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Design of longitudinal reinforcement

The design of statically required reinforcement is based on the calculation of equilibrium. This method uses an iteration routine to calculate equilibrium based on internal forces, the cross-section, material properties and position of reinforcement. Generally, this iterative method works for the interaction of the normal force (N) with uni-axial or bi-axial bending moments (M_y + M_z).

There are the following assumptions:

• Plane sections remain plane.
• Strain in bonded reinforcement, whether in tension or compression, is the same as the strain in the concrete at the same level
• Tensile strength of the concrete is ignored.
• The stresses in the concrete in compression are given by the design stress–strain relationships ( bilinear or parabola-rectangular stress-strain diagram)
• The stresses in the reinforcing steel are given by the design stress–strain relationships (bilinear with or without inclined horizontal branch stress-strain diagram)

Four methods are supported in SCIA Engineer for design of reinforcement for beams and columns, see "Design method"

• uni-axial around y axis, see "Uniaxial method for design"
• uni-axial around z axis, see "Uniaxial method for design"
• biaxial, see "Biaxial method for design"
• auto, see "Automatic method for design"

Uniaxial method around y axis is always used for type of member = beam as slab.

Biaxial method independently on selected method is always used for circular and oval columns

Designed required area is for better overview and graphical presentation recalculated to directions of cross-section (member) LCS axes, see "Recalculation reinforcement to directions"

Except of statically required longitudinal reinforcement (A_s.stat), the program calculates required longitudinal reinforcement (A_s.req). It is statically required longitudinal reinforcement with the influence of detailing provision. The program than calculates also provided longitudinal reinforcement (A_s.prov). It is required longitudinal reinforcement area recalculated to real bars , where:

• diameter of longitudinal reinforcement is taken into account (cross-sectional area of bars with input diameter)
• minimal number of bars per edge is 2
• number of bars is rounded to integer

• corner bars are taken into account for all edges (half of bar is taken into account for one edge, and half of bar for second edge)

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