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HISTORIC HIGHWAY BRIDGES OF OREGON
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Burnside Bridge (1926), Willamette River, Portland, Multnomah County
GLOSSARY
| Abutment | A substructure supporting the end of a single span or the extreme end of a multi-span structure and, in general, supporting the approach embankment. |
| Approach | The passageway structure from the roadbed onto the bridge structure. |
| Aqueduct | Bridge which carries a canal or a water conduit. |
| Balustrade | A railing or parapet consisting of a handrail on balusters (vertical support members). |
| Bascule | A moveable bridge in which the roadway deck is counterbalanced by a weight and swings upward like the hinged cover of a box. A bascule bridge may be single-leaf (one hinge) or double-leaf (two hinges). |
| Beam | A bridge type in which the roadway deck is supported by transverse members framed into the outer longitudinal structural members. |
| BPR | United States Bureau of Public Roads, the predecessor organization to the Federal Highway Administration, United States Department of Transportation. |
| Bracket | An overhanging member that projects from the structure, designed to support a vertical load, usually a sidewalk, or sometimes only the railing. |
| Bridge | A structure which provides continuous passage over a body of water, roadway, or valley. Generally, a bridge carries a pathway, road, or railroad, but it may also carry power transmission lines. (Bridges in this study were restricted to those of 20 feet or longer and which carry public highways, roads, or streets.) |
| Bush-hammered | A treatment to concrete surfaces with a steel-plated instrument which results in a textured surface instead of a flat, smooth surface. This technique is also referred to as pebble-dash. |
| Buttress | An abutting pier which strengthens a wall, sometimes taking the thrust of an inner pier. |
| Ca. | Circa or estimated date. |
| Cantilever | Any rigid structural member projecting from a vertical support, especially one in which the projections is great with relation to the depth, so that the upper part is in tension and the lower part in compression. |
| Chord | A main outer structural member of a truss. |
| Compression members | Generally stiff, heavy posts composed of channel and I-bars which withstand pressure that tends to push them together. |
| Continuous structure | A generally long bridge in which the structure is supported by more than two piers, but still distributes stress over the entire structure. |
| Counter | The adjustable diagonal in a truss, not liable to stress except upon partial application of live loads. |
| Covered bridge | A structure, usually timber, with a housing to protect the truss and other members from the elements. |
| Culvert | A drain or channel crossing under a road. Generally, culverts are small and constructed of steel or concrete. When they become large and are not continuous under the waterway, they become slab span bridges. |
| Curtain wall | The outer members in a bridge or approach span, particularly when the configuration differs from the inner members; also called fascia. |
| Deck | The roadway surface. Also, a bridge type with the roadway atop the bridge framework. |
| Dentils | A series of small projecting rectangular blocks, especially under a cornice or other overhanging structure, used for ornamentation. |
| Fascia | See Curtain wall. |
| FHWA | Federal Highway Administration, an agency in the U.S. Department of Transportation. |
| Girder | A bridge type in which the roadway deck is supported by one or more longitudinal structural members. |
| Gussett plate | A triangular piece which stiffens an angular meeting of two or more members in a framework, frequently found on metal truss bridges and secured with rivets. |
| Lattice | A vintage railing type that consists of a system of crosshatched diagonals with no verticals. |
| Moveable bridge | A bridge type which opens to allow additional vertical clearance for water navigation. |
| National Register | The National Register of Historic Places, maintained by the National Park Service, United States Department of Interior, is the list of the nation's cultural resources worthy of preservation. This list contains districts, historic and archeological sites, buildings, structures, and objects of national, state, and local significance. |
| ODOT | Oregon Department of Transportation. |
| OSHD | Formerly the Oregon State Highway Department, this state agency became the Oregon State Highway Division within the Oregon Department of Transportation in 1969. |
| Overcrossing or overpass | A bridge structure where the principal or subject transportation facility is the upper roadway (of two roadway levels). |
| Parapet | A low retaining wall or railing. |
| Pier | A structure which supports the ends of the spans of a multi-span superstructure at an intermediate location between its abutments. |
| Pin connected | A feature of early truss construction in which the truss members were joined by steel pins or bolts. |
| Polygonal | Having many angles. |
| Pony truss | A low through truss that has no overhead or enclosing truss work. (The word "pony" indicates a scale of measurement, something smaller than standard.) |
| Portal | The entrance to a bridge, especially a through truss or arch. |
| Portal message | A plaque mounted above the entrance portal of a "through" bridge, indicating the company that constructed the bridge, the date of construction, etc. |
| Rivet connected | A rigid connection of steel bridge members, which replaced pin-connections. The rivet connection increased the strength of structures. |
| Soffit | The underside of an overhanging structure. |
| Skewed | Slanted or not forming a straight line. Skew is the angle between a line crossing the roadway and a line normal to the roadway centerline. |
| SHPO | State Historic Preservation Office. |
| Slab | A bridge type, generally used in short structures, in which the roadway deck and its support are integral. |
| Span | The distance between the supports of a beam, arch, or the like. |
| Spandrel | The area between the exterior curves of an arch and the roadway. |
| Structure | In the context of this study, a term frequently substituted for "bridge". |
| Suspension | A bridge which suspends the roadway from high towers through a combination of cables. |
| Swing | A moveable bridge which pivots about a vertical axis to allow unrestricted vertical clearance of the navigation channel. |
| Tension members | Slender, attenuated members of a bridge which resist forces that pull them apart. |
| Through | Form of bridge in which traffic actually moves through the framework of a bridge. |
| Truss | A bridge with a framework of members, forming a triangle or system of triangles to support the weight of the bridge as well as the live or passing loads. (The nomenclature for the components of a representative through truss is shown on the following page.) |
| Undercrossing or underpass | A bridge structure where the principal or subject transportation facility is the lower roadway (of two roadway levels). |
| Vertical lift span | A moveable bridge which can be raised vertically by weights and pulleys operating in towers at each end of the structure. During raising and lowering, the bridge remains in a horizontal position. |
| Viaduct | Usually a bridge built over dry land or over a wide valley and consisting of a number of small spans. (Several structures in Oregon are called viaducts even though they cross waterways.) |
| WPA | Works Projects Administration, a federal agency (1935-1943) charged with instituting and administering public works during the Great Depression. Its original title was the Works Progress Administration. |
| Wrought iron | A comparatively pure form of iron, almost entirely free of carbon and having a fibrous structure that is readily forged and welded. |
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| Representative truss nomenclature. (Source: Historic American Engineering Record, National Park Service, United States Department of the Interior, Washington, D.C.) (click on image for a PDF version) |
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glossary.htm
Last Updated: 06-Aug-2008