Bridge Dictionary

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The ground end-support of a bridge superstructure, especially to resist the horizontal thrust of an arch and to connect bridges to its approach ramps. May also be used to retain backfill material.

Anchor arm

The side-span, usually of a cantilever bridge, from main pier to anchor or abutment pier, balances the cantilever.


A secure fixing, usually in mass reinforced concrete, at the extremity of a side-span or anchor arm.



A rigid, usually horizontal, structural element which may itself form an entire bridge.


The solid rock layer beneath sand or silt, especially in a river-bed.


A beam with a hollow square or rectangular section.

Brittle fracture

The fracture of steel elements at low temperatures or as a result of embrittlement.


Cable-stayed bridge

A bridge whose deck is directly supported from pylons by straight cables without vertical suspenders.


The staying or suspending bridge element; in modern suspension bridges, the main supporting cable is hung from towers, and from steel wire bound in strands.


A bridge foundation, usually embedded in a riverbed by continuously digging out the material within the bed, so that the caisson sinks.


A slight convexity on the road surface. Also, shape given to a structural member to offset its dead load deflection.


A horizontal member fixed or continuous at one end and free at the other.

Cantilever Bridge

A bridge with rigid arms extending from both sides of a base, the inner ones usually supporting a central span.

Carbon fibre

Very high-strength filaments of near-pure carbon, suitable for reinforcement.

Cast iron

A brittle alloy with high carbon content: high compressive strength, low tensile strength.

Cement mortar

The mixture of sand, cement, water and lime that binds masonry and brick.

Centre of mass

The point of balance for any object. It’s the key to structural stability. The force of gravity pulling at a structure travels along a line through the centre of its mass. If the resistance of the structure pushes through this same line, then the forces are in balance and the bridge will stay up.


The top or bottom horizontal part of a truss.


A watertight structure allowing underwater foundations to be built in the dry.

Composite construction

The use of different materials, usually steel and concrete, together in a single structure.

Compressed-air chamber

The space at the bottom of a caisson, into which air is introduced under pressure to exclude water so that excavation can take place.


The pushing force which tends to shorten a member; opposite of tension.

Compression zone

The area under compression in the upper part of a simply supported horizontal beam.

Compressive strength

The ability of a material to withstand compression.


A mixture of water, sand, stone and a binding element which hardens to a rock-like consistency.


A component of a moving bridge in which a balanced counterweight at one end of a span falls, causing the deck to rise.


The slow permanent deformation of material under long-term stress, as in creep of concrete.


Dead load

A structure’s own weight


The cutting of stone units to the required shape.


False work

Temporary sharing during construction.


A protective enclosure around a pier structure.


The material, usually rubble or earth, used to fill the space above or behind the outer surface of bridge structure.


The flat top and bottom plates of a rolled section or of a plate or box-girder.


Temporary boarding, plywood or steel forms to hold concrete in shape while it hardens.



Application by hot dipping or electroplating of a protective layer of zinc to a metal, chiefly steel, to prevent or inhibit corrosion.

Girder (main girder)

A large beam, usually steel or concrete which generally supports other beams.

Glass fibre

A reinforcing material with high tensile strength.


A hard crystalline rock, suitable for masonry bridges.



A beam or girder with an I-shaped cross-section.


King-post truss

A truss consisting of a vertical post, connected to a horizontal beam by inclined tie-beams or members.


Laminated timber

Layers of timber clamped or glued face-to-face.

Lift bridge

A form of moving bridge in which a hinged counterweight at one end of a span falls, causing the deck to rise.

Live load

The weight of traffic passing over a bridge.


Moveable bridge

A bridge superstructure that is moved to provide clearance for large ships to pass, like a drawbridge.


Navigation span

The part of a bridge with maximum clearance for shipping.


Orthotropic deck

A bridge deck which is stiffer in the direction of the span than it is laterally. A steel orthotropic deck has a steel deck plate stiffened with ribs or troughs.


The movement, usually due to wind, of bridge deck or bridge component in the wind.



An intermediate support or the adjacent ends of two bridge spans.

Pneumatic caisson

A caisson with a compressed-air chamber.


A frame with side uprights connected by a horizontal member at the top.Pont dont les poutres principales se prolongent en porte-à-faux et soutiennent des poutres de plus courtes portées.


The method of making prestressed concrete elements with steel strands tightened after the concrete has hardened.

Pratt truss

A patent truss design with diagonals in tension.


The method of making prestressed concrete elements with steel strands under tension as the concrete sets.


The manufacture of structural units in a factory, usually off-site.

Prestressed concrete

A more efficient type of concrete with stretched steel strands embedded in it to precompress the concrete allowing it to carry higher load.


Reinforced concrete

Concrete with steel bars or mesh embedded in it for increased tensile strength.



The destructive effect on submerged piers from fast-flowing water.

Shear forces

Any force that tries to cut or slice structural parts of the bridge. A sheet of paper undergoes a shear force when it is cut with a pair of scissors.


The movement of a structure from side to side in wind.

Soffit – Underside?

The under-surface of any piece of structure.


An alloy of iron with more carbon than wrought iron but less than cast iron, combining the tensile strength of the former with the compressive strength of the latter.


The vertical elements on a suspension bridge that links a cable with a deck.

Suspension bridge

Has a roadway supported by a deck that hangs from two main cables which are attached to supportive towers. Although similar to a cable stayed bridge, suspension bridges are different because their roadbeds are suspended by two sets of cables (the two main cables and the suspender cables which attach the road to the main cables). This type of bridge can extend for well over 1 220 m (4 000 feet).



A beam or girder with a T-shaped cross-section.

Tensile strength

The ability of a material to withstand tension.


The strain produced by twisting.


Highly stable beams which form a network of triangles.



The vertical plates of a girder.

Wrought iron

Soft and malleable alloy with very low carbon content; low compressive strength, high tensile strength.