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Glossary of Bridge Terminology



Eads' Pump: A pump employing a water jet to entrain air and thereby suck up mud and wet sand into a chamber where it is caught by the jet and carried out through a discharge pipe.

Earth Pressure: The lateral pressure exerted by a bank of earth when supported by a retaining wall or an abutment.

Easement Curve: A curve of gradually changing radius for passing from a tangent to a circular curve. Used in railroading to ease the train shock that comes from the changing of the direction of motion.

Eccentric: Out of centre. A disk mounted out, of centre on a driving shaft and surrounded by a collar or a strap connected with a rod. Its purpose is to convert rotary motion into reciprocating rectilinear motion.

Eccentric Axis: An axis that does not pass through the centre of gravity or the centre of figure of the body considered. The axis about which an eccentric revolves.

Eccentric Gear: A gear wheel mounted with shaft out of centre.

Eccentric Load: A load which is applied to one side of the axis of resistance, and which, consequently, produces a bending moment on the piece considered.

Eccentric Rod: The main connecting link by which the motion of an eccentric is transformed and transferred.

Eccentric Strap: The band of iron or steel which embraces the circumference of the eccentric and in which it revolves.

Eccentricity: The state or condition of being eccentric. Deviation from a centre.

Economic Depth: That depth of truss or girder, which, when everything is considered, will give results that are satisfactory from all standpoints and involving the least expenditure of money for properly combined first cost, operation, maintenance, and repairs.

Economics: The science of obtaining a desired result with the ultimate minimum expenditure of effort, money, or material.

Eddy: A whirl or backward current of water. A vortex. That portion of the water in a stream that actually swirls.

Edge: The sharp margin, or the thin, bordering or terminal line of a cutting instrument. The extreme margin of anything. The brink.

Edger: A cement finisher's tool for rounding the corners of cement or concrete constructions.

Effective Area: The gross area of a section less that lost by the rivet holes or the pinholes; the net area.

Effective Depth: The perpendicular distance between the gravity lines of a truss or girder.

Effective Depth of Girder: See "Effective Depth."

Effective Horsepower: Same as "Actual Horsepower." -- The actual horsepower of an engine as measured at the flywheel by a friction-brake or a dynamometer.

Effective Length: That length of a member or structure used for the purpose of designing it. In a girder or truss the distance between the points of support.

Effective Span: The distance from centre to centre of end pins in a bridge span, or that between centres of bearings in any structure.

Effective Span Length: Same as "Effective Span."

Efficiency: The ratio of energy utilized divided by the energy expended.

Efficiency Curve: A curve showing the relation of output to input, or the efficiency of a machine, apparatus, method, etc.

Efficiency of Tackle: The ratio of the actual load lifted to the theoretical load (i.e., the pull on the fall line multiplied by the number of parts of the rope sustaining the load.)

Efflorescence: A powder-like incrustation formed on bodies such as concrete, metals, etc.

Egg-shell Paper: A heavy drawing paper having a finish on one side resembling the surface of an egg-shell.

Ejector: A device for utilizing the momentum of a jet of steam or air under pressure to lift a liquid or a finely divided solid.

Ejector Condenser: A form of condenser operated by the exhaust steam from the engine cylinder.

Elastic Arch: An arch designed on the basis of the elastic theory of materials.

Elastic Curve: The curve formed by the neutral axis of a beam, as it deflects under the action of its own weight, and of the loads upon it.

Elastic Deformation: A change of shape without impairment of the elastic properties of the material. A deformation with resulting stress inside of the elastic limit.

Elastic-limit: The unit stress at which the deformation begins to increase in a faster ratio than the applied loads.

Elasticity: That property which many bodies have of recovering their original form after the removal of the deforming cause.

Elbow: The bend of an arm. The flexure or angle in a wall. A joint in a pipe making a bend. To jut into an angle.

Elbow Joint: A joint where two pieces of pipe meet at an angle. A form of pipe fitting for joining two such pipes.

Electric Crane: A crane operated by electricity.

Electric Hammer: An electrical apparatus for working a rock drill.

Electric Locomotive: A locomotive run by an electric current.

Electric Motor: A motor run by an electric current.

Electrical Hoist: A hoist operated by an electric motor.

Electrical Horsepower: The power in an electric current, usually measured in kilowatts and reduced to horsepower by dividing by 746.

Electrical Resistance: That property of a body or conductor by virtue of which the passage of an electric current is opposed.

Electro-magnet: A magnet which derives its magnetic properties from the magnetic flux set up by an electric current flowing through its windings.

Element: That of which anything is in part compounded, which exists in it, and which is itself not decomposable into parts of different kinds.

