Which construction type uses unprotected steel or noncombustible supports (I-beams), and when exposed to 1000 degrees F, unprotected steel expands and twists, pushing out walls?

• A. Type I
• B. Type II
• C. Type III
• D. Type IV

Answer: (B)

Unprotected steel expands and loses strength when heated, and in Type II construction the structural system often uses steel or other noncombustible supports without fireproofing. When exposed to very high temperatures, such as around 1000°F, steel lengthens and can twist or bow. If walls are bearing on or restrained by those unprotected members, the expansion and deformation can push the walls outward, compromising the structure. This behavior—unprotected steel heating, expanding, and forcing wall movement—is characteristic of Type II construction. Other types rely on fireproofing or different materials, which changes how heat affects the structural elements.