In wood truss design, which component is the weakest point and will fail quickly when exposed to heat?

In wood truss design, which component is the weakest point and will fail quickly when exposed to heat?

• A. Gusset plate
• B. Fire plate
• C. Bar joist
• D. I beam

Answer: (A)

The key idea is how a wood truss transfers load and where that transfer fails first under heat. In a wood truss, the connection between the chords and the webs is held together by gusset plates—thin steel plates fastened with nails. These plates are the critical load path: they carry shear and keep the members working together as a unit. When a fire heats the truss, the gusset plate heats up quickly and loses strength, and nails can loosen or fail at the plate. Once the plate can no longer transfer the forces between the chords and webs, the entire truss loses its integrity and can rapidly collapse. The other components listed (bar joist and I-beam) aren’t typical parts of wood trusses, and a fire plate isn’t a standard element in this context, so they don’t represent the first point of failure in a heated wood-truss assembly.

The key idea is how a wood truss transfers load and where that transfer fails first under heat. In a wood truss, the connection between the chords and the webs is held together by gusset plates—thin steel plates fastened with nails. These plates are the critical load path: they carry shear and keep the members working together as a unit. When a fire heats the truss, the gusset plate heats up quickly and loses strength, and nails can loosen or fail at the plate. Once the plate can no longer transfer the forces between the chords and webs, the entire truss loses its integrity and can rapidly collapse. The other components listed (bar joist and I-beam) aren’t typical parts of wood trusses, and a fire plate isn’t a standard element in this context, so they don’t represent the first point of failure in a heated wood-truss assembly.