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Glossary of Bridge Terminology



O.G., or Ogee Washer: A disc-shaped washer having its edge generated by an ogee curve, which was a standard curve used in Greek architecture.

Oakum: The coarse part of flax or hemp separated in hackling; also old ropes untwisted and picked into loose fibres resembling tow; used for calking the seams of vessels and caissons.

Oblique Arch: An arch in which the axis is not perpendicular to the central plane of the structure.

Oblique Crossing: A crossing in which the intersecting centre lines make an oblique angle with each other.

Ochre: A term applied to a class of natural earths consisting of mixtures of the hydrated sesquioxide of iron with various earthy materials, principally silica and alumina. Many of these earths are used for pigments in paints.

Octagon: A regular eight-sided polygon.

Odometer: An instrument for measuring distance by running a wheel over the course. The circumference of the wheel is accurately determined and a counting device attached so as to register the number of revolutions.

Offset: A short line run at right angles to a principal, or base, line. To move over from a base line to an auxiliary line called an offset line.

Ogee Curve: A reverse curve formed by the union of two circular arcs of opposing curvature, used in architecture.

Ogee Washer: Same as "O.G. or Ogee Washer."

Ohm: The unit of electrical resistance; approximately the resistance of one thousand feet of No. 10 B. & S. copper wire.

Oil Bearing: A bearing having a reservoir for oil in its base and rings running loosely over the journal, or shaft, dipping into the oil, so that their rotation continuously carries the oil to the journal and thus provides constant lubrication.

Oil Box: A box attached to certain types of bearings for holding waste saturated with oil.

Oil Can: A can having a long tapering spout, used for pouring oil into bearings.

Oil Groove: A groove cut in the interior surface of a bearing to facilitate the spreading of oil over the journal.

Oil Hardening: The process of quenching red-hot steel in oil in order to harden it.

Oil-hole: A hole drilled in the cap of a bearing for pouring oil through.

Oil-stone: A slab of fine-grained stone used for sharpening tools by rubbing them on its oiled surface.

Oil Tempering: A process of plunging red-hot steel into oil to harden it. A term frequently used for oil hardening because the effect on the steel is similar to that of quenching in water and then drawing the temper by a subsequent application of a moderate heat.

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.

Old-man: An iron frame bent into the form of a U having hooks on the ends so that it can be hung to a bar, a rail, or the flange of a girder and used to form a bearing for a ratchet drill or reamer.

One-man Stone: A rough classification for stone of a size that can be readily lifted and put into place by one man. Used to reduce the cost of concrete.

Oolitic Limestone: A granular limestone in which each grain approximates to the form of a sphere, producing a resemblance in the rock to the roe of a fish; hence the name.

Opacity: The degree of obstruction to the transmission of visible rays. Used in connection with paint.

Open Caisson: A crib and cofferdam open to the air and sunk by dredging within the crib.

Open Crib: A crib open at the top and bottom.

Open-dredging: A process of sinking piers by excavating with a dredge through an open crib.

Open-end Wrench: Same as "Forked Wrench." -- A wrench having a pair of jaws at one end of a bar, while the other end tapers to a point.

Open Hearth: The hearth of a metallurgical furnace which is exposed to the direct action of the flame.

Open-hearth Furnace: In steel manufacture, a regenerative, reverberatory furnace in which the hearth is exposed to the, action of the flame.

Open-hearth Process: A process for the production of steel by the oxidation and removal of the impurities contained in a bath of metallic iron lying on the hearth of a regenerative furnace.

Open-hearth Steel: Steel produced in a regenerative, reverberatory furnace where the hearth is open and exposed to the action of the flame.

Open Holes: Rivet holes in members and connections left open during fabrication to enable the erector to connect the parts in the field, after which field rivets are driven into them.

Open Joint: A joint in which the parts are slightly separated.

Open Spandrel Arch: An arch in which the roadway is carried on spandrel columns or cross-walls.

Open Web: A web composed of a group of members instead of solid plates

Open Web Girder: Same as "Latticed Girder." -- A riveted girder having the upper and lower flanges connected by latticing, or by diagonal bars or angles.

