247 - Calculation methods for fire resistance with Piotr Turkowski

Why Calculate Fire Resistance

Wojciech Wegrzynski 0:00

Hello everybody. Welcome to the fire. This week, uh, we're continuing the journey through the fire resistance. While last week we had, uh, Piotr Turkowski from I TB talking about the criteria of fire resistance, largely in context of furnace testing of specimens. And this week, I'm once again joined by Piotr, but this time we are talking about calculation methods. So any other way to establish fire resistance of an object other than furnace testing? Yes, they exist. Yes, it is potentially possible from calculation methods to. Ized, sources, which just give you resistance per size of your specimen, up to advanced calculation methods and, um, perhaps numerical modeling. All of those can, to some extent, predict or give you, just give you the value of far resistance for your item. However, it comes with a lot of caveats and, the. More complex material. The more complex structures we go into, the more difficult this becomes. In this podcast episode, we try to go through this world and understand what it means to calculate fire resistance with different methods, the complexities that go into that, the interactions between the properties. And the challenges that you may see. Uh, we we mainly focus on concrete and steel, but, uh, in the end we, we have our time on masonry, which is a very interesting case in if you want to predict, uh, fire resistance of, of masonry structures, especially with concrete hollow blocks. But anyway, there's a lot of knowledge. Inside a lot of complexity. It's this world is way, way, way more difficult and challenging that I have initially thought it will be. I hope you'll enjoy it. Let's spin the intro and jump into the episode. The Fire Science Show podcast is brought to you in partnership with OFR Consultants. OFR is the UK's leading independent multi-award winning fire engineering consultancy with a reputation for delivering innovative safety driven solutions. we've been on this journey together for three years so far, and here it begins the fourth year of collaboration between the Fire Science Show and the OFR. So far, we've brought you more than 150 episodes, Which translate into nearly 150 hours of educational content available, free, accessible, all over the planet without any paywalls advertisement or hidden agendas. This makes me very proud and I am super thankful to OFR for this long lasting partnership. I'm extremely happy that we've just started the year four, and I hope there will be many years after that to come So big thanks, OFR for your support to the Fire Science show and the support to the fire safety community at large that we can deliver together. And for you, the listener, if you would like to learn more or perhaps even become a part of OR, they always have opportunities awaiting. Check their website@orconsultants.com And now let's head back to the episode. Hello everybody. I am joined once again by my colleague from ITB, Dr. Piotr Turkowski. Hey,

Piotr Turkowski 3:40

Hello, Wojtek. Hello everyone.

Wojciech Wegrzynski 3:42

I hope you've enjoyed our, uh, last week's session about, uh, fire fundamentals of fire resistance. I, I have you once again for fire resistance, but this time you are not allowed to talk about furnaces.

Piotr Turkowski 3:54

Yeah, perfect. Uh, I really enjoyed the last episode, uh, and, uh, I assume we'll move on to the calculation methods.

Wojciech Wegrzynski 4:01

Yes, that's, that's exactly what I would like to do. So, um, we are in the privileged position of having a FAR testing laboratory in our, uh, home institution. ITB. But, uh, every day we meet people who want to assess fire resistance in one way or another, but without resourcing to, fire testing. One could call it costly. I'm not sure if we're allowed to call it like that in here, but, uh, yeah, I agree. It's costly, but, um, let's start with, with the, once again, far resistance, uh, definition. Last time you said it doesn't exclude stuff beyond testing. Right.

Piotr Turkowski 4:41

Yes, it doesn't, it is written with the, with a fire resistance test in mind. the new definitions, in the ISO standard, they are. Changing the bit terms, saying that the test specimen is actually not the real test specimen, but it's the object that you are assessing. So it's not necessarily linked to a physical object. So you can do it via calculations if you want to. indeed we have another mean to, to assess the fire resistance. However, it should always be noted how was it established. So if you, if you do the, the, the assessment, uh, with a furnace test, you, you'll most likely, say that you have this classification in accordance with the en N 13 5 0 1 dash two. you do it via calculation methods, then your fire resistance is Obviously, something a bit different. You, you do not apply a virtual cotton pad to assess integrity. So you do it with, Euro codes, for example, there are even standards for, for example, for steel structures where it's explicitly stated that you can do it with Euro codes. and then the, uh, ce uh, label that you'll have on your product, with the declaration of performance, you will state that my steel structure has say R 30, and that it was established with calculation method. Uh,

Wojciech Wegrzynski 6:11

Okay.

Piotr Turkowski 6:12

exactly this way that you're supposed to write it down in the declaration of performance. It's an EN 10 90 standard as far as, as far as I remember. there are, there are other ways.

Declarations Of Performance And EADs

Wojciech Wegrzynski 6:22

That, that's quite interesting because you, um, went ahead. I want to ask about that if we approach it by the means of calculation or other methods to establish the fire resistance. Is this just the knowledge that we gain or could you end up with a certificate or, or, you know, because being in the business inside, we know that, people in the end, our customers, what they want is not the knowledge, but the, the, the product marking something that allows 'em to put the product on the marking something, something that allows them to certify that this wall has the fire resistance of REI 30. When the fire brigade commissions the building, they can show them a paper that states that and no one is able to question that Is there a difference between the world of far testing through furnace as an experiment versus any other means in this final degree of the document that you, you receive?

Piotr Turkowski 7:15

the final document, that is the, statement. That the manufacturer takes responsibility with for the, uh,

Wojciech Wegrzynski 7:24

Yeah.

Piotr Turkowski 7:24

of, of

Wojciech Wegrzynski 7:25

Fine. Yeah.

