A rectangular prestressed RC beam at SERVICE stage has

$($i$)$ maximum pure compressive stress $($Sigma pure comp$)$ of $6\mathrm{.}06\frac{N}{m}{m}^2,$ and

$($ii$)$ maximum bending stresses due to the eccentric moment due to the eccentricity of the tendons $($Sigma ecc$)$ of $9\mathrm{.}33\frac{N}{m}{m}^2,$ and

$($iii$)$ maximum bending tensile stress induced in the beam due to its self weight $($Sigma Mswt$)$ of $15\mathrm{.}32\frac{N}{m}{m}^2.$

What is the magnitude of the combined stress in the beam at its top?

Give your answer in $\frac{N}{m}{m}^2$ to two decimal places, but do not include units in your answer.

If the stress is tension, then include a minus sign in your answer $($e$.$g$.-2\mathrm{.}23).$ If the stress is compression, then simply write the correct number $($e$.$g$.2\mathrm{.}23).$

wered

answer

$12\mathrm{.}05$ margin of error $+/-2\%$