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Old 07-10-2012, 03:16 PM   #1
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Beam lateral support - Joists on top


There is a 25ft, built-up (3-2x12) continuous beam that is twisting due to a lack of lateral support (Also partly due to an leaning support column near the midpoint that has since been replaced). This beam is supporting the 2nd floor a 2 story storage building on slab.


I'm planning on replacing it (either with another 25ft continuous or 12ft & 13ft beams) but can't find much information on how to laterally brace the beam when the joists are resting on top. Any information would be helpful.


Last edited by shadetree; 07-10-2012 at 03:18 PM.
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Old 07-10-2012, 03:32 PM   #2
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Pictures are priceless on topics such as this...

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Old 07-10-2012, 03:50 PM   #3
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The loading of the beam is supported by the 12 inch dimension. Composite beams such as yours gain lateral strength by increasing the thickness, or by stacking more of them together as yours is.

A beam such as that is typically only designed to support direct vertical loads, and something external to the beam or a problem with the beam caused the lateral deflection.

In short, it shouldn't have happened in the first place. If you fixed whatever was loading it laterally, the new one shouldn't do it based on the information you have provided.

I have never seen wood beams such as that laterally braced.
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Old 07-10-2012, 03:51 PM   #4
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Old post:

New post, it doesn't look it in the photo, but it's straight

Last edited by shadetree; 07-10-2012 at 03:55 PM.
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Old 07-10-2012, 05:53 PM   #5
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It is a little hard to tell from the pictures exactly what happened, however it appears that the beam twisted due to moisture content change. I am unclear why you feel it is necessary to replace it. Are you assuming that because it is twisted it is structurally compromised? That is not necessarily the case, the beam derives the majority of its load capacity from its depth, which has not changed much just because it twisted a little. If this is an aesthetics issue, that is a different matter.

Lateral bracing of beams is rarely done in residential construction. Joists are commonly X braced to improve rigidity of the floor above, however X bracing does not improve the strength of the joist itself. In heavy industrial and commercial design lateral bracing of long beams is often necessary to prevent lateral buckling, however in residential design lateral buckling is almost always prevented by the floor above the joists, and the joists which are generally attached above the beam.
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Old 07-11-2012, 10:02 AM   #6
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Originally Posted by Daniel Holzman View Post
It is a little hard to tell from the pictures exactly what happened, however it appears that the beam twisted due to moisture content change. I am unclear why you feel it is necessary to replace it. Are you assuming that because it is twisted it is structurally compromised? That is not necessarily the case, the beam derives the majority of its load capacity from its depth, which has not changed much just because it twisted a little. If this is an aesthetics issue, that is a different matter.
I 100% agree...
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Old 07-12-2012, 03:30 PM   #7
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It is a little hard to tell from the pictures exactly what happened, however it appears that the beam twisted due to moisture content change. I am unclear why you feel it is necessary to replace it. Are you assuming that because it is twisted it is structurally compromised? That is not necessarily the case, the beam derives the majority of its load capacity from its depth, which has not changed much just because it twisted a little. If this is an aesthetics issue, that is a different matter
That was my primary concern, that because it had twisted it would continue to warp as more weight was loaded onto it, eventually catastrophically failing.
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Old 07-12-2012, 03:38 PM   #8
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Here are some more photos of why I'm leaning towards replacement: Where there are joints in the beam, there tend to be cracks near the joints on the underside.




