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Glossary of Bridge Terminology



Gad: The sharp point on a steel rod, spear, pike pole, or stake.

Gad Steel: Flemish steel wrought from wedge-shaped ingots.

Gadding: In quarrying, the drilling of holes for taking out dimension stone

Gadding-machine: The drilling machine used in gadding.

Gaff: A steel or iron hook without a barb, provided with a wooden handle, used to haul in objects that have fallen overboard from a vessel. To hook or engage with a gaff.

Gaff Hook: Same as "Gaff."

Gag Press, or Gog Press: A press consisting of two fixed horns and a ram, used for straightening structural shapes. Also called "Bull Press."

Gag Process: The process of bending structural shapes in a gag press.

Gage: Same as "Gauge."

Gagger: A moulder's tool, used to lift sand from a flask in moulding.

Gain: A beveled shoulder on the end of a mortised brace, for the purpose of giving additional resistance to the shoulder. To make progress. To make grooves or mortises in timber.

Gaining: The act of cutting grooves or mortises in timbers.

Gaining Machine: An apparatus that does gaining.

Gallon: An English unit of capacity for dry or liquid measure containing 231 cubic inches.

Gallows: A set of timbers consisting of two upright posts, or props, and a bar or cap, laid across their tops and cantilevered out from the posts. Its function is the supporting of objects -- generally temporarily.

Gallows-frame: The frame of a "Gallows."

Galvanized Iron: Iron coated with zinc.

Galvanometer: An instrument for determining the strength and direction of electric currents.

Gang: A combination of several tools, machines, etc., operated by a single force, or so contrived as to be made to act as one. Also a company or crew of men.

Gang Drill: A machine tool containing in one head a number of vertical drills, each having its separate belt and pulley operated from a common shaft.

Gang Plank: A short, temporary plank used to bridge the distance from a barge or other vessel to a wharf.

Gang Punch: A machine that punches two or more holes at one operation.

Gangway: A temporary passage used during erection.

Gantry or Gauntry: A frame or scaffold which supports a crane or other structure.

Gantry Crane: A crane set upon a gantry.

Gantry Traveler: A framework of two or three bents or gallows frames, braced longitudinally and carried on a track supported on falsework and placed outside of the trusses. The traveler clears the span at all points and can be rolled back and forth as needed. It carries a number of blocks and tackles which are operated by a hoisting engine placed on a platform near the base. It is used in erection for hoisting and placing the members of a truss.

Gas Engine: An internal combustion engine using gas as a fuel.

Gas Pipe: Small wrought iron pipe.

Gasket: Rope-yarn, hemp, rubber, rainbow packing, or sheet lead, used at joints in water pipes and steam pipes, in pistons of steam engines, manholes of boilers, etc., to obtain a tight joint.

Gasoline Engine: An internal combustion engine using gasoline as a fuel.

Gate: A movable harrier. In casting, one of the various forms of openings made in the sand for the molten metal to flow through to the mould. The waste piece of metal cast in the gate. A ridge in a casting which has to be sawn off.

Gate Block: Same as "Snatch Block." -- A pulley block with one side capable of being opened for the insertion of a rope. It is used principally to change the direction of a running line.

Gate Valve: A valve having a slide or gate placed at right angles to the flow of the liquid and arranged to draw completely to one side when opened, thereby offering little obstruction to the flow, but completely stopping it when closed.

Gauge or Gage: A standard of measure. An instrument for determining dimensions, capacity, quantities, or forces. A standard of comparison. The distance between rivet lines in structural shapes. The distance between the inside faces of the heads of the rails in a track.

Gauge Glass: The exposed glass tube, connected with a boiler, which shows the height of water in the said boiler.

Gauge Length: The original length marked on a test bar for the determination of the elongation.

Gauge Pile: Ordinary piles, driven at intervals of about ten feet, to which are attached wales or runners against which are driven the sheet piles for a cofferdam.

Gauging: Making measurements. The act of judging distances, heights, etc., either by eye or by instruments. Ascertaining the volume of discharge of a stream.

Gauntry: Same as "Gantry."

Gear: A wheel having teeth on its periphery. A piece of mechanism for transmitting motion. To fit with gears. To connect one part of a mechanism at will with another.

Gear Wheel: A wheel having teeth that will mesh with those of another toothed wheel or with a toothed rack. Also called "Gear."

Geared Locomotive: A locomotive in which the motion of the engine is conveyed by gearing to the drivers.

Gearing: A train of gear wheels. A general term for the parts of a machine or mechanism, taken collectively, which transmit motion.

General Contractor: A principal contractor who sublets the whole or part of the whole contract.

