Structural Slab Supported at Corners

[EngDM]

I'm playing around with a simple 7'x12' slab in SAFE, with pin supports at the corners and I am finding that SAFE still wants me to provide top steel. If this slab is truly pinned, for instance formed onto some sort of angle or support with minimal moment restraint and moreso just shear studs to keep it from sliding, how come I am getting negative bending? The supports are currently placed directly at the corner, so it's not like the moment is being generated over top of the support.

I'm not sure if maybe since the pin support is placed at the datum, which coincides with top of slab it is taking the slab as being supported by the top? I tried shifting my supports down by my slab thickness but it throws ill conditioned warnings.

 

[BridgeSmith]

Not familiar with the program, but if the slab is deflecting down in the middle and the supports are fully rigid against lateral movement, is it generating tension at the supports due to the slab trying to pull the corners in toward the center and the rigid supports not allowing it?

 

[EngDM]

Not familiar with the program, but if the slab is deflecting down in the middle and the supports are fully rigid against lateral movement, is it generating tension at the supports due to the slab trying to pull the corners in toward the center and the rigid supports not allowing it?

I tried releasing all but 1 support for plan translation, but the contour diagrams remain same with hotspots at each corner for top reinforcing.

 

[EngDM]

I respectfully suggest that this may be due to Mxy (or warping) moments. I tend to think of this as a tendency to warp or distort the plate rather than to bend it. Since I'm more of a steel guy, I tend to related it to the Torsional Warping of I shaped beams.

I think you're right. I removed any M12 stiffness and my corner hotspots disappeared, but then I required top steel in the middle since the deflected shape was more like a saddle, due to no twisting rigidity.

 

[BAretired]

Applying reactions at each of the four corners as a concentrated load is not realistic; it creates an infinite shear stress because the reaction is applied over a zero area. Maybe you should try moving the reactions in at least half the depth of slab, and assume the area of each support to be large enough to satisfy the permissible bearing stress.