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Glossary of Bridge Terminology



D-Valve: Same as "Slide Valve." -- A valve having a reciprocating motion, used in engines to open successively the admission and the exhaust, ports.

Damper: A door or valve for admitting air to a furnace

Dangerous Section: That section or position where failure of a member is most likely to occur.

Dap: To notch a timber on its bearing.

Dapped Joint: A joint made between two pieces by cutting away corresponding portions of each so that they fit together with surfaces flush with each other.

Dash-pot: A cylinder containing a loosely fitted piston and partly filled with fluid, used to check sudden movements in the parts of a machine.

Datum: A fact either indubitably known or treated as such for the purpose of a particular discussion. A known reference. A point, line, or plane used as a basis for referring measurements.

Datum Line: A line of reference. This term is sometimes incorrectly used for "Datum Plane."

Datum Plane: A plane of reference for a system of levels which, generally, is taken as zero elevation.

Day Foreman: A foreman who directs the day shift of workmen.

Day Superintendent: The person in complete control of work during the day.

Dead Load: The weight of all the parts of a bridge itself and anything that may remain upon it for any length of time, such as tracks, water mains, telephone and telegraph lines, snow, dirt, moisture, etc.

Dead Load Stress: The stress resulting from the application of a static load. Generally means the stress produced in a structure by its own weight.

Dead-man: A timber, log, or beam buried in the ground for anchorage.

Dead Melt: In the fusion of metals, a condition of being fully or completely melted, and in which no gas is being evolved.

Dead-points: The two points in the revolution of a crank where the crank arm is parallel with the rod which connects it with the moving power.

Dead Pulley: Same as "Loose Pulley." -- A pulley which turns loosely on its shaft.

Deadening Dressing: The crushing or crumbling of soft stone under the tools while being worked, leaving irregularities in the finished surface.

Deck: The flooring of a bridge.

Deck Beam: A rolled shape having a "T" cross-section but with a slight enlargement at the lower end of the stern or web.

Deck Bridge: A bridge in which the passing loads are carried directly to the upper chords or to the upper portions of the posts.

Deck Cantilever: A cantilever bridge in which the traffic is borne by a floor system supported by the top chords or the upper portion of the posts.

Deck Girder: One of the main girders of a deck bridge.

Deck Plate Girder: One of the main plate girders in a deck bridge.

Deck Span: One of the spans of a "Deck Bridge."

Deck Truss: A loose expression for the truss of a deck span.

Decking: Flooring. Same as "Deck."

Declivity: A downward slope or descent of the ground.

Deflection: A lateral motion, a motion at right angles to the length of the piece. Also the amount of such motion expressed in some lineal unit as inches.

Deflection Indicator or Deflectometer: An apparatus for measuring the deflection of bridge spans.

Deflectometer: Same as "Deflection Indicator."

Deformation: Change of form. A change of shape in a member or combination of members without any breach of the continuity of its parts.

Deformed Bar: A reinforcing bar rolled with projections on its surface to ensure a better bond in the concrete in which it is placed.

Degree of Curvature: The angle in degrees subtended by a chord one hundred feet long. Used in railroad location.

Density: The mass or amount of matter per unit of volume.

Departure: A term used in surveying to denote the perpendicular distance from one of two assumed rectangular coordinates-often from the one running north and south.

Depreciation: The loss of value in a plant or structure during a course of years as measured by the difference between its first cost and its salvage value at the end of the allotted time.

Depth: The downward distance from the surface or top. The term generally carries the idea of verticality; but such is not always the case; for instance, the depth of any beam that is inclined to the horizontal is measured in a direction perpendicular to its length, and, therefore, on a line inclined to the vertical.

Derailing Apparatus: A device or mechanism used for derailing trains.

Derailing Switch: A switch operated by hand, by machinery, or automatically, which will derail a train of cars.

Derrick: An apparatus for lifting and moving heavy weights. It is similar to the crane; but differs from it in having the boom, which corresponds to the jib of the crane, pivoted at the lower end so that it may take different inclinations.

Derrick Boom: The long member in a derrick which supports the load at its outer end.

Derrick Car: A railroad car upon which a derrick is mounted.

Derrick Crab: A hoisting apparatus at the foot of a derrick. A special crab for a derrick.