General Drawing: A drawing showing the elevation, plan, and cross-section of the structure-also the borings for substructure and the main dimensions.

General Foreman: A man in charge of all construction work, but who generally has no part in the administration of the business.

General Layout: A drawing showing an elevation, plan, and cross section for a structure, and any other notes-such as borings.

Geometrical Progression: A progression in which any term, other than the first, is derived from the preceding term by multiplying the latter by a fixed quantity.

Geostatic: Pertaining to earth in a quiescent condition due to a balance of forces or pressures. Having the quality of maintaining earth in equilibrium.

Geostatic Arch: An arch which has a curve of such nature that the vertical pressure is proportional to the depth below a fixed horizontal plane, and the horizontal pressure bears to the vertical pressure a fixed ratio depending on the nature of the superincumbent materials.

German Steel: Steel made in Germany -- an obsolete term.

Giasticutus Rod: A term (perhaps unauthorized, but formerly in common use among bridge builders) to denote a small horizontal rod connecting the middle points of two adjacent posts of the same truss, for the professed purpose of fixing or holding the posts at the middle in order that they may be figured for half length. The benefit derived therefrom is more imaginary than real.

Gib: A piece of metal in the shape of an elongated channel, used as a clamp.

Gilbreth Pile: A corrugated reinforced concrete pile designed by a Mr. Gilbreth.

Gin: A revolving vertical pole or column, usually furnished with a rope drum, having one or more long horizontal arms by which power is applied to turn the drum and wind up the rope, thereby raising a weight.

Gin Block: A simple form of tackle block having a single wheel over which a rope runs.

Gin Pole: A mast, or vertical pole, guyed to the ground by cables. Used in connection with blocks and tackle for raising weights.

Gin Pole Derrick: Same as "Gin Pole."

Gin Tackle: A system of pulleys consisting of a double and a triple block, the standing end of the fall line being made fast to the double block, which is movable.

Gin Type Derrick: A framework with four stiff legs, used in borings, or for lifting pipes in trenches.

Girder: A beam or compound structure acting as a beam carrying principally transverse loads which develop normal reactions at the supports.

Girder Bridge: A bridge composed of plate or lattice girders.

Girder Dogs: A special pair of dogs used for lifting and moving girders.

Girder Guard-rail: A street car rail having a ball wider than the ordinary rail and with a slot in it to allow the flanges of the car wheels to roll therein. This rail is often placed on curves.

Girder Hook: Same as "Girder Dog."

Girder Iron: An old term for a structural shape in the form of a girder or I-beam.

Girder Rail: A deep, heavy rail used for street cars in cities. Its cross-section is similar to that of an I-beam with a projection on top forming the tread of the rail.

Girder Span: A span built of girders.

Girt: Well braced, as the taut guys on a derrick.

Girth: The length of the perimeter of a cross-section.

Glacis: An easy slope of earth.

Gland: A stuffing box around the piston-rod of an engine. A type of coupling for shafts.

Glass Cutter: A hand tool having a diamond edge wheel mounted on a shaft, used for cutting glass.

Glazed Iron: An iron containing a large amount of silicon.

Globe Valve: A valve having an exterior form like a globe and an interior movable disk, parallel to the flow, fitting into a circular seat in a bent partition inside the globe.

Gneiss: A rock which consists essentially of the same, elements as granite, but having the mica disposed in parallel planes, producing a moderate tendency to cleavage into thick slabs. [Also called "Banded Granite," "Bastard Granite," and "Foliated Granite."]

Go-devil: A rough sled for hauling material on snow or ice. A device for exploding dynamite cartridges in holes. A star-shaped tool with a sharp, tapering point.

Gog Press: Same as "Gag Press."

Goose-neck: An iron or steel hook fitted into the inner end of a boom for temporary attachment to a clamp or an eye bolt. A curved pipe for discharging material from a caisson by means of compressed air. A piece of steel bent in "S" shape. A flexible, coupling.

Goose-neck Dolly: A dolly that has a quickly curved bend near one end, with both ends arranged for receiving rivet heads.

Gordon's Formula: A column formula. Also called Rankine's formula

wherep = the allowable unit stress for the column
s = the allowable unit stress for blocks
a = a constant depending on end conditions, etc.
l = the unsupported length of the column
r = the least radius of gyration in reference to an axis normal to the plane in which flexure takes place

Gouge: To scoop out. A chisel with a longitudinal curved edge for cutting wood, stone, or metal.

Governor: An apparatus consisting of two balls or weights on radial arms pivoted to an upright revolving axis, so arranged as to fly outward by centrifugal reaction and in so doing to raise the radial arms and move a valve. Used as a regulator.

Grab: A mechanical device for gripping an object, such as a grab-iron.

