Civil Engineering - GATE Exam Questions - Discussion

1. 

A prestressed concrete rectangular beam of size 300 mm x 900 mm is prestressed with an initial prestressing force of 700 kN at an eccentricity of 350 mm at midspan. Stress at top of the beam due to prestress alone, in N/mm2 is

[A]. 46 (tension)
[B]. 2.59 (compression)
[C]. zero
[D]. 8.64 (compression)

Answer: Option A

Explanation:

No answer description available for this question.

Sumanthnunna said: (Jul 13, 2016)  
My Answer for this question is 3.519.

Rakesh Kumar said: (Jan 17, 2017)  
Can someone solve this with the explanation?

Priyanka said: (Mar 25, 2017)  
According to me, the answer is 3.46.

Am I right?

Priyanka said: (Mar 25, 2017)  
At top stress=p/a -pey/i.
=700 * 1000/300*900 -700*1000*350*450*12/300*900^3.
= 2.59-6.049.
= 3.46.

Chhaya said: (Jul 11, 2017)  
Thanks @ Priyanka.

Vinay said: (Aug 30, 2017)  
The answer is 8.64 (beam at the top would be in compression).

Akshay said: (Oct 24, 2017)  
Answer must be 3.46 N/sq.mm.

Sameer Sopori said: (May 26, 2018)  
@Vinay.

When compression increases in one side then tension will increase in another side.
Now here, we have prestressed (compressed) the bottom portion of the beam then the tension will come on the top side of the beam.
Also in bridge girders, we do post-stressing (means we are increasing compression at the bottom by stressing the steel cables and increasing the tension at the top.
but if its simple beam then obviously compression will be on top and tension at the bottom.

Vaish said: (Feb 23, 2019)  
Yes, it is -3.456.

Shantanu said: (Aug 30, 2019)  
D is correct.

The formula is;
Stress = p/A(1+6e/b).

Abhay Singh said: (Jun 17, 2020)  
3.46 tension.

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