Why is the side rail the most important load-bearing part?

The side rail is the most important load-bearing part because it carries the main
longitudinal bending load between supports. Cable weight is transferred from the cables to the
rungs, then from the rungs into the two side rails, and finally into brackets,
trapeze supports or floor supports.
A stronger side rail usually has a suitable combination of rail height,
material thickness, flange geometry, section shape,
and splice strength. The final load capacity should always be checked by the
manufacturer’s tested load/span data, not by appearance alone.

 

 

 

Load path: cable → rung → side rail → support
Upper side rail
Lower side rail
Rungs transfer load into side rails