Explain the concept of torsional restraint and its importance in overall bridge stability, particularly for skewed bridges.

• A. Torsional restraint limits twisting under loads; inadequate restraint in skewed bridges can lead to torsional instability, requiring proper bracing and symmetric detailing.
• B. Torsional restraint reduces bending moments in supports.
• C. Torsional restraint is only relevant for arch bridges.
• D. Torsional restraint increases torsion during deployment.

Answer: (A)

Torsional restraint means providing enough stiffness and proper connections to prevent the structure from twisting about its longitudinal axis when loads are applied. In skewed bridges, the deck and supports don’t align with the primary load paths, so the tendency to twist is amplified. Giving adequate torsional restraint through diaphragms, cross-frames, bracing, and symmetric detailing keeps the deck from rotating and helps distribute forces evenly to bearings and supports. This restraint is crucial for overall stability because torsion can couple with bending, leading to uneven displacements, increased fatigue at connections, and potential instability under live and wind or dynamic loads. So, when a bridge is skewed, lacking sufficient torsional restraint makes torsional instability more likely, which is why proper bracing and symmetric detailing are necessary. The other statements aren’t correct because torsional restraint doesn’t primarily aim to reduce bending moments in supports, it isn’t limited to arch bridges, and it certainly doesn’t increase torsion during deployment.