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Glossary of Bridge Terminology



Macadam: A type of pavement consisting of broken stone laid in courses and rolled.

MacArthur Pile: Same as "Pedestal pile." -- A patented pile formed by driving a steel shell into the ground to the required depth, putting in small quantities of concrete, and hammering them down so as to force the concrete into the earth beyond the point of the shell; thus enlarging the end and greatly increasing the bearing area. The shell is afterward withdrawn gradually, as the hole that it made is filled with concrete. If the shell were left in, the method would be far more satisfactory; as the shaft of the pile is liable to be seriously imperfect.

Machine: An apparatus, instrument, or mechanical element for the transmission of force and the conversion of motion.

Machine Bolt: A threaded bolt having a straight shank and a square or hexagonal shaped head.

Machine Chain: A chain with twisted links that form a fairly flat surface.

Machine Drill: A drill mounted in a machine and run by power.

Machine Finish: A finish on metalwork made by turning in a lathe or planing in a machine.

Machine-made: Made by a machine; used in contra-distinction to hand-made.

Machine Screw: A screw which has a straight shank and an enlarged head providing a shoulder for bearing. A slot in the head affords the means for turning with a screwdriver.

Machine Shop: A shop for metal turning, planing, and drilling.

Machine Work: The shaping, fitting, and dressing of metal such as drilling, planing, turning, milling, and grinding done by machinery.

Machinery: A general term used collectively for a number of machines.

Machinery Barge: A barge which carries machinery; used in construction work.

Machinery House: A house in which machinery is kept for its protection.

Machinist's Hammer: A hammer with a round, flat face and a cross peen.

Magnesian Lime: A term applied to limes containing more than five per cent of magnesia.

Magnesian Limestone: A limestone containing one-third part or less of carbonate of magnesia.

Magnetic: Having properties like those of a magnet-possessing magnetism.

Magnetic Needle: A thin, small bar of magnetized steel used in a surveyor's compass to determine the magnetic meridian at any place.

Main Diagonal: A web diagonal member joining the top and bottom chords of a truss, and taking its greatest stress when not less than one half of the span is covered by the live load.

Main Member, or Primary Member: A principal part of a truss or floor system--generally restricted to trusses.

Main Shaft: A principal shaft used in the transmission of power.

Main Stress: Same as "Direct Stress." -- A stress resulting from a direct application of the load.

Maintenance Cost: All expenditures for repairs and upkeep which are directly due to operating a structure or plant.

Making Iron: An iron with rounded teeth, used for driving home a strand of oakum.

Male Screw: A screw having an exterior thread.

Malleable: Capable of being shaped by a beating or rolling process.

Malleable Cast Iron: Same as "Malleable Iron."

Malleable Iron, or Malleable Cast Iron: Cast iron that has been rendered tough and malleable by long-continued high heating, while embedded in hematite, ferric-oxide, etc., and then allowed to cool slowly.

Malleable Pig: Pig iron used for making malleable castings.

Mallet: A small wooden hammer wielded with one hand.

Mallet Locomotive: A heavy freight locomotive having two sets of six, eight, or ten driving wheels each.

Man-hole: An opening or entrance by which a man can enter a closed space, such as a boiler, sewer, or conduit.

Man-power: The power exerted by a man. A mechanism by which man can exert his power to advantage.

Mandrel, or Mandril: A short shaft of uniform or varying diameter upon which various pieces pieces of metalwork can be mounted for turning in a lathe. A metallic core used in driving Raymond or Simplex piles.

Mandril: Same as "Mandrel."

Manganese: A metal resembling iron and having a strong affinity for it. Used in the manufacture of all steels, the percentage thereof generally varying between one-half and unity.

Manganese Steel: Steel containing from eleven per cent to fourteen per cent of manganese and one and one-half per cent of carbon. This is a very hard, brittle steel and has to be treated by cooling in water to remove the extreme brittleness. Used where high resistance to abrasion is necessary.

Mangle: A set of rolls for straightening plates.

Manheim Slide Rule: A slide rule of the stick type graduated on one face only. The slide has one face only flush with the rule though graduated on both faces; being thinner than the rule, it has to be reversed when using the lower face.

Manifold: A tube, usually of cast metal, with one or more flanged or screw-threaded inlets and two or more flanged or screw-threaded outlets for pipe connections. To make a number of copies of anything by a single operation.

Manila Hemp: A very fine hemp grown in the Philippine Islands.

