written 8.3 years ago by |
There are 2 provisions for serviceability criteria:
1) Deflection check
2) Calculation of crack width
1) Deflection check
Calculate fs value with help of the formulae: $Fs = 0.87fyAstr/Astp$
Find out pt% (percentage steel)
Now, from the graph at pg. 38 of IS456:2000, find the value of depth. (dp)
Calculate the required depth with the help of the formula:
Dr =short effective span/S/D ratio $\times$ M.F.
Compare dr and dp interest the result whether the check for deflection is safe. Id dr<dp then="" it="" is="" safe="" <="" p="">
2) Calculation of crack width:
The design surface crack width can be calculated from the following equation:
$ W_{cr} = 3 a_{cr} e_m/ 1 + 2(a_{cr} –C_{min})$ -------------------- H - x Where, $a_{cr} =$ distance from the point considered to the surface of the nearest longitudinal bar.
$C_{min} =$ minimum cover to the longitudinal bar
$e_m =$ average steel strain at the level considered.
H = overall depth of the member
x= depth of the neutral axis. (refer IS code 456:2000 for further reference)