Structural Frames vs. Open Web Trusses

In this three-part series, we are going to break-down the structural integrity of tension fabric buildings, reviewing structural frames vs. open web trusses, fabric panel cladding vs. monocovers, and endwall design.  By the end of the series you will be able to openly see and understand the Legacy difference while researching your next fabric building partner.

When we talk about our frames, we are talking about a very particular kind of frame. One of the first innovations Legacy introduced when we started out was presenting a new kind of frame. They were unique in the world of fabric structures, and they got the attention of customers who were looking for strength, proven engineering, design-build and long-term durability.

We chose to build all of our structures with a rigid steel tapered I-beam frame. No one argues about steel. It is the very definition of strength, but not all steel is created equal. We were the first to attach fabric cladding to a solid steel rigid I-beam frame, rather than the open web trusses used by many tension fabric structure manufacturers.

The problem with open web trusses

There is controversy in the industry regarding the structural integrity of web truss designs. One type of structural failure is “chord plastification,” where a thin steel web within the truss “punches” through the wall of the supporting cord of the truss, eventually leading to instability or structural failure. Moreover, the frame pieces of open web trusses are hollow and connected only by welded steel cords. The hollow nature of the tubes also makes them vulnerable to internal corrosion in caustic environments.

More than strength – other advantages of tapered rigid I-beam frames

Legacy uses solid steel I-beam frames. Besides strength, steel gives our customers:

• Design flexibility: rigid steel frames use proven engineering principles for unlimited design options.
• More useable space: straight sidewalls create interior space and allow large doors in any location.
• Support for equipment: we can hang cranes, conveyors, catwalks, mezzanines, HVAC, fire suppression and more from our solid steel roof beams.
• Confidence: solid steel I-beam frames instills a level of confidence in the building owners from our experience. No one has to convince their committee that I-beams are the right material for a building frame.
• Universality: we use design software that is universally recognized in the pre-engineered metal building industry. Almost any engineer can look at our blueprints and instantly understand what’s going on. No translator needed.

Secondary framing features

To further reinforce our steel I-beam frame designs, legacy includes secondary framing practices that add to the strength and lifespan of our fabric buildings.

• Purlins
• Flange braces
• Cross cables and bracing rods

All of these elements add up to fabric structures with a difference. That difference is what we provide to our customers with every project, every customized building, every solution we design.