Glossary

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ACCESSORIES: Those components used in conjunction with engineered wood products, including such items as hardware and web stiffeners.

AITC: American Institute of Timber Construction.

ALLOWABLE STRESS: Ultimate (failure) stress divided by an appropriate safety factor.

APA: American Plywood Association.

APA GLUE-NAIL FLOOR: The system specified by the American Plywood Association for gluing and nailing sheathing to floor joists which creates a partial composite action between the components. The result is increased stiffness in the floor.

BACKER BLOCKS: Blocks placed behind hangers to support the top flange of the supporting I-joist. Can be used to provide a connecting surface for hangers that face mount.

BALANCED LAYUP: A glulam beam layup where the laminations on the top are equal in strength to the bottom laminations.

BEAM: A structural member (may also be referred to as a header) which supports a load. May support other beams, girders, joists, purlins, rafters, and trusses.

BEARING: A structural support for structural components such as beams and joists.

BEARING LENGTH: Based on compressive force, it is the distance required for proper support of a beam or joist. Measured from the end of the member to the face of the support.

BEARING REACTION: The compressive force exerted on an external surface of a member. This is commonly known as the reaction occurring at a point of support, such as at hanger or wall.

BEARING WALL: A wall supporting load from above, with adequate support below (e.g., a footing or thickened slab).

BENDING MOMENT: A levering force that causes tension in one face or chord of a member and compression in the other. For example, consider a joist with a loaded overhang. At the overhang support, the joist experiences axial tension in the top flange and compression in the bottom flange. This is a bending moment at the support. Bending moments are typically maximum at continuous supports such as this, or near the middle of a span.

CAMBER: A slight arch built into a truss or beam to offset the appearance of deflection under load.

CANTILEVER (Overhang): A structural member which extends past the bearing.

CANTILEVER REINFORCEMENT: A structural panel or I-joist used over the bearing of a cantilevered joist to increase strength and stiffness.

CENTER TO CENTER SPAN: The distance measured from the middle of one support to the middle of the next support of a member.

CLEAR SPAN: The distance between the inside face of one support to the inside face of the next support of a structural member.

CLOSURE: A board of sheathing material used at the end of a cantilevered (overhanging) joist.

COMBINATION NUMBER: The identification number to describe the type of lamination lay-up in the glulam member, the associated allowable design stresses, its intended application, and if the lumber used was visually or mechanically graded.

COMPOSITE ACTION: When sheathing is glued and nailed to joists, the two components work together to create a stiffer system than nailing alone. As a result, more load can be carried at a given deflection limit. However, the strength (shear and bending) of a joist is not increased.

COMPRESSION PARALLEL TO GRAIN: Normally thought of as the "squashing" stress that occurs on a column. Thinking of the wood fiber as a collection of straws parallel to the length of the column, compression parallel is the same as trying to crush the straws in the long direction. The straws tend to buckle.

COMPRESSION PERPENDICULAR TO GRAIN: See above definition. Squash the round dimension of the straws to flatten them out.

CONCENTRATED LOAD: A code-prescribed live load applied in combination with dead load. The code specifies a concentrated load by magnitude and area. The area is typically a small square, such as 30", with the load assumed to be spread uniformly over that area. The load is to be placed so as to produce the most critical effects, typically at midspan for bending moment and end of span for bearing and shear.

CONSTRUCTION LOADS: Temporary loads experienced during building, including stacked building material.

CONTINUOUS SPAN (Multiple Span): A structural member (a beam, joist, rafter, etc.) that has more than two supports and runs over the top of each support without being cut.

CREEP: Long-term deflection that remains as permanent "set" when load is removed. May be increased by high dead loads or high moisture content.

DEAD LOAD: The permanent weight of a structure, including, but not limited to, the weight of building materials, fixtures, ceilings, etc.

DEFLECTION: The initial sag that results when loads are applied to structural members. For long-term say, see �creep.�

DURATION OF LOAD: Wood has a unique property which allows it to support higher stresses for short periods of time. Based on the expected "duration" of the load, some design stresses may be increased. For example, under the IBC code and ASD methodology, some design values can be increased by 15% for a snow-loaded roof since full snow load is expected to last no more than two months. On the other hand, values may be increased 25% for construction loads, which are expected to last no more than seven days (shorter period of time, therefore higher allowable stress). Duration factors depend on building code and design methodology.

EI: The stiffness of a building component found by multiplying the Moment of Inertia (I) by the Modulus of Elasticity (MOE or E) of the material.

