WOOD

longitudinal shrinkage is at what max %?

0.5% (max)

Name 7 types of defects in wood (draw)

1. fibre - ring orientation defects 2. knots 3. checks (lengthwise separation of wood which usually extends across the growth rings. Commonly caused by drying process) 4. Wanes (lack of wood on the face of a piece for any reason 5. shakes (separation along the grain of annual growth rings) 6. pitch pocket (opening between growth rings containing resins or bark) 7. warp

The fibre saturation point typically occurs at what moisture content?

25-30%

At what temperature will wood ignite? at what temperature will it self ignite?

250 deg C in open flame 500 degC to self ignite

Radial shrinkage is at what percent?

5%

tangential shrinkage has what range?

5-12%

Wood is known as a _____________________ material. This is when the mechanical properties change with direction.

Anisotropic

Disadvantages of wood?

Bacteria, fire fungi, instects

List the chemical composition of wood and what each component does.

Cellulose - polymer that forms strands that make up cell walls (wood fibers), high density indicates higher strength Hemicellulose - glue Lignin - glue Extractives - tannins, coloring, resins, waxes, starches, fats

When direction of fibr growth is at some angle greater than zero to the longitudinal direction, this is known as?

Cross grain

Unequal shrinkage causes what?

Distortion (warping + twisting)

Classification of Trees. There are two types. What are they and how do they differ?

Endogenous: - intertwined growth, very strong and lightweight, not generally used for engineering applications Exogenous -outward growth, fibers grow from center and add annual rings

What is the FSP?

Fiber Saturation Point the condition at which all the free water is evaporated, but cell walls are still fully saturated

Moisture exists in wood in two states.... what are they?

Free Water within the cell cavities Bound Water, absorbed in cell walls

List the Condition of Seasoning types

KD : max 19% moisture content S-GRN : over 19% MC HT : heated in a kiln to a core temp of 56C for 30min

Above the FSP, changes in moisture state content have _____ affect on mechanical properties.

No

List the structure of wood from outside to inside. "OIC-SHAP"

Outer bark Inner bark Cambium Sapwood Heartwood Annual Rings Pith

When the direction of fibre growth is in the longitudinal direction this is known as?

Parallel to the grain

What are the two types of Exogenous wood. And how are they classified?

Softwood: needle like or scale leaves (spruce, pine, douglas fir, fir cedar) Hardwood: broadleaf trees, (polar, birch, oak, ash, walnut, cheery, elm) -not common for structural purposes

On wood grade stamps there is a left and right side. the right side consists of the registered symbol of the grade stamping agency. From top to bottom of the left side list what the numbers/letters mean.

Species Identification (S-P-F) Grade Designation (grade name) Condition of Seasoning (3 types) Facility ID, Grade Rule (ID, NLGA)

What is the other type of fibre growth?

Spiral grain

Annual rings does what?

Spring wood or early wood - rapid growth, large cells, thin walls Summer wood or late wood, has thicker cell walls and is stronger mechanically

As drying occurs below the FSP what happens?

The structure becomes compacted and stronger (also shrinks)

Name the types of cells in wood: TPFV

Tracheids Parenchyma Fibres (hardwoods only) Vessels (hardwoods only)

What are vessels in hardwood?

Transport in hardwoods

What are Parencyma?

Transversely oriented cells that store food and transport horizontally - located in rays (strips of cells extending radially within a tree)

What is wood/timber?

Wood is small clear specimens free of defects Timber are sawn structural members (lumber are small timbers)

Advantages of wood?

aesthetics adequate strength/weight cost effective renewable resource minimal pollution

How does the rate of loading affect wood?

as rate of load increases, there is an increase in apparent strength (approx. 8% for 10x rate increase)

What are the four types of warp?

bow crook twist cup

Compression of wood perpendicular to the grain causes (3-10MPa)

cells to collapse or flatten

Flexural Strength. The wood will fail first in

compression

Prolonged exposure to high temperatures will _____________ wood in an ________________ manner.

