Hi There,
I have been asked to find crack widths in a column. In order to do this , I must find the stresses in the tension steel. In SLS when column is acting elastically, does anyone know how to calculate the neutral axis correctly when there is an axial force and bending both applied to the section?
Thank you and Regards, Dimuth
You can use the principle of superposition to find the neutral axis, a uniform stress distribution due to comression load =P/A, P = axial compression load, plus the bending stresses created by the bending moment = M.c/I, where M is the bending moment, c is the centroidal axis of the cross-section, and I is the second moment of area of the section. Adding the two stresses will locate the neutral axis.
Thank you very much. Using the below equations: From force equilibrium follows: NEd+ Fs−Fc−F’s= 0 Moment equilibrium around tension reinforcement gives: MEd+NEd(𝒅 −𝒉/2)−F’s(𝒅 −𝒅' )−Fc(𝒅 −y/3 )= 0
I have solved these two non linear simultaneous equations to solve for y using excel goal seek.
This allows me to find all the stresses and strains once I found the correct y value.
Dear Dimuth,
Theory for phase II calculations for RC concrete members subjected to N and M can be found in this book (in polish but obviously math is the same). Two pages in the attachment
Book Przykłady obliczeń konstrukcji żelbetowych: zarysowanie. Zeszyt 3
Simplified aproach to crack width control in columns is presented here:
Article Crack Width Control in RC and Prestressed Members - The Exte...
Best Regards,
Bartosz Grzeszykowski
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