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Section 7: Columns for Single Column Bents or Piers

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Materials

Use TxDOT Class C concrete (fc ́ = 3.6 ksi) and Grade 60 reinforcing steel. Higher concrete strengths may be used if needed in special cases.

Mass concrete may be needed depending on the size of the column.

Higher reinforcing steel grades may be used provided their use satisfies requirements in AASHTO.

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Geometric Constraints

Consider using hollow pier sections where appropriate. Hollow piers subject to the column collision load must be protected from the collision consistent with the protection requirements elsewhere in this manual.

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Structural Analysis

Account for second-order effects, with the structural model accounting for reduced stiffness from a cracked section.

Deflections from an analysis need to be consistent with boundary conditions of the actual structure.

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Design Criteria

For columns subjected to bending under unfactored dead load, satisfy the minimum reinforcement requirements of Article 5.6.7, using an exposure factor consistent with the site and other bridge elements.

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Detailing

For non-contact lap splices between the column and its foundation, meet the requirements of Article 5.10.8.4.2a.

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Column Collision

When the design choice is to redirect the collision load, follow the requirements given in Chapter 2 - Limit States and Loads. When the design choice is to provide structural resistance, follow the requirements in Chapter 4 - Substructure Design, Sections 6 - Columns for Multi-Column Bents using one shear plane for the resistance of the collision force.

Generally single-column bents have sufficient mass and will meet the requirements of Article 3.6.5. No further analysis is required for columns with a gross cross-sectional area no less than 40 sq. ft., a least dimension of no less than 5 ft. and column transverse reinforcement is composed of at least No. 4 ties at 12-in. maximum spacing or a No. 4 spiral at 9-in. maximum pitch.

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