Close up of Vessel & Cell
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Transcript of Close up of Vessel & Cell
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Introduction to Woods1
Close up of Vessel & Cell
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Introduction to Woods2
Wood Behavior
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Introduction to Woods3
Advantages of Wood
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Introduction to Woods4
Disadvantages of Woods
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Introduction to Woods5
Stresses Applied to Wood
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Introduction to Woods6
Stress – Strain Relationship
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Introduction to Woods7
Shrinkage & Swelling
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Introduction to Woods8
Shrinkage & Swelling
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Introduction to Woods9
Stress Grading
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Introduction to Woods10
Stress Grading
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Introduction to Woods11
Visual Grading
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Introduction to Woods12
Machine Grading
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Introduction to Woods13
Grading Organizations
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Introduction to Woods14
Grading Lumber
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Properties of Wood and Lumber Grades
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Sawn Lumber: Wood members that have been manufactured by cutting a member directly from a log.
Design values for sawn lumber depend onspecies groupgradeLoad durationmoisture contentSize
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Grading Structural Lumber
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Lumbers are graded based on size and number of growth (strength-reducing) characteristics they have (knots, checks, shakes, splits,...)
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Introduction to Woods18
Grade Types
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Grading Structural Lumber
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Visually Graded
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Grading Structural LumberVisually Graded WWP: Lumber Grading Agency 12 : Mill Number SEL STR: Lumber Grade DOUG FIR-L: Lumber Species S-GRN: Moisture ContentMachine Stress
Rated 1650:Nominal Bending Stress,
psi 1.5E: Modulus of Elasticity,
million psi20
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Sizes Categories
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There are three main size categories of lumber:
Boards: 1 to 1 1/2” thick, 2” and widerDimension lumber: 2 to 4” thick 2” and
widerTimbers: 5” and thicker, 5” and widerNote 1: Thickness is the smaller cross sectional
dimension and width is the larger dimension.Note 2: Dressed dimensions (S4S, Surfaced four
Sides) are less than nominal dimensions (1.5”x3.5” for a 2x4). For stress calculations, dressed dimensions are used.
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Dimension LumberJoists and Planks
Joists: 2-4 in thick and at least 6 in wide (graded based on bending strength on narrow edge)
Planks: 2-4 in thick and at least 6 in wide (graded based on bending strength on wider dimension)
Light Framing and DeckingLight Framing: 2-4 in thick and 2-4 in wide
(studs, joists and rafters)Decking: 2-4 in thick and 4 in or wider (used
on their wider dimension)
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TimbersBeams and Stringers: at least 4”thick and
at least 2” wider than they are thick; installed horizontally and ranked based on bending stress when loaded on the narrower dimension
Posts and Timbers: have a width that is no more then 2” greater than thickness (square or nearly square); installed vertically and ranked based on compression parallel to the grain
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Design Values
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An important part of wood design is being able to determine design values for the following mechanical properties:Bending stress, FbTension stress parallel to grain, FtShear stress, FvCompressive stress parallel to grain, FcCompressive stress perpendic. to grain, FcModulus of Elasticity, E
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Wet Service Factor (CM) Cont.
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The tabulated values for sawn lumber apply to members with EMC of 19% or less. If MC in service will exceed 19% for an extended period of time, the tabulated values are to be multiplied by CM (CM values are less than one and are given at the beginning of Table 4A).
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Cr= Repetitive Member Factor
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A 15% increase in the tabulated Fb for repetitive-member systems is recognized in the NDS. A repetitive-member system is defined as one that has:1. Three or more parallel members of dimension
lumber2. Members spaced not more than 24 in. o.c.3. Members connected together by a load-
distributing element such as roof, floor, or wall sheathing.
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Cr= Repetitive Member Factor
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If one member should become overloaded, parallel members come into play.
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