Timber Design Review

TIMBER DESIGN

1) Design the wooden joists so as not to exceed the allowable bending stress of 10.35 MPa. a) 50 x 200 mm c) 50 x 300 mm b) 50 x 250 mm d) 50 x 350 mm

2) Design the wooden joists so as not to exceed the allowable shearing stress of 0.85 MPa. a) 50 x 200 mm c) 50 x 300 mm b) 50 x 250 mm d) 50 x 350 mm

3) Design the wooden joists so as not to exceed the

1. CE Board Nov. 2003 A rectangular wooden beam has a span of 6 m. and carries a total uniform load of 25 kN/m including its own weight. The beam is made up of 80% stress grade Apitong with allowable stresses shown on table TM-6. Allowable Stress for Apitong 80% Stress Grade: Allowable bending - 16.5 MPa Compression parallel to grain = 9.56 MPa Compression perpendicular to grain =2.20MPa Shear parallel to grain = 1.73 MPa Modulus of elasticity = 7310 MPa

allowable deflection of 10 mm. Ew = 12135 MPa. a) 50 x 200 mm c) 50 x 300 mm b) 50 x 250 mm d) 50 x 350 mm

4. Problem The beam shown on the figure is subjected to a uniform load of 5 kN/m.

Allowable deflection = L/240 1) Which of the following gives the smallest dimension of beam that will not exceed the allowable bending stress? a) 220 x 440 mm c) 120 x 340 mm b) 320 x 540 mm d) 320 x 440 mm

2) Which of the following gives the smallest dimension of the beam that will not exceed the allowable shearing stress? a) 100 x 200 mm c) 250 x 500 mm b) 200 x 400 mm d) 300 x 600 mm

3) Which of the following gives the smallest dimension of the beam that will not exceed the allowable deflection? a) 100 x 200 mm c) 250 x 500 mm b) 200 x 400 mm d) 300 x 600 mm

2. Problem

1) Determine the placement "x" of the supports so that the shear stress in the beam is as small as possible. a) 1 m c) 3 m b) 2 m d) 4 m 2) a) b)

Determine the minimum shear stress if h = 175 mm. 0.86 MPa c) 0.66 MPa 0.96 MPa d) 0.76 MPa

3) Determine the value of "h" for a maximum flexural stress of 7.5 MPa. a) 100 mm b) 200 mm

c) 300 mm d) 400 mm

5. Problem

A floor is supported by 75 mm x 200 mm wooden joists spaced at 400 mm on centers with an effective span of 3 m. The total floor load transmitted to the joists is 5 kPa. Weight of wood of 6.3 kN/m3. Ew = 12 x 103 MPa.

The timber beam has a rectangular cross section having a width of 150 mm and a height of "h". Allowable bending stress is 10.5 MPa. and the allowable shearing stress is 0.35 MPa. Modulus of elasticity of wood is 13800 MPa.

1) Which of the following gives the maximum bending stress? a) 2.71 MPa c) 4.71 MPa b) 3.71 MPa d) 5.71 MPa

2) Which of the following gives the maximum shearing stress? a) 0.21 MPa b) 0.41 MPa

c) 0.51 MPa d) 0.31 MPa

3) Which of the following gives the maximum deflection of the joist? a) 2.18 mm c) 2.68 mm b) 3.18 mm d) 3.68 mm

3. Problem Wooden joists are used to support a floor load of 6.95 kPa. exclusive of its own weight. The joists will have an effective span of 4.25 m. and be placed at0.40 m. on centers. Weight of wood is 7.5 kN/m3.

1) Compute the height "h" so that it simultaneously reaches its allowable bending stress and allowable shearing stress. a) 150 mm c) 250 mm b) 200 mm d) 300 mm

2) Compute the maximum load P that the beam can support. a) 16 kN b) 13 kN

c) 15 kN d) 14 kN

3) Compute the max. deflection of the beam, neglecting its own weight. a) 3.71 mm c) 5.71 mm b) 4.71 mm d) 6.71 mm

6. Problem Four 50 mm x 200 mm section is to be framed to carry maximum shear on a cantilever span of 4 m. Neglecting the weight of the beam. Allowable shear stress is 0.70 MPa. 1) Compute the safe concentrated load that the beam could carry at a distance of 1.5 m. from the fixed support if the beam is arranged as shown.

