A simply supported beam of span length 6m and 75mm diameter carries a ...
Given data:
Span length of the beam = 6m
Diameter of the beam = 75mm
Uniformly distributed load = 1.5 kN/m
To find: Maximum value of bending moment
Formula used:
Maximum bending moment (Mmax) = WL²/8, where W is the uniformly distributed load and L is the span length of the beam.
Calculation:
Diameter of the beam = 75mm
Radius of the beam = 75/2 = 37.5mm = 0.0375m
Area of cross-section of the beam (A) = πr² = π(0.0375)² = 0.0044m²
Modulus of elasticity (E) for mild steel = 2.1x10⁵ MPa = 2.1x10⁸ N/m²
Maximum allowable bending stress (σ) for mild steel = 165 MPa = 165x10⁶ N/m²
Maximum allowable bending moment (M) = σI/c, where I is the moment of inertia of the beam's cross-section and c is the distance from the neutral axis to the outermost fiber.
For a circular cross-section, moment of inertia (I) = πr⁴/4
I = π(0.0375)⁴/4 = 1.483x10⁻⁷ m⁴
c = r = 0.0375m
Maximum allowable bending moment (M) = (165x10⁶ N/m²) x (1.483x10⁻⁷ m⁴) / (0.0375m) = 6,612.5 Nm = 6.6 kNm
Maximum bending moment (Mmax) = WL²/8
Mmax = (1.5 kN/m) x (6m)² / 8 = 6.75 kNm
Since the maximum allowable bending moment (6.6 kNm) is less than the calculated maximum bending moment (6.75 kNm), the beam will fail due to bending.
Therefore, the correct answer is option D, 125 kNm, which is not the maximum allowable bending moment but the maximum calculated bending moment.
A simply supported beam of span length 6m and 75mm diameter carries a ...
6.75kNm but it is not in option so correct answer is near value (a) 9kNm wl^(2)/8