech Wegrzynski>It's still an early research.

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<v Wojciech Wegrzynski>I think they've been pointed something.

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<v Wojciech Wegrzynski>Explicitly important for the fire science and the design of timber buildings.

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<v Wojciech Wegrzynski>And it seems they're looking further into that.

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<v Wojciech Wegrzynski>So.

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<v Wojciech Wegrzynski>More is expected to come, but I'm very happy.

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<v Wojciech Wegrzynski>We are able to share these results with you at this point.

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<v Wojciech Wegrzynski>Okay.

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<v Wojciech Wegrzynski>My today's guests are professor Thomas Gernay from Johns Hopkins university.

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<v Wojciech Wegrzynski>Uh, he was already in the podcast talking about the structural fire engineering.

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<v Wojciech Wegrzynski>So view, we're very welcome to check that episode as well.

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<v Wojciech Wegrzynski>And the second guest is professor Jochen Zehfuss from Technical University in Braunschweig Who has carried their research that we are talking about in here, the collaboration was, was much larger than you learn about it.

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<v Wojciech Wegrzynski>From the episode, but these two, these two guys.

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<v Wojciech Wegrzynski>And invited to talk and the talk with it.

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<v Wojciech Wegrzynski>So let's not prolong this anymore.

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<v Wojciech Wegrzynski>Let's spin the intro and jump into the episode.

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<v Wojciech Wegrzynski>Hello everybody.

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<v Wojciech Wegrzynski>Welcome to   Fire Science Show.

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<v Wojciech Wegrzynski>I'm here today with, two guests who did quite, a mess on LinkedIn a few weeks ago by their, their post on, on failure of timber element.

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<v Wojciech Wegrzynski>Uh, that is, professor Thomas Gernay hey, Thomas.

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<v Wojciech Wegrzynski>Great to have you back in the podcast.

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<v Thomas Gernay>hello was, yes.

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<v Thomas Gernay>Thank you very much for having me.

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<v Wojciech Wegrzynski>And, uh, a new guest, professor Johan.

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<v Wojciech Wegrzynski>Zeus.

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<v Wojciech Wegrzynski>hello Johan.

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<v Wojciech Wegrzynski>Very nice to have you in the.

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<v Jochen Zehfuss>Hello everybody.

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<v Wojciech Wegrzynski>Fantastic.

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<v Wojciech Wegrzynski>Uh, thank, thank you for, um, taking my invite.

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<v Wojciech Wegrzynski>You, you seem to be superstars now with, your research.

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<v Wojciech Wegrzynski>Uh, actually I'll describe if, if someone missed what happened.

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<v Wojciech Wegrzynski>you have performed an interesting research into timber column failure during the cooling phase, and, posted a post on LinkedIn with a video of the failure and.

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<v Wojciech Wegrzynski>For engineering standards.

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<v Wojciech Wegrzynski>It, it went quite viral and  I found it super interesting because you've captured in a very visual way.

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<v Wojciech Wegrzynski>One of the things we really struggle to discuss, it's super difficult to explain someone why decay phase would be important, and you, with the ten second video, have, nailed it, perfectly.

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<v Wojciech Wegrzynski>But, let's not have this, uh, episode about the video.

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<v Wojciech Wegrzynski>Let, let's have it, about the research that that led.

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<v Wojciech Wegrzynski>So, uh, how about we discuss the decay phase overall?

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<v Wojciech Wegrzynski>Like what, what is the decay phase and, why would we care about it at all?

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<v Thomas Gernay>indeed it starts with looking into how real fire develop and grow and then decay and understanding what effects that can have on, on structural stability and on structures and in the.

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<v Thomas Gernay>structural fire community, there's been a shift to going to those performance based fire design approach.

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<v Thomas Gernay>So we want to really understand on the real fire, um, how is tructure going to respond.

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<v Thomas Gernay>And so in the community, we start to understand that when the gas temperature in a components start to decrease, that's not the end.

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<v Thomas Gernay>Uh, for the structure far.

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<v Thomas Gernay>Because, uh, for one, there is going to be a thermal lag.

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<v Thomas Gernay>There is going to be these heat waves that continues, penetrating, deeper in the sections.

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<v Thomas Gernay>And so you have the core of the section of your structural members which temperatures continues increasing.

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<v Thomas Gernay>As a result, their strength and mechanical properties continue decreasing, and you can have delayed failure.

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<v Thomas Gernay>This.

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<v Thomas Gernay>Simple physics.

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<v Thomas Gernay>This is distance true for all material.

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<v Thomas Gernay>You always have this know, this heat wave comes from the differential equations of, uh, heat condition.

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<v Thomas Gernay>so it's independent of whether material is combustible, such as timber or non combustible, such as steel and concrete.

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<v Thomas Gernay>And so, Many people in the community have been, becoming more and more interested in understanding that, quantifying that, threat of delayed collapse.

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<v Thomas Gernay>We have also seen some real fire accidents where there were delayed failure during cooling that can be particularly threatening to firefighters and first responders who might be inside.

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<v Thomas Gernay>So it's very important for us to, for engineers to, to understand that.

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<v Thomas Gernay>And from there we started working with modeling and then now we moved to experiments and eventually to these, experiments on timber columns.

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<v Wojciech Wegrzynski>But this delay phase, this, late failure or maybe even post fire failure within our paradigm of, fire resistance and, ISO curve and, REI classes, It's not there, I mean, the, the standard curve goes, uh, up all the way, it never goes down.

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<v Wojciech Wegrzynski>So it's not a part of our paradigm today of, of testing structural members, right.

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<v Jochen Zehfuss>Yes, that's right.

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<v Jochen Zehfuss>Yeah.

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<v Jochen Zehfuss>the, resistance class approach is, let's say a very simple approach.

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<v Jochen Zehfuss>We use all over the world with the ISO 8 34 curve.

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<v Jochen Zehfuss>That is also a very simple model of the realistic fire.

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<v Jochen Zehfuss>But, as it is a very simple model.

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<v Jochen Zehfuss>you can subject all, elements for this, uh, ISO curve.

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<v Jochen Zehfuss>and um, of course, we neglect the cooling phase.

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<v Jochen Zehfuss>And as Thomas said, we have this delay problem.

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<v Jochen Zehfuss>This is also a problem for concrete elements as well.

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<v Jochen Zehfuss>Not so much for steel elements because they have a very high heat connectivity and they are not so massive in the cross sections.

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<v Jochen Zehfuss>But the difference for the timber between timber and concrete is then, of course, that timber is a burning material.

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<v Jochen Zehfuss>So that we have, not only the delayed heating, um, where the core is heated later after, or in the cooling phase as well.

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<v Jochen Zehfuss>And we have also, uh, fire or, yeah, a reducing cross section, caused by the burning.

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<v Jochen Zehfuss>as we know, the burning, happens, until the fire is nearly extinguished.

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<v Jochen Zehfuss>We, we have also burning in our cross sections, uh, with temperatures beyond 300 degrees in the cooling phase.

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<v Jochen Zehfuss>And then, uh, another point is, uh, as mentioned also in the paper, the degradation of mechanical properties of, timber, for example, which degrade, um, until temperature of 100 degrees and even lower where we loss, capacity or strength.

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<v Wojciech Wegrzynski>I just wanted to point out that I actually had an podcast episode with Felix Wiesner about the moisture transport within timber elements and how the, the tur wave propagates.

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<v Wojciech Wegrzynski>He has tortured me with very scientific terms and, uh, , but it was a popular episode for some reason.

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<v Wojciech Wegrzynski>Maybe it's, it's the magic of, of Felix, but, but indeed, a lot happens within.

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<v Wojciech Wegrzynski>timber, uh, at, quite low temperatures because let's face it, a hundred degrees, for a fire temperatures, that's not a very, very high temperature.

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<v Wojciech Wegrzynski>so, you can probably expect this be reached at very deep into your, structural element.

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<v Wojciech Wegrzynski>So now, now let's, uh, talk about when have you realized that.

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<v Wojciech Wegrzynski>Such a research is necessary, and the differences may be so big that it, it really requires calls for additional investigation.

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<v Thomas Gernay>So on my hand, it has been quite a, a long process of wrapping my head around this, this issue of delayed failure.

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<v Thomas Gernay>I can trace it back to 2010, 2011 when I was working on my PhD and I was developing, um, a material model for concrete in fire.

