Three ways to span 40m — steel tonnage can differ by 40%. Choose by use, not by habit.
When clients ask for a 40m span, there are at least three ways to achieve it — with tonnage and cost differing widely:
Variable-section portal frame: 40m is near its economic limit; about 45–55 kg/m² of steel, flexible roof slope, the default choice for ordinary plants and warehouses.
Truss: about 35–45 kg/m², deeper members (roughly 1/10 of span), but services can run through — good for hangars and exhibition halls where the space itself matters.
Bolted-ball space frame: suits two-way spans or irregular plans at 30–40 kg/m², with many members and demanding accuracy — typical for gymnasiums and swimming halls.
One-line logic: rectangular single-span, pick frame or truss; two-way spans or curved roofs, pick a space frame. Describing your function to the engineer saves more money than prescribing the structure.
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