Derrick Crane: A crane in which the post is supported by fixed stays in the rear, the jib being pivoted like the boom of a derrick.

Derrick Mast: The upright member of a derrick, at the bottom of which the boom is attached and which is pivoted so as to allow the boom to swing either way.

Derrick Sheaves: The stationary sheaves in the mast and boom of a derrick.

Design: To proportion all the parts of a structure. A plan, or plans, showing the various parts of a structure, their sizes, and relations.

Detail: One of the smaller parts into which any construction or design may be divided. To go into particulars. To draw the particular parts.

Detail Drawing: A drawing on a large scale showing all small parts, dimensions, details, etc.

Detail Paper: A tough paper used for pencil drawings.

Detailing: The actual work of planning and drawing the different parts and the connections of any structure. The smaller parts of any construction, speaking of them as a class.

Deviation: The variation or deflection from a straight line or course.

Diagonal: A member running obliquely across the panel of a truss. Any oblique line.

Diagonal Bracing: Bracing along diagonal lines.

Diagonal Tie: A tension diagonal incapable of resisting compression.

Diagonal Wrench: A wrench in which the axis of the jaws is set obliquely to the handle.

Diagram: A sketch, outline, or skeleton drawing. A record made by curves plotted on cross-section paper.

Diagram of Stresses: Same as "Stress Diagram." -- A skeleton drawing of a truss, upon which are written the stresses in the different members.

Diagram of Weights: A system of right lines or curves giving the weights of metal or portions of same per lineal foot of structure for bridges, trestles, etc.

Diametral Pitch: In English practice, the ratio of the diameter of the pitch line to the number of teeth which is equivalent to the ratio of the circular pitch to π [Pi]. In American practice, the ratio of the number of teeth to the diameter of the pitch circle in inches, which is equivalent to the ratio of π [Pi] to the circular pitch.

Diametral Plane: A plane passing through the diameter of a circle, or one containing the longitudinal axis of a cylinder.

Diamond Drill: A type of core drill using black diamonds set in an annular bit which is revolved by a shaft extending to the ground surface, where it connects with suitable driving machinery.

Diaphragm: A thin plate or partition across a bridge member to stiffen the same.

Diaphragm Plate: A stiffening plate used in the interior of a column to give it additional strength and rigidity.

Die: A steel former or device for shaping, impressing, or cutting out something.

Die Stock: The frame, with handles attached, used for holding and turning the dies which cut the threads on rods or pipes.

Dies: Two flat plates of hardened steel having a semi-circular groove cut in the edges making contact with each other. This groove has an internal thread, so that when the two pieces are brought together in a stock a female screw is formed. It is used for cutting threads on rods, bolts, etc.

Differential: An infinitesimal difference between two values of a variable quantity. Also often used for the expression "differential gear."

Differential Block: A double block having sheaves of different diameters.

Differential Capstan: A capstan operated by differential gears.

Differential Coefficient: The measure of the rate of change in a function relative to its variable. A term used in the calculus.

Differential Coupling: An extensible coupling designed for varying the speed of that part of the machinery which is driven.

Differential Gears: A combination of toothed gears by which a differential motion is produced.

Differential Jack: Any jack worked by differential gears.

Differential Pulley: A system of pulleys in which an endless chain passes over two upper grooved pulleys, of different diameters, and one lower pulley to which the weight to be lifted is attached. The motion of the chain is such that as it winds upon the larger pulley, it unwinds from the smaller and the weight to be lifted moves through a space equal to half the difference between the amount of chain wound up and that unwound.

Differential Screw-jack: A screw-jack having a differential screw.

Differential Tackle: Same as "Differential Block."

Differential Windlass: Same as "Chinese Windlass." -- A windlass having an axle or barrel with different diameters, so that the rope winds up on the larger and unwinds from the smaller, the difference between the two motions resulting in a slow lifting of a heavy load

Dike or Dyke: A mound of earth built to prevent the overflow of rivers or of the sea; also to keep the channels of rivers, streams, etc., in one position. A timber construction to protect a river bank against erosion or to form land by deposition of sediment.

Dimension: Bulk, size, extent, or capacity. The length, width, height, etc., in units of measure.

Dimension Stone: Large cut stone having the face left rough, used in massive masonry.

