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

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Presentation on theme: "Penn State Unversity - CE 336 Tikalsky & Tepke 1 Wood Properties, Deterioration & Preservation."— Presentation transcript:

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

2 Penn State Unversity - CE 336 Tikalsky & Tepke2 Introduction to Wood 600 Different Species of trees exist in U.S are commercially used Most are forested Growing quantities are farmed

3 Penn State Unversity - CE 336 Tikalsky & Tepke3 Common Species of Wood Fir Hemlock Pine Poplar Redwood Spruce Cedar Hickory Maple Oak Ash Birch Cypress Walnut Gum

4 Penn State Unversity - CE 336 Tikalsky & Tepke4 Anatomy of a Tree Root - absorbs moisture Trunk - mechanical strength  rigidity  height  two way transfer moisture UP sap DOWN

5 Penn State Unversity - CE 336 Tikalsky & Tepke5 Anatomy of a Tree Crown - Area of chlorophyll for photosynthesis  O 2 given off  CO 2 absorbed Bark - protective layer

6 Penn State Unversity - CE 336 Tikalsky & Tepke6 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

7 Penn State Unversity - CE 336 Tikalsky & Tepke7 Anatomy of a Tree Heartwood: storage for food.  comprised of dead cells solid filled cells  mechanically strong  No starches  Dense (nearly impermeable)

8 Penn State Unversity - CE 336 Tikalsky & Tepke8 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)

9 Penn State Unversity - CE 336 Tikalsky & Tepke9 Anatomy of a Tree Aged Sapwood (moisture removed)  same strength as heartwood  same density as heartwood  contains starches  permeable

10 Penn State Unversity - CE 336 Tikalsky & Tepke10 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

11 Penn State Unversity - CE 336 Tikalsky & Tepke11 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)

12 Penn State Unversity - CE 336 Tikalsky & Tepke12 Hardwoods Broad Leaves Deciduous Grow Slowly Expensive Cross-Section has vessels Spring and Summerwood

13 Penn State Unversity - CE 336 Tikalsky & Tepke13 Angiosperm Cells Cell Structure  cavity or Lumen in the center  fiber around the cavity  wall around fibers

14 Penn State Unversity - CE 336 Tikalsky & Tepke14 Softwoods Needles Conifer Grow Quickly Cheaper Small Summerwood pores

15 Penn State Unversity - CE 336 Tikalsky & Tepke15 Gymnosperm Cells Cells are individual tubes for transport Cells have pits  which act as permeable vents between cells

16 Penn State Unversity - CE 336 Tikalsky & Tepke16 Cell Walls and Connectivity Cellulose  Long chains of fiber  strong in tension Lignin  glue between cellulose chains  shear resistance and durability

17 Penn State Unversity - CE 336 Tikalsky & Tepke17 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

18 Penn State Unversity - CE 336 Tikalsky & Tepke18 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

19 Penn State Unversity - CE 336 Tikalsky & Tepke19 Moisture Content “shrinkage” is from the removal of bound water “swelling” will occur if water is reintroduced

20 Penn State Unversity - CE 336 Tikalsky & Tepke20 Moisture Content "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. F.S.P. E.M.C. 0% M.C. Free Water Bound Water Wt. of Solid Wood

21 Penn State Unversity - CE 336 Tikalsky & Tepke21 Moisture Content 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 % F.S.P. E.M.C. 0% M.C. Free Water Bound Water Wt. of Solid Wood

22 Penn State Unversity - CE 336 Tikalsky & Tepke22 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

23 Penn State Unversity - CE 336 Tikalsky & Tepke23 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

24 Penn State Unversity - CE 336 Tikalsky & Tepke24 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

25 Penn State Unversity - CE 336 Tikalsky & Tepke25 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

26 Penn State Unversity - CE 336 Tikalsky & Tepke26 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

27 Penn State Unversity - CE 336 Tikalsky & Tepke27 Lumber Grade Stamp Lumber Grading Association Mill number Lumber grade Species Moisture condition (at time of surfacing)

