Which level of earthquake motions is used to assess the ultimate capacity of a structure in the plastic deformation range?

• A. Level II Earthquake Motions
• B. Level I Earthquake Motions
• C. Level III Earthquake Motions
• D. Level IV Earthquake Motions

Answer: (A)

To assess a structure’s ultimate capacity in the plastic deformation range, you need ground motions that are strong enough to push the members into yielding and develop plastic hinges, revealing how the structure behaves after it yields. Level II earthquake motions are designed to produce this inelastic demand while still representing plausible, design-relevant extremes. They excite the structure enough to explore post-yield behavior and ultimate capacity, unlike motions that are too mild to cause significant plastic deformation or those that are so extreme they represent collapse scenarios beyond typical capacity assessment. So Level II provides the appropriate balance to evaluate how a structure behaves in its plastic range.