Dinkey Engine: Same as "Dinkey Locomotive."

Dinkey or Dinky Locomotive: Any small locomotive for hauling earth, rock, etc., which runs on a narrow-gauge track. Used largely by contractors.

Dip: The inclination to the horizontal of any stratum of earth or rock.

Dipper Dredge: A dredge using a dipper or cubical bucket mounted on the end of a boom.

Direct Current: An electric current which flows in the same direction constantly.

Direct Stress: A stress resulting from a direct application of the load.

Direct Tension: Tension applied parallel to the axis of the member and uniformly over its cross-section.

Direct Wind-load Stress: Stress due to the wind load applied directly to the lateral trusses of a span.

Disc or Disk: A flat circular piece of material.

Discharge: A flowing out. Used in connection with the amount of liquid passing through an orifice in a unit of time, or the amount of water in a stream passing a given cross-section in a unit of time.

Discharge Valve: A valve through which a fluid is discharged.

Discount: An amount deducted from a sum a sum of money.

Disk: Same as "Disc."

Disk Coupling: A permanent coupling consisting of two disks keyed on the connected ends of two shafts.

Disk Crank: A disk carrying a crank-pin and substituted for a crank.

Disk Pile: A steel pile with a disk at the bottom for increasing the bearing area. It is used in soft sandy soils and requires the employment of a water-jet in sinking.

Displacement Diagram: A diagram in which the relative position of points represents in magnitude and direction the relative displacement of particles.

Ditch: A trench made by digging. A narrow open passage for water on the surface of the ground.

Dive Culvert: Same as "Siphon." -- A bent tube or pipe having unequal legs, employed for drawing off water when the summit of the bend is higher than the supply, and the discharge end (the longer leg) is lower than the supply.

Diving-bell: A mechanical contrivance consisting of an inverted, or bell-shaped, chamber filled with compressed air in which persons are lowered beneath the water for the examination of the foundation of bridges, etc.

Diving Dress or Diving Suit: A submarine armor used for the same purpose as that of a diving bell.

Division Wall: Same as "Curtain Wall." -- A thin wall. A partition wall that carries no superimposed load.

Dock: An enclosed, or partially enclosed, water-space in which vessels, barges, etc., are loaded and unloaded.

Dog: A name for various mechanical devices, tools, etc., that usually grip something. The grappling iron which lifts the monkey, or hammer, of a pile driver. Any part of a machine acting as a claw or clutch. A click or pallet which restrains the back action of a ratchet wheel.

Dog Head: A round headed tool, used for breaking stones.

Dog Hook: A strong hook or a wrench used for separating iron boring rods. Also a bar of iron with a bent prong used in handling logs or timber.

Dog Iron: A short bar of iron forming a kind of cramp with its ends bent down at right angles and pointed so as to hold together the two pieces into which they are driven. Often the term "Dog Iron" is used for "Dog Hook."

Dolly: An extension piece placed on the upper end of a pile when the head of the pile is below the leads of the pile driver and out of reach of the hammer. A follower. A snap head; a tool with an indented head for holding the head of a rivet and absorbing impact while the other head is being driven.

Dolly Bar: A riveter's tool or bar, used to hold the head of the rivet against the metal and act as an anvil while the other head is being made by a hammer.

Dolomitic Limestone: A limestone containing more than one-third part of carbonate of magnesia.

Dolphin: A cluster of piles driven some distance ahead of the ends of the channel span piers of an opening bridge to protect the faces of the piers against blows from passing vessels.

Donkey Engine: A small stationary steam engine attached to a larger one. A subsidiary engine used for hoisting.

Donkey Pump: A feed pump for boilers.

Dorchester Sandstone: A sandstone found in Dorchester, New Brunswick.

Doty Tie: A timber tie affected by a certain fungous disease.

Double-acting Piston: A piston that is subjected to fluid pressure on each side alternately.

Double-bitted Axe: A double-bladed axe.

Double Block: A pulley block having two sheaves.

Double Bowstring Truss: A truss in which the joints of each chord lie in curves concave to each other. See Fig. 22r.

Fig. 22r

Double Cancellation: The arrangement of the web members of a truss having two complete systems of diagonals.

Double Cap: A cap set vertically on the top of another.

