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Top Lateral Bracing in Box girders

Because of their high torsional rigidity trapezoidal box girders are appropriate structural design for curved bridge applications.

However ,although the hardened concrete provides a close box in the finished bridge, the steel girder is an open section that is rather flexible in torsion during transport and erection.

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To improve the torsional behavior during construction a top flange lateral truss is incorporated.For design purpose, This bracing can be converted into an equivalent plate thickness