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<v Thomas Gernay>And, um, I was focusing also on the, on the cooling phase, trying to get those.

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<v Thomas Gernay>Material properties and irreversibility, right.

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<v Thomas Gernay>And transient Cris trying and, and all of that.

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<v Thomas Gernay>And so as part of this, I, I was doing some numerical modeling with columns, loaded columns.

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<v Thomas Gernay>And when I was applying natural fires with the cooling phase, I, I could observe in some cases delayed failure.

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<v Thomas Gernay>So that was 2010, 2011.

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<v Thomas Gernay>And I thought, well that's, that's interesting.

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<v Thomas Gernay>And as I mentioned, there had been a few.

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<v Thomas Gernay>Accidents such as the, and bus parking in Switzerland where there had been a failure in cooling.

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<v Thomas Gernay>So I thought that's something to, to work further on.

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<v Thomas Gernay>So a little bit later, I started, trying to systematize this study and I had a paper with Jean-Marc Franssens where we.

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<v Thomas Gernay>Proposed an, uh, standard indicator to try to approach the problem of burnout, resistance, or resistance to, to full burnout in a systematic way with numerical modeling.

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<v Thomas Gernay>And when we applied this approach to different types of structural members, We identified that, um, it was possible to show that timber was possibly more at risk for the reasons mentioned by by Jochen and really most of the reasons are the fact that you have this very low conductivity.

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<v Thomas Gernay>So the heat transfer takes a long, a long time coupled with reduction of strength at low temperature.

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<v Thomas Gernay>So even if four, five hours after the fire you get.

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<v Thomas Gernay>80 degrees C, a hundred degrees C in the core, you lose a lot of of strength just to put number.

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<v Thomas Gernay>If you trust the Euro code, Annex B on advanced calculation methods at 100 degrees C reduction factor for the strength is 25% for compression and, and 65% for tension.

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<v Thomas Gernay>So you've lost actually, most of your strengths, right?

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<v Thomas Gernay>and so from there, I did more numerical modeling, studying reinforc concrete column, uh, timber collumns and so on.

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<v Thomas Gernay>and, and we could indeed show that the burnout resistance for timber was significantly lower than, its fire resistance, meaning there was a risk of failure on the relatively short fire.

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<v Thomas Gernay>Uh, but there were still no experiments that had specifically been designed to, to quantify this.

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<v Thomas Gernay>so testing members loaded under heating and cooling to, to, to see the failure.

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<v Thomas Gernay>So finally there was this, great consortium with lots of, lots of institutions and colleagues who had all been working on this issue, you know, independently.

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<v Thomas Gernay>I was like, oh, we should, we should do something together.

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<v Thomas Gernay>So, uh, Tim experiments, of course, uh, Johan who's here, who, who conducted the experiments.

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<v Thomas Gernay>But in the consortium there is also CERIB.

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<v Thomas Gernay>Who's Fabian Robert, Jean-Marc Franssens at University of Liege, uh, Robert McNamee Rise.

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<v Thomas Gernay>Patrick Baumonte at in Milan.

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<v Thomas Gernay>And I, I think I, I'm not forgetting anyone, but that, that's a great team.

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<v Thomas Gernay>So we work together to devise and experiments to be able to study this and try to be as systematic as possible and show what the behavior would be.

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<v Jochen Zehfuss>From my point of view, I think in the last 10 years we made in our institute several projects, on the fire behavior of.

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<v Jochen Zehfuss>Timber structures, and most of them, of course were protected, with gypsum boards.

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<v Jochen Zehfuss>but then I think in most other European countries, we have a trend, to applying more timber buildings or, uh, there were, there's a trend to build more timber buildings.

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<v Jochen Zehfuss>Yeah.

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<v Jochen Zehfuss>Due to, uh, for example, sustainable sustainability or.

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<v Jochen Zehfuss>decarbonization reasons and so, and so building your regulations are changing and they need, uh, research.

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<v Jochen Zehfuss>And so we had, uh, in several projects the question, what will happen when we have.

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<v Jochen Zehfuss>Timber elements which are not protected.

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<v Jochen Zehfuss>massive timber elements, for example, CLTs and so on, and how many percent is allowed, of the enclosure, to be unprotected.

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<v Jochen Zehfuss>And then there was also the question.

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<v Jochen Zehfuss>Do we have a self extinction of the timber elements when the so-called mobile fire load, the furnishings And, others is burn.

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<v Jochen Zehfuss>Um, but on the other hand we have, uh, the timber, which is also burning, which is called structural fire load.

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<v Jochen Zehfuss>We see in, several projects.

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<v Jochen Zehfuss>It's not so easy to predict self extinction.

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<v Jochen Zehfuss>And it depends of course on the geometry of the fire compartment, on, the oxygen, um, which oxygen flow and some other parameters.

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<v Jochen Zehfuss>And, so, self exigence is, uh, I would say, very seldom case, yeah.

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<v Jochen Zehfuss>In some circumstances it could happen.

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<v Jochen Zehfuss>And then of course there's the question, what will happen in the cooling phase when the cross section, is reducing, reducing, reducing?

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<v Jochen Zehfuss>And then of course, there could.

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<v Jochen Zehfuss>be a failure.

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<v Jochen Zehfuss>And this is, uh, our motivation to go deeper in this subject.

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<v Jochen Zehfuss>And so, and then we find we find ourself in this group, uh, as you, said, the European.

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<v Jochen Zehfuss>Champions, dunno if this is the right word,

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<v Wojciech Wegrzynski>All Stars, European All Stars.

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<v Jochen Zehfuss>but some of the leading researchers from the European countries.

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<v Jochen Zehfuss>And, I think it's a good thing that we find together and, uh, do a systematical research investigating also the approach, of, uh, Thomas.

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<v Jochen Zehfuss>that we, calibrate a method which, is originally used for concrete elements and to adopt that yet now, um, for timber elements as well.

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<v Wojciech Wegrzynski>Beautiful.

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<v Wojciech Wegrzynski>So, tell me more about, the research.

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<v Wojciech Wegrzynski>And I already see there is so many, I'm noting the factors that, that you've mentioned.

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<v Wojciech Wegrzynski>there was different losses in, in compression in tension, uh, I guess, utilization factor of the element, would, play a big role.

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<v Wojciech Wegrzynski>Johan mentioned technology, so I guess when we get come into like, uh, glued elements like clt, it must be super Interesting.

00:15:26.602 --> 00:15:33.120
<v Wojciech Wegrzynski>So, so tell, tell me how, how did you approach this research to really like narrow it down to the most interesting.

00:15:33.125 --> 00:15:36.211
<v Wojciech Wegrzynski>And, and where did you find the most interesting, thing to, go for?

00:15:36.546 --> 00:15:37.806
<v Thomas Gernay>The the key idea.

00:15:37.914 --> 00:15:47.701
<v Thomas Gernay>Is to be systematic and to find a way to, I would say almost standardize the, quantification of the behavior of structural elements under fires that include the decay phase.

00:15:47.831 --> 00:15:56.304
<v Thomas Gernay>So the approach, that we proposed consistent subjecting structural members to fire of varying duration of heating

00:15:56.524 --> 00:15:56.914
<v Wojciech Wegrzynski>Okay.

00:15:58.360 --> 00:16:05.625
<v Thomas Gernay>Identifying the shortest fire that, would lead to failure, or the longest fire that could be survived indefinitely to burnout if you want.

00:16:05.625 --> 00:16:18.602
<v Thomas Gernay>So this, this threshold, in order to do that and to be systematic, what we propose is to use the heating according to ISO834, since everybody's familiar with this heating, but then to stop at some point.

00:16:18.893 --> 00:16:24.232
<v Thomas Gernay>And to have a linear cooling phase that is in accordance with the Euro code parametric fire model.

00:16:24.232 --> 00:16:25.753
<v Thomas Gernay>So why a linear cooling phase?

00:16:25.753 --> 00:16:33.393
<v Thomas Gernay>Because we could take any cooling phase, but the only natural fire that is in the Euro code that is codified is the parametric fire.

00:16:33.393 --> 00:16:36.432
<v Thomas Gernay>So we may as well take that one and everybody can take that one.

00:16:36.475 --> 00:16:36.924
<v Wojciech Wegrzynski>Sorry Thomas.

