Glossary
Abutment –
A substructure element supporting each end of a single span or the
extreme ends of a multi-span superstructure and, in general, retaining
or supporting the approach embankment.
Anchor span
– The span that counterbalances and holds in equilibrium the
cantilevered portion of an adjacent span during construction.
Anchorage –
Massive concrete structures, also called "cable anchorages"
and "shore anchors." These are placed far enough back
from the edge of the water to insure against sliding. They provide
stability where the cable end is tied, withstanding the tremendous
stress of the loaded cables.
Approach span
– The span or spans connecting the abutment with the main
span or spans.
Beam –
A linear structural member designed to span from one support to
another.
Bent – A substructure
unit supporting each end of a bridge span; also called a pier; 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.
Box girder –A
support beam that is a hollow box; its cross-section is a rectangle
or square.
Cable – The
part of a suspension bridge or cable-stayed bridge that supports
suspension support to the deck. The cable is made of many steel
wires bound together into strands and anchored at each end.
Cable saddle
– The cable saddles sit at the summit of each tower. They
hold the main suspension cable where it crosses over each tower
leg. As traffic, wind, and temperature changes affect the movement
of the cables, the saddles absorb the load and shift it to the towers.
Cable spinning
– The technique of pulling wires from the anchorage over towers
and back to form the main cable. A "spinning wheel," or
"traveler," carries the wires. At the anchorage the strands
of wire are attached to the eye-bar. The wires are grouped into
strands then bound tightly together to form strong suspension cables.
Cable-stayed
bridge – A bridge in which the superstructure is directly
supported by cables or stays, passing over or attached to a tower
or towers located at the main pier(s).
Caisson –
"Caisson" is the French word for "box." A caisson
is a huge box made of steel-reinforced and waterproof concrete with
an open central core. At the base of the caisson is its "cutting
edge" of plate steel. In a suspension bridge the caisson becomes
the foundation, the pier, supporting for the bridge's towers.
Cast-in-place
– Concrete poured within form work on site to create a structural
element in its final position.
Catwalks –
Temporary foot bridges, used by bridge workers to spin the main
cables (several feet above each catwalk), and to attach the suspender
cables that connect the main cables to the deck.
Chord – A horizontal
member of a truss.
Cross brace
– Transverse brace between two main longitudinal members.
Damping –
The action of reducing the vibration of an object. This tends to
return the vibrating object to its original position.
Dead load –
A static load due to the weight of the structure itself.
Deck – The roadway
portion of a bridge that directly supports vehicular and pedestrian
traffic.
Deck bridge
– A bridge in which the supporting members are all beneath
the roadway.
Deck truss –
A bridge whose roadway is supported from beneath by a truss.
Diagonal –
A sloping structural member of a truss or bracing system.
Eye-bar –
Steel bars that hold wire strands of the main cable, and that are
attached to beams embedded in the concrete of an anchorage.
Expansion joint
– A joint designed to provide means for expansion and contraction
movements produced by temperature changes, load, or other forces.
Fatigue –
Cause of structural deficiencies, usually due to repetitive loading
over time.
Flutter –
Self-induced harmonic motion. A self-excited aerodynamic instability
that can grow to very large amplitudes of vibrations.
Footing –
The enlarged, lower portion of a substructure that distributes the
structure load either to the earth or to supporting piles; the most
common footing is the concrete slab; “footer” is a colloquial
term for footing.
Girder – A
main support member for the structure that usually receives loads
from floor beams and stringers; also, any large beam, especially
if built up.
Hanger – A
tension member serving to suspend an attached member.
Hinge – A point
in a structure at which a member is free to rotate.
Joint – In
stone masonry, the space between individual stone; in concrete,
a division in continuity of the concrete; in a truss, the point
at which members of a truss frame are joined.
Live load –
Vehicular traffic.
Lower chord
– The bottom horizontal member of a truss.
Main beam –
A beam supporting the spans and bearing directly onto a column or
wall.
