I am trying to validate a beam analysis against hand calcs, but I am getting differing results. So I set up a simple simulation to compare to have a base line.
Using weldments I modeled a 100" long S8 x 23 beam with a 25,000 lb point load in the center. Allowing the beams ends to rotate (simply supported) I get a very reasonable error of 3.3% on the deflection in the center, however with fixed ends the error is 21.3%. Why is the FEA computed deflection so much greater than the hand calcs?
Hi Phil: I tried the solid mesh half-beam w/symmetry and half load and matched your answers.
So, that left me with an applicability question because I noticed the beam length-to-web height ratio as 100/8 = 12.5 is a bit low for B/E application.
So just for a check, I doubled the length of the beam to get a ratio of 25, and ran that.
Now, when I look at the results, it appears to match B/E theory within 4% (default mesh size).
I researched the applicability for length-to-web height ratio limit and found that B/E theory underpredicts the deflection if that ratio is less than about 20 due to transverse shear strain, which apparently the FEA is capturing for us. This statement seems to corroborate results findings for the fixed-end conditions. I suspect the corroboration is better for this case (compared to the ss-end condition) due to the heavy shearing at the ends of the fixed restraint.
I believe that's the issue, but let me know what you think!
Tony