Bad Plate Results - Shear Near Pinned Edge

[ATSE]

I'm getting unusual out-of-plane shear results for a simple plate model.
Model Description:
1) Program = RISA
2) 30ft x 30ft x 2ft thick
3) Elements are 2ft thick (out of plane) x 1ft wide x 1 ft tall
4) top edge is pinned out of plane only, free otherwise
5) sides and bottom edge are fixed
6) loading is triangular, based on fluid: 0ksf at top, 2.73ksf at base
7) E (modulus) based on f'c = 4ksi

Problem:
a) Horizontal shear Qx along top edge is very high
b) The rest of the model results agree with solid mechanics theory, except the top.
c) Top reactions agree with theory.
d) Vertical shear Qy agrees with theory.
e) Attachment: pdf plots of Qx, Qy, Mx, My

So here's the question: Is there a good theoretical explanation why the out-of-plane shear along the top edge (i.e. beam action horizontally) is so high, or is this a modeling error?

 

[ishvaaag]

See my guess at the FEM forum. Maybe because energy of deformation in shear is the only available at the region.

 

[JoshPlumSE]

I believe this is related to the "twisting" moment of the plate. Take a look at the Mxy moments.

when I look at the deflected shape, it seems reasonable that the twisting moments would be increasing towards that top surface. If the twisting moments are there, it seems reasonable that there will be some shears there as well.

0.0 shear at point of maximum moment and 0.0 moment (but not zero shear) at point of inflection. Maybe that doesn't hold perfectly for twisting moments, but it certainly provides a rational basis for understanding those shear contours.

 

[ishvaaag]

Quite imprecise, my previous statement. Anyway, it is clear the section in a vertical cut is seeing shear deformation (and stresses) there and at the top is prevented to take moment, hence the prevalent mechanism to compatibilize stresses with deformations is by shear transfer.

 

[miecz]

Could you post the .r3d file?