Ratna Steeltech is one of the leading Manufacturer of PEB Structure Explore the Strength and Versatility of Primary Members in Pre-Engineered Construction The main load carrying and support members of a pre-engineered building are “Primary Members”. Columns, rafters and other supporting members are part of main frame members. The shape and size of these members vary based on the applications and requirements. The frame is erected by bolting the end plates of connecting sections together.