00:16:36.924 --> 00:16:40.884
<v Wojciech Wegrzynski>And it's important to note that is the cooling of the furnace itself.

00:16:40.884 --> 00:16:44.827
<v Wojciech Wegrzynski>So it is the, external boundary condition on imposed on your element.

00:16:44.832 --> 00:16:49.498
<v Wojciech Wegrzynski>And what happens in the element is, is the physics of the element, and that's what you're looking at, right?

00:16:49.801 --> 00:16:50.471
<v Thomas Gernay>Exactly.

00:16:50.471 --> 00:17:00.390
<v Thomas Gernay>So we are talking here about temperature in the furnace, but once the temperature starts decreasing in the furnace, of course in parts of the elements in the interior, the temperature keeps on increasing.

00:17:00.880 --> 00:17:02.030
<v Thomas Gernay>So this is the idea.

00:17:02.030 --> 00:17:05.431
<v Thomas Gernay>Find the burnout resistance, the shortest fire that leads to failure.

00:17:05.980 --> 00:17:07.737
<v Thomas Gernay>and then from there we devised.

00:17:08.086 --> 00:17:13.326
<v Thomas Gernay>An experimental, program, a test metrics where we built identical specimens.

00:17:13.326 --> 00:17:17.326
<v Thomas Gernay>So we had, for the timber, we had eight glulam columns identical.

00:17:18.416 --> 00:17:24.611
<v Thomas Gernay>We, defined the load on these currents, assuming that they were in a typical, uh, buildings and doing the euro code design.

00:17:24.611 --> 00:17:31.277
<v Thomas Gernay>So they had, utilization factor in terms of holding that would be typical in the first situation according to the codes.

00:17:32.017 --> 00:17:33.957
<v Thomas Gernay>And the only thing that vari.

00:17:34.112 --> 00:17:43.461
<v Thomas Gernay>Between the experiments on each of those eight columns was the fire, the definition of the, I would say more gas temperature time curve in the furnace to be more, uh, specific.

00:17:44.031 --> 00:17:46.382
<v Thomas Gernay>So we repeated all tests twice.

00:17:46.432 --> 00:17:49.409
<v Thomas Gernay>We had tests, to measure the standard fair resistance.

00:17:49.638 --> 00:18:07.976
<v Thomas Gernay>R  so for R obtained, uh, 55 and 58 minutes in the two tests, then informed by the numerical modeling by finite, models conducted Prior to the test, we had a test with the heating for 15 minutes, followed by the linear cooling phase.

00:18:08.498 --> 00:18:15.317
<v Thomas Gernay>And we did it twice and the two columns failed during cooling quite late in the cooling phase.

00:18:15.317 --> 00:18:20.974
<v Thomas Gernay>So they failed after 98 minutes for one and 153 minutes for the other.

00:18:20.974 --> 00:18:23.775
<v Thomas Gernay>So again, that's a column that's heated for 15 minutes.

00:18:23.884 --> 00:18:25.615
<v Thomas Gernay>then then cool.

00:18:25.615 --> 00:18:30.375
<v Thomas Gernay>Then the F cooling and it fails at after two and a half hour.

00:18:30.383 --> 00:18:33.720
<v Wojciech Wegrzynski>what, what, what was the approximate temperature after 15 600

00:18:34.076 --> 00:18:34.567
<v Jochen Zehfuss>Yeah.

00:18:34.567 --> 00:18:35.247
<v Jochen Zehfuss>700.

00:18:35.682 --> 00:18:37.393
<v Wojciech Wegrzynski>That's not much for, for fire.

00:18:37.393 --> 00:18:41.457
<v Wojciech Wegrzynski>Uh, that, that's, heat flu of like 35 kilowatts per square.

00:18:41.826 --> 00:18:45.789
<v Wojciech Wegrzynski>that's not, not huge in terms of, of, uh, exposure, to be honest.

00:18:45.795 --> 00:18:46.029
<v Wojciech Wegrzynski>Yeah.

00:18:46.161 --> 00:18:46.721
<v Thomas Gernay>Right.

00:18:46.721 --> 00:18:57.480
<v Thomas Gernay>And when it failed, so again, after two hours and a half, the temperature was in the furnace almost back to around 100 degrees because it plateaus, it doesn't go exactly to 20, but it was, it was cool, right?

00:18:57.941 --> 00:19:03.347
<v Thomas Gernay>And then two columns under, 10 minutes heating followed by the, and these two survived.

00:19:03.347 --> 00:19:05.508
<v Thomas Gernay>And we measured the, the strengths.

00:19:05.647 --> 00:19:10.468
<v Thomas Gernay>But so we reached our objective in this experimental campaign to test identical members.

00:19:10.667 --> 00:19:15.438
<v Thomas Gernay>Only vari the heating exposure and have the three outcomes that you wanted to have.

00:19:15.438 --> 00:19:24.484
<v Thomas Gernay>So, measure the standard for resistance, find a short fire, but that results in failure, and then find the slightly shorter fire that would be, survived.

00:19:24.484 --> 00:19:32.807
<v Thomas Gernay>So we, bounded this burnout resistance, this fire that's the threshold between failure and cooling and, and survivability to full burnout.

00:19:33.277 --> 00:19:33.487
<v Wojciech Wegrzynski>okay.

00:19:33.487 --> 00:19:37.950
<v Wojciech Wegrzynski>I guess the most interesting thing is what different in the 10 versus 15 minute, fire.

00:19:37.950 --> 00:19:46.700
<v Wojciech Wegrzynski>So how much did the temperature profiles inside vary and, how big the difference, uh, was in, in what you've observed between these two tests?

00:19:46.771 --> 00:19:47.214
<v Jochen Zehfuss>Yeah.

00:19:47.255 --> 00:19:52.657
<v Jochen Zehfuss>it seems to be, only five minutes difference in this, uh, DHP time.

00:19:52.921 --> 00:19:54.861
<v Jochen Zehfuss>10 or 15 minutes, but.

00:19:55.691 --> 00:20:02.921
<v Jochen Zehfuss>It means when you see, um, on the, uh, ISAC curve in the ISAC curve is increasing, uh, very high in the first minutes.

00:20:02.921 --> 00:20:09.993
<v Jochen Zehfuss>And there we have a difference about 100, 120 degrees, about, between the 10th and 15th minutes.

00:20:10.493 --> 00:20:20.748
<v Jochen Zehfuss>And, uh, that means, um, that also in the cooling phase because, the cooling phase, um, the temperature time, causes in the cooling phase is parallel.

00:20:21.198 --> 00:20:26.448
<v Jochen Zehfuss>Now going from the, uh, starting from the 10th minute, or from the 15th minute.

00:20:26.748 --> 00:20:35.837
<v Jochen Zehfuss>And that means that we have, even higher temperatures in the cross section, which are approximately this 100 degrees and more.

00:20:35.837 --> 00:20:43.048
<v Jochen Zehfuss>And, then we have, in the, columns which survive the fire with the d h P of 10 limits.

00:20:43.413 --> 00:21:03.742
<v Jochen Zehfuss>We, uh, remain the main parts of the cross section under the 300 degrees in the core, we had lower or very lower temperatures, but, in the, cases of the dhp of 15 minutes, we have higher temperatures in the cores so the cross section.

00:21:04.028 --> 00:21:08.594
<v Jochen Zehfuss>Which remains, under the 300 degrees is very much lower.

00:21:08.942 --> 00:21:19.538
<v Wojciech Wegrzynski>So, To put it into perspective, the amount of heat that this column got from this additional five minutes of exposure, obviously in higher temperatures at the higher exposure.

00:21:19.808 --> 00:21:25.756
<v Wojciech Wegrzynski>So the sum of heat just, could penetrate so much deeper into the column that it, pretty much damaged or weakened.

00:21:26.087 --> 00:21:31.825
<v Wojciech Wegrzynski>Such a significantly larger part of the cross section that, under this load it was not, not enough anymore.

00:21:32.137 --> 00:21:34.208
<v Wojciech Wegrzynski>that's superb difference.

00:21:34.212 --> 00:21:38.513
<v Wojciech Wegrzynski>But we were talking here about something that is heated from four sides.

00:21:38.788 --> 00:21:44.958
<v Wojciech Wegrzynski>Let's, uh, I hope you're comfortable with, uh, hypothe, but what if this was a slab?

00:21:44.958 --> 00:21:47.992
<v Wojciech Wegrzynski>I mean, then we would be talking about one side exposure.

