It would be a handy option to ignore short cantilevers in beam design calcs. For example, I am checking a simple true valley beam with a 12" cantilever at the top end. ClearCalcs is showing that the beam fails because the tip is deflecting too much (0.17" L/82.7) while the main span is okay (0.88" L/237). To me, the beam is adequate, but I can’t make it pass without fudging the length or eliminating the cantilever altogether. But then that hurts the main span deflection a little bit. This is a common problem with short cantilevers.
As a suggestion and a side note, when I do check cantilevers, I often evaluate the deflection based on the linearized rotation of the member rather than the gross deflection. This is purely my own methodology, but it has served me well and allows many conditions with similar geometry to pass where it would otherwise fail, like this post is regarding. Think of it this way, we are often using deflection checks to indirectly verify that curvature of the member is not excessive to protect the finishes from cracking or otherwise failing in some way. Linearizing deflection of the cantilever creates a more realistic check than simply 2L/XXX and the cantilevers are then being checked with the same curvature as the main span.
Another option instead of “ignore” is to allow different deflection criteria for spans… e.g. for this situation: for the cantilever portion, maybe you allow 2L/120, but the main span L/240.
It would also be helpful if you have a longer span cantilever with a plaster soffit vs a main span that only only supports roof loads.
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Best I can tell, ClearCalcs does not allow a different denominator for cantilevers, and the double L/ option has already been selected for this particular calculation. Note, however, that the output only shows “L/” despite the double option being selected.
Side note: this same issue comes up with raised tie rafter checks with ClearCalcs. The program calculates the lower end of the rafter as a cantilever that can fail even with very little deflection of the rafter overall. I’ve raised this issue a couple of times in the past, but I am not sure if that has been addressed yet. My work-around was to stop using that particular calculation.
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Here’s another example - try a simple 2x8 floor with SPF #2 spanning 12ft with a 2ft cantilever. Typical first floor residential loading.
The deflection fails at 131% and there is nothing I can do to make it work unless I a) add a point load to the tip to counteract the movement, or b) fudge the deflection where it applies to the main span. Cantilever deflection is already fluffed to 2L/360 but it’s not even close.
This is a common design condition that could be better addressed. Note also that the deflection result is presented here:
The displayed deflection (L/138 or L/120) isn’t even presented correctly because it should be checking it v. 2L/XXX when the cantilever is controlling, as it is here.
I’m losing my mind on this one… I tried adding a point load on the tip of this current cantilever (dead load) but the deflection graph is not changing at all. To test the extreme, I added a 10000lb point load at the tip but still no change in the graph! It does not matter which load combination I am selecting either, the deflection graph is only showing the live load effect.
Am I crazy or is there something wrong here? Why does the deflection chart ignore dead load?
The other part of this is: natural lumber often has a curvature to it, placing wood with the “crown up” will basically negate the deflection at the end of a short cantilever.
It looks to me that the graphed combos aren’t actually graphing correctly, as it says “short-term envelope shown”… checking my own copy, it looks like custom combos (which I use everywhere) aren’t working properly with any graphs, as if I select “0.42W_dn” servicability check from the drop-down, what it’s showing is “S” my snow load case.
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