Grab Bucket: Any dredge bucket that opens up and grabs its loading.

Grab Hook: A hook formed of four large fish hooks.

Grab Iron: Same as "Grab."

Grade: The degree of inclination from the horizontal, expressed usually in percentage. To arrange in order according to size or quality. To build a roadway. To lower a hill, especially by hydraulicking.

Grade Crossing: A crossing where both roads or tracks are at the same elevation.

Grade Line: A line connecting grade points.

Grade Plug: A plug, generally of wood, driven down so that the top is at the exact elevation of the cutting at the place where the said plug is driven.

Grade Point: A point of established elevation to which a grade is to be brought.

Grade Stakes: Stakes showing by suitable notation the cut or fill required to reach the grade line.

Gradient: The rate of grade, measured by the rise or fall in one hundred feet, and generally expressed as so much per cent.

Gradienter: A small screw, with graduated head attached to an engineer's transit for turning off small vertical angles. Used in fixing grades.

Grain: The smallest unit of weight of the English system. The texture of material. The fork of a river, or a place at which two streams unite. A tine, prong, or spike. The arrangement and direction of the fibres in wood.

Granite: A rock composed of mica, feldspar, and quartz with a thoroughly crystalline, granular texture.

Granite-chips: The chippings left from granite after dressing; the crushings of granite spawls.

Granite Masonry: Masonry composed of granite blocks.

Granite Screenings: Small particles of granite screened from the larger.

Granitoid: Small chippings of any granite mixed with cement forming concrete for sidewalks, curbs, etc. Nowadays, any concrete composed of flinty, hard chippings mixed with sand and cement is erroneously termed granitoid.

Granular: Containing or bearing grains or granules.

Granular Fracture: A fracture showing grains or granules on its surface.

Granular Structure: A granular condition of iron or steel, shown in its fracture, caused by overheating in the furnace.

Graphic Diagram: A diagram in which lines are drawn to represent the elements of a problem.

Graphic Statics: A method of resolving and combining forces, determining their resultant, its direction and point of application, shears, and bending moments by graphical processes.

Graphics: The method or process of solving problems by means of drawing lines.

Graphite: A form of carbon. Used for lead pencils, lubrication of machinery, the rubbing surfaces of wood, and as a conductor in electrical construction. Also employed as a pigment for paints used in structural steel work.

Graphite Paint: A paint in which graphite is used for the pigment.

Grapline or Grapnel: A mechanical device having six arms shaped like an anchor, used to grasp things in deep water.

Grappiers Cement: A cement made in France from particles which have escaped disintegration in the manufacture of hydraulic lime.

Grapple: To cast and drag with a grapnel.

Grappling Iron: An instrument having several iron or steel claws for holding fast to things.

Gravel: Worn, round fragments of rock, occurring in natural deposits, small enough to pass through a two and one-half inch iron ring and large enough to be retained on a No. 10 screen.

Gravel Concrete: A concrete composed of cement, sand, gravel, and water.

Gravel Sieve: A coarse-meshed sieve for sifting gravel.

Gravimeter: An instrument for determining the centre of gravity of a body.

Gravity: The force of attraction exerted by the earth on bodies near it. Weight as contra-distinguished from mass.

Gray Column: A structural steel column composed of eight angle-irons riveted together in pairs, and stayed at short intervals by bent batten plates attached to the connected legs. The strut is in the form of a square cross, having the connected pairs of legs turned inward. Named after its inventor, John Gray, Esq., C.E.

Gray Iron: A pig iron in which the carbon takes the form of graphite, giving the fracture a dark color.

Green Concrete: Concrete that is fresh or has not yet gained its full strength.

Green Masonry: Masonry freshly laid, in which the mortar has not attained its full strength.

Green Sand: A sand fresh from the pit. Unburned moulding sand.

Grillage: A network of timbers laid across each other, generally at right angles. Frequently placed on the heads of piles for supporting bridge piers and other masonry. Also a network of rolled or built beams put in a pier, to distribute the weight from the shoe, or at the bottom of a shaft to spread quickly the weight over a greatly enlarged area.

Grindle Stone or Grind Stone: A medium-hard sandstone in the shape of a wheel with a broad face, mounted on a shaft for rotating. Used for sharpening tools by attrition.

Grip: To seize or hold fast. That portion of a rivet between the two heads after being driven. The thickness of material through which pins, bolts, or rivets penetrate.

Grip of a Bolt: The length of a threaded bolt measured from inside of the head to inside of the nut when the latter is screwed on far enough to provide full thread.

Grip of Rivet: The thickness of the plates or parts through which the rivet passes.

Groin or Groyne: An arch construction formed by two segmental arches intersecting each other at right angles. A construction of timber and stone built out into a stream to retard or deflect the current.

