Glossary 
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GLOSSARY 

A 

AASHTO - American Association of State Highway and Transportation Officials, name changed from 

AASHO (American Association of State Highway Officials) in 1973

American Association of State Highway and Transportation Officials (AASHTO) Manual - “Manual for 

Condition Evaluation of Bridges,” second edition, published by the American Association of State Highway 

and Transportation Officials (incorporated by reference into 23 CFR 650) 

abrasion - wearing or grinding away of material by friction; usually caused by sand, gravel, or stones, 

carried by wind or water 

absorption - the process of a liquid being taken into a permeable solid (e.g., the wetting of concrete) 

abutment - part of bridge substructure at either end of bridge which transfers loads from superstructure to 

foundation and provides lateral support for the approach roadway embankment 

ADT - Average Daily Traffic 

ADTT - Average Daily Truck Traffic 

admixture - an ingredient added to concrete other than cement, aggregate or water (e.g., air entraining 

agent) 

aggradation - progressive raising of a streambed by deposition of sediment 

aggregate - hard inert material such as sand, gravel, or crushed rock that may be combined with a 

cementing material to form mortar or concrete 

air entrainment - the addition of air into a concrete mixture in order to increase the durability and resist 

thermal forces 

alignment - the relative horizontal and vertical positioning between components, such as the bridge and its 

approaches 

alignment bearing - a bearing embedded in a bridge seat to prevent lateral movements (see BEARING) 

alligator cracking - cracks initiated by inadequate base support or drainage that form on the surface of a 

road in adjacent, rectangular shapes (like the skin of an alligator) 

alloy - two or more metals, or metal and non-metal, intimately combined, usually by dissolving together in 

a molten state to form a new base metal 

anchorage - the complete assemblage of members and parts, embedded in concrete, rock or other fixed 

material, designed to hold a portion of a structure in correct position 
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anchor bolt - a metal rod or bar commonly threaded and fitted with a nut and washer at one end only, used 

to secure in a fixed position upon the substructure the bearings of a bridge, the base of a column, a 

pedestal, shoe, or other member of a structure 

anchor span - the span that counterbalances and holds in equilibrium the cantilevered portion of an 

adjacent span; also called the back span; see CANTILEVER BEAM, GIRDER, or TRUSS 

angle - a basic member shape, usually steel, in the form of an "L" 

anisotropy - the property of certain materials, such as crystals, that exhibits different strengths in different 

directions 

anode - the positively charged pole of a corrosion cell at which oxidation occurs 

anti-friction bearing - a ball or roller-type bearing; a bearing that reduces transfer of horizontal loads 

between components 

appraisal rating - a judgment of a bridge component's adequacy in comparison to current standards 

approach - the part of the roadway immediately before and after the bridge structure 

approach pavement - an approach which has a cross section that is either the same as or slightly wider 

than the bridge deck width

approach slab - a reinforced concrete slab placed on the approach embankment adjacent to and usually 

resting upon the abutment back wall; the function of the approach slab is to carry wheel loads on the 

approaches directly to the abutment, thereby transitioning any approach roadway misalignment due to 

approach embankment settlement 

appurtenance - an element that contributes to the general functionality of the bridge site (e.g., lighting, 

signing) 

apron - a form of scour (erosion) protection consisting of timber, concrete, riprap, paving, or other 

construction material placed adjacent to abutments and piers to prevent undermining 

arch - a curved structure element primarily in compression that transfers vertical loads through inclined 

reactions to its end supports 

arch barrel - a single arch member that extends the width of the structure 

arch rib - the main support element used in open spandrel arch construction; also known as arch ring 

armor - a secondary steel member installed to protect a vulnerable part of another member, e.g., steel 

angles placed over the edges of a joint; also scour protection such as rip rap 

as-built plans - plans made after the construction of a project, showing all field changes to the final design 

plans (i.e.. showing how the bridge was actually built) 
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asphalt - a brown to black bituminous substance that is found in natural beds and is also obtained as a 

residue in petroleum refining and that consists chiefly of hydrocarbons; an asphaltic composition used for 

pavements and as a waterproof cement 

ASTM - American Society for Testing and Materials 

auger - a drill with a spiral channel used for boring 

axial - in line with the longitudinal axis of a member 

axle load - the load borne by one axle of a traffic vehicle, a movable bridge, or other motive equipment or 

device and transmitted through a wheel or wheels 

B

back - see EXTRADOS 

backfill - material, usually soil or coarse aggregate, used to fill the unoccupied portion of a substructure 

excavation such as behind an abutment stem and backwall 

backstay - cable or chain attached at the top of a tower and extending to and secured upon the anchorage to 

resist overturning stresses exerted upon the tower by a suspended span 

backwall - the topmost portion of an abutment above the elevation of the bridge seat, functioning primarily as 

a retaining wall with a live load surcharge; it may serve also as a support for the extreme end of the bridge deck 

and the approach slab 

backwater - the back up of water in a stream due to a downstream obstruction or constriction 

bank - sloped sides of a waterway channel or approach roadway, short for embankment 

bascule bridge - a bridge over a waterway with one or two leaves which rotate from a horizontal to a nearvertical position, providing unlimited overhead clearance 

base course - a layer of compacted material found just below the wearing course that supports the pavement 

base metal - the surface metal of a steel element to be incorporated in a welded joint; also known as structure 

metal, parent metal 

base plate - steel plate, whether cast, rolled or forged, connected to a column, bearing or other member to 

transmit and distribute its load to the substructure 

batten plate - a plate with two or more fasteners at each end used in lieu of lacing to tie together the shapes 

comprising a built-up member 
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batter - the inclination of a surface in relation to a horizontal or a vertical plane; commonly designated on 

bridge detail plans as a ratio (e.g., 1:3, H:V); see RAKE 

battered pile - a pile driven in an inclined position to resist horizontal forces as well as vertical forces 

bay - the area of a bridge floor system between adjacent multi-beams or between adjacent floor beams 

beam - a linear structural member designed to span from one support to another and support vertical loads 

bearing - a support element transferring loads from superstructure to substructure while permitting limited 

movement capability 

bearing capacity - the load per unit area which a structural material, rock, or soil can safely carry 

bearing failure - crushing of material under extreme compressive load 

bearing pile - a pile which provides support through the tip (or lower end) of the pile 

bearing plate - a steel plate, which transfers loads from the superstructure to the substructure 

bearing pressure - the bearing load divided by the area to which it is applied 

bearing seat - a prepared horizontal surface at or near the top of a substructure unit upon which the bearings 

are placed 

bearing stiffener - a vertical web stiffener at the bearing location 

bearing stress - see BEARING PRESSURE 

bedding - the soil or backfill material used to support pipe culverts 

bedrock - the undisturbed rock layer below the surface soil 

bench mark - an established reference point with known elevation and coordinates, used to document 

dimensions, elevations or position movement 

bending moment - the internal force within a beam resulting from transverse loading 

bent - a substructure unit made up of two or more column or column-like members connected at their top-most 

ends by a cap, strut, or other member holding them in their correct positions 

berm - the line that defines the location where the top surface of an approach embankment or causeway is 

intersected by the surface of the side slope 

beveled washer - a wedge-shaped washer used in connections incorporating members with sloped flange legs, 

e.g., channels and S-beams 

bitumen - a black sticky mixture of hydrocarbons obtained from natural deposits or from distilling petroleum; 
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tar 

bituminous concrete - a mixture of aggregate and liquid asphalt or bitumen, which is compacted into a dense 

mass 

blanket - a streambed protection against scour placed adjacent to abutments and piers 

BMS - Bridge Management System 

bolt - a mechanical fastener with machine threads at one end to receive a nut, and an integral head at the other 

end 

bolster - a block-like member used to support a bearing on top of a pier cap or abutment bridge seat; see 

PEDESTAL 

bond - in reinforced concrete, the grip of the concrete on the reinforcing bars, which prevents slippage of the 

bars relative to the concrete mass 

bond stress - a term commonly applied in reinforced concrete construction to the stress developed by a force 

tending to produce movement or slippage at the interface between the concrete and the reinforcement bars 

bowstring truss - a general term applied to a truss of any type having a polygonal arrangement of its top chord 

members conforming to or nearly conforming to the arrangement required for a parabolic truss; a truss with a 

curved top chord 

box beam - a hollow structural beam with a square, rectangular, or trapezoidal cross-section that supports 

vertical loads and provides torsional rigidity 

box culvert - a culvert of rectangular or square cross-section 

box girder - a hollow, rectangular or trapezoidal shaped girder, a primary member along the longitudinal axis 

of the bridge, which provides good torsional rigidity 

bracing - a system of secondary members that maintains the geometric configuration of primary members 

 

bracket - a projecting support fixed upon two intersecting members to strengthen and provide rigidity to the 

connection 

breastwall - the portion of an abutment between the wings and beneath the bridge seat; the breast wall 

supports the superstructure loads, and retains the approach fill; see STEM 

bridge - a structure including supports erected over a depression or an obstruction, such as water, highway, or 

railway, and having a track or passageway for carrying traffic or other moving loads, and having an opening 

measured along the center of the roadway of more than 20 feet between undercopings of abutments or spring 

lines of arches, or extreme ends of openings for multiple boxes; it may also include multiple pipes, where the 

clear distance between openings is less than half of the smaller contiguous opening 

bridge deficiency - a defect in a bridge component or member that makes the bridge less capable or less 
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desirable for use 

bridge inspection experience - active participation in bridge inspections in accordance with the NBIS, in 

either a field inspection, supervisory, or management role. A combination of bridge design, bridge 

maintenance, bridge construction and bridge inspection experience, with the predominant amount in bridge 

inspection, is acceptable. 

bridge inspection refresher training - the National Highway Institute “Bridge Inspection Refresher Training 

Course” 1

 or other State, local, or federally developed instruction aimed to improve quality of inspections, 

introduce new techniques, and maintain the consistency of the inspection program. 

1

 The National Highway Institute training may be found at the following URL: http://www.nhi.fhwa.dot.gov./

Bridge Inspector's Reference Manual (BIRM) - a comprehensive FHWA manual on programs, procedures 

and techniques for inspecting and evaluating a variety of in-service highway bridges. This manual may be 

purchased from the U.S. Government Printing Office, Washington, DC 20402 and from National Technical 

Information Service, Springfield, Virginia 22161, and is available at the following URL: 

http://www.fhwa.dot.gov/bridge/bripub.htm.

