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Wood Properties, Deterioration & Preservation

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Presentation on theme: "Wood Properties, Deterioration & Preservation"— Presentation transcript:

1 Wood Properties, Deterioration & Preservation
Penn State Unversity - CE 336 Tikalsky & Tepke

2 Penn State Unversity - CE 336 Tikalsky & Tepke
Introduction to Wood 600 Different Species of trees exist in U.S. 15-20 are commercially used Most are forested Growing quantities are farmed Penn State Unversity - CE 336 Tikalsky & Tepke

3 Penn State Unversity - CE 336 Tikalsky & Tepke
Common Species of Wood Fir Hemlock Pine Poplar Redwood Spruce Cedar Hickory Maple Oak Ash Birch Cypress Walnut Gum Penn State Unversity - CE 336 Tikalsky & Tepke

4 Penn State Unversity - CE 336 Tikalsky & Tepke
Anatomy of a Tree Root - absorbs moisture Trunk - mechanical strength rigidity height two way transfer moisture UP sap DOWN Penn State Unversity - CE 336 Tikalsky & Tepke

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Anatomy of a Tree Crown - Area of chlorophyll for photosynthesis O2 given off CO2 absorbed Bark - protective layer Penn State Unversity - CE 336 Tikalsky & Tepke

6 Penn State Unversity - CE 336 Tikalsky & Tepke
Anatomy of a Tree Cambium Layer - Growth layer for cell division. 1 ring for each growing season, Inside Layer (springwood) is hollow tube(large in softwood) Outside Layer (summerwood) is from slower growth and has thicker walls Penn State Unversity - CE 336 Tikalsky & Tepke

7 Penn State Unversity - CE 336 Tikalsky & Tepke
Anatomy of a Tree Heartwood: storage for food. comprised of dead cells solid filled cells mechanically strong No starches Dense (nearly impermeable) Penn State Unversity - CE 336 Tikalsky & Tepke

8 Penn State Unversity - CE 336 Tikalsky & Tepke
Anatomy of a Tree Sapwood: living part of tree fed by medullar ray cells which run perpendicular to the cambium cells. full of moisture (green) contains starches very permeable (can be impregnated) Penn State Unversity - CE 336 Tikalsky & Tepke

9 Penn State Unversity - CE 336 Tikalsky & Tepke
Anatomy of a Tree Aged Sapwood (moisture removed) same strength as heartwood same density as heartwood contains starches permeable Penn State Unversity - CE 336 Tikalsky & Tepke

10 Penn State Unversity - CE 336 Tikalsky & Tepke
Tree Growth Exogenous Trees Grow Diametrically with growth rings Fir, Pine, Maple, Oak Endogenous Trees Grow by intermingling cell structures in a fibrous structure. Bamboo, Palm, Hemp Penn State Unversity - CE 336 Tikalsky & Tepke

11 Penn State Unversity - CE 336 Tikalsky & Tepke
Hard vs. Soft? Hardwood and Softwood have nothing to do with density Balsa is hardwood Yew is softwood (6 times as dense as Balsa) Hardwoods are Angiosperms (fruit or nut) Softwoods are Gymnosperms (cones) Penn State Unversity - CE 336 Tikalsky & Tepke

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Hardwoods Broad Leaves Deciduous Grow Slowly Expensive Cross-Section has vessels Spring and Summerwood Penn State Unversity - CE 336 Tikalsky & Tepke

13 Penn State Unversity - CE 336 Tikalsky & Tepke
Angiosperm Cells Cell Structure cavity or Lumen in the center fiber around the cavity wall around fibers Penn State Unversity - CE 336 Tikalsky & Tepke

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Softwoods Needles Conifer Grow Quickly Cheaper Small Summerwood pores Penn State Unversity - CE 336 Tikalsky & Tepke

15 Penn State Unversity - CE 336 Tikalsky & Tepke
Gymnosperm Cells Cells are individual tubes for transport Cells have pits which act as permeable vents between cells Penn State Unversity - CE 336 Tikalsky & Tepke

16 Cell Walls and Connectivity
Cellulose Long chains of fiber strong in tension Lignin glue between cellulose chains shear resistance and durability Penn State Unversity - CE 336 Tikalsky & Tepke