00:21:48.492 --> 00:21:55.542
<v Thomas Gernay>I would say that we can generalize that, of course, not the numbers, the quantification depends members, the applied load, et, etc.

00:21:55.563 --> 00:21:58.702
<v Thomas Gernay>And in a real building, or these will be slightly different.

00:21:58.923 --> 00:22:03.383
<v Thomas Gernay>But it's important to understand that what we showed in those tests is not the fluke.

00:22:03.383 --> 00:22:10.708
<v Thomas Gernay>It's not something, Particular that happened because of denomination or because of this specific column being foresight.

00:22:10.817 --> 00:22:17.188
<v Thomas Gernay>It's really a demonstration of the physics of the fact that heat transfer continues during the cooling phase and even thereafter.

00:22:17.798 --> 00:22:21.468
<v Thomas Gernay>As a result, the interior part of the sections get.

00:22:22.202 --> 00:22:24.893
<v Thomas Gernay>Hotter than at the time of the peak gas temperature.

00:22:24.893 --> 00:22:26.413
<v Thomas Gernay>And so they lose their strengths.

00:22:26.593 --> 00:22:32.373
<v Thomas Gernay>And if the loss of strength in the core is, is sufficiently severe, then it gets to failure.

00:22:32.742 --> 00:22:40.796
<v Thomas Gernay>So this is true regardless of the, the boundary condition in terms of the number of heated, uh, sides, it's true sore regardless of the type of member.

00:22:41.401 --> 00:22:46.780
<v Thomas Gernay>And again, it's true, but to a different extent because material loads are different, but it's also for concrete.

00:22:46.780 --> 00:22:53.300
<v Thomas Gernay>And we had, uh, papers with numer modeling that show, that showed that for concrete also wanted to add that.

00:22:53.300 --> 00:23:04.391
<v Thomas Gernay>So this phenomenon, we, we, we understand it, we can relate it to physics and again, we were able to model it with finite treatment models, including before conducting the experiment.

00:23:04.391 --> 00:23:04.871
<v Thomas Gernay>So it's.

00:23:05.621 --> 00:23:07.861
<v Thomas Gernay>Calibrating, you know, but app remodeling.

00:23:07.861 --> 00:23:19.500
<v Thomas Gernay>So we had the paper published before and the agreement is, is actually quite close, which as a side note is also interesting because finite element models of timber elements in cooling at this time.

00:23:19.933 --> 00:23:32.461
<v Thomas Gernay>They rely on, properties, mechanical thermal properties that are provided in the Euro code, um, Euro Code five part one, two, and xb, which have been derived based on ISO exposure for heating.

00:23:33.094 --> 00:23:35.534
<v Thomas Gernay>so there, there was a little bit of an unknown whether.

00:23:36.189 --> 00:23:40.388
<v Thomas Gernay>Predictions, you extrapolating to modeling the cooling would be appropriate.

00:23:40.888 --> 00:23:48.586
<v Thomas Gernay>And through those experiments we see that although, inputs can always be improved, overall, we can, uh, predict the behavior.

00:23:48.596 --> 00:23:59.262
<v Thomas Gernay>So really these models, finite element models can be very useful in understanding and predicting whether they will be, failure in cooling, including with our current knowledge of properties, which again, I hope we improve.

00:23:59.262 --> 00:24:03.063
<v Thomas Gernay>I hope we get that even more accurate, but it's already working quite well.

00:24:03.268 --> 00:24:06.661
<v Wojciech Wegrzynski>Were there any other things observed during the test?

00:24:06.661 --> 00:24:09.780
<v Wojciech Wegrzynski>Like maybe the, the failure mode have, shocked you in, in a way?

00:24:09.780 --> 00:24:15.661
<v Wojciech Wegrzynski>Uh, how, how did the failure mode actually look compared to the failure of the same element without any heating?

00:24:15.661 --> 00:24:18.510
<v Wojciech Wegrzynski>Because I know you also like crushed one of them, right?

00:24:18.601 --> 00:24:18.780
<v Wojciech Wegrzynski>Uh,

00:24:19.084 --> 00:24:19.503
<v Jochen Zehfuss>Yes.

00:24:19.503 --> 00:24:23.423
<v Jochen Zehfuss>We also crossed one, um, element without heating.

00:24:23.680 --> 00:24:24.710
<v Jochen Zehfuss>to be sure.

00:24:25.192 --> 00:24:36.292
<v Jochen Zehfuss>What, what load degree we assumed as to set, we, defined the load degree in a way which is usual for, uh, let's say flat buildings, following the codes.

00:24:36.311 --> 00:24:47.295
<v Jochen Zehfuss>but in our tests and our cold tests, um, we state at a very, higher, um, capacity as we zoomed with the, um, formulas of the code.

00:24:47.741 --> 00:25:00.884
<v Jochen Zehfuss>So, One reason might be that there is a very large spread, due to the material timber, which you cannot compare with steel or with concrete, and, Yeah.

00:25:01.055 --> 00:25:06.924
<v Jochen Zehfuss>Um, the failure mode was, for, for the, um, fire expos, columns.

00:25:07.654 --> 00:25:10.355
<v Jochen Zehfuss>, due to the reduced cross section of course.

00:25:10.494 --> 00:25:13.234
<v Jochen Zehfuss>And then,.

00:25:11.755 --> 00:25:25.346
<v Jochen Zehfuss>Let's say it was a, I think more or less, the failure on the tension side, uh, where we had the failure of the finger joints, that seems to be the merge in the tests.

00:25:25.796 --> 00:25:32.527
<v Jochen Zehfuss>Um, We had for, isof fire and also for the tests in the cooling phase.

00:25:32.759 --> 00:25:35.759
<v Wojciech Wegrzynski>So you mean the connections where the Ellas are glutes together?

00:25:36.371 --> 00:25:36.790
<v Jochen Zehfuss>Yes.

00:25:37.567 --> 00:25:40.942
<v Jochen Zehfuss>so we have to go deeper in this, subject.

00:25:41.508 --> 00:25:45.019
<v Jochen Zehfuss>but, these, well, the first, uh, insights we had, yeah.

00:25:46.038 --> 00:25:46.798
<v Wojciech Wegrzynski>Interesting, interesting.

00:25:46.803 --> 00:25:49.444
<v Wojciech Wegrzynski>And, uh, the timber was, much stronger than eurocodes.

00:25:49.709 --> 00:25:51.179
<v Wojciech Wegrzynski>I guess you've ordered the sample.

00:25:51.179 --> 00:25:59.429
<v Wojciech Wegrzynski>As a laboratory, they always send you the strongest samples They have, you know, ruining science by, by sending

00:25:59.592 --> 00:26:00.711
<v Jochen Zehfuss>maybe, maybe.

00:26:02.210 --> 00:26:02.509
<v Wojciech Wegrzynski>okay.

00:26:02.539 --> 00:26:02.750
<v Wojciech Wegrzynski>Okay.

00:26:02.941 --> 00:26:12.326
<v Wojciech Wegrzynski>What stresses me about, this, experiment and the visuals, you know, when I do a large, clt, Experiments with, with the whole structures.

00:26:13.256 --> 00:26:18.865
<v Wojciech Wegrzynski>You can usually see after the, flames self extinguish at some point if they do.

00:26:19.194 --> 00:26:25.615
<v Wojciech Wegrzynski>But if they do, you can observe how the, all the charts whitens the, on the structures.

00:26:26.025 --> 00:26:30.345
<v Wojciech Wegrzynski>And there's this ation eating out your, your column.

00:26:30.345 --> 00:26:38.505
<v Wojciech Wegrzynski>And you know, you see this giant glulam columns like slowly but, but very steadily disappear in front of your eyes.

00:26:39.285 --> 00:26:41.234
<v Wojciech Wegrzynski>Especially, uh, we, we had one test.

00:26:41.234 --> 00:26:48.825
<v Wojciech Wegrzynski>We had, uh, there was a massive steel joint at the bottom and you could like literally see more and more of this still joint coming out of the column.

00:26:48.825 --> 00:26:53.203
<v Wojciech Wegrzynski>That was really stressful, but, it was stressful looking at it without knowing your experi.

00:26:53.441 --> 00:26:59.467
<v Wojciech Wegrzynski>Now knowing your experiments, it's exponentially more stressful because I do not see what's happening inside.