bridge pad - the raised, leveled area upon which the pedestal, masonry plate or other corresponding element of 

the superstructure bears on the substructure; also called bridge seat bearing area 

bridge seat - the top surface of an abutment or pier upon which the superstructure span is placed and 

supported; for an abutment it is the surface forming the support for the superstructure and from which the 

backwall rises; for a pier it is the entire top surface 

bridge site - the position or location of a bridge and its surrounding area 

bridging - a carpentry term applied to the cross−bracing fastened between timber beams to increase the rigidity 

of the floor construction, limit differential deflection and minimize the effects of impact and vibration 

brittle fracture - the failure of a steel member occurring without warning, prior to plastic deformation 

brush curb - a narrow curb, 9 inches or less in width, which prevents a vehicle from brushing against the 

railing or parapet 

buckle - to fail by an inelastic change in alignment (deflection) as a result of compression in axial loaded 

members 

buckle plate - an obsolete style of steel deck using dished steel plates as structural members 

built-up member - a column or beam composed of plates and angles or other structural shapes united by 

bolting, riveting or welding to enhance section properties 

bulb t-girder - a t-shaped concrete girder with a bulb shape at the bottom of the girder cross section

bulkhead - a retaining wall-like structure commonly composed of driven sheet piles or a barrier of wooden 
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timbers or reinforced concrete members 

buoyancy - upward pressure exerted by the fluid in which an object is immersed 

butt joint - a joint between two pieces of metal that have been connected in the same plane 

buttress - a bracket-like wall, of full or partial height, projecting from another wall; the buttress strengthens 

and stiffens the wall against overturning forces; all parts of a buttress act in compression 

buttressed wall - a retaining wall designed with projecting buttresses to provide strength and stability 

butt weld - a weld joining two plates or shapes end to end; also splice weld 

C

cable - a tension member comprised of numerous individual steel wires or strands twisted and wrapped in such 

a fashion to form a rope of steel; see SUSPENSION BRIDGE 

cable band - a steel casting with clamp bolts which fixes a floor system suspender cable to the catenary cable 

of a suspension bridge 

cable-stayed bridge - a bridge in which the superstructure is directly supported by cables, or stays, passing 

over or attached to towers located at the main piers 

caddisfly - a winged insect closely related to the moth and butterfly whose aquatic larvae seek shelter by 

digging small shallow holes into submerged timber elements 

caisson - a rectangular or cylindrical chamber for keeping water or soft ground from flowing into an 

excavation 

camber - the slightly arched or convex curvature provided in beams to compensate for dead load deflection; in 

general, a structure built with perfectly straight lines appears slightly sagged 

cantilever - a structural member that has a free end projecting beyond a support; length of span overhanging 

the support 

cantilever abutment - an abutment that resists lateral earth pressure through the opposing cantilever action of 

a vertical stem and horizontal footing 

cantilever bridge - a general term applying to a bridge having a superstructure incorporating cantilever design 

cantilever span - a superstructure span composed of two cantilever arms, or of a suspended span supported by 

one or two cantilever arms 

cap - the topmost portion of a pier or a pile bent serving to distribute the loads upon the columns or piles and 

to hold them in their proper relative positions; see PIER CAP, PILE CAP 
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cap beam - the top member in a bent that ties together the supporting members 

capstone - the topmost stone of a masonry pillar, column or other structure requiring the use of a single 

capping element 

carbon steel - steel (iron with dissolved carbon) owing its properties principally to its carbon content; ordinary, 

unalloyed steel 

cast-in-place (C.I.P.) - the act of placing and curing concrete within formwork to construct a concrete element 

in its final position 

cast iron - relatively pure iron, smelted from iron ore, containing 1.8 to 4.5% free carbon and cast to shape 

catch basin - a receptacle, commonly box shaped and fitted with a grilled inlet and a pipe outlet drain, 

designed to collect the rainwater and floating debris from the roadway surface and retain the solid material so 

that it may be periodically removed 

catchment area - see DRAINAGE AREA 

catenary - the curve obtained by suspending a uniformly loaded rope or cable between two points 

cathode - the negatively charged pole of a corrosion cell that accepts electrons and does not corrode 

cathodic protection - a means of preventing metal from corroding by making it a cathode through the use of 

impressed direct current or by attaching a sacrificial anode 

catwalk - a narrow walkway for access to some part of a structure 

causeway - an elevated roadway crossing a body of water 

cellular abutment - an abutment in which the space between wings, abutment stem, approach slab, and 

footings is hollow. Also known as a vaulted abutment 

cement mortar - a mixture of sand and cement with enough water to make it plastic 

cement paste - the plastic combination of cement and water that supplies the cementing action in concrete 

centerline of bearings - a horizontal line that passes through the centers of the bearings, used in abutment/pier 

layout and beam erection 

center of gravity - the point at which the entire mass of a body acts; the balancing point of an object 

centroid - that point about which the static moment of all the elements of area is equal to zero 

chain drag - a chain or a series of short medium weight chains attached to a T-shaped handle; used as a 

preliminary technique for sounding a large deck area for delamination 

chamfer - an angled edge or corner, typically formed in concrete 
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channel - a waterway connecting two bodies of water or containing moving water; a rolled steel member 

having a C-shaped cross section 

channel profile - a longitudinal section of a channel along its centerline 

check - a crack in wood occurring parallel with the grain and through the rings of annual growth 

cheek wall - see KNEE WALL 

chipping hammer - hammer such as a geologist's pick or masonry hammer used to remove corrosion from 

steel members and to sound concrete for delamination; a welder's tool for cleaning slag from steel after welding 

chloride - an ingredient in deicing agents that can damage concrete and steel bridge elements 

chord - a generally horizontal member of a truss 

 

circular arch - an arch in which the intrados surface has a constant radius 

clearance - the unobstructed vertical or horizontal space provided between two objects 

clear headroom - the vertical clearance beneath a bridge structure available for navigational use 

clear span - the unobstructed space or distance between support elements of a bridge or bridge member 

clip angle - see CONNECTION ANGLE 

closed spandrel arch - a stone, brick or reinforced concrete arch span having spandrel walls to retain the 

spandrel fill or to support either entirely or in part the floor system of the structure when the spandrel is not 

filled 

coarse aggregate - aggregate that stays on a sieve of 5 mm (1⁄4") square opening 

coating - a material that provides a continuous film over a surface in order to protect or seal it; a film formed 

by the material 

coefficient of thermal expansion - the unit change in dimension produced in a material by a change of one 

degree in temperature 

cofferdam - a temporary dam-like structure constructed around an excavation to exclude water; see SHEET 

PILE COFFERDAM 

cold chisel - short bar with a sharp end used for cold-cutting soft metals when struck with a hammer 

column - a general term applying to a vertical member resisting compressive stresses and having, in general, a 

considerable length in comparison with its transverse dimensions 

column bent - a bent shaped pier that uses columns incorporated with a cap beam
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compaction - the process by which a sufficient amount of energy (compressive pressure) is applied to soil or 

other material to increase its density 

complex bridge - movable, suspension, cable stayed, and other bridges with unusual characteristics

component - a general term reserved to define a bridge deck, superstructure or substructure 

composite action - the contribution of a concrete deck to the moment resisting capacity of the superstructure 

beam when the superstructure beams are not the same material as the deck 

composite construction - a method of construction whereby a cast-in-place concrete deck is mechanically 

attached to superstructure members by shear connectors 

comprehensive bridge inspection training - training that covers all aspects of bridge inspection and enables 

inspectors to relate conditions observed on a bridge to established criteria (see the Bridge Inspector's Reference 

Manual for the recommended material to be covered in a comprehensive training course). 

compression - a type of stress involving pressing together; tends to shorten a member; opposite of tension 

compression failure - buckling, crushing, or collapse caused by compression stress 

compression flange - the part of a beam that is compressed due to a bending moment 

compression seal joint - a joint consisting of a neoprene elastic seal squeezed into the joint opening 

concentrated load - a force applied over a small contact area; also known as point load 

concrete - a stone-like mass made from a mixture of aggregates and cementing material, which is moldable 

prior to hardening; see BITUMINOUS CONCRETE and PORTLAND CEMENT CONCRETE 

concrete beam - a structural member of reinforced concrete designed to carry bending loads 

concrete pile - a pile constructed of reinforced concrete either precast and driven into the ground or cast-inplace in a hole bored into the ground 

concrete tee team - "T" shaped section of reinforced concrete; cast-in-place monolithic deck and beam system 

condition rating - a judgment of a bridge component condition in comparison to its original as-built condition 

conductor - a material that is suitable for carrying electric current 

connection angle - a piece of angle serving to connect two elements of a member or two members of a 

structure; also known as clip angle 

consolidation - the time dependent change in volume of a soil mass under compressive load caused by water 

slowly escaping from the pores or voids of the soil 
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construction joint - a pair of adjacent surfaces in reinforced concrete where two pours have met, 

reinforcement steel extends through this joint 

continuous beam - a general term applied to a beam that spans uninterrupted over one or more intermediate 

supports 

continuous bridge - a bridge designed to extend without joints over one or more interior supports 

continuous footing - a common footing that is underneath a wall, or columns

continuous span - spans designed to extend without joints over one or more intermediate supports 

continuous truss - a truss without hinges having its chord and web members arranged to continue 

uninterrupted over one or more intermediate points of support 

continuous weld - a weld extending throughout the entire length of a connection 

contraction - the thermal action of the shrinking of an object when cooled; opposite of expansion 

coping - a course of stone laid with a projection beyond the general surface of the masonry below it and 

forming the topmost portion of a wall; a course of stone capping the curved or V-shaped extremity of a pier, 

providing a transition to the pier head proper, when so used it is commonly termed the "starling coping," "nose 

coping," the "cutwater coping" or the "pier extension coping" 

corbel - a piece constructed to project from the surface of a wall, column or other portion of a structure to serve 

as a support for another member 

core - a cylindrical sample of concrete or timber removed from a bridge component for the purpose of 

destructive testing to determine the condition of the component 

corrosion - the general disintegration of metal through oxidation 

corrugated - an element with alternating ridges and valleys

counter - a truss web member that undergoes stress reversal and resists only live load tension; see WEB 

MEMBERS 

counterfort - a bracket-like wall connecting a retaining wall stem to its footing on the side of the retained 

material to stabilize the wall against overturning; a counterfort, as opposed to a buttress, acts entirely in tension 

counterforted abutment - an abutment that develops resistance to bending moment in the stem by use of 

counterforts. This permits the breast wall to be designed as a horizontal beam or slab spanning between 

counterforts, rather than as a vertical cantilever slab 

counterforted wall - a retraining wall designed with projecting counterforts to provide strength and stability 

counterweight - a weight which is used to balance the weight of a movable member; in bridge applications 
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counterweights are used to balance a movable span so that it rotates or lifts with minimum resistance. Also 

sometimes used in continuous structures to prevent uplift 

couplant - a viscous fluid material used with ultrasonic gages to enhance transmission of sound waves 

couple - two forces that are equal in magnitude, opposite in direction, and parallel with respect to each other 

coupon - a sample of steel taken from an element in order to test material properties 

course - a horizontal layer of bricks or stone 

cover - the clear thickness of concrete between a reinforcing bar and the surface of the concrete; the depth of 

backfill over the top of a pipe or culvert 

covered bridge - an indefinite term applied to a wooden bridge having its roadway protected by a roof and 

enclosing sides 

cover plate - a plate used in conjunction with a flange or other structural shapes to increase flange section 

properties in a beam, column, or similar member 

crack - a break without complete separation of parts; a fissure 

cracking (reflection) - visible cracks in an overlay indicating cracks in the concrete underneath 

crack initiation - the beginning of a crack usually at some microscopic defect 

crack propagation - the growth of a crack due to energy supplied by repeated stress cycles 

creep - an inelastic deformation that occurs under a constant load, below the yield point, and increases with 

time 

creosote - an oily liquid obtained by the distillation of coal or wood tar and used as a wood preservative 

crib - a structure consisting of a foundation grillage combined with a superimposed framework providing 

compartments or coffers which are filled with gravel, concrete or other material satisfactory for supporting the 

structure to be placed thereon 

cribbing - a construction consisting of wooden, metal or reinforced concrete units so assembled as to form an 

open cellular-like structure for supporting a superimposed load or for resisting horizontal or overturning forces 

acting against it. 

cribwork - large timber cells that are submerged full of concrete to make an underwater foundation 

critical finding - a structural or safety related deficiency that requires immediate follow-up inspection or action 

cross - transverse bracings between two main longitudinal members; see DIAPHRAGM, BRACING 

cross frame - steel elements placed in "X" shaped patterns to act as stiffeners between the main carrying 
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superstructure members 

cross girders - transverse girders, supported by bearings, which support longitudinal beams or girders 

cross-section - the shape of an object cut transversely to its length 

cross-sectional area - the area of a cross-section 

crown - the highest point of the transverse cross section of a roadway, pipe or arch; also known as soffit or 

vertex 

crown of roadway - the vertical dimension describing the total amount the surface is convexed or raised from 

gutter to centerline; this is sometimes termed the cross fall or cross slope of roadway 

culvert - a drainage structure beneath an embankment (e.g., corrugated metal pipe, concrete box culvert) 

