Here you visualize how to transform Surface Loads into Linear Loads. If there is no continuity in the plate (we have two independent plates, left and right of the central beam, with a joint in the middle) the loads that the central beam receive are easy to calculate.
The blue box, like in another example (Loads-Water), represent the Surface Load over the beam. Operate the sliders "Load", "Span" and "Spacing". Which parameters are relevant for calculating the Linear Load? How do you do it?