Determination of Punching Load at Wall Ends and Wall Corners in RFEM 6

When selecting a nodal support or a column connection to a reinforced concrete slab, the punching shear load can be derived directly from the support reaction or from the internal forces of the column. However, if a node at a wall corner or wall end is selected for the verification, the punching shear load cannot be determined directly from the support reaction or the internal forces in the connected walls.

Shear Stress to be Resisted at Wall End and Wall Corner

Determination of the punching shear load at wall ends and wall corners

In principle, the punching shear load at wall ends and wall corners is not determined from the support reactions or the internal forces of the connected walls, but from the internal forces of the slab to be designed. This approach offers the advantage that the influence of singular stress peaks in the immediate nodal area is largely reduced. At the same time, punching due to pure line loads, for example from connected wall panels, can also be taken into account in this way.

Average shear force along the critical perimeter

When selecting a punching point, RFEM 6 automatically creates a critical control perimeter at a distance of 2.0 d in accordance with Section 6.4.2 [1].

To determine the punching shear load, the 'Concrete Design' add-on automatically creates a cut along the critical control perimeter in order to evaluate the relevant internal forces. For the verification, the internal force v_{Ed,int,geglättet} from RFEM is used.

By default, RFEM 6 predefines the option smoothed distribution of shear force over the length of the critical control perimeter for wall ends and wall corners. In this case, the averaged distribution of the shear force along the critical control perimeter is used to determine the applied shear force.

The influence of load eccentricities is then taken into account by the load increase factor β. RFEM 6 offers various methods for determining this factor:

• Determination based on the fully plastic shear stress distribution according to Section 6.4.3 (3) [1]
• Use of constant factors in accordance with Section 6.4.3 (6) [1]
• User-defined specification of an individual load increase factor

Determined, Smoothed Shear Force

The applied shear force V_Ed is given by:

V_Ed = u₁ ⋅ v_{Ed,int,geglättet}

with:

• u₁ = length of the critical control perimeter
• v_{Ed,int,geglättet} = smoothed shear force along the critical control perimeter

For the example shown, the result is:

V_Ed = 2.199 m ⋅ 131.319 kN/m ≈ 288.97 kN

Alternative verification using v_Ed,int,max

Alternatively, in RFEM 6 it is possible to select the option unsmoothed shear force distribution along the critical control perimeter in the 'Concrete Design' add-on. In this case, the applied shear force V_Ed is determined on the basis of the maximum shear force v_Ed,int,max along the critical control perimeter.

Maximum Shear Force Along Critical Perimeter

Since the maximum shear force value is already used directly in this case, no additional load increase factor β may be used to account for load eccentricities.