 

curb - a low barrier at the side limit of the roadway used to guide the movement of vehicles 

curb inlet - see SCUPPER 

curtain wall - a term commonly applied to a thin wall between main columns designed to withstand only 

secondary loads. Also the wall portion of a buttress or counterfort abutment that spans between the buttresses 

or counterforts 

curvature - the degree of curving of a line or surface 

curved girder - a girder that is curved in the horizontal plane in order to adjust to the horizontal alignment of 

the bridge 

cutoff wall - vertical wall at the end of an apron or slab to prevent scour undermining 

cutwater - a sharp-edged structure, facing the water channel current, built around a bridge pier to protect if 

from the flow of water and debris in the water 

cyclic stress - stress that varies with the passage of live loads; see STRESS RANGE 

D

damage inspection - this is an unscheduled inspection to assess structural damage resulting from 

environmental factors or human actions

dead load - a static load due to the weight of the structure itself 

debris - material including floating wood, trash, suspended sediment or bed load moved by a flowing stream 

deck - that portion of a bridge which provides direct support for vehicular and pedestrian traffic, supported by 

a superstructure 
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deck arch - an arch bridge with the deck above the top of the arch 

deck bridge - a bridge in which the supporting members are all beneath the roadway 

decking - bridge flooring installed in panels, e.g., timber planks 

deck joint - a gap allowing for rotation or horizontal movement between two spans or an approach and a span 

deficiency - see BRIDGE DEFICIENCY 

deflection - elastic movement of a structural member under a load 

deformation - distortion of a loaded structural member; may be elastic or inelastic 

deformed bars - concrete reinforcement consisting of steel bars with projections or indentations 

(deformations) to increase the mechanical bond between the steel and concrete 

degradation - general progressive lowering of a stream channel by scour 

delamination - surface separation of concrete into layers; separation of glulaminated timber plies 

design load - the force for which a structure is designed; the most severe combination of loads 

deterioration - decline in quality over a period of time due to chemical or physical degradation 

diagonal - a sloping structural member of a truss or bracing system 

diagonal stay - a cable support in a suspension bridge extending diagonally from the tower to the roadway to 

add stiffness to the structure and diminish the deformations and undulations resulting from traffic service 

diagonal tension - the tensile force due to horizontal and vertical shear in a beam 

diaphragm - a transverse member placed within a member or superstructure system to distribute stresses and 

improves strength and rigidity; see BRACING 

diaphragm wall - a wall built transversely to the longitudinal centerline of a spandrel arch serving to tie 

together and reinforce the spandrel walls, together with providing a support for the floor system in conjunction 

with the spandrel walls; also known as cross wall 

differential settlement - uneven settlement of individual or independent elements of a substructure; tilting in 

the longitudinal or transverse direction due to deformation or loss of foundation material 

dike - an earthen embankment constructed to retain or redirect water; when used in conjunction with a bridge, 

it prevents stream erosion and localized scour and/or so directs the stream current such that debris does not 

accumulate; see SPUR 

discharge - the volume of fluid per unit of time flowing along a pipe or channel 
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displacement induced stress - stresses caused by differential deflection of adjacent parts 

distributed load - a load uniformly applied along the length of an element or component of a bridge 

ditch - a trough-like excavation made to collect water 

diver - a specially trained individual who inspects the underwater portion of a bridge substructure and the 

surrounding channel 

dolphin - a group of piles driven close together or a caisson placed to protect portions of a bridge exposed to 

possible damage by collision with river or marine traffic 

double movable bridge - a bridge in which the clear span over the navigation channel is produced by joining 

the arms of two adjacent swing spans or the leaves of two adjacent bascule spans at or near the center of the 

navigable channel; see MOVABLE BRIDGE 

dowel - a length of bar embedded in two parts of a structure to hold the parts in place and to transfer stress 

drainage - a system designed to remove water from a structure 

drainage area - an area in which surface run-off collects and from which it is carried by a drainage system; 

also known as catchment area 

drain hole - hole in a box shaped member or a wall to provide means for the exit of accumulated water or 

other liquid; also known as drip hole; see WEEP HOLE 

drain pipes - pipes that carry storm water 

drawbridge - a general term applied to a bridge over a navigable body of water having a movable 

superstructure span of any type 

drift bolt - a short length of metal bar used to connect and hold in position wooden members placed in contact; 

similar to a dowel 

drift pin - tapered steel rod used by ironworkers to align bolt holes 

drip notch - a recess cast on the underside of an overhang that prevents water from following the concrete 

surface onto the supporting beams 

drop inlet - a type of inlet structure that conveys the water from a higher elevation to a lower outlet elevation 

smoothly without a free fall at the discharge 

 

duct - the hollow space where a prestressing tendon is placed in a post-tensioned prestressed concrete girder 

ductile - capable of being molded or shaped without breaking; plastic 

ductile fracture - a fracture characterized by plastic deformation 
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ductility - the ability to withstand non−elastic deformation without rupture 

dumbbell pier - a pier consisting of two cylindrical or rectangular shaped piers joined by an integral web 

dummy member - truss member that carries no primary loads; may be included for bracing or for appearance 

E

E - modulus of elasticity of a material; Young's modulus; the stiffness of a material 

efflorescence - a deposit on concrete or brick caused by crystallization of carbonates brought to the surface by 

moisture in the masonry or concrete 

elastic - capable of sustaining deformation without permanent loss of shape 

elastic deformation - non-permanent deformation; when the stress is removed, the material returns to its 

original shape 

elasticity - the property whereby a material changes its shape under the action of loads but recovers its original 

shape when the loads are removed 

elastomer - a natural or synthetic rubber-like material 

elastomeric pad - a synthetic rubber pad used in bearings that compresses under loads and accommodates 

horizontal movement by deforming 

 

electrolyte - a medium of air, soil, or liquid carrying ionic current between two metal surfaces, the anode and 

the cathode 

electrolytic cell - a device for producing electrolysis consisting of the electrolyte and the electrodes 

electrolytic corrosion - corrosion of a metal associated with the flow of electric current in an electrolyte 

elevation view - a drawing of the side view of a structure 

elliptic arch - an arch in which the intrados surface is a full half of the surface of an elliptical cylinder; this 

terminology is sometimes incorrectly applied to a multicentered arch 

elongation - the elastic or plastic extension of a member 

embankment - a mound of earth constructed above the natural ground surface to carry a road or to prevent 

water from passing beyond desirable limits; also known as bank 

end block - in a prestressed concrete I-beam, the widened beam web at the end to provide adequate anchorage 

bearing for the post tensioning steel and to resist high shear stresses; similarly, the solid end diaphragm of a 
 G-17 

box beam 

end post - the end compression member of a truss, either vertical or inclined in position and extending from 

top chord to bottom chord 

end section - a concrete or steel appurtenance attached to the end of a culvert for the purpose of hydraulic 

efficiency, embankment retention or anchorage 

end span - a span adjacent to an abutment 

 

epoxy - a synthetic resin which cures or hardens by chemical reaction between components which are mixed 

together shortly before use 

epoxy coated reinforcement - reinforcement steel coated with epoxy; used to prevent corrosion 

equilibrium - in statics, the condition in which the forces acting upon a body are such that no external effect 

(or movement) is produced 

equivalent uniform load - a load having a constant intensity per unit of its length producing an effect equal to 

that of a live load consisting of vehicle axle or wheel concentrations spaced at varying distances 

erosion - wearing away of soil by flowing water not associated with a channel; see SCOUR 

expansion - an increase in size or volume 

expansion bearing - a bearing designed to permit longitudinal or lateral movements resulting from 

temperature changes and superimposed loads with minimal transmission of horizontal force to the substructure; 

see BEARING 

expansion dam - the part of an expansion joint serving as an end form for the placing of concrete at a joint; 

also applied to the expansion joint device itself; see EXPANSION JOINT 

expansion joint - a joint designed to permit expansion and contraction movements produced by temperature 

changes, loadings or other forces 

expansion rocker - a bearing device at the expansion end of a beam or truss that allows the longitudinal 

movements resulting from temperature changes and superimposed loads through a tilting motion 

expansion roller - a cylinder so mounted that by revolution it facilitates expansion, contraction or other 

movements resulting from temperature changes, loadings or other forces 

expansion shoe - expansion bearing, generally of all metal construction 

exterior girder - an outermost girder supporting the bridge floor 

extrados - the curve defining the exterior (upper) surface of an arch; also known as back 

eyebar - a member consisting of a rectangular bar with enlarged forged ends having holes for engaging 
 G-18 

connecting pins 

F

failure - a condition at which a structure reaches a limit state such as cracking or deflection where it is no 

longer able to perform its usual function; collapse; fracture 

falsework - a temporary wooden or metal framework built to support the weight of a structure during the 

period of its construction and until it becomes self-supporting 

fascia - an outside, covering member designed on the basis of architectural effect rather than strength and 

rigidity, although its function may involve both 

fascia girder - an exposed outermost girder of a span sometimes treated architecturally or otherwise to provide 

an attractive appearance 

fatigue - the tendency of a member to fail at a stress below the yield point when subjected to repetitive loading 

fatigue crack - any crack caused by repeated cyclic loading at a stress below the yield point 

fatigue damage - member damage (crack formation) due to cyclic loading 

fatigue life - the length of service of a member subject to fatigue, based on the number of cycles it can undergo 

fender - a structure that acts as a buffer to protect the portions of a bridge exposed to floating debris and waterborne traffic from collision damage; sometimes called an ice guard in regions with ice floes 

fender pier - a pier-like structure which performs the same service as a fender but is generally more 

substantially built; see GUARD PIER 

field coat - a coat of paint applied after the structure is assembled and its joints completely connected; quite 

commonly a part of the field erection procedure; field painting 

fill - material, usually earth, used to change the surface contour of an area, or to construct an embankment 

filler - a piece used primarily to fill a space beneath a batten, splice plate, gusset, connection angle, stiffener or 

other element; also known as filler plate 

filler metal - metal prepared in wire, rod, electrode or other form to be fused with the structure metal in the 

formation of a weld 

filler plate - see FILLER 

fillet - a curved portion forming a junction of two surfaces that would otherwise intersect at an angle 

fillet weld - a weld of triangular or fillet shaped cross−section between two pieces at right angles 
 G-19 

filling - see FILL 

fine aggregate - sand or grit for concrete or mortar that passes a No. 4 sieve (4.75 mm) 

finger dam - expansion joint in which the opening is spanned by meshing steel fingers or teeth 

fish belly - a term applied to a girder or a truss having its bottom flange or its bottom chord constructed either 

haunched or bow−shaped with the convexity downward; see LENTICULAR TRUSS 

fixed beam - a beam with a fixed end 

fixed bearing - a bearing that allows only rotational movement; see BEARING 

fixed bridge - a bridge having constant position, i.e., without provision for movement to create increased 

navigation clearance 

fixed end - movement is restrained 

fixed-ended arch - see VOUSSOIR ARCH 

fixed span - a superstructure span having its position practically immovable, as compared to a movable span 

fixed support - a support that will allow rotation only, no longitudinal movement 

flange - the (usually) horizontal parts of a rolled I-shaped beam or of a built-up girder extending transversely 

across the top and bottom of the web 

flange angle - an angle used to form a flange element of a built-up girder, column, strut or similar member 

floating bridge - see PONTOON BRIDGE 

floating foundation - used to describe a soil-supported raft or mat foundation with low bearing pressures; 

sometimes applied to a "foundation raft" or "foundation grillage" 

flood frequency - the average time interval in years in which a flow of a given magnitude will recur 

flood plain - area adjacent to a stream or river subject to flooding 

floor - see DECK 

floorbeam - a primary horizontal member located transversely to the general bridge alignment 

floor system - the complete framework of members supporting the bridge deck and the traffic loading 

flow capacity - maximum flow rate that a channel, conduit, or culvert structure is hydraulically capable of 

carrying 
 G-20 

flux - a material that protects the weld from oxidation during the fusion process 

footbridge - a bridge designed and constructed to provide means of traverse for pedestrian traffic only; also 

known as pedestrian bridge 

footing - the enlarged, lower portion of a substructure, which 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 

foot wall - see TOE WALL 

force - an influence that tends to accelerate a body or to change its movement 

forms - the molds that hold concrete in place while it is hardening; also known as form work, shuttering; see 

