Dimensioning intermediate floor

[Zedo]

I'm going to make an intermediate floor structure in an extension that will house a living room. The span is 7900 mm and I had hoped to use 45x220 on cc 600 with a beam in the middle for support. The beam needs to be 5000 mm long. Anyone knowledgeable who can calculate what type of glulam beam or steel beam is required? Or can recommend a suitable structural engineer who has time for someone who’s running late

 

[bossespecial]

Should the beam span freely for 5m or should you have columns along the length?

 

[Zedo]

Should the beam span freely 5m or will you have pillars along its length?

The idea is for it to span freely. It won't be the full 5m but almost.

 

[justusandersson]

There will be too much deflection for the 45x220 beams with only a central beam unless you go to extremes in stiffening measures. You should reconsider. Why do you want it open without columns or supporting walls on the floor below? All houses need structure.

 

[Zedo]

Det blir för mycket svikt för 45x220 bjälkarna med bara en mittbalk om du inte ska gå till överdrifter i uppstyvande åtgärder. Du bör tänka om. Varför vill du ha fritt utan pelare eller stödjande väggar i våningen under? Alla hus behöver struktur.

Jag såg framför mig ett öppet rum på ca 40 kvm utan väggar eller pelare som begränsar användandet. Tänkte att en limträbalk eller HEA-balk på 115x115 limträpelare skulle klara att hålla upp bjälklaget i mitten, men får kanske tänka om då. Får väl bygga en vägg där istället då som tar upp lasten.

 

[justusandersson]

It is not forbidden to have open spaces, if you have thought it through. You should know that it comes at a cost. If you are going to continue with this concept, you need two central beams. There are many alternative solutions that @bossespecial can describe better than I can. Keep in mind that you may need to pass through the floor with various installations.

 

[bossespecial]

What should be upstairs? As I interpret it, the living room is downstairs, or was it the other way around?

 

[Zedo]

What should it be upstairs, as I interpret it's the living room downstairs, or was it the other way around?

Living room upstairs

 

[Zedo]

Excuse an ignorant person, but if we reverse the reasoning then. Suppose you use a 115x405 glulam beam and attach the floor joists with joist hangers on each side, what free span would it support?

 

[justusandersson]

There are many different solutions to the problem, depending on what is important. If you want to build a standard floor structure, without columns under the beams, you can use two glulam beams approximately 115x360 that divide the long dimension into three compartments of 2.6 m each. In these compartments, you can lay 45x170 joists (if you use screw-laminated chipboard on top, otherwise it will be 45x195). The glulam beams will then be visible from the underside. I think it can look quite nice if the ceiling height is sufficient. If you want to lower the beam height, you can use 165x315 or place columns under the beams in the middle. It always results in a better outcome to place the floor joists on top of the glulam beams rather than recessing them with joist hangers.

 

[Zedo]

This is what the floor plan looks like, which I probably should have included from the beginning. The ceiling height is limited on the ground floor.