The uppermost member of the capital of a column; often a plain square slab.
ABATE. In stone carving or sand blasting clay masonry, to cut away material, leaving parts in relief.
ABSORPTION. The weight of water a brick unit absorbs, when immersed in water for a stated length of time, expressed as a percentage of the weight of the dry unit. See ASTM Specification C 67.
ABUTMENT. The supporting wall or pier that receives the thrust of an arch.
ACCELERATOR. In masonry, any ingredient added to mortar to speed drying and solidifying. (Compare retarding agent.)
ACI. American Concrete Institute.
ACTUAL DIMENSION. Exact size of masonry unit (see nominal dimension.)
ADHERED VENEER. Veneer secured and supported through adhesion to bonding material applied over backing. (UBC)
ADMIXTURES. Materials added to mortar to impart special properties to the mortar.
AGGREGATE. Inert material that is mixed with cement, lime and water to produce grout or mortar.
AIR DRYING. The process of drying block or brick without any special equipment, by exposure to ambient air.
AISC. American Institute of Steel Construction.
ANCHOR. A piece or assemblage, usually metal, used to attach building parts (e.g., plates, joists, trusses, etc.) to masonry or masonry materials.
Adjustable Anchor. Anchor which is vertically and/or horizontally adjustable.

Adjustable anchor

Strap Anchor

ANCHORED VENEER. Veneer secured to and supported by approved mechanical fasteners attached to backing. (UBC)
ANGLE CLOSER. A portion of a whole brick that is used to close the bond of brickwork at corners.
ANSI. American National Standards Institute.
ARCADE. From latin arcus, an arch. A row of arches on pillars or columns; a colonnade.
ARCH. (1) A form of construction in which a number of units span an opening by transferring vertical loads laterally to adjacent units and thus to the supports. As arch is normally classified by the curve of its intrados. (2) Curved compressive structural member spanning openings or recesses; also built flat.
Abutment. The skewback of an arch and the masonry that supports it.
Arch Axis. The median line of the arch ring.
Arch. A concealed arch carrying the back of a wall where the exterior facing is carried by a lintel.
Camber. The relatively small rise of a jack arch.
Constant-Cross-Section Arch. An arch whose depth and thickness remain constant throughout the span.
Crown. The apex of the arch ring. In symmetrical arches, the crown is at mid-span.
Depth. The depth of any arch is the dimension that is perpendicular to the tangent of the axis. The depth of a jack arch is taken to be its greater vertical dimension,
Extrados. The exterior curve that bounds the upper extremities of the arch.
Fixed Arch. An arch whose skewback is fixed in position and inclination. Plain masonry arches are, by nature of their construction, fixed arches.
Gothic or Pointed Arch. An arch, with relatively high rise, whose sides consist of arcs or circles, the centers of which are at the level of the spring line. The Gothic arch is often referred to as a drop, equilateral, or lacent arch, depending on whether the spacings of the center are respectively less than, equal to, or more than the clear span.
lntrados. The interior curve that bounds the lower extremities of the arch (see Soffit.) The distinction between soffit and intrados is that the intrados is linear, whereas the soffit is a surface.
Jack Arch. A flat arch.
Major Arch.
Arch with span greater than 6 ft. and having equivalent uniform loads greater than 1000 lb/ft. Typically, a Tudor arch, semicircular arch, Gothic arch, or parabolic arch. Rise-to-span ratio greater than 0.15.
Minor Arch. Arch with maximum span of 6 ft. and loads not exceeding 1000 lb/ft. Typically, a jack arch, segmental arch, or multicentered arch. Rise-to-span ratio less than or equal to 0.15.
Multicentered Arch. An arch whose curve consists of several arcs of circles which are normally tangent at their intersections.
Relieving Arch.
One built over a lintel, flat arch, or smaller arch to divert loads, thus relieving the lower member from excessive loading. Also known as discharging or safety arch.
Rise. The rise of a minor arch is the maximum height of arch soffit above the level of its spring line. The rise of a major parabolic arch is the maximum height of arch axis above its spring line.
Segmental Arch.
An arch whose curve is circular but less than a semicircle.
Semicircular Arch. An arch whose curve is a semicircle (Roman Arch).
Skewback. The inclined surface on which the arch joins the supporting wall. For jack arches the skewback is indicated by a horizontal dimension.
Soffit. The undersurface of the arch.
The horizontal distance between abutments. For minor arch calculations the clear span of the opening is used. For a major parabolic arch the span is the distance between the ends of the arch axis at the skewback.
Spring Line. For minor arches the line where the skewback cuts the soffit. For major parabolic arches, the term commonly refers to the intersection of the arch axis with the skewback.
Trimmer Arch. An arch (usually a low-rise arch of brick) used for supporting a fireplace hearth.
Tudor Arch. A pointed four-centered arch of medium rise-to-span ratio.
Voussoir. One of the wedge-shaped masonry units which forms an arch ring.

Common Arch forms

Lowermost unit of an entablature, carried by columns (or their capitals) or pilasters. Beam over columns (also epistyle).
ARGILLITE. Metamorphic rock resulting from the hardening of siltstone and/or claystone and shale.
ARKOSE. Sandstone containing feldspar grains in abundance.
ARRIS. External angular intersection between two planar faces, or two curved faces (as in moldings), or between two flutes on a Doric column, or between a flute and the fillet on an Ionic or a Corinthian column.
ARTIFICIAL STONE. A contradiction in terms, as stone is a naturally occuring earth material. This phrase is used to describe materials variously called art marble, artificial marble, cast stone, terazzo, patent stone, and reconstructed stone. A mixture of stone chips or fragments embedded in a matrix of cement or plaster with the surface ground, polished, molded, or otherwise treated to simulate stone.
ASHLAR MASONRY. Masonry composed of rectangular units of burned clay or shale, or stone, generally larger in size than brick and properly bonded, having sawed, dressed or squared beds, and joints laid in mortar. Often the unit size varies to provide a random pattern, random ashlar.
ASHRAE. American Society of Heating, Refrigerating, and Air-Conditioning Engineers.
ASTM. American Society for Testing and Materials.
Spanish azul blue wall tiles of burnt clay with colored glazed patterns.

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