closeup of the most twisted section, the string is vertical
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Old 07-12-2012, 03:44 PM   #9
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The beam looks to be supported on it's ends by studs from completely "rolling". It doesn't look structurally catastrophic from where I'm sitting unless you can see variations in the floor deck. Is there a "bowl" on the floor deck above near the mid point of the beam spans? Is there sag in the beam? Run that string along the length of the beam to see it's vertical movement...
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Old 07-12-2012, 03:59 PM   #10
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Wow. That is not a continuous beam. It might go 25' but I can see in a few spots they aren't solid pieces of lumber. I would say that thing is undersized. It is hard for me to see the attachments, but it looks like it starts in a wall on one side and then ends in a room just sitting on a column? How old is this home? Typical would be sitting on post in walls, with studs running up each side of it, which does give it some lateral bracing on the bottom. And I have never lateral braced the bottom of a beam in residential, but many times in commercial applications. In closing... That beam is undersized and not continuous. My guess without being there, a 5 1/8'' x 16'' glulam would be typical, but of course you will be getting an engineer to calc the loads.
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Old 07-13-2012, 02:18 PM   #11
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Originally Posted by AGWhitehouse View Post
The beam looks to be supported on it's ends by studs from completely "rolling". It doesn't look structurally catastrophic from where I'm sitting unless you can see variations in the floor deck. Is there a "bowl" on the floor deck above near the mid point of the beam spans? Is there sag in the beam? Run that string along the length of the beam to see it's vertical movement...
Nope, no significant warping in the floor above, however the floor isn't loaded with anything more than a sub-floor, so there isn't a whole lot of weight on it.
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Old 07-13-2012, 02:33 PM   #12
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Wow. That is not a continuous beam. It might go 25' but I can see in a few spots they aren't solid pieces of lumber. I would say that thing is undersized. It is hard for me to see the attachments, but it looks like it starts in a wall on one side and then ends in a room just sitting on a column? How old is this home? Typical would be sitting on post in walls, with studs running up each side of it, which does give it some lateral bracing on the bottom. And I have never lateral braced the bottom of a beam in residential, but many times in commercial applications. In closing... That beam is undersized and not continuous. My guess without being there, a 5 1/8'' x 16'' glulam would be typical, but of course you will be getting an engineer to calc the loads.
What should this beam be called? I'm kinda new to this so I'm not real familiar with the terminology, but I thought it called was a built-up continuous beam because it runs over the central column without two simple beams abutting?

It's sitting on 3 2x6 posts on either end, both in the walls, the building is about 30 years old
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Old 07-13-2012, 03:23 PM   #13
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Unless you plan on storing a whole bunch of stuff up there, I wouldn't be overly worried. There's no sag which means the beam is not undersized, it's just a little warped like Holzman stated earlier. Save your $...
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Old 07-13-2012, 04:10 PM   #14
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A continuous beam is a solid member that goes from bearing point all the way to another bearing point. In your case, if you had 3 individual 2x12's that were 25' long, nailed together then that would be continuous. However, I can see at least 3 places where it appears they are not continuous. Meaning they nailed 16' lengths and staggered their joints. That is not considered continuous. If on the plans for your home stated " continuous (3)2x12's with 3 nails every 16inches " then if the inspector did indeed notice it wasn't continuous then it would have failed. A structural beam has to bear on something if it isn't continuous. Is that red brick/ column midspan on that beam? Also, with it not being continuous is why it is leaning in such a manor. The top is tied together with a double 2x4 or 6 which locks the spliced pieces together, if they had done the same on the bottom, it probably wouldn't be so bad. You say that column is new? So a welder came out, cut a post that crooked, welded a cap on it, and then rebolted the thing? Did you ask him what he thought?
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Old 07-13-2012, 04:54 PM   #15
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Copperclad, your understanding of the term continuous is incorrect. A continuous beam simply means a beam which carries moment across a support. If the beam is made of individual elements, which is pretty common, all it requires to be continuous is that the elements are fastened together in such a way as to carry full moment across each joint, and carry full horizontal shear.

Take a look at highway girders sometime. Long girders are rarely made up of individual pieces that span the full length, it would be impossible to transport them. Individual pieces are either bolted, riveted (pre 1930's primarily), or welded. You can see the splice points clearly on almost any bridge. Then look at the supports, if the beams are continuous it means that the beams cross the supports as moment bearing elements. Simple span beams have a gap between spans across each joint. So the concept of continuity is defined by the geometry of the beam at each support, not by the length of individual members.

In the case of residential wood frame construction, the concept is identical, except that wooden members are typically nailed together. Whether they are continuous or not is a matter of how they are connected to the posts, not how many pieces they are made of.

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