Manila Rope: Rope made from the fibre of the Musa textilis, a tall perennial herb of the same genus as the banana, which grows in the Philippine Islands.

Map: A descriptive drawing or delineation of a section of the country.

Margin: A space along an edge or boundary line, a border.

Margin Draft: A chisel draft around the edges of a stone.

Marking Gauge: Same as "Hand Gauge." -- The ordinary wooden scratch gauge used by carpenters for marking off a line parallel to the edge of a board.

Marline: A small rope made of two strands loosely twisted together, used for winding around ropes, cables, etc.

Marline Spike: A tapering, sharp-pointed, iron pin used in separating the strands of a rope for splicing.

Masonry: A general term applied to structures made of stone, brick, or concrete.

Masonry Joint: A joint between masonry stones that is filled with mortar.

Masonry Pier: A pier constructed of stone masonry.

Masonry Plate: A plate used under a bridge-shoe for the purpose of distributing the load on the masonry.

Masonry Stone: Stone employed in masonry construction.

Masonry Wall: Any wall made of masonry.

Mason's Hammer: A square-faced hammer with a peen in line with the handle.

Mass: The quantity of matter in a body. It is measured by the ratio of its weight to the acceleration due to gravity.

Mast: An upright post of timber or steel, as the mast of a derrick.

Mast Pin: A vertical pin at the top of the mast of a derrick.

Mast Seat: The casting at the foot of a mast on which it rests and turns.

Mastic: A well-agitated mixture of several different small-grained constituents, one of which has a cementing or binding power.

Mat: Same as "Mattress."

Mat Work: A general term for extended mattress construction used in river protection.

Match Joint: Same as "Tongue and Groove Joint." -- A joint made by one part having a projecting tongue fitting into a corresponding groove in the other part.

Match-marking: A system of marking the parts or members of a structure, so that they always may be connected up in exactly the same order and manner.

Matching: A fitting together of two or more parts.

Material: Any substance entering into the construction of a bridge.

Matrix: A term used in connection with concrete to denote the cementing material which fills the voids of the aggregate.

Mattock: A form of pick with broad cutting edges for digging.

Mattress: A combination of willow poles and wire rope woven together, forming a mat which is placed on the bed or the bank of a stream to prevent scouring.

Maul: A type of large hammer or mallet having both ends flat for beating.

Maximum Stress: The greatest stress that comes on a piece, or sometimes the greatest stress a member can have with its allowable load.

Meager Lime: A lime that is lacking in the protoxide of calcium.

Meander Line: A traverse line run along the banks of a stream so as to conform with its changes of direction and to enable it to be plotted.

Mechanical Curve: Same as a "Transcendental Curve." -- A curve expressed by an equation containing transcendental functions of one or more of the ordinates.

Mechanics: The science of force and its effect upon matter. While the word was originally used to mean the theory of machines, it has, by extension, come to denote the doctrine of force and the resulting motions or tendencies to motion of particles and systems of particles. As such, it is the fundamental one of all the physical sciences.

Mechanism: The structure of a machine, engine, or other contrivance for controlling or utilizing natural forces.

Medium Steel: Steel neither very hard nor very soft, containing from one-fourth to one-half per cent of carbon.

Megohm: An electrical unit of resistance equal to one million ohms. See also "Ohm."

Melan Arch: A type of reinforced concrete arch in which ribs of rolled I-beams, or built tip lattice girders, spaced two or three feet centres, are used to strengthen the concrete arch barrel.

Melt: To fuse or liquify by applying heat. A term employed by blast-furnace men to denote the metal fused, or the charge or heat, as it is sometimes called.

Melt-numbers: The number given a heat or charge and carried by the product throughout the processes of rolling and fabrication.

Melting-point: The temperature at which a metal passes from the solid to the liquid state.

Member: A component part of a bridge or other structure, complete in itself.

Merchants Bar: Wrought-iron bars in their finished form ready for sale.

Meridian Section: A section of a sphere made by a plane passing through and containing a diameter.

Mesh: An open space between the wires of a screen or sieve. Sometimes used to denote the netting composed of wires. Also used to denote the engaging of one gear with another.

Meshing of Gearing: The engaging or interlocking of the teeth of one gear with those of another.

Meta-centre: Same as "Metacenter."

Metacenter: The point of intersection of a vertical line through the center of buoyancy and a line of symmetry through the center of gravity of a floating body.

Metal: As used in bridgework, this term means steel, unless specifically stated otherwise.

Metal Lath: A perforated metal sheet used for reinforcing concrete.

