MOD 1-6 CEA 413

Compression Members

Structural members subjected to axial compression, which is stress acting along the axis of the member.

Short Columns

Columns that fail by crushing, characterized by a small ratio of unbraced length to cross-sectional dimension.

Intermediate Columns

Columns with moderate $\frac{l}{d}$ ratios that fail through a combination of crushing and buckling.

Long Columns

Columns that fail by elastic buckling, having a high ratio of length to lateral dimension.

Slenderness Ratio

The ratio of a column's effective unbraced length to its radius of gyration $\left(\frac{l_e}{r}\right)$, or simplified for wood columns as $\frac{l_e}{d}$.

Critical Slenderness Ratio

The larger of the two slenderness ratios calculated along the two principal axes of a cross-section.

Radius of Gyration

A measure of the distribution of a column's cross-sectional area around its centroidal axis.

Simple Solid Wood Columns

Compression members consisting of a single piece of wood or of pieces glued together to function as a single member.

Spaced Column, Connector Joined

Columns formed by two or more individual members with parallel longitudinal axes, joined by connectors.

Built-Up Column

A column fabricated from a combination of two or more simple solid wood columns.

Buckling Factor ($K_e$)

A design factor used to compute effective length ($l_e = K_e L$) based on ideal end restraint conditions for rotation and translation.

Modified Allowable Compressive Stress ($F'_c$)

The adjusted allowable compressive stress parallel to grain used to determine column load capacity ($F'_c = \frac{P}{A}$).

Beams

Structural members that resist pure bending action or are stressed primarily in bending.

Girders

Large horizontal structural members that support smaller beams.

Wood

A cellular organic material composed mainly of cellulose structural units cemented together by lignin.

Timber

Wood attached to the ground with bark intact, or square/nearly square sawn lumber not less than $125\,\text{mm}$ wide.

Lumber

Processed wood material that can be either rough or finished.

Rough Lumber

Unfinished sawed wood displaying saw marks on all four longitudinal surfaces.

Finished Lumber

Processed wood that has been planed smooth and cut into specific standard sizes.

Wood Cell

The basic structural element of wood, roughly rectangular in cross-section with overlapping tapered ends.

Cellulose

The primary load-carrying material that provides strength to wood cell walls.

Lignin

The natural binder that cements and stiffens cellulose fibers together in wood.

Hardwoods

Wood species derived from deciduous trees with broad leaves.

Softwoods

Wood species derived from evergreen conifers with needle-like or scale-like leaves.

Sapwood

The light-colored outer layer of wood surrounding heartwood, containing active living cells.

Heartwood

The darker, inner zone of wood that is more resistant to decay fungi than sapwood.

Pith

The soft center core in a cross-section of a log.

Earlywood (Springwood)

Wood produced during rapid spring growth, featuring large cell cavities and thin walls.

Latewood (Summerwood)

Wood produced later in the growing season, characterized by smaller cavities, thicker walls, and higher density than earlywood.

Annual Growth Ring

A layer of wood created in one growth season, consisting of a band of earlywood and latewood.

Medullary Rays

Radial ribbonlike bundles of cells extending perpendicular to annual growth rings from the pith to the bark.

Cambium

The active cell-producing layer in trees that adds new wood cells internally and inner bark externally.

Pores (Vessels)

Large, thin-walled tubular structures in hardwoods responsible for conducting water.

Moisture Content (MC)

The weight of water in wood expressed as a percentage of its oven-dry weight.

Equilibrium Moisture Content (EMC)

The moisture level at which wood neither gains nor loses moisture relative to the surrounding environment.

Orthotropic Behavior

The material characteristic of wood having distinct physical and mechanical properties along three mutually perpendicular axes.

Strength-Reducing Defects

Imperfections or irregularities in timber that reduce its structural load-bearing capacity.

Shakes

Separations along or between annual growth rings in timber.

Bow

A warp along the length of a board bending flatwise in a single plane.

Crook

A warp along the length of a board bending edgewise along its width.

Twist

A helical distortion of wood resulting from rotation around its longitudinal axis.

Checks

Longitudinal cracks in wood caused by uneven drying across growth rings.

Splits

Cracks extending through the entire thickness of a timber member along the grain.

Knotholes

Voids remaining in timber when a knot detaches or falls out.

Wane

The presence of bark or lack of wood on an edge or corner of a piece of lumber.

Cup

A transverse distortion causing curvature across the width of a board.

Seasoning

The controlled process of drying timber to achieve an acceptable moisture content.

Air Drying

The natural drying process of stacking lumber in open-sided sheds with adequate airflow.

Kiln Drying

Rapid drying of timber in controlled heated and humidified ovens that sanitize fungal decay.

Grading

The systematic classification of lumber based on quality and structural integrity for specific applications.

Visual Strength Grading

A subjective assessment of lumber quality based on visual inspection of defects.

Machine Strength Grading

Structural grading using mechanical bending tests to evaluate deflection and Modulus of Elasticity.

Yard Lumber

Standard size lumber intended for general construction and building framing.

Strips

Yard lumber less than $50\,\text{mm}$ ($2''$) thick and less than $200\,\text{mm}$ ($8''$) wide.

