University of Iowa Libraries

Lichtenberger Engineering Library

Glossary of Bridge Terminology

T

T-Abutment: A straight or stub abutment with a stem running back into the fill.

T-Beam: A reinforced concrete-beam or a rolled structural shape having a cross-section resembling the letter "T."

T-Beam Girder: A girder built in the shape of the letter T.

T-Iron: Iron rolled into the shape of a bar having a cross section resembling the letter T.

T Rail: A rail having a section similar o the letter T.

T-Square: See "Square."

Table of Data: A list of the known circumstances that affect the designing of a structure.

Tackle: A combination of ropes and pulley-blocks used in hoisting or lowering where a multiplication of force is desired. Same as "Block and Falls."

Tackle Hook: A hook on a pulley-block opposite the becket.

Tag Line, or Tail Line: A rope attached to a load in order to direct its movement. A loose hanging line for pulling down an object. A tripping line for a collapsible bucket.

Tail Block: An accessory pulley block having a rope fastened around the shell to take the place of the usual becket.

Tail line: Same as "Tag Line."

Tail Wall: The wall in a T-abutment set at right angles to the head wall to support the same.

Tailings: Refuse material from the mines. Also called chats. Used for making concrete.

Take-up: A device for taking up lost motion.

Talus: The mass of fragmentary rock or soil which accumulates at the foot of a hill, slope, or cliff as disintegration proceeds above.

Tamp: To consolidate a material by pounding.

Tamping Bar: A bar used for tamping material.

Tangent: A straight line passing through two consecutive points of a curve. The straight part of a railroad track.

Tangential Stress: A stress which acts along a plane in the interior of a body.

Tank Locomotive: A locomotive permanently connected with its tender.

Tap: A tool for cutting threads in a hole.

Tap Bolt: A bolt which is screwed into the material which it holds instead of being screwed by a nut. Also called a tap screw.

Tap Wrench: A cross-handled wrench used for turning a tap.

Tape: A long, narrow ribbon of flexible material graduated in lineal units.

Tape Measure: Same as "Tape."

Taper: To diminish in section regularly and gradually.

Taper File: A file having a tapering body.

Taper Shank Drill: A drill having a tapered shank.

Tar: A thick, dark, viscous liquid obtained by the destructive distillation of substances such as wood, coal, peat, etc.

Target: A sliding disk on a level rod, used for fixing the position of the line of sight as determined by an engineer's level.

Tarpaulin: A heavy canvas sheet used to cover materials and to protect work temporarily.

Tarred Paper: A paper saturated or coated with tar.

Tassel: Same as "Corbel." -- A small shelf cantilevered out from a beam, wall, or column in order to support a beam or a superincumbent load.

Taut: Tight; tense; not slack.

Teat: Same as "Tit."

Teat Drill or Tit Drill: A square-faced cylindrical drill, with a sharp, pyramidal projection issuing from the centre of the cutting face.

Tee-beam: Same as "T-Beam."

Tee-iron: Same as "T-Iron."

Telemeter Rod: Same as "Stadia Rod." -- A rod divided into feet and tenths with special markings which are visible at long distances. It is used in connection with the stadia wires of the transit to read distances directly.

Telescope: That part of an engineer's transit or level used for sighting on and magnifying objects.

Telltale: An indicator. A row of straps or ropes hung over and across a railway track so as to strike any one standing on a car-roof and warn him that the train is about to pass under or through a bridge or similar structure.

Temper: To bring a metal, such as steel, to a proper degree of hardness. The condition of steel relative to the degree of hardness. Temperature: The intensity of the sensible heat of a body.

Temper of Steel: Degree of hardness produced in high carbon steel by water or oil treatment of cooling. See "Temper" and "Tempering."

Temperature Stress: A stress due to the contraction or expansion of a body from changes in temperature.

Tempered Steel: Steel that has undergone the tempering process.

Tempering: The act of producing a temper in steel or other metal.

Tempering Mortar: The mixing and working of mortar to secure a uniformly plastic condition.

Template: Same as "Templet."

Template Punch: Same as "Spacing Punch." -- A punch with an arm extending horizontally and having on the end of this arm a small tool, called a spotter, which engages a template working on a frame, to which is attached the sheet to be punched. When the frame is moved so that the spotter enters the hole in the template, the punch acts.

Templet, or Template: A full-sized pattern, generally made of wood and used to lay off work in bridge shops.