14 MPa for bending, 0.80 MPa for shear parallel to the grain and deflection is 1/360 of span. 1) Which of the following gives the uniform load it could support if bending stress controls? a) 3.49 kN/m c) 2.49 kN/m b) 4.49 kN/m d) 5.49 kN/m

2) Which of the following gives the uniform load it could support if shear controls? a) 3.61 kN/m c) 2.61 kN/m b) 4.61 kN/m d) 5.61 kN/m 3) Which of the following gives the uniform load it could support if deflection controls? a) 3.32 kN/m c) 2.32 kN/m b) 4.32 kN/m d) 5.32 kN/m

8. Problem A 50 mm x 200 mm Guijo floor joists carries a dead load including its own weight of 2.5 kPa and a live load of 2 kPa. The joist has a simple span of 3.6 m. Weight bf wood is 7.5 kN/m3. Allowable stress: Bending = 15.8 MPa Shear = 0.90 MPa Modulus of elasticity of wood = 13800 MPa

a) 14.32 kN b) 15.32 kN

c) 11.67 kN d) 12.67 kN

2) Compute the safe concentrated load that the beam could carry at distance of 1.5 m. from the fixed if the beam is arranged as shown.

a) 14.32 kN b) 15.32 kN

c) 11.67 kN d) 12.67 kN

3) Compute the safe concentrated load that the beam could carry at a distance of 1.5 m. from the fixed support if it is arranged as shown.

Allowable deflection = 1/300 of span. Assume no impact allowance for live load.

1) Which of the following gives the spacing of the joists if bending controls? a) 0.52 m c) 0.72 m b) 0.62 m d) 0.82 m 2) Which of the following gives the spacing of the joists if shear controls? a) 0.54 m c) 0.74 m b) 0.64 m d) 0.84 m

3) Which of the following gives the spacing of the joists if deflection controls? a) 0.56 m b) 0.66 m

c) 0.76 m d) 0.86 m

9. Problem a) 18.667 kN b) 15.333 kN

c) 19.667 kN d) 16.333 kN

7. Problem

A simply supported beam carrying a uniform load has a span of 9 m. The beam has adequate lateral supports. Allowable stress: Bending = 10.21 MPa Shear = 0.85 MPa Modulus of elasticity of wood =13790 MPa

A masonry terrace of 75 mm concrete surface with 25 mm cement tiles rests on a 75 mm x 200 mm lumber spaced at 300 mm on centers acting as simple beam with an effective span of 3.6 m. Weight of wood is 7.5 kN/m3 and masonry to be 24 kN/m3. Ew= 13800 MPa. The allowable stresses are

Allowable deflection = 1/360 of span 1) Which of the following gives the depth of the beam so that when the allowable bending stress is reached the deflection of the beam is 1/360 of span?

a) 200 mm b) 300 mm

c) 400 mm d) 500 mm 2) Which of the following gives the value of the safe uniform load it could carry if shearing stress governs for a width of 250 mm? a) 14.741 kN/m c) 16.741 kN/m b) 15.741 kN/m d) 17.741 kN/m 3) Which of the following gives the value of the safe uniform load it could carry it bending stress governs for the same width? a) 9.50 kN/m c) 11.50 kN/m b) 10.50 kN/m d) 12.50 kN/m

10. CE Board May A timber beam having a simple span of 4 m. carries a total load including its own weight of 10 kN/m. lt has a width of 200 mm and a depth of 260 mm, used dressed dimension by reducing its dimensions by 10 mm. The wooden section is made up of 80% grade Apitong. Allowable bending stress, Fb = 16.5 MPa Modulus of elasticity of wood, Ew = 7310 MPa Allowable shearing stress, Fv = 1.75 MPa 1) Which of the following gives the max. flexural stress of the beam? a) 16.50 MPa c) 12.80 MPa b) 17.50 MPa d) 13.80 MPa

2) Which of the following gives the max. shearing stress of the beam? a) 2.73 MPa b) 1.73 MPa

1) Compute the width of the beam so that it will not exceed the allowable bending stress. a) 147 mm c) 183 mm b) 127 mm d) 163 mm 2) Compute the width of the beam so that it will not exceed the allowable shearing stress. a) 147 mm c) 183 mm b) 127 mm d) 163 mm

3) Compute the shearing stress at point C 50 mm below the top of the beam. a) 0.36 MPa b) 0.56 MPa

13. m

c) 0.42 MPa d) 0.62 MPa

Proble

A wooden rectangular beam 200 mm x 350 mm has a simple span of 6 m. Neglecting the weight of the beam.

c) 2.36 MPa d) 1.36 MPa

3) Which of the following gives the max. deflection of the beam? a) 16.43 mm b) 18.43 mm

11. m

c) 15.66 mm d) 17.66 mm

Proble

A 100 mm x 300 mm rectangular beam caries a uniformly distributed load of “W” kN/m over its entire span. The beam is freely supported at its ends. lf the. max. allowable bendlng stress is 8.27 MPa and simullaneously the max. allowable shearing stress is 0.70 MPa. 1) Which of the following gives the value of max. vertical shear? a) 16 kN c) 15 kN b) 13 kN d) 14 kN