Double Concentration: A term descriptive of the method of figuring stresses in bridges for a live load, consisting of a string of cars of uniform weight per lineal foot headed by an excess load equal to the difference between the total weight of an engine and tender and the product of the length of the two by the weight per lineal foot of the cars, and followed by another similar and equal excess load two panel lengths (about fifty feet) back of the head of the train. This type of live load is no longer used, as it has been replaced by the "equivalent uniform live load."

Double Deck: A condition of a span having two decks, one over the other.

Double Drill: A drill with two cutters for making countersunk holes.

Double End File: A file having both ends cut for service.

Double Ender Locomotive: A locomotive having two fire boxes and two sets of engines.

Double-faced Hammer: A forging apparatus for striking on opposite sides, as in case of a bloom.

Double Intersection: Same as "Double Cancellation."

Double Intersection Truss: A truss having two intersecting diagonals for each panel. See Fig. 22i.

Double Lacing: Erroneously used for "Latticing."

Double Latticing: Same as "Latticing." -- A system of bars crossing each other at mid-length, used to connect the two leaves of a strut in order to make them act as one member. Generally the crossed bars are riveted together at their intersection.

Double Locomotive Excess-Load: A live load composed of a uniform carload per lineal foot preceded by one concentrated load and followed by another about fifty feet behind, or the length of a locomotive with its tender. This loading is no longer used in American bridge engineering.

Double Piston Locomotive: A locomotive in which each cylinder has two pistons with rods projecting from each end, and working on crank-pins set at 180 degrees from each other.

Double Refined Iron: Iron made by a process of cutting up bars of refined iron, placing the pieces in piles, then reheating and rerolling into shape.

Double Rim Bearing Draw: A draw span supported on two rims or a double drum.

Double Rim-bearing Turntable: A turntable comprising two concentric circular girders or rims, each transferring its part of the load to an independent set of rollers.

Double Riveted Lacing: Lacing in which each bar is connected by two rivets at each end.

Double Riveting: A term applied to riveted joints in which a double row of staggered rivets is used for a lap joint and two double rows for a butt joint-one double row on each side of the joint.

Double Rotating Cantilever Draw: A movable structure composed of two adjacent, swing spans, the inner ends of which are mechanically connected, and the outer ends of which engage with anchorages.

Double Shear: A sliding on two different but parallel planes.

Double Shear Steel: Steel made by a process in which the shearing and welding described for single shear steel is repeated.

Double-speed Pulley: A combination of two loose pulleys and toothed gearing with one fast-driven pulley, whereby two different speeds of rotation may be obtained with pulleys of the same diameter by shifting the band from the fast pulley to one of the loose pulleys.

Double-step Joint: A dapped joint in which the projecting timber has two steps.

Double Tracing Diagram: A diagram on cross-section paper containing two related groups of curves, and involving four variable quantities. See Figs. 55uu and 55vv.

Double Track: A track consisting of two pairs of rails.

Double Triangular Truss: Same as "Double Intersection Truss."

Double Truck Tank Locomotive: A locomotive which has two trucks, and carries boilers and tenders on a single frame.

Double Wrench: A wrench having a set of jaws at each end.

Douglas Fir: A species of the pine family found on the Pacific Coast. Grows very large and furnishes hard durable timber.

Dovetail: A manner of making joints by having a series of projections in one piece fitting into corresponding recesses in another piece. A joint in carpenter work. It is a poor joint in timber where much stress has to be provided for. The shape of the tongue of the joint is like that of the spread tail of a dove.

Dowel: A straight pin of wood or metal driven part way into each of the two faces which it unites. Also called a dowel-pin.

Dowel Joint: A joint that is strengthened by a pin or a dowel.

Doweled Masonry: Masonry in which dowel pins are used to bind the several courses together and thereby prevent sliding.

Draft: The depth to which a floating vessel or box sinks in the water. Also a cut or a groove.

Drafted Dressing: A finish in stonework having a narrow chisel-draft cut around the face or margin.

Drafted Stone: Stone having a narrow chisel-draft cut around the face or margin.

Drainage: The run-off in a drainage area. A system of piping to carry off water.

Drainage Area: The area drained by a stream or streams.

Draught: A drawing: A narrow level strip which a stone-cutter first cuts around the edges of a rough stone, to guide him in dressing off the face thus enclosed by the draught. To make drawings. Spelled also "draft."