Member – An
individual angle, beam, plate, or built piece intended to become
an integral part of an assembled frame or structure.
Oscillation
– A periodic movement back and forth between two extreme limits.
An example is the string of a guitar that has been plucked. Its
vibration back and forth is one oscillation. A vibration is described
its size (amplitude), its oscillation rate (frequency), and its
timing (phase). In a suspension bridge, oscillation results from
energy collected and stored by the bridge. If a part of the bridge
has to store more energy than it is capable of storing, that part
will probably fail.
Panel – The
portion of a truss span between adjacent points of intersection
of web and chord members.
Pier – A vertical
support or substructure unit that supports the spans of a multi-span
superstructure at an intermediate location between its abutments.
Pile – A shaft-like
linear member that carries loads through weak layers of soil to
those capable of supporting such loads.
Pile bent –
A row of driven or placed piles with a pile cap to hold them in
their correct positions; see Bent.
Plate girder
– A large solid web plate with flange plates attached to the
web plate by flange angles or fillet welds.
Portal – The
clear, unobstructed space of a bridge forming the entrance to the
structure.
Reinforced
concrete – Concrete with steel reinforcing bars bonded
within it to supply increased tensile strength and durability.
Resonance –
The regular vibration of an object as it responds in step (at the
same frequency) with an external force.
Rigid frame bridge
– A bridge with moment-resistant connections between the superstructure
and the substructure to produce an integral, elastic structure.
Riveted connection
– A rigid connection of metal bridge members that is assembled
with rivets. Riveted connections increase the strength of the structure.
Safety hangers
– Back-up for original connections to provide redundancy;
often added for seismic retrofit.
Span – The distance
between piers, towers, or abutments.
Stable – Able
to resist forces that can cause material deformation or structural
collapse.
Steel – A very
hard and strong alloy of iron and carbon.
Stay – Diagonal
brace installed to minimize structural movement.
Strand shoe
– The device at the end of an eye-bar that holds the wires
of each strand for the main suspension cable. The strands loop around
the shoes to form a continuous cable from anchorage to anchorage.
Stringer –
A longitudinal beam supporting the bridge deck.
Strut – A piece
or member acting to resist compressive stress.
Substructure
– The parts of a suspension bridge that are below water or
land; the piers, or tower foundations, and anchorages.
Superstructure
– The parts of a suspension bridge that are above water or
land; the towers, main cables, suspender cables, and related parts.
Suspension bridge
– A bridge in which the floor system is supported by two cables
that are supported upon towers and are anchored at their ends.
Suspended span
– A simple span supported from the free ends of cantilevers.
Suspender cables
–The vertical wires hung at regular intervals connecting the
main suspension cables to the deck. The connection is made using
a cable band.
Tension –
A force that pulls or stretches.
Tie – A member
carrying tension.
Torsion –
A twisting force or action.
Tower – The
vertical structure in a suspension bridge (or cable-stayed bridge)
that holds up the suspension cables.
Trestle –
A bridge structure consisting of spans supported upon frame bents.
Truss – A rigid,
jointed structure made up of individual straight pieces arranged
and connected, usually in a triangular pattern, so as to support
longer spans.
Truss bridge
– A bridge having a pair of trusses for the superstructure.
Tunnel – An
underground passage open to daylight at both ends.
Upper chord
– The top longitudinal member of a truss.
Viaduct –
A series of spans carried on piers at short intervals.
Vortex – A
rotary, swirling, circular motion of a fluid, like wind or water.
The vortex forms a vacuum at its center that draws objects toward
it. Examples of vortex motion are tornadoes and whirlpools, including
the small whirlpool formed by water draining from a sink.
Warren truss
– A triangular truss with sloping members (and no vertical
members) between the top and bottom chords, forming the letter "W."
Web – The portion
of a beam located between and connected to the flanges.
Web members
– The intermediate members of a truss, not including the end
posts, usually vertically or inclined.
Welded joint
– A joint in which the assembled elements and members are
united through fusion of metal.
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