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Glossary - Engineered Wood


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Beam: Primary structural member resting on supports, which holds up transverse loads. Beams are normally used to support joists, rafters, trusses, and various other secondary and (sometimes primary beam) members.

Bearing: a structural support; usually a wall, beam, or post.

Bending Moment: The resistance of a member to bend or sag, measured in terms of force times distance.

Blocking Panel: Short pieces of joists that are cut to fit into the joist spacing. They are used for lateral stability, vertical transfer of external loads, and general closure.

Bracing: That part of the floor or roof system which provides lateral stability during and/or after construction.

Bridging: That part of the floor or roof system which “may” be required to make each joist or truss act with those next to it in a load sharing manner, and to minimize or equalize deflections. Should not be confused with bracing, which has a different purpose.

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Chamber: The curvature built into a member usually for the purpose of offsetting sag.

Ceiling Joist: Ceiling Joists have two prime functions. The first is to tie the walls of a structure or a room together, effectively completing a box configuration. The second is, as the name implies, to support the ceiling of the structure, or room. Ceiling joist framing is undertaken after the walls are erected.

Checking: The cracks or splits normal in lumber due to drying or lowering of the moisture content.

Clearspan : The distance between inside face of bearings.

Collar Tie: A tie beam connecting rafters considerably above the wall plate and usually just below the ridge line. Also called a wind strut, or wind bracing. Collar ties offer very little resistance against horizontal thrust at the walls. The primary use for Collar Ties are to transfer wind load from one side of the roof to the other.

Compression: A pushing force or stress shortening a member. (Top flange always in compression in a simple span.).

Concentrated Load: Any load acting on a member at a single point, often referred to as a point load. EXAMPLE: A header framing perpendicular to a span usually connected by a hanger, such as at a stairwell opening, or simply the connection of one beam framing into another.

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Dead Load: The weight of the structure itself. Any load of a permanent nature.
       pad & carpet = 2.0 psf
       3/4" plywood = 2.3 psf
       11 7/8" TJI® = 1.2 psf
       6" batt insulation = 0.6psf
       1/2" drywall = 2.2 psf
       Misc = 1.5 psf

       Total Load = 9.8psf.

Deflection : The movement or “sag” caused by loading. Sometimes expressed as a fraction of the span in inches. (All structural members deflect!).

Design Load: A total of all loads which a member is designed to support.

Diaphragm: A thin “skin” forming a rigid wall, roof, or floor; usually of plywood or other structural panels. It is one of several means of achieving diagonal stability. Used to resist movement caused by wind loads and earth movements.

Dormer: The projection from the inclined surface of a roof to form a room within; contains one or more windows, and has a roof of its own.

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Eave: The lower part of a roof that projects beyond the house wall.

Elevation: The front view of an object. Seen as if one was standing outside a building at street level and looking at that object (as if taking a picture). There are usually four: front, rear, left side, and right side.

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Fascia: Trim board applied to the end of the overhang (i.e., end of joist).

Fire Stop: A block or stop used either in a wall of a building or between joists to prevent the spread of fire and smoke through air space.

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Gable: The walls at the ends of a building directly under the sloping roof planes. Ordinarily the shape is triangular.

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Intermediate Bearing: A middle bearing between two spans. The intermediate reactions… will carry 5/8 of the total load. will be 25% greater compared to that of two simple spans. Where joist are in continuity will deflect around 28% less than two simple span joist.

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Joist: Any secondary member arranged in parallel from bearing to bearing, used to support floor or ceiling loadings.

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Kip: 1,000 pounds.

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Lintel: The horizontal piece (usually of steel) which covers the opening of a door, window, or other opening to carry the weight of the walls above (usually masonry).

Live load: Any load on the structure exclusive of the actual construction materials. It is a moving or variable load such as snow, wind, people, furniture, etc., and construction load.

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Nicola® LVL Laminated Veneer Lumber: is the Trus Joist Laminated Veneer Lumber (LVL) brand name. This LVL is manufactured by laminating veneer with all grain laid‑up parallel. Microllam® can be manufactured using various species of wood fiber in various thicknesses.

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Parallam® PSL Parallel Strand Lumber: is the Trus Joist Parallel Strand Lumber (PSL) brand name. This material is manufactured by laminating strips of veneer with all grain laid‑up parallel. Parallam® PSL can be manufactured using various species of wood fiber in various sizes.

Plan View: Top view of an object, looking down. Usually the most important of the three principle architectural views.

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Rafters: The timbers that form the frame of a roof.

Reaction: Force needed at the ends of a beam to support that beam. For a simple span, the two end reactions are equal to the total load carried by the beam. (Remember that for every action, there is an equal and opposite reaction.).

Ribbon: A board attached to the ends of joists at the bearing walls to provide lateral stability, closure, and to transfer vertical wall loads around the joists directly to the bearing wall. Also called band, rim, skirt, or box.

Ridge: The uppermost horizontal line of a roof, where two inclines meet.

Roof Pitch: The degree of slope of a roof, expressed as a number over 12. For 5/12 slope, the joist will rise vertically 5" for every 12" horizontal length, i.e., horizontal span = 20'0", rise = 20 × 5 or 100".

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Safe Load: A concentrated load considered to be distributed over a 2½ foot square area in a building. The safe load in an office floor is typically 2000 pounds, and is added to the normal live and dead design loads.

Section View: Looking through an object, as if hinging it and opening the building.

Shear: Forces (Arrows) acting as a pair of scissors which tend to cut, tear, or slide two parts of a member along a plane. Shear is highest at the ends of a single span member.


Span: The overall distance of a continuous member from one end to the other.


Square: The amount of roofing needed to cover 100 square feet of roof area.

Squash Block: A block of wood slightly taller than the depth of the joist that is used to transfer external loads (created by walls above) around the joist into the bearing. The squash block is placed in a vertical position tightly alongside the I-joist.

Stress Increase (Load Duration Factor): A percentage increase in the stress permitted in a wood member, based on the length of time that the load causing the stress acts on the member. The shorter the duration of the load, the higher the percent increase in the allowable stress.

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Tension: A pulling force or stress trying to lengthen a member. (Bottom flange is always in tension in a simple span.

TimberStrand® LSL Long Strand Lumber: is the Trus Joist Long Strand Lumber (LSL) brand name. This LSL is manufactured from thin wafers of wood up to 12" in length with all grain laid‑up parallel. TimberStrand® LSL can be manufactured using various species of wood fiber in various dimensions. TimberStrand® LSL utilizes a steam injection press which densifies wood fiber.

Tributary Width: It is the sum of ½ the distance to the next support on each side of the member. For a uniformly spaced system, the tributary width is equal to On Center (OC) spacing.

Truss: A structural framework composed of a series of members geometrically arranged and fastened together to mutually support each other, so that loads applied along the trusses are shared and carried through the framework.

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Uniform Pounds Per Lineal Foot: The load along the length of a member in p.l.f. (pounds per lineal foot), which is determined by multiplying the tributary area width in feet times the design load in p.s.f. (pounds per square foot).
Important: PLF = PSF x oc-spacing (in feet) or PLF = PSF × oc-spacing (in feet)
Example: 50 psf x (16"/12) = 66.7 PLF.

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Valley: The angle or channel where low roof slopes meet.

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Web Stiffener: A small block of plywood that fits flush against the web of a wooden I‑Joist, attached with nails and used to transfer internal stresses through the beam.

Web: The inside member of the “I” configuration that connects and aligns the flanges. Made of Performance Plus® wood panels.

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