Question
When modeling a simple beam using Plate and Beam elements, the results for member forces differ.
Answer
Unlike Beam elements, the member forces for Plate elements are output as member forces per unit width.
For example, consider the case where you have a beam element and a plate element subjected to bending, as shown below
[Image-1] Beam [Image-2] Plate
In the case of the beam element, the member forces represent the summation of stresses over the entire cross-section, expressed as a resultant force at the centroid.
[Image-3] Member Forces for the Beam Element
On the other hand, for the plate element, the member forces are calculated by integrating the stresses in the thickness direction and then expressing them as forces per unit width (1m).
[Image-4] Member Forces for the Plate Element
In essence, the member forces for the plate element represent the same force per unit width regardless of the size of the plate element.