Elevation: The altitude or height above some given line or datum plane; such as sea level, low water, etc. The act of raising. The projection of an object on a vertical plane, used in drafting.

Elevator: An apparatus for hoisting loads. A lift. The term often includes the entire hoisting apparatus: i.e., the shaft, cage, and motor.

Ellipse: A curve such that the sum of the distances from two fixed points, called the foci, to any point on the curve is a constant.

Ellipse of Stress: A relation between stresses such that if a pair of principal stresses, of the same or opposite kinds, be represented by the semi-major and semi-minor axes of an ellipse, respectively, the intensity of the stress in any direction in the same plane is represented by the semi-diameter of the ellipse in that direction.

Elliptical Arch: An arch having the form of a semi-ellipse.

Elliptical Curve: Same as "Ellipse."

Elongation: The stretching or extension of a part beyond its natural dimensions.

Embankment: A bank, a dike, or an earthwork raised for any purpose.

Emerson's Foundation Pump: A pump specially adapted for pumping out cofferdams or cribs.

Empirical: Pertaining to or derived from experience or experiments.

Empirical Coefficient: A coefficient established by experience or observation rather than by scientific deduction from fundamental principles.

Empirical Formula: A formula pertaining to or derived from experience or experiments.

Encased Knot: A timber knot which is surrounded wholly or in part by bark or pitch.

End Floor-beam: The floor-beam at the end of a span.

End-lifting Apparatus: An apparatus consisting of a toggle, operated by screws, which lifts and latches the ends of a swing span.

End Pin: A truss pin at the end of a span connecting the truss to the shoe.

End Post: The post at the end of a truss.

End Reaction: The reaction set up at the end of a beam, girder, or truss by the loads thereon plus its own weight.

End Shear: The shear at the end of a beam or girder.

End Stiffener: Vertical angles riveted to the web of a plate girder at its ends for the purpose of stiffening it and transferring the end shear to the shoe or base plate.

Endless Chain: Any chain in the form of a loop without an end.

Energy: The capability of doing work.

Engage: To bring two pieces into contact. To mesh, as to connect gears.

Engine: An apparatus or machine for converting some form of energy into mechanical power for the doing of useful work.

Engineering News Formula: A formula proposed by the late A. M. Wellington, C.E., for determining the safe load on piles.

whereW denotes the weight of the drop or steram hammer
H denotes the fall in feet or the stroke in a steam hammer
ands denotes the average penetration of the pile per blow in inches under the last few blows

For steam hammer work this formula is modified by substituting 0.1 in place of unity in the denominator

Engineer's Hammer: Usually a two faced cylindrical hand hammer, though some times having a cylindrical poll and a triangular peen.

Engineer's Level: A leveling instrument consisting of a telescope, having cross hairs, mounted on a supporting frame which can be brought to a level by means of screws, and which can be rotated about a vertical axis. A tripod serves to hold the instrument at a convenient height for the observer.

Engineers' Scale: A scale in which the units are divided decimally.

English Bond: Same as "Old English Bond." -- A masonry bond formed by laying alternately entire courses of headers or stretchers. Sometimes, though, only one course of headers is laid for every two or three courses of stretchers.

Enlarged Scale: An oversized delineation of an object.

Entasis: A slight convex curve in the vertical outline of a pilaster or of the shaft of a column.

Epicycloid: A curve generated by the motion of a point on the circumference of circle which rolls on the convex side of a fixed circle.

Epicycloidal Curve: Same as "Epicycloid."

Epicycloidal Tooth: A form of gear tooth having both faces and flanks curved to conform with arcs of an epicycloid.

Equalizer: An adjuster; a leveler. A device for distributing a load equally over several parts.

Equilibrium: A state of balance produced by the counteraction of two or more forces. The state of a body so acted upon by a balanced system of forces that it has no tendency to change its condition of motion or rest.

Equilibrium of Three Parallel Forces in One Plane: Same as "Laws of the Lever." -- An early day expression used to denote the conditions of equilibrium of three forces in one plane. They are as follows: First, The three parallel forces applied to one body must balance each other and lie in the same plane. Second, The two extreme forces must act in the same direction. Third, The middle force must act in the opposite direction. Fourth, The magnitude of each force must be proportional to the distance between the other two.

Equilibrium Polygon: A term used in graphic statics to designate the polygon drawn through a system of non-concurrent forces in order to determine the position of the resultant thereof. The sides of the polygon are made parallel to the rays of an accompanying force polygon.

