Hello!
My uncle has asked me for help, but I know nothing about this, so I'm turning to you.
He has a concrete floor that is starting to sag a bit. It needs to be reinforced, but what size steel beam should be used? He's considering an I-beam, HEA-beam, or square beam (which is best?).
The space is 5x5 meters, so a 5-meter-long beam is needed. The concrete ceiling is maybe 3-4 dm thick. Under the steel beam, 4-5 posts and a similar steel beam in the floor to distribute the load evenly.
This is the information I've received from him, can anyone help solve the problem?
Thanks in advance!
My uncle has asked me for help, but I know nothing about this, so I'm turning to you.
He has a concrete floor that is starting to sag a bit. It needs to be reinforced, but what size steel beam should be used? He's considering an I-beam, HEA-beam, or square beam (which is best?).
The space is 5x5 meters, so a 5-meter-long beam is needed. The concrete ceiling is maybe 3-4 dm thick. Under the steel beam, 4-5 posts and a similar steel beam in the floor to distribute the load evenly.
This is the information I've received from him, can anyone help solve the problem?
Thanks in advance!
You mention roofs and floors interchangeably - is it a concrete slab (ceiling) that needs to be supported to a floor?
How much does the slab sag?
Are there large cracks from the deformation?
Is it really 400mm thick?
Do you know anything about the reinforcement in the slab?
Is the underlying floor on ground?
Is there insulation under the floor on ground?
Are you sure it's cast-in-place concrete and not prefabricated concrete elements, lightweight aggregate concrete elements, or aerated concrete elements?
Is the slab supported by four walls or just two?
How much load is the slab subjected to?
How much does the slab sag?
Are there large cracks from the deformation?
Is it really 400mm thick?
Do you know anything about the reinforcement in the slab?
Is the underlying floor on ground?
Is there insulation under the floor on ground?
Are you sure it's cast-in-place concrete and not prefabricated concrete elements, lightweight aggregate concrete elements, or aerated concrete elements?
Is the slab supported by four walls or just two?
How much load is the slab subjected to?
You mention alternating ceiling and floor - is it a concrete slab (ceiling) that needs to be supported to a floor? - Yes.
How much does the slab sag? - 6 cm.
Are there large cracks from the deformation? - What are large cracks? A crack is two mm. All others are less than 1 mm.
Is it really 400mm thick? - Well, it might be 25 - 30 cm. What was normal at the end of the 40s?
Do you know anything about the reinforcement in the slab? - No.
Is the underlying floor on the ground? - Yes. The underlying floor is basement floor.
Is there insulation under the floor on the ground? - Hardly.
Are you sure it's cast-in-place concrete and not prefabricated concrete elements, lightweight aggregate concrete elements, or lightweight concrete elements? - As sure as one can be. It looks like it was cast in place. Judging from the traces of the casting forms.
Is the slab laid on four walls or just two? - Don't know. I would think it's laid on four walls.
How much load is on the slab? - It's the concrete itself with reinforcement + the load present in a kitchen of 25 sqm.
How much does the slab sag? - 6 cm.
Are there large cracks from the deformation? - What are large cracks? A crack is two mm. All others are less than 1 mm.
Is it really 400mm thick? - Well, it might be 25 - 30 cm. What was normal at the end of the 40s?
Do you know anything about the reinforcement in the slab? - No.
Is the underlying floor on the ground? - Yes. The underlying floor is basement floor.
Is there insulation under the floor on the ground? - Hardly.
Are you sure it's cast-in-place concrete and not prefabricated concrete elements, lightweight aggregate concrete elements, or lightweight concrete elements? - As sure as one can be. It looks like it was cast in place. Judging from the traces of the casting forms.
Is the slab laid on four walls or just two? - Don't know. I would think it's laid on four walls.
How much load is on the slab? - It's the concrete itself with reinforcement + the load present in a kitchen of 25 sqm.
Since it is unusual for a concrete slab of 250-300mm to sink 60mm due to only self-weight and residential load, I'm wondering if it might be built with poor concrete quality, so-called savings concrete or wartime concrete with a lot of aggregate and little cement... Placing a beam under a free-spanning slab means you're getting top edge moments in the slab over the beam, and if the slab does not contain any top edge reinforcement (or very little), the slab will crack over the beam with further creep (slow time-dependent sinking). Ideally, you should place two beam lines under the slab to distribute the support moments and avoid cracking over the support. Since a large part of the slab's load will be on the alternating beam and pillar, I recommend placing the pillars on new foundation piers instead of distributing beams on the floor. The floor is likely only a few cm thick and almost unreinforced if it was made in the 1940s.