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ENGINEERING TERMS

This section provides a glossary of contemporary civil and mechanical engineering terms.

Abutment: a support for an arch or bridge.

Active layer: the surficial ground layer which is subject to seasonal volume changes due to freezing and changes of moisture content.

Angle section: a rolled steel or other metal section with an L-shaped cross-section.

Arch: a beam curved in a vertical plane for carrying loads. The load-bearing part is termed the arch ring.

Arch, trussed: a steel arch built of rolled-steel sections.

Ash content: the percentage of incombustible material in a fuel, particularly coal.

Back cutting: the additional excavation required to provide material for an embankment over and above that supplied by the cutting.

Balanced earthworks: an excavation scheme designed so that the volume of cuts equals that of the fills.

Ballast: the aggregate on which the track is laid. Typically this material consists of two layers: a lower spread of hardcore which may cover the whole of the formation, depending on the drainage conditions, and an upper layer of angular rock chippings in which the track is set. This 'top ballast' prevents movement of the sleepers. Blanketing, an intermediate layer, may be spread between the formation and the hardcore of the ballast, to prevent clay subsoil from working upwards into the ballast. The blanketing may consist of sharp gravel, sand-grade material or concrete.

Banking: superelevation (e.g. of trackwork).

Barrel vault (=tunnel vault): a continuous plain arch or vault of semicircular shape, longer than its diameter.

Batter: a uniform steep slope as of a cutting, or its inclination.

Beaching: coarse gravel used in revetting embankments below the level of the pitching.

Beam: a structural member designed to resist loads which bend it.

Bearing capacity: the load per unit area which a type of ground can safely carry.

Bench: see berm.

Bent: a two-dimensional frame which is self-supporting within these dimensions.

Berm: a horizontal ledge cut into an earth bank or cutting to improve its stability.

Binder: the material used for joining masonry.

Blinding: a sealing coat, mat or mattress of lean concrete spread on soils such as clay to seal it.

Bolster: a support for a bridge truss on an abutment.

Boom: a beam used in lifting tackle e.g. the jib of a crane.

Borrow: material dug to provide fill elsewhere i.e. from a borrow pit.

Bottoming: the lower layer of ballast.

Box culvert or drain: one with a rectangular cross-section.

Boxing: a bed of ballast between the sleepers.

Bridge, bascule: a bridge which is hinged in the fashion of a drawbridge.

Bridge bearing: the support at the bridge pier which carries the weight of the bridge.

Bridge, cantilever: typically a symmetrical three-span bridge of which each of the outer spans (cantilever arms) is anchored to the ground and overhangs into the centre section to support a suspended span.

Bridge deck: the load-bearing floor of a bridge.

Bridge pier: the support for a bridge.

Bridge, pivot: a swing bridge.

Bridge, skew: a bridge which spans obliquely and is therefore longer than the gap.

Bridge, suspension: a bridge hung by vertical rods (suspenders) from a pair of cables, each carried by two towers and anchored to the ground at its extremities.

Bridge, swing: a bridge which is pivoted at its centre and swings open in the horizontal plane.

Bridge, through: a bridge in which the lower flange carries the road bed.

Bridge, traversing: a bridge which can move backwards from an opening.

Bridge, trestle: a lightweight bridge supported by trestle bents.

Buttress: a pier built against a wall to provide further support.

Caisson: a cylindrical or rectangular structure for keeping water or soft ground from flowing into an excavation while foundations are set. It is later incorporated in the foundation masonry.

Cant: super-elevation.

Catenary: the curve formed by a uniformly loaded rope when hung between two points. Hence the term catenary suspension applied to overhead electricity conductors.

Caulking: the sealing of a seam or joint.

Cess: a drain along the foot of a cutting.

Check valve: see clack valve.

Chevron drain: gravel-filled drains laid out in a herringbone pattern on cutting-slopes.

Clack valve: (or non-return valve or check valve) one which allows flow in only one direction.

Clearance: the space between a railway vehicle and a stationary object e.g. a bridge.

Cofferdam: a temporary dam to exclude water, consisting either of sheet piles or a dam built above ground, to provide access to ground which is ordinarily submerged or waterlogged.

Concrete, pre-stressed: that which is compressed either by stretched wires within it or by abutments.

Concrete, reinforced: that which contains a reinforcement of steel rods or mesh.

Construction way: temporary trackwork laid during the building of permanent way.

Contraction joint: a break in a structure, made to allow for shrinkage of concrete or masonry.

Corrosion fatigue: the weakening of steel by small fatigue cracks which are entered by water during reversals of stress.

Counterfort: a strengthening pier built behind a retaining wall to provide additional stability.

