How to Design Steel Trusses

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While the boundary between art and architecture is frequently blurred, steel trusses can often qualify as an example of both disciplines. From bridges to libraries to tall buildings, steel trusses provide structural support while simultaneously embodying a beautiful aesthetic. The rigidity of a steel truss, in combination with its geometric assembly, allows it to be used in situations where an architect or engineer wishes to dissipate the forces of compression and tension over a much wider area than can be provided by a typical I-beam.

Determine the total structural load that the steel truss will have to bear. Calculate this load by estimating the weight of the material used in the construction, the types of vehicles or numbers of people likely to use the structure and how these vehicles or people will use the structure. Overhead trusses will bear weight differently than trusses mounted underneath a structure. Choose a triangular truss design to maximize the strength of the truss; if the load suddenly increases, the truss will remain intact unless one of the triangular members buckles.

Determine the type of steel to be used to manufacture the truss. Design the steel truss in accordance with the total stress load — a standard grade of steel, ASTM 36, can accept a yield stress value of 36,000 pounds per inch. Consult the "Manual of Steel Construction," published by the American Steel Institute of Construction, for details on the stress load of each type of steel.

Determine whether the steel truss will have welded or bolted joints. Design the steel truss to account for each distinct type of stress — welded joints will place the tension on the overall cross-section of the steel truss, while a bolted joint will also have specific stress on the bolt itself.