Equivalent thin-walled closed cross-section

Equivalent thin-walled cross-section can be calculated by 4(5) possibilities in SCIA Engineer depending on parameter Equivalent thin-walled cross-section. This parameter can be changed in Concrete setting (if 1D concrete member data is not defined) or in 1D concrete member data for Advanced model level.

Concrete setting	1D concrete member data

There are the following options:

• Automatic - program calculates equivalent thin-walled cross-section according one method below. It means that program tries to create equivalent thin-walled cross-section from stirrup for torsion at first, and if this method is not successful, program uses method based on shape of cross-section. This is the default setting.
• From stirrups for torsion - program tries to create equivalent thin-walled cross-section around stirrup, where check box Torsion is ON, see "Stirrup for torsion". If equivalent thin-walled cross-section was not successful created or stirrup for torsion is not defined, program finishes with some warning/error. This method is not supported for design of shear reinforcement, because user(practical) reinforcement is not taken into account and therefore for design method From used cross-section is used, if this method is selected.

• From used cross-section. The program tries to create equivalent thin-walled cross-section from current cross-section by offsetting the value t_ef. If equivalent thin-walled cross-section was not successfully created program finishes with warning/error.

• From the effective rectangular cross-section. The program tries to create an equivalent rectangular concrete thin-walled cross-section the perimeter and area of which are the same as the perimeter and area of the original cross-section. It follows, that effective rectangular cross-section with the following dimension will be created:

h_ef = [u + √(u² - 16 ∙ A)] / 4

b_ef = A / h_ef

where

A	is cross-sectional area of source cross-section
u	the outer circumference of the source cross-section

If equivalent thin-walled cross-section was not successfully created program finishes with some warning/error.

• User input - equivalent thin-walled cross-section can be defined directly by the user, it means, that user has to define following properties:
  • area of thin-walled cross-section (A_k,user)
  • outer circumference of thin-walled cross-section (u_k,user)
  • effective wall thickness (t_ef,user)

  This method is available only in 1D concrete member data. If the member is not prismatic (arbitrary member or member with haunches), equivalent thin walled cross-section is recalculated to each section of the member according to formulas below:

  A_ki = A_i ∙ A_k,user / A_m

  u_ki = u_i ∙ u_k,user / u_m

  t_efi = A_i / u_i ∙ u_m / A_m ∙ t_ef,user

  where

  Ai	cross-sectional area of concrete cross-section in i-th section
  Am	cross-sectional area of concrete cross-section in the middle of the member
  Ak,user	user input area of thin-walled cross-section
  ui	outer circumference of concrete cross-section in i-th section
  um	outer circumference of concrete cross-section in the middle of the member
  uk,user	user input outer circumference of thin-walled cross-section
  tef,user	user input effective wall thickness

The user(practical) reinforcement is not taken into account for design of shear reinforcement, therefore when method From stirrups for torsion is used, the thin-walled cross-section from current cross-section is created