Under fire conditions, which type of building construction presents the greatest potential for collapse?

Under fire conditions, which type of building construction presents the greatest potential for collapse?

• A. Lightweight wood-frame construction
• B. Masonry bearing-wall construction
• C. Reinforced concrete construction
• D. Steel frame construction

Answer: (A)

The most collapse-prone under fire is lightweight wood-frame construction. Its structural system relies on small, combustible wooden members and lightweight attic trusses with few redundant supports. When exposed to heat, wood loses strength and stiffness rapidly as it chars, connections loosen, and fasteners fail. With little mass to absorb heat or hold loads, floors and roofs can give way quickly, sometimes in a sudden collapse, especially if fire spreads into concealed spaces or reaches the roof structure. In contrast, masonry bearing-wall construction uses heavy, noncombustible walls that resist fire longer; reinforced concrete masses also endure heat well, and steel frames tend to retain strength longer if fireproofed.

The most collapse-prone under fire is lightweight wood-frame construction. Its structural system relies on small, combustible wooden members and lightweight attic trusses with few redundant supports. When exposed to heat, wood loses strength and stiffness rapidly as it chars, connections loosen, and fasteners fail. With little mass to absorb heat or hold loads, floors and roofs can give way quickly, sometimes in a sudden collapse, especially if fire spreads into concealed spaces or reaches the roof structure.

In contrast, masonry bearing-wall construction uses heavy, noncombustible walls that resist fire longer; reinforced concrete masses also endure heat well, and steel frames tend to retain strength longer if fireproofed.