Introduction

Shear check

General concept of "strut-and-tie" model is used for the prediction of shear effects in concrete. In this model, the top compression and bottom tensile members represent the compressive concrete and tensile reinforcement, respectively. The horizontal members are connected by the compressive virtual struts and reinforcement tensile ties. The axial forces in tensile ties should be transmitted by the shear reinforcement.

Torsion check

In normal building structures, torsion generally arises as a secondary effect, and specific calculations are not necessary. Torsional cracking is generally adequately controlled by reinforcement provided to resist shear. Even when torsion occurs, it rarely controls the basic sizing of the members, and torsion check is often a check calculation after the members have been checked for flexure. In some cases, the loading that causes the maximum torsional moment may not be same that induces the maximum flexural effect. In some cases, reinforcement provided for flexure and the other forces may prove adequate to resist torsion.

The torsion check is commonly based on the theory of the concrete truss-model too. In this theory a virtual truss-model is imagined in a concrete beam. This truss-model has a set of vertical (or slightly diagonal), horizontal and diagonal members. The vertical bars are considered to be the stirrups; the horizontal bars are the main reinforcement and the diagonal bars are the concrete struts.

Assumptions and limitation

There are the following assumptions:

• The parameters of plane of equilibrium (value, d, z and h) are recalculated to direction of resultant shear force
• The torsional cracking moment (T_Rd,c) is calculated according to clause 6.3.2(5) in EN 1992-1-1
• Design value of maximum of torsional resistance moment (T_Rd,max)is calculated according to clause 6.3.2(4) in EN 1992-1-1
• The angle of compression strut can be calculated automatically or defined by user
• The angle of stirrups for check is always perpendicular to member axis.

With the following limitations:

• only one stirrup can be taken into account for torsion check

All checks mentioned above are calculated according to clause 6.1 - 6.3 in EN 1992-1-1. The following preconditions are used for calculation :

• The checks are calculated for beams and columns and for general load (N+M_y+M_z)
• Cross-section with one polygon and one material is taken into account in version SCIA Engineer 20.
• The material of all reinforcement bars and stirrups have to be same in SCIA Engineer 20.
• The checks should be used only in case, that the angle between gradient of the strain plane and the resultant of shear forces is not greater than 15 °.

Interaction V+T

The interaction of shear and torsion has to be taken into account, if the member is loaded by shear and torsion effect. The shear and torsion checks are commonly based on the theory of the concrete truss-model,

There are the following assumptions:

• Only minimum reinforcement is required provided that condition clause 6.3.2(5) in EN 1992-1-1 is satisfied:

• The maximum resistance of a member subjected to torsion and shear is limited by the capacity of the concrete struts. In order not to exceed this resistance the condition in clause 6.3.2(4) in EN 1992-1-1 should be satisfied

With the following limitations

• Inclined compression chord or inclined tensile chord are not taken into account
• The widths of cross-section for shear checks (value b_w and b_w1) are calculated automatically. There is no possibility for definition of user value in SCIA Engineer.