D9.B.2.1 Design Capabilities

All types of available shapes like H-Shape, I-Shape, L-Shapes, CHANNEL, PIPE, TUBE, etc. can be used as member property and STAAD.Pro will automatically adopt the design procedure for that particular shape if Steel Design is requested. STEEL TABLE available within STAAD.Pro or UPTABLE facility can be used for member property.

D9.B.2.2 Methodology

For steel design, STAAD.Pro compares the actual stresses with the allowable stresses as required by AIJ specifications. The design procedure consist of following three steps.

1. Calculation of sectional properties

   The program extracts section properties cross sectional area, A, moment of inertia about Y and Z axes, I_yy and I_zz, and the St. Venant torsional constant, J, from the built-in steel tables. The program then calculates the elastic section moduli, Z_z and Z_y, torsional section modulus, Z_x, and radii of gyration, i_y and i_z, using the appropriate formulas.

2. Calculation of actual and allowable stresses

   Program calculates actual and allowable stresses by following methods:

   1. Axial Stress:

      Actual tensile stresses,

      FT = force / ( A × NSF )

      where

      NSF

      =

      Net Section Factor for tension input as a design parameter

      Actual compressive stress , F_C = force / A

      Allowable tensile stress, f_t

      • = FYLD / 1.5 (For Permanent Case)
      • = FYLD ( For Temporary Case )
      where

      FYLD

      =

      Yield stress input as a design parameter

      Allowable compressive stress, f_c

      $f_c=\{\begin{array}{c}\frac{[1-0.4{\left(\frac{\lambda }{\Lambda }\right)}^2]F}{\nu }\text{ when }\lambda \le \Lambda \\ \frac{\begin{array}{c}0.277F\end{array}}{{\left(\frac{\lambda }{\Lambda }\right)}^2}\text{ when }\lambda >\Lambda \end{array}$

      = fc x 1.5 (for Temporary case)

      where

      Λ	=	$\sqrt{\frac{{\pi }^{2}E}{0.6F}}$
      ν	=	$\frac{3}{2}+\frac{2}{3}{\left(\frac{\lambda }{\Lambda }\right)}^2$
      λ	=	maximum slenderness, considering both principal axis
      E	=	Modulus of elasticity of steel (Young's Modulus)

      Actual torsional stress, f_t = torsion / Z_x

      where

      Zx	=	J / max(tf, tw)
      tf	=	flange thickness
      tw	=	web thickness

   2. Bending Stress:

      Actual bending stress for My for compression:

      ( F_bcy) = M_y / Z_cy

      Actual bending stress for Mz for compression

      ( F_bcz) = M_z / Z_cz

      Actual bending stress for My for tension

      ( F_bty ) = M_y / Z_ty

      Actual bending stress for Mz for tension

      ( Fbtz ) = Mz / Ztz

      where

      Zcy, Zcz	=	elastic section modulus for compression due to bending about the y and z axes, respectively
      Zty, Ztz	=	elastic section modulus for tension due to bending about the y and z axes, respectively

      Allowable bending stress for M_y

      (f_bcy) = f_t

      Allowable bending stress for M_z

      When λ_b ≤ _pλ_b , f_b = F/ν

      When _pλ_b < λ_b ≤ _eλ_b ,

      $f_b=\frac{F(1-0.4\frac{{\lambda }_b-{{}_p\lambda }_b}{{}_e{\lambda }_b-{{}_p\lambda }_b})}{\nu }$

      When _eλ_b < λ_b ,

      $f_b=\frac{1}{{\lambda }_b^2}\frac{F}{2.17}$
      where

      λb	=	$\sqrt{M_y/M_e}$
      eλb	=	$1/\sqrt{0.6}$
      ν	=	$\frac{3}{2}+\frac{2}{3}{\left(\frac{{\lambda }_b}{{{}_e\lambda }_b}\right)}^2$
      Me	=	$C\sqrt{\frac{{\pi }^{4}E{I}_{y}E{I}_w}{I_b^4}+\frac{{\pi }^{2}E{I}_{y}GJ}{I_b^2}}$
      pλb	=	$0.6+0.3\left(\frac{M2}{M1}\right)$ or taken as the value of PLB if not 0
      C	=	1.75 + 1.05 (M2 / M1) + 0.3 (M2 / M1)2 ≤ 2.3
      M1	=	the larger of end moments about the major axis
      M2	=	the smaller of end moments about the major axi

      Note: M2/M1 will be +ve for double curvature and -ve for single curvature.

      For Temporary case, f_bcz = 1.5 x (f_bcz for Permanent case)

      where

      ft	=	Allowable bending stress for My, fbty
      fbcz	=	Allowable bending stress for Mz, fbtz

      Note: The parameter CB can be used to specify a value for C directly.

   3. Shear Stress

      Actual shear stresses are calculated by the following formula:

      Qy = Fy / Aww

      where

      Aww

      =

      web shear area = depth times web thickness

      Qz = Fz / Aff

      where

      Aff

      =

      flange shear area = 2/3 times total flange area

      Allowable shear stress:

      • Permanent Loads: f_s = (F_y/√(3))/ 1.5
      • Temporary Loads: f_s = F_y / √(3)
      where

      Fy

      =

      yield strength of steel, specified by the FYLD parameter.

3. Checking design requirements:

   User provided RATIO value (default 1.0) is used for checking design requirements:

   The following conditions are checked to meet the AIJ specifications. For all the conditions calculated value should not be more than the value of RATIO. If for any condition value exceeds RATIO, program gives the message that the section fails.

   Conditions:

   1. Axial tensile stress ratio = F_T / f_t
   2. Axial compressive stress ratio = F_C / f_c
   3. Combined compression & bending compressive ratio = F_C / f_c+F_bcz/f_bcz+F_bcy/f_bcy
   4. Combined compression & bending tensile ratio = (F_btz+F_bty-F_C) / f_t
   5. Combined tension & bending tensile ratio = (F_T+F_btz+F_bty) / f_t

   6. Combined tension & bending compressive ratio = F_bcz/f_bcz+F_bcy/f_bcy- F_T/f_t

   7. Shear stress ratio in Y = q_y / f_s
   8. Shear stress ratio in Z = q_z / f_s
   9. von Mises stress ratio (if the von Mises stresses were set to be checked) = f_m/(k⋅f_t)