Download Section Resistance for Android
Section Resistance is a user-friendly Android App that allows you to calculate the moment resistance (Mn) of a Reinforced Concrete rectangular section . The necessary input data for the application to process are :
- Concrete and steel class
- Width and depth of the rectangular section ( b , h )
- Cover of steel members (d1)
- The area of compressive and tensile steel of the existing section ( As2 , As1 )
In order to calculate the nominal moment (Mn) Section Resistance follows a certain procedure that can be described with 3 steps :
- Define the Strain/Stress Profile
- Determine the Neutral Axis depth (x)
- Calculate the nominal moment (Mn)
- Strain / Stress Profile
Assumptions- The section fails when the compressive upper side is crushed
- a = 0.8x
Due to assumption No.1 and knowing the concrete class we can determine concrete's strain εc :
- Determine the Neutral Axis depth (x)
The value of x is determined from force equilibrium :
In order to solve the above equation assumption need to be made such as :
Assumptions
- The compression steel yields
- The tensile steel yields
- The inelastic behaviour of steel is descibed from the conservative Inelastic-Perfectly Plastic Model of Stress-Strain curve
Due to these assumptions we can now calculate the forces of the above equation and find the neutral axis depth :
Verify Assumptions
The next stage is to verify the first two assumptions considering the value of compressive and tensile steel's strain . This can be done by estimating these values using similar triangles from the strain profile . 
Afterwards we compare εs1 and εs2 with εyd and check if the assumptions we made are either correct or false . In case are were correct , we move to the next step and calculate the nominal moment . Otherwise , if one or both assumptions are incorrect we must recalculate the neutral axis depth by changing the formula we used to find Fs1 or Fs2 depending on which assumption is false or which steel member did not yield ( εs < εyd ) . If a steel member is in the elastic region then the corresponding force equals with :
Having recalculated the necessary forces we find the neutral axis depth (x) from the force equilibrium and afterwards the compressive and tensile strains as we did before using similar triangles . Finally , we check if the relevance between εs1 , εs2 and εyd is the same as before and if not we follow the same procedure until we verify the assumption we make at the start of every step .
Flowchart
- Calculate section's Moment Resistance (Mn)
Mn is calculated from the moment equilibrium about the compression force resultant and the result is :
