Causes of Bumps at Pavement-Bridge Interface

AKM Anwarul Islam, Ph.D., P.E.Associate Professor

Youngstown State University

Amar ShuklaGraduate Student

Youngstown State University

Presenter: Amar Shukla

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Definition of Bumps

• Differential settlement of bridge and approach slab and/or approach slab and pavement

• Approach slabs are provided for smooth transition of vehicles

• Briaud et al. (1997) summarized that 25% of total bridges in the USA had bridge bumps that cost almost $100 million per year for repair

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Behavior of approach slab due to pavement settlement and bump mechanism

Original Position of Approach Slab Bridge Limit

Deck Slab Approach Slab After Soil SettlementBump

Bent or Broken Sleeper SlabBeam Approach Slab (optional)

BackfillBackwall

Pavement Surface End Bent After Soil Settlement

Pile (optional)

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Goals of Research

• Cost-effective solution to the existing problems of the bumps

• Reduce safety hazards and maintenance cost• Smoother ride to drivers

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Causes of Bumps

• Movement of soil beneath slab• Strength deficient approach slabs• Continual impact of vehicles running over

already compacted area• Insufficient compaction of soil especially of

the embankment backfill• Types of soil

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Causes of Bumps (contd.)

• Short-term and long-term settlement• Bridge-end conditions• Construction methods, roadway paving and

bridge/roadway joint• Water seepage• Traffic volume

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Experimental Investigations

• 2 bridges with bumps and 3 bridges without bumps were visited

• Atterberg Tests (Liquid Limit and Plastic Limit) and Sieve Analysis tests were conducted

• Soil samples were collected from the surface

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Experimental Investigations (contd.)

Results onBridges without bumps Bridges with bumps

COL 30 2578 COL 30 2667 COL 30 11 2L COL 30 2670 COL 30 3182

Liquid Limit 34.1 21.5 24.9 33.6 32.2

Plastic Limit 24.5 25.5 21.9 30.7 38.4

Plasticity

Index

9.6 NP 3.4 2.9 NP

AASHTO Soil

Classification

A-2-4 (0) A-3 (0) A-1-b (0) A-1-b (0) A-3 (0)

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Experimental Investigations (contd.)

• Soil is granular• Various methods through which proper

compaction of granular soil can be obtained:

Pneumatic rubber-tired rollers

Vibratory rollers

Handheld vibrating plates

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Approach slab designs in state DOTs

State Lmin (ft) h (in)

fc‘ (ksi)

As (in2/ft)

As’

(in2/ft)d‘

(in)Cc

(in)Φ Mn

(k*ft/ft)Mu

(k*ft/ft)

AZ 15 12 3 1.053 0.133 2.5 3 37.57 9.77

FL* 30 12 4.5 1.053 0.310 2.5 4 32.57 80.03

IN 20 10 4 0.630 0.203 2.5 2 19.14 30.16

KY 25 17 3.5 1.58 0 0 3 90.10 61.72

MI* 20 12 4.5 0.895 0.895 3 3 21.87 31.72

OH 30 17 4.5 2.345 0.207 3 3 129.81 90.4

PA 25 16 3.5 1.693 0.31 2.5 3 85.22 60.5

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Geometric Parameters

• Approach slab of L = 30 ft. and B = 20 ft.• Bottom Steel: #10 reinforcing bars @ 6.5 in.

c.c.

Top Steel: #5 reinforcing bars @ 18 in. c.c.

Bent Steel:#5 reinforcing bars @18 in. c.c.

Vertical Steel: #5 reinforcing bars @ 6 in. c.c.

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Model Parameters

• Surface to surface contact b/w approach slab and sleeper slab

• Bonded contact b/w approach slab and end bent

• HL-93 truck single lane loading conditions• Model was built as a simple supported• 2 models were built considering soil

underneath and soil completely moved out

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Model with soil underneath

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Model without soil underneath

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Analytical Simulation Results

• Soil underneath slab:

Deflection = 0.057 in.

Maximum Beam Stress = 569.245 lb/in2.• Soil moved out

Deflection = 0.179 in.

Maximum Beam Stress = 3028.978 lb/in2.

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Approach Slab Model under HL-93 with soil underneath

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Approach Slab Model under HL-93 without soil underneath

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Recommendations for Ohio Approach Slab

• ΦMn calculated by using ODOT specs. = 128.91 kip-ft.

• Mu calculated by using ALGOR values = 139.95 kip-ft.

• Design of approach slab

L = 30 ft. B = 20 ft.

Bottom reinforcement = #10 @ 5.5 in c.c

Top reinforcement = #5 @ 18 in c.c.

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References

• American Association of State Highway and Transportation Officials, LRFD Bridge Design Specifications, 4th edition, 2007.

• Briaud, J. L., James, R. W., and Hoffman, S. B. (1997). NCHRP synthesis 234: “Settlement of Bridge Approaches (the bump at the end of the bridge),” Transportation Research Board, National Research Council, Washington, D.C., 75 pp.

• Cai, C.S., Voyiadjis, G.Z., and Shi, X. (2005). “Determination of Interaction between Bridge Concrete Approach Slab and Embankment Settlement,” Report No. FHWA/LA. 05/403, Louisiana Transportation Research Center, Louisiana Department of transportation, 152 pp.

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Causes of Bumps at Pavement-Bridge Interface

Thank You!

Any Questions?

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