Open-webbed Girder: Same as "Open Web Girder."

Operating Cost: All expenditures incurred in running a plant or operating a structure not pertaining to upkeep nor to repairs.

Operating House: A bridge-tender's house from which the operation of the drawspan is controlled.

Orange Peel Bucket: A dredging bucket composed of four curved and tapered pieces, hinged at their tops and so arranged that when closed they form a large cup for carrying materials. When opened to their full extent, four tooth-like prongs are presented for digging into the material. Loading is completed by closing up the four prongs or leaves.

Orange-peel Dredge: A dredge using an orange-peel bucket attached to a hoisting apparatus like a derrick.

Order Bill: A form of bill used in ordering material from the manufacturers.

Ordinate: One of the coordinates in a system of rectangular coordinates defining the position of a point.

Ore Bridge: A gantry crane used for handling ore at a blast furnace.

Origin of Coordinates: The initial point in a system of coordinates to which other points are referred. In the rectangular system, it is the intersection of the two axes; in the polar system it is the point in the directrix about which the radius vector turns.

Ornamental Work: That portion of a structure which is added to the main portion in order to enhance its aesthetic qualities.

Ornamentation: A general term for the entire ornamental work on a structure.

Orthographic Projection: That system of projection in which the rays are parallel. This is the system which is most largely used in engineering work.

Oscillation: A vibratory movement of any body of appreciable size.

Out of Gear: A condition in a system of mechanism when the driving gear does not mesh with the driven gear and, in consequence, no motion is transferred.

Out of Square: Askew, oblique.

Out of Wind: Free from twist; not warped.

Outer Guard-rails: Guard-rails placed outside the rails of a car track.

Outer Hip: The hip at the outer end of one of the arms of a swing span.

Outhaul: A method used by erectors for assembling a member which is beyond the reach of the boom of the derrick. It consists in placing a pulley block ahead of the member beyond the derrick and doubling back the lead line to the hoisting engine.

Outline: The exterior line defining the shape of a body.

Output: The production of a mill, plant, or company for a certain period.

Outrigger: A beam or joist projecting from a structure, used to support a load at its end.

Outrigger Hoist: A hoist supported by an outrigger.

Outside Caliper: A caliper for measuring the outside diameter of a cylinder or tube.

Outside Lock Tender: The man outside of the air-lock who assists in operating it.

Outside Stringer: Same as "Jack Stringer." -- A stringer placed outside the line of main stringers.

Oval: A closed curve, everywhere convex, without nodes or cusps and having sharper curvature at one end than at the other.

Oval Curve: Same as "Oval."

Over Load: A load which produces intensities of stress beyond the allowable unit stresses.

Overblown: A term applied to Bessemer steel which has been blown too long and is overoxidized and hence inclined to be wild.

Overhaul: The excess haul or movement of earth or rock beyond a specified distance named in the contract. To examine thoroughly with a view to repairs. To take up slack in a rope by pulling thereon.

Overhead Balanced Crane: A combination of an overhead and a balanced crane.

Overhead Bracing: The upper lateral or the vertical sway bracing in through bridges. The term is usually applied to the vertical sway bracing, if there be any; if not, to the upper lateral bracing.

Overhead Crane: A crane which travels on elevated girders in a shop.

Overhead Crossing: A crossing where one road or track is above the other.

Overhead Girder: A girder that is overhead-usually moving on an overhead track as in a traveling crane.

Overhead Strut: A strut in the overhead portion of the sway bracing of a bridge.

Overheat: To heat metal to a temperature near the melting point, causing it to become coarse grained and reducing the cohesion between the particles.

Overlap: To extend over and rest upon; to fold over.

Overlapping Joint: Same as "Lap Joint." -- A joint in which the pieces extend over each other.

Overload: Same as "Over Load."

Overmelt: To keep steel too long in a state of fusion.

Overtime: The excess time over the regular schedule of hours which a workman labors.

Overturning Moment: The moment of the external forces tending to overturn a structure.

Ovolo: A projecting convex moulding of a quarter of a circle in section.

Oxide of Iron: Same as "Iron Oxide." See also "Ochre."