Templet Punch: Same as "Template Punch."

Ten-Wheeled Locomotive: A locomotive with six coupled driving wheels, and a four wheeled truck in front of the drivers.

Tenacity: That property of a body by which it, resists being pulled apart.

Tender: The attendant at a bridge or on a part of construction work. A bid on a piece of construction work. An offer to do work for a consideration. A car attached to a locomotive for carrying a supply of fuel.

Tenon: A projection, properly of rectangular cross-section, at the end of a piece of timber, to be inserted into a socket or mortise in another timber, so as to make a joint.

Tensile: Pertaining to tension. The character of the force which tends to separate, in the most direct manner possible, the adjoining parts of a body.

Tensile Resistance: The ability of a member to resist elongation.

Tensile Strain: The deformation produced by an external tensile force. Also called "Stretch" or "Elongation."

Tensile Strength: Same as "Tensile Resistance." The resistance which a body can offer to an external tensile force.

Tensile Stress: A stress resisting the elongation of a body.

Tension: The state or condition of being stretched.

Tension Bar: Any bar subjected to tension.

Tension Beam: A beam subjected to tension as well as to cross-bending.

Tension Brace: A brace which resists tension.

Tension Joint: A splice in tension.

Tension Member: A member of a structure subjected to tension only.

Tension Rod: Any rod subjected to tension.

Teredo Navalis: A worm-shaped, marine mollusc having a shell with two small valves at its head with which it bores into submerged wood.

Terra Cotta: A hard pottery used for building purposes.

Test: A method for determining the properties of a material. The act of testing.

Test Bar: A sample bar used in testing the strength of a material.

Test Load: A live load applied to any finished construction as an ocular proof of its safety. It is of no real value.

Test Piece: A piece, portion, or specimen of any material, used for testing or determining its qualities and properties.

Test Pile: A pile in place loaded with a known weight in order to test the bearing capacity of the soil.

Testing Machine: A machine provided with the mechanism for exerting a force on a specimen of some material and thereby determining its properties.

Thacher Slide Rule: A slide rule of the revolving type having an exterior frame of twenty graduated bars attached to rings at their ends. The slide is an interior cylinder and is capable of both rotation and sliding inside the bars. The exterior frame of bars is also capable of rotation. A most valuable instrument in any bridge engineer's office.

Theorem of Three Moments: A theorem used in connection with continuous girders expressing the relation of the moment at any support to the moments at the preceding and following supports in terms of the loading and span lengths.

Thickening Washer: An additional washer used on a bolt to take up space.

Thimble: A sleeve or bushing used to join the ends of pipes, shafting, etc.; or to fill an opening, or to cover an axle.

Thimble Coupling: Same as "Sleeve Coupling." -- A permanent connection in which the coupling consists of a wide band of metal extending over both ends of the shafts to be joined.

Thimble Joint: An expansion sleeve-joint in a pipe line.

Thinner: A liquid, such as turpentine, which is added to paint in order to thin it, or to reduce its viscosity. Should be used with great caution in bridge painting.

Third-class Masonry: A term applied to rubble when of a good, substantial quality and laid in cement mortar.

Thoroughfare: Any street, alley, watercourse, or passageway used for public travel of any kind.

Thread: The helix cut on the shank of a bolt or screw.

Thread Cutter: A tool, consisting of a stock and set of dies, used for cutting threads on rods and pipes.

Three-hinged Arch: An arch hinged at the piers, or abutments, and at the crown.

Through Bolt: A bolt which passes from side to side of the members which it fastens.

Through Bridge: A bridge with overhead bracing and carrying its floor near the elevation of the bottom chords.

Through Cantilever: A cantilever bridge in which the traffic passes between the trusses, in contra-distinction to a deck cantilever where it passes above the top chords.

Through Girder: Incorrectly used for a "Half-through Girder." Strictly speaking, a through girder would mean a main girder of a tubular bridge. See "Half-through Span."

Through Span: A span in which the traffic is carried between the trusses and which has lateral bracing in the plane of the upper chords.

Through Truss: A loose expression for a truss of a through span.

Thrust: To push. The amount of push.

Thrust Angle: A short angle inserted between the outstanding legs of a column at the bottom of the cantilever bracket to carry the thrust from the latter to the cross-girder. An angle member in traction bracing.