LAGGING, STAY-IN-PLACE FORMS 

form work - see FORMS 

foundation - the supporting material upon which the substructure portion of a bridge is placed 

foundation excavation - the excavation made to accommodate a footing for a structure; also known as 

foundation pit 

foundation failure - failure of a foundation by differential settlement or by shear failure of the soil 

foundation grillage - a construction consisting of steel, timber, or concrete members placed in layers; each 

layer is perpendicular to those above and below it and the members within a layer are generally parallel, 

producing a crib or grid-like effect. Grillages are usually placed under very heavy concentrated loads 

foundation load - the load resulting from traffic, superstructure, substructure, approach embankment, 

approach causeway, or other incidental load increment imposed upon a given foundation area 

foundation pile - see PILE 

foundation pit - see FOUNDATION EXCAVATION 

foundation seal - a mass of concrete placed underwater within a cofferdam for the base portion of structure to 

close or seal the cofferdam against incoming water; see TREMIE 

fracture - see BRITTLE FRACTURE 

fracture critical member (FCM) - a steel member in tension, or with a tension element, whose failure would 

probably cause a portion of or the entire bridge to collapse 

fracture critical member inspection - a hands-on inspection of a fracture critical member or member 

components that may include visual and other nondestructive evaluation 

frame - a structure which transmits bending moments from the horizontal beam member through rigid joints to 
 G-21 

vertical or inclined supporting members 

framing - the arrangement and connection of the component members of a bridge superstructure 

free end - movement is not restrained 

friction pile - a pile that provides support through friction resistance between the pile and the surrounding 

earth along the lateral surface of the pile 

friction roller - a roller placed between members intended to facilitate change in their relative positions by 

reducing the frictional resistance to translation movement 

frost heave - the upward movement of, or force exerted by, soil due to freezing of retained moisture 

frost line - the depth to which soil may be frozen 

functionally obsolete – a bridge that has deck geometry, load carrying capacity, clearance or approach 

roadway alignment that no longer meets the criteria for the system of which the bridge is a part 

G

gabion - rock filled wire baskets used to retain earth and provide erosion control 

galvanic action - electrical current between two unlike metals 

galvanize - to coat with zinc 

gauge - the distance between parallel lines of rails, rivet holes, etc; a measure of thickness of sheet metal or 

wire; also known as gage 

geometry - shape or form; relationship between lines or points 

girder - a horizontal flexural member that is the main or primary support for a structure; any large beam, 

especially if built up 

girder bridge - a bridge whose superstructure consists of two or more girders supporting a separate floor 

system as differentiated from a multi-beam bridge or a slab bridge 

girder span - a span in which the major longitudinal supporting members are girders 

glue laminated - a member created by gluing together two or more pieces of lumber 

grade - the fall or rise per unit horizontal length; see GRADIENT 

grade crossing - a term applicable to an intersection of two highways, two railroads or a railroad and a 

highway at a common grade or elevation; now commonly accepted as meaning the last of these combinations 
 G-22 

grade intersection - the location where two roadway slopes meet in profile; to provide a smooth transition 

from one to the other they are connected by a vertical curve and the resulting profile is a sag or a crest 

grade separation - roadways crossing each other at different elevations; see OVERPASS, UNDERPASS 

gradient - the rate of inclination of the roadway and/or sidewalk surface(s) from the horizontal, applying to a 

bridge and its approaches; it is commonly expressed as a percentage relation (ratio) of horizontal to vertical 

dimensions 

gravity abutment - a thick abutment that resists horizontal earth pressure through its own dead weight 

gravity wall - a retaining wall that is prevented from overturning or sliding by its own dead weight 

grid flooring - a steel floor system comprising a lattice pattern that may or may not be filled with concrete 

grillage - assembly of parallel beams, usually steel or concrete, placed side by side, often in layers with 

alternating directions; see FOUNDATION GRILLAGE 

groin - a wall built out from a river bank to check scour 

grout - mortar having a sufficient water content to render it free-flowing, used for filling (grouting) the joints 

in masonry, for fixing anchor bolts and for filling cored spaces; usually a thin mix of cement, water and 

sometimes sand or admixtures 

grouting - the process of filling in voids with grout 

guard pier - a pier-like structure built to protect a swing span in its open position from collision with passing 

vessels or water-borne debris; may be equipped with a rest pier upon which the swing span in its open position 

may be latched; see FENDER PIER 

guardrail - a safety feature element intended to redirect an errant vehicle 

guide rail - see GUARDRAIL 

gunite - the process of blowing Portland cement mortar or concrete onto a surface using compressed air 

gusset plate - a plate that connects the members of a structure and holds them in correct position at a joint 

gutter - a paved ditch; area adjacent to a roadway curb used for drainage 

guy - a cable member used to anchor a structure in a desired position 

H 

H Loading - a combination of loads used to represent a two-axle truck developed by AASHTO
 G-23 

hairline cracks - very narrow cracks that form in the surface of concrete due to tension caused by loading 

hammer - hand tool used for sounding and surface inspection 

hammerhead pier - a pier with a single cylindrical or rectangular shaft and a relatively long, transverse cap; 

also known as a tee pier or cantilever pier 

hand hole - hole provided in component plate of built-up box section to permit access to the interior for 

construction and maintenance purposes 

hand rail - commonly applies only to sidewalk railing presenting a latticed, barred, balustered or other open 

web construction 

hands-on - inspection within arms length of the component. Inspection uses visual techniques that may be 

supplemented by nondestructive testing

hands-on access - close enough to the member or component so that it can be touched with the hands and 

inspected visually 

hanger - a tension member serving to suspend an attached member; allows for expansion between a 

cantilevered and suspended span 

haunch - an increase in the depth of a member usually at points of support; the outside areas of a pipe between 

the spring line and the bottom of the pipe 

haunched girder - a horizontal beam whose cross sectional depth varies along its length 

H-beam - a rolled steel member having an H-shaped cross-section (flange width equals beam depth) 

commonly used for piling; also H-pile 

head - a measure of water pressure expressed in terms of an equivalent weight or pressure exerted by a column 

of water; the height of the equivalent column of water is the head 

head loss - the loss of energy between two points along the path of a flowing fluid due to fluid friction; 

reported in feet of head 

headwall - a concrete structure at the ends of a culvert to retain the embankment slopes, anchor the culvert, 

and prevent undercutting 

headwater - the source or the upstream waters of a stream 

heat treatment - any of a number of various operations involving controlled heating and cooling that are used 

to impart specific properties to metals; examples are tempering, quenching, and annealing 

heave - the upward motion of soil caused by outside forces such as excavation, pile driving, moisture or soil 

expansion; see FROST HEAVE 

heel - the portion of a footing behind the stem 
 G-24 

helical - having the form of a spiral 

high carbon steel - carbon steel containing 0.5 to 1.5% dissolved carbon 

high strength bolt - bolt and nut made of high strength steel, usually A325 or A490 

highway - the term ‘highway’ includes: 

A) a road, street, and parkway; 

B) a right-of-way, bridge, railroad-highway crossing, tunnel, drainage structure, 

sign, guardrail, and protective structure, in connection with a highway; and 

C) a portion of any interstate or international bridge or tunnel and the approaches 

thereto, the cost of which is assumed by a State transportation department, 

including such facilities as may be required by the United States Customs and 

Immigration Services in connection with the operation of an international 

 bridge or tunnel 

hinge - a point in a structure at which a member is free to rotate 

hinged joint - a joint constructed with a pin, cylinder segment, spherical segment or other device permitting 

rotational movement 

honeycomb - an area in concrete where mortar has separated and left spaces between the coarse aggregate, 

usually caused by improper vibration during concrete construction 

horizontal alignment - a roadway’s centerline or baseline alignment in the horizontal plane 

horizontal curve - a roadway baseline or centerline alignment defined by a radius in the horizontal plane 

Howe truss - a truss of the parallel chord type with a web system composed of vertical (tension) rods at the 

panel points with an X pattern of diagonals 

HS Loading - a combination of loads developed by AASHTO used to represent a truck and trailer 

hybrid girder - a girder whose flanges and web are made from steel of different grades 

hydraulics - the mechanics of fluids 

hydrology - study of the accumulation and flow of water from watershed areas 

hydroplaning - loss of contact between a tire and the roadway surface when the tire planes or glides on a film 

of water 

I

I-beam - a structural member with a cross−sectional shape similar to the capital letter "I" 
 G-25 

ice guard - see FENDER 

impact - A factor that describes the effect on live load due to dynamic and vibratory effects of a moving load; 

in bridge design, a load based on a percentage of live load to include dynamic and vibratory effects; in fracture 

mechanics, a rapidly applied load, such as a collision or explosion 

incomplete fusion - a weld flaw where the weld metal has not combined metallurgically with the base metal 

in-depth inspection - a close-up, inspection of one or more members above or below the water level to 

identify any deficiencies not readily detectable using routine inspection procedures; hands-on inspection may 

be necessary at some locations 

indeterminate stress - stress in a structural member which cannot be calculated directly; it is computed by the 

iterative application of mathematical equations, usually with an electronic computer; indeterminate stresses 

arise in continuous span and frame type structures 

individual column footing - footing supporting one column 

inelastic compression - compression beyond the yield point 

initial inspection - the first inspection of a bridge as it becomes a part of the bridge file to provide all Structure 

Inventory and Appraisal (SI&A) data and other relevant data and to determine baseline structural conditions. 

inlet - an opening in the floor of a bridge leading to a drain; roadway drainage structure which collects surface 

water and transfers it to pipes 

inspection frequency - the frequency with which the bridge is inspected -- normally every two years 

integral abutment - an abutment cast monolithically with the end diaphragm of the deck; such abutments 

usually encase the ends of the deck beams and are pile supported 

integral deck - a deck which is monolithic with the superstructure; concrete tee beam bridges have integral 

decks 

intercepting ditch - a ditch constructed to prevent surface water from flowing in contact with the toe of an 

embankment or causeway or down the slope of a cut 

interior girder - any girder between exterior or fascia girders 

interior span - a span of which both supports are intermediate substructure units 

intermittent weld - a noncontinuous weld commonly composed of a series of short welds separated by spaces 

of equal length 

intrados - the curve defining the interior (lower) surface of the arch; also known as soffit 

inventory item - data contained in the structure file pertaining to bridge identification, structure type and 
 G-26 

material, age and service, geometric data, navigational data, classification, load rating and posting, proposed 

improvements, and inspections 

inventory rating - the capacity of a bridge to withstand loads under normal service conditions based on 55% 

of yield strength 

invert elevation - the bottom or lowest point of the internal surface of the transverse cross section of a pipe or 

culvert 

iron - a metallic element used in cast iron, wrought iron and steel 

isotropic - having the same material properties in all directions, e.g., steel 

J

jack arch - a deck support system comprised of a brick or concrete arch springing from the bottom flanges of 

adjacent rolled steel beams 

jacking - the lifting of elements using a type of jack (e.g., hydraulic), sometimes acts as a temporary support 

system 

jack stringer - the outermost stringer supporting the bridge floor in a panel or bay 

jacket - a protective shell surrounding a pile made of fabric, concrete or other material 

jersey barrier - a concrete barrier with sloping front face that was developed by the New Jersey Department of 

