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A Glossary of Glulam Terminology

Appearance Classification

This defines the surface finish of the beam.
Architectural, Industrial and Framing are the most common appearance classifications.
Premium appearance beams are available as custom orders.
The structural quality of glulam has no relation to the appearance grade specified.

Beam

Normally a horizontal or sloping member that is designed to carry vertical loads.
Simple Span: A member supported at both ends.
Continuous: A single member supported at more than two bearing locations.
Cantilever: A member which has one or both supports away from the ends; one of which overhangs its support.

Camber

The curvature built into a beam (in a direction opposite to the expected deflection) to prevent it from appearing to sag under a loaded condition.

Column

Normally a vertical member that is designed to carry loads from a beam.
Concentrically Loaded: When the resultant load acts parallel to the axis of the member and is applied at its centerline.
Eccentrically Loaded: When the resultant load acts parallel to the axis of the member but is applied away from its centerline.

Combination Number

The identification used to describe the type of lamination layup in the glulam member, the associated allowable design stresses, and if the lumber used was visually or mechanically graded.

Deflection

The vertical displacement that occurs when a beam is loaded, generally measured at positions between supports or at the end of a cantilever.

Deflection Limit

The maximum amount the beam is permitted to deflect under load. Different deflection limits are normally established for live load and total load.

Design Values

Allowable stress values as they are established for each glulam beam, described in terms of
Bending (Fb)
Horizontal Shear (Fv)
Modulus of Elasticity (E)
and other stresses.

Equilibrium Moisture Content

Any piece of wood will give off or take on moisture from the surrounding atmosphere until the moisture in the wood comes to equilibrium with that in the atmosphere. The moisture content of wood at the point of balance is called the equilibrium moisture content and is expressed as a percentage of the weight of the oven-dried wood.

Header

A beam which is used to support walls and/or floor and roof joists that run perpendicular to it.

Lamination Layup

The physical arrangement of different grades of laminations throughout the depth of a glulam member.

Laminations

Individual pieces of lumber that are glued together end to end for use in the manufacture of glued laminated timber. These end-jointed laminations are then face bonded together to create the desired member shape and size.

Moisture Content

The amount of water contained in the wood, usually expressed as a percentage of the weight of oven-dry wood.

Purlin

A secondary structural framing member such as a joist or rafter that is normally supported by walls or primary beams.

Radius of Curvature

A dimension that is commonly used as a means of describing the camber requirements in a glulam beam.

Stock Glulams

Glulams which are manufactured to common, standard dimensions and characteristics, and kept in inventory by distributors or dealers for immediate job site delivery (may be cut to customer-specified lengths).

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