joint ractions and moment

[nith1234]

I would like to know why the moments and the joint reactions change with increasing member sizes? THe Y gravity was set to 0 (not -1). So its not the dead load. I started out with w8 x 10 for a propped cantilever.Solved it, got the reactions.
Then i increased the member size to w12 x 336. It changed the joint reactions.
I can't think of any other reason other than the dead load that caused this change. But again, the dead load (Y gravity was turned off)

please someone explain...

 

[JoshPlumSE]

What sort of span are you talking about? Shear deformation can make the results deviate from the "simple beam theory" results we get from a hand calculation.

Though this is usually only noticeable where there is a large difference in span to dept ratio (W8 vs a W24). It would be odd to see a significant change from a W8 to a W12. But, you can test this by go to the solution tab of the global parameters and turning off the shear deformation. If the results now become equal, then you know it was due to shear deformation.