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Wing wall
Wing wall
Wing wall
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The entrance to Hassenplug Covered Bridge in Mifflinburg, Pennsylvania is flanked by wing walls.

A wing wall (also "wingwall" or "wing-wall") is a smaller wall attached or next to a larger wall or structure.

Bridges

[edit]

In a bridge, the wing walls are adjacent to the abutments and act as retaining walls. They are generally constructed of the same material as those of abutments. The wing walls can either be attached to the abutment or be independent of it. Wing walls are provided at both ends of the abutments to retain the earth filling of the approaches. Their design depends upon the nature of the embankment and does not depend upon the type or parts of the bridge.[1]

The soil and fill supporting the roadway and approach embankment are retained by the wing walls, which can be at a right angle to the abutment or splayed at different angles. The wing walls are generally constructed at the same time and of the same materials as the abutments.

Classification of wing walls

[edit]

Wing walls can be classified according to their position in plan with respect to banks and abutments. The classification is as follows:

  1. Straight wing walls: used for small bridges, on drains with low banks and for railway bridges in cities (weep holes are provided).
  2. Splayed wing walls: used for bridges across rivers. They provide smooth entry and exit to the water. The splay is usually 45°. Their top width is 0.5 m, face batter 1 in 12 and back batter 1 in 6, weep holes are provided..
  3. Return wing walls: used where banks are high and hard or firm. Their top width is 1.5 m and face is vertical and back battered 1 in 4.[2] Scour can be a problem for wing walls and abutments both, as the water in the stream erodes the supporting soil.[3]

Other uses

[edit]

Wing walls provide smooth entry of water into the bridge site and provide support and protect the embankment. Wing walls can serve as buttresses to support walls.[4] They can also be purely decorative.[5]

References

[edit]
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Wing wall

View on Grokipedia
from Grokipedia
A wing wall is a structure integral to bridge substructures, positioned at the ends of s to contain and stabilize the approach roadway embankment fill, thereby supporting the roadway while minimizing the volume of earth required and preventing or lateral movement. These walls are typically constructed from and can be either integral to the or independent, depending on design needs, and they play a critical role in maintaining the structural integrity of bridges by retaining fill behind the stem. Wing walls are essential components in , particularly for and bridges, where they extend from the to guide the transition from the elevated bridge deck to the ground level approach. Their primary functions include retaining , directing flow away from the to reduce scour, and providing lateral support to the embankment, which enhances overall stability and longevity of the . In addition to bridges, wing walls may be adapted for culverts or other retaining applications, but their most common use remains in systems to balance costs with site-specific and geometric constraints. Design variations of wing walls are selected based on factors such as depth, site topography, and embankment height, with three principal types: extension wings, which project straight from the parallel to the bridge centerline for simplicity but require more fill; return wings, which follow the superstructure's to minimize fill volume at the expense of additional concrete; and flared wings, which angle outward to bisect the roadway and centerline for an optimal balance of cost and earth retention. abutments often mandate extension wings to accommodate movements, while flared configurations are prevalent in standard designs due to their efficiency in diverse conditions. Proper , drainage provisions, and foundation detailing are vital to withstand lateral earth pressures, hydrostatic forces, and potential seismic loads.

Bridge Engineering

Definition and Components

A wing wall in bridge engineering is defined as a retaining wall that extends laterally from the ends of a bridge , typically at an oblique angle, to support the approach roadway embankment and prevent along the bridge approaches. These structures are essential substructure elements that transition the bridge to the surrounding terrain by containing fill material and stabilizing slopes. Wing walls originated in 19th-century bridge designs, where they were incorporated into abutments of early stone and timber structures to enhance embankment stability, as seen in numerous historic U.S. bridges from that era. The primary components of a wing wall include its connection to the , which is usually integral for load transfer; the wall face, a vertical or slightly battered surface that directly retains the ; the backfill interface, where compacted or is placed behind the wall to distribute loads; the foundation footing, often shared with the abutment for support against settlement; and internal , such as embedded in to resist tensile forces from earth pressure. In typical configurations, wing wall height aligns with the height to ensure uniform embankment support, while lengths are determined by site-specific and conditions. For instance, in standard designs, wall thickness is commonly 1 foot, with footings extending 2.5 to 3 feet in depth for foundational stability. These elements collectively form a cohesive unit that also aids in directing water flow away from the .

