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Section 3: Abutments

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Materials

Use Class C concrete (= 3.6 ksi), and design for Grade 40 reinforcing steel, but allow use of Grade 40 or Grade 60 in the plans. Higher strengths may be required in special cases.

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Geometric Constraints

For abutments supporting Tx62 or Tx70 girders, use a cap width of at least 4.00 ft. and 42 in. drilled shafts. For all other TxGirder types, use a cap width of 3.50 ft. and 36 in. drilled shafts.

For abutments supporting Type IV beams or U beams, use a cap width of at least 3.25 ft. and 36 in. drilled shafts. For abutments supporting Type VI or VI(Mod) beams, use a cap width of at least 4.00 ft. and 42 in. drilled shafts. For all other I beam types, use a cap width of 2.75 ft. and 30 in. drilled shafts.

For all other structure types refer to the bridge standard drawings for recommended cap widths.

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Design Criteria

Use the following design practice for standard type “stub” abutments with backwalls:

  • Position the backwall, wing wall lengths, wing wall support, and various other standardized items as shown in the Bridge Detailing Manual, or applicable bridge standard drawings.
  • Cap, backwall, and wing wall reinforcing should conform to the Bridge Detailing Manual. Structural analysis is not required for abutments within the geometric constraints noted in the Bridge Detailing Manual.
  • Calculate the horizontal forces using 40 pcf equivalent fluid pressure at the bottom of the cap. If no approach slab is used, include a surcharge of , where k = 0.25, = 120 pcf. For abutments with d < 5 ft. take = 4.0 ft. For all other abutments see Table 3.11.6.4-1. Retaining type abutments in questionable soils may justify a more rigorous analysis.
  • Provisions of Article 5.7.3.4 need not be satisfied. Limit spacing of primary flexural reinforcing bars to no more than 18 in.

For pile foundations, use battered pairs of piling for all abutments that are not otherwise restrained from horizontal movement. Examples of sufficient restraint are slab spans and pan form spans that are doweled into the abutment, and abutments within a mechanically stabilized fill. Never use battered piling adjacent to MSE walls because of the difficulty of installing the backfill.

The maximum spacing of drilled shafts or pile groups should not exceed 16 ft. with beams 40 in. and less deep nor 12.5 ft. with deeper beams.

Maximum spacing of drilled shafts or pile groups should be within the following limits:

  • TxGirders less than or equal to 40 in. in depth - 13.50 ft.
  • TxGirders greater than 40 in. in depth - 11.00 ft.
  • All other beam types less than or equal to 40 in. in depth - 16.00 ft.
  • All other beam types greater than 40 in. in depth - 12.50 ft.

Drilled shaft loads may be calculated as the total vertical load on the cap divided equally among the cap shafts. Wing wall shaft or pile load is usually taken as 10 tons per shaft or pile.

Calculate pile loads as the total vertical load on the cap divided equally among the cap pilings. For abutments with battered piling, add the horizontal force specified above to the vertical load. The back pile should not be allowed to go into tension due to the lateral load, considering dead load and soil pressure only.


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