1. Spiral reinforcement is less expensive to fabricate than tied reinforcement
2. Tied reinforcement creates construction conflicts with longitudinal bars
3. Spiral reinforcement provides greater confinement and ductility
4. Spiral reinforcement allows larger column spacing in multi-column bents

Explanation

Explanation: Spiral reinforcement provides continuous confinement of the concrete core, enhancing ductility by restraining lateral dilation of concrete under compressive loads —critical in seismic zones where columns must maintain capacity through multiple displacement cycles. Per AASHTO LRFD (Section 5.10.11), spiral reinforcement offers superior performance compared to tied reinforcement because it maintains confinement pressure throughout the column height, whereas ties provide intermittent confinement. Fabrication costs (A) typically favor ties, not spirals; bar conflicts (B) aren't significantly different between types; and column spacing (D) is determined by superstructure needs, not reinforcement type.

Learning Resources:

• Review AASHTO LRFD Bridge Design Specifications, 9th Edition (2020), Section 5.10.11 for column reinforcement requirements.
• Study the Loma Prieta Earthquake (1989) Cypress Street Viaduct collapse as a case study in insufficient column confinement.
• Digital Resource: Explore PEER's Bridge Column Test Database (https://peer.berkeley.edu/research/databases)
• Tip: When designing spiral reinforcement, pay special attention to termination details at column-to-cap beam interfaces, where seismic demands are highest.