Well, in that visualization the crossbars appear solid (thick-shells&beams style on) but in the model only the corner joints are solid bodies and they are connected through beams from their holes (faces) with crossbars end-points (vertex), modelled as line-bodies (beam elements) and with brackets holes (edges) as surface-bodies (shell elements):

On top of that, bonded-contacts are defined between solid-joints, surface-brackets and board and crossbar-beams...