Timber Design Lecture

SUBJECT COURSE CODE TIME ROOM NUMBER TOPIC

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INSTRUCTOR

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Timber Design (Lec) for Archie’s CEET 512 / T01 14:30-17:30 W CET 606 Defects and other Mechanical Properties of structural wood Engr. Esmeraldo C. Baula

I. Objective : To discuss the problems of timber design and construction and to present information that will enable the students to appreciate the relevance and importance of the subject matter to the actual application. II. Course Outline : 1. Characteristics and classifications of wood 2. Unit stresses 3. Working stresses for structural members 4. Properties of sections 5. Bending moments and shear 6. Shearing stress in beams 7. Compression perpendicular to grain 8. Deflection of beams 9. Design of beams 10. Notched Beams 11. Joists and Rafters 12. Plank and laminated floors 13. Wood columns 14. Combined bending and axial loading 15. Bolted joints 16. Timber connectors 17. Stresses in trusses 18. Trussed Rafters and Framing Anchors 19. Trussed beams 20. Timber Purlins 21. Compound beams 22. Stud walls 23. Laminated lumbers 24. Plywood Construction

Definitions: Timber – is a wood used as a structural material III. Characteristics and Classification of Wood 1. Characteristics of wood as building materials – it is an organic material (not processed like; steel, concrete etc.) 1.1 Factors that influence the strength of structural timber materials are: a. density b. material defects c. moisture content 1.2 Two groups of structural members used for building purposes. a. Softwoods – coniferous or cone bearing pines or cypress. Two most extensively used in United States. a.a) Southern Pines a.b.) Douglas firs b. Hardwoods – Non-Cone bearing, broad leaves b.a Oak b.b Maples

1.3 Density of Wood - strength of wood is closely related to its density 1.3a Weight of wood is approximately 1.53 times the weight of water. 1.3b Density of wood is 40 lb/cu.ft. or 317 N/m3 1.4 Defects in Lumber – brought about by processing of seasoning. Defect of a wood affects its strength and durability * check – separation across the annual ring.

* Shake - separation along the annual ring – reduces the resistance to shear not to longitudinal compression.

* Split - separation along the longitudinal fibers.

* Decay - disintegration of wood substance due to the action of wood destroying fungi: (solve by impregnation of wood preservatives paint)

* Wave – inadequate cross-sectional area brought about by decays.

* Knot – is a portion of a branch incorporated in the body of a tree. Allowable working stresses are affected. * Pitch Pocket - opening parallel to the annual rings containing pitch either solid or liquid.

1.5 Classification of Softwood lumber Lumber – is defined as the product of the saw and planing mill not further manufactures thru by sawing, resawing. Three main classes of softwood lumber under American Lumber Standard System (ALSS) 1. Yard lumber 2. Structural material (Timber) 3. Factory and Shop lumber 1.5.1 – Yard Lumber a) less than 5 inches thick b) found in retail lumber yards c) includes boards and sidings less than 2 inches thick: C.1) flooring C.2) laths C.3) shingles C.4) Pickets C.5 Finishing materials

C.6 Planks of less than 4 inches C.7 Joists less than 4 inches thick C.8 Studdings and common sizes of joists.

1.6 Structural Materials – timbers a) Joists and Planks (2”-4” thick or more wide) b) Beams and stringers (5” or more thick and 8” or more wide) c) Posts and timbers (5” x 5” and larger) 1.7 Factory and Shop lumber – it is used for general millwork and other industrial commodities. a) Factory plank graded for door b) Sash and other cuttings 1/4m or more thick and 5 inches or more wide. ENGINEERING UNITS AND ABBREVIATIONS Unit

General Usage

Force Length Area Force (or load) per Unit of length Force (or load) per Unit of area

Newton, N. kN Mm, m Mm2 m2 N per mm N per m N per mm2 N per m2

Volume Weight (force) per Unit volume

Mm3 , m3 N per m3

Illustrations and solutions N, kN

Solutions and answers N, kN

N/mm N/m N/mm2 Mpa N/m2

N/mm N/m N/mm2 , kN/mm2 N/m2 , MPa GN/m2 , GPa

N/m3

N/m3

Classification of Softwood Lumber: Finish *4 in. and under thick and 16 in. and under wide).

SOFT WOOD LUMBER (This classificati on applies to rough or dressed lumber sizes given are nominal).

YARD LUMBER (lumber less than 5 in. thick, intended for general building purposes grading based on used of the entire piece).

Common boards (less than 2 in, thick and 1 or more in. wide).

STRUCTURAL LUMBER (lumber 5 or more in. thick and wide, except joists and planks grading based on strength and on use of entire piece).