Piotr Turkowski 7:26

is the declaration of performance. Yes. How you get to that point is written in the harmonized standard or the EAD, and there are many harmonized standards and many European assessment documents, eads, which gives you the possibility to use euro codes or other calculation methods in order to establish the fire resistance performance. As I said, one of them for steel structures is the EEN 10 90 dash one or two, like that. It is explicitly written that you use euro codes. In order to do that, you do not have to do furnace test. There are other standards for prefabricated concrete elements, and they often give many options. Uh, as far as I remember, there are three. One of them is obviously the test. So it's, it's written like, do a classification in accordance with EN 13 5 0 1 dash two. So furnace test B, use for from Euro code for concrete. Option C use calculation methods from Euro code. so, so you have these options. Another example, very common one are metal anchors for concrete. For think that the first document was technical report, uh, 48 or something like that. Now it's an EAD with a way longer number, I can't remember it. But with that document, you have the option to do, do the test or do a calculation method that is not eurocode. It, it, it's a method given in that document on how to calculate the, fire resistance of that metal anchor 30, 60, 90, or 120 minutes. Sometimes it's, it's, it is as simple as multiplying the load bearing capacity by some factor, like 25% or 20% for given time period. But otherwise it, it, it, it's, it's more of a calculation method. So absolutely they are applicable, but, and in the end, manufacturer based on these documents, puts that value in a declaration of performance and he takes then responsibility for it. in my opinion, nobody should discuss it. Like it's, uh, the, the way the the CPR works is that the manufacturer claims the responsibility of the product. And then you have the designer or the contractor. Uh, that uses this product, uh, on site and, then he takes responsibility that he use that product correctly. So

Wojciech Wegrzynski 9:56

Yeah.

Piotr Turkowski 9:57

if, uh, the manufacturer declared that that parameter at all. Or, or that he do it in other way.

Wojciech Wegrzynski 10:03

Okay. Uh, one sentence clarification for non-European listeners was EAD.

Piotr Turkowski 10:09

Uh, so EAD it's a European assessment document. It's a document that is written by eta, which is a European organization for technical assessment. And, uh, this document gives the rules and shows how a European technical assessment should be written for given product. There were first, uh, 50 or 100 eads written, previously, uh, known as e tax. but now they've been converted to a Eads. And every product that doesn't have a harmonized standard can get an EAD. And in order to do it, a manufacturer has to go to a technical as assessment body. And, uh, say that he wants to write it and

Wojciech Wegrzynski 10:55

Yep.

Piotr Turkowski 10:55

assessment body has to write it for free.

Wojciech Wegrzynski 10:58

Yeah.

Piotr Turkowski 10:59

time, but they do it for free. And then this way they establish a kind of harmonized standard, so to say,

Wojciech Wegrzynski 11:07

I, I, I think it's a fair, I think it's fair to say it's standard replacement for products that don't have harmonized standard. Yeah.

Piotr Turkowski 11:14

That's the best definition.

Fire Protection Products And Equivalency

Wojciech Wegrzynski 11:16

so, basically there's a, there, there, there's a technical reference document, a standard EAD, national, uh, assessment document, whatever that tells you whether it's fine or not to use these other methods in layer of, of fire testing. And I assume product per product is different. What about products in which, like, I, I know it's really complicated, like spray motors, tumescent paint, like in, in, in those complex materials, In those, I'm not even sure if we have calculation methods. Maybe, you know, you probably know better than I am, but do, but, uh, I think it's, it's very complicated to replace fire testing.

Piotr Turkowski 11:53

That's a very good example that you've picked because yes, there are eads for sprayed mortars, for fire protective boards and intumescent coatings. And these eads, they only ask for a furnace test. there is a series of tests, EN 13 381, what, what they do, they do not give you a fire resistance class, uh, explicitly, but they calculate some parameters of the fire protection product that then can be used in order to establish a fire ance performance. So, for example, for concrete, you do not get, uh, an explicit classification. When you apply 10 millimeters of that super spray, you'll get REI 240. No. What they do is they establish a parameter called equivalent thickness of concrete. So they, the, the result will be saying something like the 10 millimeters of that super spray for 240 minutes is equal to 60 millimeters of concrete. So, the way you will then use it If you have a reinforced concrete structure and it doesn't get the classification you'd want, then see what you are lacking off. If you are lacking the distance, the, the concrete cover for reinforcement or maybe thickness of the, of the element. And if you're lacking the, the concrete cover, say 30 millimeters, you are looking for a product that gives you this equivalent thickness of concrete of 30 millimeters. So that, so this 10 millimeters of super spray will be just, just fine. Yes. Or e. E even better.

Wojciech Wegrzynski 13:32

or, or one nanometer of magical spray. Uh, but, uh, but why thickness of con, what is this proxy measure giving you in this case? What is it a proxy of? Like, because it must be a proxy of, of minutes of fire resistance to be, to, to be honest.

Piotr Turkowski 13:49

I, I, I wouldn't say it's a proxy of minutes or, or of time. This, this equivalent thickness of concrete, is a way to express, uh, concrete

Wojciech Wegrzynski 14:00

Okay.

Piotr Turkowski 14:01

a, a a as simple as that. When you look into a Euro code and you'll see that, uh, a column, for example, is the el, the element that is exposed usually to fire on all four sides, doesn't, it doesn't have quite big dimension. So when it's small, when it's exposed to four sites, it'll heat up very fast and you'll see that for high instance classes, you get insane amount of concrete cover that

Wojciech Wegrzynski 14:25

Okay.

Piotr Turkowski 14:26

sane designer would do, because if you get something like 90 millimeters of concrete cover, then that concrete cover, concrete cover has problems to even stick to the reinforcement. You have to use some intermediate meshes

Wojciech Wegrzynski 14:38

Yeah.

Piotr Turkowski 14:38

like that, just for the corrosion purposes. You need something like 25, maybe 30 millimeter. one thing is that, uh, when you get that very high concrete cover, the concrete cover doesn't stick very well. That's first thing, but second thing, even more important, you are reducing the distance between the reinforcement. So if there's bending in the column and, the tensile, forces are carried by, by, by the reinforcement, you are virtually reducing the, the, the column size.

Wojciech Wegrzynski 15:10

Hmm.

Piotr Turkowski 15:10

it, it doesn't have as much strength as it would have if the reinforcement was closer to the surface. So, it, it's way easier to make smaller concrete cover and then to replace the missing 50 or 70 millimeters. By some material that is so much better than concrete that it provides that fire protection

Wojciech Wegrzynski 15:30

Hmm.

Piotr Turkowski 15:30

the way you assess it is you compare the temperature at a certain depth in the, in the element, a concrete slab or a concrete beam, depending on the type of the element, and you compare it with the temperature in unprotected element, and you see how much further you have to go in order to get the same temperature in the concrete, thus establishing this equivalent thickness of concrete.

Wojciech Wegrzynski 15:55

Uh, I, I love this. let's do this once again and, and properly, uh, for the non-structural fire science business. So If you could walk me through the process of calculating fire resistance for a concrete member? It can be a column, and then walk me through the same process for a wall.

