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The following outline is inspired by something I noticed today and couldn't figure out.

It shows what I guess is a fairly common generic situation - an upper floor masonry partition wall supported by a beam, with further loads (ceiling/next floor joists?) supported in turn by it.

enter image description here

I've tried to make it generic. So the supported wall (grey) is toothed into the adjacent wall (brown, left) as is common for partition walls, and the beam (red) is supported by that wall and another internal partition wall (brown, right). Ignoring s/w and eccentricity, it's a pretty simple beam situation, where the beam supports just a wall and whatever is on the wall. I haven't given values or dimensions as I'm interested in how it's assessed, rather than some specific solution.

What has me puzzled is, it's not clear what governs the parts of these loads supported by the beam. There is load spreading, full-height support by the left hand wall, and the corbel angle to consider.

The toothed support and corbel angle suggest only a small part of the load will be supported by the beam. None of the arbitrary top loads, and maybe only a third of the wall masonry, are within the corbel angle. Can that be right? Does one reckon to include all of the topmost loads? or part of them? or none of them (and just the masonry within the corbel angle)? What is the right way to think about it?

How can we tell which loads to include as beam loading, when loads spread throughout a wall before that wall is supported on the beam?

My thinking so far

In theory, I've got the following points:

  1. The loads at the top of the wall will load-spread at (say) 45 degrees within the wall. They are likely to present as a UDL due to spreading, even if they began as point loads.
  2. Much of the load will be taken by the left hand wall, as "our" wall is toothed into it throughout its height. (It's not like it is supported by the beam alone.) So some of the load is taken by the adjacent wall => not the beam.
  3. Looking at the beam alone, the corbel angle of 60 degrees (yellow triangle) suggests the beam load includes none of the loads at the top of the wall, and only about a third of the wall's weight, because those are all ultimately outside the corbel angle and will be supported by the two masonry walls directly. Can that be right?
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1 Answer 1

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A "corbel" is a short cantilever beam that is cast integrally with the support. The connection, through continuity, must be capable of preventing the translation and rotation displacements that cause separation of the beam and its support. In this sense, the support will take 100% of the weight of the wall and the loads on it. Lacking this continuity, the corbel will fail.

enter image description here

On the sketch above, the red lines indicate the potential failure planes (plane of separations). Once the failure is imminent, the exact force distribution is a complicated matter; for safety reasons, it is usually assumed the support no longer effective in carrying any load, so all the loads will be transferred to the additional support system below throgh gravity.

enter image description here

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  • $\begingroup$ In other words, de-compacting the 2d sentence, the ability of the structure beyond the corbel area to carry the load depends on its ability to resist the rotation and translation forces involved. So in this example it comes down to "can the left vertical wall and its toothed connection hold the supported wall (grey) in position, or does it fail by collapsing to the right, or by allowing the grey wall to move to the right or down (as drawn)?" $\endgroup$
    – Stilez
    Apr 10, 2022 at 5:47
  • $\begingroup$ ... and if not, then for prudence we assess if the red beam can support each load,as spread over its load spread area, as you have very clearly drawn. Is that about right? $\endgroup$
    – Stilez
    Apr 10, 2022 at 5:47
  • $\begingroup$ Yes, correct. In your case, the left wall is just too skinny to support the gray wall, so the wall has to be supported by the red beam. $\endgroup$
    – r13
    Apr 10, 2022 at 14:06
  • $\begingroup$ Thanks! Mechanically that makes total sense, but I wasn't seeing it, until you pointed it out. Your drawings were incredibly helpful! $\endgroup$
    – Stilez
    Apr 10, 2022 at 22:50
  • $\begingroup$ You are welcome. $\endgroup$
    – r13
    Apr 10, 2022 at 23:41

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