If a box-girder type bridge is purposely chosen because of its torsional strength, then the torsional stiffness and resistance should be considered in design. However, it is commonly accepted to assume that torsional stiffness of a beam to be negligible so that it saves the complexity to provide reinforcement to resist torsion. As such, this would result in higher bending moments induced in the beam.
If the torsional stiffness has been incorporated in computer model during the structural analysis, then it is necessary to check the torsional resistance of the beam.
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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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