Civil Engineering - Strength of Materials - Discussion
Discussion Forum : Strength of Materials - Section 5 (Q.No. 20)
20.
A 8 metre long simply supported rectangular beam which carries a distributed load 45 kg/m. experiences a maximum fibre stress 160 kg/cm2. If the moment of inertia of the beam is 640 cm4, the overall depth of the beam is
Discussion:
18 comments Page 1 of 2.
Abinaya Rajendran said:
6 years ago
M/I = sigma/y ..........(1).
Where M = wl^2/8=45*8^2/8.
= 360kg-m.
= 36000kg-cm.
From eqn(1),
36000/640 = 160/y.
Y = 2.844.
Y = d/2 = 2.844.
d = 2*2.844 = 5.68 means 6 cm.
Which is nearer to 10 cm.
So option A is correct.
Where M = wl^2/8=45*8^2/8.
= 360kg-m.
= 36000kg-cm.
From eqn(1),
36000/640 = 160/y.
Y = 2.844.
Y = d/2 = 2.844.
d = 2*2.844 = 5.68 means 6 cm.
Which is nearer to 10 cm.
So option A is correct.
(3)
Manjunath.R said:
9 years ago
Actually its M.I = bd3/12 then Already Given b=8, M.I=640, and now we need Depth, d=?
Now, bd3/12 = 640 As per he given then,
bd3 = 640 * 12 i.e, d3 = 960.
Only d = (960)whole power 1/3 therefore d = 9.8 Approxmtly d = 10.
Now, bd3/12 = 640 As per he given then,
bd3 = 640 * 12 i.e, d3 = 960.
Only d = (960)whole power 1/3 therefore d = 9.8 Approxmtly d = 10.
Sathya h d said:
6 years ago
The answer is 5.6 cm, otherwise he has to give the relationship between b and d like b is twice the d, or 2.5 times the d etc, then first find out b, then by using given relationship find D.
Vishal kumar said:
9 years ago
As per my knowledge, it is,
Max moment M = (w * l * L)/8 = (45 * 8 * 8)/8 = 360kg - m;
M/I = (sigma)/y = y = (sigma * I)/M;
(160 * 640)/36000 = 2.84cm,
y = d/2;
So, d = 5.68 = 6cm.
Max moment M = (w * l * L)/8 = (45 * 8 * 8)/8 = 360kg - m;
M/I = (sigma)/y = y = (sigma * I)/M;
(160 * 640)/36000 = 2.84cm,
y = d/2;
So, d = 5.68 = 6cm.
Kewal krishan said:
7 years ago
It's answer is 10cm because depth formula is l/10 to l/8 so we apply the formula.
L/8 = 8000/8 = 1000mm = 10cm.
L/8 = 8000/8 = 1000mm = 10cm.
(1)
Asif Wazir said:
6 years ago
The correct answer is 5.68 cm but as per minimum requirements that is d=l/8, we have to select 10 cm.
(1)
Murali said:
8 years ago
d= 5.6 is correct and over all depth.
D=(effective depth+cover) so D is 10 cm.
D=(effective depth+cover) so D is 10 cm.
Akash said:
9 years ago
Answer is wrong 8m long doesn't mean b=8m, it means span is 8m.
D kumar said:
8 years ago
M=wl2/8=45*8*8/2=1440kg.m.
Y=d/2.
I=640cm4m/i=f/y.
B=8cm.
Y=d/2.
I=640cm4m/i=f/y.
B=8cm.
Ramniwas said:
5 years ago
I = bd^3/12.
Generally b=d/2 take,
640 = d^4/24,
d = 10.
Generally b=d/2 take,
640 = d^4/24,
d = 10.
(1)
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