What collapse scenario is listed for the 1940s era, commercial Type III medium building?

What collapse scenario is listed for the 1940s era, commercial Type III medium building?

• A. Reinforced concrete column collapse
• B. Unreinforced masonry collapse
• C. Steel frame buckling
• D. No collapse

Answer: (B)

The scenario being tested is that, for a 1940s era commercial building with Type III medium construction, the walls themselves drive how the structure would fail. In this type of building, exterior walls are typically masonry and not reinforced, so they’re the primary lateral-load-resisting elements but lack the steel reinforcement that would prevent brittle failure. Under lateral forces such as earthquakes or strong wind, those unreinforced masonry walls can crack, tilt, or collapse around openings, leading to a collapse pattern that is driven by the walls failing—i.e., unreinforced masonry collapse. The other possibilities would require structural systems that aren’t characteristic of that era and type, whereas the URM collapse matches the common weakness of 1940s Type III medium buildings.

The scenario being tested is that, for a 1940s era commercial building with Type III medium construction, the walls themselves drive how the structure would fail. In this type of building, exterior walls are typically masonry and not reinforced, so they’re the primary lateral-load-resisting elements but lack the steel reinforcement that would prevent brittle failure. Under lateral forces such as earthquakes or strong wind, those unreinforced masonry walls can crack, tilt, or collapse around openings, leading to a collapse pattern that is driven by the walls failing—i.e., unreinforced masonry collapse. The other possibilities would require structural systems that aren’t characteristic of that era and type, whereas the URM collapse matches the common weakness of 1940s Type III medium buildings.