Thrust Axle: An axle subjected to a longitudinal thrust.

Thrust Bearing: A support for a shaft adapted to take up the end thrust therefrom.

Thrust Collar: A collar on a shaft set to resist end thrust.

Thrust of Arch: The horizontal reaction of an arch against its abutment. Also the resulting pressure normal to the face of a radial section of an arch ring.

Thumb Nut: A nut having a flat projection, or wings, so that it can be turned by the thumb and finger.

Thumb Screw: A screw having flat wing-like projections on the head for convenience in turning with thumb and fingers.

Tide Gauge: A device for indicating, and in some cases registering, the height of the tide at any time.

Tie: A piece of timber used in railroads for supporting and holding the rails together. A sleeper. A tension member of a truss.

Tie Bar: A bar connecting two parts of a structure. Also a bar used for connecting the two rails of a track.

Tie Beam: A timber that serves as a tie between walls.

Tie Bolt: A round bolt with a square shank and lip for hooking ties to the flanges of stringers.

Tie Hammer: A stamping hammer used on ties during inspection.

Tie Line: A hitching rope for a barge or other vessel.

Tie Plate: Same as "Batten Plate." A plate used between a rail and a tie.

Tie Rod: A rod connecting two parts of a structure. The tension rod in a wooden Howe truss bridge. Also a bar or rod used to connect the two rails in a railway track to prevent their spreading.

Tie Spacing: The interval between ties. Also the distance from centre to centre of ties.

Tier: A row or series. Restricted to vertical direction. A vertical division or paneling in a trestle tower.

Tile: An earthenware pipe used for drainage.

Tile Floor: A floor laid with tile.

Tilt: To forge with a tilt hammer.

Tilt Hammer: A power hammer having a head mounted on the end of a lever that is raised by a cam and then allowed to fall by gravity, although frequently a spring is used to give an additional impulse to the ram.

Timber Bent: Same as "Framed Bent." -- A bent composed of framed timbers.

Timber Bolt: Any bolt used in connecting timbers.

Timber Buggy: A compact frame mounted on a single roller, used for transporting heavy sticks of timber.

Timber Casing: Timber sheathing used on the outside of caissons.

Timber Dogs: A special pair of hooks for hoisting and moving timber.

Timber Floor: A floor consisting of timber joists and planks.

Timber Girder: A girder built mainly of timber.

Timber Hook: Same as "Timber Dog."

Timber Jack: An apparatus for lifting timber.

Timber Joists: Joists made of timber.

Timber Lath: A lath made from timber.

Timber Lathe: A lathe used exclusively for turning timber.

Timber Pier: A pier constructed of timbers, usually in conjunction with piles.

Timber Strut: A strut made of timber.

Timber Truck: A frame mounted on four wheels which run on rails, used for transporting timber short distances. Any small, wheeled apparatus for moving timber.

Tint: A color produced by the admixture of a coloring material not white, with a white pigment or paint, the white predominating.

Tinting Strength: The power of coloring a given quantity of paint or pigment selected as a medium standard for estimating such power.

Tipper: A type of draw span supported at each of the two ends of the Centre panel by a beam which, in turn, rests upon wedges or cams. The arrangement is such as to produce an equal reaction at each support under the bearings of the trusses.

Tit: A small accidental projection on a casting. Spelled also "Teat."

Tit Drill: Same as "Teat Drill."

Toe: The foot of a slope. The front part of the base of an abutment or retaining wall.

Toe-nail: To fasten aboard or timber to the surface of another by driving nails obliquely through the end or edge of the first timber and into the second.

Toggle: A mechanical device consisting of two bars or plates hinged together at their common ends and pivoted at the other ends; used for transmitting a force laterally to its line of application.

Toggle Bolt: A bolt connecting the parts of a toggle.

Toggle Iron: A connecting detail for a toggle.

Toggle Joint: A union of two parts by means of a toggle.

Toggle Riveter: A riveting machine using a toggle mechanism to give the pressure required to upset the stem and form the rivet head.

Ton: A unit of weight, generally equal to two thousand pounds.

Ton-foot: Same as "Foot-ton." -- A unit of work equal to that involved in overcoming one ton of resistance through the space of one foot, or in raising one ton one foot high.

Tone: The color which principally modifies a hue or a white or black.

Tongs: A tool for grasping objects, consisting of two flat, curved bars pivoted about a common centre.