Joists and planks (2 to 4 in. thick and 4 or more in. wide). Beams and stringers (5 or more in. thick and 8 or more in. wide). Posts and timbers (5 x 5 in. and larger.

Common dimension (2 in. and under 5 in. thick and under 5 in. in wide).

Factory plank FACTORY AND graded for door, SHOP LUMBER sash and other (grading based cuttings 1 ½ or area of piece more in. thick suitable for and 5 or more cuttings of certain in. wide. Shop size and quality). lumber graded for general cut-

Grades A. B. C. D. No. 1 No. 2 No. 3 No. 4 Plans (2in. No. 5 and under 4 No. 1 in. thick No. 2 and 8 or No. 3 more in. No. 1 wide) No. 2 Scantling (2 No. 3 in. and No. 1 under 5 in. No. 2 thick and No. 3 less than 8 in. wide). Heavy joists (4 in. thick and 8 or more in wide).

Association grading rules should be referred to for standard grades and sizes.

up purposes.

1.8 Dimension Lumber – is yard lumber 2 in. but less than 5 in. thick and 2 in. or more wide. It includes all yard lumber except boards, strips, and timbers. Planks, scantling, studding, and heavy joists are included under dimension lumber, and their sizes are given in table.

1.9 Structural Materials Beams and stringers - nominal thickness, 5 in. or more; nominal widths, 8 in. or more; standard sizes, SIS, SIE, S2S, S4S ½ in. off each way.

in. off,

Joists and planks – nominal thickness, 2 in. to, but not including, 5 in. nominal widths, 4 in. or more; standard thickness, SIS or S2S, 3/8 in. off; standard widths, SIE or S2E, 4 in., 3/8 and 6 in. or more, ½ in. off. Posts and timbers - Nominal sizes, 5 x 5 in. and larger; standard sizes, S1S, S1E. S2S, or S4S, ½ in. off each way.

Standard lengths of all three classes are in multiples of 2 ft. except for the following odd lengths which are allowed. 2” x 4”, 6” x 8” 2” x 8” 2” x 10” 8” x 8”, 10” x 10”, 12” x 12”, 14” x 14”,

9’ and 11’ 13’ 13’ and 15’

16” x 16”, 18” x 18” 6” x 16”, 6” x 18”, 8” x 16”, 8” x 18”

11’ and 13’

Allowable Unit Stresses in Pounds per Square Inch Species and Commercial Grade

CYPRESS, SOUTHERN, INLAND TYPE 1700 f Grade 1300 f Grade 1450 c Grade 1200 c Grade DOUGLAS FIR, COAST REGION

Extreme fiber in Bending Horizont f1 al Shear, and H Tension Parallel to Grain, t J.& P.-B.&S. J.& P.-B.&S. P.&T. P.&T.

Compression Compression Modulus of Perpendicular Perpendicular Elasticity, to Grain, to Grain, E c1 c

1700 1300 …. ….

145 120 …. ….

360 360 360 360

1425 1125 1450 1200

1,320,000 1,320,000 1,320,000 1,320,000

J.&P. J.&P. J.&P. J.&P J.&P B.&S. B.&S. B.&S. B.&S. P.&T. P.&T. P.&T. P.&T.

2050 1900 1750 1500 1200 2050 1900 1750 1500 1900 1750 1500 1200

120 120 120 120 95 120 120 120 120 120 120 120 120

455 415 455 390 390 455 415 455 390 455 415 455 390

1650 1500 1400 1200 1000 1500 1400 1200 1000 1650 1500 1400 1200

1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000

Select Structural Prime Structural Common Structural Utility Structural Select Structural PINE SOUTHERN

J.& P.-B.&S. J.&P. J.&P. J.&P. P.&T

1300 1200 1100 950 ….

85 60 60 60 …

360 360 360 360 360

850 775 650 600 850

1,210,000 1,210,000 1,210,000 1,210,000 1,210,000

Dense Structural 86 Dense Structural 72 Dense Structural 65 Dense Structural 58 No. 1 Dense SR No. 1 SR No. 2 Dense SR No. 2 SR Dense Structural 86 Dense Structural 72

3”&4” thick “ “ “ “ “ “ “ 5”thick & up “

2900 2350 2050 1750 1750 1500 1400 1200 2400 2000

150 135 120 105 120 120 105 105 150 135

455 455 455 455 455 390 455 390 455 455

2200 1800 1600 1450 1750 1500 1059 900 1800 1550

1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000

Dense Select Structural Select Structural Dense Construction Construction Standard Dense Select Structural Select Structural Dense Construction Construction Dense Select Structural Select Structural Dense Construction Construction HEMLOCK EASTERN

