M6 Grand Rapids consists of 187-ft long S02 and 223-ft long S03 simple span bridges with twin box girder bridge superstructures. These bridges required the replacement of the existing superstructure which had plate girders as steel erection issues were experienced by the previous design (by others) due to heavy skew and moderate curvature. Sena Kumarasena, Ph.D., PE served as the bridge Task Manager and Technical Lead for replacement design. The new box girder designs incorporated two design advancements. The first development relates to the top lateral bracing layout where primary bracing forces due to bending and torsion were positioned mitigating one another thereby reducing the member and connection forces by 50%. The second advancement is the use of full-depth diaphragms between the two boxes at several locations along the span to make the twin box superstructure system redundant to the extent that these simple span bridges can be shown by analysis to be failure resistant to complete damage to anyone of the two boxes.
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