Groined Arch: An arch in which the curved intersections, or arrises, of simple vaults cross each other at any angle.

Groove: A small channel. A cut in material.

Groove Joint: A joint in a board with a groove in the edge for receiving the tongue.

Grooved Rail: Same as "Girder Guard-rail."

Groover: A cement finisher's hand tool for marking cement surfaces with indentations.

Ground Finish: A finish made on an object by grinding.

Ground-hog: A laborer who digs in the ground or who works under the ground. In contradistinction to a "Sand-hog," who works under water in a pneumatic caisson.

Ground Joint: A joint between metallic pieces where the contact surfaces have been ground.

Ground Line: The line of intersection of the vertical and horizontal planes of reference. The line showing the surface of the ground on a profile.

Grout: A mortar composed of sand, cement, and water of such liquid consistencythat it can easily be poured. To pour grout into a void.

Grouting: The pouring of grout.

Groyne: Same as "Groin."

Grubbing: The removing of stumps and roots from foundation sites. Applied specially to railway embankments.

Guard: Any part of an appliance, structure, or attachment designed to prevent the injuring of persons, vehicles, etc. A fender.

Guard-rail: Same as "Felloe Plank." Also the inner steel rails between the main rails of a railway track. -- A guard rail on a roadway, so placed as to catch the felloe of a wheel and thus prevent the vehicle from striking the truss. In wide bridges, a felloe plank is often placed midway between the trusses, to prevent vehicles passing from one side to the other. [Felloe: The circular rim of a wheel into which the outer ends of the spokes fit.]

Guard Timber: A guard-rail made of a timber, usually dapped over the ties for railway bridges.

Gudgeon: That part of a shaft resting in the bearing, especially when made of a separate piece. A metallic journal-piece let into the end of a wooden shaft. A metallic pin used for securing together two blocks or slabs of stone. A cramp.

Gudgeon Pin: Same as "Gudgeon."

Guide: Any apparatus or contrivance intended to direct or to keep to a desired course or motion.

Guide Bar: One of the guides upon which the cross-head of an engine slides. Any bar used as a guide to a moving piece.

Guide Block: Same as "Guide Bar."

Guide Chair: A device resembling a chair, used as a guide.

Guide Frame: A framework used as a guide.

Guide Pile: A pile driven near a caisson to act as a guide during sinking.

Guide Pin: One of the pins which keep a hub and felloe central with the axis of the machine to which they pertain.

Guide Pulley: A pulley employed to alter the course of a belt.

Guide Rail: An additional rail placed inside of and close to one of the ordinary rails to prevent trains from leaving the track on curves.

Guide Rollers: A roller on a fixed axle serving as a guide to anything passing along in contact with it.

Guide Ropes: Ropes used as guides for a hoisting cage.

Guide Screw: A screw for directing or regulating certain movements in machinery.

Guide Tube: A contrivance by which a boring bit or drill is guided, commonly a fixed tube to prevent swinging.

Guide Wedge: A wedge-shaped apparatus used as a guide.

Guide-yoke: A yoke-shaped piece for supporting the guides in a machine or engine.

Gun: A device for discharging missles through a tube. Also a hammer operated by air.

Gun Metal: Same as "Bronze."

Gunnel or Gunwale: The upper edge of a boat's side.

Gunny-sack: A bag made of coarse, heavy sacking of jute or hemp.

Gunnysack: A coarse sack of jute or hemp for various uses, such as holding cement in transit or to contain sand for revetment.

Gunpowder: An explosive mixture of nitre, charcoal, and sulphur.

Gunpowder Pile Driver: A device for exploding successive charges of gunpowder on top of the pile and, by the concussion, forcing the pile into the ground.

Gunwale: Same as "Gunnel."

Gusset: An angular piece of iron or steel, or a steel plate fastened to angles, channels, or the members of a structure to give strength and stiffness to them, or to connect them to the construction.

Gusset Plate: A large connecting plate used at panel points to join the chord and the web members.

Guy: A line for bracing the top of a pole, derrick, or any other similar appaatus.

Guy Derrick: A derrick in which the mast is guyed with cables to an anchorage.

Guy Line: Same as "Guy."

Guy Ring: A ring attachment on a derrick, etc., for connecting guy lines.

Guy Rope: A rope used as a guy-line.

Gypsum: A chalk formation containing the native hydrous sulphate of calcium.

Gyrate: To revolve about an axis or a point.

Gyration: The act of revolving or gyrating.

Gyroscope: An instrument consisting of a fly-wheel so mounted that its axis is free to turn in any direction. It is used to illustrate the dynamics of rotating bodies.