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Section 9: Lateral Restraint of Bridge Superstructures on Substructure

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General

Lateral movement of superstructures can occur on water crossings due to flooding events and on grade separations due to cross slope with certain beam types. Provide effective lateral restraint in the form of shear keys as described in this section.

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Bridges Crossing Water Features

Provide details for shear keys on abutment and bent caps of I-girder, U-beam, and spread box beam (X-beam) bridges that cross water features and meet any of the following criteria:

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  • River and stream crossings: the distance between the bottom of the beam and the 100 year high water level, as shown on the layout, is less than 4 feet
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  • Tidally influenced bridges: Refer to the AASHTO Guide Specifications for Bridges Vulnerable to Coastal Storms for guidelines.
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I-Girder Bridges

Crossing Water Features:

Locate shear keys between the exterior and first interior beam on the upstream side of the bridge. This design practice supplements the use of dowels, if dowels are required.

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U-Beam Bridges

Grade Separations:

Design U-beam bridges with shear keys on bent caps when the roadway has a single-direction cross-slope. Locate shear keys between the exterior and first interior beam on the high side of cross-slope.

Crossing Water Features:

Locate shear keys between the exterior and first interior beam on the upstream side of the bridge.

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Spread Slab Beam and Spread Box Beam (X-beam) Bridges

Grade Separations:

Include shear keys on bent and abutment caps of X-beam and spread slab beam superstructures, for all allowable skews (0° through 30°) when the roadway has single direction cross-slope. Locate shear keys between the exterior and first interior beam on the high side of cross-slope.

Crossing Water Features:

Locate shear keys between the exterior and first interior beam on the upstream side of bridge.

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Slab Beam, Box Beam, Decked Slab Beam, and Double-Tee Beam Bridges

Additional lateral restraint measures are not required for slab beam, box beam, decked slab beam, and double-tee beam structures, unless the bent cap does not have an earwall.

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Steel Beam or Girder Bridges

Crossing Water Features:

Provide lateral restraints on steel bridges crossing water features.

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