What might cause the moment diagram (red) on this simple 14ft 2x10 cantilevered floor joist jump at around 10ft?
Hi @WilsonEngineers -
Any chance you have Load Patterning turned on? (The radio button for that is just below the screenshot of your loads inputs).
Patterned loads could result in the envelope shown there. The apparent jump at ~10ft would is an admittedly-confusing anomaly of our graphing, where we’re actually showing the signed absolute maximum of your moment curve - and you could get a jump like that if the +/- sign of the absolute maximum moment at a point suddenly changes.
On a related note, assuming the above theory is correct, how would you prefer to see results for patterned loads graphed? Would you prefer to see only one pattern at a time, or all the patterns graphed simultaneously, or some shaded envelope, or …? That feature is currently in “BETA”, not because of any doubts of its technical functionality but because we don’t yet have a great UI for displaying the results!
I’m going to say this without thinking long and hard about it, but load patterning is more useful when evaluating max reactions, not max moments or deflections. That was at least the case with the cantilevered deck joist I posted about the other day where unloading the cantilever created a larger reaction at the back span. Patterning would also help find possible uplift conditions with cantilevers.
In that regard, I am not looking to see the different moment or deflection diagrams. I am content knowing that CC has presented me with the max reaction, (LCmax 
). That is even more important when using linked loads.
On a related note, have you considered supports that resist positive reactions only? 3-support wood beams with an offset center support can have uplift at the short end. I will manually pattern loads and toggle the support on/off at those locations when the reaction is negative.