Piotr Turkowski 16:13

Okay. So, uh. For concrete elements, we will most likely use Euro code two. So the EN 1992 dash one dash two standard, that standard gives, three methods of assessment of fire resistance. And, uh, usually this, the Discal calculation methods, they are all, uh, they're either one of the three. So the first one, the most complex one that we will definitely not use, will not use it because it's so complex and it requires such validation in the test that, in my opinion, is virtually impossible to use, which is the advanced calculation method. The advanced calculation methods they take into account the entire building. You do not do the calculations for one simple element. You do it for the entire building at the same time.

Wojciech Wegrzynski 17:04

Are we talking about the previous Euro codes or the Euro codes in development?

Piotr Turkowski 17:08

this one is actually already, uh, published,

Wojciech Wegrzynski 17:11

okay.

Piotr Turkowski 17:12

the same in both.

Wojciech Wegrzynski 17:13

Perfect. Yeah, I, I just, super necessary disclaimer. Sorry. Continue.

Piotr Turkowski 17:17

Yeah. So it's a second generation of Euro codes and the first one as well. So, uh, so the advanced calculation methods, you will have, uh, most likely two models or maybe one, uh, coupled, uh, model that will, first assess the thermal terminal response of the entire structure, and then it'll assess the mechanical response of the entire structure. And, uh. everything in this, this method comes from the person that does it because there are no criteria, no explicit criteria given in Euro code on

Wojciech Wegrzynski 17:49

Hmm.

Piotr Turkowski 17:49

is the structure safe. Uh, there's no limiting deflection. There's no limiting temperature. It's, it's basically zero one, uh, assessment of has my structure collapsed or didn't.

Wojciech Wegrzynski 18:02

Is it only arc right here?

Piotr Turkowski 18:04

well, interior, you can assess also also the insulation performance and the, and you will assume for concrete. the integrity is maintained. Unless of course you have some precast elements that are joint with, that consist of a joint panels and maybe some linear joints in between that, that can be tricky. But when it's monolithic structure, you just assume the integrity is,

Wojciech Wegrzynski 18:27

Okay.

Piotr Turkowski 18:29

But because of this complexity, even when you use standard fire for the entire analysis, because you're analyzing the entire structure, this is not exactly fires and specification. This is fire safety engineering. Uh, I even remember, European Commission Workshop that was held like 14 years ago. uh, I remember per Vassar, uh, presenting about. this approach in the Euro code. And, uh, he made, uh, some slides and in one on one of them we can see that, this is exactly also, also his faults, that this is fire safety Jing. This is not classification. You wouldn't use it get the REI classification. You would use it to obtain general, more global information about the performance of the structure in

Wojciech Wegrzynski 19:20

Like load bearing capacity and fire.

Piotr Turkowski 19:22

Yes. then we get to a simpler method, which is called the simplified Calculation method. It used to be two methods in the previous edition of your code, of them is, uh, so-called the Isotherm 500 cent Degrees method. That is not present in the current edition of Eurocode. but I have to say I really like that method. I know it has its cons, but it was very simple. It was really nice to use. Uh, and the second one of them that is, uh, that was in the first generation and is also now in the second generation, is the method based on zones. The way you do it, uh, with the second method is, well, maybe I'll start with the first one, even though it's, uh, now, uh, being removed from the Euro code.

Wojciech Wegrzynski 20:09

And missed.

Piotr Turkowski 20:12

uh, if I may, uh, hello? Uh, voce, if you're listening from, Polytechnical ska, I know you don't like the method. I do, I do. uh. so, uh, in the Isotherm 500, uh, method, what you do is you do a thermal, transfer analysis.

Wojciech Wegrzynski 20:32

Mm-hmm.

Piotr Turkowski 20:32

you are basically heating up your element and you, you check how the isotope look you are looking, uh, exactly for one of them, which is 500 C degrees.

Wojciech Wegrzynski 20:44

So a line that connects the dots with 500 degrees in your structure when you do heat transfer analysis.

Piotr Turkowski 20:50

yes. And if it's a beam in bending, then both sides and the bottom of the

Wojciech Wegrzynski 20:54

Hmm.

Piotr Turkowski 20:54

uh, is more than 500 C degrees. So you are removing that from the equation. Your, your cross section of the entire element was reduced by, let's say 40 millimeters on each side. If

Wojciech Wegrzynski 21:07

Hmm.

Piotr Turkowski 21:07

calculation for something like 90 minutes, having that reduced your new cross section of concrete. It's a bit smaller, so it's also a bit weaker. and the steel temperature, you calculate exactly what it is for each rebar. So you will have the, the coronary rebars of let's say 650 cent degrees, maybe the one in the middle of a bit less. What you do then is apply, coefficient of strength reduction for material for steel, saying that, that my steel at 650 cent degrees, it's something like 40 to 35% of, uh, of its original strength and my concrete that was above 500 cent degrees has zero load bearing capacity, the one that has below has 100% capacity. This is the way that metal worked. The, the zone method is very similar, but is not so, 1 0 0 1. It's dividing this cross section of concrete into zones of smaller dimensions. So you'll have some zone that is, that on average has 970 degrees and that concrete has zero strength. You will have some zone that is maybe 700, 600 and it has some strength left, and then more so you are basically doing a more precise calculations, but more or less the idea is, is the same here.

Wojciech Wegrzynski 22:33

What do you know? It failed when? For a span of a beam, the the loading will be higher than its capacity. How do you know it failed?

Piotr Turkowski 22:43

So at the time, zero. Of, uh, fire of this virtual fire, uh, you calculate the resistance of the beam, the load bearing capacity of the beam, the bending resistance, uh, or

Wojciech Wegrzynski 22:56

Okay,

Piotr Turkowski 22:56

resistance, as if there is no heating whatsoever. So all the values of, of strength of your materials they're not exactly the same as in a cold calculation, so to say, but they're very close to these

Wojciech Wegrzynski 23:10

but, but this, but this is not for the whole building. It's for the design span and some design loads.

Piotr Turkowski 23:16

this is for, particular elements. So you do not do it for the entire structure.

Wojciech Wegrzynski 23:21

Okay?

