University of Iowa Libraries       Lichtenberger Engineering Library

Glossary of Bridge Terminology



U-Abutment: A straight abutment with additions of two wing walls at right angles to the face.

U-Bolt: A rod bent in the shape of the letter U with threads and nuts on the ends.

U-Nut: A piece of iron or steel in the shape of a letter U, through which passes the threaded end of a rod, and which affords a bearing for the nut, with room to screw up the latter. Its use is not permissible in first-class bridge construction.

Ultimate Resistance: The greatest resistance that a body can develop.

Ultimate Strength: Same as "Ultimate Resistance."

Ultimate Stress: The greatest stress which can be produced in a body before rupture occurs.

Unbalanced Bid: A bid in which some of the unit prices are abnormal, either too high or too low, or generally both.

Unbalanced Load: A load without a counterpoise. Refers generally to loads from locomotive drivers.

Unbalanced Wheel: Statically, any wheel in which the centre of rotation is not coincident with the centre of gravity. Dynamically, any wheel in which the centre of rotation is not coincident with the centre of gravity and the centrifugal force of the rotating system does not reduce to zero.

Uncoursed Rubble: Same as "Random Rubble." -- Rubble masonry laid up without regard to courses.

Under Crossing: A crossing where one of the roads or tracks is below the other.

Underdrain: To drain by forming channels underground.

Undermine: To excavate beneath a structure.

Underpin: To pin or support an existing wall by excavating at intervals beneath it and building in piers, after which further excavation is made between the piers and the spaces then are filled with solid walls.

Underpinning: The process of placing underpins. The collective name for the group of underpins.

Unequal Coursing: Same as "Random Coursing = Irregular Coursing." -- Coursing in which the thicknesses of the stones vary at intervals.

Unexaggerated Scale: A term used to denote that the scale used in making a drawing is the same in all directions.

Unfilleted: Without fillets. Sharp cornered.

Uniform Load: A load which is uniformly distributed, or the same per lineal foot of span.

Uniform Load Stress: A stress resulting from the application of a load uniformly distributed over the structure.

Uniform Resistance: Resistance that is uniform over the whole cross-section.

Uniform Section: The condition of having the same section for all parallel positions of the secant plane.

Uniform Strength: Same as "Uniform Resistance."

Uniform Stress: A stress which has a uniform intensity throughout its area of action.

Uniformly Varying Stress: A stress, the intensity of which varies as its distance from a fixed point.

Union: A form of coupling, used for connecting two pieces of pipe.

Union Joint: A pipe coupling. Also called a "Pipe Union."

Unit Cost: The cost of a unit quantity of material or service.

Unit Price: The price per unit of magnitude, such as the price per hour, per ton, per square foot, per cubic yard, etc.

Unit Stress: The stress per unit of area; the measure of intensity of stress.

Unit Weight: The weight per unit of magnitude, as the weight per cubic foot.

Universal Grinder: A grinding machine having an emery wheel mounted on a shaft with a universal joint admitting of a swinging motion in any direction.

Universal Joint: An arrangement by which one part may be made to move freely in all directions while rotating with another part.

Universal Mill: A four-roll mill for rolling plates on both edges as well as on the faces.

Universal Mill Plate: A plate rolled on a universal mill, giving thereto smooth, square edges.

Unreeve: To withdraw a rope from a set of blocks.

Unstable: Not fixed; not in permanent equilibrium.

Unstable Equilibrium: That condition of a body when a slight displacement of it is followed by a further displacement.

Unsupported Length: The length of a compression member between the nearest points of lateral restraint.

Unsupported Width: The width of a plate between the nearest points of lateral restraint.

Uphead: Same as "Upset."

Uplift: The tendency of a structure, due to special loading conditions, to rise from its supports. Negative reaction.

Uplift Stress: A stress due to an uplift action, as that from the end lifting machinery in a swing span.

Upper Chord: Same as "Top Chord." -- The upper member of a truss, usually resisting compression.

Upper Deck: The top deck of a span.

Upper Falsework: The falsework above the elevation of the bottom chords. It is no longer used in erection, as its object is more readily accomplished by the traveler, which apparatus has replaced it entirely.

Upper Lateral Bracing: Same as "Top Lateral Bracing." -- Lateral bracing in the plane of the top chords.

Upper Lateral Rod: Any rod in the upper lateral system. See also "Lateral Rod."

Upper Lateral Strut: Any strut in the upper lateral system.

Upper Laterals: Same as "Top Laterals." -- Laterals in the plane of the upper chords.

Upper Track: In rim-hearing draw spans, the plate attached to the bottom of the rim and bearing on the rollers.

Upper Track Segment: One of the pieces composing the upper track.

Upset: To thicken a piece of metal by heating and hammering on the end.

Upset-end: The end of a bar or rod which has undergone the process of upsetting.

Upset Rod: A rod having one or both of its ends enlarged by an upsetting process.

Upward Reaction: A reaction having an upward direction. This is generally the same as "Positive Reaction."

Uses: A rough block to be made into small forgings.