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Civil Engineering/Biaxial moment coulmn design per BS8110


Dear Sir,

   When I design a column subjected to biaxial moments, Bs8110 proposed a simplified methods as below:

   "When it is necessary to consider biaxial bending and in the absence of more rigorous calculations in
   accordance with, symmetrically-reinforced rectangular sections may be designed to withstand an
   increased moment about one axis given by the following equations:

   if Mz/h' > My/b' then M'z = Mz + b(h'/b')My
   if Mz/h' < My/b' then M'y = My + b(b'/h')Mz


   The area of rebar As then is calculated as single axis bending with an increased moment M'z or M'y.

   Could you please explain my question?

   Rebar shall be arranged as single bending which concentrate on top (As/2) and bottom (As/2) of axis bending or it will be arranged regularly around 4 sides (As) with equal spacing or we can accept every arrangement

   Thank you very much

Dear Alex

I suggest you to calculate the Rebar area for both sides and then arrange the bars so that you have the needed area in each direction without adding them up. Each direction must have its own area arranged as you said : As/2 on the top and As/2 on the bottom.


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Babak Esmailzadeh Hakimi


I can answer questions in Structural Engineering, Earthquake Engineering, Project Management and Project Control topics!


I am experienced in the area of earthquake engineering in electrical power industry, i.e. Lifeline Earthquake Engineering. My focus has been on structural seismic design of power installations. Recently I have got involved in project management in the category of constructional engineering.

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Bs degree in Civil Engineering from Ferdowsi University ,1988, Mashhad Iran, Ms degree in Earthquake Engineering, Sharif University of Technology, 1993, Tehran, Iran

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