Soft-story construction is most accurately described as:

• A. A building with a first floor that provides extra lateral bracing, improving stability
• B. A building with no lateral bracing on any floor
• C. A building with a first floor that lacks adequate lateral bracing, making it more vulnerable to collapse
• D. A building with uniform stiffness on all floors

Answer: (C)

The main concept is how uneven lateral resistance between stories affects seismic behavior. A soft-story occurs when the first floor lacks enough lateral bracing, making it much weaker to side-to-side forces than the upper floors.

In practice, the first floor often has large openings (like garages or storefronts) or fewer shear walls, so its lateral stiffness is reduced relative to the upper stories. When an earthquake hits, this weaker level deforms more, causing large differences in movement between floors. That increased interstory drift puts the upper floors at greater risk of damage or collapse, which is the defining risk of a soft-story building.

So the description that best fits is that the first floor lacks adequate lateral bracing, making it more vulnerable to collapse. The other statements describe scenarios that would not characterize a soft-story, such as the first floor providing extra bracing, having no bracing on any floor, or having uniform stiffness on all floors.