17 Density and Strength of Wood
Density and Strength are related high density thicker walls 6 to 15 rings per inch is good strength 6 (porous hardwoods) 15 (softwoods) Part of Rating System Penn State Unversity - CE 336 Tikalsky & Tepke

18 Penn State Unversity - CE 336 Tikalsky & Tepke
Moisture Content living tree may have 200% M.C. free water water contained in cell cavities removed without volumetric changes bound water water contained within the cell walls removal of this water caused volumetric changes Penn State Unversity - CE 336 Tikalsky & Tepke

19 Penn State Unversity - CE 336 Tikalsky & Tepke
Moisture Content “shrinkage” is from the removal of bound water “swelling” will occur if water is reintroduced Penn State Unversity - CE 336 Tikalsky & Tepke

20 Penn State Unversity - CE 336 Tikalsky & Tepke
Moisture Content F.S.P. E.M.C. 0% M.C. Free Water Bound Water Wt. of Solid Wood "fiber saturation point" the moisture content of wood with 100% bound water and 0% free water. Typical value for f.s.p. is about 30 percent Decreases below the FSP will increase strength properties. Penn State Unversity - CE 336 Tikalsky & Tepke

21 Penn State Unversity - CE 336 Tikalsky & Tepke
Moisture Content F.S.P. E.M.C. 0% M.C. Free Water Bound Water Wt. of Solid Wood Equilibrium Moisture Content (E.M.C.) the average moisture content the wood will assume under service conditions typically less than the fiber saturation point and greater than 5 % Penn State Unversity - CE 336 Tikalsky & Tepke

22 Penn State Unversity - CE 336 Tikalsky & Tepke
Moisture Content there is an optimum M.C. for each species (typically between 7-14 percent m.c.) specification allow 19 percent maximum (some say 15%) High M.C.--- promotes warping, fungus, insects Low M.C. --- brittleness Penn State Unversity - CE 336 Tikalsky & Tepke

23 Stress Grading Methods
Allowable Stress including an avg. factor of safety » 2.5 99% of the time the f.s. will be > 1.25 Permissible Bending Stress Permissible Shear Stress Permissible Compressive Stress (perp.) Permissible Compressive Stress (// ) Modulus of Elasticity Penn State Unversity - CE 336 Tikalsky & Tepke

24 Stress Grading Methods
I) Visual Grading species (6 classes) number of rings per inch proportion of summerwood to springwood (summerwood is denser and stronger) heartwood vs. aged sapwood (decay resistance) II) Mechanical Grading Penn State Unversity - CE 336 Tikalsky & Tepke

25 Penn State Unversity - CE 336 Tikalsky & Tepke
Seasoning Air Seasoning open sheds Inexpensive No loss in quality of lumber No loss in the quality of the timber Takes up a lot of space for a long time Penn State Unversity - CE 336 Tikalsky & Tepke

26 Penn State Unversity - CE 336 Tikalsky & Tepke
Seasoning Kiln Seasoning vented humidified oven is used to gradually reduce M.C. below 17 percent to prevent cracking. Air circulation and air interchange Faster than air seasoning energy required Penn State Unversity - CE 336 Tikalsky & Tepke

27 Penn State Unversity - CE 336 Tikalsky & Tepke
Lumber Grade Stamp Lumber Grading Association Mill number Lumber grade Species Moisture condition (at time of surfacing) Penn State Unversity - CE 336 Tikalsky & Tepke

28 Grade Stamps – Dimensional Lumber
Penn State Unversity - CE 336 Tikalsky & Tepke

29 Penn State Unversity - CE 336 Tikalsky & Tepke
Timber Defects Cracks - "shakes, checks, and splits" Heart shakes Radial shakes, "check" Seasoning problem: tangential shrinkage is greater than radial shrinkage Ring shake these are caused by resin pockets in the living tree. Penn State Unversity - CE 336 Tikalsky & Tepke

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Timber Defects Penn State Unversity - CE 336 Tikalsky & Tepke

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Timber Defects Penn State Unversity - CE 336 Tikalsky & Tepke

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Lumber Sizes - Dressed lumber: sides of members are planed or surfaced. 2 x 4 is really 1 1/2" x 3 1/2" dressed size, "nominal" Rough Sawn lumber: ussually 1/8" greater in size than the dressed lumber. Full Sawn lumber: not available commercially Penn State Unversity - CE 336 Tikalsky & Tepke

