In the event of an extension to the house, I realize that the intermediate floor is too weak as it is today, 3x5 inches at 100 centers with an internal span of 6.2m. On one half it's probably okay because there's an internal wall about halfway, but in the living room (6.2x3.6m) it becomes a problem. An extra load-bearing beam across the living room feels less ideal, but is it possible to place it on the top side? I was thinking of first reinforcing the floor with 2x5 inches so that it becomes at 50 centers and then adding a sturdy glulam beam across the joists and attaching them with angle brackets. There are limitations on the top side because you basically have to have an internal wall where the glulam beam protrudes, but the question is whether this is a reasonable solution or if I'm missing something?
If you assume that the main beam will take the entire load, it does not matter from a static/structural point of view if it is on top of or supporting the underside. The only difference with a beam on top is that you need to hang the flooring from it.
In that case, you have two options. Either, you use BMF building brackets designed for crossing joists p.b.s. around the beam and joist. This way, the load is distributed centrically on the beam, and the risk of tilting is avoided. Or, you drill a fully-threaded rod through the beam and joist at the intersection point (with pressure distributing washers and nuts p.b.s.) and get a slight weakening in the beam and joist (almost negligible) and still a centric load on the beam.
You can also, of course, try with simple angles p.b.s. around the beam down to the crossing joist, but then you get withdrawal forces in the screw on the joist and shearing forces in the screw attached to the side of the beam. It's not the same as when using BMF brackets, which offer better distribution at the attachment points and only shearing forces on the attachment points in both the joist and the beam.
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The Builder
In that case, you have two options. Either, you use BMF building brackets designed for crossing joists p.b.s. around the beam and joist. This way, the load is distributed centrically on the beam, and the risk of tilting is avoided. Or, you drill a fully-threaded rod through the beam and joist at the intersection point (with pressure distributing washers and nuts p.b.s.) and get a slight weakening in the beam and joist (almost negligible) and still a centric load on the beam.
You can also, of course, try with simple angles p.b.s. around the beam down to the crossing joist, but then you get withdrawal forces in the screw on the joist and shearing forces in the screw attached to the side of the beam. It's not the same as when using BMF brackets, which offer better distribution at the attachment points and only shearing forces on the attachment points in both the joist and the beam.
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The Builder
Why not temporarily support the joist in the intended position for the support beam and let it extend all the way down to the underside of the joists (which you can cut off and connect with angles or beam shoes to the support beam)? This way, you might avoid having to step over the support beam on the floor above in the doorways. You could even consider making a hole in the outer wall and inserting an IPE or HEA profile through it as a support beam, allowing the joists to rest on the top side of the lower flange. This way, you probably won't have anything protruding at all.
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Builder
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Builder
Is it really so??imported_Byggaren said:
If the hole would be horizontally in the middle of the joist, I would be 100% on board with the reasoning, but a vertical hole does after all take up much of the area where the shear forces in the material are high...
I would never dare to do it unless an experienced designer says so, which you probably are...
Feel free to elaborate a bit. I have all respect for you and your expertise, you provide a lot of really good and well-founded advice here all the time.
However, I think the building fittings should work fine, and the cost should be quite negligible in this context.
Thanks for the answers, but I need to chew on them a bit before I can comment.
Some additional reasons why I'm asking as I do. In my thread about mansard roofs http://forum.byggahus.se/byggmaterial-byggteknik/81119-mansardtak-med-balkar-och-stolpar.html it is stated that I have two levels in the house and this is on the upper level where I absolutely do not want to lose ceiling height, meaning no additional flooring. I want to reinforce what exists so that it can be used (no bathroom will be there). Another reason is that the ceiling on the lower floor is nailed directly to today's flooring and replacing the flooring basically means tearing up the entire damn ceiling on the lower floor, not so fun
Some additional reasons why I'm asking as I do. In my thread about mansard roofs http://forum.byggahus.se/byggmaterial-byggteknik/81119-mansardtak-med-balkar-och-stolpar.html it is stated that I have two levels in the house and this is on the upper level where I absolutely do not want to lose ceiling height, meaning no additional flooring. I want to reinforce what exists so that it can be used (no bathroom will be there). Another reason is that the ceiling on the lower floor is nailed directly to today's flooring and replacing the flooring basically means tearing up the entire damn ceiling on the lower floor, not so fun
Mikael_L said:
If you drill a hole horizontally right in the neutral layer (the layer where tension at the bottom goes towards zero and further into compression at the top), the hole-making doesn't affect it at all, provided that the hole isn't made near the supports where shear forces and transverse forces are the greatest.
