Parabola
A form of arch defined by a moving point that remains equidistant from a fixed point inside the arch and a moving point along a line. This shape when inverted into an arch structure results in a form that allows equal vertical loading along its length.
Parapet
A low wall along the outside edge of a bridge deck used to protect vehicles and pedestrians.
Pier
A vertical structure that supports the ends of a multi-span superstructure at a location between abutments. Also see column and pile.
Pile
A long column driven deep into the ground to form part of a foundation or substructure. Also see column and pier.
Pile Bent
A row of driven or placed piles with a pile cap to hold them in their correct positions.
Pile Driver
A machine that repeatedly drops a heavy weight on top of a pile until the pile reaches solid soil or rock or cannot be pushed down any farther.
Pile-Supported Bridge
Pile-supported structures are supported by timber piling at regular intervals (typically 10 to 15 feet on center). A pile-supported structure can be built to any length and virtually any height.
Pin
A cylindrical bar that is used to connect various members of a truss; such as those inserted through the holes of a meeting pair of eyebars.
Pony Truss
A truss that carries its traffic near its top chord, but not low enough to allow crossbracing between the parallel top chords. Compare to deck truss and through truss.
Portal
The opening at the ends of a through truss with forms the entrance. Also the open entrance of a tunnel.
Post
One of the vertical compression members of a truss that is perpendicular to the bottom chord.
Pre-Cast Girder
Girder is fabricated off-site Portland cement using reinforcing steel and post -tensioning cables. These girders are shipped to the construction site by truck and hoisted into place by cranes.
Project Number A specific number assigned to all federal, state and local projects. The funding source (prefix), functional classification, a sequential number and possible suffix compose the elements of a project number.
Public Hearing
Meeting held with purpose of receiving public comments on proposed projects.
Pylon
A monumental vertical structure marking the entrance to a bridge or forming part of a gateway.
Railing
A fence-like construction built at the outermost edge of the roadway or the sidewalk portion of a bridge to protect pedestrians and vehicles.
Range of Stress
The algebraic difference between the minimum and maximum stresses in a member.
Reaction
The resistance of a support against the pressure of a loaded member.
Redundancy
A structural condition where there are more elements of support than are necessary for stability.
Redundant Member
Amember in a bridge that renders it a statically indeterminate structure; the structure would be stable without the redundant member whose primary purpose is to reduce the stresses carried by the determinate structure.
Reinforced Concrete
Concrete with steel bars or mesh embedded in it for increased strength in tension.
Reinforcement
Adding strength or bearing capacity to a structural member. Examples include the placing of metal rebar into forms before pouring concrete or attaching gusset plates at the intersection of multiple members of a truss.
Resonance
The regular vibration of an object as it responds in step (at the same frequency) with an external force.
Retractile Draw Bridge
A bridge with a superstructure designed to move horizontally either longitudinally or diagonally from "closed" to "open" position, the portion acting in cantilever being counterweighted by that supported on rollers; also known as traverse draw bridge.
Revet
The process of covering an embankment with stones.
Revetment
A facing of masonry or stones to protect an embankment from erosion.
Rib
Any one of the arched series of members that is parallel to the length of a bridge, especially those on a metal arch bridge.
Rigger
An individual who erects and maintains scaffolding or other inspection access equipment.
Rigid
Ability to resist deformation when subjected to a load.
Rigidity
The measure of a structure's ability not to change shape when subjected to a load.
Rigid Frame
A structural frame in which the members are connected together without hinges. Rigid Frame Bridge
A type of girder bridge in which the piers and deck girder are fastened to form a single unit. Unlike typical girder bridges that are constructed so that the deck rests on bearings atop the piers, a rigid frame bridge acts as a unit. Pier design may vary.
Rigid Frame Pier
A pier with two or more columns and a horizontal beam on top constructed monolithically to act like a frame.
Rip Rap
Gabions, stones, blocks of concrete or other protective covering material of like nature deposited upon river and stream beds and banks, lake, tidal or other shores to prevent erosion and scour by water flow, wave or other movement .
Rivet
A metal fastener used in pre-1970 construction; made with a rounded preformed head at one end and installed hot into a predrilled or punched hole; the other end was hammered into a similar shaped head thereby clamping the adjoining parts together. Riveted Connection
A rigid connection of metal bridge members that is assembled with rivets. Riveted connections increase the strength of the structure.
Riveted Joint
A joint in which the assembled members are fastened by rivets.
Rocker Bearing
A bridge support that accommodates expansion and contraction of the superstructure through a rocking action.
