What is the primary purpose of continuity detailing in long-span bridges, and what is the role of diaphragms?

• A. Continuity detailing ensures loads are properly transferred across spans, and diaphragms distribute lateral shear to connect girders and maintain overall stability.
• B. It reduces dead load and increases stiffness only at supports.
• C. It eliminates all joints to create continuous spans.
• D. It allows independent movement between spans.

Answer: (A)

Continuity detailing is about making the bridge act as a single continuous structure, so bending moments and shear can be transferred from one span to the next rather than being concentrated at individual supports. This helps control deflections, improve stiffness, and enhance overall stability under live loads, wind, and seismic effects.

Diaphragms are transverse bracing that connect adjacent girders, forming a rigid frame at key locations. They create a path for lateral shear and torsional forces, distribute loads among the girders, and prevent differential movement between spans. In short, continuity detailing enables load transfer across spans, and diaphragms provide the structural connection that makes that transfer effective and stable.