I'm interested in knowing how one would go about replacing part of the main beam (basement) of a 1926 house.
I've consulted a structural engineer to figure out the required size/ strength of the new beam (probably steel). He will also be specifying the size of the required column and its footing. I'm currently trying to figure out how the work can be accomplished and would appreciate some input.
The beam to be replaced is made of 3 wooden 3x12. My issue is with the fact that the floor joists are hanging from that beam (as opposed to being supported by it). Sitting on this beam is also a 4-feet section of a load-bearing wall.
I figured that I could support the floor joists with jack posts or some temporary load-bearing wall on both sides of the existing beam, but how can I support the 4-feet section of wall without being in the way of the new beam to put in place?
Whatever I put in place there must be removed in order to put in the new beam, but I can't put in the new beam without supporting that wall... What kind of approach would you suggest to take here?
What's the engineer say since he has access to all the particulars?
I'm curious about why this is needed now in an 80+ yr dwelling. Unless there's a definite need for replacement, I'd be more for simply adding adequate hangers and _perhaps_ some additional support if it does have some deflection issues in the beam itself.
As per usual, too little info from afar, particularly for structural questions...
What is the 4 foot section of wall supporting, and can you unload that section of wall? For example, if it is carrying ceiling joists, you could build temporary walls directly above the temporary walls carrying the floor joists.
Why not ask the engineer? He can see it, we cannot. I'm not even going to try to tell you because no matter how I read your post and no matter how well you read my reply, there is a potential for serious error. I'd want to see it in front of me. Ask the engineer or a good contractor.
I think some pictures or drawing are needed to get any useful advice ouf of the newsgroup. Typically you build temporary walls or use jack posts to take the load off. In the case of the wall you would need to build one or two temporary walls along it. You may also need to nail some cross pieces at the ends to keep it from falling thorugh when you remove the 3x12 under it.
I do agree with some of the other posters, is it not possiel to repair what you have? Or are you trying to get an uninterrupted span where I'm guessing there must be some posts holding up these 3x12s?
Thanks for all the replies. I didn't provide enough information, so I'll to give some more here. Please let me know if were still missing important bits!
The goal is not to repair, but to remove a column in the basement. I'd like to have an uninterrupted span of 16 feet in the basement to use as a family room.
The current situation is as follows: the beam is in 3 sections of 12 feet. It's currently supported by 3 columns: one at 8 feet, 16 feet and 24 feet from the front wall. On the ground floor, the previous owners made some modifications and removed part of the original load- bearing wall. From the front wall: there is now a 4-feet section of remaining wall, a 16 feet opening and 6.5 feet of wall. That opening is supported by a steel beam with columns on either ends (approx 4 feet and 20 feet from the front wall).
Here's some amazing ASCII art that depicts the current situation. If you look at this with a mono-spaced font (such as courier) it should come out ok:
U |||||||||||||||||||||||||| ------------------ G ||||| ||||| =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D---------------=
------- B || | | | ||
- Legend - U : Upper floor (roof left out) G : Ground floor B : Basement
- : existing beam | : existing column ||: existing wall (load-bearing or foundation wall) =3D : existing section of beam to be replaced
By replacing that section of beam, I can remove that first column and only have a single one at 16 feet which is ok in regards to what's around it.
I did look into another solution: move the 2 columns in the basement directly under the columns on the ground floor: 4 feet and 20 feet. Then place a re-enforcing steel plate to hold up the two sections of wood beam. The engineer made those plans and made the specs of the columns, footings and steel plate. The downside of this plan is that I have to take down additional walls in the basement, the footings are quite large (4x4x1) and I end up having 2 columns in the basement. So I asked the engineer to look into a single-column solution to see if this alternative plan is feasible and what are its downsides. I'll be getting these plans in the next few days.
Obviously, I'll also be asking the engineer about how to support this wall section and the floor joist. But I thought I could get some insight here also.
The goal is to know how one goes about doing this before I call contractors. I like being informed independently from the people that will be doing the job, otherwise they could be doing some nasty stuff and I wouldn't the wiser... I'm trying to stay out of trouble, not get into it!
