We are going to build an attefallshus 7 x 4.3 m with a loft at one end and open up to the ridge elsewhere.
We have received a quote for the materials, which includes a glulam beam 90x315. The house will be built in Halland, snow zone 1.5, with concrete tiles on the roof.
Yes, that's correct. I hesitated to mention it in my previous post. I refrained because I perceived that you already had the beam. This is because you can exploit a continuity effect when the beam (note unjoined) rests over a central support and is only subjected to a uniformly distributed load. An upward moment occurs over the post which counteracts the deflection. 90x270 and 140x225 are entirely equivalent in terms of stiffness. There should have been a vot under the slab. The post receives a load of about 20 kN. With a 115x115 post, it becomes 17 MPa, which is a bit much, so you need something for pressure distribution, unless you want to break up the slab.
Yes, that's correct. I hesitated whether to mention it in my previous post. I refrained because I understood that you already had the beam. It depends on being able to take advantage of a continuity effect when the beam (note unspliced) is over a support and only exposed to a uniformly distributed load. An upward moment occurs over the post that counteracts the deflection. 90x270 and 140x225 are entirely equivalent from a stiffness perspective. There should have been a base under the slab. The post receives a load of about 20 kN. With a 115x115 post, it becomes 17 MPa, which is on the high side, so you need something for pressure distribution unless you want to break up the slab.
No, we haven't bought the beam yet.
It's a shame we didn't know that during the casting. Can the pressure be distributed sufficiently in some way so that we don't have to break up the slab? If the entire wall at the entrance to the loft is made load-bearing and then there is a post from the loft up to the ridge?
Would there be less pressure on the post with the 90x315 beam?
The beam's dimensions have only marginal significance. It is about distributing the post's load over a sufficiently large area in relation to what the slab can withstand. Perhaps with a strong steel plate. Use the formula load/area=pressure. kN/sqm = kPa.
The beam's dimensions only have marginal significance. It's about distributing the post's load over a sufficiently large area relative to what the slab can withstand. Maybe with a strong steel plate. Use the formula load/area=pressure. kN/sqm = kPa.
What pressure do you need to reduce to for the concrete slab to handle it?
I might not have fully understood how you calculated 17 MPa above. Isn't it 20 / 0.115^2 / 1000 ~= 1.5 MPa? Or am I thinking wrong?
You're absolutely right, it should be 1.5 MPa. There must have been some other number floating around in the calculator. I just thought the sequence of numbers seemed reasonable. What the slab can withstand depends on the concrete quality, etc. But 1.5 MPa sounds more manageable. Otherwise, you can increase the beam dimension and skip the post, e.g., 190x360.
Yes, it is an intelligent thought. Either a regular wall with a beam on top or perhaps a brick story?
Edit: When I look at the floor plan, I see a transverse wall stump that can be utilized for this purpose.
I interpret the numbers in the calculation tool as indicating that the post in the middle will take the largest load (30 kN), the post in the far outer wall 12 kN, and the outer wall by the loft only 2.5 kN. Is that correct?
Do you think it will work to distribute 30 kN in the small wall by the loft? How do you design it to spread it sufficiently over the slab?
There's something fishy with that calculation. The numbers don't match internally. It might be a program bug. It might expect the middle pillar to be at the center. According to my calculation, the load on the middle pillar should be around 20 kN. The outer post by the loft should have a load that is about half of the other's. The transverse wall is absolutely sufficient to even out the pillar load.
There is something fishy with the calculation. The numbers do not match mutually. It might be a program bug. It might expect that the middle pillar stands in the center. According to my calculation, the load on the middle pillar should be around 20 kN. The outer post at the loft should have a load that is about half of the other's. The transverse wall is absolutely sufficient to equalize the pillar load.
Ok, strange that it calculates it wrong, but sounds good that we can solve it that way! Thanks for the help!
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Can the pressure be distributed sufficiently in some way so that we don't have to break up the slab? If the entire wall at the entrance to the loft is made load-bearing and then there is a post from the loft up to the ridge?