Thickness ratio of the plate element
Could you please clarify the 'Thickness Ratio'? What do TS and M mean? Why is set as 0.8333?
You can find the explanation on the page 49 of Analysis Reference.
TS: Shear deformation thickness
M: In-plane thickness
When slab is subjected to bending, the actual shear stress distribution is as shown below.
This distribution can exactly be simulated with 3D solid elements, but not possible with 2D plate elements. The shear strain, and hence the shear stress, across the thickness of the plate is assumed constant across the thickness of the plate. This cannot be accurate since the shear stress is known to be parabolic. To account for the inaccuracy in the shear strain, a shear correction factor is applied so that the shear resultant across the thickness is the same as the applied shear force. Generally, 5/6 (= 0.83333) is used for this factor, which will give the shear deformation close to the actual value.