2) Which of the following gives the value of the span of the beam? a) 6.45 m b) 5.45 m

c) 4.54m d) 3.54 m

3) Which of the following gives the value of “W” in kN/m? a) 6.91 b) 7.91

12. m

c) 8.91 d) 9.91

Proble

A laminated wooden beam supports a uniform distributed loading of 12 kN/m. Allowable bending stress is 9 MPa and allowable shear stress is 0.6 MPa. Neglecting the weight of the beam and assuming the beam lo have a height to width ratio of 1.5.

1) Which of the following gives the value of the concentrated load it could carry at its midspan if the allowable bending stress is 10.35 MPa? a) 29.17 kN c) 27.19 kN b) 28.17 kN d) 26.19 kN

2) Which of the following gives the value of the shear force at the support if there is beam which is 100 mm deep stress is 1.10 MPa? a) 29.17 kN b) 28.17 kN

a notch at the end of the if the allowable shearing c) 27.19 kN d) 26.19 kN

3) Which of the following gives the value of the concentrated load at the midspan that it could support if there is a notch of 100 mm deep at the end support? a) 42.38 kN c) 47.97 kN b) 52.38 kN d) 57.97 kN

14. m

Proble

A wooden beam having a span of 4 m. Is subjected to a uniform load of 10 kN/m. lt has a triangular cross section having a base width of 140 mm and an altitude of 300 mm. Neglecling the weight of the beam.

b)

19.37 kN/m

d) 14.95 kN/m

3) Which of the following gives the max. uniform load so that the allowable deflection is not exceeded? a) 6.12 kN/m c) 4.34 kN/m b) 9.12 kN/m d) 7.34 kN/m

17. m 1) Which of the following gives the section modulus of the beam? a) 525000 mm3 c) 636000 mm3 3 b) 252000 mm d) 363000 mm3

2) Which of the following gives the flexural stress of the beam? a) 38.09 MPa b) 39.09 MPa

c) 35.47 MPa d) 36.47 MPa

3) Which of the following gives the max. shearing stress developed on the beam? a) 1.73 MPa c) 1.36 MPa b) 1.43 MPa d) 1.66 MPa

Proble

An old Apitong post 200 mm x 300 mm x 4.25 m. long has been previously designed with an allowable compressive stress of 9.56 MPa. and a modulus of elasticity of 7310 MPa. It is designed to substitute the old post with a Yakal post of the same length as the old post. Allowable compressive stress for Yakal is 15.8 MPa with a modulus of elasticity of 9780 MPa. 1)

What is the capacity of Apitong? c) 203300 N d) 213300 N

a) 184400 N b) 194400 N

2) What size of Yakal post is required to replace Apitong? a) 150 x 150 mm b) 200 x 200 mm

c) 250 x 250 mm d) 300 x 300 mm

3) What is the percentage increase in the capacity of

15. m

Proble

A 150 mm x 350 mm wooden beam carries a concentrated load of 30.36 kN at its midspan. It has a simple span of 8 m. long. Allowable shear stress is 0.85 MPa. 1) Which of the following gives the depth of notches at the support if notching is allowed using the NSCP specifications? a) 100 mm c) 300 mm b) 200 mm d) 400 mm 2) Which of the following gives the allowable depth of notches at the bottom and top faces of the beam at quarter points? a) 41 mm c) 61 mm b) 51 mm d) 71 mm 3) Which of the following gives the flexural stress at the quarter points after deducting for notching? a) 17.74 MPa c) 19.74 MPa b) 18.74 MPa d) 20.74 MPa

16. CE Board Nov. A timber beam has a circular cross section having a diameter of 250 mm. lt has a simple span of 4 m. NSCP specs. states that in a circular beam the strength is equal to the strength of square section having the same area. Allowable stresses of wood are as follows: Shearing stress parallel to the grain fv= 1.73 MPa Bending stress fb = 16.5 MPa Allowable deflection 1/240 of span Modulus of elasticity of wood = 7.31 GPa 1) Which of the following gives the maximum uniform load so that the allowable shear stress parallel to the grain is not exceeded? a) 31.56 kN/m c) 25.31 kN/m b) 34.56 kN/m d) 28.31 kN/m

2) Which of the following gives the max. uniform load so that the allowable bending stress is not exceeded? a) 16.37 kN/m c) 11.95 kN/m

the new post to the dd post? a) 11.74% b) 22.74%

c) 33.74% d) 44.74%