Transportation 

joint - in masonry, the space between individual stones or bricks; in concrete, a division in continuity of the 

concrete; in a truss, point at which members of a truss are joined 

K

keeper plate - a plate, which is connected to a sole plate, designed to prohibit a beam from becoming 

dislodged from the bearing 

key - a raised portion of concrete on one face of a joint that fits into a depression on the adjacent face 

keystone - the symmetrically shaped, wedge−like stone located in a head ring course at the crown of an arch; 

the final stone placed, thereby closing the arch 

king-post - the vertical member in a "king-post" type truss; also known as king rod 
 G-27 

king-post truss - two triangular panels with a common center vertical; the simplest of triangular system 

trusses 

kip - a kilo pound (1000 lb.); convenient unit for structural calculations 

knee brace - a short member engaging at its ends two other members that are joined to form a right angle or a 

near-right angle to strengthen and stiffen the connecting joint 

knee wall - a return of the abutment backwall at its ends to enclose the bridge seat on three of its sides; also 

called cheek wall 

knife edge - a condition in which corrosion of a steel member has caused a sharp edge 

knuckle - an appliance forming a part of the anchorage of a suspension bridge main suspension member 

permitting movement of the anchorage chain 

K-truss - a truss having a web system wherein the diagonal members intersect the vertical members at or near 

the mid-height; the assembly in each panel forms a letter "K" 

L

L-abutment - a cantilever abutment with the stem flush with the toe of the footing, forming an "L" in cross 

section 

laced column - a riveted, steel built-up column of usually four angles or two channels tied together laterally 

with lacing 

lacing - small flat plates, usually with one rivet at each end, used to tie individual sections of built up members; 

see LATTICE 

lagging - horizontal members spanning between piles to form a wall; forms used to produce curved surfaces; 

see FORMS 

lamellar tear - incipient cracking parallel to the face of a steel member 

laminated timber - timber planks glued together face to face to form a larger member; see GLUE 

LAMINATED 

lane loading - a design loading which represents a line of trucks crossing over a bridge 

lap joint - a joint between two members in which the end of one member overlaps the end of the other 

lateral - a member placed approximately perpendicular to a primary member 

lateral bracing - the bracing assemblage engaging a member perpendicular to the plane of the member; 

intended to resist transverse movement and deformation; also keeps primary parallel elements in truss bridges 

and girder bridges aligned; see BRACING 
 G-28 

lattice - a crisscross assemblage of diagonal bars, channels, or angles on a truss; also known as latticing, lacing 

lattice truss - in general, a truss having its web members inclined but more commonly the term is applied to a 

truss having two or more web systems composed entirely of diagonal members at any interval and crossing 

each other without reference to vertical members 

leaching - the action of removing substances from a material by passing water through it 

lead line - a weighted cord incrementally marked, used to determine the depth of a body of water; also known 

as sounding line 

leaf - the movable portion of a bascule bridge that forms the span of the structure 

legal load - the maximum legal load for each vehicle configuration permitted by law for the State in which the 

bridge is located 

lenticular truss - a truss having parabolic top and bottom chords curved in opposite directions with their ends 

meeting at a common joint; also known as a fish belly truss 

levee - an embankment built to prevent flooding of low-lying land 

leveling course - a layer of bituminous concrete placed to smooth an irregular surface 

light-weight concrete - concrete of less than standard unit weight; may be no-fines concrete, aerated concrete, 

or concrete made with lightweight aggregate 

link - a hanger plate in a pin and hanger assembly whose shape is similar to an eyebar, e.g., the head (at the 

pinhole) is wider than the shank 

link and roller - a movable bridge element consisting of a hinged strut−like link fitted with a roller at its 

bottom end, supported upon a shoe plate or pedestal and operated by a thrust strut serving to force it into a 

vertical position and to withdraw it therefrom; when installed at each outermost end of the girders or the trusses 

of a swing span their major function is to lift them to an extent that their camber or droop will be removed and 

the arms rendered free to act as simple spans; when the links are withdrawn to an inclined position fixed by the 

operating mechanism the span is free to be moved to an open position 

live load - a temporary dynamic load such as vehicular traffic that is applied to a structure; also accompanied 

by vibration or movement affecting its intensity 

load - a force carried by a structure component 

load factor design - a design method used by AASHTO, based on limit states of material and arbitrarily 

increased loads 

load indicating washer - a washer with small projections on one side, which compress as the bolt is tightened; 

gives a direct indication of the bolt tension that has been achieved 
 G-29 

load rating - the determination of the live load carrying capacity of a bridge using bridge plans and 

supplemented by information gathered from a field inspection 

load and resistance factor design (LRFD) - design method used by AASHTO, based on limit states of 

material with increased loads and reduced member capacity based on statistical probabilities 

local buckling - localized buckling of a beam’s plate element, can lead to failure of member 

longitudinal bracing - bracing that runs lengthwise with a bridge and provides resistance against longitudinal 

movement and deformation of transverse members 

loss of prestress - loss of prestressing force due to a variety of factors, including shrinkage and creep of the 

concrete, creep of the prestressing tendons, and loss of bond 

low-carbon steel - steel with 0.04 to 0.25% dissolved carbon; also called mild steel 

lower chord - the bottom horizontal member of a truss 

luminaire - a lighting fixture 

M

macadam - roadway pavement made with crushed stone aggregate, of coarse open gradation, compacted in 

place; asphaltic macadam included asphalt as a binder 

main beam - a horizontal structural member which supports the span and bears directly on a column or wall 

maintenance - basic repairs performed on a facility to keep it at an adequate level of service 

maintenance and protection of traffic - the management of vehicular and pedestrian traffic through a 

construction zone to ensure the safety of the public and the construction workforce; MPT; TRAFFIC 

PROTECTION 

marine borers - mollusks and crustaceans that live in water and destroy wood by digesting it 

masonry - that portion of a structure composed of stone, brick or concrete block placed in courses and usually 

cemented with mortar 

masonry cement - Portland cement and lime used to make mortar for masonry construction 

masonry plate - a steel plate placed on the substructure to support a superstructure bearing and to distribute 

the load to the masonry beneath 

mattress - a flexible scour protection blanket composed of interconnected timber, gabions, or concrete units. 

meander - a twisting, winding action from side to side; characterizes the serpentine curvature of a narrow, 
 G-30 

slow flowing stream in a wide flood plain 

median - separation between opposing lanes of highway traffic; also known as median strip 

member - an individual angle, beam, plate, or built component piece intended ultimately to become an integral 

part of an assembled frame or structure 

metal corrosion - oxidation of metal by electro-galvanic action involving an electrolyte (moisture), an anode 

(the metallic surface where oxidation occurs), a cathode (the metallic surface that accepts electrons and does 

not corrode), and a conductor (the metal piece itself) 

midspan - a reference point half−way between the supports of a beam or span 

mild steel - steel containing from 0.04 to 0.25% dissolved carbon; see LOW CARBON STEEL 

military loading - a loading pattern used to simulate heavy military vehicles passing over a bridge 

mill scale - dense iron oxide on iron or steel that forms on the surface of metal that has been forged or hot 

worked 

modular joint - a bridge joint designed to handle large movements consisting of an assembly of several strip 

or compression seals 

moisture content - the amount of water in a material expressed as a percent by weight 

moment - the couple effect of forces about a given point; see BENDING MOMENT 

monolithic - forming a single mass without joints 

mortar - a paste of portland cement, sand, and water laid between bricks, stones or blocks 

movable bridge - a bridge having one or more spans capable of being raised, turned, lifted, or slid from its 

normal service location to provide a clear navigation passage; see BASCULE BRIDGE, VERTICAL LIFT 

BRIDGE, PONTOON BRIDGE, RETRACTILE DRAW BRIDGE, ROLLING LIFT BRIDGE, and SWING 

BRIDGE 

movable span - a general term applied to a superstructure span designed to be swung, lifted or otherwise 

moved longitudinally, horizontally or vertically, usually to provide increased navigational clearance 

moving load - a live load which is moving, for example, vehicular traffic 

MPT - see MAINTENANCE AND PROTECTION OF TRAFFIC 

MSE - mechanically stabilized earth; see REINFORCED EARTH 

multi-centered arch - an arch in which the intrados surface is outlined by two or more arcs symmetrically 

arranged and having different radii that intersect tangentially 
 G-31 

N

nail laminated - a laminated member produced by nailing two or more pieces of timber together face to face 

NBIS - National Bridge Inspection Standards, first established in 1971 to set national policy regarding bridge 

inspection frequency, inspector qualifications, report formats, and inspection and rating procedures 

NCHRP - National Cooperative Highway Research Program 

NICET - National Institute for Certification in Engineering Technologies, the NICET provides nationally 

applicable voluntary certification programs covering several broad engineering technology fields and a number 

of specialized subfields. For information on the NICET program certification contact: National Institute for 

Certification in Engineering Technologies, 1420 King Street, Alexandria, VA 22314–2794. 

NDE - nondestructive evaluation 

NDT - nondestructive testing; any testing method of checking structural quality of materials that does not 

damage them 

necking - the elongation and contraction in area that occurs when a ductile material is stressed 

negative bending - bending of a member that causes tension in the surface adjacent to the load, e.g., moment 

at interior supports of a span or at the joints of a frame 

negative moment - bending moment in a member such that tension stresses are produced in the top portions of 

the member; typically occurs in continuous beams and spans over the intermediate supports 

neoprene - a synthetic rubber-like material used in expansion joints and elastomeric bearings 

neutral axis - the internal axis of a member in bending along which the strain is zero; on one side of the 

neutral axis the fibers are in tension, on the other side the fibers are in compression 

nose - a projection acting as a cut water on the upstream end of a pier; see STARLING 

notch effect - stress concentration caused by an abrupt discontinuity or change in section 

O

offset - a horizontal distance measured at right angles to a survey line to locate a point off the line 

on center - a description of a typical dimension between the centers of the objects being measured 

open spandrel arch - a bridge that has open spaces between the deck and the arch members allowing "open" 

visibility through the bridge 
 G-32 

open spandrel ribbed arch - a structure in which two or more comparatively narrow arch rings, called ribs, 

function in the place of an arch barrel; the ribs are rigidly secured in position by arch rib struts located at 

intervals along the length of the arch; the arch ribs carry a column type open spandrel construction which 

supports the floor system and its loads 

operating rating - the capacity of a bridge to withstand loads based on 75% of yield strength; the maximum 

permissible live load to which the structure may be subjected for the load configuration used in the rating 

operator's house - the building containing control devices required for opening and closing a movable bridge 

span 

orthotropic - having different properties in two or more directions at right angles to each other (e.g., wood); 

see ANISOTROPY 

outlet - in hydraulics, the discharge end of drains, sewers, or culverts 

out-of-plane distortion - distortion of a member in a plane other than that which the member was designed to 

resist 

overlay - see WEARING SURFACE 

overload - a weight greater than the structure is designed to carry 

overpass - bridge over a roadway or railroad 

overturning - tipping over; rotational movement 

oxidation - the chemical breakdown of a substance due to its reaction with oxygen from the air 

oxidized steel - rust 

P

pack - a steel plate inserted between two others to fill a gap and fit them tightly together; also known as 

packing; fill; filler plate 

pack rust - rust forming between adjacent steel surfaces in contact which tends to force the surfaces apart due 

to the increase in material volume 

paddleboard - striped, paddle-shaped signs or boards placed on the roadside in front of a narrow bridge as a 

warning of reduced roadway width 

panel -the portion of a truss span between adjacent points of intersection of web and chord members 

panel point - the point of intersection of primary web and chord members of a truss 

parabolic arch - an arch in which the intrados surface is a segment of a symmetrical parabolic surface (suited 

to concrete arches) 
 G-33 

parabolic truss - a polygonal truss having its top chord and end post vertices coincident with the arc of a 

parabola, its bottom chord straight and its web system either triangular or quadrangular; also known as a 

parabolic arched truss 

parapet - a low wall along the outmost edge of the roadway of a bridge to protect vehicles and pedestrians 

pedestal - concrete or built-up metal member constructed on top of a bridge seat for the purpose of providing a 

specific bearing seat elevation 

pedestal pier - one or more piers built in block-like form that may be connected by an integrally built web 

between them; when composed of a single, wide block−like form, it is called a wall or solid pier 

pedestrian bridge - see FOOT BRIDGE 

penetration - when applied to creosoted lumber, the depth to which the surface wood is permeated by the 

creosote oil; when applied to pile driving; the depth a pile tip is driven into the ground 

physical testing - the testing of bridge members in the field or laboratory 

pier - a substructure unit that supports the spans of a multi-span superstructure at an intermediate location 

between its abutments 

pier cap - the topmost horizontal portion of a pier that distributes loads from the superstructure to the vertical 

pier elements 

pile - a shaft-like linear member which carries loads to underlying rock or soil strata 

pile bent - a row of driven or placed piles extending above the ground surface supporting a pile cap; see BENT 

pile bridge - a bridge carried on piles or pile bents 

pile cap - a slab or beam which acts to secure the piles in position laterally and provides a bridge seat to 

receive and distribute superstructure loads 

pile foundation - a foundation supported by piles in sufficient number and to a depth adequate to develop the 

bearing resistance required to support the substructure load 

pile pier - see PILE BENT 

piling - collective term applied to group of piles in a construction; see PILE, SHEET PILES 

pin - a cylindrical bar used to connect elements of a structure 

pin-connected truss - a general term applied to a truss of any type having its chord and web members 

connected at each panel point by a single pin 

pin and hanger - a hinged connection detail designed to allow for expansion and rotation between a 
 G-34 

cantilevered and suspended span at a point between supports. 