Functions in Bridge Structures

Wing walls in bridge structures primarily function to retain the approach roadway fill material, thereby containing the embankment and preventing lateral spread of behind the abutments. They also direct water flow under the bridge openings, guiding stream currents away from the abutment foundations to reduce turbulence and associated . Additionally, wing walls stabilize the s by resisting lateral earth pressures exerted by the retained fill and any surcharge from traffic loads on the approaches. These components offer several key benefits, including the reduction of settlement risks in the approach embankments by ensuring compaction and load support. Wing walls enhance the overall load distribution from the bridge to the foundation by providing a rigid extension that transfers horizontal forces effectively into the . Furthermore, they minimize at the bridge ends by channeling high-velocity flows and protecting the embankment toes from scour, particularly when combined with armoring like . In skewed bridges, where the alignment crosses the waterway at an oblique angle, wing walls are typically splayed or flared to better align with the natural flow direction, thereby avoiding hydraulic issues such as increased shear stresses or localized scour hotspots. The 2015 collapse of the Tex Wash Bridge over was partly due to inadequate wing wall design, as the perpendicular orientation to flood flows exacerbated scour and led to embankment during a severe storm event.

Classification

By Geometry

Wing walls in bridge engineering are classified by their geometry, which refers to their shape and orientation relative to the bridge abutment and roadway alignment, influencing how they integrate with the surrounding embankment. This classification helps engineers select designs that accommodate site-specific conditions such as skew angles and terrain constraints, ensuring structural efficiency and minimal disruption to natural flow patterns. Straight wing walls, also known as parallel wing walls, extend perpendicular to the abutment face and run parallel to the roadway direction. They are typically employed in bridges with minimal or zero skew angles, where the roadway alignment is straightforward. The primary advantage of this geometry is its simplicity in design and construction, allowing for straightforward reinforcement and formwork. However, straight wing walls can experience higher lateral earth pressures due to their direct confrontation with the embankment soil, potentially requiring thicker sections or additional reinforcement to maintain stability. Splayed or flared wing walls diverge outward from the at an , commonly between 15 and 45 degrees relative to the abutment face. This configuration is particularly effective for directing embankment fill material away from the bridge structure and facilitating the natural diversion of runoff, thereby reducing hydrostatic pressures on the wall. By angling outward, splayed walls effectively lower the retained soil height at the abutment interface, which can decrease the overall structural demands compared to straight designs. Return wing walls feature a curved or folded-back profile that bends toward the embankment, often forming a U-shape or returning parallel to the roadway after an initial . These are suited for bridges with sharp skew angles exceeding 30 degrees or in constrained urban environments where space is limited and direct extension might encroach on adjacent properties. The return geometry minimizes the while providing a smoother transition to the natural ground, though it may introduce complexities in earth pressure distribution due to the . Selection of wing wall depends primarily on the bridge's skew and the embankment slope. Straight walls are preferred for low skew angles on moderate slopes, while splayed designs are recommended for moderate to high skews to better accommodate oblique alignments and reduce soil thrust. In cases of steep embankments or severe skews, return walls offer optimal adaptation by aligning more closely with the , as outlined in standard highway design guidelines. These choices also briefly support functional benefits, such as improved water guidance along the structure.

By Construction Type

Wing walls in bridge engineering are classified by construction type based on their structural integration with the , which influences load transfer, movement accommodation, and suitability for site conditions. The primary types include cantilevered, free-standing, and hybrid configurations, each addressing different requirements for support and durability. Cantilevered wing walls are constructed monolithically with the abutment, relying on a moment-resisting connection to transfer loads directly from the wing to the abutment stem. This design treats the wing as a horizontal cantilever extending from the abutment body, typically limited to lengths of 6 to 8 feet for straight or U-back configurations to prevent excessive deflection. Reinforcement layout includes vertical torsion blocks at the corners to resist high torsional moments, with additional #5 bars lap-spliced to horizontal reinforcement in the abutment and wing, alongside 5 #8 or #9 bars for tension and bi-axial bending per AASHTO LRFD specifications. Such walls are suitable for short spans and high earth pressures, providing a rigid system that settles as a unit with the abutment. Free-standing wing walls function as independent structures tied to the via construction joints, allowing differential settlement and designed as nominal retaining walls with separate foundations. This approach accommodates longer extensions than cantilevered designs, and includes expansion joints—such as 1-inch preformed fillers or joints—to permit thermal and seismic movements without stressing the main . They are preferred in seismic zones for their flexibility, as the independent support reduces the risk of cracking from differential displacements during earthquakes, requiring seismic in categories C or D. In integral abutments, cantilevered wing walls are preferred over free-standing types to eliminate joints and simplify , enhancing overall structural by minimizing potential leak paths and movement interfaces. Hybrid types combine elements of both, such as cantilevered sections transitioning to free-standing for extended lengths on complex sites with varying or load demands, allowing optimized support while balancing rigidity and flexibility.