Rocker Bent
A bent hinged or otherwise articulated at one or both ends to provide the longitudinal movements resulting from temperature changes and superimposed loads.
Roller
A steel cylinder intended to provide longitudinal movements by rolling contact.
Roller Bearing
A single roller or a group of rollers so housed as to permit longitudinal movement of a structure.
Roller Nest
A group of steel cylinders used to facilitate the longitudinal movements resulting from temperature changes and superimposed loads.
Rolling Lift Bridge
A bridge of bascule type devised to roll backward and forward upon supporting girders when operated through an "open and closed" cycle.
Segmental Arch
An arch formed along an arc that is drawn from a point below its spring line, thus forming a less than semicircular arch. The intrados of a Roman arch follows an arc drawn from a point on its spring line, thus forming a semi-circle.
Shaft
A vertical, load bearing structure that uses end bearing and friction to support loads.
Shear
A force that causes parts of a material to slide past one another in opposite directions. Shoefly
A temporary bridge taking the place of the main bridge while construction is completed on the main bridge.
Silt
Sediment particles ranging from 0.00016 to 0.0024 inches in diameter.
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 acute 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. May be used as a noun or a verb.
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.
Spandrell
The roughly triangular area above an arch and below a horizontal bridge deck. A closed spandrell encloses fill material. An open spandrel carries its load using interior walls or columns.
Specifications
A document that explains all material and construction requirements of the bridge structure to be constructed, usually used by engineers or architects in the planning stages of construction.
Splice Plate
A plate that joins two girders. Commonly riveted or bolted.
Springer
The first voussoir resting on the impost of an arch.
Smith Truss
Tipp City, Ohio, native Robert W. Smith received truss patents in 1867 and 1869.
Stanchion
One of the larger vertical posts supporting a railing. Smaller, closely spaced vertical supports are ballusters.
Stay
Diagonal brace installed to minimize structural movement.
Steel Stringers
Load-carrying beams in the viaduct’s superstructure that rest on abutments and other intermediate supports.
Stiff
Ability to resist deformation.
Stiffener
On plate girders, structural steel shapes, such as an angle, are attached to the web to add intermediate strength.
Stringer
A beam aligned with the length of a span which supports the deck.
Structurally Deficient and Sufficiency Rating
A bridge sufficiency rating includes a multitude of factors: inspection results of the structural condition of the bridge, traffic volumes, number of lanes, road widths, clearances, and importance for national security and public use, to name just a few.
The sufficiency rating is calculated per a formula defined in Federal Highway Administration’s Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s Bridges. This rating is indicative of a bridge’s sufficiency to remain in service. The formula places 55 percent value on the structural condition of the bridge, 30 percent on its serviceability and obsolescence, and 15 percent on its essentiality to public use.
The point calculation is based on a 0-100 scale and it compares the existing bridge to a new bridge designed to current engineering standards.
The bridge’s sufficiency rating provides an overall measure of the bridge’s condition and is used to determine eligibility for federal funds. Bridges are considered structurally deficient if significant load carrying elements are found to be in poor condition due to deterioration or the adequacy of the waterway opening provided by the bridge is determined to be extremely insufficient to point of causing intolerable traffic interruptions.
Every bridge constructed goes through a natural deterioration or aging process, although each bridge is unique in the way it ages.
The fact that a bridge is classified under the federal definition as “structurally deficient" does not imply that it is unsafe. A structurally deficient bridge, when left open to traffic, typically requires significant maintenance and repair to remain in service and eventual rehabilitation or replacement to address deficiencies. To remain in service, structurally deficient bridges are often posted with weight limits to restrict the gross weight of vehicles using the bridges to less than the maximum weight typically allowed by statute.
To be eligible for federal aid the following is necessary (a local match is required):
Replacement: bridge must have a sufficiency rating of less than 50 and be either functionally obsolete or structurally deficient.
Repair: bridge must have a sufficiency rating of less than 80 and the jurisdiction is prevented from using any additional federal aid for 10 years.
Strut
A compressive member.
Substructure
The substructure consists of all parts that support the superstructure. The main components are:
Abutments or end-bents
Piers or interior bents
Footings
Piling
Superstructure
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
Suspension
Legally halting a company or individuals ability to bid or participate in construction proceedings for a defined period of time.
Suspended Span
A simple beam supported by cantilevers of adjacent spans, commonly connected by pins.
Suspenders
Tension members of a suspension bridge which hang from the main cable to support the deck. Also similar tension members of an arch bridge which features a suspended deck. Also called hangers.