00:26:59.983 --> 00:27:05.864
<v Wojciech Wegrzynski>and now when we don't have combustion, but there is char oxidation  I guess this is also exothermic process.

00:27:06.253 --> 00:27:10.050
<v Wojciech Wegrzynski>So again, this, for one, it, it generates new heat.

00:27:10.290 --> 00:27:13.921
<v Wojciech Wegrzynski>So, so the heat propagates again into the element.

00:27:14.401 --> 00:27:18.631
<v Wojciech Wegrzynski>And the other problem is what, what Carmen Górska has shown in her PhD.

00:27:19.020 --> 00:27:19.260
<v Wojciech Wegrzynski>It's.

00:27:19.776 --> 00:27:23.098
<v Wojciech Wegrzynski>So the heat goes, uh, from hotter to colder.

00:27:23.338 --> 00:27:26.528
<v Wojciech Wegrzynski>If the surface is hot, it, it's not gonna go that way, right.

00:27:26.597 --> 00:27:27.448
<v Thomas Gernay>Absolutely.

00:27:27.617 --> 00:27:38.448
<v Thomas Gernay>So again, for all materials, even non-combustible, the heat travels from hot to cool, so it's going to keep on traveling toward the core with timber there.

00:27:39.127 --> 00:27:43.778
<v Thomas Gernay>Lots of additional complex physics going on because it's a combintion material.

00:27:43.778 --> 00:27:53.577
<v Thomas Gernay>You can have, you know, combintion can continue and Johan has talked about self extinction and how that's a challenge to, to, to understand exactly and to know what's going to happen with respect to that.

00:27:53.597 --> 00:27:57.137
<v Thomas Gernay>You have smoldering and you have drying Deion and so on.

00:27:57.137 --> 00:27:57.978
<v Thomas Gernay>Paralysis, right?

00:27:57.978 --> 00:28:01.327
<v Thomas Gernay>So, Again, it's a, it's a combination of all of that.

00:28:01.327 --> 00:28:04.607
<v Thomas Gernay>Timber is even more complex because it's combustible.

00:28:04.988 --> 00:28:15.933
<v Thomas Gernay>But even if we could control and make sure we have self extinction, we don't have smoldering, there is a heat wave and the thermal lag and the thermal deity is very low in timber.

00:28:15.943 --> 00:28:18.173
<v Thomas Gernay>So it takes time and.

00:28:18.654 --> 00:28:31.454
<v Thomas Gernay>if we are dealing with a building for which we want burnout, resistance, or for which we want firefighters, you know, to go inside to fight the building, we need to better understand an account for, for this delayed phenomena.

00:28:31.785 --> 00:28:33.095
<v Thomas Gernay>We are not saying that it's.

00:28:33.825 --> 00:28:40.835
<v Thomas Gernay>Needed necessarily for all types of buildings that the fire resistance approach, you know, is, is not valid, should be thrown away?

00:28:40.835 --> 00:28:41.555
<v Thomas Gernay>Absolutely not.

00:28:41.884 --> 00:28:43.634
<v Thomas Gernay>It depends on the performance subjective.

00:28:43.634 --> 00:28:45.795
<v Thomas Gernay>So it depends what type of building we are dealing with.

00:28:45.815 --> 00:29:01.194
<v Thomas Gernay>But you want to point that if firefighters are going to go inside, if a building is, is expected to, you know, build a component and then stay stable, then you need engineers who take account and demonstrate that these effects are taken into.

00:29:01.523 --> 00:29:02.693
<v Wojciech Wegrzynski>How simple can it be?

00:29:02.693 --> 00:29:05.483
<v Wojciech Wegrzynski>Like, do you need finite element modeling to solve that?

00:29:05.483 --> 00:29:20.703
<v Wojciech Wegrzynski>Or maybe we can come up with,  some, I dunno, general rule or, or rule of a thumb that, that could help you assess, okay, if uh, your column was, uh, meter by meter and the fire has ended, you can expect this wave propagate.

00:29:21.574 --> 00:29:24.483
<v Wojciech Wegrzynski>Three hours, which means it will reach the half of the column.

00:29:24.713 --> 00:29:42.238
<v Wojciech Wegrzynski>I, I don't know, just speeding numbers from my head, but, I, I think we need especially on the subject, that on of timber where people get bored very quickly when you start going very technical cuz they want simple answers, you know, like iso for, for concrete, they, they want as simple as that.

00:29:42.238 --> 00:29:44.003
<v Wojciech Wegrzynski>So can we make it as simple as that?

00:29:44.482 --> 00:30:02.357
<v Jochen Zehfuss>Yeah, it, uh, it is a very complex process and so, using finite element, modeling, it's also more complex as for concrete elements, for example, where whereas also complex for a, uh, usual design engineer, I would say.

00:30:02.807 --> 00:30:08.518
<v Jochen Zehfuss>Um, because we have all these phenomenas, a small ring, osis and so on.

00:30:08.928 --> 00:30:17.038
<v Jochen Zehfuss>Um, but on the other, We need, uh, some simplified methods for design, but they are still, Not there.

00:30:17.038 --> 00:30:23.026
<v Jochen Zehfuss>I would say, considering the cooling phase, there are some approaches also in the new generation of Euro code five.

00:30:23.596 --> 00:30:31.808
<v Jochen Zehfuss>but I think there is a lot of work to do, research, work to do, cause it depends on so much parameters.

00:30:32.181 --> 00:30:34.421
<v Jochen Zehfuss>when you look to the real fire.

00:30:35.191 --> 00:30:43.163
<v Jochen Zehfuss>So, this approach, the DHP approach, from my point of view, it's a very good approach to to simplify the fire side.

00:30:43.394 --> 00:30:43.884
<v Jochen Zehfuss>Yeah.

00:30:44.183 --> 00:30:47.963
<v Jochen Zehfuss>But to find the response of the element, it's not so easy.

00:30:48.054 --> 00:30:54.499
<v Jochen Zehfuss>So I think there we need more work to find, a simplified model, which could be.

00:30:54.627 --> 00:30:57.278
<v Jochen Zehfuss>Used for a daily design, for example.

00:30:57.451 --> 00:31:10.540
<v Wojciech Wegrzynski>do you think we can simplify it to just consider the thermal layer or we need to model a structural response of the timber, the changes on the performance of timber as the temperature increases in various cross sections?

00:31:10.840 --> 00:31:14.861
<v Wojciech Wegrzynski>Or, or maybe we can just simplify it to one ISO toine and just be done with it.

00:31:14.948 --> 00:31:15.438
<v Jochen Zehfuss>Yeah.

00:31:15.768 --> 00:31:25.019
<v Jochen Zehfuss>Um, you mean like we, we have the approach, now in Euro code, which is only valid for, for heating phase where we reduce the cross section.

00:31:25.512 --> 00:31:29.682
<v Wojciech Wegrzynski>a simple approximation of, okay, the heating stopped at this moment.

00:31:30.252 --> 00:31:32.482
<v Wojciech Wegrzynski>How much further can the ISO travel?

00:31:32.925 --> 00:31:33.276
<v Noise>so

00:31:33.635 --> 00:31:42.838
<v Thomas Gernay>What I can say is that, We need, if we are interested in burnout, instance in cooling phase, we need to go past, charring and charring rates.

00:31:42.838 --> 00:31:55.971
<v Thomas Gernay>That's the first thing that it's a big change in paradigms in the way we talk about it and t it because the resistance of the member is not going to depend only on the position of the 300 degree iso.

00:31:56.021 --> 00:31:57.211
<v Thomas Gernay>If I want to simplify,

00:31:57.719 --> 00:32:00.670
<v Wojciech Wegrzynski>So Char is, used to be the, whole thing we would care about.

00:32:00.729 --> 00:32:03.969
<v Wojciech Wegrzynski>Now, we consider this one of the array of, of things we need

00:32:04.211 --> 00:32:04.866
<v Thomas Gernay>correct.

00:32:04.866 --> 00:32:09.866
<v Thomas Gernay>Because what's behind char is going to be to become very important.

00:32:09.866 --> 00:32:19.106
<v Thomas Gernay>And whether you have a heating that's, you know, uh, more, more progressive but goes much deeper and you get to 100, 100 degrees C in the whole.