degrade wood in an irreversible

What are the advantages of Wood I - Joists

dimensionally stable known engineering properties well suited for longer span joists 'I' shape gives high strength to weight ratio

List the organisms that degrade wood

fungi, spruce beetle, termites,

List 5 manufactured wood products

glued laminated timber (glulam) parallel strand lumber (PSL) Plywood Oriented Strandboard (OSB) Wood I-joists

What is PSL?

high strength structural composite lumber product manufactured by gluing long and parallel strands of wood together under pressure

Below the Fibre Saturation Point, the mechanical properties are general......?

improved

What is the rule of thumb with respect to the mechanical properties and wood

in a range of -18degC to 66degC a 1degree change in temperature will change the mechanical property by 0.6 - 1.0%

Creep increases in wood from what?

increase in temperature and high moisture condition

cycling of diff temperatures and moisture contents does what?

increases creep

how does the duration of loading affect wood?

increasing load duration will reduce strength

Heartwood does what?

inner non living core - more resistant to decay

Describe shear parallel to the grain

involves the sliding of microfibrils parallel along their long axes, requiring the breaking of mostly secondary bonds

Failure strain of wood under tension perpendicular to the grain is?

larger due to the distortion of tubes

Cambium does what?

layer of tissue 1 cell thick between bark and wood -cell division at the cambium forms new wood

In which direction is wood the wood grains the strongest?

longitudinal

What are tracheids?

longitudinally oriented cells, about 90% of the volume in softwoods Responsible for: Mechanical support of tree and conduction

What is mechanical or machine stress grading?

machine measures the stiffness of timber, empirical relationship between modulus of E, and strength is used to give a strength rating

Explain Wood I-joists

made by gluing solid sawn lumber or laminated veneer (LVL) flanges to a plywood or OSB panel web

What are fibres in hardwood?

mechanical support in hardwoods

Why is this?

microfibrils are aligned vertically and when water is lost they are attracted closer together

Sapwood does what?

moisture conduction and food storage

Tensile strength (perpendicular to the grain)?

much lower secondary bonds between tubes are weaker

What is the longitudinal direction?

parallel to the long grain

What is the radial direction?

perpendicular to the growth rings

What are two wood preservations?

petroleum based solutions (creosote) waterborne preservatives (salts)

The tensile strength of wood is high and failure requires breaking.......? (parallel to the grain)

primary bonds

What is OSB?

produced from short strands of uniform thickness, piles are made by gluing together the strands

Outer bark does what?

protection

There are six principle shear types divided into three main groups:

shear perpendicular to the grain shear parallel to the grain rolling shear

The strongest is? why?

shear perpendicular to the grain, which would require the breaking largely of primary bonds

What is plywood?

sheets of softwood veneer glued together. direction of grain is rotated 90deg each sheet

Compression of wood parallel to the grain causes (25-60MPa)

small kinks within microfibrils at failure, and localized buckling of cell walls

What is affected by the directions?

strength, modulus, thermal expansion, shrinkage, etc

What is the tangential direction?

tangent to the growth rings

In which direction is the wood grains the weakest and experience the most shrinkage?

tangential

Describe rolling shear

the direction of sliding is also perpendicular to the grain, but the mode of failure involves the tracheids "rolling over" each other (think bundle of straws)

below the FSP volumetric shrinkage is approximately proportional to what?

the volume of water lost

What is the purpose of grading?

to permit the designer to choose appropriate mechanical properties for structural puprposes

Inner bark does what?

transports sap from the leaves to the growth parts

Wood shrinks more ___________ than _______________.

transversely than longitudinally

Mechanical properties must be reduced to account for?

variability (use 5% limit) conversion from small wood to lumber or timber size service conditions, temperature

The failure strain of wood under tension is? (when parallel to the grain)

very small (about 1%)

What are glued laminated timbers?

wood pieces glued together with adhesive -long beams, curved beams

Does wood creep?

yes, creep will occur even low stresses and for a very long period of time

Is wood affected by fatigue?

yes, numerous cycles of loading will reduce ultimate strengths