Tongue and Groove: A term applied to lumber in which one edge of a board has a recess for receiving the projecting tongue of the adjacent board, while the opposite edge has a projecting tongue to fit into the recess of the next board.

Tongue-and-groove Joint, or Tongue Joint: A joint made by one part having a projecting tongue fitting into a corresponding groove in the other part.

Tongue Joint: Same as "Tongue-and-groove Joint."

Tongue Plate: A plate riveted on to the end of a member and projecting beyond it, in order to make a connection with another member.

Tool: Any thing, device, or apparatus used to facilitate mechanical operations; usually restricted to small implements.

Tool Box: A box for holding tools, generally provided with a handle in the centre for convenience in carrying it about.

Tool Chest: A chest or covered box for the storing or shipping of tools.

Tool Dressing: See "Tooled Dressing."

Tool Finish: Same as "Tool Dressing."

Tool House: A house for the storage and safe-keeping of tools.

Tool Steel: Steel which, by special treatment or peculiar composition with alloying metals, is adapted to retain a cutting edge at comparatively high temperatures so as to permit of high cutting speeds. Messrs. Taylor and White give the following as the best composition for such steel. Vanadium, 0.29 per cent; tungsten, 18.19 per cent; chromium, 5.47 per cent; carbon, 0.674 per cent; manganese, 0.11 per cent; and silicon, 0.043 per cent.

Tooled Ashlar: Ashlar blocks that have been dressed on the face with a mason's tool.

Tooled Dressing: A dressing in stonework in which the face of the stone is tooled to a plane.

Tooling: The act of operating with a tool upon an object.

Tooth: The projection or cog on a gear wheel which meshes with a like projection on another similar gear.

Tooth Axe: A mason's tool with a double wedge-shaped head and teeth on the cutting edges.

Tooth-axed Dressing: A form of stonework dressing made with a tooth-axe.

Tooth Chisel: Same as "Pitching Chisel." -- A stone mason's chisel for making a well-defined edge to the face of a stone block.

Tooth Pitch: Same as "Circular Pitch." -- The distance between centres of teeth, measured on the pitch circle of a gear.

Tooth Pressure: The pressure exerted by a tooth of a gear on the opposing gear.

Toothed Dressing: A type of stone dressing made with a mason's tooth chisel.

Toothed Wheel: A wheel having teeth projecting from its face.

Toothing: A general term for a system of teeth.

Top Chord: The upper member of a truss, usually resisting compression.

Top Lateral Bracing: Lateral bracing in the plane of the top chords.

Top Laterals or Upper Laterals: Laterals in the plane of the upper chords.

Topographic Map: A map showing the configuration of land by contour lines, or lines of equal elevation.

Torque: The moment of a force or a system of forces tending to produce rotation. The starting capacity of a machine.

Torsion: The twist or deformation of a body set up by a torque.

Torsional Strain: A deformation in a member caused by a twisting moment.

Torsional Stress: The stress arising from the deformation set up by a torque or twisting moment.

Total Energy: The sum of the kinetic and the potential energies.

Total Haul: The total distance that a material is hauled.

Total Splice: Same as "Full Splice." -- A splice capable of developing the full strength of a member.

Total Stress: The sum of all the stresses at a section of a body.

Touch Micrometer: A micrometer in which the final adjustment is determined by the sense of feeling.

Tow: A boat or barge, or a collection of boats or barges, hauled by another vessel. A raft of logs hauled by a power vessel.

Tow Line: Any line used for towing.

Tower: A vertical structure consisting of two or more bents of framework connected by bracing.

Tower Bracing: Bracing attached to the posts of towers.

Tower Crane: Same as "Column Crane." -- A crane built in the form of a latticed column with a curved overhang at the top.

Tower Panel: The longitudinal space or bay in a trestle or viaduct occupied by the tower.

Tower Post: A member of a tower which carries load directly to the pedestal. A tower column.

Tower Span: A span directly over and supported by a tower in a trestle or viaduct.

Town Truss: A form of lattice truss having double chord systems and two web systems in different planes. See Fig. If.

Tracing: A drawing made on transparent cloth. The act of copying on tracing cloth a drawing placed beneath.

Tracing Cloth, or Tracing Linen: A fine linen fabric covered with a gelatinous material or sizing making it transparent so that it can be used for copying drawings.

Tracing Linen: Same as "Tracing Cloth."

