Cantilever beam with dead load at the tip

I don’t know how ClearCalcs tracks these posts, but can one of the developers review my “Option to ignore short cantilevers” thread in the Feature Request section and advise on two possible bugs?

One, the output deflection check is not correctly reflecting when a “2L/XXX” check is made. It only shows “L/XXX” even when the 2L option is selected.

Two, the governing short-term live load deflection results are not changing at all when a dead load is placed at the tip of a cantilevered joist. I get that ClearCalcs is trying to generate the deflection result as if it is checking the middle of a clear span, or similar, but that approach cannot be applied to a cantilever with a dead tip load on it. The deflection result is a nonsense result.

Thanks for sharing @WilsonEngineers !

If I understand your first point correctly, you mean the L/XXX indicator should show 2L/XXX when the governing deflection is on a cantilever?

For the governing short-term live load deflection, as you mentioned we don’t include dead load at all in that combination - given that it’s not a short-term load. We do consider it in the long-term deflection (the creep component). I’d be curious how you’d expect this point dead load at cantilever tip to be handled?

Correct, if you are showing a result based on 2L, then the deflection ratio should show 2L.

The most common cantilever condition for floor joists is a house that has the 2nd floor cantilever beyond the first. These would always/typically have a wall with additional load on it from above. I can’t think of any scenario where this check should ignore that effect from above, other than the very rare cantilevered balcony.

Furthermore, floor joist deflection ratios in houses are based on historical applications minimizing bounce/shake of a floor. If you are checking the live load deflection of a cantilever, then it should be linearized, or possibly based on live load on the cantilever only. I.e. discount joist rotation at the support point and calculate only the relative deflection of the cantilevered portion. Checking L or even 2L of very short cantilevers is practical only with longer cantilevers. The math blows up on extra short cantilevers all the time.

Here is an example: a 13ft long 2x8 joist with a support at 12ft. The main span is fine at L/378 but the cantilever is L/124 (or 2L/248?). The math doesn’t start to work correctly until the cantilever exceeds 25%L or more. We would be doing our clients a disservice if we upsized all of our floor joists because we couldn’t override this deflection error. In this case, it would mean 2x10 joists where 2x8s would be fine: