Structures and Hydraulics Website- Glossary

Abutment – A solid structure, usually a retaining wall or pier that also supports a vertical load, such as an arch or bridge.

Accelerated Bridge Construction (ABC) – Approach to bridge construction that provides an accelerated construction time frame utilizing short term road closures and minimizing impacts to resources, the environment, traveling public, etc.

Accelerated Bridge Program (ABP) – VTrans program that aims to accelerate bridge construction projects through the project delivery and construction phases.

American Association of State and Highway Transportation Officials (AASHTO) – Nationally recognized organization that represents highway and transportation departments in the United States representing various transportation modes. Provides numerous standards relating to the transportation sector including the specifications for the design and construction of bridges in the United States.

Annual Exceedance Probability (AEP) – The likelihood that a natural event (i.e. storm/ flood) will occur in any given year, reported as a percent.

Approach Railing – Section of guardrail used to transition from or to bridge railing.

Approach Slab – Concrete slab placed before and after a bridge to protect against settlement of the roadway and earthwork directly behind a bridge substructure and to provide a smooth transition on and off the bridge riding surface.

Average Annual Daily Traffic (AADT) – Total volume of vehicle traffic on a bridge or roadway segment for a year divided by 365.

Average Daily Traffic (ADT) – The average daily vehicle traffic on a bridge or roadway segment in a given period.

Bankfull Width (BFW) – The distance between channel bankfull elevations, which is the elevation at which flow first floods over the bank into the floodplain.

Bituminous Concrete Pavement – Technical term for a composite material containing aggregate bound with asphalt and compacted. Typically used as a finish surface for roadway networks, parking lots, and drive ways. Also known as Hot Mix Asphalt (HMA), pavement, and blacktop.

Boring – A drilled core sample of earth that provides information regarding the subsurface conditions of an area.

Bridge Bearing – Device placed under a bridge superstructure that allows controlled movement of a bridge due to effects such as temperature change, vibration, and seismic activity.

Bridge Expansion Joint – Joint between adjacent bridge spans or between the bridge surface and the approach roadway surface. Intentional joints help prevent cracking of pavement and concrete, as well as reduce significant stresses on a bridge from effects caused from movement due to temperature change, vibration, and seismic activity.

Bridge Railing – Longitudinal barriers connected directly to a bridge that protect vehicular and pedestrian traffic from leaving the travel way. Typically bridge railing is crash tested and is designed to prevent penetration from a crash.

Bridge Seat – Surface in which the superstructure of a bridge sits on top of the abutment. Often times there is a bridge bearing that is placed between the surface of the bridge seat and the bottom surface of the superstructure.

Camber – Intentionally fabricating a structural element with a slight upward curve in order to counter the dead load deflection that the element will experience.

Cantilever – A rigid structural element, such as a beam or a plate, anchored at only one end to a (usually vertical) support from which it is protruding.

Channel – A type of landform consisting of the outline of a path of relatively shallow and narrow body of fluid, most commonly the confine of a river.

Channel Armoring – A technique used to protect a channel embankment from erosion due to flowing water by armoring the bank with stone fill.

Cofferdam – An enclosed temporary barrier that is installed to prevent the flow of water onto a construction zone or to reroute a water source in order to provide a dry area in a normally wet environment.

Cold Planing – The process of removing part of the surface of a paved area such as a roadbridge, or parking lot in order to provide enough thickness for a new pavement layer(s). Also known as pavement milling.

Concrete – A mixture of cement, fine aggregate, coarse aggregate, and water, with or without admixtures.

Condition Based Bridge Maintenance – Activities that are performed on bridge elements as needed and identified through the bridge inspection process to restore the structural integrity and correct major safety defects.

Construction Load – Dead and live load effects from construction materials, equipment, vehicles, and personnel.

Continuous Span – A bridge span extending over three or more supports that are continuously or rigidly connected so forces are transmitted from one segment to the next.

Cross Frames – A structural element used between adjacent bridge beams to brace them during construction and to provide resistance from lateral load effects.

Culvert – A structure that allows water to flow under a road, railroad, trail, or similar obstruction from one side to the other side. Typically embedded so as to be surrounded by soil, a culvert may be made from a pipe, reinforced concrete, or other material.

Cyclical Bridge Preventative Maintenance – Bridge maintenance activities performed on a pre-determined interval and aimed to preserve the existing bridge element or component conditions. Bridge elements or component conditions are not always directly improved as a result of these activities, but the deterioration is expected to be delayed.

Dead Load – Inert, inactive loads, that are primarily due to the weight of a structure or stationary structures permanently placed on a structure such as guardrail.

Deflection – The degree to which a structural element is displaced due to dead and live load effects.

Design Event – The simulated storm or flood used to predict the behavior of a proposed hydraulic system.

Design Hour Volume (DHV) – The highest hourly expected volume of vehicular traffic on a bridge or road segment.

Diaphragms – A single structural element used between adjacent bridge beams to brace them during construction and to provide resistance from lateral load effects.

Downspout – A pipe used to carry stormwater from a rain event off of a bridge. Typically, downspouts are vertical pipes made of plastic or metal that discharge directly into a river or stream below a bridge.

Drainage Area – The specific portion of the earth’s surface upon which falling precipitation flows to a given location. With respect to a highway, this location may either be a culvert, the farthest point of a channel, or an inlet to a roadway drainage system.

Drilled Shaft – A high-capacity, cast-in-place deep foundation element constructed using an auger in which an abutment or pier sits on. Also known as a caisson.

Drop Inlet – A drainage inlet with a horizontal or nearly horizontal opening.

Earth Pressure – The force that acts upon a structure due to the pressure of the soil retained behind and above the structure.

Easement – A right to use or control the property of another for designated purposes.

Embankment – A raised structure constructed of natural soil from excavation or borrow sources.

Erosion – The action of surface processes (such as water flow or wind) that remove soil, rock, or dissolved material from one location, then transport it away to another location.

Erosion Prevention and Sediment Control (EPSC) – Measures put in place to control the erosion of earthwork and transport of sediment during a project.

Excavation – The process of moving earth, rock or other materials with tools, equipment or explosives. It includes earthwork, trenching, wall shafts, tunneling and underground. 

Fascia – The exposed vertical, outside face of a bridge deck.

Federal Aid System (FAS) – State roadway system that receives federal financial assistance for construction, maintenance, and operation activities.

Finished Grade – The condition and elevation of a surface, element, or structure in its final condition.

Footing – A structural element, typically made of reinforced concrete, that prevents structures from settling by transferring loads from a structure to the ground.

Fracture Critical – A component of a bridge in which failure of that component would cause a portion of or the entire bridge to collapse.

Functionally Obsolete – Status used to describe a bridge that is no longer functionally adequate. Reasons for this status include a bridge that doesn't have enough lanes to accommodate the current traffic flow.

Galvanizing – A protective layer of zinc that is applied to steel or iron that is durable and has low maintenance requirements. Typically used as a substitute for paint in locations that would see excessive deterioration from the environment.

Geotechnical – Branch of civil engineering concerned with the engineering behavior of earth materials. Uses principles of soil mechanics and rock mechanics to investigate subsurface conditions and materials, design earthworks and structure foundations, and monitor site conditions, earthwork and foundation construction.

Geotextile – A planar, permeable, polymeric (synthetic or natural) textile material that may be woven, nonwoven, or knitted. Typically used to prevent erosion and to control excess sediment from washing into water resources.

Grout – A fluid concrete material typically used in small quantities for closure pours to connect adjacent structural elements, to repair deteriorated concrete, and to embed rebar sections.

Grubbing Material – Vegetated earthwork material that is used on stone fill along streams to promote the growth of vegetation.

Guardrail – A barrier on the side of the road or between adjacent roadways that protect vehicles from leaving the travel way and reduce the risk of serious accidents.

Headwall – A small retaining wall placed at the outlet of a stormwater pipe or culvert.

Headwater – The water depth measure from the flow line (invert) of the culvert inlet to the water surface elevation.

Historic Preservation – VTrans department that specializes in protecting the historic integrity of a structure or area during a transportation related project.

Horizontal Alignment – The aspect of a roadway network pertaining to the horizontal plane, which consists of a series of tangents (straight sections) and curves.

Hydraulics Manual – VTrans manual developed by the Hydraulics section to identify approaches to the analysis of roadway and highway hydraulics.

Hydraulics/ Hydrology – The science of dealing with the occurrence and movement of water upon and beneath the surface of the earth. Overlaps and includes portions of other sciences such as meteorology and geology. The particular branch of hydrology that a design engineer is generally interested in is the surface runoff which is the result of excess precipitation.

Integral Abutment – A concrete bridge substructure that is supported by steel piles and allows a bridge superstructure to move with the substructure, eliminating the need for bearings and bridge expansion joints.

Invert – The inside bottom of the structure; for an open-bottom culvert or bridge, the invert is the elevation of the channel’s low point at the location of analysis.

Lateral Slide – A bridge construction technique that allows a bridge to be built alongside an existing structure, while maintaining traffic on the existing bridge. The existing bridge is then removed and the new bridge slid into place.

Limits – The entire area that will be disturbed during a transportation related project.

Live Load – The weight of all non-permanent objects in a structures, including vehicles and people. Live load does not include seismic or wind loading.

Load Rating – The determination of the live load carrying capacity of a bridge.

Low Beam Elevation – The lowest elevation of the components of a bridge superstructure. This elevation is used to determine the hydraulic capacity of a bridge opening and whether sufficient clearance from the waterway will be provided in storm events.

Manual for Assessing Safety Hardware (MASH) – Federal guidance for crash testing safety hardware devices for use on the National Highway System (NHS).

Mechanically Stabilized Earth (MSE) Wall – A soil-retaining system with steel or geosynthetic reinforcement in the reinforced zone connected to vertical facing elements. It can be used for retaining wallsbridge abutments, seawalls, etc.

Membrane – A material or structure acting as a boundary, lining, or partition between two surfaces such as between a concrete bridge deck and a paved surface.

National Highway System (NHS) – A network of strategic highways within the United States, including the Interstate Highway System and other roads serving major airports, ports, rail or truck terminals, railway stations, pipeline terminals and other strategic transport facilities.

Ordinary High Water (OHW) – The line on the shore established by the fluctuations of water and indicated by physical characteristics such as a clear, natural line impressed on the bank, shelving, changes in the character of soil, destruction of terrestrial vegetation, the presence of litter and debris, or other appropriate means that consider the characteristics of the surrounding area.

Overhang – The area on a bridge deck that extends from the outermost girder or beam to the edge of the bridge deck.

Peak Flow – Maximum momentary stage or discharge of a stream in a flood.

Permit Trucks – Large trucks that require special permits in order to traverse across a state owned bridge or roadway network.

Phased Construction – Construction practice in which portions of a bridge, culvert, or roadway are built in multiple phases in order to maintain traffic through the project site during construction.

Pier – A vertical structure that acts as an intermediate support on a bridge in order to span across a landscape feature such as a canyon or body of water.

Pile – A vertical structural element of a deep foundation that is driven or placed in a pre-drilled hole into the ground to support a structure or foundation. Can be made of timber, steel, or concrete.

Plate Girder – A steel beam comprised of a top and bottom plate (flanges) and a web that connects them using a weld to form an I shape.

Precast Bridge Unit (PBU) – Bridge superstructure that is composed of precast concrete deck segments poured on steel rolled beams or steel plate girders. Typically fabricated for a project off-site and then assembled in the field with a crane and a concrete closure pour that ties the segments together. 

Precast Concrete – A construction product that casts concrete in a controlled environment and is later delivered to a project site for use. Typically used in applications when it is necessary to expedite the project closure period.

Prefabricated Bridge Elements and Systems (PBES) – Structural components and systems of a bridge superstructure or substructure that are prefabricated off site in a controlled environment. Typically used to accelerate the bridge construction process.

Prestressed Concrete – Structural concrete in which internal stresses have been introduced to reduce potential tensile stresses in the concrete resulting from loads. This introduction of internal stresses is usually accomplished through the use of tendons that are tensioned or pulled tight prior to being anchored to the concrete.

Project Initiation and Innovation – Division of the Structures section at VTrans that initiates a project by collecting all the necessary site specific information and developing possible design alternatives.

Rebar – Steel bar or mesh of steel wires used as a tension device in reinforced concrete Also known as reinforcing steel.

Redundancy – The ability of a structure to absorb the failure of a main component without the collapse of the structure. In the case of a bridge, a structure with three beams is fracture critical since if one beam fails the entire structure may collapse, whereas a bridge with four or more beams has redundancy since if one beam fails the bridge will not collapse.

Retaining Wall – A structure designed to resist the lateral pressure of soil when there is a desired change in ground elevation.

Right of Way – The legal right, established by usage or grant, to pass along a specific route through grounds or property belonging to another.

Roadway Crown – A high point along the centerline of a roadway surface that allows water to run off each side of the roadway and prevent pooling in the center of the roadway.

Rolled Beam – Standardized steel shape developed by the American Institute of Steel Construction that is fabricated by passing it through a hot rolling mill.