Metal Lathe: A lathe which is used exclusively for turning metals.

Metal Saw: A. saw having a blade tempered hard enough to cut metals.

Metallic Tape: A tape made of cloth, but having metallic wires interwoven to give strength and to reduce the stretching.

Meteoric Iron: Iron obtained from meteorites, generally containing about ten per cent of copper.

Meter: A unit of length in the metric system which equals 39.37 inches in the English and American systems. An apparatus for measuring quantities.

Metope: A square slab, decorated or plain, inserted in the opening between adjoining ceiling beams.

Metric Rod: A level rod graduated in meters and decimal parts thereof.

Metric System: A system of units of weights and measures depending upon the meter. It is the standard in Continental Europe and in Latin America, and ought to be adopted throughout the entire world.

Metric Ton: A French ton, equivalent to 2,205 pounds nearly.

Micrometer: An instrument for the, precise measurement of small lengths and angles. The usual form consists of a screw with a very fine thread and a large graduated head.

Micrometer Caliper: A caliper having a micrometer screw.

Micrometer Gauge: Same as "Micrometer Caliper."

Micrometer-measurement: A precise determination of the diameter of a test piece by a micrometer-screw.

Micrometer Screw: Same as "Micrometer."

Mid-span: The centre of a span.

Middle-third: A term in masonry construction used in connection with the line of pressure to denote a condition which must obtain in order to prevent tension at a joint of the structure; that is, the line of pressure must pass within the middle third of the section.

Mikado Locomotive: A heavy locomotive having two pilot, eight driving, and two trailer wheels.

Mild Steel: A soft steel. Same as "Low Steel." -- A soft steel containing a small amount of carbon-less than one-fourth of one per cent.

Mill: A machine for rolling plates, shapes, rails, etc. The plant where steel shapes etc., are rolled. To remove metal by a circular tool having teeth as in a milling machine.

Milled Lead: Same as "Sheet Lead." -- A thin plate of lead made by passing a flat ingot repeatedly through rollers.

Milling: The process of removing metal with a circular cutter in a milling machine.

Milling Machine: A machine consisting of a rotating mandrel carrying a milling cutter, and a movable table, operated by a feed screw, to which is bolted the object to be milled.

Mineral Paint: Any paint in which a mineral pigment is used.

Mirror Iron: A white, cast metal containing manganese-largely used in the manufacture of steel. Also called spiegel, spiegel iron, and spiegeleisen.

Miter: To cut at a bevel of forty-five degrees. A bevel of forty-five degrees.

Miter Gears: A pair of beveled gears in which an element of the conical pitch surface makes an angle of forty-five degrees with the axis.

Miter Joint: A special case of a beveled joint in which the contact surfaces make angles of forty-five degrees with the axes of their respective parts.

Mixer: A machine for mixing materials.

Modulus: A number, coefficient, or quantity that measures a force, function, or effect.

Modulus of Crushing: A number denoting the average value of the crushing resistance of a material.

Modulus of Elasticity: Same as "Coefficient of Elasticity." -- The ratio of the direct stress per unit of area to the corresponding relative deformation, sometimes called Lineal Modulus. The numerical value is equal to the stress per unit of area in tension that would be required to double the length of a piece, were the material of which it is composed perfectly elastic.

Modulus of Rupture: The unit stress at which a piece fails.

Mogul Locomotive: A type of freight engine with three coupled driving wheels on each side and a swinging, two-wheeled truck in front.

Molecule: The smallest part into which any substance can be divided without destroying its chemical character.

Moment: The tendency of a force to produce rotation or of a stress or mass-inertia to resist rotation. This tendency is measured by the product of the force into its lever arm.

Moment Area: Sometimes called area moment. The area enclosed by a moment curve. See also "Moment-Area Method."

Moment-area Method: The method for finding deflections in a framed structure by use of the moment area curve.

Moment Diagram: A curve showing the values of the bending moments in a beam or truss at various sections thereof.

Moment of a Couple: The tendency of a couple to produce rotation, measured by the product of one of the two equal forces by the perpendicular distance between them.

Moment of Inertia: A function of some property of a body or figure-such as weight, mass, volume, area, length, or position-equal to the summation of the products of the elementary portions of such property, of said body or figure, by the squares of their distances from a given axis.

Moment of Resistance: The sum of the moments of all the resisting forces at a section of a member.

Moment of Stability: The resistant moment of a structure due to its weight acting with a lever arm equal to the distance between its centre of gravity and the edge of the structure about which it tends to rotate.