Piotr Turkowski 23:21

to do it separately for a beam, for a column, for a wall, floors, et, et

Wojciech Wegrzynski 23:25

Okay.

Piotr Turkowski 23:26

So it's, it is not a global analysis, it's a element analysis. So this way. It actually has some similarity to furnace testing because sub furnace

Wojciech Wegrzynski 23:36

Hmm.

Piotr Turkowski 23:37

uh, 99.9%, of an element. And then, so, so at the time, zero, it has its strength. And then when it hits up, you get this cross-section being reduced more and more,

Wojciech Wegrzynski 23:52

Mm-hmm.

Piotr Turkowski 23:52

strength of materials being reduced more and more. And at some point, as the, as the, as the material, uh, performance is being reduced, the entire, bending resistance or sheer resistance of the element is also being reduced. And at some point you will meet, the resistance at the level of the load

Wojciech Wegrzynski 24:09

Mm-hmm.

Critical Temperature For Steel Design

Piotr Turkowski 24:11

But the load is also reduced in, in calculations, uh, with, uh, coefficient eta fi, we will, we, we can get back to it a bit later. a very important parameter. So at some point you'll meet uh, that value. And when you do, you declare the loss of flood bearing capacity, that that's the way you do it In general, Eurocode provide a framework of, let's say three so-called domains to do the calculations. So the, the domain that we've just discussed is the so-called strength domain the, the general equation for, for, for the domain states that, well the load bearing, uh, capacity of the element in fire, the design value of it after some time. 60 minutes, 90 minutes, whatever it is, has to be greater than the actions on that structure in fire as well. And the design values as well after that time. Yes. So, so it, it, it's, it's, it's as simple as that. and there's another, and another domain that is very often used for steel elements. It's a temperature domain. The temperature domain. I remember very famous quote uh, I, I saw on LinkedIn once, can't remember by who it was. Maybe it was Luke Biby. 'cause uh, he would be very fond of

Wojciech Wegrzynski 25:34

Look local. Luke would never say something controversial.

Piotr Turkowski 25:38

The, the temperature domain, basically stating that your critical temperature of the element has to be greater than the temperature of that element in fire. So what does it mean most easily

Wojciech Wegrzynski 25:52

now, now you have to explain the critical temperature.

Piotr Turkowski 25:54

yeah, the critical temperature, it's a concept at some point in, in time when the element heats up to a certain temperature, which we'll call the, the critical temperature, the load bearing capacity of the element will be lower than the actions. it's, it's another way of expressing this strength domain. I will walk you through an example, and maybe this will be the easiest to, to understand. So imagine the, the strength of steel. in accordance with the Euro code, because in reality, it's, it's always a bit different than your Euro code, but we have to get some safe assumption. The, the strength of steel looks something like this. At the temperature of zero or 20 cent degrees, you have full 100% strength. Then throughout, temperatures of 100, 200, approximately to 250, 300 C degrees, nothing happens. The steel maintains full strength. I will already address yes, the, the modulus, the elastic modulus will be lower a bit, but the strength, the yield, yield, strength of steel is, uh, untouched. Then at 300 cent degrees or 215. It'll start to decline it'll decline, to a level of something like 60% that original strength at about 500, 550 cent degrees, and then decline even more reaching zero after something like 900 centimes like that. So when you design a steel structure for 100% of its load bearing capacity, like

Wojciech Wegrzynski 27:47

I cannot lose 1% of my load bearing capacity.

Piotr Turkowski 27:50

yes, but what you'll do is you will apply that safety, that coefficient to the load, which is usually something like oh 0.65 or oh 0.7. if you don't want to make, calculations, you will apply one of these values. that value. Corresponds to something like 550 cent degrees.

Wojciech Wegrzynski 28:12

Okay,

Piotr Turkowski 28:13

Why?

Wojciech Wegrzynski 28:13

so, so you assume that you don't need a hundred percent strength in fire because the load of a hundred percent is like uncommon combination of stuff happening. Wind, snow, people, materials inside, et cetera. It's un unlikely it's gonna happen in fire. Exactly. So not, and the fi, we assume you would probably need 60% of the, of the Max. Max, so that corresponds to that temperature.

Piotr Turkowski 28:37

exactly that?

Wojciech Wegrzynski 28:39

Okay.

Piotr Turkowski 28:39

could, uh, less.

Wojciech Wegrzynski 28:41

Yeah.

Piotr Turkowski 28:41

that your, uh, your structure wasn't, uh, utilized at 100%. Maybe it was only at 50%. So what you then, you, what you would do then is you would multiply oh 0.5 by oh point 65, getting something like oh 0.3, let's say, or maybe even less so, you do not even need 100%. You do not need 65%. You need only 30%. Of that strength of steel in fire.

Wojciech Wegrzynski 29:09

Which could be like 700.

Piotr Turkowski 29:10

yes. Then it gets to levels of 650, maybe even 700 C degrees, you usually don't go much further. Like, we stop at 700, 750, uh, max. There are some elements of, uh, cross section class four when,

Wojciech Wegrzynski 29:29

I am, I'm not even gonna ask you for definition of class four con, just continue.

Piotr Turkowski 29:32

I think that people who design steel structure know, know exactly what

Wojciech Wegrzynski 29:36

Uh, I'm sorry, listeners, I failed you. Like,

Piotr Turkowski 29:40

Uh, elements is so, so in short, these elements will lose their load bearing capacity before steel loses its strength.

Wojciech Wegrzynski 29:49

okay.

Piotr Turkowski 29:50

will.

Wojciech Wegrzynski 29:50

you.

Piotr Turkowski 29:51

will get buckling. They will get some deformation. that that will happen faster than you will, than you lose the strength of steel. So you cannot allow that utilization level to be only, based on the steel strength. It has to take into account other factors. So another simple value to, to use it to use is, uh, you just assume that 350 cent degrees of the critical temperature be before anything starts happening with the steel,

Wojciech Wegrzynski 30:19

They, they are just more vulnerable to fire damage and, and, uh, you would just go conservative because you lose less of the

Piotr Turkowski 30:26

there

Wojciech Wegrzynski 30:26

inherent.

Piotr Turkowski 30:27

more, more vulnerable, vulnerable to load in cold,

Wojciech Wegrzynski 30:31

Okay?