Tracing Paper: A thin, tough, translucent paper used for tracing drawings.

Track: A set of rails or plates and their supports on which may be rolled a body or structure provided with wheels or rollers.

Track Bolt: A bolt used for connecting railway rails through splice bars. It has an elliptical shank and a hexagonal nut. Often a square head is used.

Track Gauge: The distance between the treads of the rails. Also the tool or device for measuring or laying off that distance.

Track Jack: A lever jack having a tongue near the bottom of the stem and on the side opposite the lever. This tongue can readily be inserted under a rail or tie and a portion of the track raised by pumping the lever.

Track Joists: A joist or a stringer which is placed under a track.

Track Maul: Same as "Spike Maul." -- A maul having one end long and tapering, used for driving railroad spikes.

Track Pile Driver: A driver mounted on a flat car in order to be readily moved along the track.

Track Rail: A rail composing a part of a track.

Track Segment: A part or unit of a circular track used to carry the rollers of a rimbearing draw-span.

Track Spacing: The arrangement of tracks with respect to each other. The distance between track centres of adjacent tracks.

Track Stringer: A beam or girder carrying a track.

Track Tie: Same as "Cross Tie." -- A railroad tie or sleeper.

Track Walker: A man who makes regular inspection trips along the track by walking.

Track Wrench: A long-handled, forked wrench, used by trackmen for tightening nuts on rail joints.

Traction: The force required to draw a body. The adhesive resistance of a driving-wheel on a rail.

Traction Bracing: Same as "Train Thrust Bracing."

Traction Load: A load due to the kick back of the locomotive drivers running on the rails (equal to the draw-bar pull), or the thrust from a braked train.

Traction Stress: A stress caused by the thrust of a braked train due to the friction of the wheels on the rails when skidding, or by the horizontal effort of the locomotive wheels against the rails.

Train-thrust Bracing: Bracing in the plane of the bottom laterals which transfers the thrust of a braked train from the stringers to the trusses.

Tram: A small car used on a tramway.

Tram Crane or Traveling Crane: A crane mounted on wheels and capable of being moved from place to place.

Trammel: A drawing instrument for describing circles of large radii, consisting of a bar and two sliding parts which can be adjusted to the desired radius by sliding them along the bar. One sliding part is provided with a point for centering and the other with a pen or pencil for drawing the curve. Called also a "Beam Compass."

Tramway: A temporary track built near a bridge and used in connection with tramcars for transporting materials to the work.

Transcendental Curve: A curve expressed by an equation containing transcendental functions of one or more of the ordinates.

Transferred Load: A load which has been carried over from another part of the structure to the member in question.

Transferred Load Stress: The stress in a member caused by the transferring of a load from another member.

Transformed Catenary: A curve formed by an increasing or decreasing of all the ordinates of a common catenary according to a given ratio.

Transformed Catenary Curve: Same as "Transformed Catenary."

Transit: An engineer's instrument for running lines, measuring or laying off angles, obtaining differences in elevations, etc., in field work. It consists of a telescope mounted on a horizontal axle and capable of a complete revolution. The standards supporting the axle are attached to a horizontal plate capable of rotation in its own plane. These two rotations permit of the measurement of vertical and horizontal angles and the projection of a line in any direction.

Transit Point: A point over which the transit is set.

Transition Curve: Same as "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.

Transitman: The man who operates the transit.

Transverse: Extending across. Crosswise direction.

Transverse Beam: Any beam of a bridge that passes from one truss to an adjacent truss.

Transverse Bracing: Bracing which is perpendicular (or but slightly inclined) to the centre line of the structure.

Transverse Component: A component in a transverse direction, generally intended for a component perpendicular to the planes of the trusses.

Transverse Girder: Same as "Cross Girder." -- Any girder passing across a bridge from one truss or main girder to another, and, generally, perpendicular to the truss or girder planes.

Transverse Load: A load which is applied perpendicularly to the plane of the longitudinal axis of the member or the structure, such.as a wind load.

Transverse Section: Same as "Cross-section."

Transverse Shear: A shearing action parallel to the transverse axis of a body.

Transverse Strain: A deformation caused by a force acting at right angles to the axis of a member.

Transverse Stress: A stress at right angles to the axis of a member.

Transverse Vertical Bracing: Same as "Transverse Bracing."

