Surface Load Inside the Critical Perimeter in RF-PUNCH Pro

Technical Article

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RF-PUNCH Pro performs the punching shear design on concentrated load application locations (column connection, nodal support and nodal load) as well as on wall ends and wall corners.

If you perform the punching shear design in RF-PUNCH Pro on a concentrated load application location, the punching load can be determined directly from the axial force of a column, the support force or directly from the nodal load.

Determination of the punching load from the shear force distribution in the surface

It is difficult to transfer the punching load directly from the support forces in case of linear load application locations (wall corner and wall end). For these application cases, RF-PUNCH Pro uses the shear force in the critical perimeter of the analyzed surface and determines the punching load which is then applied for the design. The method for determining the punching load on wall corners and wall ends has already been described in this technical article.

Punching Load for Flat Slabs

However, it is also possible to determine the punching load from the "smoothed" or "unsmoothed shear force over the critical perimeter" for flat slabs located on nodal supports or columns.

In the commentary to EN 1992-1-1 [2], the section "To (5)" indicates that the load components from a uniformly distributed load within the critical perimeter must not be neglected or subtracted when using flat slabs.

Considering the Surface Load Inside the Critical Perimeter

Since the program version RFEM 5.20.01, RF-PUNCH Pro offers an option to consider the surface load within the critical perimeter. This option is available in Table "1.5 Nodes of Punching Shear".

Figure 01 - Input Table 1.5 Nodes of Punching Shear

The following three options are available:

  • Do not consider the surface load inside the critical perimeter
  • Enter the surface load inside the cirtical perimeter
  • Determine the surface load inside the critical perimeter

Distingushing Between the Options "Enter" and "Determine"

RF-PUNCH Pro is able to determine the surface load inside the critical perimeter automatically by means of the load distribution on the surface in the respective load case.

Figure 02 - Setting for Determining and Considering the Surface Load Inside the Critical Perimeter Automatically

The intermediate results for the automatic determination of the surface load inside the critical perimeter are documented in Result Table "2.1 Punching Shear Design" in the "Applied Maximum Shear Stress" section. The applied size of the surface is also documented here.

Figure 03 - Table 2.1 with Result Details for Determining the Surface Load Automatically

The surface load applied in the add-on module can be checked graphically by displaying the "Load Distribution" for the governing CO (in this case CO9, see Results in Figure 03) for the 2D elements. You can find the distribution of load in the Results navigator when results display is activated for CO9.

Figure 04 - Load Distribution on the Surface for the Governing CO

If you select the "Enter" option, the dialog box changes and you can directly specify the load value.

Figure 05 - Enter Surface Load Inside the Critical Perimeter

Distingushing Between Load and Result Combinations

You can use the "Determine" option if there is a clearly defined load. This is the case if load combinations (COs) have been selected for the design in the "1.1 General Data" dialog box. If result combinations (RCs) are selected instead of COs, there is no clear load situation. In this case, message 58) will be displayed which says that the surface load inside the critical section cannot be determined for result combinations.

Figure 06 - Note on Calculation No. 58) When Applying a Result Combination

Keywords

Punching shear Wall corner Wall end Surface load Perimeter Shear force Punching Punching Shear Design

Reference

[1]   Eurocode 2: Design of concrete structures - Part 1‑1: General rules and rules for buildings; EN 1992‑1‑1:2004 +&nbso;AC:2010
[2]   Fingerloos, F.; Hegger, J.; Zilch, K.: Eurocode 2 für Deutschland - Kommentierte Fassung, 2., überarbeitete Auflage. Berlin: Beuth, 2016

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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