Wood and Wood Joist Design

Comprehensive vocabulary flashcards covering wood classification, structure, properties, defects, and structural design principles based on the lecture transcript.

Endogenous

A classification of trees with intertwined growth, such as palm trees, which are not generally used for building applications.

Exogenous

A classification of trees that grow outward from the center by adding concentric layers, providing predictable engineering properties; includes most other trees used in construction.

Deciduous

Broad-leaf trees categorized as hardwood, such as ash, oak, maple, and walnut, which are generally expensive and slow-growing.

Coniferous

Cone-bearing evergreen trees categorized as softwood, such as Douglas fir, pine, spruce, and cedar, commonly used for framing.

Earlywood (Springwood)

The light-colored ring in wood consisting of hollow, thin-walled cells formed during rapid spring growth.

Latewood (Summerwood)

The dark-colored ring in wood consisting of dense, thick-walled cells that are much harder and stronger, formed during summer growth.

Pith

The center stem of a tree located at the very center axis.

Heartwood

The darker wood surrounding the pith that provides structural support to the tree.

Sapwood

The lighter-colored wood that functions to transport sap within the tree.

Cambium

A very thin layer in the tree structure which is the specific location of wood growth.

Anisotropic

A characteristic of wood where physical properties like strength, modulus, and shrinkage differ based on the direction (longitudinal, radial, or tangential).

Longitudinal Direction

The direction parallel to the long axis (grain) of the wood; it is the strongest direction and exhibits the least shrinkage.

Tangential Direction

The direction tangent to the growth rings; it is the weakest direction and exhibits the most shrinkage.

Cellulose

A polymer that forms strands making up cell walls, comprising $50\%$ of wood by weight, with a specific gravity of $1.5$.

Lignin

The chemical component that acts as glue binding the wood fibers together; it makes up $23\text{-}33\%$ of softwood and $16\text{-}25\%$ of hardwood by weight.

Moisture Content ($Mc$) Formula

$$Mc = \frac{\text{Wet weight} - \text{dry weight}}{\text{dry weight}} \times 100$$

Fiber Saturation Point (FSP)

The moisture content, typically between $21\text{-}32\%$, where cells are saturated with bound water but contain no free water in the voids; changes below this point strongly affect physical and mechanical properties.

Dimensional Lumber

Lumber that is $2"$ to $5"$ thick, commonly used for light framing such as studs, joists, beams, and rafters.

Heavy Timber

Lumber sized $4 \times 6$, $4 \times 8$, $8 \times 8$ or larger, usually rough sawn and used for heavy framing or railroad ties.

Flat-sawn

Lumber where the grain is less than $45$ degrees from the flat side; typically lower quality with more defects.

Rift-sawn

Lumber where the grain is at an angle of $45\text{-}80$ degrees.

Quarter-sawn (Vertical/Edge sawn)

Lumber where the grain is at an angle of $80\text{-}90$ degrees; highest quality with the most regular grain and least shrinkage problems.

S4S

An abbreviation for "surfaced 4 sides," meaning the lumber has been dressed or planed on all four sides.

Nominal Size

The rough-sawn dimensions of lumber in inches before surfacing; for example, a $2 \times 4$ has actual dimensions of $1.5" \times 3.5"$.

Knots

Common defects where a branch base grew, causing grain discontinuity and degrading mechanical properties, especially if located on the edge.

Shakes

A wood defect characterized by separations between the annual rings.

Wane

A defect where bark or soft wood is left on the edge of the board.

Check (or split)

A wood defect characterized by a rupture across the annual rings caused by drying.

Bowing

A type of warping involving lengthwise curvature from end to end.

Crooking

A type of warping involving lengthwise curvature from side to side.

Cupping

A type of warping where the edge of the board rolls up.

Twisting

A type of warping where one corner of the board lifts up.

Modulus of Elasticity ($E$)

A measure of wood stiffness ranging from $1 \times 10^6\,\text{PSI}$ to $2 \times 10^6\,\text{PSI}$, depending on species, moisture, and grain direction.

Plywood

An engineered wood panel made of thin sheets (plies) glued with grain at right angles to ensure uniform properties in both directions.

Oriented Strand Board (OSB)

An engineered panel made of wood chips and strands oriented in specific directions and glued with resin; commonly used for subfloors and roof sheathing.

GLULAM

Glue-Laminated Timbers made by bonding standard lumber with parallel grain, used to create large structural members with varying cross sections.

Dead Loads

Permanent loads such as self-weight (density of $25\text{-}50\,\text{pcf}$) and floor panels (estimated at $1.5\,\text{psf}$ for OSB/plywood).

Live Loads

Non-permanent occupancy loads from people or furniture; common values are $40\,\text{psf}$ for 1st floors and $30\,\text{psf}$ for bedrooms.

Deflection Limit

The code limit for live load deflection to prevent bouncy floors or cracked plaster, usually restricted to a maximum of $L/360$ where $L$ is the span.