Truss Profile and Layout

• The profile, spacing and layout of a truss must be woven into a larger structural and architectural system.

  • Decking, beams, lateral bracing, supports.

  • Modifying one of these components typically requires adjusting others.

• Preliminary design of a truss involves selecting a profile (e.g. configuration of chords), depth, panel spacing, and configuration of web members.

  • These decisions can be driven by many factors.

  • Structural considerations may include the following:

    • Orient diagonals to keep compression members short, to reduce buckling.

    • Keep diagonals at roughly 45 degree angles, to avoid highly acute angles at connections.

• Preliminary design seeks to validate that the concept is doable, rather than to detail and size every member.

  • Focus on critical members that may be "concept killers".

  • Use quick, approximate methods where appropriate.

    • e.g., estimate the chord force of the truss by dividing the bending moment of an equivalent beam by the depth of the truss.

  • Identify critical members by reasoning about global behavior.

    • e.g. the critical chord member on a parallel-chord truss is the compression member in the region of highest bending moment for the span and support condition.