Piotr Turkowski 30:31

cold design. So, uh, yeah, so you are, you are more on the safety side. So you see the, the higher the critical temperature,

Wojciech Wegrzynski 30:40

Yep.

Piotr Turkowski 30:40

less of steel strength need.

Wojciech Wegrzynski 30:44

Mm-hmm.

Piotr Turkowski 30:44

as you said, three 50 when you're very conservative, 500 approximately when you do not do any, uh, calculations. And then if the utilization is not so great, it can be 600, 650, maybe 700. So this is the critical temperature and the steel element will heat up during fire, uh, very nicely, especially when it's unprotected. So when it's unprotected, you may get maybe something like 15 minutes of fire resistance, because, uh, and when it's quite massive, uh, it can get 50 minutes for very massive elements and for very low utilization levels. In theory, you can get something like 30 minutes. And this has also actually been confirmed because something like 10 years ago, we've had an eagle front robin on bare steel being. When there was no fire protection, the beam was made of HEB 300. So it's a very massive section. never use that for a beam, probably it's more for like, for a column, but it was used for a beam. The utilization was something like 20% only. and the beam got something like 20, uh, 28, 29 minutes in a test. And with the calculation method, it gets, uh, something very similar.

Wojciech Wegrzynski 32:00

is that the secret test in which we were the reference lab?

Piotr Turkowski 32:03

maybe

Wojciech Wegrzynski 32:04

It could be. It could be

Piotr Turkowski 32:05

wink, maybe.

Wojciech Wegrzynski 32:06

perhaps.

Piotr Turkowski 32:08

Yeah. So, uh, uh, so yeah, so when you heat up that element, you get the standard fire curve, obviously, uh, for, for the classification. So after 30 minutes. in, in a, uh, with a standard fire, you have something like 834 cent degrees. when you have a massive element, it'll get a delay because of its inertia to, to heat up, you'll get less. You will have something like 700. So if your critical temperature was above that, you'll get 30 minutes and even easier for 15 minutes, because after 15 minutes it's something like 740 or something like that. So it's quite easy, but not much. Not, not much more. Maybe for external element, if you use external fire curve, which, uh, caps at 670 cent degrees, you can get some R 30 dash ef dash external fire because we use the same, uh, designations here in the Euro codes as well

Wojciech Wegrzynski 33:05

Yep.

Piotr Turkowski 33:06

in the furnace testing but, but you, you can't get much more. So what you do is you use fire protection and in order to use the fire protection, uh, you basically have to do the, do the test. I will not explain how the test exactly works. Uh, we have a three day long course for it. So, uh, I, I really can't squeeze it into five minutes.

Wojciech Wegrzynski 33:29

no problem. let's finish the, the concrete beam, because that's where we started. I assume the, the steel deviation was to understand the rebar temperatures and the, the role of zones in the, in the second, uh, simplified calculation method. Let, let, let's finish on that and then we can venture into funny things. I.

Piotr Turkowski 33:44

we'll have to get back to steel, uh, again, but, uh, but okay, let's finish the concrete beam. so the concrete beam has this strength domain, uh, where you compare the, the resistance and the actions and. Temperature domain that we have for most likely steel. And there's time domain, which is this global analysis for advanced calculation methods. The equation very simple is something like the for which the structures maintain its performance in fire is more than the time required of it. So, so basically if you're ana analyzing structure for, let's say 60 minutes your global analysis, it can't collapse or,

Wojciech Wegrzynski 34:28

Mm.

Piotr Turkowski 34:28

misbehave for at least 60 minutes. Yes.

Tables Versus Calculations In Practice

Wojciech Wegrzynski 34:32

Yep. Global ac r sets. Yeah. And the third method from from Eurocodes.

Piotr Turkowski 34:36

And the third method is the tabulated data.

Wojciech Wegrzynski 34:39

What do you mean?

Piotr Turkowski 34:40

data. It's a very simple set of tables Um, the, the, the, the simplest one is for non-no bearing walls, which tells you if you do a non-no bearing wall and it has to, uh, maintain, Fiberon class of 20, then it has to be at least of thickness 120 millimeters. That's it, that it's like the only rule. And if it's supposed to be for, let's say 60 minutes, then it's, uh, 80 millimeters or so.

Wojciech Wegrzynski 35:08

if we have a table for that, why would anyone calculate?

Piotr Turkowski 35:10

because these tables are conservative at, at least for concrete, uh, they are, they're a bit conservative. They are based on tests mostly, some based on test and, calculation methods. They don't show all uh, possibilities. They are very often, at a hundred percent utilization level.

Wojciech Wegrzynski 35:34

Mm-hmm.

Piotr Turkowski 35:34

will give you option for, uh, full utilization or maybe two options for let's say 50% and 100% In the second generation for columns, we got way more. 'cause now it's not only a hundred percent, but there are actually four levels. So it's nice, but in general it's very conservative and very simple. And you'll find some, uh, some buildings or some, some, some situations where you really need these 10 millimeters less, or maybe you need, this cross section a bit smaller or maybe this concrete cover a bit smaller. I don't know if I can say, but you probably remember one of the, uh, tall buildings, uh, near Metro Street, Toka, one mentioned the name. There are many high rise buildings, but there was one very specific where they were really fighting for every millimeter of thickness of the floors because they wanted to get as many floors as possible, and they were very limited with the reaction forces that they could apply to the elements below.

Wojciech Wegrzynski 36:36

by the weight of the building. That's it.

Piotr Turkowski 36:38

so that's it. Sometimes, sometimes it's really, uh, these 10 millimeters, they, they adapt. When you have 30 stories, they give you an extra story.

Wojciech Wegrzynski 36:47

A, a follow up question to all of those methods, how much do you need to know about the material, like. It is not like concrete. Universally, you have different types of different strengths of concrete, like vastly different types of concrete out there, and I assume for other materials you also have different types of materials, so, so how much you need to know about the material itself, when you want to do the test and where you get the knowledge,

Piotr Turkowski 37:12

Well, uh, probably, you do not need to know much.

Wojciech Wegrzynski 37:17

okay?

Piotr Turkowski 37:18

code is very simple in, uh, in this application. It gives one model of concrete. There are some tiny deviations based on the type of aggregate maybe, but they give you one, one formula to feed them all, and

Wojciech Wegrzynski 37:33

Mm-hmm.

