# Convert Strain gauge readings to stress

Hello i am trying to convert the strain gauge readings i took in a lab from an I beam that was subjected to torsion. I am trying to convert the microstrain readings to stress and shear stress. I have the following information the Yield strength of the I beam and the youngs modulus but not the poissons ratio.

I thought the formula would be $$\tau$$= Tr/J but because it is an I beam i am unsure how to calculate the r and the J. also i know what the T (torsion) that the beam is subjected to.

any help would be very much appreciated.