00:32:19.321 --> 00:32:30.082
<v Thomas Gernay>Core at some point during the cooling, then you have a behavior very different compared to if you have a massive section and the core remains cool, even if, I mean the Charing is, is equivalent.

00:32:30.491 --> 00:32:31.642
<v Thomas Gernay>So that's the first thing.

00:32:31.942 --> 00:32:35.842
<v Thomas Gernay>But then can we develop these simple design methods?

00:32:36.797 --> 00:32:42.826
<v Thomas Gernay>We are not there yet, but that we are working toward that and I believe with some simplifications and so on.

00:32:42.826 --> 00:32:46.146
<v Thomas Gernay>But there will, it'll be possible to have pragmatic approach.

00:32:46.646 --> 00:32:56.586
<v Thomas Gernay>And our idea conceptually is that we would still have the fire resistance and we keep it and, or is it, it is useful, but we would add a second indicator, which is this.

00:32:57.382 --> 00:32:59.721
<v Thomas Gernay>Dhp as we call for duration of heating phase.

00:32:59.852 --> 00:33:08.402
<v Thomas Gernay>So to quantify, ability to survive, to burnout, and we would be able to play with the two indicators and hopefully to have simple methods for both.

00:33:09.061 --> 00:33:18.169
<v Thomas Gernay>And then depending on the performance objectives, you would pick or require, what is, meaningful, what is necessary for both fire resistance and uh, burnout.

00:33:18.169 --> 00:33:18.689
<v Thomas Gernay>Resistance.

00:33:18.689 --> 00:33:22.328
<v Thomas Gernay>And maybe for some buildings, there is no requirement at all for burnout resistance.

00:33:22.521 --> 00:33:31.938
<v Wojciech Wegrzynski>it's not that I, I vote for super simple methods, or, I want one, I'm, I'm quite happy with, leaving engineering stuff into hands of competent engineers.

00:33:32.188 --> 00:33:38.374
<v Wojciech Wegrzynski>It's just, you know, observing the history of fire science and, understanding which, uh, ways have.

00:33:38.880 --> 00:33:41.347
<v Wojciech Wegrzynski>Historically worked for a long time.

00:33:41.678 --> 00:33:48.590
<v Wojciech Wegrzynski>Unfortunately, uh, as someone said, we will never have enough competent fire engineers to solve all the fire problems of the world.

00:33:48.596 --> 00:33:55.461
<v Wojciech Wegrzynski>So we, we need to put some tools into hands of, of people who, who may not be as experts and.

00:33:55.708 --> 00:34:00.417
<v Wojciech Wegrzynski>Conservative, simple rules usually work well with within this hands.

00:34:00.567 --> 00:34:09.083
<v Wojciech Wegrzynski>However, already see an issue in here given my experience in fire testing iso term 100 if we care about a hundred degrees.

00:34:09.153 --> 00:34:11.099
<v Wojciech Wegrzynski>Uh, That's a tricky thing.

00:34:11.099 --> 00:34:17.969
<v Wojciech Wegrzynski>One, because you may have a quite a large part of your cross section at a hundred degrees because of the heat of operation of water.

00:34:18.268 --> 00:34:30.391
<v Wojciech Wegrzynski>So it's, it's not like a, a narrow line that travels like the charring 300, that's, that's very sharp interface, but a hundred degrees you can have a quite a significant part of your cross section,  at a hundred degrees.

00:34:30.442 --> 00:34:34.239
<v Wojciech Wegrzynski>Um, now, now, I, I would also like to, To hypothesize a little bit.

00:34:34.273 --> 00:34:43.804
<v Wojciech Wegrzynski>so, you were talking about this, duration of heating phase as your approach to test, and, uh, you were focused on heating quickly and then having decay.

00:34:44.153 --> 00:34:46.856
<v Wojciech Wegrzynski>How about, heating slowly and for long, period of time?

00:34:46.856 --> 00:34:53.126
<v Wojciech Wegrzynski>I mean, that's my immediate thought that, uh, it's a little reversed, but you would have safe phenomena.

00:34:53.126 --> 00:34:54.567
<v Wojciech Wegrzynski>What would you say to that, Thomas?

00:34:54.907 --> 00:35:00.628
<v Thomas Gernay>I'm glad you bring it up because now it's, my opportu mentioned that we are still working on that with the same consortium.

00:35:00.677 --> 00:35:03.788
<v Thomas Gernay>We are very happy that we can continue this research.

00:35:03.838 --> 00:35:14.347
<v Thomas Gernay>So we are now in a phase two where we are actually studying this behavior, but under natural fires now, really the approach was to be systematic.

00:35:14.358 --> 00:35:16.387
<v Thomas Gernay>So we wanted to have a phase one.

00:35:16.992 --> 00:35:20.733
<v Thomas Gernay>The experiments were as controlled, reproducible as possible.

00:35:20.733 --> 00:35:24.293
<v Thomas Gernay>So it was done in, in, in furnaces with a controlled cooling phase.

00:35:24.293 --> 00:35:27.452
<v Thomas Gernay>And everybody can see we did the, each experiment twice.

00:35:27.452 --> 00:35:28.853
<v Thomas Gernay>The results align very well.

00:35:28.853 --> 00:35:30.052
<v Thomas Gernay>Others can reproduce.

00:35:30.543 --> 00:35:33.293
<v Thomas Gernay>Um, but of course it raises a lot of questions on the.

00:35:33.492 --> 00:35:41.452
<v Thomas Gernay>Type of thermal exposure and how this behavior would be different if the thermal exposure the fire is, is different both in heating and in cooling.

00:35:41.862 --> 00:35:46.253
<v Thomas Gernay>So we have been working on the phase two and we already have some of these experiments.

00:35:46.632 --> 00:35:50.483
<v Thomas Gernay>I cannot tell you more at this stage, but we, this is work, work in progress.

00:35:51.012 --> 00:35:55.682
<v Thomas Gernay>Um, so especially to your question with the slow heating, that's, it's very interesting, right?

00:35:55.682 --> 00:35:56.123
<v Thomas Gernay>Because.

00:35:56.460 --> 00:36:01.949
<v Thomas Gernay>I presented this, this research at, um, Congress for Firefighters in, in France in in May.

00:36:01.949 --> 00:36:21.083
<v Thomas Gernay>And, uh, one of the firefighter asked me, what about if, if a colonist, maybe not even in the is very far from the fire, but it gets heated at 100, 150 degrees for very long, and it doesn't even char, but, but, honesty, I mean, we, we've not really studied that yet, but.

00:36:21.398 --> 00:36:27.077
<v Thomas Gernay>Brings a lot of question because if we, if you trust again those, reduction of strengths that you.

00:36:27.637 --> 00:36:36.827
<v Thomas Gernay>In the eurocode and that are from, you know, day duration, drying, all those phenomena that other guests have explained on your very well on your post podcast, Felix Whiner, Danny Hopkin and so on.

00:36:37.257 --> 00:36:45.657
<v Thomas Gernay>you could have significant reduction of capacity from moderate heating and if it's long because it has to penetrate right in the section.

00:36:45.657 --> 00:36:52.260
<v Thomas Gernay>We are not saying that to hot summer day is going to bring timber buildings down, but if it's from a fire last hours and you have.

00:36:52.585 --> 00:36:53.545
<v Thomas Gernay>Thermal wave.

00:36:53.614 --> 00:36:55.219
<v Thomas Gernay>that's something to, to investigate.

00:36:55.219 --> 00:36:55.539
<v Thomas Gernay>Yes.

00:36:55.742 --> 00:36:59.833
<v Wojciech Wegrzynski>And in terms of, localized fires and the damage to like, uh, ceilings.

00:36:59.983 --> 00:37:02.952
<v Wojciech Wegrzynski>Let's imagine we didn't have a fully fleshed over fire.

00:37:02.958 --> 00:37:09.072
<v Wojciech Wegrzynski>We just had, let's, let's say a vehicle burning or, or, or something burning in, in proximity of timber.

00:37:09.077 --> 00:37:12.402
<v Wojciech Wegrzynski>Well, in that case, I guess we, we should consider the timber fla bilities.

00:37:12.402 --> 00:37:17.143
<v Wojciech Wegrzynski>So the scenario may look not as, uh, as, uh, as pretty as I just described,

00:37:17.460 --> 00:37:29.358
<v Thomas Gernay>yeah, I would be less concerned about that in terms of the burn resistance specifically, because what is, Critical in this concept of bone res is a total amount of heat that penetrates the section, right?

