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45 Cards in this Set
- Front
- Back
Other than defects, name 5 things that can affect wood |
Duration of load, rate of loading, preservative treatment (pressure treatment), temperature,moisture content, size, cyclical loading (fatigue), direction of loading (axis), species |
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What is the role of lignin in the tree |
Lignin acts as the glue that binds the cellulose units and cells together |
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What is the role of hemi-cellulose in the tree? |
together wth lignin, the hemi-cellulose surrounds the cellulose units, bonding themtogether |
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What is the typical tensile strength range of small clear pieces of wood parallel to the grain? |
70 to 150 MPa |
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State the microfibril orientation in the following cell wall layers Primary Wall Secondary Wall, Outer Layer (S1) Secondary Wall, middle layer (S2) |
Primary Wall - Random (S1) - double spiral/left and right hand or helix inclined at 50 70 degrees (S2) - Single/right-hand helix inclined at 10 to 30 degrees |
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What are four things needed for fungi to survive |
Warmth Moisture Food Oxygen |
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What is the structural significance of the tube structure of wood cells |
Tube structure provides high strength to weight raio. They are orientated in the same direction held together in a matrix for high strength |
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What are 2 advantages of wooden I joists to sawn lumber joists |
strength to weight raio dimensional stability |
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What is a stress modification factor? give an example |
Applied to the allowable stress for a structure to account for a specific condition Ex: Duration of Load (Kd) - Can either increase or decrease allowable load. Short term loads increase the stress allowable and long term loads decrease the stress allowable. |
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What is the most abundant cell type in trees and what is its role or purpose? |
Tracheids - provide mechanical support in the vertical direction and conducts water in the vertical direction |
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What are microfibrils made of and where are they located and their orientation? |
Made up of bundles of tracheids. Held together by hemicellulose and lignin. They are orientated axial (longitudinal) direction. Located in the trunk within the bark |
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Machine stress rated lumber uses what mechanical property to predict what other property? |
It uses the modulus of elasticity to predict the ultimate tensile strength. (using force deflection) |
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Do the mechanical properties of wood increase or decrease with density? Suggest a reason why? |
Generally increase with density. As density increases porosity decreases. Since the cell wall is very strong and dense, an increase in cell wall thickness will lead to an increase in strength and density |
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Is wood isotropic or anisotropic? |
Anisotropic, microfibrils are orientated in the longitudinal direction. Properties are not the same in each direction. (Ex. Tensile strength parralle to the grain is much higher than perpendicular to the grain. |
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What are two primary disadvantages to wood as a structural material? |
Variability Food source (fungi, termites) |
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Why can austenite accomodate more carbon than ferrite or delta iron? |
Bc austenite has an FCC lattice structure |
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Pearlite consists of what two phases? |
Ferrite and iron carbide |
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What are the 3 ways that veneer and PSL and LVL are sorted? |
Visual quality, strength, and moisture content |
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Advantages to wood |
Reusable, recyclable, biodegradable renewable resource good aesthetics cost effective locks up CO2 |
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Microfibrils |
Threadlke bundles of cellulose molecules that are arranged approximately parallel Bound together be hemi-cellulose and lignin |
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Softwood vs Hardwood |
Softwood: needle trees, used more for structural spruce, pine, douglas fir (Primary bld material), cedar
Hardwood: broadleaf trees, used more for furniture and cabinetry oak, maple, birch |
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2 states of moisture in wood |
Free water: liquid in the cell cavities Bound water: pysically absorbed in the cell wall |
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Fibre saturation point |
Condition at which all the free water is evaporated, but cell walls are still fully saturated
Typically occurs at a moisture content of 25 to 30% Below FSP the molecular structure is compacted resulting in shrinkage and increased strength |
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Mechanical Properties in wood |
Modulus of elasticity Tensile strength Compressive strength Flexural strength Shear strength Effects of temperature |
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Knots and Checks |
Portion of limb surrounded by subsequent wood growth Lengthwise sepation of wood which usually extends across the growth rings. Caused by the outer surfaces of lumber drying more rapidly than the inner core |
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Wanes and Shakes |
Lack of wood on the face of a piece for any reason at all Separation along the grain bt the annual growth rings |
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Pitch pocket and warp |
Opening bt growth rings containing resins or bark bow, twist, crook, cup |
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Stress Modification Factors |
Load Sharing Factor Load Duration Factor Treatment Factor Service Condition Factor Size Factor Temperature Factor |
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What are the main cells in softwood lumber |
Parenchyma and trachiads |
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What are cracks in wood due to wind damage called? |
Shakes |
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Rebar is normally protected from corrosion in concrete due to what condition? |
The concrete has high pH |
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Why does pearlite have a layered structure? |
bc carbon atoms need to diffuse only a short distance to form this structure |
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What type of wood has the lowest moisture content at manufacture? |
plywood and OSB |
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The movement of dislocations and the resulting interference or locking up bt dislocations describes the process of what? |
work (strain) hardening |
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What is cellulose made of? |
glucose |
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What is used to predict if a type of steel can be welded? |
summation of weighted values of various steel alloy elements |
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What is the major difference bt laminated veneer lumber and plywood? |
the grain direction of plywood veneers alternate 90 degrees, in LVL the do not |
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Mill Test Certificates |
Chemical - Samples are taken from the molten metal Physical - Samples from finished products; tensile yield, strength and elongations tests are done |
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Potential problems with rebar |
low elongation low strain hardening ratio plastic strain not uniform along bar |
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Purpose of rebar |
To carry tension crack control restraint of bursting stress absorb energy during seismic loading |
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Properties of steel are generally controlled by |
chemical composition temperature of rolling rate of cooling re-heating treatments |
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increased carbon results in |
increased strength increased hardness decreased ductility decreased toughness |
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Strengthening mechanisms of steel |
alloying work (strain) hardening (cold working) heat treatment |
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Corrosion control of steel |
Coatings galvanizing cathodic protection corrosion resistant metal |
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3 Primary Categories of shear in wood |
Parallel to grain Perpendicular to grain Rolling shear |