Question

The bearing stress on concrete after accounting for all losses due to relaxation of steel, elastic shortening, creep of concrete, slip and seating of anchorage shall not exceed ______

1. \(0.25\;{f_{ci}}\sqrt {\frac{{{A_{br}}}}{{{A_{pun}}}}} \)or 0.8 f_ci whichever is smaller
2.

\(\;0.48\;{f_{ci}}\sqrt {\frac{{{A_{br}}}}{{{A_{pun}}}}} \;\;\)or 0.8 f_ci whichever is smaller

3. \(0.16\;{f_{ci}}\sqrt {\frac{{{A_{br}}}}{{{A_{pun}}}}} \) or 0.8 f_ci whichever is smaller
4. \(0.34{f_{ci}}\sqrt {\frac{{{A_{br}}}}{{{A_{pun}}}}} \)or 0.8 f_ci whichever is smaller

Answer 1

Correct Answer - Option 2 :

\(\;0.48\;{f_{ci}}\sqrt {\frac{{{A_{br}}}}{{{A_{pun}}}}} \;\;\)or 0.8 f_ci whichever is smaller

Explanation:
Bearing stress:

• It is contact pressure between two separate bodies and can be defined as the compressive force divided by the characteristic area perpendicular to it.
   

According to IS-1343:2012, 

Bearing stress on the post-tensioned beam on the areas immediately behind external anchorages, the permissible unit bearing stress on the concrete, after accounting for losses due to relaxation of steel, elastic shortening, and seating of anchorages, shall not exceed

\(0.48{f_{ci}}\sqrt {\frac{{{A_{br}}}}{{{A_{pun}}}}} \)  OR 0.8f_ci, Whichever is smaller

Where, f_ck = characteristic strength of concrete, A_br = Area of bearing, A_pun = Area on which punching occur, and f_ci = Cube strength at transfer

Note:  During tensioning, the allowable bearing stress specified above may be increased by 25 percent, provided that this temporary value not exceed f_ci