Beam Analysis Incorrect

[scratchy]

I have carried out a very simple Beam Deflection Calc on Inventor Nastran 2024.

The Calc has a load in the centre of the beam which is held at each end.

The Calc is correct for the weaker axis but gives a different result to the hand calc for the stronger axis.

All materials etc are the same in the Nastran Calc to the Hand Calc....

I have attached the hand calc and a screen shot of both Nastran Analysis showing the resulting deflection.

Any Help would be appreciated

[John_Holtz]

Hi @scratchy 

Your hand calculation and Nastran model are completely different arrangements.

• The factor of 48 in the hand calculation is for a beam that is simply supported on each end.
• The analysis is a beam that is fixed on each end. The factor would be 192 instead of 48.

Then you mixed the hand calculated result for "Tz Deflection" which used Iy (bending about strong axis) for the inertia with the Nastran calculated result for bending about the weak axis! Because 192/48=4 and Iy/Iz=4, the two errors cancel, and one result matches by coincidence.

John

[scratchy]

John.... Thanks for that. Just happens that the result for one axis using 48 was the same as the other axis using 192... Totally confused us.... Needed a fresh pair of eyes... All re calculated and FEA run and all ties up...