Piotr Turkowski 37:34

doesn't fit them all. And uh, I remember when doing a research for my PhD, concrete is everywhere. Uh, there, there are so many models of concrete, even for the thermal performance of concrete. Now not even saying about the strength of it, but just for the thermal conductivity, they couldn't get consensus. So what we've got with the second generation is, like, like basically we used to have two terminal conductivity lines. One was so-called lower terminal conductivity, and one, the, the second one was higher. for the 15 years that we've waited for the second generation, they couldn't figure out which one to use. So now they drew a, a line that, uh, for the first 160, uh, 60 some degrees or so is the higher value. And then it connects with a straight line with the, with the lower thermal conductivity boundary. So we have something that is not physical, but let's say for calculation purposes it works. but it doesn't look like, like it came from tests. Like it, like you've actually measured these values. It's, it's, uh, some kind of

Wojciech Wegrzynski 38:42

Uh, something that ans Lo can write about in 10 years about how it happened. Sorry, continue.

Piotr Turkowski 38:49

yeah, so, so the less, you know, the easier it is to use these methods

Wojciech Wegrzynski 38:53

Okay.

Piotr Turkowski 38:54

the, the more you know, uh, the, the more you start to wonder, what will the outcome actually be,

Wojciech Wegrzynski 39:00

Any more complex materials like fire protection materials?

Piotr Turkowski 39:03

ah, very complex. Uh, but just finishing off the,

Wojciech Wegrzynski 39:06

Yeah.

Why Material Properties Break Assumptions

Piotr Turkowski 39:07

'cause concrete properties will depend on basically everything on the type of cement, the type of aggregate, the size of the aggregate, the cement to water ratio, the additives that you'll use, uh, polypropylene fibers content may be, some other, uh, additives, uh, like ashes are really good in Increasing the, the concrete grade, but not so good in fire. are so different that when it comes to tunnels and testing of concrete, for tunnels, for spalling, which is one of the adopted, uh, criteria, um, there is no simple rule. Each concrete has to be tested separately and there is no exchange of data, let's say between tunnels, to the point that if your aggregate comes from two different sites, your, you are obliged to do the test for each site separately. So, uh, yeah, that, that's concrete. Fire protection is, uh, is another material that is very complex and very, uh, different in its performance. So I, I, I want to get back now to steel. Because still, uh, on one hand, in order to get the virus and specification, you, you have to test the performance of the product steel sections. And then you get the famous tables where you have section factor design, temperature, and then a values of required thickness of fire protection. But the Euro code itself has a way to calculate the temperature of steel that is protected. There is a model for it. It's not very hard to It's probably something like 15 minutes in, in Axl and, and, and you get it. The only problem is that you, you need to get the thermal conductivity of that fire protection material, and the specific heat.

Wojciech Wegrzynski 41:06

As a, as a function of temperature.

Piotr Turkowski 41:08

as a function of temperature. Yes. 'cause if you use the values from 20 C degrees, it's.

Wojciech Wegrzynski 41:12

Have fun.

Piotr Turkowski 41:13

Not worth much. Yes. every material changes its properties with the temperature, especially when they lose moisture. They will, uh, some material like mineral wool, they will tend to get their thermal conductivity up. So, uh, it's worse. I mean, it's conducting heat more. some materials will get lower values. Uh, some because of the moisture content will get, uh, so-called, uh, moisture plateau or very high specific heat that represents that moisture. Uh, in the material at around 100 C degrees for gypsum material, you get two peaks. Uh, so yeah, the material is everywhere. And, and not even starting with intumescent coating on how to, uh, how to describe these where, uh. Well, you start with let's say, maybe one millimeter of that coating, and during test or during fire, it'll expand 50, maybe 100 times. So you end up with, let's say 100, uh, uh, of that material. Uh, and the properties change change a lot. So, so there are ways to calculate these values, but they all start with tests, so you need them I've seen some people try to, to apply these methods and, uh, and prove that the material, allows to, assess the, the entire element in a particular fi class. But there is one thing that is really difficult and that I would personally never, never take responsibility for, is, uh, the stickability of the material. a very difficult thing for many products to maintain stickability in fire. what you assess in this test is also stickability.

Wojciech Wegrzynski 43:06

You mean how well it's able to stick to the place where it's attached.

Piotr Turkowski 43:11

stick form, cracks, detach, maybe partially detached everything.

Wojciech Wegrzynski 43:16

Stay in place.

Piotr Turkowski 43:17

ev everything, then goes under the so-called stickability correction factor. and if it's 1.0, says that, okay, deflection doesn't influence the stickability of that product. It will stay in place if it, if it form cracks, they don't matter and so on. But if that factor is lower and typically it is lower, then it says that something is happening with the product. You can imagine when we were talking about the, the deflection that the limiting deflection of elements last time. These deflections are gigantic, like

Wojciech Wegrzynski 43:52

Yep.

Stickability And Fire Protection Failures

Piotr Turkowski 43:52

centimeters deflection for a concrete slab. That is insane. So imagine you have a very stiff board applied to that concrete member, and then it deflects 40 centimeters. Well. break. If,

Wojciech Wegrzynski 44:06

Yep.

Piotr Turkowski 44:07

maybe it'll detach, maybe it'll collapse fully.

Wojciech Wegrzynski 44:10

Or, or just expose a part of the structure.

Piotr Turkowski 44:13

and for steel, you, you, you can expose only a tiny part of it and it'll lose the load brain capacity and in, in this place. And, uh, then it'll gradually collapse, uh, the entire element. um, for sprayed mortar, you will get cracks. Maybe you will get some partial detachment of the material. or maybe it'll not stick at all if there is no reinforcing mesh in it. So there are many issues that, and many things that can happen to that fire protection during that, this deflection that will influence it performance. It is all summarized in that thickness of concrete for, for concrete elements.

Wojciech Wegrzynski 44:52

Hmm.

