# Civil Engineering - GATE Exam Questions - Discussion

Discussion Forum : GATE Exam Questions - Section 6 (Q.No. 1)
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
46 (tension)
2.59 (compression)
zero
8.64 (compression)
Explanation:
No answer description is available. Let's discuss.
Discussion:
14 comments Page 1 of 2.

Balram said:   2 years ago
It should be 3.46.

Prabhakar Maurya said:   3 years ago
Top stress = -3.5.
Bottom stress = +8.6.

Angelica A. said:   3 years ago
8.64 (Compression).

Top Stress= - (P/A) - (Pey/I).

=-(700, 000 N /(300mm * 900mm)) - ((700,000 N * 350mm * 450mm * 12)/(300mm * 900 mm ^3)).

Abhay singh said:   4 years ago
3.46 tension.

Shantanu said:   5 years ago
D is correct.

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

Vaish said:   5 years ago
Yes, it is -3.456.

Sameer sopori said:   6 years ago
@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.

Akshay said:   6 years ago