Runoff – (1) Water that runs off at the surface during precipitation or snowmelt event when infiltration and/or storage is exceeded or unavailable. (2) Drainage or flood discharge after rainfall or snowmelt event which leaves an area as surface flow or as piped flow and is not infiltrated.

Scour – The removal of sediment such as sand and rocks from around a structural foundation compromising the structural integrity. Usually caused by swiftly moving water from a flowing river or excessive runoff.

Scupper – A vertical hole through a bridge deck for the purpose of deck drainage. A horizontal opening in the curb or barrier is sometimes also referred to as a scupper.

Silane – A sealer applied to exposed concrete surfaces to protect them from surface damage, corrosion, and staining.

Skew – The angle between a normal/perpendicular to the alignment/centerline of the bridge and the centerline of the substructure. This is usually done to accommodate the natural flow of water that a bridge spans without increasing the bridge length significantly.

Slip-lining – A trenchless method of rehabilitating a segment of existing pipeline by fitting a smaller pipe inside the original pipe, fitting the space between the pipes with grout, and sealing both the upstream and downstream ends.

Spalling – Flakes of a material that are broken off a larger solid body produced by a variety of mechanisms, including as a result of projectile impact, corrosionweatheringcavitation, or excessive rolling pressure.

Span – The distance from the centerline of one bridge support to the centerline of the adjacent bridge support.

Splice – To join two similar materials such as piles, reinforcing steel, or girders together at the ends.

Stone Fill – Rocks used to protect a channel, ditch, slope, or structural component from erosion. The size of rocks depends on the flow characteristics and grade of an area.

Stopping Sight Distance – The distance that allows a driver traveling at the maximum speed to stop before hitting an object.

Structurally Deficient – A bridge that has a deck, superstructure, substructure, or culvert that is rated in poor condition.

Structures Design Manual – Comprehensive VTrans manual for the design and analysis of bridges specific to the State of Vermont.

Subbase – A layer of aggregate placed on the existing soil as a foundation for the base.

Substructure – The part of the bridge structure, i.e. piers and abutments, which supports the superstructure and transfers the structural load to the foundations and earth.

Superelevation – Roadway banking on a horizontally curved roadway or bridge that allows vehicles to maintain the traveled speed.

Superstructure – The entire portion of a bridge structure which primarily receives and supports loads and, in turn, transfers the reactions to the bridge substructure. The superstructure consists of everything above the bridge bearings including the beams, girders, truss, deck, pavement, sidewalk, and guardrail.

Swale –A natural ditch or long, shallow depression through which accumulated water from adjacent watersheds drain to lower areas.

Temporary Bridge – A bridge that is intended for non-permanent use to either replace a deteriorated structure temporarily or to bypass the construction of a new bridge.

Thalweg – The line of lowest elevation along a stream bottom.

Underdrain – A perforated pipe at the bottom of a detention basin, channel or swale that allows the feature to drain.

Vertical Alignment – The aspect of a roadway network pertaining to the vertical plane, which consists of crests (upward curves), sags (downward curves), and the straight grade lines connecting them.

Watershed – An area or ridge of land that separates waters flowing to different rivers, basins, or sea.

Wearing Surface – The top layer of a road that carries the traffic; road surface.

Weathering Steel – A group of steel alloys which were developed to eliminate the need for painting, and form a stable rust-like appearance as if exposed to the weather for several years.

Wetlands – A land area that is saturated with water, either permanently or seasonally, such that it takes on the characteristics of a distinct ecosystem. Wetlands are considered some of the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal life.

Wingwall – Retaining walls that are adjacent to the abutment of a bridge and can either be attached directly to the abutment or stand independently.


AASHTO LRFD Bridge Design Specifications, Seventh Edition, 2014. American Association of State Highway and Transportation Officials, Washington, DC.

Integral Abutment Bridge Design Guidelines. Second Edition, 2008. Vermont Agency of Transportation, Structures Section, Montpelier, VT.

Lindeburg, Michael R. Civil Engineering Reference Manual for the PE Exam, Thirteenth Edition, 2012. Belmont, CA: Professional Publications.

Oxford Dictionary of Construction, Surveying, and Civil Engineering.

US Department of Transportation, Federal Highway Administration (FHWA).

VTrans Hydraulics Manual. 2015. Vermont Agency of Transportation, Hydraulics Unit, Montpelier, VT.

VTrans Structures Design Manual. Fifth Edition, 2010. Vermont Agency of Transportation, Structures Section, Montpelier, VT.

Wikipedia, The Free Encyclopedia.