Cribwork: large timber cells which are sunk full of concrete to provide bridge foundations or crossed timbers used to give support on soft ground.

Crown: the highest part of an arch or tunnel (see invert).

Cut and cover: a method of tunnel construction which involves the building of the tunnel lining in an open cutting which is subsequently backfilled.

Cut and fill: typical railway construction which involves excavation of cuttings and building of embankments.

Cut-off: a construction below ground-level designed to reduce movement of groundwater.

Derrick: a type of crane which has a lifting arm pivoted at the foot to a central mast.

Diaphragm: a stiffening plate in a bridge between main girders.

Diaphragm wall: a separating wall or cut-off, constructed in situ of plain or reinforced concrete; the initial excavation is filled with bentonite mud suspension which is then replaced with tremied concrete.

Dog: a simple track spike.

Drop on: a portable rail crossing for transferring wagons between parallel tracks.

Dumpling: a mass of unexcavated ground in the centre of a cutting construction which serves as an abutment for timbering the side of the dig and which is finally removed when other works are complete.

Elevation: a view of a structure, drawn without perspective, as if projected on to a vertical plane.

Embankment wall: a retaining wall built at the foot of the bank.

Expansion joint: a space between two parts of a structure which allows for thermal movement.

Facing wall: a concrete lining used against the earth face of an excavation prior to the construction of a retaining wall.

Falsework: the temporary support for concrete formwork or arch construction.

Fill: the material used to form the earthwork of an embankment or backfill of an excavation.

Flange: a disc forged on to the end of a pipe or cast on to engine parts for fixing purposes; the wide strips of a girder; the projecting rim of a railway wheel; the basal part of a flanged rail.

Formwork: shuttering erected to contain concrete during placement and hardening.

Girder, bowstring: a girder shaped like a longbow.

Girder, box: a hollow girder, rectangular in cross-section.

Girder, compound: a rolled-steel joist with plates fixed to the flanges.

Girder, plate: a steel girder, reinforced with lengths of angle section.

Girder, stiffening: a girder built into a suspension bridge to distribute the loads evenly.

Girder, Warren or half-lattice girder: a triangular truss construction.

Gravity retaining wall: a retaining wall which is stable by virtue of its own weight and not by the weight of any soil it carries.

Grout: a cement slurry for pouring into masonry joints or injecting into voids in rocks.

Gullet: a narrow cut dug to formation level ahead of the cutting being excavated in order to take the construction way.

Horsepower: 550 ft-lb of work per second in Imperial measure.

Idler: a wheel interposed between two others in a gear train in order to cause them to turn in the same direction.

Impulse turbine: a turbine driven by the speed of the fluid rather than by its change in pressure.

Incline: a length of track laid on a uniform slope.

Invert level: the lowest part of a culvert or tunnel.

Iron, cast: pig iron.

Iron, chilled cast: iron cast in a metal mould in order to harden the margin of the casting.

Iron, malleable cast: iron castings which have been heat treated in the presence of an oxidising agent to increase their strength.

Iron, wrought: the purest form of iron which lacks the brittleness of cast iron.

Journal: accurately turned part of shaft or axle that rests on bearings

Knife-edge loading: in calculations of the loading of bridges two factors are considered at the design stage: 1. a uniform load which varies with span, 2. a knife-edge load of 2700 lb. per ft. at the weakest point in any span (M.o.T. 1931).

Lacing: light metal members fixed to four angle sections to form a composite open beam.

Landslip: a movement of soil down-slope. See mass movement.

Lattice: see lacing.

Live load: a load which may be removed or replaced on a structure.

Lurching allowance: an allowance for extra load on the outer girders of a railway bridge caused by the swaying of the train.

Mass movement: the movement of soil or rock on a slope when gravity induced stresses exceed the strength of the ground. The movement may be in the form of sliding, toppling, creep, flow (when fluids are present) or rock falls.

Navvy: a labourer who worked on railway construction. The term is believed to be derived from the navigation labourers who dug the canals in the 19th century.

Neat lines or net lines: the lines defining the sides of an excavation to be paid for in tunnelling. Any excess material excavated is termed overbreak.

Nosing: the lateral load from the wheels of a locomotive which is taken into account in bridge design (as 10 tons perpendicular to the track).

Overbreak: the additional rock excavated above that strictly required to form a tunnel. See neat lines.

Pantograph: rods connected in the form of a parallelogram, hence the term applied to expanding overhead electrical pick-up gear.

Permanent way: the trackwork and ballast in its final constructed form. See construction way.

Pier: a wide column or wall of masonry forming a support for a bridge.

Pile: a heavy (commonly vertical) beam emplaced below foundation level to provide support for a structure.

Pile, batter: a pile driven at an angle to the vertical.