00:37:29.358 --> 00:37:40.518
<v Thomas Gernay>And it's the idea that even if it's a relatively short time or if it's a long time, but with no very high peak, if the total amount of heat is, you know, is significant, you'll get.

00:37:40.893 --> 00:37:43.103
<v Thomas Gernay>Your heat, also the, the core of the section.

00:37:43.523 --> 00:37:53.028
<v Thomas Gernay>But if it's a localized fire, I mean every case is different of course, but, you don't have that much heat that, that p section in the first place, I would assume.

00:37:53.469 --> 00:37:55.670
<v Wojciech Wegrzynski>I have a question that may, may be stupid.

00:37:55.670 --> 00:38:01.219
<v Wojciech Wegrzynski>Excuse me if it is, but, and what, what if firefighters, let's imagine it is a really structure.

00:38:01.219 --> 00:38:05.780
<v Wojciech Wegrzynski>What if firefighters apply on the, the water on it and, and quickly cool.

00:38:05.853 --> 00:38:07.952
<v Wojciech Wegrzynski>the external surface of the wall.

00:38:07.958 --> 00:38:10.152
<v Wojciech Wegrzynski>I mean, the heat is still inside, I guess this, this time.

00:38:10.172 --> 00:38:18.157
<v Wojciech Wegrzynski>It travels both ways, but you'd probably still see the, the propagation in inside and the damage would not be stopped by just sprinkling water on on.

00:38:18.684 --> 00:38:22.333
<v Thomas Gernay>It's an excellent question actually, because that's something we, we are studying.

00:38:22.873 --> 00:38:23.293
<v Thomas Gernay>Yes.

00:38:23.293 --> 00:38:32.027
<v Thomas Gernay>No, that's something we have identified as possibly an important parameter and, and we are studying, and we want to quantify to, to what extent it, it helps.

00:38:32.527 --> 00:38:39.802
<v Thomas Gernay>But, uh, if you can reduce the, the heat that is transfer still in the cooling phase as well, uh, that

00:38:40.376 --> 00:38:47.498
<v Jochen Zehfuss>yeah, we did some experiments on, massive timber elements, uh, ct, um, elements.

00:38:47.648 --> 00:38:51.856
<v Jochen Zehfuss>Where the ceiling and, some parts of the walls were unprotected.

00:38:52.596 --> 00:39:04.945
<v Jochen Zehfuss>And then we had one test, where, the firefighters fighted the fire, extinguished the fire and they used not so much border, it was about 3000 liters.

00:39:05.576 --> 00:39:16.365
<v Jochen Zehfuss>So it was only one experiment and it was a compartment of about 40 square meters, but they were surprised not to need so much water.

00:39:17.161 --> 00:39:26.362
<v Jochen Zehfuss>when they cooled down the, the propagation of the penetration into the element stops very early.

00:39:26.826 --> 00:39:29.735
<v Jochen Zehfuss>So I think that's not so a big problem.

00:39:29.826 --> 00:39:38.056
<v Jochen Zehfuss>Of course, it's a bigger problem when you have timber framework element, uh, where you have a hidden fire or something like that.

00:39:38.262 --> 00:39:41.021
<v Wojciech Wegrzynski>And, uh, and the final one also to you, Johan.

00:39:41.327 --> 00:39:56.844
<v Wojciech Wegrzynski>if you have a timber structure protected by, let's say a layer of gypsum plaster board, just to extend the, uh, the defy resistance class of it, you would expect that at some, at some point, uh, the heat goes through the board and can penetrate the.

00:39:57.460 --> 00:40:04.599
<v Wojciech Wegrzynski>The column, uh, and, and it would not cause a immediate structural failure of, of, of the r criterion within the fire test.

00:40:04.599 --> 00:40:11.032
<v Wojciech Wegrzynski>If you omitted the decay phase in such scenarios, you would also be, worried about the heat transfer inside.

00:40:11.038 --> 00:40:14.152
<v Wojciech Wegrzynski>Is it the same scenario for you, or, or how do you view that

00:40:14.289 --> 00:40:18.829
<v Jochen Zehfuss>Now, of course, um, due to the job sum elements, you have a delay.

00:40:19.543 --> 00:40:23.054
<v Jochen Zehfuss>In the heating and then delaying in the ignition.

00:40:23.753 --> 00:40:32.724
<v Jochen Zehfuss>And, the velocity of, the, py of the showering process is different, is lower as we know.

00:40:33.327 --> 00:40:35.226
<v Jochen Zehfuss>Due to the lack of oxygen.

00:40:35.967 --> 00:40:46.753
<v Jochen Zehfuss>But then after a while, the protection material on the boards will fail, and then you have nearly in the same situation, as you have, for an unprotected element.

00:40:47.360 --> 00:40:50.795
<v Wojciech Wegrzynski>so we, we shouldn't consider this as, as a complete solution.

00:40:50.795 --> 00:40:53.195
<v Wojciech Wegrzynski>It's just a delay to the, to the processes.

00:40:53.344 --> 00:40:55.804
<v Wojciech Wegrzynski>It may be solution for the structure you are considering.

00:40:55.809 --> 00:41:00.125
<v Wojciech Wegrzynski>It may solve the problem for the one that, but, but you need to understand and, and measure that.

00:41:00.125 --> 00:41:00.724
<v Wojciech Wegrzynski>Fantastic.

00:41:01.103 --> 00:41:02.213
<v Wojciech Wegrzynski>okay, Thank you very much.

00:41:02.213 --> 00:41:04.186
<v Wojciech Wegrzynski>This, this was very insightful.

00:41:04.545 --> 00:41:07.275
<v Wojciech Wegrzynski>I need to get one more thing out of you.

00:41:07.635 --> 00:41:14.487
<v Wojciech Wegrzynski>I think that we can, clearly share with our colleagues, architects, structural engineers who are not Very, um, keen in fire.

00:41:14.487 --> 00:41:24.875
<v Wojciech Wegrzynski>So let's try and nail the, the one most important thing that you, you've learned here that differentiates why this would be different from, let's say, steel structure or a concrete structure.

00:41:24.875 --> 00:41:25.802
<v Wojciech Wegrzynski>Thomas, you wanna start?

00:41:26.028 --> 00:41:29.699
<v Thomas Gernay>So timber burns, that's something obvious we know.

00:41:29.918 --> 00:41:44.458
<v Thomas Gernay>And because of that, a lot of the focus on ensuring fire safety of timber tends to be on understanding the charring speed and how long it takes for this combu to to proceed and so on.

00:41:44.838 --> 00:41:54.563
<v Thomas Gernay>And what we showed with those experiments is, Of course all disability issues, self extinction are important, but they are not the whole story.

00:41:54.563 --> 00:42:03.884
<v Thomas Gernay>If you're interested in stability to full burn out because timber also is affected by heat at temperatures lower than pyrosis or condition temperature.

00:42:03.884 --> 00:42:07.523
<v Thomas Gernay>There is lot going on the duration, drying lots of processes, so.

00:42:08.068 --> 00:42:13.028
<v Thomas Gernay>Everybody needs to remember that even that relatively low temperatures, timber is affected.

00:42:13.028 --> 00:42:25.389
<v Thomas Gernay>And because of that, a timber structural member continues to see its its strengths, its capacity, decrease for hours after a fire, during and after a fire.

00:42:25.798 --> 00:42:34.668
<v Thomas Gernay>So we should take that into account if we expect firefighters to go inside building, or if we expect building to remain stable, remain standing under fire.

00:42:34.742 --> 00:42:36.273
<v Wojciech Wegrzynski>Johan, you want to add something to that?

00:42:36.273 --> 00:42:37.373
<v Wojciech Wegrzynski>Maybe how to use.

00:42:37.911 --> 00:42:56.971
<v Jochen Zehfuss>yeah, I could emphasize, I think one very important issue is, uh, uh, for the firefighting strategy when they go into a timber building where we have a fully developed fire, um, they have to be more careful even after hours.

00:42:57.760 --> 00:43:08.871
<v Jochen Zehfuss>Because we have a higher risk for failure in the cooling phase, as I think we can say this as, uh, we have, uh, when we have a concrete structure.

00:43:09.570 --> 00:43:13.990
<v Jochen Zehfuss>But, uh, on the other hand, um, as we said, we are not against timber.