Draw: The movable portion of a draw-bridge. To make drawings. To haul.

Draw Bridge: A bridge that may be drawn or turned to one side, or lifted up, either bodily or in sections, so as to permit boats to pass under or through it.

Draw Plate: A plate having tapered holes through which wires are drawn.

Draw Rest: A pile and timber structure, ballasted with rock, built approximately at right angles to the bridge tangent and extending up and down stream so as to underlie the draw span when it is open, thereby affording protection from passing vessels arid providing a support for the ends of the span when open. Built sometimes of masonry.

Draw Span: A movable span in a bridge over a navigable stream, to permit the passage of vessels.

Drawing: The act of pulling or hauling. The making of a plan on paper, etc. Also the plan itself.

Drawing Down: Reducing gradually the sectional area.

Dredge: An apparatus or machine for lifting mud, sand, silt, and small boulders from the bottom of a stream or the bed of an arm of the sea. To excavate with a dredge.

Dressed and Matched Flooring: Planks that are dressed on both sides and matched, i.e., tongued and grooved.

Dressed Ashlar: Ashlar blocks in which the faces have been dressed or smoothed off to a greater or less degree.

Dressing: The sizing, shaping, and facing of stones for masonry work.

Drier: A material containing metallic compounds added to paints and painting materials for the purpose of accelerating the drying.

Drift: A horizontal or inclined passage in a tunnel. To float away with a current. Debris, such as trees, timbers, brush, etc., carried along by freshets. To match holes in steel work by drift-pins. To swing bridge members into place by means of a double set of ropes and blocks, one set releasing as the other set takes up. To enlarge a hole with a conical pin.

Drift Bolt: A short rod or square bar to drive into holes bored in timber for attaching adjacent sticks to each other or to piles. The length generally varies from one foot to two feet. A drift bolt may or may not be provided with a head or with a sharpened end.

Drift Ice: Masses of detached floating ice which drift with the wind and current.

Drift Pin: A hand tool made of tempered steel with tapering ends and of a size that will permit its being pushed through a rivet hole. Used to draw together the component parts of a member or adjacent members. A short, tapered rod for enlarging rivet holes.

Drill: To bore a hole in a material with a tool revolved by a suitable mechanism. The tool itself or the apparatus holding and turning it.

Drill Barrow: Same as "Drill."

Drill-bit: The cutting tool used in a drilling machine. Also called "Drill."

Drill Chuck: A type of chuck which holds a drill.

Drill Gauge: A gauge for determining the angle of a twist; drill bevel.

Drill Plate: A breast-plate for hand-drilling operations.

Drill Press: A machine tool for drilling holes, having one or more spindles carrying drill points that are moved forward by an automatic feed.

Drill Stock: The holder which receives the shank of a drill.

Drilling Machine: A machine for boring holes in metals, rock, etc.

Drillings: The cuttings, or shavings, arising during the process of drilling. Also the holes that are drilled in the ground.

Drip: A small channel cut under the lower projecting edge of a coping, etc., so that when rain reaches that point, it will drip or fall off.

Drip Pipe: A small pipe used to convey away the water of condensation from a steam pipe.

Drip Stone: A moulding or cornice projecting from a column to prevent rain water from trickling down.

Driven Pulley: The pulley which receives the motion from the belt.

Driver: -One of the large wheels which drive any machine or apparatus.

Driving Axle: An axle which communicates motion to other parts of a machine. The axle of a locomotive which receives power from a steam piston through connecting rods.

Driving Belt: A band, rope, strap, or belt which transmits motion from one machine to another, or from one part of the same machine to another part.

Driving Box: The journal box of a driving axle.

Driving-fit: In steel work, a fitting for a bolt so tight that the diameter of the hole is practically the same as that of the bolt, which has to be driven in place with a hammer.

Driving Gears: Those gears which drive other gears or mechanisms.

Driving Nut: A special, flat-headed, hollow, round nut temporarily screwed on one end of a pin to receive the blows of the hammer or ram during the driving of the pin home.

Driving Pulley: The pulley transmitting motion to the belt.

Driving Shaft: A shaft from the driving wheel communicating motion to machinery.

Driving Wheel: The main wheel which communicates motion to another or others.

