Oregon DOT Integral Abutment Design Criteria Bruce Johnson, PE, SE Oregon DOT State Bridge Engineer

Factors that effect deck joint movements: Use Integral Abutments whenever site conditions and structure geometry are suitable to achieve these benefits: Structure redundancy Simplified construction Reduced construction cost and time Reduced maintenance cost Stiffer longitudinal seismic response at abutments

Factors that effect deck joint movements: Properties Material in the structure Coefficient of thermal expansion Modulus of elasticity Poison ratio Sizes of structural components Construction tolerances Method and sequence of construction

Factors effects joint Movements: Properties Skew and curvature Approach pavement growth Substructure movement due to embankment construction Static and dynamic structural responses and their interaction

More Benefits of Integral Abutments Greater end span ratio ranges Simplified widening and replacement Improved ride quality Enhance protection for weathering steel Tolerance problems are reduced

Potential Savings from Integral Abutments Eliminates expansion joints and bearings Cost less to construct and maintain Provide additional efficiencies in overall structure design Simple design Jointless construction Rapid construction

Applicability of Integral Abutments? 80% of the U.S. bridges have total length of 180 ft. or less

When to use I.A? When the end bent is founded on piles. When bedrock is a minimum of 15 feet from the bottom of the pile cap. Avoid using pre bored piles when bedrock is close to the surface, since this type of construction has been uneconomical.

When to use Semi-Integral Abutments

When to use Integral Abutments When the radius of horizontal curvature is greater than 1200 ft.

When to use Integral Abutments When the skew angle is less than 30 degrees.

Temperature Fall

When to use I.A? When there is negligible potential of abutment settlement. Riding limit comfort (Wahls and Stark et l.)

Soil Improvement Methods Waiting periods Surcharging Installation of vertical drains Dynamic compaction Compaction piles Compaction grouting Stone columns Deep soil mixing (flyash, cement, soil) Embankment piles

Design Criteria Specify placement and compaction requirements and an increased frequency of field density test requirements (minimum of two tests per stage of construction at each end bent) of the backfill material to achieve consistent soil stiffness behind both end bents.

Design Criteria Detail piles of integral abutments to resist uplift force from temperature movement generated from differential heat on the deck.

Design Criteria UPLIFT, solar energy

Design Criteria

Design Criteria Consider the friction force between the base of the impact panel and structure back fill (compression and tension) in the superstructure design at the service limit state (assume friction coefficient of 0.54 unless specific consideration is made to reduce friction).

Design Criteria Consider longitudinal loads induced into integral abutment piles at the lower elevation end bent due to braking force in addition to temperature change. This force increases as the grade profile becomes steeper. Similarly, piles at the lower elevation end bent shall be designed to resist the component of the earth pressure (lateral and vertical) from the higher elevation end bent.

Design Criteria

Design Criteria Use H-pile with strong axis in the direction of temperature movement.

Abutment movement of skewed and/or curved bridges

Design Criteria Limit the maximum range of each end bent movement due to temperature rise and fall at all service limit states to three (3.0) inches, and limit yielding of each H-pile flange to 20% of the flange area.

Design Criteria Consider relative stiffness of the super-structure, substructure, and any asymmetric span lengths in calculating end bent movement. The movement of the end bents due to temperature fall or rise may require a limitation less than three (3.0) inches when the structure has multiple spans with fixed interior bents

Design Criteria Consider the combination of worst case events (except seismic) with temperature rise and fall.

Effect of temperature rise

Design Criteria Consider the effect of torsion in all components connected to abutment in integral abutment design. Embed piles into the pile cap to develop moment fixity.

Design Criteria

Design Criteria Do not use integral abutments supported by an MSE retaining wall. Semi-integral abutments are preferred in these cases.

Design Criteria Connect superstructure and end bents with a closure pour. Require a minimum of three days wait period between concrete deck placement and closure pour to release shrinkage stress in bridges with steel superstructures and include long term creep in your design for concrete superstructures. Include a note which requires backfill behind the abutment after closure pour.

Design Criteria Provide an expansion joint between the end panel and the approach pavement where the range of abutment movement is one (1) inch or less. Where the range of abutment movement exceeds one (1) inch, fix the end panel to the superstructure and provide an expansion joint between the end panel and the deck.

Bridge End Panel

Design Criteria In a staged bridge construction, to minimize rocking effects of girders in next stage of construction due to adjacent traffic loading, provide an expansion joint or closure segment in the pile cap located between the stages of construction. For integral abutments, consider the effects of traffic vibrations on adjacent bridge girders and the concrete deck in next stage of construction.

Design Criteria Specify deck casting sequences and deck closure pours at integral abutment connections and specify the range of temperature when the contractor may place the concrete on the plans and in the special provisions.  Keep the range of temperature in the closure pour to not adversely affect the pile behavior during temperature fall or rise.

Design Criteria

NCHRP Synthesis 234 Settlement of Bridge Approaches

NCHRP Synthesis 234 Settlement of Bridge Approaches

Design Criteria  Develop a LPILE model using the full pile for soil and pile interaction. Use a U-abutment (wingwalls parallel to roadway alignment) if possible.

Construction and Maintenance of Integral Abutments (isolated comments) Longer wingwalls may be necessary with cast-in-place, post-tensioned bridges for backwall containment; The proper compaction of backfill material is critical; Careful consideration of drainage at the end of the bridge is necessary; Wingwall concrete should be placed after stressing of cast-in-place, post-tensioned bridges;

Const. & Maint. IA (isolated comments) continued The effects of elastic shortening after post-tensioning should be carefully considered, especially on single span bridges; Proper placement of piles is more critical than for conventional abutments; Wingwalls may need to be designed for heavier load to prevent cracking; Adequate pressure relief joints should be provided in the approach pavement to avoid interference with the function of the abutment;

Const. & Maint. IA (isolated comments) continued Possible negative friction forces on the piles should be accounted for in the design; and Wide bridges on high skews require special consideration including strengthening of diaphragms and wingwall-to-abutment connection.

Thanks for your attention!