Chap 1 : Stress
Learning Outcomes:
At the end of this chapter, students should be able to: • Determine the internal resultant loadings by applying methods of sections and equations of equilibrium • Determine the average normal and average shear stresses in loaded members • Produce a safe design by incorporating the concepts of allowable stresses and factors of safety

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Chap 1 : Stress
Course Outcomes Addressed
CO1: Analyze the stress-strain relationship in various structural members subjected to single loadings; axial load, torsion, bending and shear load; CO4: Design for dimension and strength of structural members subjected to various external loads, determine their deformation, and select the suitable material for a specific engineering application.

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Chap 1 : Stress
1.1 Introduction
• intensity of the internal forces distributed over a given section (area)

• basic units:  N/m2 or pascal  psi (pounds per square inch)
• prefixes used for units :  kilo, k (103)  mega, M (106)  giga, G (109)

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Chap 1 : Stress
• Normal Stress  – Force per unit area acting normal to A

Fz  z  lim A 0 A
• Shear Stress  – Force per unit area acting tangent to A

Fx  zx  lim A 0 A Fy  zy  lim A0 A

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Chap 1 : Stress
1.2 Average Normal Stress
P  A

where

 = average normal stress
P = internal resultant normal force A = cross-sectional area

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Chap 1 : Stress
Example 1
The bar in Figure E1 has a constant width of 35mm and a thickness of 10mm. Determine the maximum average normal stress in the bar when it is subjected to the loading shown.

Figure E1
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Chap 1 : Stress
1.3 Average Shear Stress
 avg
V  A

where
avg = average shear stress

V = internal resultant shear force
A = cross-sectional area

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Chap 1 : Stress
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