pin joint - a joint in a truss or other frame in which the members are assembled upon a single cylindrical pin 

pin packing - arrangement of truss members on a pin at a pinned joint 

pin plate - a plate rigidly attached upon the end of a member to develop the desired bearing upon a pin or pinlike bearing, and secure additional strength and rigidity in the member; doubler plate 

pintle - a relatively small steel pin engaging the rocker of an expansion bearing, in a sole plate or masonry 

plate, thereby preventing sliding of the rocker 

pipe - a hollow cylinder used for the conveyance of water, gas, steam etc. 

piping - removal of fine particles from within a soil mass by flowing water 

plain concrete - concrete with no structural reinforcement except, possibly, light steel to reduce shrinkage and 

temperature cracking 

plan and profile - a drawing that shows both the roadway plan view and profile view in the same scale; see 

PLAN VIEW, PROFILE 

plan view - drawing that represents the top view of the road or a structure 

plastic deformation - permanent deformation of material beyond the elastic range 

plate - a flat sheet of metal which is relatively thick; see SHEET STEEL 

plate girder - a large I-shaped beam composed of a solid web plate with flange plates attached to the web plate 

by flange angles or fillet welds 

plug weld - a weld joining two members produced by depositing weld metal within holes cut through one or 

more of the members; also known as slot weld 

plumb bob - a weight hanging on a cord used to provide a true vertical reference 

plumb line - a true vertical reference line established using a plumb bob 

pneumatic caisson - an underwater caisson in which the working chamber is kept free of water by compressed 

air at a pressure nearly equal to the water pressure outside it 

pointing - the compacting of the mortar into the outermost portion of a joint and the troweling of its exposed 

surface to secure water tightness or desired architectural effect; replacing deteriorated mortar 

ponding - accumulation of water 

pontoon bridge - a bridge supported by floating on pontoons moored to the riverbed; a portion may be 

removable to facilitate navigation 
 G-35 

pony truss - a through truss without top chord lateral bracing 

pop-out - conical fragment broken out of a concrete surface by pressure from reactive aggregate particles 

portable bridge - a bridge that may be readily erected for a temporary communication-transport service and 

disassembled and reassembled at another location 

portal - the clear unobstructed space of a through truss bridge forming the entrance to the structure 

portal bracing - a system of sway bracing placed in the plane of the end posts of the trusses 

portland cement - a fine dry powder made by grinding limestone clinker made by heating limestone in a kiln; 

this material reacts chemically with water to produce a solid mass 

portland cement concrete - a mixture of aggregate, portland cement, water, and usually chemical admixtures 

positive moment - a force applied over a distance that causes compression in the top fiber of a beam and 

tension in the bottom fiber 

post - a member resisting compressive stresses, located vertical to the bottom chord of a truss and common to 

two truss panels; sometimes used synonymously for vertical; see COLUMN 

posting - a limiting dimension, speed, or loading indicating larger dimensions, higher speeds, or greater loads 

cannot be safely taken by the bridge 

post-stressing - see POSTTENSIONING 

posttensioning - a method of prestressing concrete in which the tendons are stressed after the concrete has 

been cast and hardens 

pot bearing - a bearing type that allows for multi-dimensional rotation by using a piston supported on an 

elastomer contained on a cylinder ("pot"), or spherical bearing element 

pot holes - irregular shaped, disintegrated areas of bridge deck or roadway pavement caused by the failure of 

the surface material 

Pratt truss - a truss with parallel chords and a web system composed of vertical posts with diagonal ties 

inclined outward and upward from the bottom chord panel points toward the ends of the truss; also known as 

N-truss 

precast concrete - concrete members that are cast and cured before being placed into their final positions on a 

construction site 

prestressed concrete - concrete with strands, tendons, or bars that are stressed before the live load is applied 

prestressing - applying forces to a structure to deform it in such a way that it will withstand its working loads 

more effectively; see POSTTENSIONING, PRETENSIONING 
 G-36 

pretensioning - a method of prestressing concrete in which the strands are stressed before the concrete is 

placed; strands are released after the concrete has hardened, inducing internal compression into the concrete 

primary member - a member designed to resist flexure and distribute primary live loads and dead loads 

priming coat - the first coat of paint applied to the metal or other material of a bridge; also known as base 

coat, or primer 

probing - investigating the location and condition of submerged foundation material using a rod or shaft of 

appropriate length; checking the surface condition of a timber member for decay using a pointed tool, e.g., an 

ice pick 

Professional engineer (PE) - an individual, who has fulfilled education and experience requirements and 

passed rigorous exams that, under State licensure laws, permits them to offer engineering services directly to 

the public. Engineering licensure laws vary from State to State, but, in general, to become a PE an individual 

must be a graduate of an engineering program accredited by the Accreditation Board for Engineering and 

Technology, pass the Fundamentals of Engineering exam, gain four years of experience working under a PE, 

and pass the Principles of Practice of Engineering exam

profile - a section cut vertically along the center line of a roadway or waterway to show the original and final 

ground levels 

program manager - the individual in charge of the program, that has been assigned or delegated the duties 

and responsibilities for bridge inspection, reporting, and inventory. The program manager provides overall 

leadership and is available to inspection team leaders to provide guidance

programmed repair - those repairs that may be performed in a scheduled program 

protective system - a system used to protect bridges from environmental forces that cause steel and concrete to 

deteriorate and timber to decay, typically a coating system 

PS&E - Plans, Specifications, and Estimate; the final submission of the designers to the owner 

public road. - the term ``public road'' means any road or street under the jurisdiction of and maintained by a 

public authority and open to public travel

punching shear - shear stress in a slab due to the application of a concentrated load 

Q

quality assurance (QA) - the use of sampling and other measures to assure the adequacy of quality control 

procedures in order to verify or measure the quality level of the entire bridge inspection and load rating 

program 
 G-37 

quality control (QC) - procedures that are intended to maintain the quality of a bridge inspection and load 

rating at or above a specified level 

queen-post truss - a parallel chord type of truss having three panels with the top chord occupying only the 

length of the center panel 

R

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; see HANDRAIL 

rake - an angle of inclination of a surface in relation to a vertical plane; also known as batter 

ramp - an inclined traffic-way leading from one elevation to another 

range of stress - the algebraic difference between the minimum and maximum stresses in a member 

raveling - the consistent loss of aggregate from a pavement resulting in a poor riding surface 

reaction - the resistance of a support to a load 

rebar - see REINFORCING BAR 

redundancy - the quality of a bridge that enables it to perform its design function in a damaged state. 

redundant member - a member in a bridge which 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 

rehabilitation - significant repair work to a structure 

reinforced concrete - concrete with steel reinforcing bars embedded in it to supply increased tensile strength 

and durability 

reinforced concrete pipe - pipe manufactured of concrete reinforced with steel bars or welded wire fabric 

Reinforced Earth - proprietary retaining structure made of earth and steel strips connected to concrete facing; 

the steel strips are embedded in backfill and interlock with the facing; see MSE 

reinforcement - rods or mesh embedded in concrete to strengthen it 

reinforcing bar - a steel bar, plain or with a deformed surface, which bonds to the concrete and supplies 

tensile strength to the concrete 

relaxation - a decrease in stress caused by creep 
 G-38 

residual stress - a stress that is trapped in a member after it is formed into its final shape 

resistivity of soil - an electrical measurement in ohm-cm that estimates the corrosion activity potential of a 

given soil 

resurfacing - a layer of wearing surface material that is put over the approach or deck surface in order to create 

a more uniform riding surface 

Retained Earth - proprietary retaining structure made of weld wire fabric strips connected to concrete facing; 

see MSE 

retaining wall - a structure designed to restrain and hold back a mass of earth 

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 

rib - curved structural member supporting a curved shape or panel 

rigger - an individual who erects and maintains scaffolding or other access equipment such as that used for 

bridge inspection 

rigid frame - a structural frame in which bending moment is transferred between horizontal and vertical or 

inclined members by joints 

rigid frame bridge - a bridge with moment resisting joints between the horizontal portion of the superstructure 

and vertical or inclined legs 

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 - stones, blocks of concrete or other objects placed upon river and stream beds and banks, lake, tidal or 

other shores to prevent scour by water flow or wave action 

rivet - a one-piece metal fastener held in place by forged heads at each end 

riveted joint - a joint in which the assembled members are fastened by rivets 

roadway - the portion of the road intended for the use of vehicular traffic 

roadway shoulder - drivable area immediately adjoining the traveled roadway 

rocker bearing - a bridge support that accommodates expansion and contraction of the superstructure through 

a tilting 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 
 G-39 

rolled shape - forms of rolled steel having "I", "H", "C", "Z" or other cross sectional shapes 

rolled-steel section - any hot-rolled steel section including wide flange shapes, channels, angles, etc. 

roller - a steel cylinder intended to provide longitudinal movements by rolling contact 

roller bearing - a single roller or a group of rollers so installed 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 

routine inspection - regularly scheduled inspection consisting of observations and/or measurements needed to 

determine the physical and functional condition of the bridge, to identify any changes from initial or previously 

recorded conditions, and to ensure that the structure continues to satisfy present service requirements. 

routine permit load - a live load, which has a gross weight, axle weight or distance between axles not 

conforming with State statutes for legally configured vehicles, authorized for unlimited trips over an extended 

period of time to move alongside other heavy vehicles on a regular basis. 

rubble - irregularly shaped pieces of stone in the undressed condition obtained from a quarry and varying in 

size 

runoff - the quantity of precipitation that flows from a catchment area past a given point over a certain period 