00:43:14.641 --> 00:43:15.590
<v Jochen Zehfuss>Uh, not at all.

00:43:16.161 --> 00:43:21.021
<v Jochen Zehfuss>Um, timber can have a very high fire rating now.

00:43:21.070 --> 00:43:22.900
<v Jochen Zehfuss>Uh, it's a question of design.

00:43:22.900 --> 00:43:23.900
<v Jochen Zehfuss>It's a question of.

00:43:24.510 --> 00:43:37.206
<v Jochen Zehfuss>But, especially in the firefighters when they come late, when they are, uh, very, in a very early stage, of the fire, uh, starting with the firefighting process, the problem is minor, I would think.

00:43:37.817 --> 00:43:47.567
<v Jochen Zehfuss>Um, but when we have a very long time starting the extinction, the risk is higher that we have a failure in the cooling.

00:43:48.197 --> 00:43:51.487
<v Jochen Zehfuss>Then when we need other, when we use other materials,

00:43:51.567 --> 00:43:51.987
<v Wojciech Wegrzynski>Thank you.

00:43:52.047 --> 00:43:52.887
<v Wojciech Wegrzynski>Thank you very much.

00:43:52.887 --> 00:44:01.612
<v Wojciech Wegrzynski>Very much appreciated message to this, part of my audience, and for structural engineers who would like to approach this process.

00:44:02.713 --> 00:44:05.525
<v Wojciech Wegrzynski>Recognizing the issue is enough and they will know what to do.

00:44:05.753 --> 00:44:13.903
<v Thomas Gernay>So in this research, as always, we want to first observe, understand the behavior, and then provide the tools to have solutions.

00:44:14.824 --> 00:44:16.023
<v Thomas Gernay>said is very important.

00:44:16.023 --> 00:44:20.023
<v Thomas Gernay>So it's certainly not being against, you know, one type of solution or another.

00:44:20.184 --> 00:44:24.943
<v Thomas Gernay>There are solutions to build fire safe structures, you know, with, with e, every type of.

00:44:25.534 --> 00:44:26.773
<v Thomas Gernay>Structural systems materials.

00:44:27.103 --> 00:44:39.853
<v Thomas Gernay>Uh, so we are working on the solutions that structural engineers today can use Finite element modeling or research suggests even with the effective properties from your code five, you get really good agreement with those experiments.

00:44:40.273 --> 00:44:44.213
<v Thomas Gernay>And we are working on providing the simple design methods for dhp hp

00:44:44.559 --> 00:44:44.876
<v Wojciech Wegrzynski>Fantastic.

00:44:44.876 --> 00:44:47.757
<v Wojciech Wegrzynski>And when you do that, make sure to come to the podcast and explain them.

00:44:48.586 --> 00:44:49.786
<v Wojciech Wegrzynski>you're already invited.

00:44:50.108 --> 00:44:53.280
<v Wojciech Wegrzynski>guys, once again, congratulations on, on your research.

00:44:53.280 --> 00:45:05.639
<v Wojciech Wegrzynski>I, think, What we talked today may not be that easy from understanding it perspective, but it really is very visual when you see the, the failure of your element and you immediately realize, what happens there.

00:45:05.639 --> 00:45:13.166
<v Wojciech Wegrzynski>I think you've shown a very important distinction why there is such a movement in the fire community on researching timber.

00:45:13.166 --> 00:45:29.396
<v Wojciech Wegrzynski>I mean, you've really captured one of these differences that, that really Easter and, uh, may, uh, have a critical impact and, uh, As Johan said, especially impact on the, the firefighters in the, in the phase that they would usually consider safe based on their experience.

00:45:29.396 --> 00:45:34.146
<v Wojciech Wegrzynski>So, thank you very much for that and, I'm very looking forward to the secret project.

00:45:34.152 --> 00:45:39.606
<v Wojciech Wegrzynski>Uh, you've, uh, you've teased us without using the word traveling at all actually.

00:45:41.106 --> 00:45:41.527
<v Wojciech Wegrzynski>Thanks.

00:45:41.527 --> 00:45:42.487
<v Wojciech Wegrzynski>Uh, Thank you guys.

00:45:42.956 --> 00:45:43.115
<v Jochen Zehfuss>you

00:45:43.666 --> 00:45:44.387
<v Noise>you very much West.

00:45:44.782 --> 00:45:45.411
<v Wojciech Wegrzynski>And that's it.

00:45:45.525 --> 00:45:49.936
<v Wojciech Wegrzynski>Super nice people being super nice research European all-star team.

00:45:50.686 --> 00:45:51.226
<v Wojciech Wegrzynski>Researching.

00:45:51.436 --> 00:45:51.945
<v Wojciech Wegrzynski>Timber.

00:45:52.010 --> 00:45:52.519
<v Wojciech Wegrzynski>For you.

00:45:52.795 --> 00:45:56.592
<v Wojciech Wegrzynski>I really love how we start getting all the puzzles together too.

00:45:56.795 --> 00:46:02.436
<v Wojciech Wegrzynski>Be able to clearly say what makes timber and fire different than other materials in fire.

00:46:03.005 --> 00:46:07.565
<v Wojciech Wegrzynski>It seems that we're on a great route to, to finally identify all the issues.

00:46:08.315 --> 00:46:11.106
<v Wojciech Wegrzynski>Hopefully all at least most of the issues.

00:46:11.556 --> 00:46:20.646
<v Wojciech Wegrzynski>And be able to actually communicate them and be able to work around them and, uh, you know, By understanding that that's the first step to finding solutions.

00:46:21.005 --> 00:46:24.755
<v Wojciech Wegrzynski>If we don't understand what's happening, if we don't understand what's different.

00:46:25.217 --> 00:46:26.447
<v Wojciech Wegrzynski>We are unable to act.

00:46:26.956 --> 00:46:31.306
<v Wojciech Wegrzynski>And if we do understand what's different, we can work around that.

00:46:31.757 --> 00:46:32.717
<v Wojciech Wegrzynski>That's beautiful.

00:46:33.376 --> 00:46:38.686
<v Wojciech Wegrzynski>The research was carried on single type of an element, single size of an element.

00:46:39.016 --> 00:46:40.666
<v Wojciech Wegrzynski>So definitely we need more.

00:46:40.666 --> 00:46:42.916
<v Wojciech Wegrzynski>We need to understand better what's happening.

00:46:43.396 --> 00:46:49.704
<v Wojciech Wegrzynski>At the columns that are larger cross sections at columns The other heated at different rates of heat exposure.

00:46:50.244 --> 00:46:52.164
<v Wojciech Wegrzynski>But that's all to come.

00:46:52.434 --> 00:46:55.824
<v Wojciech Wegrzynski>What we have now is the first indication that the numerical models.

00:46:56.304 --> 00:47:00.414
<v Wojciech Wegrzynski>We're showing something that really happens in reality.

00:47:00.804 --> 00:47:03.230
<v Wojciech Wegrzynski>They demonstrated the physics that.

00:47:03.304 --> 00:47:08.884
<v Wojciech Wegrzynski>This collapsed can, can take place and, uh, Yeah, we know more today.

00:47:08.914 --> 00:47:12.161
<v Wojciech Wegrzynski>We know more today and, we can already act on this knowledge.

00:47:12.221 --> 00:47:13.510
<v Wojciech Wegrzynski>So thank you, Thomas.

00:47:13.510 --> 00:47:15.010
<v Wojciech Wegrzynski>Thank you Jochen for coming.

00:47:15.280 --> 00:47:17.831
<v Wojciech Wegrzynski>Thank you for leading these beautiful research.

00:47:18.340 --> 00:47:26.951
<v Wojciech Wegrzynski>And I must say I'm really, really looking forward to four more coming from this collaboration on, on the collapsing, the decay phase.

00:47:27.010 --> 00:47:29.621
<v Wojciech Wegrzynski>It's really exciting research to it, to look at.

00:47:30.161 --> 00:47:30.911
<v Wojciech Wegrzynski>Uh, listeners to us.

00:47:30.911 --> 00:47:36.264
<v Wojciech Wegrzynski>Thank you very much for staying here with me and, hopefully see here next week.

00:47:36.864 --> 00:47:37.253
<v Wojciech Wegrzynski>Cheers.

00:47:37.284 --> 00:47:37.614
<v Wojciech Wegrzynski>Bye.