Interior load bearing wall and fire design

[molibden]

I have load bearing interior CLT walls (or any other structural system, doesn't matter in this case) in multi-residential building. Each apartment is a fire compartment. Each apartment has several rooms as usual. My question is when to consider a wall with fire on both sides at once. For external walls and separating walls between fire compartments I'm confident to design them with fire on one side. For interior walls within one room I'm sure to design them with fire on both sides at once. But for interior walls between rooms I'm not sure. I can't find my answer in any code or publication.

I'm using Eurocodes, but would love any insight how you view this issue.

 

[kostast88]

I don't know the answer to your question but I am intrigued by the "design for fire". I've never come across structural fire design of walls or other timber elements. So I don't understand what design are you talking about. We provide Fire protection for a specific amount of time depending on the importance of the element and that's it. Unless you are talking about some fire modelling with finite elements (research?)

Also fire protection is Architect's responsibility, not the Engineer's (UK).

Finally,fire regulations are different for every country, so Eurocodes is not enough, UK is different than Germany, etc.

You would probably get more replies with a bit more explaining

 

[molibden]

kostast88, fire engineer defines for how long does a structural element need to "hold" during fire (R30, R60, R90, R120min). Our job as structural engineers is to accomplish this using fire protection, structure itself or combination of both. For all materials there are calculation methods in Eurocodes. For timber this is in EN 1995-1-2: Design of timber structures - Part 1-2: General - Structural fire design. Most of the time timber elements them selves cannot provide enough fire resistance (unless architects want exposed wood, then we make section bigger). We cover them with fire protection and calculate how much time this protection holds. For the remaining time we then consider charring of timber elements. So in the end it is a combination of fire protection and charring.

It is a bit surprising you never dealt with this with other materials.

My question is when to consider fire on both sides of the wall at once. And when only on one side.

 

[molibden]

I got my answer. For future reference, the answer is that within fire compartment fire can spread everywhere. So you need to consider charring on all sides. Table below is in German but it is very helpful to understand the concept. This is probably the logic for almost all Europe.

 

[MIStructE_IRE]

Kostas, in the UK you would presumably be checking RC beams/walls/slabs/columns for this?? There’s entire section of codes dedicated to it.

 

[jayrod12]

As per his OP, CLT loadbearing walls. There's plenty of testing out there for CLT. Essentially there's a char layer, and a heat effected layer that must be neglected on all sides exposed to the fire, and the remaining thickness is checked for it's capacity to support service level loads.

I don't agree that you need to check each side of the wall if it is a demising wall protecting one suite from the adjacent suite. If it is fully inside one fire compartment (one suite) then I agree that you would need to check it from both sides.

 

[MIStructE_IRE]

That’s my usual approach also Jayrod. If its a dividing fire wall, it essentially shouldn’t allow fire to spread onto both sides. If you have fire on both sides of a firewall then that’s doomsday stuff beyond design.