When drilling vertically, the width is reduced with the hole’s diameter, but since the formula for bending resistance is the width x height squared divided by eight, the reduction of the width doesn't affect it much. If the beam (as in this case) is 7.5 x 12.5 cm and you drill a hole with a ten diameter, you get a reduction with: 6.5 x 12.5/8 compared to 7.5 x 12.5/8, which gives 127 vs. 146 cubic centimeters on Wx. That is, 13% less flexural stiffness. But then note that the beam becomes shorter in the direction through this midpoint support to the load-bearing beam and since it doesn't exist yet, h*n can add a centimeter to the width and thus get an equally strong beam as without the drilled hole.
And no. The transverse forces aren't high in the middle of the field (or near it). However, they are at the supports. On the other hand, the moment is highest in the middle of the field on beams if they are supported on 2 sides and the tension and compression forces from that are maximal. Hanging the beams to a load-bearing beam (or supporting them underneath) also results in an existing transverse force, but it will be only half as large as the transverse force at the outer ends is today. Therefore, nothing that worsens the durability. It's sufficient with bolt M6 or max M8 to hang the beams to the load-bearing beam. The steel can withstand it. The only thing that must be considered is that there is proper pressure distribution around the bolt against the wood so that there is no punching through. This can be elegantly managed with a thick square washer of larger size.
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Byggaren
So, I've been thinking a bit. I was a little tired last night after 2 hours of beach volleyball...
Regarding BMF, which was a new word for me, I concluded after a bit of googling that it's just a product brand, Simpson Strong Tie, is that correct?
And then I feel a bit slow regarding p.b.s.??? I think I basically understand how you're thinking, but what does it stand for?
Mounting hardware seems like an easier solution, but a rod going all the way through seems more robust, in my opinion. However, I guess a designer would have the final say.
If you're going to insert an HEA beam so that the beams rest on the lower flange, the beams must be detached from the ceiling and cut out so that the flange fits between the beam and the ceiling, not an easy task, but perhaps the most elegant solution. An easier approach is to cut through half of the beam for a glued laminated beam. Then perhaps, for example, a 90x270 would only protrude 10-15 cm (which is admittedly bad enough and you would be forced to have a wall where the beam protrudes, but that is admittedly not entirely impossible, rather almost likely).
Another solution, but one that involves a bit of construction, is perhaps to place glued laminated beams between the existing beams (which would need to be built up so that they are the same height). According to Moelven Töreboda's calculation program, a 66x315 would suffice, even if they are spaced at cc100, perhaps a 90x270 would then suffice, which would only extend just over a decimeter above the existing floor structure.
Regarding BMF, which was a new word for me, I concluded after a bit of googling that it's just a product brand, Simpson Strong Tie, is that correct?
And then I feel a bit slow regarding p.b.s.??? I think I basically understand how you're thinking, but what does it stand for?
Mounting hardware seems like an easier solution, but a rod going all the way through seems more robust, in my opinion. However, I guess a designer would have the final say.
If you're going to insert an HEA beam so that the beams rest on the lower flange, the beams must be detached from the ceiling and cut out so that the flange fits between the beam and the ceiling, not an easy task, but perhaps the most elegant solution. An easier approach is to cut through half of the beam for a glued laminated beam. Then perhaps, for example, a 90x270 would only protrude 10-15 cm (which is admittedly bad enough and you would be forced to have a wall where the beam protrudes, but that is admittedly not entirely impossible, rather almost likely).
Another solution, but one that involves a bit of construction, is perhaps to place glued laminated beams between the existing beams (which would need to be built up so that they are the same height). According to Moelven Töreboda's calculation program, a 66x315 would suffice, even if they are spaced at cc100, perhaps a 90x270 would then suffice, which would only extend just over a decimeter above the existing floor structure.
No no, "på bägge sidor" of course ...mattiasp said:
Run both variants to be sure.
6 it should obviously be. Got the 8 from qxL2/8 in haste.
BMF is a manufacturer's mark for building fittings owned by the well-known Gunnebo Bruks AB.
p.b.s. = on both sides, of course.
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The Builder
BMF is a manufacturer's mark for building fittings owned by the well-known Gunnebo Bruks AB.
p.b.s. = on both sides, of course.
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The Builder
Oh no, you prop up temporarily p.b.s on the future load-bearing beam. Break down from above and cut the beams centrally + half the web thickness (and maybe a few mm extra) on each side of it. Then take a Feinmeister and cut out the beams in uk. for the flanges. It's a bit of a fiddly job, but you don't need to touch the ceiling below and will get down to the level of the floor's top with the right HEA or possibly HEB beam.Dr.SiC said:
Regarding the Feinmeister, there is now a competing and cheaper brand (Bosch?) as an alternative. Both are tools that saw with a reciprocating side-to-side movement.
Inserting glulam beams between existing beams means you must break up the entire floor on the upper floor to put them in place (assuming the floor is laid, of course).
Additional:
If you cut the beams and they function as tie beams in conjunction with the roof truss, you need to run a rod through the web of the steel profile and pull the ends together somehow. Otherwise, the outer walls will bulge outward on you.
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Byggaren
P.S.
uk. = underside
öv. = upper floor
D.S.