34 Sawing Patterns / Timber Defects
Penn State Unversity - CE 336 Tikalsky & Tepke

35 Penn State Unversity - CE 336 Tikalsky & Tepke
Lumber Timbers (posts, beams, girders and stringers) Dimension lumber (light framing) Boards (siding, flooring, planking) Penn State Unversity - CE 336 Tikalsky & Tepke

36 Timber for Marine structures
close grained, dense wood, natural resistance to: impact (from sea vessels) infestation (sea creatures, borers) fungal attack (wet rot, other fungi) salt or wave erosion temperature variations. Oak, Larch, and Teak natural oils for preservatives Penn State Unversity - CE 336 Tikalsky & Tepke

37 Heavy Construction Work (Timber Construction)
Bridges, piles, shoring, abutments and transfer girders Close grained high density impact resistant (deliberate and accidental loadings) Chemical resistance Oak, Larch, Douglas Fir, Southern Pine Penn State Unversity - CE 336 Tikalsky & Tepke

38 Medium/Light Construction
Roof trusses, partition, floors, walls resistance to insects and fungal attack, minimum dimension changes flame resistance market availability Douglas Fir, Southern Pine, Hemlock, Redwood, (other softwoods) Penn State Unversity - CE 336 Tikalsky & Tepke

39 Penn State Unversity - CE 336 Tikalsky & Tepke
Falsework Plywood, board, formwork, glue lam supports inexpensive available weight ease of handling and storage resistance to impact and abrasion (reuse and stripping ease) any graded wood, hemlock, pine, softwood Penn State Unversity - CE 336 Tikalsky & Tepke

40 Penn State Unversity - CE 336 Tikalsky & Tepke
Glu-Laminated Timber geometry, long spans Engineered Properties Shape X-section Changes Penn State Unversity - CE 336 Tikalsky & Tepke

41 Penn State Unversity - CE 336 Tikalsky & Tepke
Reaction Wood Hard brittle wood formed on the underside of a leaning or crooked tree, usually denotes uneven wood grain. not acceptable if identified tension wood in hardwoods compression wood in softwood Penn State Unversity - CE 336 Tikalsky & Tepke

42 Deterioration Mechanisms
Fungi & bacteria deterioration Insect deterioration Marine borer deterioration Weathering & photochemical deterioration Mechanical wear Thermal deterioration Fire damage Chemical deterioration Connection deterioration Penn State Unversity - CE 336 Tikalsky & Tepke

43 Fungi & Bacteria Bacteria
Only a problem if member is constantly submerged Primarily a surface problem Can increase permeability of wood structures Much less degree of degradation than fungi…

44 Fungi & Bacteria Fungi Non decay types (cosmetic problems only) Molds
Serviceability problem Stains

45 Fungi Deterioration Causes Decay type fungi need… A food source (wood)
Small amount of oxygen Suitable temperatures (about 40 oF up to about 90 oF to 100 oF) Suitable pH (best at 4-6) Absence of poisons or toxins Moisture Above F.S.P.

46 Fungi Deterioration Types of Decay Fungi Manifestations
Brown-rot (soft woods – mostly) White-rot (hard woods – mostly) Soft-rot Manifestations Cubical, spongy, pocket, stringy Depends on type

47 Penn State Unversity - CE 336 Tikalsky & Tepke
Fungi Deterioration Dry rot (A type of brown rot) 30 to 40 percent M.C. in wood with low ventilation Wet rot (collective term for white and brown rots) very wet wood discolors and gets brittle eliminate moisture, remove growths, cut out or burn adjoining timber and treat timber Penn State Unversity - CE 336 Tikalsky & Tepke

48 Decay Fungus Typical Structure(s) Characteristics Environ. Type of Rot
Serpual Lacrymans (Dry-rot) Buildings White cotton-like or gray felt-like substance, then red rust-like and finally cubical fracture Humid Brown, cubical Fibroporia Vaillantii Buildings, coal mines White, fluffy substance, then white spores Caniophoria Puteana (Cellular fungus) Longitudinal splits or cracks, then nearly identical to dry-rot. Brittle. Very high humidity – water leaks, condensation Paxillus Panuoides Softwoods, buildings Fibrous, yellow, purple Very moist conditions Donkioporia Expansa Oak timbers, softwoods, buildings (damp walls) White, fibrous, brown pores. In advanced stages, the wood is soft, white substance Usually near water leakage White Lentinus Lepideus Outdoor timber (telephone poles, railway sleepers, paving blocks) Brown woody mushroom Moist Amyloporia xantha greenhouses Thin plate, small yellow pores, smells like lemons --- Phellinus Contiguus External joints (softwood window frames) Fibrous strings, brown wooly Penn State Unversity - CE 336 Tikalsky & Tepke