Moment of Torsion: The sum of all the moments of the internal forces in a body that is resisting a twisting moment. It is equal to the sum of the moments of all the applied forces that tend to produce torsion.

Momentum: The quantity of motion in a body, measured by the product of its mass into its velocity.

Monier Arch: An arch in which the reinforcement consists of wire netting, one net being placed near the intrados and one near the extrados.

Monier-Construction: A form of reinforced concrete in which wire netting is used for reinforcement.

Monkey: An early type of pile-driver hammer.

Monkey Engine: A hoisting engine used to raise a pile-driver hammer.

Monkey Pile Driver: Same as "Hand Pile Driver." -- A small pile driver operated by hand.

Monkey Wrench: A wrench having an adjustable jaw moved by a screw.

Mooring: A fastening; that to which anything is fastened.

Mooring Line: A line used to fasten an object. Generally applied to a vessel or barge.

Mooring Piles: Piles used for fastening boats and barges.

Mortar: A mixture of cement or lime with sand and water forming a thick paste, used in masonry work for bedding the stones and filling the joints.

Mortar-board: A platform on which mortar is mixed.

Mortar Box: A box in which mortar is mixed.

Mortise: The slot or hole cut in a timber to receive the tenon.

Mortised Joint: The joint formed between two pieces when one has a hole mortised in it to receive the tenon of the other piece.

Motor: A machine for producing or translating power.

Motor Bridge: A draw bridge operated by a motor, or a bridge which carries motor cars.

Motorway: The passageway on a bridge used by motor cars.

Mottled Iron: An iron in which part of the carbon appears as graphite, giving rise to alternate white and gray spots.

Mould: A form or model pattern of a particular shape, used in fixing the shape of a plastic mass. Sometimes spelled "Mold."

Moulded Gears: Same as "Cast Gears." -- Gears made by casting and not trimmed.

Moulding: The process of shaping a plastic substance into a given form by the use of moulds. Also a decorative member in construction.

Moulding Planks: Planks on which ornamental mouldings are placed while in a soft condition.

Mountain Locomotive: A heavy locomotive having four pilot, eight driving, and two trailer wheels.

Mousing: A string or wire wound around the end of a rope to prevent raveling.

Movable Bridge: A bridge with a "Movable Span." More correctly speaking, "Movable Span."

Movable Cofferdam: A cofferdam constructed of timber, hinged at one corner and joined on the diagonal corner in such a way that it can be opened, after the pier is built, and moved away to another pier site.

Movable Span: Any span of a bridge that may be moved in any manner to allow passage for vessels through or under the bridge.

Moving Load: An advancing load on a structure,.

Muck: Soft mud containing vegetable matter.

Muck Bar: The bar made by the first rolling of the bloom.

Muck Iron: The lowest grade of wrought iron. Iron ready for the rollers or squeezers.

Mucking: Excavating or working in muck.

Mud Line: The line of intersection of the mud surface with an object imbedded therein. The earth line in a profile of a river crossing.

Mud Pump: A pump used for pumping mud out of an excavation, usually a centrifugal pump, although sometimes a jet pump, such as the Eads' pump is employed.

Mud Sill, or Sub Sill: A sill placed on short cross blocks resting on the earth, to support a framed bent.

Muffler: A device to prevent the noise of steam or gas when escaping from an exhaust pipe.

Mule Traveler: Same as "Creeper Traveler." -- A small movable derrick running on a track on the upper chord of a truss. It usually has two booms.

Multi-centered Arch: An arch having an outline composed of a series of circular arcs with different radii, giving an approximation to an ellipse. These arcs are symmetrically disposed about a vertical axis and occur in odd numbers.

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

Multiple Intersection: Same as "Multiple Cancellation."

Multiple Punch: Same as "Gang Punch." -- A machine that punches two or more holes at one operation.

Multiple System: A truss system having more than one system and usually more than two systems of cancellation.

Multiple Truss: A truss having a multiple cancellation web system.

Murphy Truss: A Whipple Truss having eye-bars for the lower chords.

Mushet Steel: A steel containing one and one-half per cent of carbon and from five to eight per cent of tungsten, which when hardened by air cooling holds its temper until it becomes red-hot. A steel produced by the Mushet process of recarburization, which consists of adding spiegel or other form of manganese.

Mushroom Anchor: An anchor made in the shape of a mushroom-used on muddy bottom.

Mushy: The condition of a casting containing an excessive number of blow holes, rendering it unsound.