Drop: A contrivance arranged so as to hang, drop, or fall from a higher position to a lower one.

Drop Forging: A forging produced by a drop press.

Drop Hammer: A heavy weight, working in guides, which is raised by means of a rope or cable and then allowed to drop.

Drop Hammer Pile Driver: A driver in which a heavy hammer is repeatedly raised in a frame and dropped on to the pile.

Drop of Beam: A term used in testing materials to indicate that a test piece has passed the yield point as shown by the sudden dropping of the weighing beam of the testing machine.

Droved Dressing: A finish in stonework wrought with a broad chisel or hammer in parallel flutings across the face from end to end.

Drum: A revolving cylinder around which ropes or belts either travel or are wound. The main portion of a turntable for either locomotives or swing spans.

Dry Blow-out: A process for removing sand or mud from the working chamber of a pneumatic caisson by the pressure of air on the material piled around the mouth of the discharge pipe, no water being added nor sump used.

Dry Dock: A dock from which water is withdrawn after the vessel is floated in for repairs.

Dry Masonry: Masonry in which the stones are laid up without mortar.

Dry Process in Cement Manufacture: The process of making Portland cement by mixing the ingredients dry and then burning them into a clinker.

Dry Puddling: The old process of puddling iron in which very little, if any of the phosphorus was removed, while the sand lining of the furnace combined with the iron which was oxidized, thus causing a heavy loss.

Dry Rot: A decay affecting dry timber, caused by a fungus growth.

Dry Rotten Wood: Wood subject to dry rot.

Dry Seam: An open crack in a rock.

Duchemin's Formula: A wind pressure formula for surfaces inclined to the direction of the wind:

wherePn = the normal component of wind pressure
P = the pressure per square foot on a vertical surface
A = the angle of inclination of the surface with the horizontal

Dumb-bell Pier: A pier composed of two cylindrical piers connected by a solid web.

Dump: The place where material such as earth, clay, rock, etc., is deposited. To deposit such material.

Dump Car: A truck car having a body pivoted so that it can be turned partly over when emptying.

Dump Scow: A drop-bottom scow from which material is dumped.

Dumpy Level: An engineer's level having a short telescope rigidly fixed to the supporting bar and vertical axis.

Duplex Hammer: Same as "Double Faced Hammer."

Duplex Slide Rule: A slide rule of the stick type having an interior slide of the same thickness as the rule and its two faces flush with those of the exterior portions. Both rule and slide are graduated on both faces.

Durometer: An apparatus for testing the hardness of steel rails.

Dust Guard: Steel plates placed around rockers, rollers, etc., on shoes to keep out dirt and dust. A thin piece of wood, leather, or fabric fitted to a journal-box to keep out the dust from the bearings, and to prevent the escape of oil and waste from the box.

Dutch Brick: A dirty-looking, brimstone brick used for paving yards and stables.

Dutchman: A wooden block or wedge used to hide an opening in a badly made joint.

Duty: The number of foot-pounds of work delivered for each hundred pounds of coal burned under a boiler. Also the number of foot-pounds of work delivered for each one thousand pounds of dry steam.

Dyke: Same as "Dike."

Dynamic Deflection: The additional deflection caused by the live load being in motion.

Dynamic Equilibrium: That condition of a body in uniform motion in which the resultant of all the forces acting thereon is zero.

Dynamic Horsepower: Same as "Indicated Horsepower." -- The power developed in the cylinder of a steam engine as determined from an indicator diagram. It is equal to the mean effective pressure in pounds per square inch, multiplied by the area of the piston in square inches, by the piston speed in feet per minute, and divided by thirty-three thousand (33,000).

Dynamics: That branch of the science of mechanics which treats of the motion of bodies and of the forces acting thereon.

Dynamite: An explosive of great power, consisting of a mixture of nitroglycerin with some absorbent material such as sawdust. To blow up, destroy, or break up with dynamite.

Dynamo: A machine for converting mechanical power into electrical power or vice versa. In the latter case the machine is called a motor. The essential elements are a field of magnetic flux, produced usually by electro-magnets called field magnets, and a moving set of conductors passing through the magnetic flux so as to cut the lines of force. The moving set of conductors is called the armature.

Dynamometer: An apparatus for measuring the amount of pull exerted by any machine or engine.