ENGINEERED WOOD PRODUCTS: The broad category of wood building products that are created by rearranging wood fiber from logs to meet specific needs. Manufactured for structural frame applications, as opposed to panel products and non-dimensional wood building products, engineered wood products include glulam, I-joist, LSL, LVL, PSL and a growing family of other products.

FACE-MOUNT HANGER: A hanger that is attached only to the side of the supporting member. It does not hook over the top of the supporting member.

FILLER BLOCK: An engineered wood or solid-sawn block sandwiched between the webs in multiple I-joist construction. Nailed from both sides to connect the joists together.

FLANGES: The top and bottom components of an I-joist which resist bending and deflection. I-joist flanges may be made from LVL, LSL or solid sawn lumber.

GLULAM: An engineered wood product (EWP) manufactured by laminating individual pieces of lumber to make a single structural member.

HEADER (Beam): A horizontal structural member used to support vertical loads across an opening. Window header, garage door header, etc.

I-JOIST: A composite joist manufactured by connecting a top and bottom flange and a web together to form a structural member whose cross section resembles the capital letter "I".

INTERMEDIATE BEARING: Any bearing which is not at the end of a beam or joist when there are three or more bearings, or the beam or joist overhangs the bearing.

JOISTS: Structural members arranged parallel to each other and supporting floor, ceiling or roof loads. I-joists in the roof may also be called rafters.

LAMINATIONS: Individual boards that are glued together to make a glulam beam.

LAMINATION LAYUP: The arrangement of different grades of lumber in a glulam beam.

LVL (LAMINATED VENEER LUMBER): Structural lumber made by laminating veneer with all grain parallel. Primary structural use as I-joist flanges and beam and header products.

LAYUP: The "recipe" describing the location of varying grades of lamina in glulam or veneer in LVL.

MEMBER: Term for a joist, beam or any single structural assembly that is carrying load.

MODULUS OF ELASTICITY (E or MOE): A measurement of stiffness. Given equal load and identical cross section, a member with a high MOE will deflect less than a member with a lower MOE.

OSB: Oriented Strand Board. Commonly used as I-joist web stock and as a structural panel.

PARTITION LOAD: Load applied to office floors or other buildings with partition locations that may change in the future. Typical partition load is 15 psf live load (2021 IBC).

PLF: Pounds per lineal foot.

POINT LOAD: A load which is applied at a single point on a supporting member. Such loads are often produced by columns above or by beams, headers and walls running perpendicular to the supporting member.

PSF: Pounds per square foot.

RADIUS: Commonly used to describe the camber in a glulam. A 40 ft long beam with a 3500 ft radius is cambered 5/8".

RIM BOARD (Rim Joist, Band Board, Band Joist): A "joist" over a support, at the end of an I-joist, that closes off the system and transfers the load from above around the end of the joist. Provides lateral stability to the joist and transfers lateral loads from the structure above to the support below.

ROAMING LOAD: A point load placed anywhere on an open-web truss top or bottom chord. The load is in addition to other design loads. Locations are chosen to produce the most critical effects, such as midspan for chord axial stress and midpanel for chord bending stress.

TENSION PARALLEL TO GRAIN: A measurement of the strength of wood when tension is applied in the same direction as the wood grain.

TENSION PERPENDICULAR TO GRAIN: A measurement of the strength of wood when tension is applied across the direction of the wood grain.

TOP MOUNT HANGER: A hanger which attaches to the top of the supporting member.

TRIANGULAR LOAD: A distributed load of linearly varying magnitude. In RedSpec this is called a tapered load.

TRIBUTARY WIDTH: The amount of a supported member contributing to the load on the carrying member. For example, a 12' joist bearing on a glulam contributes � of that 12' or 6' of load onto the beam. If loading is 40 psf LL and 10 psf DL, the floor joists would require the glulam to carry 240 plf LL and 60 plf DL.

UNIFORM LOAD: A distributed load of constant magnitude.

UNSUPPORTED LENGTH: The distance between lateral (side to side) supports of a compression member.

UPLIFT: A vertical force which causes a structural component to rise up or lift off its support.

VENEER: A thin sheet of wood which is peeled, sawn, or sliced from a log, usually less than one-quarter inch in thickness. Commonly used in plywood and LVL.

WEB: The center panel of an I-joist which connects and aligns the flanges. Made of plywood or OSB, webs resist the shear forces in the joist.

WEB STIFFENER: A solid block of wood installed on both sides of the web of I-joists. May be required at bearing points (supports or point loads).