Section 3: Abutment
Anchor: #i1350581Materials
Use Class C concrete (ƒ'c = 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.
Anchor: #i1350606Geometric Constraints
For abutment supporting Type IV beams, Type VI beams, or U beams, use a cap width of at least 3 ft. 3 in. For all other I-beam types, use a cap width of 2 ft. 9 in. For other structure types refer to the bridge standard drawings for recommended cap widths.
Anchor: #i1350637Design Criteria
For calculating horizontal forces, use 40 lbs. per cu. ft. equivalent fluid pressure with 2 ft. of surcharge if no approach slab is used. Retaining type abutments in questionable soils may justify a more rigorous analysis.
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, available at http://crossroads/org/gsd/books/det/index.htm, or applicable bridge standard drawings, available at http://www.dot.state.tx.us/ insdtdot/orgchart /cmd/cserve/standard/bridge-e.htm.
- 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.
- If no approach slab is used, calculate the horizontal
forces using 40 pcf equivalent fluid pres-
sure with a surcharge of
,
where k = 0.25, 
= 120 pcf. For
abutments with d < 5 ft. take 
= 4.0 ft. For all other
abutments see AASHTO LRFD Table 3.11.6.4-1. Retaining type abutments
in questionable soils may justify a more rigorous analysis.
- Provisions of AASHTO LRFD Bridge Design Specifications, 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.
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 to the vertical load the load caused by 40-lb. per cu. ft. fluid pressure from the bottom of the cap to 2 ft. above the roadway surface. The back pile should not be allowed to go into tension due to the lateral load, considering dead load and soil pressure only.