These are employed to guard against the superstructure collapsing from piers as a result of a support loss capacity and to prevent a significant displacement between the superstructure and substructure. Which are they?

• A. Guard rails
• B. Unseating prevention devices
• C. Bridge collapse prevention device
• D. Expansion joints

Answer: (B)

The key idea here is providing a physical restraint that keeps the bridge deck from moving off its supports if a pier loses bearing capacity, so the structure does not collapse and the superstructure remains aligned with the substructure. Unseating prevention devices are specifically designed to prevent the deck from unseating or slipping relative to its bearings when the supports are compromised, by acting as stops or friction restraints at the bearing seats. They help maintain the load path and limit large displacements between the superstructure and substructure, which is crucial during events like bearing failure, scour, or seismic action. Guard rails protect vehicles, expansion joints accommodate thermal movement and are not intended to stop unseating, and a vague “bridge collapse prevention device” isn’t a defined, specific mechanism. So the device that directly addresses preventing unseating and preserving the integrity of the load transfer is the unseating prevention device.