Design Steps of Flanged Section

Table of Contents

Section Size is given and Area of “Steel” is to be Calculated.

Step I : Calculate Xu,lim

Step II : Based on Xu,lim with respect to depth of flange (Df), Compute MoR,lim.

Step III : If BMu>MoR,lim, Doubly Reinforced Section would be designed; If BMu < MoR,lim then Singly Reinforced Section is designed.

Step IV: Assume Xu = Df and Compute MoR.

Step V :If BMu<MoR1, The Neutral Axis is in flange and section behaves as rectangular section and Ast is given as,

Step VI: If MoR1 < BMu < MoR,lim; then Neutral axis is in web region.

Now,

Xu = 7/3 Df and Compute MoR2

Step VII : If MR2 < BMu <MoR,lim ; Xu > 7/3 Df

Df < 3/7 Xu

Calculate exact depth of Neutral axis,

BMu = MoR

Xu = ?

To Compute Ast, C=T

Ast = ?

Step VIII : If MoR1<BMu<MR2

Df < Xu < 7/3 Df

Df > 3/7 Xu

To compute exact depth of Neutral Axis,

BMu = MoR

For Ast,

Step 9 : Ast Computed above must be within Permissible Limit.

Ast/(b_w d) > 0.87/fy

Ast should be less than equal to min of {Ast,lim and 0.045 b_w d}

Design Example :

Que. Design a section shown below for Ultimate BM of 700 KN-m. This section is used in simply Supported beam of effective span of 7m.