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The beam considered has a rectangular section of 0.35x0.95 m and a length of 10 m. The concrete class is 25/30 and the steel is S500.The loads on beam are the following:

The torsion work ratio is calculated with the formula below:

The longitudinal and transversal torsion reinforcement will be added to the longitudinal bending and transversal shear reinforcement.
The torsion verification and dimensioning of the torsion reinforcement is done according article 6.3 of the EN1992-1-1.

Section TMax, Abscissa 0.0 mm, Combination 102: +1.35 x[1G]

Design torsional moment

TEd = 135 kN x m

Design torsional resistance moment

Design transverse force

TRD,max = 478.79 kN x m

Maximum design shear resistance

υ 1 strength reduction factor for concrete cracked in shear

αcw coefficient taking account of the state of the stress in the compression chord

αcw = 1.00 for non-prestressed structures

fcd = 16.67 MPa

Θ = 45°

The value for strut angle can be defined in the Design Assumptions dialog, Transversal reinforcement section, as Strut slope:

Ak is the area enclosed by the centre-lines of the connecting walls, including inner hollow areas

tef,iis the effective wall thickness. It may be taken as A/u, but should not be taken as less than twice the distance between edge and centre of the longitudinal reinforcement.

A is the total area of the cross-section within the outer circumference, including inner hollow areas

A= 35 X 95 = 3325 cm 2

μ is the outer circumference of the cross-section

μ = 2 x (35+95) = 260 cm

di the distance between edge and centre of the longitudinal reinforcement

di = 25 mm

The required cross-sectional area of the longitudinal reinforcement for torsion may be A s1calculated from the following formula

μk is the perimeter of the area A k

The required cross-sectional area of the transversal reinforcement for torsion A swmay be calculated from the following formula:

The required cross-sectional area of the longitudinal reinforcement for torsion will be split equally between the top and bottom part of the beam.

Let’s consider the beam in our example in two situations:

  • no torsion
  • torsion is considered

As1 = 17.76 cm 2

=> 8.88 cm2added at the top and 8.88 cm 2 added at the bottom required reinforcement area (with blue)

5.2 + 8.88 = 14.08 cm2 longitudinal reinforcement area at the top part of the beam considering torsion

7.0 + 8.88 = 15.88 cm2 longitudinal reinforcement area at the bottom part of the beam considering torsion

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