Equivalent Uniform Live Load: A load of the same weight for each unit of its length and practically equivalent in its effect to an assumed typical live load composed of varying wheel concentrations with various wheel spacings.

Erecting-bill: A bill of material for a bridge, so arranged as to facilitate the finding and placing of members during erection.

Erection: The assembling of the members of a bridge in the field and making the necessary permanent connections.

Erection Car: A car specially fitted with a derrick and accessories, used for the erection of bridges.

Erection Diagram: A skeleton drawing of a truss or span showing all pieces in their relative positions, properly lettered and numbered in order to facilitate the process of erection.

Erection Drawing: Same as "Erection Diagram."

Erection Gang: A gang that does the work of erection.

Erection Stress: Stress induced by loads applied during the erection of a structure.

Escarpment: A nearly vertical natural face of rock or soil.

Estimate: To figure quantities, weights, costs, etc. A statement of such quantities, weights, costs, etc.

Euler's Formula: A formula expressing the resistance of long columns to buckling, viz.

whereP = the external load or pressure
E = the modulus of elasticity
I = the least moment of inertia
l = length
a = constant depending on end conditions
π = 3.14159

Even Bearing: A bearing in which the pressure is uniformly distributed.

Evolute: A curve which is the locus of the centre of curvature of another curve, or the envelope of the normals to the latter.

Evolute Curve: Same as "Evolute."

Exaggerated Scale Drawing: A drawing on which two scales are used, as a railroad profile. But little used by bridge engineers.

Excavating Shaft: A shaft or hole through which excavation is carried on.

Excavation: The act of taking out material. An open cutting, as in a railway. A hollow or cavity formed by removing the interior substance.

Excavator: A horsepower or steam-power machine for digging, moving, or transporting earth, loose gravel, sand, or any kind of soil.

Excentric: Same as "Eccentric."

Excentric Load: Same as "Eccentric Load."

Excess Load: An "Over Load." See also "Locomotive Excess."

Expanding Reamer: A reamer having a device that can be expanded after its insertion in a hole so as to make an undercut.

Expansion: Enlargement, lengthening due to heat, or to increase in moisture content.

Expansion Bearing: A support at the end of a span where provision is made for the expansion and contraction of the structure.

Expansion Bolt: Any bolt similar to the "Brohard Expansion Bolt."

Expansion-end: The movable end of a structure, trestle, span, truss, etc.

Expansion Girder: Any girder one end of which is allowed to move.

Expansion Joint: A joint in which movement for expansion and contraction is allowed.

Expansion Pocket: A bracket or pocket carrying a sliding end of a girder.

Expansion Rollers: A group of steel cylinders nested in a box or suitable frame placed under the shoe of a span to facilitate its movement during temperature changes and loading.

Explosive: Pertaining to, or of the nature of, explosion. Any substance by the decomposition of which gas is generated with such great rapidity that an internal pressure is suddenly set up, producing the effect of tremendous impact, and the rupture of the restraining medium.

Extension Bar: A bar riveted to the end of a strut-channel, and projecting beyond it, to permit the passage of a pin.

Extension Plate: Same as "Jaw Plate." -- The unsupported portion of the end of a compression member remaining after the outstanding legs of flange angles have been cut away, and its pin plates, which extend below the transverse diaphragm to allow the packing of other members on the same pin.

Extensometer: An apparatus for measuring minute degrees of expansion or contraction in metal bars under the influence of temperature or under stress.

External Wall: The outside wall of a structure.

Extrados: The convex curve of a masonry arch. The upper surface of the voussoirs when in position.

Extreme Fibre: The fibre which is most remote from the neutral axis.

Extreme Fibre Stress: In members subjected to bending, the intensity of stress on the fibre (or elementary strip) farthest removed from the neutral axis.

Extreme High Water: The highest known water elevation of a stream or tide.

Extreme High-water-mark: A mark left by the highest known flood.

Eye: The hole in the end of a member to permit the passage of a pin.

Eye and Strap: A hinge which fits over an eye.

Eye-bar: A bar with an eye at either one end or each end.

Eye-bar Dog: A special pair of tongs for lifting and moving eye-bars.

Eye-bar Head: The enlarged end of the eye-bar through which the pin passes.

Eye-bar Hook: Same as "Eye-bar Dog"

Eye-bar Upsetter: A machine for enlarging the end of a plain bar sufficiently to permit the forming of an eye that will develop the full strength of the bar.

Eye Bolt: A bolt having a loop or eye at one end in place of the customary flat head.

Eye-piece: The lens in the small end of a transit or level.

Eye Splice: A splice formed by bending back the end of a rope or cable and weaving it into the body of the rope so as to form a loop, or an eye.