How to Choose the Perfect Frame for your Steel Building

Published February 19, 2018 by Whirlwind Team

choose steel building frame

Designing your steel building starts with the selection of the type of frame that best suits the intended use of the building, how it fits into the site, and the desired outward appearance of the building. Steel buildings provide the most versatility and flexibility in frame design and use compared to wood frame primarily due to the high strength to weight ratio of steel.

The strength and durability of steel provide the ability to create a wide range of frame designs and styles to match almost any requirement. Paired with low maintenance and total cost of ownership, steel adds the most value for your money.

Before heading to your supplier, take a moment to learn about the various types of frames so you can choose the perfect frame for your steel building.


I-Beam and Tapered Beam

I-beam style frames are, by far, the most common frame type in use.

  • The frame is made of built-up plate sections welded together or from hot-rolled beams.
  • The "I" in I-beam comes from the cross-section of the beam that is shaped just like the letter that identifies it.
  • The I-beam design was instrumental in building high-rise structures with maximum strength and minimum material.

I-beam structures are also known as straight column buildings where the columns are of equal width across their length.

The tapered beam is a straight column rigid frame that maximizes interior space. Smaller buildings that require clear spans are best served with tapered beam construction. A tapered beam building can be easily partitioned into interior bays and is an optimal design for using small crane support systems.

Tapered beam is also called tapered column. The thicker end of the column is attached to the thicker end of the crossbeam at the joint between wall and roof, providing an extraordinarily strong joint at the eave. The narrow ends meet at the roof line or extend to the ground. The lower interior space is maximized while the column is strong enough to support cranes and other equipment for moving items within.

Open Web Design

Open webs are also known as trusses. The web is created using a top and bottom chord connected with diagonal angles. For clear spans of 250 feet and larger, an open web design is an economical choice. However, it is slightly more complex to fabricate than other designs.

Open web design allows you to incorporate HVAC, wiring, and sprinkler systems directly into the truss framework, leaving the interior open and column-free.

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Clear Span Framework

Only steel makes the clear span frame possible. The span indicates the width of the frame.

  • Clear span can be designed using either I-beam or open web style framework to create a wide, open space with no interior columns.
  • You can have unobstructed spans up to 150 feet or more, making this frame popular for airplane hangars and sports arenas.
  • Open-floor factories, warehouses and agricultural buildings also make excellent use of a clear span building, as do churches and other venues that need unobstructed sight lines.

Clear span frameworks also allow you versatility and flexibility in using your floor space. A clear span building is easily divided into rooms or sections using partition walls. The partitions do not need to bear weight so you can rearrange sections easily.

Alternatively, the wide open space provides room for maneuverability for large equipment such as airplanes, agricultural machinery, or warehouse equipment.

The only limit to clear span construction is the increase in cost as the structure grows wider. Increased width requires a proportionally heavier frame to bear the increased load and the height of the side walls increase as well. The cost per square foot rises until the cost-effectiveness is lost.

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Modular Framework

Modular frame designs are used for extra-wide buildings for which clear span design is not suitable. Modular framework provides interior columns to support the greater width of the roof. The load is more evenly distributed, reducing the cost of the frame and the foundation of extremely wide buildings.

Modular framework designs are generally used in factories and other very large structures and in buildings where a wide open, clear span is not required.

Frame Types

  • Main frame refers to a rigid-frame steel building with a backbone of I-beam main frames. Each frame is created from two or more columns supporting a rafter running laterally from one side of a building to the other. The frames are spaced between the two endwalls and bear a majority of the building load.
  • Endwall frames support half the load of the main frame in most steel buildings and are similar in design to main frames. The endwall frame can be built using lighter beams to save costs unless there are plans to expand the building in the future.
  • Single slope frames have different eave heights on each side wall. The roof slopes upward from front to back, creating the look of a house cut in half along the roof peak. Retail centers and strip malls are often created using single slope frames.
  • Lean-to frames are similar in appearance to single slope frames, but they are not free-standing. A lean-to frame relies on the main frame of a separate, free-standing building as one of its side walls.

Secondary Framing

The frame types above are all primary framework. Secondary framing provides support for the wall and roof panels, and carry little of the building’s overall weight. The secondary framework also transfers loads to the primary frame to stabilize the structure.

  • Girts are the secondary spanning members for wall panel connection. They can run flush with the column on an endwall, also known as inset or flush mount, on side walls they can overlap on the outside, known as outset or bypass.
  • Purlins are the secondary spanning members for roof panel connection.
  • Eave struts are located at the joint between the roof and the exterior walls. Eave struts act as the first purlin and the last, or highest, girt.

Girts, purlins and eave struts are placed according to the design and needs of your building frame.

Your steel building design begins with the intended size and use of the building. If the intended use requires clear sight lines and wide open floor space, a clear span frame is highly recommended. If you need an extremely wide building and can accommodate interior columns, a modular frame will do the job.

For smaller retail and office spaces, you may consider single slope frames while a lean-to can increase space on a lower level or act as additional storage.

The perfect frame is out there for any steel building. Armed with the knowledge of the various types of frames, you are ready to go forth and design your perfect steel building.

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