28 Penn State Unversity - CE 336 Tikalsky & Tepke28 Grade Stamps – Dimensional Lumber

29 Penn State Unversity - CE 336 Tikalsky & Tepke29 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.

30 Penn State Unversity - CE 336 Tikalsky & Tepke30 Timber Defects

31 Penn State Unversity - CE 336 Tikalsky & Tepke31 Timber Defects

32 Penn State Unversity - CE 336 Tikalsky & Tepke32

33 Penn State Unversity - CE 336 Tikalsky & Tepke33 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

34 Penn State Unversity - CE 336 Tikalsky & Tepke34 Sawing Patterns / Timber Defects

35 Penn State Unversity - CE 336 Tikalsky & Tepke35 Lumber Timbers (posts, beams, girders and stringers) Dimension lumber (light framing) Boards (siding, flooring, planking)

36 Penn State Unversity - CE 336 Tikalsky & Tepke36 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

37 Penn State Unversity - CE 336 Tikalsky & Tepke37 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

38 Penn State Unversity - CE 336 Tikalsky & Tepke38 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)

39 Penn State Unversity - CE 336 Tikalsky & Tepke39 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

40 Penn State Unversity - CE 336 Tikalsky & Tepke40 Glu-Laminated Timber geometry, long spans Engineered Properties Shape X-section Changes

41 Penn State Unversity - CE 336 Tikalsky & Tepke41 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

42 Penn State Unversity - CE 336 Tikalsky & Tepke42 Deterioration Mechanisms Fungi & bacteria deterioration Insect deterioration Marine borer deterioration Weathering & photochemical deterioration Mechanical wear Thermal deterioration Fire damage Chemical deterioration Connection deterioration

43 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 44 Fungi & Bacteria Fungi  Non decay types (cosmetic problems only) Molds  Serviceability problem Stains

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

46 46 Fungi Deterioration Types of Decay Fungi  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 & Tepke47 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

48 Penn State Unversity - CE 336 Tikalsky & Tepke48 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 Humid Brown, cubical Caniophoria Puteana (Cellular fungus) Buildings Longitudinal splits or cracks, then nearly identical to dry- rot. Brittle. Very high humidity – water leaks, condensation Brown, cubical Paxillus Panuoides Softwoods, buildings Fibrous, yellow, purple Very moist conditions Brown, cubical 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 mushroomMoist Brown, cubical Amyloporia xantha greenhouses Thin plate, small yellow pores, smells like lemons --- Brown, cubical Phellinus Contiguus External joints (softwood window frames) Fibrous strings, brown woolyMoistWhite

49 49 Fungi Deterioration Mechanisms  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 & Tepke50 Decay Prevention Durable, seasoned wood Protection from water sources (vapor barriers, ventilation)  Pipes Removal of deteriorated elements Heartwood (extractives) Treatments

51 Penn State Unversity - CE 336 Tikalsky & Tepke51 Resistant & Very ResistantModerately ResistantSlightly or Non-Resistant Bald Cypress (old growth)Bald Cypress (new growth)Alder CatalpaDouglas FirAshes CedarsHoney LocustAspens Black CherryWestern LarchBasswood Arizona CypressSwamp Chestnut OakBeech JunipersEastern White PineBirches Black Locust a Longleaf PineCottonwood Red Mullberry a Slash PineElms Bur OakTamarackHackberry 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 Yew a Willows Western Red Cedar Yellow Poplar

52 Penn State Unversity - CE 336 Tikalsky & Tepke52 Preservation of Timber Preservation Treatments (advantages + problems)  Oil-borne ($)  Water-soluble (most used)  Organic solvents

53 Penn State Unversity - CE 336 Tikalsky & Tepke53 Preservation of Timber Desired preservative properties  Toxic to fungi, insects, borers  No leaching  Easy penetration  Corrosion resistant  Economic  Unscented

54 Penn State Unversity - CE 336 Tikalsky & Tepke54 Preservation of Timber Application  Apply preservatives to dry lumber Techniques  Pressure  Diffusion  Immersion  Spraying  Hot & cold open tank

55 Penn State Unversity - CE 336 Tikalsky & Tepke55 Preservation of Timber Oil-Borne Preservatives (eg. Coal-Tar Creosote)  Pressure impregnation  Brush-on  Flammable unless weathered  Odor and unfinishable  No indoor use