49 Fungi Deterioration Mechanisms Effects Regions
Fungi use wood cells as food source Cellulose & Hemicellulose (Brown rot) Cellulose & Lignin (White rot) Effects Reduced strength & other properties Degradation Regions Lower susceptibility to attack from SE to NW

50 Penn State Unversity - CE 336 Tikalsky & Tepke
Decay Prevention Durable, seasoned wood Protection from water sources (vapor barriers, ventilation) Pipes Removal of deteriorated elements Heartwood (extractives) Treatments Penn State Unversity - CE 336 Tikalsky & Tepke

51 Resistant & Very Resistant Moderately Resistant
Slightly or Non-Resistant Bald Cypress (old growth) Bald Cypress (new growth) Alder Catalpa Douglas Fir Ashes Cedars Honey Locust Aspens Black Cherry Western Larch Basswood Arizona Cypress Swamp Chestnut Oak Beech Junipers Eastern White Pine Birches Black Locusta Longleaf Pine Cottonwood Red Mullberrya Slash Pine Elms Bur Oak Tamarack Hackberry Chestnut Oak Hemlock Oregon White Oak Hickories Post Oak Maples White Oak Red or Black Oak Osage Orange Pines Redwood Spruces Sassafras Sweet gum Black Walnut Sycamore Pacific Yewa Willows Western Red Cedar Yellow Poplar Penn State Unversity - CE 336 Tikalsky & Tepke

52 Preservation of Timber
Preservation Treatments (advantages + problems) Oil-borne ($) Water-soluble (most used) Organic solvents Penn State Unversity - CE 336 Tikalsky & Tepke

53 Preservation of Timber
Desired preservative properties Toxic to fungi, insects, borers No leaching Easy penetration Corrosion resistant Economic Unscented Penn State Unversity - CE 336 Tikalsky & Tepke

54 Preservation of Timber
Application Apply preservatives to dry lumber Techniques Pressure Diffusion Immersion Spraying Hot & cold open tank Penn State Unversity - CE 336 Tikalsky & Tepke

55 Preservation of Timber
Oil-Borne Preservatives (eg. Coal-Tar Creosote) Pressure impregnation Brush-on Flammable unless weathered Odor and unfinishable No indoor use Penn State Unversity - CE 336 Tikalsky & Tepke

56 Preservation of Timber
Water-Soluble Preservatives (Copper-Chrome-Arsenic) odorless nonstaining interior uses wood must be allowed to re-dry Organic Solvent preservatives flammable unless painted Penn State Unversity - CE 336 Tikalsky & Tepke

57 Marine Borer Deterioration
Causes Marine environments Crustaceans, mollusks Tropical climates Mechanisms Shipworm (mollusk) consumption Up to 1 meter in length or more Create large holes in wood Limnoria Surface eater Penn State Unversity - CE 336 Tikalsky & Tepke

58 Marine Borer Deterioration
Manifestations Large horizontal or vertical tunnels (internal) Shipworms Surface degradation Limnoria Prevention Same as for fungi but some immunizations (creosote) Physical / mechanical implications Complete degradation Reduction in cross-section Penn State Unversity - CE 336 Tikalsky & Tepke

59 Penn State Unversity - CE 336 Tikalsky & Tepke
Insect Deterioration Causes Termites, bees, ants, beetles, grubs Food Dwelling Oxygen & some carbon dioxide Moisture Mechanisms Biological destruction Termites – bore holes Beetles – hatching larvae Penn State Unversity - CE 336 Tikalsky & Tepke

60 Penn State Unversity - CE 336 Tikalsky & Tepke
Insect Deterioration Manifestations Tunnels Large holes Fecal matter “Fingerprints” Prevention Same as for fungi Mechanical barriers Regional problems… Penn State Unversity - CE 336 Tikalsky & Tepke

