Steel Frame Vs Purlin Optimal Choices for Farm and Commercial Buildings

Imagine a sudden storm sweeping across your farm, with howling winds and torrential rain. Your hard-earned agricultural machinery, commercial supplies, and livestock all depend on the steel structure that shelters them. In such moments, do you question whether your building can withstand nature's harsh tests? In agricultural and commercial settings, selecting the right steel structure is crucial—it directly impacts asset safety and operational stability.

With a wide array of steel products available—from structural steel to purlins, from wide-span to compact designs—how can you make an informed choice to create a sturdy and reliable shelter for your farm or business?

This article explores the key differences between purlin structures and structural steel frames, helping you understand their advantages and disadvantages to make the best decision for your steel building project.

What Are Purlins?

Purlins are cold-formed structural support systems primarily used in framed steel structures to provide support for roofs and walls. They are made from flat steel sheets rolled into specific shapes. Depending on their profile, purlins can be categorized into C-purlins and Z-purlins.

• C-Purlins: These feature equal-length flanges and are suitable for single-span or non-overlapping continuous spans. They are commonly used in multi-span buildings and steel structures.
• Z-Purlins: These have one wide flange and one narrow flange, allowing for tight overlapping connections. Z-purlins of the same depth but different thicknesses can be combined in overlapping configurations.

Advantages of Purlins

For small steel structures (with spans under 12 meters), purlin-based construction can be a cost-effective solution. Purlins provide adequate support for such sizes and meet most basic requirements. Additionally, purlins are typically screw-fastened rather than bolted, helping reduce manufacturing costs.

Disadvantages of Purlins

Purlin structures have limitations in strength and structural integrity. Although additional bracing can enhance stability, their load-bearing capacity remains restricted, making them unsuitable for large steel buildings (spans exceeding 12 meters). They are also not ideal for storing heavy machinery—accidental impacts from tractors or forkllifts could cause significant damage.

Notably, purlin-based buildings may be more vulnerable to extreme weather conditions. Due to their inherent structural limitations, they are more prone to damage during severe storms.

What Is Structural Steel?

Structural steel is a hot-rolled specialty steel formed at high temperatures through rolling processes. It is generally thicker than purlins, with thicknesses ranging from 5 mm to 20 mm.

In structural steel buildings, the main framework and roof trusses are welded from robust steel sections and then bolted together. Purlins and wall girts may supplement the structure to support cladding. This design approach is more durable and reliable for steel construction.

Structural steel buildings typically consist of the following components:

• Universal Beams (UB): Also known as I-beams, H-beams, or RSJs, these resemble the letter "I" in cross-section. They come in various shapes, sizes, and thicknesses.
• Welded Web Trusses: These trusses form a sturdy skeleton for steel buildings, engineered to balance weight and strength optimally.

Advantages of Structural Steel

For large steel buildings or commercial structures, structural steel offers numerous benefits. As mentioned earlier, it is a robust and durable material—structural steel buildings weigh approximately six times more than purlin-based structures. They also offer superior weather resistance, making them better suited to harsh climates.

Structural steel frames can be cut and welded to meet design specifications, allowing for high customizability. There are more options for design, shape, and size. Additionally, structural steel buildings can support additional features such as overhead cranes in workshops.

Another key advantage is that structural steel components are prefabricated as large welded sections, significantly speeding up on-site assembly—a critical factor for large-scale commercial projects.

Given these advantages, structural steel is the recommended choice for large agricultural or industrial steel buildings.