Practices for Bridge Approach Systems (2021) / Chapter Skim
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From page 7... ...
7 Literature Review A comprehensive literature review was completed to collect information on bridge approach design and construction practices used by the state DOTs. The information presented in this chapter was compiled from the design and inspection guides and standard specifications, details, and drawings of 33 DOTs, as shown in Appendix A, and includes different components of the bridge approach system (abutments, foundations, approach slabs and wearing surfaces, expansion joints, wingwalls, backfill, and surface and sub-surface drainage systems)
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8 Practices for Bridge Approach Systems Figure 1. Schematic identifying the typical components of a bridge approach system.
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Literature Review 9 they are relatively simple to design and construct; require less complicated formwork, fewer piles, and shorter construction times; and eliminate bearings and joints. However, integral abutments are not always appropriate and the following limitations are common: • Foundation Type.
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10 Practices for Bridge Approach Systems 2.2.2 Open and Closed Abutments Abutments may also be categorized depending on whether they retain the backfill. Closed abutments fully retain the embankment and backfill by the abutment stem and backwall.
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Literature Review 11 driven deeply such that the soil provides the necessary support. These systems are typically proprietary.
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12 Practices for Bridge Approach Systems 2.3 Foundations Bridge abutments are most commonly supported on spread footings or on piles. Piles may be steel H-piles, steel pipe piles, precast-prestressed concrete piles, and CIP piles, and they may resist loads by friction along their length, by bearing at their ends, or a combination of the two.
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Literature Review 13 • Potential for Scour. At sites where there is a risk of scour, deep foundations are used because they can carry loads below the potential depth of scour.
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14 Practices for Bridge Approach Systems (West Virginia DOT 2004) -- only require approach slabs for bridges on state-owned roads or interstates, and for all bridges with integral or semi-integral abutments.
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Literature Review 15 require a bituminous overlay; Florida requires an asphalt overlay with a minimum thickness of 1.75 in. if the approach roadway is flexible pavement (Florida DOT 2020)
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16 Practices for Bridge Approach Systems – Mean Ride Index (MRI)
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Literature Review 17 potentially erosion, void formation, and clogged subdrains. As a result, most DOTs, such as Pennsylvania, Indiana, South Carolina, and West Virginia, favor configurations that eliminate joints at the abutment (Pennsylvania DOT 2019; Indiana DOT 2013b, c; South Carolina DOT 2006; West Virginia DOT 2004)
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18 Practices for Bridge Approach Systems 2.6 Expansion Joints and Sleeper Slabs Expansion joints are designed to accommodate the thermal movement and other volumetric changes of the bridge superstructure. In select scenarios, an expansion joint may be deemed unnecessary.
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Literature Review 19 suited for roads where rutting or shoving of the PMA is a risk as a result of high traffic and/or truck traffic volumes and large slopes. 2.6.2 Strip Seal Joints Versus Compression Joints Strip seal joints and compression seal joints are similar in that they both use preformed elastomeric seals and they have similar restrictions on their use.
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20 Practices for Bridge Approach Systems elastomeric concrete cures quickly and bonds well to fully cured concrete if the concrete substrate is sufficiently dry. Elastomeric concrete has higher toughness to reduce cracking and spalling resulting from traffic impacts.
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Literature Review 21 requires the calculated thermal movement of the joint to be multiplied by 1.5 or increased by 0.5 in. if the skew is between 30° and 45°, and to be multiplied by 1.75 or increased by 0.75 in.
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22 Practices for Bridge Approach Systems skew angle limits for compression joints vary widely, from a maximum of 15° to a maximum of 30°. New York State DOT states that there is no restriction on skew angle for compression joints as long as they are armorless, but acknowledges that bridges with higher skew angles perform relatively poorly compared to those with lower skew angles (New York State DOT 2019)
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Literature Review 23 Modular joints consist of a series of individual seals (called "cells") clamped between steel center beams.
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24 Practices for Bridge Approach Systems slab and the roadway pavement. Designs include buried rectangular beams, and inverted T-beams and L-beams that form part of the riding surface.
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Figure 11. Excerpt of views of approach and sleeper slabs and expansion joint detail in one of the standard drawings used by Florida DOT (Source: Florida DOT 2019)
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26 Practices for Bridge Approach Systems The details used by Arizona DOT show that a sleeper slab and foam pressure-relief joint are used when the roadway is made of rigid pavement, and a simple steel edge rail is used when the approach slab is adjacent to flexible pavement. A bond breaker consisting of hardboard and two layers of roofing paper is specified to be placed between the sleeper slab and the approach slab and pavement.
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Literature Review 27 2.7.2 Wingwall-Approach Slab Configurations Wingwalls may be integral with translating abutments and approach slabs or independent of them. When independent U-wingwalls are used, a joint permitting relative movement between the wingwall and the approach is required.
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28 Practices for Bridge Approach Systems and/or moisture content at placement, and erosion, both of which cause loss of support to the approach slabs. Occasionally, an elastic inclusion, such as a cellular material on the order of an inch thick, may be present between the backfill and the abutment to accommodate cyclic thermal movements of the abutment.
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Literature Review 29 extends to the top of the piles or the top or bottom of the footing and may run up to the approach slab or, in some cases, a subbase supporting the approach slabs. If a subbase does not support the approach, the backfill material may be extended in a horizontal layer to the roadway end.
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30 Practices for Bridge Approach Systems Moisture content must be controlled to ensure adequate compaction. DOTs generally specify that the fill is to be brought near the optimum moisture content during placement, although some permit the contractor to use the best moisture content for compaction based on their experience.
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Literature Review 31 to a sidewalk. Sometimes the decision is made based on which scenario calls for the shortest amount of pipe.
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32 Practices for Bridge Approach Systems bridge deck drains are not typically designed to accommodate additional runoff from the highway approach and to reduce joint leakage. Other DOTs such as Maine (Maine DOT 2003)
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Literature Review 33 and Other (Code 00)
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34 Practices for Bridge Approach Systems BMEs within the bridge approach system include approach slabs, wearing surfaces, and joints. Backfill and embankment material, sleeper slabs, and components of drainage systems such as inlets and underdrains are not discussed in the AASHTO MBEI.
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From page 35... ...
Literature Review 35 spreading, which are discussed in greater detail in Section 2.12, Performance Issues and Mitigation Strategies. 2.11.2 State DOT Inspection Requirements State DOTs commonly publish their own bridge inspection manuals, which identify how state policy deviates from the AASHTO MBEI.
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36 Practices for Bridge Approach Systems Figure 16. Bump between a concrete approach slab and bridge deck (Source: White et al.
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Literature Review 37 was realized in earlier studies that recommended some strategies for preventing bumps, including the following (Briaud et al. 1997; Wahls 1990)
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38 Practices for Bridge Approach Systems the approach slab was also observed, which likely resulted in erosion and a longer length of voids observed at the parapets compared to the centerline of the approach. It is noted that even though significant voids were detected, the performance of the reinforced approachslabs system was deemed satisfactory as no cracking or significant settlement was detected as a result of the presence of the voids.
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Literature Review 39 2.12.4 Lateral Spreading Lateral spreading is a relatively uncommon problem and is expensive to correct when it occurs. Lateral spreading is defined as horizontal displacement of the abutment caused by horizontal movement of the soil and can be on the order of a few inches to tens of feet (Youd 1993)
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40 Practices for Bridge Approach Systems failure, buckling of the deck, and tilt of the abutments (Youd 1993)
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