Design and Construction

Materials and Specifications

Wing walls in bridge engineering are predominantly constructed using , which provides the necessary strength and to withstand pressures and environmental loads. The typically achieves a of 4,000 to 5,000 psi, ensuring structural integrity while allowing for economical construction. This material choice aligns with standard practices outlined in state guidelines, where 4,000 psi is commonly specified for wing walls and headwalls in reinforced concrete structures. For historic bridges, masonry—often stone or brick—is used for wing walls, offering aesthetic continuity and proven longevity in older designs. These materials were selected for their availability and resistance to weathering prior to the widespread adoption of reinforced concrete. In modern applications seeking lightweight alternatives, geosynthetic-reinforced soil systems incorporate geotextiles or geogrids within compacted soil to form wing walls, reducing material volume and construction time in geotechnically challenging sites. Key specifications for wing walls follow AASHTO LRFD Bridge Design Specifications, 10th edition (2024), mandating a minimum of 2 to 3 inches over to protect against and environmental exposure. Reinforcing bars are typically Grade 60 deformed , providing a yield strength of 60,000 psi for adequate tensile capacity. Drainage provisions, such as weep holes spaced at maximum 3 meters horizontally and positioned to avoid , are required to relieve hydrostatic pressure behind the walls and prevent water buildup. Precast concrete panels are increasingly employed for wing walls in urban bridge projects, enabling rapid on-site installation—often in a single day—due to their factory fabrication and modular assembly, which minimizes traffic disruptions. In coastal environments, epoxy-coated reinforcing bars are specified to enhance resistance against saltwater exposure, extending the of the structure by forming a barrier that inhibits ingress. Thicknesses for wing walls vary depending on height, jurisdiction, and design standards; for example, DOT guidelines specify thicknesses from 10 inches for heights around 3 feet to 34 inches for heights approaching , balancing structural demands with constructability and ensuring sufficient rigidity while optimizing material use in low- to medium-height applications.

