Which structural members use less material and are lighter than a comparable beam or joist of an equal span?

Which structural members use less material and are lighter than a comparable beam or joist of an equal span?

• A. Trusses
• B. Beams
• C. Columns
• D. Purlins

Answer: (A)

A truss carries loads mainly as axial forces in its many slender members arranged in triangles. Because those members are in tension or compression rather than bending, the overall structure can span longer distances with much less material and weight than a solid beam or joist of the same span. The load path in a truss is efficient, with the top and bottom chords handling compression and tension and the web members sharing the interior forces, so you achieve a strong, light assembly. Beams and joists must resist bending and shear, which requires larger cross-sections or heavier members to achieve the same span and load-carrying capability. Columns carry vertical compression but do not span horizontally. Purlins are horizontal roof members that support roofing material and are typically lighter-weight components compared with a full spanning beam or joist, but they don’t provide the same long-span efficiency as a truss. So, for a given span with less material and lighter weight, a truss best fits the scenario.

A truss carries loads mainly as axial forces in its many slender members arranged in triangles. Because those members are in tension or compression rather than bending, the overall structure can span longer distances with much less material and weight than a solid beam or joist of the same span. The load path in a truss is efficient, with the top and bottom chords handling compression and tension and the web members sharing the interior forces, so you achieve a strong, light assembly.

Beams and joists must resist bending and shear, which requires larger cross-sections or heavier members to achieve the same span and load-carrying capability. Columns carry vertical compression but do not span horizontally. Purlins are horizontal roof members that support roofing material and are typically lighter-weight components compared with a full spanning beam or joist, but they don’t provide the same long-span efficiency as a truss.

So, for a given span with less material and lighter weight, a truss best fits the scenario.