Dead load is the strength that is designed into a truss to hold up the trusses, the purlins, the roof steel etc. This strength is used up when the building is erected and therefore also does not contribute to the real strength of the building. The only load ratings that mean anything ...
Then, roof frame units 10 are arranged parallel, combined by girders 5, purlins and the like, and roof members are installed thereon. And after a bending is generated to the truss beams 1 by the constant load of the dead load of the members, nuts are screwed on the screws at both ...