Piotr Turkowski 44:53

When you assess it for steel, it is in the correction factor that is applied to the thermal data. So the tables you get already include this phenomena that will happen during fire. So it is, if the material falls off, it's not the end of the world. It's just that it'll shorten or it'll reduce the performance, but it can still be useful in some places. So, but you have to know this, you, you cannot just assume that, yeah, I will mix some cement in some gypsum and maybe I will add some magic component, mix it with water, apply it to my element, and it'll all work. No, it'll not. Most likely it'll not. uh. The deflection is one part. Even the shape of the steel section is very important. the times when we were using the previous edition of the method the previous edition of the method for sprayed mortars required the testing of two hollow sections, a square tube, and a circular tube. There were so many sprayed mortars and intumescent coatings that had problems to maintain stickability these shapes that they were only classified for, so-called INH section. So open sections like I-P-E-H-E-B and so on, and couldn't be used for, uh, with hollow elements. They just couldn't be used. Let's get back to that interes coating. Imagine you have a, uh, you have a circular hollow sections of section of diameter of let's say. millimeters,

Wojciech Wegrzynski 46:31

Mm-hmm.

Piotr Turkowski 46:32

You apply one millimeter of coating, it expands 100 times. You get suddenly the internal diameter at which we applied the coating was, uh, that diameter of 60 millimeters, but now it's 100 plus 60 plus 100. It's two 60. It's way, way more. So the material cannot, expand uniformly, or it'll expand, but there will be cracks in between the, the portions of the materials. only way to assess it is through testing, but when you do, you will get enough data that maybe then you can start using these euro code equations. Keeping in mind the behavior of the, of the material from the test, but

Wojciech Wegrzynski 47:15

Yeah.

Piotr Turkowski 47:16

only because you've assumed perfect stickability and no changes to the thermal conductivity during heating.

Can Numerical Models Replace Tests

Wojciech Wegrzynski 47:24

Okay. Uh, let's assume I have a black belt in numerical methods. Am I allowed to use some advanced computer modeling for, for this type of assessments as well? Does it fall into your advanced calculation method or.

Piotr Turkowski 47:38

It'll most likely, uh, fall under advanced calculation methods. And on one hand, they are allowed in the Euro code. On the other hand, you have very general statements in, in the Euro codes, telling you only what to do, that you should know what you're doing, that you should validate your models in testing, but they would not allow you. As far as I know, I'm not an legal expert and I can imagine all types of legal, uh, discussions here. In my opinion, they do not form resistance classification that is equivalent to what is required currently by the law. it's here in Poland or many, or many other European countries, this, this advanced calculation, models, they can be used with standard fire. But if you're going that far, you will go even further. You

Wojciech Wegrzynski 48:30

Hmm.

Piotr Turkowski 48:31

the natural fire model. You will see what is exactly happening in that building.

Wojciech Wegrzynski 48:35

So just little burning fire.

Piotr Turkowski 48:37

yeah, and you will not get it from one person. You will get, uh, a team of experts that will discuss it, and you will do it not for a household or an office building. You would do it for a very important, uh, or very expensive buildings where, you actually can argue why you can use them and why you should maybe be able to save some, uh, millions because When you do, it's most likely because of, uh, finance issues you and you want to save money on fire protection. you know, the way our prescriptive rules are given is they very often re require fire safety equipment, uh, beyond fire protection. They will ask you for sprinklers. They will ask you for, maybe some smoke controls for alarms. many, many other things. And as we know from the the previous talk, they're not included in an assessment of fire resistance. Yes, the, the beam that we are assessing for fire resistance can be submerged in water, buried underground, no combustible materials within a hundred meters from the element

Wojciech Wegrzynski 49:50

Doesn't matter.

Piotr Turkowski 49:51

doesn't matter. Standard fire somehow.

Wojciech Wegrzynski 49:54

Yeah. I love it, especially in airports when you design for like. 50 meters of open space underneath it. We've once calculated it with other pi, uh, that you needed. Like, if I recall correctly, it was like three trucks filled with furniture one on top of another to, to get something like standard curving, like 30 meter tall airport, which is quite interesting thing to do. Um, I mean, tha thank you p for, for, uh, showing me this, this methods, I think it's very interesting and especially it spans from something as simple as I have a, a table in Euro code that tells me what's my thickness of, of fire protection and I'm done. or, or that tells me what's the fire resistance and I'm done up to extremely complicated methods where you have to know so, so many intrinsic details of your. Materials and structure and, and whatever you're having up to even assimilating the whole response of entire structure, that's actually quite complicated. Engineering. So the span of those methods is, is in the end quite insane. And in the end you also get the same rating, which I kind of find ridiculous after all this.

Piotr Turkowski 50:58

Yes. But the that, uh, as we discussed in the, in the beginning, uh, well, it, it, it, it has to be allowed. It, it,

Wojciech Wegrzynski 51:06

I, I, I mean, it falls into conservatism. It, it is, it's, it's a discussion of conservatism, like how much you can save by doing. It's simpler with the assumption that you're probably gonna use more.

Masonry Tables That May Be Unsafe

Piotr Turkowski 51:16

But if we still have time, I'd like

Wojciech Wegrzynski 51:18

Yeah.

Piotr Turkowski 51:19

touch just one more topic,

Wojciech Wegrzynski 51:21

Hmm.

Piotr Turkowski 51:21

because for steel, you will, uh, okay. Right now we get this R 15 and, uh, maybe, uh, there will be, cases where, the, the, the fire reasons will be assessed only with calculations.

Wojciech Wegrzynski 51:35

Mm-hmm.

Piotr Turkowski 51:36

They should be treated as if somebody carried out the test, especially regarding that harmonized standard that explicitly allows you to, we have concrete for which, uh, well, it's concrete. It's very easy to design elements out of it for 120 minutes. Uh, for four hours. It's a bit more tricky. But still, you take the effort to do it before you cast the elements, you can, uh, it's achievable without any fire protection.

Wojciech Wegrzynski 52:06

Oh my God. They're going for masonry.

Piotr Turkowski 52:08

Yes, I am. I am

Wojciech Wegrzynski 52:10

Ah,

Piotr Turkowski 52:11

I am now energized because my paper was accepted and I'm, I, okay. I don't

Wojciech Wegrzynski 52:18

it is. It is a, it is a good paper. So you go for it.