Allowable Unit Stresses in Pounds per Square Inch Species and Commercial Grade

Extreme fiber in Bending Horizont f1 al Shear, and H Tension Parallel to Grain, t

Compression Compression Modulus of Perpendicular Perpendicular Elasticity, to Grain, to Grain, E c1 c

PINE SOUTHERN Dense Structural 65 Dense Structural 58 No. 1 Dense SR No. 1 SR No. 2 Dense SR No. 2 SR

5”thick & up “ “ “ “ “

1800 1600 1600 1400 1400 1200

120 105 120 120 105 105

455 455 455 390 455 390

1400 1300 1500 1300 1050 900

1,760,000 1,760,000 1,760,000 1,760,000 1,760,000 1,760,000

J.&P. J.& P.-B.&S J.& P.-B.&S J.& P.-B.&S B.&S. P.&T. P.&T. P.&T.

2150 1900 1700 1450 1300 …. …. ….

145 145 145 120 120 … … …

600 600 600 600 600 600 600 600

1550 1375 1200 1050 950 1325 1200 1075

1,650,000 1,650,000 1,650,000 1,650,000 1,650,000 1,650,000 1,650,000 1,650,000

J.& P.-B.&S J.& P.-B.&S P.&T. P.&T.

1700 1300 …. ….

110 95 … …

320 320 320 320

1450 1100 1450 1100

1,320,000 1,320,000 1,320,000 1,320,000

J.&P. J.&P J.&P

1450 1300 1200

110 95 95

300 300 300

1050 975 900

1,320,000 1,320,000 1,320,000

OAK, RED and WHITE ‘2150 f Grade 1900 f Grade 1700 f Grade 1450 f Grade 1300 f Grade 1325 c Grade 1200 c Grade 1075 c Grade REDWOOD Dense Structural Heart Structural Dense Structural Heart Structural SPRUCE, EASTERM 1450 f Structural Grade 1300 f Structural Grade 1200 f Structural Grade

VALUES OF SIN2 θ AND COS2 θ FOR VARIOUS VALUES OF θ Sin2 θ 1.00000

θ (degree) 0

Cos2 θ 1.00000

Sin2 θ 0.50000

θ (degree) 45

Cos2 θ 0.50000

0.00760 0.03015 0.06698 0.11698 0.17860 0.25000 0.32899 0.41318 0.50000

5 10 15 20 25 30 35 40 45

0.99240 0.96985 0.93302 0.88302 0.82140 0.75000 0.67101 0.58682 0.50000

0.58682 0.67101 0.75000 0.82140 0.88302 0.93302 0.96985 0.99240 1.0000

50 55 60 65 70 75 80 85 90

0.41318 0.32899 0.25000 0.17860 0.11698 0.06698 0.03015 0.00760 0.0000

PROPERTIES OF AMERICAN STANDARD SIZES OF YARD LUMBER AND TIMBER Nominal Size, in Inches

b

American Standard Dressed Size (S4S) in Inches

Area of Section in Inches2

Moment of Inertia, in Inches Ix – x = bh3 /12

IY-Y = b3h/12

Section Modulus, in Inches2 Sx-x = bh2/6

SY – Y = b2h/6

h 2x4 2x6 2x8 2 x 10

b h 1 5/8 x 3 5/8 1 5/8 x 5 5/8 1 5/8 x 7 ½ 1 5/8 x 9 1/2

A=bxh 5.89 9.14 12.19 15.44

6.45 24.10 57.13 116.10

1.30 2.01 2.68 3.40

3.56 8.57 15.23 24.44

1.60 2.48 3.30 4.18

2 x 12 2 x 14 2 x 16 2 x 18

1 5/8 x 11 ½ 1 5/8 x 13 ½ 1 5/8 x 15 ½ 1 5/8 x 17 1/2

18.69 21.94 25.19 28.44

205.95 333.18 504.27 725.75

4.11 4.83 5.54 6.25

35.82 49.36 65.07 82.94

5.06 5.94 6.82 7.70

3x4 3x6 3x8 3 x 10

2 5/8 x 3 5/8 2 5/8 x 5 5/8 2 5/8 x 7 ½ 2 5/8 x 9 ½

9.52 14.77 19.69 24.94

10.42 38.93 92.29 187.55

5.46 8.48 11.30 14.32

5.75 13.84 24.61 39.48

4.16 6.46 8.61 10.91

3 x 12 3 x 14 3 x 16

2 5/8 x 11 ½ 2 5/8 x 13 ½ 2 5/8 x 15 ½

30.19 35.44 40.69

332.69 538.21 814.60

17.33 20.35 23.36

57.86 79.73 105.11

13.21 15.50 17.80

3 x 18

2 5/8 x 17 1/2

45.94

1,172.36

26.38

133.98

20.10

4x4 4x6 4x8 4 x 10 4 x 12 4 x 14 4 x 16 4 x 18

3 5/8 x 3 5/8 3 5/8 x 5 5/8 3 5/8 x 7 ½ 3 5/8 x 9 1/2 3 5/8 x 11 ½ 3 5/8 x 13 ½ 3 5/8 x 15 ½ 3 5/8 x 17 ½

