It feels like there's a hidden agenda.Bob_the_builder said:Possible, but at least the industry's designers agree...
With your reasoning, the conclusion is that everything is just fine if the beam is cut in the middle, right at the support point. We can agree, however, that pressure/lifting forces arise in different places depending on whether there is a support point in the middle.
Another thing: Does anyone have any opinions on not using K-wood in joists and instead relying on carefully selected wood (no large knots) of normal quality (whatever that is called)? It concerns spans of around 3.5-4 meters.
Comment on the post above:
1.
Wood is a "crap material" from an engineer's perspective because it has such poor shear capacity.
Here's how it is:
For a single-span, simply supported beam, half of the load (0.5ql) goes to the left and the other half to the right.
With a continuous beam, with two equally long spans, you could say the middle support "absorbs" some of the load which has the beneficial effect of reducing bending moments and deformations. But since the middle support has absorbed 0.625ql of the load, the shear force has increased at the middle support compared to the single-span beam.
The conclusion is that you can have longer single-span beams because you utilize the material better concerning shear, but you get a shaky floor which is likely experienced as unpleasant.
2.
Personally, I wouldn't be afraid of lumber with a lower K-class because what you are doing then is redoing the visual inspection that some poor soul has been doing at a conveyor belt in a sawmill.
3.
Cross bracing vs blocking. At one point, I strolled by a full-scale test that southern forest owners paid for regarding their 5-story buildings where they tested just this. I don't work with wood myself but still manage to remember that the result from both full-scale tests and FE analyses, somewhat surprisingly, was that blocking provides better "performance."
/OK
1.
Wood is a "crap material" from an engineer's perspective because it has such poor shear capacity.
Here's how it is:
For a single-span, simply supported beam, half of the load (0.5ql) goes to the left and the other half to the right.
With a continuous beam, with two equally long spans, you could say the middle support "absorbs" some of the load which has the beneficial effect of reducing bending moments and deformations. But since the middle support has absorbed 0.625ql of the load, the shear force has increased at the middle support compared to the single-span beam.
The conclusion is that you can have longer single-span beams because you utilize the material better concerning shear, but you get a shaky floor which is likely experienced as unpleasant.
2.
Personally, I wouldn't be afraid of lumber with a lower K-class because what you are doing then is redoing the visual inspection that some poor soul has been doing at a conveyor belt in a sawmill.
3.
Cross bracing vs blocking. At one point, I strolled by a full-scale test that southern forest owners paid for regarding their 5-story buildings where they tested just this. I don't work with wood myself but still manage to remember that the result from both full-scale tests and FE analyses, somewhat surprisingly, was that blocking provides better "performance."
/OK
No, that doesn't sound good... Having two freely supported beams with their ends against each other, I don't think the subfloor would hold up. You would likely crack the chipboard as they would be able to move independently of each other.MathiasS said:
Yes, that doesn't sound like a good idea either. The thing is, the wood that meets the K24 standard is also sold as K24 (unless you buy wood from some local sawmill that doesn't sort K lumber themselves).
The last time I bought a K-balk, it cracked, so the stamp is no guarantee. Luckily, it isn't placed in a critical spot. I believe you can find equally good timber at a normal price if you have enough experience, luck, and patience. But that's what you pay for when you buy graded timber.
Maybe, maybe not. But getting an insurance company to cover damages that might be caused by incorrect material choice is probably just a pipe dream.
I discussed this with K-virke with "my" sawmill, Lissma Såg. We agreed that for the spans we talked about (2-4 meters), it is just as good to sort out timber from the "regular" lumber pile. Exclude anything with cracks and large knots (=> something resembling K12).
The price difference between Kvirke and normal quality class was just under 15 SEK per meter, both types were on the shelf.
I will place selected regular timber in the flooring structure and complement with cross braces.
Bob: I agree with your reasoning that the subfloor hardly likes split beams. But from a strength perspective, it solves the issues.....
The price difference between Kvirke and normal quality class was just under 15 SEK per meter, both types were on the shelf.
I will place selected regular timber in the flooring structure and complement with cross braces.
Bob: I agree with your reasoning that the subfloor hardly likes split beams. But from a strength perspective, it solves the issues.....
Hello, I have a couple of questions that relate to roughly the same issue.
I have floor joists that are 190x70 cc60 and there's a bit of sway in the floor, which is about 4.5 meters wide. There are no cross braces, but there is a cross beam running through the entire room, attached to about every other floor joist with a small angle bracket. It is not a load-bearing beam as I understand it, but rather instead of cross braces. It is about 7 meters long and joined in the middle. (Shoddy construction?)... Now I wonder, since I only have about 2 meters of ceiling height - 15 cm under the joist, in the basement, if I can remove this and instead put in cross braces, or is it simply under-dimensioned so I have to put a couple of load-bearing posts in the middle of the room???
In conclusion, ideally, I want to remove this cross beam, which doesn't seem to serve much of a function, and preferably reduce the sway in the floor. It's not very wobbly, but still...
Has anyone seen such a construction before? The house was built at the end of the 70s, one and a half stories with a basement...