Piotr Turkowski 52:21

thank you dear co-author, who helped me very much with it, with the insanely low amount of time we had to prepare it. But really for masonry, we do not have advanced calculation methods. I mean, we have, but they're unusable because they require more testing than five sense testing. We used to have simplified calculation methods, but they were so, so unusable, not because they were difficult, because they were. I dunno if I can say shit, but they really were, and from the very beginning everybody was saying that. So now they are gone, they're gone from the Euro code. We are only left with tabulated data. The tabulated data that, that have national annexes in France saying, well, it's really nice you had them, but you know, you can't use them here. The tabulated data that got like 90 page long national annex in Germany that uh, you know, said the same, like really nice set of tables, but you know, we have our, our own in Netherlands. What they also say, you know, not so useful these tables, it all depends on the material, but for concrete masonry, for mass, especially for the elements of group two, where you have openings in these, uh, elements, uh, which look basically like a, a concrete frame with a rip in, in the middle. The second generation of eurocodes gives you some insane values of fire resistance. Like you can get REI 240 with a wall of 14 centimeter thickness. This is unheard of. It's even from the conductivity point of point of view. Impossible this, if that wall was full of concrete, not only three ribs connected with some, uh, webs and shells, you, you, you couldn't get, the en enough thermal, uh, thermal insulation to get that classification. Maybe for E not for ei. so yeah, we wrote that paper. Uh, we've presented results of 15 fire resistance tests that we've carried out over the last 20 years, something like that. And. None of these cases we've met what the new Euro code tells you that you are actually getting. So I'm talking about mass concrete masonry here. I would really strongly advise caution when using them. are unsafe. It's not only our, our opinion, uh, we found many papers written before us that stated the same. They give unsafe assumption of the material properties, of the behavior of the material. Just don't use them. Please, please don't. For other materials like, Autoplays, aerated concrete, or maybe for Cate, they are more in line with what we get in tests, uh, for ceramics. Uh, it, it's, it's also close, but I, I know that the manufacturers of these elements, they do prefer to have their own testing, just to be sure, because sometimes they're on the safe side. Sometimes they on, on the, uh, uns unsafe side. So, what I wanted to say, in short to not, to not make it much longer, are some materials concrete where you can calculate it and be pretty confident in your calculations. Even for steel structures. Unprotected steel structures now, would now requirement of R 15 here in Poland, you can also use calculations and I'm also pretty confident that it'll work. Just one or two

Wojciech Wegrzynski 55:50

Hmm,

Piotr Turkowski 55:51

we've carried out another test of unprotected steel the manufacturer calculated the viruses to be like 16 minutes, and we've obtained 18. So really perfect result. But for masonry. Oh, please. It's like, just forget that

Wojciech Wegrzynski 56:08

the, the,

Piotr Turkowski 56:09

codes for, for masonry.

Wojciech Wegrzynski 56:11

the, the link is in the show notes. You can read and, uh, I, I, but it's not published yet. I still hope we can turn it around right. With these papers and stuff.

Piotr Turkowski 56:19

The,

Wojciech Wegrzynski 56:20

I.

Piotr Turkowski 56:20

the official English version is already being published. Well, now it is up to every country to create, uh, national

Wojciech Wegrzynski 56:28

Alliance.

Piotr Turkowski 56:29

uh, because all these tables are, uh, are claimed to be NDPs, so national dependent parameters, so they can all be changed like they used to be. so at least that, and I really hope, uh, I've already wrote with, uh, after the, our, our paper paper was published, I already wrote to our standardization committee that here is the paper you've asked for. Now, please revise the tables at least for concrete masonry because of simply safety reasons. Yes. Nothing more to say. They are, they are, they're unsafe the way they are, uh, in, in the Euro code right now.

Wojciech Wegrzynski 57:05

Fantastic. Good. Uh, thank, thank you so much for taking us to the beautiful world of structural foreign engineering again, and, uh, this time with, uh, the calculation methods. And I think, uh, perhaps one day we should do a full masonry episode. That could be potentially fun.

Piotr Turkowski 57:20

We didn't touch one, uh, one material, which is

Wojciech Wegrzynski 57:23

no,

Piotr Turkowski 57:24

Yes. But I

Wojciech Wegrzynski 57:25

no, no. You're not allowed to talk about them right here.

Piotr Turkowski 57:27

exactly. Uh, but I, I really, uh, I, I'm looking forward for your episode on timber. Like you, you've already had few. Uh, but I, I, I would really like to hear more about timber from an expert about also the second generation of Euro code because it changes everything about the CLT, the Charing of the materials. Now we have many layers, like everything is different. So I would really love to hear about it. Uh, if, if, if I may make this,

Wojciech Wegrzynski 57:59

I, I take this request. I'll, I'll find one That, that, that's gonna be a good one. Okay. Thank you. Thank you Kurt, so much. And yeah, nice day, man.

Piotr Turkowski 58:07

Have a good day too to you. Thank you all. Thank you for having me again, and uh, have a great day. All of you listeners.

Wojciech Wegrzynski 58:13

And that's it. Thank you for listening. I hope you've enjoyed this conversation on how to calculate fire resistance. I mean, it would've be beautiful if we just had table ice methods for all materials and all kinds of solutions, but as Piot said, if you would like to do that, you probably would end up, uh, having more far tests than just. The number of tests you need to establish for resistance of them by fire testing. So that, that's an interesting, problem. One thing Piot has not mentioned, because it's not part of the current paradigm of calculating the fire resistance was machine learning and, Perhaps the future methods of predicting those properties of, uh, building partitions. I think this is something growing, this is something potentially quite interesting. And actually with the complexities we have, machine learning could fit a nice role as an additional tool. However, uh, hard for me to see how we could have, um. Let's say, uh, a compliant standard, compliant neural network or, or validated, uh, models for, for this particular need. It, it's probably still a lot of, a lot of work. Uh, ahead of the fire community to reach to that point. But, um, I think we will eventually get there. And, uh, for now as we have the revisions, the new generations of Euro codes coming out, we're getting more and more new models, new methods, new. Possibilities to, to calculate far resistance, and I hope all the fire engineers will be able to, to use those for their benefit. And, uh, yeah, also see that far testing is not going away, which, uh, perhaps is good use for, for my laboratory. Uh, in general, we need more data anyway if we want to have, uh, machine learning models in the future. So fire testing is here to stay. Um, that would be it for today's episode. I hope you've enjoyed this conversation. I hope you've learned something new. I've learned a lot of new things, uh, from my office colleague, even though we've worked together for many, many years and I've seen those tests. Uh. Firsthand. I still learn, uh, about this and I find this quite a fascinating part of fire science. Anyway, that would be for today. Thanks for being here with me. Cheers. Bye.