Question

Which one of the following is the correct expression to estimate the development length of deformed reinforcing bar as per IS code in limit state design?

• A. $\frac{\varphi {\sigma }_s}{4.5{\tau }_{bd}}$
• B. $\frac{\varphi {\sigma }_s}{5{\tau }_{bd}}$
• C. $\frac{\varphi {\sigma }_s}{6.4{\tau }_{bd}}$
• D. $\frac{\varphi {\sigma }_s}{8{\tau }_{bd}}$

Answer 1

The correct option is C $\frac{\varphi {\sigma }_s}{6.4{\tau }_{bd}}$

As per clause 26.2.1 of IS:456-2O00, the development length L${}_d$ is given by

$L_d=\frac{\varphi {\sigma }_s}{4{\tau }_{bd}}$

where $\varphi$ = nomimal dia meterof bar
${\sigma }_s$ = stress in the bar at the section considered at design load

${\tau }_{bd}$ = design bond stress for plain bars

The value of ${\tau }_{bd}$ be increased by 60% for deformed bars.

$\therefore$ $L_d=\frac{\varphi {\sigma }_s}{({\tau }_{bd}+\frac{60}{100}{\tau }_{bd})}$

$L_d=\frac{\varphi {\sigma }_s}{6.4{\tau }_{bd}}$