Load Analysis and Stability

Wing walls in bridge structures are subjected to various lateral and vertical loads that must be analyzed to ensure structural integrity. The primary lateral load is earth pressure from the retained soil, typically calculated using the active Rankine earth pressure theory for cohesionless backfill. This theory assumes a vertical wall face and horizontal backfill surface, with the soil reaching a state of plastic equilibrium where the lateral stress is minimized. The active earth pressure coefficient KaK_a is derived from analysis, considering the soil's internal friction angle ϕ\phi, and is given by Ka=1−sin⁡ϕ1+sin⁡ϕK_a = \frac{1 - \sin \phi}{1 + \sin \phi} For typical granular soils with ϕ\phi ranging from 30° to 35°, KaK_a values are approximately 0.3 to 0.27. The total active earth pressure force PP per unit length of the wall acts triangularly, increasing linearly with depth, and is computed as P=12KaγH2P = \frac{1}{2} K_a \gamma H^2 where γ\gamma is the soil unit weight and HH is the height of the retained soil. This force is applied at H/3H/3 above the base of the wing wall footing for stability evaluations. In wing wall design, HH includes the abutment height plus any approach embankment, and the pressure distribution is integrated with the abutment to assess combined effects. Additional loads include surcharge from traffic, which induces extra lateral pressure on the backfill. Per AASHTO LRFD specifications, 10th edition (), this is modeled as an equivalent height or uniform pressure Δp=Ka×\Delta p = K_a \times surcharge intensity, often 2 feet of equivalent for loads (Section 3.11.6.4). Hydrostatic pressure from must also be considered if the rises behind the wall, adding a uniform triangular or trapezoidal load per AASHTO Section 3.11.5, with magnitude 12γwhw2\frac{1}{2} \gamma_w h_w^2 where γw\gamma_w is water unit weight and hwh_w is submerged height; drainage systems like weep holes are typically incorporated to mitigate this. Seismic loads are evaluated using AASHTO Section 3.10, incorporating horizontal acceleration coefficients to amplify earth pressures via Mononobe-Okabe modifications to for dynamic cases, particularly in higher seismic zones. Stability against these loads is verified through checks for sliding, overturning, and at the footing level. For sliding, the (FS) is the ratio of resisting (base area times resistance) to driving horizontal forces (earth pressure plus surcharge and seismic), required to exceed 1.5 under service loads. Overturning stability compares resisting moments (from self-weight and vertical loads) to overturning moments (from lateral forces), with FS > 2.0 mandated to prevent rotation about the . ensures the beneath the footing can support eccentric vertical loads without excessive settlement or , using AASHTO Section 10.6.3 with ultimate capacity qu=cNc+γDNq+0.5γBNγq_u = c N_c + \gamma D N_q + 0.5 \gamma B N_\gamma adjusted for eccentricity, typically limited to 5-10 ksf for allowable pressures. These checks are performed at strength limit states with load factors, though traditional FS criteria are applied in serviceability assessments for wing walls integrated with abutments. Integrated analysis of wing walls with abutments often employs specialized software such as FB-MultiPier, a nonlinear finite element program that models -structure interactions, including p-y curves for lateral resistance and combined loading effects, to simulate real-world under static and dynamic conditions.

Other Applications

In Culverts and Retaining Systems

Wing walls in culverts serve a scaled-down role compared to their application in bridges, primarily retaining embankment fill around pipe or box culverts to prevent and maintain structural integrity in low-flow waterways such as small or ditches. These structures are typically integrated with headwalls at the inlet and outlet ends, flaring outward to direct flow and stabilize the surrounding , with designs often following hydraulic optimization principles to minimize head loss and scour. For instance, box culverts commonly feature wing walls flared at 30 to 75 degrees for improved performance, as outlined in (FHWA) hydraulic design criteria. As standalone retaining systems, wing walls are employed on slopes adjacent to roads or railways, where they absorb lateral pressure from embankments without supporting any , thereby providing cost-effective stabilization for earth retention in projects. These applications are particularly suited to low-volume roads, where wing walls transition fill slopes and prevent lateral movement, often designed as or types with considerations for backfill drainage and compaction to ensure long-term stability. Heights for such standalone wing walls in retaining contexts are generally limited to under 20 feet to rely on semi-empirical methods, avoiding the need for more complex analyses. In both and standalone retaining applications, reinforcement enhances wing wall performance for higher embankments, offering a cost-effective alternative by reducing use and time—often by up to 50% compared to conventional —while improving resistance to seismic and hydraulic loads. FHWA guidelines highlight -reinforced (GRS) wing walls in like the Geosynthetic Reinforced Integrated Bridge (GRS-IBS), adaptable to culverts and embankments, where layers of (e.g., with tensile strengths of 2400–4800 lbs/ft) are placed at spacings of 12 inches or less to encapsulate and extend into slopes for . Connections in culvert wing walls vary by method: cast-in-place for monolithic integration in smaller installations, or bolted plates for precast elements to accommodate modular assembly and differential settlement.

Architectural and Landscaping Uses

In , the term "wing wall" may refer more broadly to short walls that project from a main structure, such as a building facade, to define boundaries, provide privacy, or enhance , distinct from their primary use as retaining structures in . These are often seen flanking entryways or steps in residential designs to create a sense of and . In , wing walls can serve as low retaining elements for terracing sloped sites, managing retention in gardens or around patios while integrating with hardscape features for and visual appeal. They may be finished with materials like stone to blend with natural surroundings, though such applications emphasize decorative and functional harmony over structural demands.

