BRIDGE TERMS - D

dead load
debris
deck
deck bridge
decking
deficiency
deflection
deformation
deformed bars
degradation
delamination
design load
deterioration
diagonal
diagonal stay
diagonal tension
diaphragm
diaphragm wall
differential settlement
dike
discharge
displacement induced stress
distributed load
ditch
diver
dolphin
double movable bridge
dowel
drainage
drainage area
drain hole
drain pipes
drawbridge
drift bolt
drip notch
drop inlet
ductile
ductile fracture
ductility
dumbbell pier

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

debris  - any 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 

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

decking -  a term specifically applied to bridges having wooden floors and used to designate the flooring only; it does not include the members serving to support the flooring 

deficiency - see BRIDGE DEFICIENCY

deflection - elastic movement of a structural member under a load 

deformation - distortion of a loaded structural member; includes plastic, non-recoverable movement 

deformed bars - concrete reinforcement consisting of steel bars with projections or indentations to increase the mechanical bond between the steel and concrete 

degradation -  general progressive lowering of the channel stream bed by erosion 

delamination - subsurface separation of concrete into layers 

design load - the force for which a structure is designed; the worst possible combination of loads 

deterioration - decline in quality over a period of time due to chemical or physical action of the environment 

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

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

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

dike - an earthen embankment constructed to retain floodwater; 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; also known as dyke; see SPUR DIKE 

discharge - the volume of fluid per unit of time flowing along a pipe or channel  

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 and 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 for navigation 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 short 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 matter; also known as drip hole; see WEEP HOLE 

drain pipes - pipes below the ground that remove rainwater 

drawbridge -  a general term applied to a bridge over a navigable body of water having a movable superstructure span of any type permitting the channel to be freed of its obstruction to navigation; popular but imprecise term 

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

drip notch - a recess cast on the underside of a parapet which prevents water from following the concrete into the supporting beams and causing deterioration of the members 

drop inlet -  a type of inlet structure which conveys the water from a higher elevation to a lower outlet elevation smoothly without a free fall at the discharge 

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

ductile fracture  -  a fracture characterized by plastic deformation 

ductility - the ability to withstand non-elastic deformation without rupture 

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