Engineering Answers

A timber wall 75 mm wide, 75 mm deep and 3.50 m high is assumed to be fixed at the top and bottom.

It is subjected to uniformly distributed load of 388 N/m acting along the weaker axis of its entire height. The wall is made up of Apitong wood with 80% stress grade with properties as shown:

Bending and tension parallel to the grain = 16.5 MPa

Modulus of Elasticity in Bending = 7310 MPa

Compression parallel to the grain = 9.56 MPa

Compression perpendicular to the grain = 2.20 MPa

Compute for the following:

a) Allowable compressive stress

b) Allowable bending stress

c) Maximum axial load

A simple span member is 6.65 m in length is made up of Apitong 185 mm x 270 mm wooden section,

with an allowable stress based on 80% stress grade of 16.5 MPa in bending and tension parallel to grain. The beam carries a concentrated load of 18 kN at the center and neglecting its own weight.

Weight of wood = 7.5kN/m3. The beam carries an axial tensile load of 192 kN. Bending and tension parallel to the grain = 16.5 MPa Modulus of Elasticity in Bending = 7310 MPa

Compression parallel to the grain = 9.56 MPa

Compute for the following:

a) actual tensile stress if only tensile force is acting.

b) interaction value for both bending and tensile stress

c) ratio of the difference between its actual bending and tensile stress to the adjusted bending

stress for slenderness

A cantilever beam is 8.85 m in length is made up of Apitong 165 mm x 350 mm wooden section, with

an allowable stress based on 80% stress grade of 16.5 MPa in bending and tension parallel to grain.

The beam carries a uniform load of 32 kN/m besides its own weight. Weight of wood = 7.5kN/m3. The beam carries an axial tensile load of 225 kN. Bending and tension parallel to the grain = 16.5 MPa Modulus of Elasticity in Bending = 7310 MPa Compression parallel to the grain = 9.56 MPa

Compute for the following:

a) actual tensile stress if only tensile force is acting.

b) interaction value for both bending and tensile stress

c) ratio of the difference between its actual bending and tensile stress to the adjusted bending

stress for slenderness

Wooden joists are used to support a floor load of 8.95 kPa exclusive of its own weight. The joists will

have an effective span of 5.42 m and be placed at 0.48 m on centers. The unit weight of wood is 7.5

kN/m3. Design the wooden joists so as not to exceed the allowable

a) Bending stress of 12.11 MPa

b) Shear stress of 0.96 MPa

A laminated beam is composed of three planks, two 175 mm x 80 mm on the outer sides with one 175 mm x 90 mm on the middle, glued together to form a section 175 mm wide by 250 mm high. The beam has a span of 3.50 m.

Allowable stresses:

Shear stress in the glue = 650 kPa

Shear stress in wood = 975 kPa

Flexural stress in wood = 8.75MPa

Find the uniform load that can be carried if

a) allowable shear stress in the glue is not to be exceeded

b) allowable shear stress in wood is not to be exceeded

c) allowable flexural stress in wood is not to be exceeded

A made up bridge has a span of 25 m between centers of end supports. Two logs of approximately

constant diameter are to be used. Each log must be capable of supporting a uniform load of 12 kN/m.

If the allowable stresses are 9.8 MPa in bending and 0.78 MPa in shear,

1) what diameter of the log must be used if

a. bending governs?

b. shear governs?

2) What is the safest diameter of log must be used?

A timber beam having a simple span of 4m carries a total load including its own weight of 15kN/m. It

has a trapezoidal section having width of 250 mm at the top and 200 mm at the bottom and a depth of 360 mm, dressed dimension is used by reducing its dimensions by 15 mm. The wooden section is made up of 80% grade Apitong with the properties as follows:

fb = 16.5 MPa

fv = 1.75 MPa

Compute the following:

a. Maximum flexural stress

b. Maximum shear stress

A two-point bending test was performed on a 2 x 4 wood lumber according to ASTM D198 procedure

with a span of 4 ft and the 4 in. side is positioned vertically. If the maximum load was 240 kips, calculate the modulus of rupture.

A static center-point bending test was performed on a 75 x 75 x 950 mm wood sample according to

ASTM D143 procedure (span between supports = 900 mm) If the maximum load was 4.59 kN, calculate the modulus of rupture.

A third-point bending test was performed on a 2 x 8 wood lumber according to ASTMD198 procedure

with a span of 8ft and the 8in. side is positioned vertically. If the maximum load on both loading bearings was 7,930 lb, calculate the modulus of rupture.