This load combination represents an extra safeguard for bridge superstructures where the unfactored dead load exceeds seven times the unfactored live load.

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

Answer: (D)

The main idea is that bridge designers use different load combinations to check safety under different dominant-loading conditions. When the unfactored dead load is far larger than the unfactored live load, you need a combination that emphasizes dead load and minimizes live-load effects to ensure the structure can resist a heavy permanent-load scenario.

Strength IV is the most dead-load–dominated of the standard strength combinations. It weights the dead load more heavily and reduces the influence of live load, providing an extra safeguard for the superstructure when D/L is extremely high (such as when D exceeds seven times L). This makes it the most conservative check for extreme dead-load conditions.

The other strength combinations are more balanced between dead and live loads or give more weight to live-load effects, so they are not as protective for this particular scenario.