Some additional info: House is located in very safe, non-seismic place of the world (lived here 30 years, we've had 2 below 5) No hurricanes or tornadoes have ever gone by Ground is very dense Neighbours are attached on both sides
Support the floor joists with temporary walls or jack posts with beams on top. Put a couple temporary walls on either side of the wall that is on top of the 3x12. These can be pretty simple. Lag a couple
2x6's to the ends of the wall directly on top of the floor to support it while the 3x12s are removed. It might hang from above but I wouldn't take the chance. Remove the 3x12 and replace it. Since the present beam is a 3x12 I'd also look at a 3x12 manufactured beam instead of steel. It will be easier to reattach the floor joists. And I suspect the manufactured beam can handle the 16' span. Your engineer could tell you.
The current beam is 3 pieces of 3x12. I expect that the new beam will be steel and that it will be 12 inches high to support the 16 feet span. I don't know how wide it's going to be though (7 inches maybe?)
The current floor joists are attached to the current wood beam. That is, the beam does not run *under* the joists; rather, the ends of the joists are nailed to the beam. So if I remove the beam, there's nothing directly under that 4 feet section of wall to support it. That's what I'm trying to figure out: how do I support this wall while I'm replacing the beam?
If the new beam is not as wide as the old one (say 7 inches instead of
9), I suppose I could use those 2 inches to support the wall on either side. But an inch on either side seems pretty slim!
If the new beam is not as high (say 11 inches), then I thought I could use some type of steel plate supported by jack posts on either side. Then slide in the new beam and simply leave the steel plate there after removing the posts.
Otherwise, I thought I'd need to raise the wall a little, but I'm not sure I like this very much. Anybody do anything similar? What can I expect by doing this?
Alternate suggestion -- instead of trying to replace the whole thing, why not ask what it would take in a steel plate bolted alongside the existing beam to get the span? (I'd guess 1/2" would do it, but I didn't try any calc's, that's just gut feel).
That would only require supporting the floor joists on one side, cutting them back to allow sliding in the (predrilled judiciously :) ) plate bolting it through the beam and attaching the joists. If carefully measured, you could even have the hangers welded in the proper locations and simply attach the joists instead of both directions in place...
So you're proposing to support the ground-floor wall from the ground floor itself. Interesting. This moves the weight of the wall on either side which would be supported by the temporary walls (or posts) in the basement.
There's a column in that wall that supports a 16 feet beam in the ceiling there. I suppose that means that I'd have to support that beam in a similar way, by making some temp walls on the ground floor that would support this beam (and, while were at it the 4-feet section of wall).
Could I support the 4-feet wall from its top instead of its ends? The reason is that one end is not very reachable and the other is obstructed by the column supporting the beam.
That's Plan A, or close to it at least. The steel plate has been speced-out and requires some, as you say, judiciously placed brackets for the joists. The downside is that the engineer didn't seem to think that I could get the 16 feet span using this. When we discussed this plan, we immediatly thought we needed to place the basement columns under the gound-floor columns to get proper support. You're right though, I should get him to check if we can get a 16 feet span using the steel plates solution.
I'm having hard time thinking that's not feasible/adequate unless there's a lot more going on here than a simple two-story. What's he say is the limiting criterion, deflection or loading (stress)?
But, if the engineer's convinced the plate alone isn't enough, have a lower flange welded to it -- either a wide leg angle or T. In essence a channel w/o the upper flange that you really don't have need for.
In the extreme, one could even go the "U" but that would surely seem overkill (again unles....).
We actually did not discuss the possibility of a 16 feet span with steel plates only. So I can't say what his opinion is. But based on his proposed solution, I figured he didn't think it was possible. I'll have to chat with him to know for sure.
His proposed solution *is* a steel U. 40 inches long with 9 blots on both ends. He says that a U is required due to the compression constraints on top of the beam and the tension constraints on the bottom. He seems to think that simply putting in plates is not sufficient for proper support.
Keep in mind that the engineer is going with the safest solution here. So it's probably somewhat overkill.
His proposed solution states that the columns (one a 4.5 feet and one at 19.5 feet) both require material to support 25 000 pounds. So he speced the columns as 5.25x5.5 PSL.
