Cantilevered Beam on Wall 1

[Zoobie777]

Hey,

I come across the situation often enough and I want to know if I'm designing things right or if I am cheating. I use iStruct but I imagine other software is similar. When I put a beam in line with a wall with a cantilever I can only get the beam to pass if there are two bearings. I get the beam to work by creating a gap between the walls at the corner where the cantilever starts. This is usually an inch or two. For example if I had a cantilever of 2 ft extending out from the wall, the beam analysis would show 2ft unsupported, 5.5" bearing, 2" gap, 6' of bearing. Is this OK? I can't think of anything else. In reality the beam would be sitting on the very top plate and there would likely be a stud pack at the corner.

If the gap is too small, I get a shear failure on the wall bearing. If I increase the gap by an inch or two, the shear goes away. How (in real life) would I have to install the beam? Is there something else I should be doing to analyze this correctly?

In the example below, the second output that fails shows the same size bearing length on the diagram but B2 but its actually 2" longer (2" closer to B1).

Thanks,

 

[Greenalleycat]

Re

Taking into consideration that I am a thick-headed chemical engineer and that the software at my disposal does not allow for straps, springs, pinned vs roller bearings, nails, screws, duct tape or anything else of the sort, would this be the best representation of what would happen if I strapped the beam at each stud assuming 24" oc (which is the norm for exterior walls where I am from).

View attachment 10749

Refer back to Celts model, he covered this

Not wanting to be rude, but being blunt, if you are a chemical engineer then why are you designing this beam?

 

[Zoobie777]

Re

Refer back to Celts model, he covered this

Not wanting to be rude, but being blunt, if you are a chemical engineer then why are you designing this beam?

That was my past life. I now am designing roof trusses, EWP roof and floor systems (including beams). Key word being designer. As an engineer I know the difference between the two and I stick to my lane. A lot of the questions I post are for my curiosity and learning.

 

[Eng16080]

I'm a little late to this party. This is certainly an interesting problem and one I've pondered before. My approach would be to:

1. model the beam with two supports, one at "B1" and the other at "B7" (per the diagram above)
2. load the beam fully (we'll call this load case A) as well as with only the cantilever loaded (load case B)
3. be sure the beam is braced laterally for both positive and negative bending
4. design an uplift connection as necessary at support "B7".
5. provide a detail showing that the beam is continuous over the wall (and not broken at some intermediate point over the wall) and showing only the uplift connection at the end. I would tend to think that additional holddowns along the length would not be a problem as long as the beam is continuous, although the comments by Greenalleycat above seem to be at odds with this (I'll admit I did not yet read the report referenced).

That was my past life. I now am designing roof trusses, EWP roof and floor systems (including beams). Key word being designer.

Hopefully there's some engineering oversight at your job and you're not just relying on us at eng-tips for guidance. That said, I appreciate your desire to understand this stuff. There are way too many designers and even engineers just plugging shit into the computer and not giving it a second thought.

EDIT: Also, I should mention that the model per the diagram above is unlikely to give realistic results because the stiffness of the supports isn't being accounted for (as noted by others). You would likely get large resultant forces at B1 and B2. If this were to happen in reality, I think the connections at those locations would start to fail/deform and the load would then be redistributed to the other supports moving down the line to the right. This assumes adequate ductility at the connections (which is probably realistic for wood framing).