Trap: A hard, dark-colored, volcanic rock used for concrete roadway pavements, and ballast for railroads. Also a device that will intercept material in flowing water.

Trass: A gray, yellow, or whitish earth made up in large part of comminuted pumice or other volcanic material. Resembles pozzuolana. Used for making hydraulic cement.

Traveler: A form of derrick mounted on wheels, used in the erection of bridges.

Traveler Wheel: One of the wheels supporting a traveler on its track.

Traveling Crane: Same as "Tram Crane."

Traveling Girder: A girder that moves on rails.

Traverse Line: Often called a "Traverse." A series of connected lines of which the lengths and bearings have been determined.

Tread: The bearing surface of a wheel or of a rail. The steps of a stairway.

Treated Tie: A tie which has been subjected to a preservative process, such as saturation with creosote under heat and pressure.

Treated Timber: Timber which has been subjected to a preservative process.

Treenail: A cylindrical pin of hard wood used to fasten timbers together.

Trémie: A long tube or box used for depositing concrete under water by a process of continuous filling at the upper end and discharging at, the lower, accomplished by a slight churning motion.

Trench: A long, narrow excavation.

Trestle: A bridge structure composed of bents or towers and supporting stringers or girders forming the floor system.

Trestle Bent: In trestle construction, one of a series of bents carrying a deck.

Trestle Bridge: A bridge composed of bents or towers carrying the deck. May be of either timber or metal.

Trestle Cap: The upper horizontal beam in the timber framing supporting the deck of a trestle bridge.

Trestle Work: A general term covering trestle construction.

Triangle: A figure bounded by three straight sides.

Triangular File: Any file having a triangular cross section.

Triangular Girder: A latticed girder having a system of web members all inclined to the vertical.

Triangular Lattice Truss: See Fig. 22t.

Fig. 22t

Triangular Scale: A scale made on a triangular shaped stick, permitting of six different sets of graduations.

Triangular Truss: A truss having inclined web members. See Fig. 22g.

Fig. 22g

Triangulation: The process of locating points or determining distances by a system of triangles constructed on a measured base line, permitting the measurement of adjacent angles.

Triangulation Hub: A hub used at the corner of a triangulation system.

Triangulation Point: The point at the corner of the triangle over which the transit is set in order to measure the angle.

Triangulation Sheet: The drawing upon which is shown the triangulation system for a bridge with the dimensions thereof.

Tricalcic-silicate: The chief constituent of Portland cement, which is the active element composed of calcium, oxygen, and silicon, as defined by the chemical formula 3CaO.SiO2.

Trigonometric Functions: Certain functions of an angle or arc used in trigonometry, such as sine, cosine, tangent, or their several reciprocals.

Trip: A device for tripping or releasing a hammer, or for opening a collapsible bucket.

Trip Hammer: Same as "Tilt Hammer."

Trip Line: A rope, by which a trip is operated.

Triple Block: A block having a set of three sheaves.

Triple Cancellation: The arrangement of the web members of a truss having three separate systems of diagonals.

Triple Intersection: Same as "Triple Cancellation."

Tripod: An arrangement of three legs pivoted to a headpiece, used for supporting an instrument such as a transit or a level.

Trolley: A small flanged wheel arranged to run upon a wire or rod.

Trough Plate: A rolled steel shape having a cross-section similar to that of a trough with sloping sides. Used for floor plates.

Trough Plate Floor: A bridge floor system composed of trough plates.

Trowel: A mason's tool consisting of a handle and a flat triangular-shaped blade for handling mortar.

Troweled Finish: A finish on cement work made by troweling.

Troy Rod: A level rod made of two sliding pieces and carrying two targets, one on the top and the other on the bottom, the upper target being fixed to the extension member and the lower target arranged to move on the main rod.

Truck: A small vehicle consisting of a frame mounted on two or four wheels. A group of four or more wheels in a frame supporting one end of a railway car.

Truck Jack: A lifting jack hung from a truck.

True Discount: The present worth of the interest computed on the face value of the note.

True 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).

True Stress: A stress as measured by the deformation as it actually occurs.

Truncated Bow-string Truss: A bow-string truss with squared ends.

Trundle: Same as "Lantern Wheel." -- A gear wheel composed of two parallel discs set some distance apart on an axle with round rods parallel to the axle, set at equal intervals around the periphery of the discs. These rods mesh with the teeth of another gear.

