Question

A steel beam is replaced by a corresponding aluminium beam of same cross-sectional shape and dimensions, and is subjected to same loading. The maximum bending stress will

• A. be unaltered
• B. increase
• C. decrease
• D. vary in proportion to their modulus of elasticity

Answer 1

The correct option is A be unaltered

From the theory of pure bending, we have

$\frac{f}{y}=\frac{M}{I}$

$\Rightarrow f=\frac{M}{I}\times y$

Now, from the above formula, it can be concluded that bending stress depends on bending moment (loading condition), moment of inertia (dimensions) and the distance of any fibre from neutral axis. Since the loading condition and cross-sectional shape and dimensions are unchanged, therefore the maximum bending stress will be unaltered.