From attic to 1.5 floors with open plan - Dimensioning

[scorp1on]

I agree with you that there is no need to use FEM for this.
Thanks for the guidance on EKS11 and the Swedish wood handbooks. I will take a look at them.

However, if you or anyone else already has something available based on EKS11 that can calculate this with experience, feel free to do it while I try to get into the handbooks.

No FEM tools are required at all. EKS11 and Swedish wood are a good starting point but can be a bit confusing if you don't know what to look for. Let me know if you need help with the dimensioning or anything like that.

 

[Digitala_tvillingen]

Absolutely no FEM tools are required. EKS11 and Svensk trä are a good starting point but can be a bit confusing if you don't know what to look for. Feel free to contact me if you need help with the sizing or anything like that.

Please feel free to help me with the sizing if you have the opportunity?

 

[scorp1on]

You are welcome to help me with the sizing if you have the opportunity?

Sure, I am a bit short on time, but I can see what I can do. I can help and answer questions and the like otherwise.

 

[bossespecial]

Having a freely laid beam of a full 7.6m is probably not the right way to go as it would require unreasonably large dimensions for the beam in order to have a well-functioning floor structure. Therefore, you should probably plan to place an extra pillar. Another alternative could be to skip the beam and use frame roof trusses instead. "Lundqvist trusses" has a drawing example of a truss that can handle the span without support in the middle, though with hefty upper chords.

 

[Digitala_tvillingen]

Having a simply supported beam of 7.6m in length might not be the right way to go as it would require unreasonably large dimensions for the beam to have a well-functioning floor. Therefore, you should probably consider placing an extra column. Another option could be to skip the beam and use framework trusses instead. "Lundqvist trusses" has a drawing example of a truss that can handle the span without support in the middle, though with hefty top chords.

Yes, it feels more and more like that...
My plan is to use framework trusses, though I didn't think they could handle the spans.
I'll look more into this, maybe it's just as well to send an inquiry to Lundqvist or Arvidssons directly, thanks for the tip!

 

[Gabbe1]

I did a quick calculation on what would be required for the steel beam.

I made the following assumptions:
Area: 60m2
Load: 200 kg/m2 (including self-weight) (half of which affects the beam in question)
Max allowed deflection: 20mm
Evenly distributed load
Simply supported beam on two supports

This gives a requirement for a moment of inertia of just over 8000 cm4.
An HEA 240 almost manages this, but an HEB 220 would be a slightly better choice. These are quite hefty beams weighing around 500-650 kg and consequently costing a fair amount as well.

If you can imagine a support (pillar) in the middle, you could have a significantly more slender beam.

 

[bossespecial]

I would probably have gone up another notch to at least a HEB240, then the deflection would be about L/500 of the useful load and the natural frequency would be around 7Hz. However, it is preferable to perform a dynamic analysis to study the accelerations since the beam is quite long. If you're not sensitive to it potentially swaying and shaking a bit, I would go with a HEB240.

 

[Digitala_tvillingen]

I quickly calculated what would be required for the steel beam.

I made the following assumptions:
Area: 60m2
Load: 200 kg/m2 (including self-weight) (where half of it affects the beam in question)
Max allowable deflection: 20mm
Evenly distributed load
Simply supported beam on two supports

This results in the need for a moment of inertia of just over 8000 cm4.
This is almost handled by a HEA 240, but an HEB 220 would be a slightly better choice. These are quite massive beams that weigh around 500-650 kg and consequently cost a fair bit.

If you can consider a support (column) in the middle, you could have a considerably slimmer beam.

I would probably go up another notch to at least an HEB240, resulting in a deflection of approximately L/500 of the live load and a natural frequency around 7Hz. However, it is preferable to conduct a dynamic analysis to study accelerations since the beam is quite long. If one is not sensitive to the possibility that there might be some swaying and shaking, I would go with an HEB240.

Thanks for the help with the calculations!
Now I know the range we're in for the beam.
According to Stena Steel's price lists, HEB240 costs 23.2kr/kg and weighs 83.2kg/m, so for a 10m (assuming one has to buy the whole length), it would be almost 20kkr excluding cutting, shipping, etc.

What I'm most uncertain about now is if the slab can handle the pressure from the columns supporting it... What would be the force at each end? Additionally, the bearing pressure would probably be quite significant for a couple of wooden columns... if the slab holds... What are the standard criteria for a regular slab if one assumes it's reinforced along the edges?

It feels like going the truss route seems more realistic right now.

 

[Gabbe1]

60m2 loft, 200 kg/m2 load, half the load on the beam (the other half in the outer walls), half the beam load on each pillar -> 60x200/2/2 = 3000kg pressure on each pillar (plus a few hundred kg for the beam's own weight).

That is, there is absolutely no problem handling the point loads from the pillars (of course, the concrete slab should be equipped with reinforcement and insulation quality calculated based on these point loads), much more troublesome with such a heavy beam that needs to be handled and built in.

 

[Digitala_tvillingen]

60m2 loft, 200 kg/m2 load, half the load on the beam (the other half in the outer walls), half the beam load on each pillar -> 60x200/2/2 = 3000kg pressure in each pillar (plus a few hundred kg for the weight of the beam itself).

That means there is absolutely no problem handling the point loads from the pillars (naturally, the concrete slab should be equipped with reinforcement and insulation quality calculated according to these point loads), much more troublesome with such a heavy beam that needs to be handled and built in.

Sounds good! However, this is on an existing slab that hasn't been calculated for these point loads... A small risk factor there perhaps or what can a normally reinforced edge handle in point load?