# Civil Engineering - Strength of Materials - Discussion

### Discussion :: Strength of Materials - Section 3 (Q.No.5)

5.

The section modulus of a rectangular light beam 25 metres long is 12.500 cm3. The beam is simply supported at its ends and carries a longitudinal axial tensile load of 10 tonnes in addition to a point load of 4 tonnes at the centre. The maximum stress in the bottom most fibre at the mid span section, is

 [A]. 13.33 kg/cm2 tensile [B]. 13.33 kg/cm2 compressive [C]. 26.67 kg/cm2 tensile [D]. 26.67 kg/cm2 compressive [E]. none of these.

Explanation:

No answer description available for this question.

 Aspire said: (Sep 21, 2016) How to solve this?

 Akscivilian said: (Sep 27, 2016) Question is wrong ,there is needed cross-sectional area, not given so we can't find the answer. B.S = M/Z + P/A. M = WL/4. But A is not given.

 Deb said: (Jun 19, 2017) Please, someone solve it clearly.

 Thakur said: (Nov 19, 2017) Please explain the details.

 Paul said: (Jan 5, 2018) How to find out A? Please explain in detail.

 Pranjul said: (Aug 13, 2019) Area calculate from bending equation M = f * Z and f = force/area.

 Basanth Babu said: (Nov 22, 2019) The cross sectional area of the beam is needed to solve this problem.

 Vipin Sainath said: (Apr 12, 2020) Bending Stress (Sigma) = M/Z x P/A. First, we have to calculate Depth and Breadth ..From span/depth ratio we get Depth Span/20 = 25m/20 = 1.25m or 125cm so D= 125cm, Then B/D=0.5 to 0.67 from this ratio we get breadth B, B = Dx0.5 = 125X0.5 = 62.5 say B= 60cm, So we got B and D. M/Z = (4000x2500/4) / 12.6 = 2,00,000 kg/cm2. P/A = 10000/7500 =1.33 kg/cm2. Therefore, Sigma = 200000 kg/cm2 x 1.33 kg/cm2 = 266000 Kg/cm2 or 26.6 Kg/m2 finally we got Max stress = 26.6kg/m2.

 Shraddha said: (Sep 7, 2020) @Vipin Sainath. Why Σ = (M/Z)*(P/A)?

 Kajal said: (Sep 23, 2020) @Vipin Sainath. Why multiplying p/A?

 Chris said: (Mar 11, 2021) @Shraddha @Kajal. P/A represents stress. The bending formula: M/I = f/y. Stress f = P/A. Section Modulus Z = I/y.

 Shahid Khan said: (Nov 24, 2021) Here is the solution: Length= 2.5m=250 cm, Z=12500 cm^3, Z=bh^2/6=12500, Bh^2=75000, H=50cm. B=30 cm. Sigma=m/z + p/A. M=4000*250/4=250000, A=1500 cm2. Sigma =250000/12500 +10000/1500, = 20+6.66, = 26.66 kg/cm2.