S

sacrificial anode - the anode in a cathodic protection system 

sacrificial coating - a coating over the base material to provide protection to the base material; examples 

include galvanizing on steel and aluclading on aluminum 

sacrificial protection - see CATHODIC PROTECTION 

sacrificial thickness - additional material thickness provided for extra service life of a member in an 

aggressive environment 

saddle - a member located upon the topmost portion of the tower of a suspension bridge which acts as a 

bearing surface for the catenary cable passing over it 

safe load - the maximum load that a structure can support with an appropriate factor of safety 
 G-40 

safety belt - a belt worn in conjunction with a safety line to prevent falling a long distance when working at 

heights; no longer acceptable as fall protection under OSHA rules 

safety curb - a curb between 9 inches and 24 inches wide serving as a limited use refuge or walkway for 

pedestrians crossing a bridge 

safety factor - the difference between the ultimate strength of a member and the maximum load it is expected 

to carry 

safety harness - harness with shoulder, leg, and waist straps of approved OSHA design used as personal fall 

protection in conjunction with appropriate lanyards and tie off devices 

sag - to sink or bend downward due to weight or pressure 

scab - a plank bolted over the joint between two timber members to hold them in correct alignment and 

strengthen the joint; a short piece of I−beam or other structural shape attached to the flange or web of a metal 

pile to increase its resistance to penetration; also known as scab piece 

scaling - the gradual disintegration of a concrete surface due to the failure of the cement paste caused by 

chemical attack or freeze/thaw cycles 

scour - removal of a streambed or bank area by stream flow; erosion of streambed or bank material due to 

flowing water; often considered as being localized around piers and abutments of bridges 

scour critical bridge - a bridge with a foundation element that has been determined to be unstable for the 

observed or evaluated scour condition. 

scour protection - protection of submerged material by steel sheet piling, rip rap, concrete lining, or 

combination thereof 

scuba - self-contained underwater breathing apparatus; a portable breathing device for free swimming divers 

scupper - an opening in the deck of a bridge to provide means for water accumulated upon the roadway 

surface to drain 

seam weld - a weld joining the edges of two members placed in contact; in general, it is not a stress-carrying 

weld 

seat - a base on which an object or member is placed 

seat angle - a piece of angle attached to the side of a member to provide support for a connecting member 

either temporarily during its erection or permanently; also known as a shelf angle 

secondary member - a member that does not carry calculated live loads; bracing members 

section loss - loss of a member's cross sectional area usually by corrosion or decay 
 G-41 

section view - an internal representation of a structure element as if a slice was made through the element 

seepage - the slow movement of water through a material 

segmental - constructed of individual pieces or segments which are collectively joined to form the whole 

segmental arch - a circular arch in which the intrados is less than a semi-circle 

segregation - in concrete construction, the separation of large aggregate from the paste during placement 

seismic - a term referring to earthquakes (e.g., seismic forces) 

semi-stub abutment - cantilever abutment founded part way up the slope, intermediate in size between a full 

height abutment and a stub abutment 

service load design - AASHTO’s description for Working Stress Design 

settlement - the movement of substructure elements due to changes in the soil properties 

shear - the load acting across a beam near its support 

shear connectors - devices that extend from the top flange of a beam and are embedded in the above concrete 

slab, forcing the beam and the concrete to act as a single unit 

shear spiral - a coil-shaped component welded to the top flange of a beam, as a shear connector 

shear stress - the shear force per unit of cross−sectional area; also referred to as diagonal tensile stress 

shear stud - a type of shear connector in the form of a road with a head that is attached to a beam with an 

automatic stud-welding gun 

sheet pile cofferdam - a wall-like barrier composed of driven piling constructed to surround the area to be 

occupied by a structure and permit dewatering of the enclosure so that the excavation may be performed in the 

open air 

sheet piles - flattened Z-shaped interlocking piles driven into the ground to keep earth or water out of an 

excavation or to protect an embankment 

sheet piling - a general or collective term used to describe a number of sheet piles installed to form a crib, 

cofferdam, bulkhead, etc.; also known as sheeting 

sheet steel - steel in the form of a relatively thin sheet or plate; for flat rolled steel, specific thicknesses vs. 

widths are classified by AISI as bar, strip, sheet or plate 

shelf angle - see SEAT ANGLE 

shim - a thin plate inserted between two elements to fix their relative position and to transmit bearing stress 
 G-42 

shoe - a steel or iron member, usually a casting or weldment, beneath the superstructure bearing that transmits 

and distributes loads to the substructure bearing area 

shop - a factory or workshop 

shop drawings - detailed drawings developed from the more general design drawings used in the manufacture 

or fabrication of bridge components 

shoring - a strut or prop placed against or beneath a structure to restrain movement; temporary soil retaining 

structure 

shoulder abutment - a cantilever abutment extending from the grade line of the road below to that of the road 

overhead, usually set just off the shoulder; see FULL HEIGHT ABUTMENT 

shoulder area - see ROADWAY SHOULDER 

shrinkage – a reduction in volume caused by moisture loss in concrete or timber while drying 

sidewalk - the portion of the bridge floor area serving pedestrian traffic only 

sidewalk bracket - frame attached to and projecting from the outside of a girder to serve as a support for the 

sidewalk stringers, floor and railing or parapet 

sight distance - the length of roadway ahead that is easily visible to the driver; required sight distances are 

defined by AASHTO's "A Policy on Geometric Design of Highways and Streets" 

silt - very finely divided siliceous or other hard rock material removed from its mother rock through erosive 

action rather than chemical decomposition 

simple span - beam or truss with two unrestraining supports near its ends 

S-I-P forms - see STAY-IN-PLACE FORMS, FORMS 

skew angle - the angle produced when the longitudinal members of a bridge are not perpendicular to the 

substructure; the skew angle is the acute angle between the alignment of the bridge and a line perpendicular to 

the centerline of the substructure units 

skewback - the inclined support at each end of an arch 

skewback shoe - the member transmitting the thrust of an arch to the skewback course or cushion course of an 

abutment or piers; also known as skewback pedestal 

slab - a wide beam, usually of reinforced concrete, which supports load by flexure 

slab bridge - a bridge having a superstructure composed of a reinforced concrete slab constructed either as a 

single unit or as a series of narrow slabs placed parallel with the roadway alignment and spanning the space 

between the supporting substructure units 
 G-43 

slide - movement on a slope because of an increase in load or a removal of support at the toe; also known as 

landslide 

slip form - to form concrete by advancing a mold 

slope - the inclination of a surface expressed as a ratio of one unit of rise or fall for so many horizontal units 

slope protection - a thin surfacing of stone, concrete or other material deposited upon a sloped surface to 

prevent its disintegration by rain, wind or other erosive action; also known as slope pavement 

slot weld - see PLUG WELD 

slump - a measurement taken to determine the stiffness of concrete; the measurement is the loss in height after 

a cone-shaped mold is lifted 

soffit - underside of a bridge deck; also see INTRADOS 

soldier beam - a steel pile driven into the earth with its projecting butt end used as a cantilever beam 

soldier pile wall - a series of soldier beams supporting horizontal lagging to retain an excavated surface; 

commonly used in limited right-of-way applications 

soil interaction structure - a subsurface structure that incorporates both the strength properties of a flexible 

structure and the support properties of the soil surrounding the structure 

sole plate - a plate attached to the bottom flange of a beam that distributes the reaction of the bearing to the 

beam 

solid sawn beam – a section of tree cut to the desired size at a saw mill 

sounding - determining the depth of water by an echo-sounder or lead line; tapping a surface to detect 

delaminations (concrete) or decay (timber) 

spall - depression in concrete caused by a separation of a portion of the surface concrete, revealing a fracture 

parallel with or slightly inclined to the surface 

span - the distance between the supports of a beam; the distance between the faces of the substructure 

elements; the complete superstructure of a single span bridge or a corresponding integral unit of a multiple 

span structure; see CLEAR SPAN 

spandrel - the space bounded by the arch extrados and the horizontal member above it 

spandrel column - a column constructed on the rib of an arch span and serving as a support for the deck 

construction of an open spandrel arch; see OPEN SPANDREL ARCH 

spandrel fill - the fill material placed within the spandrel space of a closed spandrel arch 

spandrel tie - a wall or a beam-like member connecting the spandrel walls of an arch and securing them 
 G-44 

against bulging and other deformation; in stone masonry arches the spandrel tie walls served to some extent as 

counterforts 

spandrel wall - a wall built on the extrados of an arch filling the space below the deck; see TIE WALLS 

special inspection - an inspection scheduled at the discretion of the bridge owner, used to monitor a particular 

known or suspected deficiency

specifications - a detailed description of requirements, materials, tolerances, etc., for construction which are 

not shown on the drawings; also known as specs 

spider - inspection access equipment consisting of a bucket or basket which moves vertically on wire rope, 

driven by an electric or compressed air motor 

spillway - a channel used to carry water away from the top of a slope to an adjoining outlet 

splice - a structural joint between members to extend their effective length 

spread footing - a foundation, usually a reinforced concrete slab, which distributes load to the earth or rock 

below the structure 

spring line - the horizontal line along the face of an abutment or pier at which the intrados of an arch begins 

spur - a projecting jetty-like construction placed adjacent to an abutment or embankment to prevent scour 

stage - inspection access equipment consisting of a flat platform supported by horizontal wire-rope cables; the 

stage is then slid along the cables to the desired position; a stage is typically 20 inches wide, with a variety of 

lengths available 

staged construction - construction performed in phases, usually to permit the flow of traffic through the site 

state transportation department - the term “state transportation department” means that department, 

commission, board, or official of any State charged by its laws with the responsibility for highway construction 

statics - the study of forces and bodies at rest 

station - 100 feet (U.S. customary); 100 meters (metric) 

stationing - a system of measuring distance along a baseline 

stay-in-place forms - a corrugated metal sheet for forming deck concrete that will remain in place after the 

concrete has set; the forms do not contribute to deck structural capacity after the deck has cured; see FORMS, 

S.I.P FORMS 

stay plate - a tie plate or diagonal brace to prevent movement 

steel - an alloy of iron, carbon, and various other elements 
 G-45 

stem - the vertical wall portion of an abutment retaining wall, or solid pier; see BREASTWALL 

stiffener - a small member attached to another member to transfer stress and to prevent buckling 

stiffening girder - a girder incorporated in a suspension bridge to distribute the traffic loads uniformly among 

the suspenders and reduce local deflections 

stiffening truss - a truss incorporated in a suspension bridge to distribute the traffic loads uniformly among the 

suspenders and reduce local deflections 

stirrup - U-shaped bar used as a connection device in timber and metal bridges; U-shaped bar placed in 

concrete to resist diagonal tension (shear) stresses 

stone masonry - the portion of a structure composed of stone, generally placed in courses with mortar 

straight abutment - an abutment whose stem and wings are in the same plane or whose stem is included 

within a length of retaining wall 

strain - the change in length of a body produced by the application of external forces, measured in units of 

length; this is the proportional relation of the amount of change in length divided by the original length 

strand - a number of wires grouped together usually by twisting 

strengthening - adding to the capacity of a structural member 

stress - the force acting across a unit area in a solid material 

stress concentration - local increases in stress caused by a sudden change of cross section in a member 

stress range - the variation in stress at a point with the passage of live load, from initial dead load value to the 

maximum additional live load value and back 

stress raiser - a detail that causes stress concentration 

stress reversal - change of stress type from tension (+) to compression (−) or vice versa 

stress sheet - a drawing showing all computed stresses resulting from the application of a system of loads 

together with the design composition of the individual members resulting from the application of assumed unit 

stresses for the material to be used in the structure 

stress-laminated timber – consists of multiple planks mechanically clamped together to perform as 

one unit

stringer - a longitudinal beam spanning between transverse floorbeams and supporting a bridge deck 

strip seal joint - a joint using a relatively thin neoprene seal fitted into the joint opening 
 G-46 

structural analysis - engineering computation to determine the carrying capacity of a structure 

structural member - an individual piece, such as a beam or strut, which is an integral part of a structure 

structural redundancy - the ability of an interior continuous span to resist total collapse by cantilever action 

in the event of a fracture 

structural shapes - the various types of rolled iron and steel having flat, round, angle, channel, "I", "H", "Z" 

and other cross-sectional shapes adapted to heavy construction 

structural stability - the ability of a structure to maintain its normal configuration, not collapse or tip in any 

way, under existing and expected loads 

structural tee - a tee-shaped rolled member formed by cutting a wide flange longitudinally along the centerline 

of web 

structurally deficient – bridges where 1) significant load carrying elements are found to be in poor or worse 

condition due to deterioration and/or damage or, 2) the adequacy of the waterway opening provided by the 