56 Penn State Unversity - CE 336 Tikalsky & Tepke56 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

57 Penn State Unversity - CE 336 Tikalsky & Tepke57 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

58 Penn State Unversity - CE 336 Tikalsky & Tepke58 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

59 Penn State Unversity - CE 336 Tikalsky & Tepke59 Insect Deterioration Causes  Termites, bees, ants, beetles, grubs Food Dwelling  Oxygen & some carbon dioxide  Moisture Mechanisms  Biological destruction  Termites – bore holes  Beetles – hatching larvae

60 Penn State Unversity - CE 336 Tikalsky & Tepke60 Insect Deterioration Manifestations  Tunnels  Large holes  Fecal matter  “Fingerprints” Prevention  Same as for fungi  Mechanical barriers Regional problems…

61 Penn State Unversity - CE 336 Tikalsky & Tepke61 Weathering & Photochemical Deterioration Causes  Sunlight, wind, rain, snow exposure Mechanisms  Photochemical cell damage  Oxidation  Shrinkage & Swelling from wetting & drying cycles  Erosion from wind & water

62 Penn State Unversity - CE 336 Tikalsky & Tepke62 Weathering & Photochemical Deterioration Manifestations  Lightening, darkening of wood  Ultimately, a gray or silver color Protection  Paint or other coatings Comments  Precursor to decay

63 Penn State Unversity - CE 336 Tikalsky & Tepke63 Mechanical Wear Causes  Friction Mechanisms  Erosion Applications  Stairs, bridge decks Protection  Hard wood  Metal plates

64 Penn State Unversity - CE 336 Tikalsky & Tepke64 Thermal Deterioration Causes  Temps above about 140 o F Very slow degradation (many years)  Temps above 212 o F Faster degradation (months to years) Mechanisms  Microstructure Degradation  Pyrolysis  Conversion of components to CO 2, CO, methane, water vapor, acids

65 Penn State Unversity - CE 336 Tikalsky & Tepke65 Thermal Deterioration Manifestations  Color changes  Odors  Charcoal Physical / Mechanical Implications  Strength reduction  Weight reduction  Impact resistance reduction

66 Penn State Unversity - CE 336 Tikalsky & Tepke66 Fire Damage Causes  High temperatures Above 500 o F, will ignite and support itself  Fire! Mechanisms  Degradation of microstructure through combustion Manifestations  Char

67 Penn State Unversity - CE 336 Tikalsky & Tepke67 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

68 Penn State Unversity - CE 336 Tikalsky & Tepke68 Chemical Deterioration Causes  pH > 11  pH <2  Foreign species Mechanisms  Dissolution of extractives and hemicelluloses  Delignification (high pH)  Hydrolysis (low pH)  Oxidation

69 Penn State Unversity - CE 336 Tikalsky & Tepke69 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

70 Penn State Unversity - CE 336 Tikalsky & Tepke70 Connection Deterioration Causes  Chemical related issues  Moisture in… Acidic wood Wood treated w/ salts Wood near salt water Mechanisms  Corrosion  Wood degradation

71 Penn State Unversity - CE 336 Tikalsky & Tepke71 Connection Deterioration Preservation  Dense wood  Impermeable wood  Corrosion-resistant fasteners  Selection of preservation treatment Manifestations / Implications  Soft wood  Corrosion stains  Complete connection degradation

72 Penn State Unversity - CE 336 Tikalsky & Tepke72 Code Provisions NDS ASD & LRFD code  Assertions in frontal matter  Load factors Moisture (19 percent threshold) Temperature (100 o F for no reduction; 150 o F threshold) Preservation (based on testing) Fire-retardation (based on testing) AWPA test standards  Procedure for evaluating preservation products and wood products

73 Penn State Unversity - CE 336 Tikalsky & Tepke73 Termite Damage

74 Penn State Unversity - CE 336 Tikalsky & Tepke74 Cubical Wood Rot

75 Penn State Unversity - CE 336 Tikalsky & Tepke75 Powder Beetle Damage

76 Penn State Unversity - CE 336 Tikalsky & Tepke76 Termite Regions

77 Penn State Unversity - CE 336 Tikalsky & Tepke77 Shipworm Borings

78 Penn State Unversity - CE 336 Tikalsky & Tepke78 Delignification

79 Penn State Unversity - CE 336 Tikalsky & Tepke79 Connection Deterioration

80 Penn State Unversity - CE 336 Tikalsky & Tepke80 Dry Rot


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