What other loads would you need to have a better idea? I can ask him to give me the values.
It's true though that if the second column is at 16 feet instead of
20, then the first column might not be required if the steel U is strong enough. I should've thought about that earlier!
I have a similar set up with beam and joists, I just added supports and thick plate steel under the beam the leveled it slowly. Why do you need a new beam, why cant you just add supports to what you have. When you start jacking to make it level things may break, I had a few joists I had to sister on new joists but your idea of removing what is there is full of risks you cant imagine, like everything failing completely, the money and time you will waste in proper jacks to support everything while removing the old beam is taking a little job and making it major.
Yeah, that's what I started to realize. I figured it would be simple to replace the existing beam, but I think now that this is full of traps and a much bigger job than I expected.
I don't need to replace anything, I'm trying to get rid of a column in the basement. If it's too complex/expensive, I can live with the column there. Currently, I'm still looking at the different possibilities to assess their complexity and cost. I'll take a decision once I have all the info I think I need.
Getting some external insight is very helpful for taking this decision.
Well, he ought to be making something adequate but minimal to do the job, not over-designing; that's not engineering.
...
I'm totally confused now -- where did the 20' span come from? Your objective stated up top was a 16-ft clear span for a family room. Yes, a 20-ft span is going to cause the requirements to go up quadratically to a first approximation on deflection which would be ~1.5X and linearly on stress, though.
Oh, OK, I went back to your drawing and sketched it out on paper w/ dimensions. I see what he did was to automatically place his columns under the upstairs walls to get the direct support transmitted vertically. That's kewl...but what strikes me is that he doesn't need additional beam to transmit that (locally distributed) point load; the existing beam is (apprently) doing that fine w/o crushing so it will continue to do so.
It would seem the only real function the additional structural member has to do is to handle the distributed load across the longer gap which shouldn't be that great it would seem.
It almost sounds like he's discounting the existing beam entirely owing, I suppose, to the point I didn't catch early on of it being a 12-ft run on 8-ft supports. I'm not going to second-guess the guy but I'd wonder if it really is needed to actually get that full U section under the existing beam at the outside end.
I see w/ that location of the two columns you do have roughly the 16-ft open space; I'm just surprised since the bulk of the loading is on the ends instead of distributed it requires so much heft. What's the dimension on the U he's given, including thicknesses?
To do any calculation would require knowing all the loads assumed, live/dead/additional code-required for the jurisdiction, etc. They ought to be on the design documents if you have access to those but if all you've contracted for is a design, that may not be part of the deal.
As others noted, it would be possible to rig up ways to get it there but it does just seem pretty stout for the application from afar and w/o actually doing any real numerics, of course... :)
Yes, moving the columns under the ones from the ground floor was automatically considered. Turns out that the required footing is much larger than I had expected, so I have to tear down a whole lot more basement for this solution. This is why I'm looking for alternatives.
The additional member here is the steel piece?
So, the proposed steel piece is a U: its legs are 10 inches high, the base is 9 inches wide and would run along 40 inches of the beam. It's
1/4 inch thick.
Since the beam is made of 3 sections of 12 feet, this piece is there only to support the connection of 2 of those sections. The steel piece would cover 20 inches on both sides of the split.
In my mind, the proposed columns (at 4.5 feet and 20 feet) are doing all the work really since they're directly below the ones on the ground floor.
I asked him to look into another solution that has only one column at
16 feet (instead of 2: one at 4 and 20). The reason is that this 16 feet span would better suit what's around it: more specifically, the staircase. As mentioned above, a single column would have less impact due to the size of the required footing.
Yes, the codes are on the drawing, but not the assumed loads. I can get him to add these numbers I suppose.
I understand all the complexities involved here, so I'm not looking for formal advice: that's why the engineer is working for me.
In your mind, a 16 feet span with steel support around the split at 12 feet, a proper column at 16 feet, w/ proper footing *could* handle this? Again, not looking for formal advice, here, I just want to steer my engineer in the proper direction. They don't come cheap!
Yeah. Seems like a much larger job than I really expected...
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