13.14 20.39 27.19 34.44 41.69 48.94 56.19 63.44

14.39 53.76 127.44 259.00 459.43 743.24 1,124.92 1,618.98

14.39 22.33 29.77 37.71 45.65 53.59 61.53 69.47

7.94 19.12 33.98 54.53 79.90 110.11 145.15 185.03

7.94 12.32 16.43 20.81 25.19 29.57 33.95 38.33

6x6 6x8 6 x 10

5½x5½ 5½x7½ 5½ x9½

30.25 41.25 52.25

76.25 193.36 392.96

76.26 13.96 131.71

27.73 51.56 82.73

27.73 37.81 47.90

6 x 12 6 x 14 6 x 16 6 x 18

5 ½ x 11 ½ 5 ½ x 13 ½ 5 ½ x 15 ½ 5 ½ x 17 ½

63.25 74.25 85.25 96.25

697.07 1,127.67 1,706.78 2,456.38

159.44 187.17 214.90 242.63

121.23 167.06 220.23 280.73

57.98 68.06 78.15 88.23

8x8 8 x 10 8 x 12

7½x7½ 7½x9½ 7 ½ x 11 ½

56.25 71.25 86.25

263.67 535.86 950.55

263.67 333.98 404.30

70.31 112.81 165.31

70.31 89.06 107.81

8 x 14 8 x 16 8 x 18

7 ½ x 13 ½ 7 ½ x 15 ½ 7 ½ x 17 1/2

101.25 116.25 131.25

1,537.73 2,327.42 3,349.61

474.61 544.92 615.23

227.81 300.31 382.81

126.56 145.31 164.06

10 x 10 10 x 12

9½x9½ 9 ½ x 11 ½

90.25 109.25

678.76 1,204.03

678.76 821.65

142.90 209.40

142.90 172.98

10 x 14 10 x 16 10 x 18

9 ½ x 13 ½ 9 ½ x 15 ½ 9 ½ x 17 ½

128.25 147.25 166.25

1,947.80 2,948.07 4,242.84

964.55 1,107.44 1,250.34

288.56 380.40 484.90

203.06 233.15 263.23

12 x 12 12 x 14 12 x 16 12 x 18 14 x 14 14 x 16 14 x 18 14 x 20

11 ½ x 11 ½ 11 ½ x 13 ½ 11 ½ x 15 ½ 11 ½ x 17 1/2 13 ½ x 13 ½ 13 ½ x 15 ½ 13 ½ x 17 ½ 13 ½ x 19 1/2

132.25 155.25 178.25 201.25 182.25 209.25 236.25 263.25

1,457.51 2,357.86 3,568.71 5,136.07 2,767.92 4,189.36 6,029.30 8,341.73

1,457.51 1,710.98 1,964.46 2,217.94 2,767.92 3,177.98 3,588.05 3.998.11

253.48 349.31 460.48 586.98 410.06 540.56 689.06 855.56

253.48 297.56 341.65 385.73 410.06 470.81 531.56 592.31

ALLOWABLE UNIT STRESSES FOR STRESS-GRADE TIMBER. MPa

Species and commercial grade Cypress, southern: Select Common

Tension and Longitudi extreme nal shear fiber in bending 11.7 9.0

1.00 0.83

Compression Perpendi Parallel cular to to grain grain 2.50 2.50

9.85 7.75

Modulus of elasticity

9 100

Douglas fir, coast: Dense select Select Dense structural Common Hemlock, western: Select Common Oak, red and white: Select Common Pine, southern: Dense select Select Dense structural Common Spruce, eastern: Select common

14.8 13.0 11.7 10.0

1.0 0.83 1.00 0.83

3.14 2.86 3.14 2.70

10.70 10.00 9.15 8.30

12 200

11.1 10.0

0.69 0.69

3.48 3.48

7.60 7.42

10 650

13.0 10.0

1.00 0.83

4.15 4.15

9.50 7.25

11 400

16.6 13.8 11.1 8.3

0.83 0.83 0.83 0.83

3.14 3.14 3.14 2.70

12.10 9.65 7.95 6.90

12 200

10.1 8.3

0.76 0.66

2.07 2.07

7.25 6.20

9 100