Sagging joists

[DrGonzo]

I would be extremely grateful for experienced advice on how we can reinforce a floor/ceiling that is sagging. We are total novices in this area, so I apologize if something in the description below sounds off.

We have a sagging joist between the 1st and 2nd floors. The construction is somewhat unusual as the joist rests on two outer walls and then a sturdy steel post in the middle of the room, with a steel beam extending to the wall. Around the post, there is thus an open space. From the post to the walls, it is about 3.5 m in three directions, in the fourth direction, it is open to the ridge.
After having a substantial bookshelf above, the construction between the post and one of the outer walls has now started to sag. The joists are perhaps 70 cm apart and the dimension might be 2 by 6 inches?? (this is said by a complete amateur, it might be totally incorrect measurement). But there's no point in calculating the strength - reality shows, so to speak, that it is overloaded.

The question is: is it possible to break up the ceiling/floor and install a reinforcing steel beam or laminated beam parallel to the old joists? Down in the existing joist structure, that is?
Since the ceiling is low, we don't want to install a transverse beam under the joist structure, which would lower the ceiling height - but we would like to have a floor that can support the bookshelf.

 

[Tyresö]

No, in that case, the supporting crossbeam must lie under all beams in the vault for there to be any load-bearing capacity.

 

[DrGonzo]

Absolutely, I'm with you so far. But I don't want to lay anything across the old beams, rather place a new stronger beam in the same direction as the others.

 

[Krawk]

You can't draw a picture? I think I understand how it looks but it's a bit unclear where the walls and beams are located.

 

[Jan-Å]

Are you planning to lay new joists parallel to your current 2"6? As long as you can get the new beams to support the outer walls, it should work.
In that case, I would get help from a structural engineer to calculate where to reinforce and with what.

 

[DrGonzo]

Yep, hope this makes it a bit clearer. The dashed lines represent the floor joists that are deflecting, the number is probably not accurate, it's just an illustration of the construction. Not all the beams are deflecting, the problem is concentrated around the area near the heavy bookshelf. The question is whether I can install something like an HEA beam along with the other beams to achieve a floor that holds better.

http://sphotos.ak.fbcdn.net/hphotos...0100078090579_628495578_7399154_3247816_n.jpg

 

[Jan-Å]

Yes, of course, it can be done; there's nothing wrong with the construction itself, but the problem lies in the weak dimensions of the floor joists. However, I'm not skilled enough in this area to say that an HEA beam is the best solution, so I'll leave that question to someone who really knows. I would probably do the same throughout the entire floor/ceiling, not just fix the part that will carry the bookshelf.

 

[pbengtsson]

Assuming you don't want to crawl up in height because there will be a difference either at the top or bottom.
An alternative is to install glulam or kertu beams at 300 centers, it's weak with 2"6 as you have today, measure again, it should be thicker beams.
Try some beams at
http://www.iat.inadire.se/WebLagerbalk/Lagerbalk.aspx

I have kertu 45x300 with a span of 4.5m and there's no bounce at all.
But now you have a steel beam underneath, and there will always be some bounce no matter what you do with the beams, if it were a wall you could almost completely eliminate the bounce with reasonable dimensions.

 

[Krawk]

So it's just the wooden beams that are sagging? The steel isn't moving?
Does it sag the most in the middle, or is the entire floor sloping?

It's likely that the issue is the 2"x6" being too weak for your spans. The steel shouldn't noticeably sag if it's a reasonable size.
The neat solution is to open up the floor and simply add more beams like the existing ones. Ideally, glue and screw a board on top as well. You may need to replace existing beams if they have a permanent deflection.

 

[DrGonzo]

An alternative is to install glued laminated timber or kertu beams at cc 300, it's weak with 2"6 as you have today, measure again, it should be thicker beams.

It is 2 by 6 inches, according to the original drawings of the house. It aligns with the overall picture that the dimensions are simply too weak.

Thank you very much for the advice! I interpret it as a matter of finding the right type of beam, and that's it.
Can one generally say how the beams are usually attached to the wall/load-bearing steel beam? In short: how much floor/wall do I need to tear down to be able to install one or more new beams? Is it difficult to attach them, or is it more or less just demolishing to gain access and then laying on new ones?

 

[pbengtsson]

Unfortunately, you'll probably need to tear up all the flooring, it's important that the beam provides good support both on the outer wall and on the steel beam. Since the bookshelf weighs so much, the flex is indeed reinforced, is there no other solution, e.g., to screw it onto the wall so that not all the weight is on the floor?

 

[DrGonzo]

So it's only the wooden beams that are flexing? The steel isn't moving? Does it dip the most in the middle or does the whole floor slant?

Most likely, the problem is that 2"6" is too weak for your spans. The steel shouldn't flex significantly if it's a reasonable dimension. The neat solution is to open up the floor and simply add more beams like the existing ones. Ideally, glue-screw a board on top as well. You might need to replace the existing beams if they have a permanent deflection.

The neat solution is tempting. Replace those that have bent and then load in double joists on the part of the floor that flexes, that sounds good. Do you think more 2x6 will be enough to significantly increase the strength?
It's a bit difficult to determine where the flex is worst, it's stable near the steel beam, then the floor quickly dips down. But a good bit in from the exterior walls, it's steady, so it's a quite limited area, maybe three beams affected by the flex.

 

[injonil]

It should be 2"9 for that span (3.5m). 2"6 is considerably weaker, so I don't think it will work well even if you use glued laminated timber. Check tables at www.traguiden.se.

 

[Krawk]

If the existing beams today are C24 (or older equivalent), it should work to complement with an additional 45x145 at each. If you can reach the bearing in the outer wall, you can extend these all the way out. Otherwise, make them as long as possible and glue and screw tightly along the entire beam so that they hopefully work together properly. As you understand, there is an uncertainty here about how strong it will be. It's also important that you glue and screw the floor chipboard.

However, almost as much work with all this that you might as well build it with new slightly higher beams.