Prolyte Campus blog: Round or Square?

It is generally accepted that our entertainment trusses are equipped with chords made of round tubes. There is not an organisation that specifies this common diameter in a law, not even in a standard. Such a common understanding is what I call a ‘silent standard’: it is not stated on paper, but generally accepted as normal.

We also accept it that these tubes have an outer diameter (OD) of 48-50mm (read also the blog: just one single tube). This is within the same range as ‘standard’ scaffolding tubes: 48,3mm OD. Less of a coincidence is that in many new or newly installed theatres, the batten size of the fly bars is often in that same 50mm range.

A Silent Standard, why?

Well, if we combine all types of show-related material, we have uncountable kinds of hooks, clamps, claws, triggers, snappers, lockers, brackets etc.. A lot of the material is used every day again, often in different venues to suspend the millions of entertainment equipment units.

The size of 50mm diameter became the widely accepted size of the round tubes in our business. If that dimension might not be sufficient for reasons of strength, it has to be decided which other size is suitable. Very soon there will be a discussion about what the standard of choice should be.

What about other shapes?

Even though the round tubes of 50mm are commonly accepted, we see different shapes appearing in our industry. Some manufacturers produce oval shape aluminium extrusion battens for their fly bars systems, in circa 80x50mm’s. A (slight) increase in vertical capacity, but not any stronger in horizontal direction. 

Some trusses are made of 50mm square tubes, easier to cut, weld and definitely a bit stronger than the round tubes. A conspicuous square tube chords type is the Prolyte BGR70, with 80x80x5mm extrusions. The BGR70 is designed to create large spans that can hold heavy loads. The rectangular profiles create a truss that can be used for spans up to 45 meters, still allowing a centre point load of 750 kg. Usage for another purpose can influence the choice for round or square tubes.

Once the trusses are leaving the territory of 50mm chords for reasons of capacity, they enter into the realm of (temporary) support structures. At that very moment the round cross section shape of the chords have become less important anyway. The application of fixtures or similar equipment is not the first requirement.


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Hendrik Deitert HVMC Show- & Veranstaltungstechnik, Germany