61 Weathering & Photochemical Deterioration
Causes Sunlight, wind, rain, snow exposure Mechanisms Photochemical cell damage Oxidation Shrinkage & Swelling from wetting & drying cycles Erosion from wind & water Penn State Unversity - CE 336 Tikalsky & Tepke

62 Weathering & Photochemical Deterioration
Manifestations Lightening, darkening of wood Ultimately, a gray or silver color Protection Paint or other coatings Comments Precursor to decay Penn State Unversity - CE 336 Tikalsky & Tepke

63 Penn State Unversity - CE 336 Tikalsky & Tepke
Mechanical Wear Causes Friction Mechanisms Erosion Applications Stairs, bridge decks Protection Hard wood Metal plates Penn State Unversity - CE 336 Tikalsky & Tepke

64 Thermal Deterioration
Causes Temps above about 140 oF Very slow degradation (many years) Temps above 212 oF Faster degradation (months to years) Mechanisms Microstructure Degradation Pyrolysis Conversion of components to CO2, CO, methane, water vapor, acids Penn State Unversity - CE 336 Tikalsky & Tepke

65 Thermal Deterioration
Manifestations Color changes Odors Charcoal Physical / Mechanical Implications Strength reduction Weight reduction Impact resistance reduction Penn State Unversity - CE 336 Tikalsky & Tepke

66 Penn State Unversity - CE 336 Tikalsky & Tepke
Fire Damage Causes High temperatures Above 500 oF, will ignite and support itself Fire! Mechanisms Degradation of microstructure through combustion Manifestations Char Penn State Unversity - CE 336 Tikalsky & Tepke

67 Fire Damage Preservation
Large sections better (char acts as a barrier) Gypsum board Fire-retardants Foamers or Non-combustable gas producers Non-toxic, water-borne Application Caution Corrosion of Connectors Possible Strength Reduction Penn State Unversity - CE 336 Tikalsky & Tepke

68 Chemical Deterioration
Causes pH > 11 pH <2 Foreign species Mechanisms Dissolution of extractives and hemicelluloses Delignification (high pH) Hydrolysis (low pH) Oxidation Penn State Unversity - CE 336 Tikalsky & Tepke

69 Chemical Deterioration
Preservation Impermeable & dense woods Implications Reduction in strength and toughness Wood embrittlement (low pH) Shrinkage (high pH) Comments In general, wood is a good resister Penn State Unversity - CE 336 Tikalsky & Tepke

70 Connection Deterioration
Causes Chemical related issues Moisture in… Acidic wood Wood treated w/ salts Wood near salt water Mechanisms Corrosion Wood degradation Penn State Unversity - CE 336 Tikalsky & Tepke

71 Connection Deterioration
Preservation Dense wood Impermeable wood Corrosion-resistant fasteners Selection of preservation treatment Manifestations / Implications Soft wood Corrosion stains Complete connection degradation Penn State Unversity - CE 336 Tikalsky & Tepke

72 Penn State Unversity - CE 336 Tikalsky & Tepke
Code Provisions NDS ASD & LRFD code Assertions in frontal matter Load factors Moisture (19 percent threshold) Temperature (100 oF for no reduction; 150 oF threshold) Preservation (based on testing) Fire-retardation (based on testing) AWPA test standards Procedure for evaluating preservation products and wood products Penn State Unversity - CE 336 Tikalsky & Tepke

73 Penn State Unversity - CE 336 Tikalsky & Tepke
Termite Damage Penn State Unversity - CE 336 Tikalsky & Tepke

74 Penn State Unversity - CE 336 Tikalsky & Tepke
Cubical Wood Rot Penn State Unversity - CE 336 Tikalsky & Tepke

75 Penn State Unversity - CE 336 Tikalsky & Tepke
Powder Beetle Damage Penn State Unversity - CE 336 Tikalsky & Tepke

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Termite Regions Penn State Unversity - CE 336 Tikalsky & Tepke

77 Penn State Unversity - CE 336 Tikalsky & Tepke
Shipworm Borings Penn State Unversity - CE 336 Tikalsky & Tepke

78 Penn State Unversity - CE 336 Tikalsky & Tepke
Delignification Penn State Unversity - CE 336 Tikalsky & Tepke

79 Connection Deterioration
Penn State Unversity - CE 336 Tikalsky & Tepke

80 Penn State Unversity - CE 336 Tikalsky & Tepke
Dry Rot Penn State Unversity - CE 336 Tikalsky & Tepke


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