Experience has shown the unprotected engineered steel & wooden trusses can fail after ______ to ______ minutes.

Experience has shown the unprotected engineered steel & wooden trusses can fail after ______ to ______ minutes.

• A. 3 to 5
• B. 5 to 10
• C. 10 to 15
• D. 15 to 20

Answer: (B)

When exposed to fire, unprotected engineered steel and wooden trusses lose strength quickly and can give way within a short window. Without fireproofing or protective coverings, steel heats up fast and loses load-carrying capacity, while wood burns and chars, reducing its cross-section and stiffness. Together, these effects typically lead to structural failure in the early minutes of the fire, around five to ten minutes after ignition. That is why the commonly observed range is five to ten minutes. The other ranges either reveal too brief or too prolonged a failure window compared with real-fire behavior of unprotected trusses.

When exposed to fire, unprotected engineered steel and wooden trusses lose strength quickly and can give way within a short window. Without fireproofing or protective coverings, steel heats up fast and loses load-carrying capacity, while wood burns and chars, reducing its cross-section and stiffness. Together, these effects typically lead to structural failure in the early minutes of the fire, around five to ten minutes after ignition. That is why the commonly observed range is five to ten minutes. The other ranges either reveal too brief or too prolonged a failure window compared with real-fire behavior of unprotected trusses.