Boards

Yard lumber less than $50\,\text{mm}$ ($2''$) thick and $200\,\text{mm}$ ($8''$) or wider.

Timbers

Large structural lumber measuring $125\,\text{mm}$ ($5''$) or more in its smallest dimension.

Dimension Lumber

Framing lumber ranging from $50\,\text{mm}$ ($2''$) to $100\,\text{mm}$ ($4''$) in nominal thickness.

Factory / Shop Lumber

Lumber intended for remanufacturing into doors, window frames, moldings, and trim.

Structural Lumber

Lumber graded for structural applications where allowable working stresses are required.

Beams and Stringers (B&S)

Rectangular timber with width $\ge 250\,\text{mm}$ ($10''$) and depth more than $50\,\text{mm}$ ($2''$) greater than width, graded for bending on the narrow face.

Joists and Planks (J&P)

Rectangular lumber with thickness $50\,\text{mm}$ to $250\,\text{mm}$ and depth $\ge 100\,\text{mm}$, graded for bending on either face.

Posts and Timbers (P&T)

Square or nearly square lumber measuring at least $250\,\text{mm} \times 250\,\text{mm}$ with depth not exceeding width by more than $50\,\text{mm}$.

S4S

Abbreviation for lumber surfaced on all four sides.

Nominal Size

Commercial size designation specifying rough, unplaned dimensions of lumber.

Actual Size (Dressed Size)

The real dimensions of lumber after surfacing and planing operations.

Dressed Lumber

Lumber that has been planed smooth on one or more surfaces (S1S, S2S, S1E, S4S).

Worked Lumber

Dressed lumber shaped with matching patterns such as tongue-and-groove or shiplap.

Board Foot

A unit of volumetric lumber measurement equivalent to a piece $1\,\text{ft}$ long with a cross-sectional area of $12\,\text{in}^2$.

Allowable Stress (Safe Working Stress)

Maximum permissible stress determined experimentally to ensure safe design under expected service loads.

Actual Stress

Calculated internal stress in a structural member resulting from applied external loads.

Factor of Safety

A design margin applied to account for uncertainties in loads, material strength, and manufacturing.

Allowable Stress Design (ASD)

A design approach ensuring induced working stresses do not exceed specified allowable stress thresholds.

Load Resistance Factor Design (LRFD)

A structural design method applying load factors and resistance factors to ultimate limit states.

Limit State Design

Design methodology evaluating structures against failure limit states using partial safety factors.

Dead Loads

Permanent stationary loads caused by the weight of structural members and fixed attachments.

Live Loads (Imposed Loads)

Transient or moving loads caused by occupancy, furniture, vehicles, and equipment.

Wind Loads

Lateral environmental forces exerted on structures by wind pressures.

Seismic Loads

Inertial forces produced on a structure due to earthquake-induced ground accelerations.

Deformation

The change in shape or size of a structural element when subjected to external forces.

Elastic Limit (Proportional Limit)

The upper stress limit below which strain remains directly proportional to stress and deformations fully recover.

Elasticity

The ability of a material to regain its original dimensions upon removal of applied loads.

Permanent Set

Irreversible deformation that remains in a material after stress exceeds the elastic limit.

Ultimate Strength

The maximum stress a material can withstand before fracture or structural collapse.

Modulus of Elasticity ($E$)

The ratio of stress to strain within the elastic limit, quantifying material stiffness.

Size Factor Adjustment ($C_F$)

An adjustment factor applied to allowable bending stress when sawn lumber depth exceeds $300\,\text{mm}$ or circular diameter exceeds $340\,\text{mm}$.

Form Factor Adjustment ($C_f$)

An adjustment factor applied to allowable bending stress for non-prismatic members ($1.180$ for circular, $1.414$ for diamond cross-sections).

Truss

A framed structural framework composed of interconnected members carrying axial tension or compression forces.

Pitch

The ratio of total rise to span in a roof truss.

Slope

The ratio of total rise to half-span in a roof truss.

Bay

The longitudinal space or structural interval enclosed between two consecutive roof trusses.

Width of the Bay

The center-to-center distance separating adjacent structural trusses.

Purlin

A longitudinal beam spanning between trusses that supports roof decking and transfers loads to truss joints.

Panel

The structural section of a truss chord bounded between two adjacent joint locations.

Panel Point

A joint location where concentrated external loads are applied along a truss chord.

Panel Load

The total gravity load transferred to a single panel point, calculated as roof load multiplied by panel length and bay width.

King Post Truss

A simple truss featuring a central vertical tension member supporting a beam over spans up to $8\,\text{m}$.

Queen Post Truss

A roof truss incorporating two vertical posts, suitable for spans around $10\,\text{m}$.

Howe Truss

A truss composed of vertical tension members and diagonal compression members, spanning $6\,\text{m}$ to $30\,\text{m}$.

Pratt Truss

An efficient truss with vertical compression members and diagonal tension members sloping toward center, spanning $6\,\text{m}$ to $10\,\text{m}$.

Fan Truss

A simple pitched roof truss with radiating web members, spanning $10\,\text{m}$ to $15\,\text{m}$.