bridge is determined to be extremely insufficient to the point of causing intolerable traffic interruptions 

structure - something, such as a bridge, that is designed and built to sustain a load 

strut - a member acting to resist axial compressive stress; usually a secondary member

stub abutment - an abutment within the topmost portion of an embankment or slope having a relatively small 

vertical height and usually pile supported; stub abutments may also be founded on spread footings 

subbase - a layer of material placed between the base course and the subgrade within a flexible pavement 

structure 

subgrade - natural earth below the roadway pavement structure 

sub-panel - a truss panel divided into two parts by an intermediate web member, generally a subdiagonal or a 

hanger 

substructure - the abutments and piers built to support the span of a bridge superstructure 

superelevation - the difference in elevation between the inside and outside edges of a roadway in a horizontal 

curve; required to counteract the effects of centrifugal force 

superimposed dead load - dead load that is applied to a compositely designed bridge after the concrete deck 

has cured; for example, the weight of parapets or railings placed after the concrete deck has cured 

superstructure - the entire portion of a bridge structure that primarily receives and supports traffic loads and 

in turn transfers these loads to the bridge substructure 

surface corrosion - rust that has not yet caused measurable section loss 
 G-47 

suspended span - a simple span supported from the free ends of cantilevers 

suspender - a vertical wire cable, metal rod, or bar connecting the catenary cable of a suspension bridge or an 

arch rib to the bridge floor system, transferring loads from the deck to the main members 

suspension bridge - a bridge in which the floor system is supported by catenary cables that are supported upon 

towers and are anchored at their extreme ends 

suspension cable - a catenary cable which is one of the main members upon which the floor system of a 

suspension bridge is supported; a cable spanning between towers 

swale - a drainage ditch with moderately sloping sides 

sway anchorage - a guy, stay cable or chain attached to the floor system of a suspension bridge and anchored 

upon an abutment or pier to increase the resistance of the suspension span to lateral movement; also known as 

sway cable 

sway bracing - diagonal brace located at the top of a through truss, transverse to the truss and usually in a 

vertical plane, to resist transverse horizontal forces 

sway frame - a complete panel or frame of sway bracing 

swedged anchor bolt - anchor bolt with deformations to increase bond in concrete; see ANCHOR BOLT 

swing span bridge - a movable bridge in which the span rotates in a horizontal plane on a pivot pier, to permit 

passage of marine traffic 

T

tack welds - small welds used to hold member elements in place during fabrication or erection 

tail water - water ponded below the outlet of a waterway, thereby reducing the amount of flow through the 

waterway; see HEADWATER 

tape measure - a long, flexible strip of metal or fabric marked at regular intervals for measuring 

team leader - individual in charge of an inspection team responsible for planning, preparing, and performing 

field inspection of the bridge 

tee beam - a rolled steel section shaped like a "T"; reinforced concrete beam shaped like the letter "T" 

temperature steel - reinforcement in a concrete member to prevent cracks due to stresses caused by 

temperature changes 

temporary bridge - a structure built for emergency or interim use, intended to be removed in a relatively short 

time 
 G-48 

tendon - a prestressing cable, strand, or bar 

tensile force - a force caused by pulling at the ends of a member; see TENSION 

tensile strength - the maximum tensile stress at which a material fails 

tension - stress that tends to pull apart material 

thermal movement - contraction and expansion of a structure due to a change in temperature 

three-hinged arch - an arch that is hinged at each support and at the crown 

through arch - an arch bridge in which the deck passes between the arches 

through girder bridge - normally a two-girder bridge where the deck is between the supporting girders 

tie - a member carrying tension 

tie plate - relatively short, flat member carrying tension forces across a transverse member; for example, the 

plate connecting a floor beam cantilever to the main floor beam on the opposite side of a longitudinal girder; 

see STAY PLATE 

tie rod - a rod-like member in a frame functioning to transmit tensile stress; also known as tie bar 

tie walls - one of the walls built at intervals above an arch ring connecting and supporting the spandrel walls; 

any wall designed to serve as a restraining member to prevent bulging and distortion of two other walls 

connected thereby; see DIAPHRAGM WALL 

timber - wood suitable for construction purposes 

toe - the front portion of a footing from the intersection of the front face of the wall or abutment to the front 

edge of the footing; the line where the side slope of an embankment meets the existing ground 

toe of slope - the location defined by the intersection of the embankment with the surface existing at a lower 

elevation; also known as toe 

toe wall - a relatively low retaining wall placed near the "toe−of−slope" location of an embankment to protect 

against scour or to prevent the accumulation of stream debris; also known as footwall 

 

ton - a unit of weight equal to 2,000 pounds 

torque - the angular force causing rotation 

torque wrench - a hand or power tool used to turn a nut on a bolt that can be adjusted to deliver a 

predetermined amount of torque 

torsion - twisting about the longitudinal axis of a member 
 G-49 

torsional rigidity - a beam’s capacity to resist a twisting force along the longitudinal axis 

tower - a pier or frame supporting the catenary cables of a suspension bridge 

traffic control - modification of normal traffic patterns by signs, cones, flagmen, etc. 

transducer - a device that converts one form of energy into another form, usually electrical into mechanical or 

the reverse; the part of ultrasonic testing device which transmits and receives sound waves 

transverse bracing - the bracing assemblage engaging the columns of bents and towers in planes transverse to 

the bridge alignment that resists the transverse forces tending to produce lateral movement and deformation of 

the columns 

transverse girder - see CROSS GIRDER 

travel way - the roadway 

tremie - a piece of construction equipment (e.g., pipe or funnel) used to place concrete underwater 

trestle - a bridge structure consisting of spans supported on braced towers or frame bents 

 

truck loading - a combination of loads used to simulate a single truck passing over a bridge 

truss - a jointed structure made up of individual members primarily carrying axial loads arranged and 

connected in triangular panels 

truss bridge - a bridge having a pair of trusses for a superstructure 

trussed beam - a beam stiffened to reduce its deflection by a steel tie-rod that is held at a short distance from 

the beam by struts 

truss panel - see PANEL 

tubular sections - structural steel tubes, rectangular, square or circular; also known as hollow sections 

tubular truss - a truss whose chords and struts are composed of pipes or cylindrical tubes 

tunnel - an underground passage, open to daylight at both ends 

turnbuckle - a long, cylindrical, internally threaded nut with opposite hand threads at either end used to 

connect the elements of adjustable rod and bar members 

two-hinged arch - a rigid frame that may be arch-shaped or rectangular with hinges at both supports
 G-50 

U

U-bolt - a bar bent in the shape of the letter "U" and fitted with threads and nuts at its ends 

ultimate strength - the highest stress that a material can withstand before breaking 

ultrasonic thickness gage - an instrument used to measure the thickness of a steel element using a probe 

which emits and receives sound waves 

ultrasonic testing - nondestructive testing of a material's integrity using sound waves 

underpass - the lowermost feature of a grade separated crossing; see OVERPASS 

underwater diver bridge inspection training - training that covers all aspects of underwater bridge 

inspection and enables inspectors to relate the conditions of underwater bridge elements to established criteria 

(see the Bridge Inspector's Reference Manual section on underwater inspection for the recommended material 

to be covered in an underwater diver bridge inspection training course). 

underwater inspection - inspection of the underwater portion of a bridge substructure and the surrounding 

channel, which cannot be inspected visually at low water by wading or probing, generally requiring diving or 

other appropriate techniques. 

uniform load - a load of constant magnitude along the length of a member 

unit stress - the force per unit of surface or cross−sectional area 

uplift - a negative reaction or a force tending to lift a beam, truss, pile, or any other bridge element upwards 

upper chord - the top longitudinal member of a truss 

V

vertical - describes the axis of a bridge perpendicular to the underpass surface 

vertical alignment - a roadway’s centerline or baseline alignment in the vertical plane 

vertical clearance - the distance between the structure and the underpass 

vertical curve - a sag or crest in the profile of a roadway, usually in the form of a parabola, to transition 

between grades 

vertical lift bridge - a bridge in which the span moves up and down while remaining parallel to the roadway 

viaduct - a series of spans carried on piers at short intervals 
 G-51 

vibration - the act of vibrating concrete to compact it 

Vierendeel truss - a truss with only chords and verticals joined with rigid connections designed to transfer 

moment 

voided slab - a precast concrete deck unit cast with cylindrical voids to reduce dead load 

voids - an empty or unfilled space in concrete 

Voussoir - one of the truncated wedge-shaped stones composing a ring course in a stone arch; also known as 

ring stone 

voussoir arch - an arrangement of wedge shaped blocks set to form an arched bridge 

W

wale, waler - horizontal bracing running along the inside walls of a sheeted pit or cofferdam 

Warren truss - a triangular truss consisting of sloping members between the top and bottom chords and no 

verticals; members form the letter W 

washer - a small metal ring used beneath the nut or the head of a bolt to distribute the load or reduce galling 

during tightening 

water/cement ratio - the weight of water divided by the weight of portland cement in concrete; this ratio is a 

major factor in the strength of concrete 

waterproofing membrane - an impervious layer placed between the wearing surface and the concrete deck, 

used to protect the deck from water and corrosive chemicals that could damage it 

waterway opening - 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 portion of a beam located between and connected to the flanges; the stem of a dumbbell type pier 

web crippling - damage caused by high compressive stresses resulting from concentrated loads 

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 
 G-52 

weld - a joint between pieces of metal at faces that have been made plastic and caused to flow together by heat 

or pressure 

weldability - the degree to which steel can be welded without using special techniques, such as pre-heating 

welded bridge structure - a structure whose metal elements are connected by welds 

welded joint - a joint in which the assembled elements and members are connected by welds 

welding - the process of making a welded joint 

weld layer - a single thickness of weld metal composed of beads (runs) laid in contact to form a pad weld or a 

portion of a weld made up of superimposed beads 

weld metal - fused filler metal added to the fused structure metal to produce a welded joint or a weld layer 

weld penetration - the depth beneath the original surface to which the structure metal has been fused in the 

making of a fusion weld; see PENETRATION 

weld sequence - the order of succession required for making the welds of a built-up piece or the joints of a 

structure, to minimize distortion and residual stresses 

weld toe - particularly in a filet weld, the thin end of the taper furthest from the center of the weld cross section 

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; see AXLE LOAD 

weep hole - a hole in a concrete element (abutment backwall or retaining wall) used to drain water from behind 

the element; any small hole installed for drainage 

Whipple truss - a double-intersecting through Pratt truss where the diagonals extend across two panels 

wide flange - a rolled I-shaped member having flange plates of rectangular cross section, differentiated from 

an S-beam (American Standard) in that the flanges are not tapered 

wind bracing - the bracing systems that function to resist the stresses induced by wind forces 

wind lock - a lateral restraining device found on steel girder and truss bridges 

wingwall - the retaining wall extension of an abutment intended to restrain and hold in place the side slope 

material of an approach roadway embankment 

wire mesh reinforcement - a mesh made of steel wires welded together at their intersections used to reinforce 

concrete; welded wire fabric 
 G-53 

wire rope - steel cable of multiple strands which are composed of steel wires twisted together 

working stress - the unit stress in a member under service or design load 

working stress design - a method of design using the yield stress of a material and a factor of safety that 

determine the maximum allowable stresses 

wrought iron - cast iron that has been mechanically worked to remove slag and undissolved carbon 

wythe - a single layer of brick or stone in the thickness direction 

X 

X-ray testing - nondestructive testing technique used for detecting internal flaws by passing X-rays 

through a material to film or other detector 

Y

yield - permanent deformation (permanent set) which a metal piece takes when it is stressed beyond the elastic 

limit 

yield point - see YIELD STRESS 

yield stress - the stress at which noticeable, suddenly increased deformation occurs under slowly increasing 

load 

Z 

zee - steel member shaped like a modified "Z" in cross section 
 G-54 

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