Abutment
A retaining wall supporting the ends of a bridge, and, in general, retaining or supporting the approach embankment.
Approach
The part of the bridge that carries traffic from the land to the main parts of the bridge.
Approach Span
The span or spans connecting the abutment with the main span or spans.
Backwater
The increase in the upstream water elevation resulting from an obstruction to flow, such as a bridge and/or embankment placed in the floodplain.
Barrier Rail
A low, reinforced concrete wall along edges of a bridge to help prevent vehicles from going over the sides.
Beam
A horizontal structural member supporting vertical loads by spanning from one support to another. A girder is a larger beam, especially when made of multiple plates. A box beam (or girder) is a hollow box; its cross-section is a rectangle or square.
Bearing
A device at the ends of beams that is placed on top of a bent, pier or abutment. The ends of the beam rest on the bearing. The bearing transmits load from the superstructure to the substructure as well as allows for movement caused by temperature changes and rotations due to traffic.
Bedrock
The solid rock layer beneath soil, sand or silt.
Bent
A substructure unit supporting each end of a bridge span; also called a pier. It’s made up of two or more columns or column-like members connected at their top most ends by a cap, strut or other member holding them in their correct positions.
Bent Cap
A horizontal substructure element that receives the load from the superstructure and transfers the load to columns or piles.
Condition Ratings
According to the National Bridge Inspection Standards (NBIS), condition ratings are used to describe an existing bridge or culvert compared with its condition if it were new. The ratings are based on the materials, physical condition of the deck (riding surface), the superstructure (supports immediately beneath the driving surface) and the substructures (foundation and supporting posts and piers), or an overall rating for a culvert. General condition ratings range from 0 (failed condition) to 9 (excellent).
Through periodic safety inspections, data is collected on the condition of the primary components of a structure. Condition ratings, based on a scale of 0-9, are collected for the following components of a bridge. A condition rating of 4 or less on one of the following items classifies a bridge as poor.
· The bridge deck, including the wearing surface
· The superstructure, including all primary load-carrying members and connections
· The substructure, considering the abutments and all piers
The lower of the three ratings is the overall rating of the bridge:
| 9 – Excellent 8 – Very Good 7 – Good 6 – Satisfactory 5 – Fair |
4 – Poor 3 – Serious 2 – Critical/Closed 1 – Imminent Failure |
Camber
A positive, upward curve built into a beam which compensates for some of the vertical load and anticipated deflection.
Cantilever
A structural member that projects beyond a supporting column or wall and is counterbalanced and/or supported at only one end.
Cast-in-Place
Concrete poured within formwork on site to create a structural element in its final position.
Continuous Span
A superstructure that extends as one piece over multiple supports.
Crown
On road surfaces, where the center is the highest point and the surface slopes downward in opposite directions, assisting in drainage.
Culvert
A drain, pipe or conduit that allows water to pass under a road or railroad embankment.
Dead Load
The weight of the structure itself, independent of traffic or the environment, which must be supported by the structure. Compare to “live load.”
Deck
The roadway portion of a bridge, including shoulders, that directly supports vehicular and pedestrian traffic.
Drilled Shaft
The “legs” of the bridge that support the piers and pile cap or footing located underneath the water or ground line; a deep foundation unit embedded in the ground by placing fresh concrete in a drilled hole with steel reinforcement. Sometimes referred to as caissons, bored piles or drilled piers.
Embankment
A raised area, or angled grading of fill used in roadway approaches.
Fill
Earth, stone or other material used to raise the ground level, form an embankment or fill the inside of an abutment or pier.
Footing
The enlarged lower portion of the substructure or foundation that transfers load from a column directly to the soil, bedrock or piles; usually below grade and not visible.
Freeboard
The clearance between the bottom of the superstructure and the design high-water elevation.
Gabion
A galvanized wire box filled with stones used to form an abutment or retaining wall.
Live Load
The dynamic or moving weight, such as traffic, carried by a structure. Compare to “dead load.”
MSE Wall
MSE stands for Mechanically Stabilized Earth, and is soil constructed with artificial reinforcing that can be used for retaining walls, bridge abutments, dams, seawalls and dikes. The reinforcing elements used can vary but include steel and geosynthetics. MSE walls stabilize unstable slopes and retain the soil on steep slopes. The wall face is often of precast, segmental blocks, panels or geocells. The walls are infilled with granular soil, with or without reinforcement, while retaining the backfill soil. Reinforced walls utilize horizontal layers typically of geogrids. They are more easily and quickly constructed than conventional reinforced concrete walls.
Parapet
A railing system made of reinforced concrete along the outside edge of a bridge deck used to help protect vehicles and pedestrians.
Pier
Also called bent. Typically bents with one column are called piers.
Pile
A vertical shaft driven into the ground that carries loads through weak layers of soil to those capable of supporting such loads.
Poor
Significant condition issues requiring replacement or major rehab (condition rating of 4 or less).
Post-tensioning
A type of prestressing in which reinforcing tendons are fed through tubes that are covered by concrete poured into the form. Once the concrete cures and the forms are removed, the tendon is clamped on one end and jacked tighter on the other until the required tension is achieved. This produces a reinforced concrete beam with a positive camber that is able to withstand greater loads without deflection as compared to un-reinforced beams of similar dimensions.
Pre-Cast Girder
Girder is fabricated off-site of Portland cement using reinforcing steel. These girders are shipped to the construction site by truck and hoisted into place by cranes.
Prestressed Concrete
A type of pre-cast concrete girder in which compressive stresses are introduced by the application of prestressing forces in a fabrication facility. The prestressing tendons are stretched, the concrete cast and set around them and then released from the form. These forces allow the member to carry larger loads than conventional reinforcement.
Reinforced Concrete
Concrete with steel bars or mesh embedded in it for increased strength and durability.
Revetment
A facing of masonry or stones to protect an embankment from erosion.
Rip Rap
Gabions, stones, blocks of concrete or other protective covering material of like nature deposited upon river and stream beds and banks, to prevent erosion and scour by water flow.
Scour
Removal of material from the streambed or embankment as a result of erosive action of stream flow.
Simple Span
A span in which the effective length is the same as the length of the spanning structure. The spanning superstructure extends from one vertical support, abutment or pier to another without crossing over an intermediate support or creating a cantilever.
Skew
When the superstructure is not perpendicular to the substructure, a skew angle is created. The skew angle is the angle between the alignment of the superstructure and the alignment of the substructure.
Span
The horizontal space between two supports of a structure. Also refers to the structure itself. The clear span is the space between the inside surfaces of piers or other vertical supports. The effective span is the distance between the centers of two supports.
Superstructure
The component of a bridge which supports the deck or riding surface of the bridge. The superstructure consists of the components that actually span the obstacle the bridge is intended to cross. It includes:
· Bridge deck,
· Structural members
· Parapets, handrails, sidewalk, lighting and drainage features
Tendon
Steel strands used for post tensioning.
Wearing Surface
The topmost layer of material applied upon a roadway to receive the traffic loads and to resist the resulting disintegrating action; also known as wearing course.
Weight Restricted
A sign is posted at each end of the bridge advising drivers that the bridge cannot safely support the weight of any vehicles that exceed the posted weight limit even if they are otherwise legal.
Wing Walls
The retaining wall extension of an abutment intended to retain the side slope material of an approach roadway embankment.