Suspension Bridge
A bridge which carries its deck with many tension members attached to cables draped over tower piers.
Swing Bridge
A movable deck bridge that opens by rotating horizontally on an axis. Compare to bascule bridge and vertical lift bridge.
Tension
A stretching force that pulls on a material.
Tension Member
Any timber or rod of a truss that is subjected to pull or stretch.
Through Truss
A truss that carries its traffic through the interior of the structure with crossbracing between the parallel top and bottom chords. Compare to deck truss and pony truss.
Tie
A tension member of a truss.
Tied Arch
An arch that has a tension member across its base connecting one end to the other.
Timber Freespan
Timber freespan bridges can freespan up to 26 feet. A timber freespan is generally used to span a creek or other relatively small crossings.
Torsion
An action that twists a material.
Tower
A tall pier or frame supporting the cable of a suspension bridge. Trestle A bridge structure consisting of spans supported upon frame bents.
Truss In addition to classifying metal truss bridges by name, their form is further distinguished by the location of the bridge deck in relation to the top and bottom chords, and by their structural behavior.
In a deck configuration, traffic travels on top of the main structure; in a pony configuration traffic travels between parallel superstructures, which are not cross-braced at the top; in a through configuration, traffic travels through the superstructure (usually a truss), which is cross-braced above and below traffic.
Trussed Arch
A metal arch bridge that features a curved truss.
Two-Hinged Arch and Three-Hinged Arches Arches use a curved structure that provides a high resistance to bending forces. Unlike girder and truss bridges, both ends of an arch are fixed in the horizontal direction (i.e., no horizontal movement is allowed in the bearing). Thus when a load is placed on the bridge (e.g., a car passes over it) horizontal forces occur in the bearings of the arch. These horizontal forces are unique to the arch and as a result arches can only be used where the ground or foundation is solid and stable.
Like the truss, the roadway may pass over or through an arch or in some cases both Structurally, there are four basic arch types: hinge-less, two-hinged, three hinged, and tied arches.
The three-hinged arch adds an additional hinge at the top or crown of the arch. The three-hinged arch suffers very little if there is movement in either foundation (due to earthquakes, sinking, etc.) However, the three-hinged arch experiences much more deflection and the hinges are complex and can be difficult to fabricate. The three-hinged arch is rarely used anymore.
Vault
An enclosing structure formed by building a series of adjacent arches.
Vertical Curve
A sag or crest in the profile of a roadway.
Vertical Lift Bridge
A movable deck bridge in which the deck may be raised vertically by synchronized machinery at each end.
Viaduct
A long, multi-span structure, especially one constructed of concrete. More commonly used in relation to structures carrying motor vehicles. Trestle is the term for a similar structure when used in relation to railroads.
Void
An empty or unfilled space in concrete.
Voussoir
Any one of the wedge shaped block used to form an arch.
Voussoir Arch
An arrangement of wedge shaped blocks set to form an arched bridge.
Waterway
The available width for the passage of water beneath a bridge.
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.
Web
The system of members connecting the top and bottom chords of a truss. Or the vertical portion of an I-beam or girder.
Web Members
The intermediate members of a truss, not including the end posts, usually vertical or inclined.
Web Plate
The plate forming the web element of a plate girder, built-up beam or column.
Web Stiffener
A small member welded to a beam web to prevent buckling of the web.
Weephole
A hole in a concrete retaining wall to provide drainage of the water in the retained soil.
Weigh in Motion (WIM)
Equipment that measures the weight of moving trucks. Is used by state highway agencies for monitoring pavement loadings.
Weld
A joint between pieces of metal at faces that have been made plastic by heat or pressure.
Welded Bridge Structure
A structure whose metal elements are connected by welds.
Welded Joint
A joint in which the assembled elements and members are united through fusion of metal.
Wheel Guard
A raised curb along the outside edge of traffic lanes to safeguard constructions outside the roadway limit from collision with vehicles.
Wheel Load
The load carried by and transmitted to the supporting structure by one wheel of a traffic vehicle, a movable bridge or other motive equipment or device.
Wichert Truss
The Wichert Truss, designed by E.M. Wichert of Pittsburg, PA, in 1930, is a cantilever spandrel-braced deck arch that is not a "true arch" bridge. The curved lower chord gives the bridge the form of an arch, but it does not rely on arch action to carry the load. The open diamond panel above each pier is the easily recognized mark of this truss type; without a vertical truss member in this hinged location.
Wire Rope
Steel cable.
Working Stress
The unit stress in a member under service or design load.