Regards,
Asfaltoz
I have floor joists that are 190x70 cc60 and there's a bit of sway in the floor, which is about 4.5 meters wide. There are no cross braces, but there is a cross beam running through the entire room, attached to about every other floor joist with a small angle bracket. It is not a load-bearing beam as I understand it, but rather instead of cross braces. It is about 7 meters long and joined in the middle. (Shoddy construction?)... Now I wonder, since I only have about 2 meters of ceiling height - 15 cm under the joist, in the basement, if I can remove this and instead put in cross braces, or is it simply under-dimensioned so I have to put a couple of load-bearing posts in the middle of the room???
In conclusion, ideally, I want to remove this cross beam, which doesn't seem to serve much of a function, and preferably reduce the sway in the floor. It's not very wobbly, but still...
Has anyone seen such a construction before? The house was built at the end of the 70s, one and a half stories with a basement...
Regards,
Asfaltoz
One option is to nail a parallel plank onto each existing beam, say a 45x195. Use a jack to lift the existing beam slightly upward (not much, a few mm) and then nail. Also, add cross braces. This should significantly increase stability without building downward. This requires quite a bit of work, as you have to remove the ceiling, insulation, etc., so it might be more advanced.
You can also use a so-called Kerto beam instead of regular solid K wood in the example above, which provides even better stability but is, of course, more expensive.
Another option is to replace the transverse plank with a steel beam in H or I profile; it can probably be made somewhat slimmer than your existing wooden beam. It builds downward but provides a decent reinforcement, even though a span of 7 m is quite much. The best would be to place a post somewhere in the middle under this beam, but that's not ideal.
Before starting such extensive exercises, I would discuss with a structural engineer, as there may be details that need to be considered which affect the choice of solution. It might become tricky discussions with insurance companies if something goes wrong and you don't have a proper calculation/design drawing to rely on.
You can also use a so-called Kerto beam instead of regular solid K wood in the example above, which provides even better stability but is, of course, more expensive.
Another option is to replace the transverse plank with a steel beam in H or I profile; it can probably be made somewhat slimmer than your existing wooden beam. It builds downward but provides a decent reinforcement, even though a span of 7 m is quite much. The best would be to place a post somewhere in the middle under this beam, but that's not ideal.
Before starting such extensive exercises, I would discuss with a structural engineer, as there may be details that need to be considered which affect the choice of solution. It might become tricky discussions with insurance companies if something goes wrong and you don't have a proper calculation/design drawing to rely on.
The thread is somewhat old, but still relevant to me, so I hope I can still get some sensible advice.
I live in a house with a crawl space foundation from the late 1800s. I began a major renovation in about 1/3 of the house during the summer of 2009. So far, I've replaced the floor beams and windows on the ground floor, and now the ceiling, including the intermediate beams, will be visible before the walls are finished.
The existing intermediate beam made of timber has dimensions ~200x170 with a spacing of ~1100 and a span of 7m.
It's a two-bay construction, where the partition wall that the beam rests on is placed ~2.40m from the outer wall. Both the ceiling on the ground floor and the floor on the upper floor consist of tongue-and-groove planks of varying widths ~22mm (I hardly need to mention that it sways on the upper floor?)
The idea was also to raise the ceiling height on both floors for the renovated section (since I have full standing height in the attic). I planned to keep the existing beam visible from the ground floor (it turned out to be damaged due to previous water damage). A new ceiling on the ground floor (13x120 smooth panel) would be attached to the beams from above.
To support the upper floor and provide sound insulation, my thought was the following:
In the outer walls (longitudinally), a stud of the same dimension as the new beam would be anchored (with French wood screws or possibly bolted through the wall timbers) to create a flat surface to connect the new beam to. The new beam would then be anchored to this stud with joist hangers (anchor nails or anchor screws).
I initially considered 45x170 with CC-600, but after following the thread, I am now unsure if anything other than 45x220 should be considered?? It feels like a substantial, perhaps unnecessarily over-dimensioned improvement compared to the existing construction, or?
Thankful for tips and advice regarding dimensioning and spacing!
I live in a house with a crawl space foundation from the late 1800s. I began a major renovation in about 1/3 of the house during the summer of 2009. So far, I've replaced the floor beams and windows on the ground floor, and now the ceiling, including the intermediate beams, will be visible before the walls are finished.
The existing intermediate beam made of timber has dimensions ~200x170 with a spacing of ~1100 and a span of 7m.
It's a two-bay construction, where the partition wall that the beam rests on is placed ~2.40m from the outer wall. Both the ceiling on the ground floor and the floor on the upper floor consist of tongue-and-groove planks of varying widths ~22mm (I hardly need to mention that it sways on the upper floor?)
The idea was also to raise the ceiling height on both floors for the renovated section (since I have full standing height in the attic). I planned to keep the existing beam visible from the ground floor (it turned out to be damaged due to previous water damage). A new ceiling on the ground floor (13x120 smooth panel) would be attached to the beams from above.
To support the upper floor and provide sound insulation, my thought was the following:
In the outer walls (longitudinally), a stud of the same dimension as the new beam would be anchored (with French wood screws or possibly bolted through the wall timbers) to create a flat surface to connect the new beam to. The new beam would then be anchored to this stud with joist hangers (anchor nails or anchor screws).
I initially considered 45x170 with CC-600, but after following the thread, I am now unsure if anything other than 45x220 should be considered?? It feels like a substantial, perhaps unnecessarily over-dimensioned improvement compared to the existing construction, or?
Thankful for tips and advice regarding dimensioning and spacing!