Understanding Portal Frame Steel Structure Members
Portal frame steel buildings serve warehouses, workshops, and industrial facilities. Knowing the key structural members and their roles ensures clear communication in drawings, quotations, and technical discussions. This guide provides a professional overview of the main components, based on authoritative references such as the American Institute of Steel Construction (AISC) .
1. Primary Structural Members
Primary structural members carry the main building loads and form the frame’s backbone. In standard single-storey portal frames, girder is not typically present; it mainly appears in mezzanines or special roof designs.
| Member | Function |
|---|---|
| Column | Columns support the roof and walls vertically |
| Portal Frame Column | Portal frame systems use these columns to bear vertical loads |
| Rafter | Rafters carry roof loads horizontally along the roof slope in portal frames |
| Ridge Beam (Optional) | Ridge beams provide additional support at the roof ridge for large spans, heavy roof loads, or roof continuity. Not all portal frames require them |
| Crane Girder / Crane Beam | Crane systems rely on these members to carry crane loads |
| Beam | Horizontal members transfer loads across spans |
2. Secondary Structural Members
Secondary members support cladding, floors, and other elements. Girder primarily appears in mezzanine or partial floor systems.
2.1 Roof and Wall Supports
| Member | Function |
|---|---|
| Purlin | Purlins hold roof panels and transfer loads to rafters |
| Girt | Girts carry wall panel loads to columns |
| Purlin Cleat / Bracket | Cleats and brackets attach purlins to primary members |
2.2 Floor and Mezzanine Members
| Member | Function |
|---|---|
| Girder | Girders hold mezzanine joists and transfer loads to columns; generally used only in mezzanine or partial floor systems |
| Mezzanine Girder | Mezzanine girders support partial mezzanine areas |
| Joist | Joists carry floor deck loads directly |
| Mezzanine Joist | Mezzanine joists distribute loads within mezzanine zones |
| Floor Deck | Floor decks provide walking surfaces for floors and mezzanines |
3. Bracing and Tie Members
Bracing and tie members maintain stability and resist lateral forces.
| Member | Function |
|---|---|
| Column Bracing | Bracing keeps columns stable against lateral movement |
| Roof Bracing | Bracing stabilizes the roof plane |
| Horizontal Bracing | Horizontal members resist lateral loads |
| Cross Bracing | Cross bracing forms an X-type configuration for stability |
| Knee Brace | Knee braces support joints between columns and rafters |
| Tie Rod | Tie rods maintain structural tension |
| Sag Rod / Tie Bar | Rods prevent purlins from buckling under load |
| Sleeve / Coupling Sleeve | Sleeves adjust tie member lengths as needed |
4. Connection and Detailing Components
| Member | Function |
|---|---|
| Gusset Plate | Plates connect bracing and structural members |
| Base Plate | Base plates support columns and transfer loads to foundations |
| Stiffener | Stiffeners strengthen local beam or column areas |
| High-Strength Bolt | Bolts secure connections according to ASTM/ISO standards |
5. Terminology Notes
Using accurate member names improves clarity in drawings and quotations. Additionally, understanding these members and their functions helps engineers, clients, and contractors communicate effectively while presenting a professional and precise overview of portal frame steel structures.