A single span member is 3 m in length is made up of Apitong 150 mm x 300 mm wooden section with an allowable stress based on 80% stress grade. Bending and tension parallel to grain = 16.5 MPa Modulus of elasticity in bending = 7310 MPa Compression parallel to grain = 9.56 MPa Compression perpendicular to the grain = 2.20 MPa Shear parallel to the grain = 1.73 MPa. The beam carries a uniform load of 18 kN/m besides its own weight. Weight of wood = 7.5 kN/m³. The beam carries an axial tensile load of 180 kN. 1. Compute the actual tensile stress if only tensile force is acting. a. 6 MPa b. 4 MPa c. 8 MPa d. 10 MPa 2. Compute the interaction value of both bending and tensile stress. a. 0.8025 b. 0.5465 c. 0.6890 d. 0.716 3. Find the ratio of the difference between its actual bending and tensile stress to the adjusted bending stress for slenderness. a. 0.521 b. 0.425 c. 0.378 d. 0.316
Design Against Fluctuating Loads
Machine elements are subjected to varieties of loads, some components are subjected to static loads, while some machine components are subjected to fluctuating loads, whose load magnitude tends to fluctuate. The components of a machine, when rotating at a high speed, are subjected to a high degree of load, which fluctuates from a high value to a low value. For the machine elements under the action of static loads, static failure theories are applied to know the safe and hazardous working conditions and regions. However, most of the machine elements are subjected to variable or fluctuating stresses, due to the nature of load that fluctuates from high magnitude to low magnitude. Also, the nature of the loads is repetitive. For instance, shafts, bearings, cams and followers, and so on.
Design Against Fluctuating Load
Stress is defined as force per unit area. When there is localization of huge stresses in mechanical components, due to irregularities present in components and sudden changes in cross-section is known as stress concentration. For example, groves, keyways, screw threads, oil holes, splines etc. are irregularities.
A single span member is 3 m in length is made up of Apitong 150 mm x 300 mm wooden section with an allowable stress based on 80% stress grade.
Bending and tension parallel to grain = 16.5 MPa
Modulus of elasticity in bending = 7310 MPa
Compression parallel to grain = 9.56 MPa
Compression perpendicular to the grain = 2.20 MPa
Shear parallel to the grain = 1.73 MPa.
The beam carries a uniform load of 18 kN/m besides its own weight.
Weight of wood = 7.5 kN/m³.
The beam carries an axial tensile load of 180 kN.
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