Trunnion: A form of short axle attached to the side of a body.

Trunnion Bascule: A type of bascule which is supported by an axle or trunnions, about which it rotates without translation.

Truss: A framed or jointed structure designed to act as a beam while each of its members is primarily subjected to longitudinal stress only.

Truss Block: A bearing block of metal placed between the truss rod and the strut of a trussed beam.

Truss Bridge: A bridge made up of truss spans.

Truss Deformation: An alteration in the lengths and positions of the members composing a truss.

Truss Depth: The vertical distance between the centre lines of the upper and lower chords.

Truss Element: A component part of a truss.

Truss Girder: A girder having a latticed web system forming with the flanges a truss in all essential features.

Truss Joint: Any joint in a truss.

Truss Member: Same as "Truss Element."

Truss Pin: A pin used at the panel point of a truss to connect the several intersecting members.

Truss Rod: A rod used for trussing or bracing a beam, also called Hog Chain. Any rod employed as a part of a truss.

Truss Shop: A shop where bridge trusses are manufactured.

Truss Spacing: The perpendicular distance between the central planes of trusses of a bridge.

Truss Span: A span supported by trusses.

Trussed Arch: Same as "Braced Arch." -- An open-work truss in the form of an arch.

Trussed Beam: A beam braced by one or more vertical posts supported by inclined rods attached to the ends of the beam.

Trussed Eye-bar: An eye-bar supported by trussing so as to resist compression or bending.

Trussed Girder: A girder stiffened and strengthened by means of trussing.

Trussing: A system of rods attached to the ends of a beam, girder, or column and held therefrom by short struts between the member and the rods.

Tube: A pipe of small size. A hollow cylinder.

Tube-mill: A shop where tubes are drawn.

Tubular Arch Bridge: A bridge in which the primary supporting members are arched tubes.

Tubular Bridge: A plate-girder structure covered with metal construction on top and bottom, forming a boxed space through which the traffic passes.

Tuck Joint: A joint in masonry presenting the appearance of tucks.

Tug: A small, powerful boat for towing.

Tumbler: Same as "Rattler." -- A cylinder with ends closed, as in a barrel, set on trunnions for rotating. It is used for cleaning small castings by rolling and tumbling them over each other, and also for making abrasion tests of stone, brick, etc.

Tungsten Steel: Steel usually containing from five to ten per cent of tungsten (sometimes as much as twenty-four per cent) and from four-tenths to two per cent of carbon.

Tunnel: An excavated passageway tinder the ground or the water.

Tup: A ram.

Turnbuckle: A device for tightening or drawing together two parts of a rod, consisting of a sleeve having an interior right-hand thread at one end and an interior left hand thread at the other. This sleeve engages the threaded ends of the two pieces of rod so that a turning thereof in one direction screws up on the rods and in the reverse direction unscrews on them.

Turned Bolt: A machine bolt, ordinarily with hexagonal head, turned down so that when put in place it has a driving fit.

Turned Shafting: Shafting which has received its truing-up and final finish by being turned in a lathe.

Turning Bridge: Same as "Swing Bridge." -- A span that rotates about a vertical axis, so as to provide openings for the passage of vessels.

Turning Point: A point of reference on some firm object, used in levelling for resetting the instrument.

Turnout: A railroad switch or siding.

Turnstile: A revolving gate.

Turntable: The framework under the swing span which transmits the load to the bearings.

Turntable Girder: A fish-bellied girder that is used for a turn-table.

Turpentine: An oleoresin exuding from several varieties of coniferous trees, used as a thinner in mixing paints.

Tuyère: A tube or pipe through which air is blown directly into a blast furnace.

Twist: A rotation of one body about another, or of a part of a body about another part of the same body.

Twist Drill: A cylindrical drill having two parallel, spiral grooves on opposing sides and the point sharpened to an obtuse angle.

Twist Drill Grinder: An emery wheel mounted on a shaft in a frame having an adjustable rest for holding the twist drill during grinding.

Twist Joint: An ordinary wire splice made by twisting.

Twisting Moment: Same as "Torque."

Two-blocks: An expression used by bridge erectors in hoisting to signify that a stopping point or limit has been reached; derived from the condition of a block and tackle being overhauled until the two blocks come together when no further motion in the same direction is possible. A synonym for this is "Chock-a-block."

Two-hinged Arch: An arch hinged only at the piers or abutments.