Structural Engineering · Steel Detailing
Types of PEB Portal Frame Structures: Geometry, Spans & Selection Guide
The portal frame is the primary lateral and gravity load-resisting structural component of a Pre-Engineered Building. Selecting the proper frame geometry directly dictates floor efficiency, steel consumption, and cost per square foot. Here is an overview of the five primary portal frame configurations engineered by Fusion Developers.
The Five Primary PEB Portal Configurations
- 1. Clear-Span Rigid Frame (Gable Symmetrical): The most popular configuration. Offers 100% unobstructed floor space up to 60 meters (200 ft) width. Ideal for wedding marquees, aircraft hangars, and sports arenas.
- 2. Multi-Span Rigid Frame (Interior Column Supported): Features one or more internal pipe or H-columns supporting continuous rafters. Used for massive mega-warehouses (150 to 500 ft wide) where interior columns do not obstruct automated racking.
- 3. Lean-To Frame: A single-slope addition bolted onto the exterior column line of an existing primary frame. Provides economical office, dispatch, or loading bay extensions.
- 4. Single-Slope (Mono-Pitch) Frame: Features a continuous roof slope in one direction, facilitating concentrated rainwater harvesting and rooftop solar photovoltaic orientation.
- 5. Curved Radial / Dome Portal Frame: Features faceted or rolled radial arches converging at a central compression ring, as demonstrated in our Sphere 150ft Round Marquee dome.
Portal Frame Selection Matrix
| Frame Type | Optimal Span Range | Relative Steel Economy | Best Commercial Fit |
|---|---|---|---|
| Clear-Span Rigid | 50 ft – 180 ft | Optimal for <120 ft; moderate for >150 ft | Marquees, aircraft hangars, event halls |
| Multi-Span (1 Interior Col) | 100 ft – 250 ft | Highly economical (25% steel savings) | Logistics parks, bulk warehouses |
| Lean-To Extension | 20 ft – 60 ft | Extremely economical | Office annexes, equipment bays |
| Mono-Slope | 30 ft – 100 ft | Moderate economy | Commercial showrooms, strip malls |
Frequently Asked Questions
What is the most economical portal frame spacing (bay length)?
In Pakistan, the most economical bay spacing (distance between portal frames) typically ranges from 20 to 25 feet (6 to 7.6 meters). This optimizes the span-to-weight ratio of secondary cold-formed Z-purlins without requiring excessively heavy rafter profiles.