References

  1. https://www.maine.gov/dot/sites/maine.gov.dot/files/inline-files/chpt3.pdf
  2. https://www.dot.ny.gov/divisions/engineering/structures/repository/manuals/brman_4th_edition/glossary_4-06.pdf
  3. https://wsdot.wa.gov/publications/manuals/fulltext/m23-50/chapter7.pdf
  4. https://ftp.txdot.gov/pub/txdot-info/cmd/cserve/specs/2004/standard/s466.pdf
  5. https://www.dot.ny.gov/divisions/[engineering](/page/Engineering)/structures/repository/manuals/brman_4th_edition/glossary_4-06.pdf
  6. https://www.modot.org/common-bridge-terms
  7. https://www.fhwa.dot.gov/publications/research/infrastructure/structures/04098/07.cfm
  8. https://www.pa.gov/content/dam/copapwp-pagov/en/penndot/documents/public/pubsforms/publications/pub-862.pdf
  9. https://dot.ca.gov/-/media/dot-media/programs/engineering/documents/bridge-design-practices/202210bdpchapter111abutmentsa11y.pdf
  10. https://www.cedengineering.com/userfiles/Abutments%20and%20Wingwalls%20%28Part%201%29.pdf
  11. https://wisconsindot.gov/dtsdManuals/strct/manuals/bridge/ch12.pdf
  12. https://www.nj.gov/transportation/business/research/reports/FHWA-NJ-2005-027.pdf
  13. https://avestia.com/CSEE2016_Proceedings/files/paper/ICSENM/118.pdf
  14. https://structville.com/wing-walls-in-bridges
  15. https://www.vdot.virginia.gov/media/vdotvirginiagov/doing-business/technical-guidance-and-support/technical-guidance-documents/structure-and-bridge/manuals-of-structure-and-bridge-acc/part2/chapter17.pdf
  16. https://www.atiner.gr/presentations/CIV2018-0094.pdf
  17. https://massdot.docs.mass.gov/hwy-bridge-manual/part-1/ch3-bridge-design-guidelines.pdf
  18. https://www.in.gov/dot/div/contracts/standards/rsp/sep06/sep06r/723-R-282f.doc
  19. https://stonearchbridges.com/2020/08/25/wingwalls-importance-and-repair/
  20. https://highways.dot.gov/media/5211
  21. https://wsdot.wa.gov/publications/manuals/fulltext/m23-50/chapter5.pdf
  22. https://www.dot.ny.gov/divisions/engineering/structures/repository/manuals/brman-usc/Section_15_US_2014.pdf
  23. https://www.ardot.gov/wp-content/uploads/2020/09/40m-RCB-1.pdf
  24. https://www.lindsayprecast.com/bridge-box-wing-walls
  25. https://www.cmc.com/en-us/landing-pages/epoxy-coated-rebar
  26. https://ftp.dot.state.tx.us/pub/txdot-info/cmd/cserve/standard/bridge/CD-PW-20.pdf
  27. https://highways.fhwa.dot.gov/sites/fhwa.dot.gov/files/FHWA-NHI-10-024.pdf
  28. https://www.fhwa.dot.gov/bridge/lrfd/us_ds7.cfm
  29. https://bsi.ce.ufl.edu/products/Default.aspx
  30. https://www.fhwa.dot.gov/publications/research/infrastructure/hydraulics/06138/chapt7.cfm
  31. https://pdhonline.com/courses/h136/FHWA-NHI-01-020.pdf
  32. http://glat.aegfoundation.org/wp-content/uploads/2010/08/2011_Retaining-Wall-Design-Guide-USFS_-Mohney_5_LVR_Slope-Stability.pdf
  33. https://www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/17080/17080.pdf
  34. https://www.in.gov/dot/div/contracts/standards/rsp/sep04/735r468.pdf
  35. https://www.dot.ny.gov/divisions/engineering/design/dqab/hdm/hdm-repository/chapt_19.pdf
  36. https://www.paradisevalleyaz.gov/DocumentCenter/View/132/Article-24---Walls--Fences
  37. https://www.stlouis-mo.gov/government/departments/planning/cultural-resources/preservation-plan/Part-II-Property-Types-Glossary.cfm
  38. https://columbiasc.gov/depts/planning-preservation/docs/preservation/Newsletter_CommonArchitectureTerms_Feb2020.pdf
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