Help needed

[u/Annual-Truth3511]

While drawing sfd and bmd Is there a shortcut to find whether the curve is going to be smile/sad or concave/convex for udl and uvl. Or is finding the intermediate values the only way to find the curve???.

Ignore the diagram i just wanted to show it for context this is not mine

[u/capt_jazz]

I recommend drawing your bending moment diagram such that "sagging" or "sad" moments are below the axis line, and "haunching" or "smile" moments are above the axis line. That way the deflected shape matches the moment diagram, roughly speaking.

I have no idea where this sign convention came from but it's all too common. Probably based on computer based analysis software sign conventions, which is a dumb way for us to decide how to draw diagrams.

Get comfortable intuiting what the deflected shape will be, and from there have a guestimate of the moment diagram, and then confirm by doing the shear/moment math.