Determination of Punching Load on Wall Ends and Wall Corners in RF-PUNCH Pro

Technical Article

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The RF-PUNCH Pro add‑on module allows you to perform punching shear design of slabs and foundation plates (floor slabs) on wall ends and wall corners.

When selecting a nodal support or a column connection on a reinforced concrete floor, it is possible to derive the punching load directly from the support force or from the internal forces of the column. However, if a node at a wall corner or a wall end is selected for the design, the punching load can not be determined directly from the support force or the internal forces in the connected walls.

Figure 01 - Absorbed Shear Force on Wall End and Wall Corner

Determination of the punching load on a wall end

Basically, it should be noted that the punching load is not determined from a support force or the surface internal forces of the connected walls, but from the surface internal forces of the plate for which the punching shear design is to be performed. This approach has the advantage that the influence of singular results directly on the node can be largely avoided. Furthermore, this type of load determination can also consider punching for a pure line load (pure load from adjacent wall slab).

Figure 02 - Wall Replaced by Line Load

RF-PUNCH Pro generates a critical perimeter at a distance of 2.0 d when selecting a punctured point according to [1], Section 6.4.2.

To determine the punching load, a section is created inside the module in order to be able to access the surface internal forces from RFEM in the critical control perimeter. To determine the punching load, the program considers the surface internal force v max, b from RFEM. The definition of the surface's internal forces v max, b is described in [2] Chapter 8.16 Surfaces - Principal Internal Forces.

In RF-PUNCH Pro, the default setting for the determination of the punching load on wall ends and corners is set to "unconstrained shear force distribution over the length of the critical control perimeter". This means that the maximum value along the critical perimeter is applied for the determination of the acting shear force.

Figure 03 - Shear Force at Critical Perimeter

The acting shear force V Ed results in:

V Ed = length of critical control perimeter ∙ max. Shear force along the critical perimeter
V Ed = u 1 ∙ v max, b
V Ed = 2.289 m ∙ 156.11 kN / m = 357.34 kN

Figure 04 - Resulting Shear Force VEd

Check of the determined punching load

The punching load V Ed determined in the module can be checked by creating a line in the critical perimeter where a new section can be defined. Thus, you can visualize and evaluate the distribution of the shear force along the critical or perimeter in the RFEM graphic window or in the result diagram of the section.

The following graphic shows the result diagram of the shear force v max, b determined in RFEM. With the result diagram, you can see the acting shear force V Ed determined in RF-PUNCH Pro.

Figure 05 - Result Diagram in Section: Principal Internal Force vmax,b

As already mentioned above, RF-PUNCH Pro applies the non-smoothed distribution of shear forces along the critical control perimeter for the determination of the punching load. Since in this analysis the maximum value of the shear force is already applied along the critical perimeter, the load increasing factor ß is set to 1.00 for the further design.

Consideration of load increasing factor ß

Alternatively, RF-PUNCH Pro also offers the option "Smoothed distribution of shear force along the critical perimeter" for the determination of the acting shear force V Ed . The acting shear force is determined with the "smoothed" shear force v max, b, average .

In this case, the load increasing factor ß is taken into account for the further design. Either the determination of the LO-factor by means of the fully plastic shear stress distribution according to 6.4.3 (3) or by means of the constant factors according to 6.4.3 (6) is available for selection. In addition to the options described above for determining the load factor ß, the user-defined specification of a load increase factor is also available in RF-PUNCH Pro.

References

[1]  Eurocode 2: Design and construction of reinforced concrete and prestressed concrete structures - Part 1-1: General design rules and rules for building construction; EN 1992-1-1: 2011-01
[2]  Manual RFEM 5. Tiefenbach: Dlubal Software, February 2016. Download ...

Keywords

Punching Punching Punching Shear Design Wall corner Wandende

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RFEM Main Program
RFEM 5.xx

Main Program

Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

Price of First License
3,540.00 USD
RFEM Concrete Structures
RF-PUNCH Pro 5.xx

Add-on Module

Punching shear design of foundations and slabs with nodal and line supports

Price of First License
760.00 USD