The 'box girder' bridge cross-section is preferred for curved alignments because:
Choose the correct answer
Box girders are easier to formwork than T-beams
Closed section provides very high torsional stiffness (Bredt''s formula) — essential for curved bridge where torsion is dominant
Box girders need no prestressing
Only for shallow water crossings
Correct Answer
B. Closed section provides very high torsional stiffness (Bredt''s formula) — essential for curved bridge where torsion is dominant
Why is this the answer?
Box girder (hollow rectangular or trapezoidal cross-section): very high torsional stiffness (closed thin-walled section: T = 2×A_enclosed×t×τ per Bredt''s formula). On curved alignment: dead load and live load eccentric → high torsional moments. Box girder: torsional rigidity ~100× I-section → handles curve torsion efficiently. Also: high bending stiffness, reduced self-weight, smooth aerodynamic shape. RC box girder: 30–60 m spans; prestressed: 60–250 m.
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