Pile, bearing: a pile which carries a load rather than lateral thrust.

Pile, bored: a pile formed by pouring concrete into a borehole containing reinforcement.

Pile, driven: a pile of steel or reinforced concrete (i.e. a precast pile) which is forced into the ground by a pile hammer.

Pile, driven cast in place: a reinforced concrete pile cast in a steel casing which has been driven into the ground. The casing is usually removed as soon as the concrete is emplaced.

Pile, end-bearing: a bearing pile which carries its load down to hard ground at its lower end.

Pile, friction: a bearing pile which is supported by friction with the soil surrounding it.

Pile, in situ concrete: a pile which is formed by pouring concrete into a borehole.

Pile, jacked: a pile forced into the ground by jacking against the structure above as in underpinning.

Piles, sheet: closely set piles driven vertically into the ground to keep earth or water out of a subsequent excavation.

Pitching: large stones placed on edge and wedged by gravel forming a layer above beaching to form a revetment.

Portal: the entrance to a tunnel and its abutments.

Quenching: the cooling of steel from above the critical temperature to harden it.

Reaction turbine: a turbine in which the propulsion jets or nozzles are on the moving wheel.

Refuge: a recess in a tunnel or retaining wall where men can shelter while a train passes.

Retaining wall: a wall built to hold back a weak soil or other material.

Retarder: a set of braking bars parallel with the rails in a shunting yard.

Revetment: a protective covering to a soil e.g. on a cutting slope, to protect it from erosion

Road bed: the ballast.

Rocker bearing: a bridge or truss support which is free to rotate but not to move laterally.

Roller bearings: bearings which contain hard steel cylinders. The Timken-tapered roller bearings have rollers of tapered form, which run on conical races.

Rolling resistance: the part of tractive resistance due to the friction between rails and wheels.

Ruling gradient or limiting gradient: the maximum gradient for a given stretch of railway, up which normal traffic can climb without resorting to a second (pilot) engine.

Running resistance: the frictional resistance encoutered by a moving train. It is made up of the rolling resistance, bearing friction, air resistance and additional resistances due to curvature or gradient of the track. It is the ratio of the drawbar pull to the weight of the train.

Scotch block: a wedge or block placed against a wheel to prevent movement.

Self-acting incline or brake incline or gravity plane: a rope incline on which the weight of descending loaded wagons pulls up the empties.

Settlement: the response of the ground to loading when a structure is built. This may be total, at one point or differential, between two points.

Sheer legs or shear legs: a hoist consisting of two (or more) poles attached near the top and fitted with a pulley at the point of attachment.

Soil: in an engineering sense includes all soft strata such as sands, clays and gravels, as well as topsoil.

Stanchion or stauncheon: a vertical steel strut.

Stand-up time: the period before support is required in a tunnelling excavation.

Stay: a tie bar or diagonal brace.

Steel, alloy: a steel which contains elements not in carbon steel, such as chromium, nickel, manganese, molybdenum or vanadium.

Steel, cast: steel which has not been forged or rolled since casting.

Steel, dead-mild: steel which contains between 0.07 and 0.15% carbon and is used for bending, drawing, pressing and flanging.

Steel, high-carbon: steel which contains between 0.5 and 1.5% carbon, such as spring steel.

Steel. high-tensile: steel used for structural work which contains up to 0.3% of carbon, up to 0.5% copper and up to 1.5% manganese.

Steel, manganese: steel which contains more than one percent of manganese and is harder as a consequence.

Steel, mild: steel which contains between 0.15 and 0.25% of carbon. This cannot be hardened by quenching but is more ductile than high-carbon steel.

Stuffing box: a recess, filled with packing, fitting tightly around a piston rod to prevent leakage of steam.

Temper: the state of hardness of a metal; to temper is to reduce the hardness of steel by reheating and quenching

Tractive effort: a theoretical figure measured in lb. for the propulsive force exerted by a driving wheel at its point of contact with the rail. For steam locomotives, the equation includes the diameter of the cylinders, the length of the piston stroke, the working pressure of the boiler and the diameter of the driving wheel.

Tractive force: the amount of pull available at the drawbar of an engine, approximately 0.25 X the weight of a locomotive under ideal conditions.

Tractive resistance: the frictional resistance to motion per ton hauled. At starting this is 2 to 3 times the running resistance.

Traverser: a mobile platform for moving rolling stock between parallel tracks.

Tunnel lining: the covering over the rock or soil of a tunnel to maintain its stability and water tightness e.g. concrete cast in place, precast concrete segments, cast iron rings, brickwork or masonry.

Wing wall or abutment wall: a wall at the abutment of a bridge which extends beyond the bridge to retain the soil behind the abutment.

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