Design of local load introduction according to EN 1993-1-3

The design of cold-formed steel products is regulated in the standard EN 1993-1-3 [1]. Typical shapes of cold-formed cross-sections include U, C, Z, Hat, and Sigma profiles. These profiles are made from thin-walled sheets using roll forming or bending processes.

When verifying the ultimate limit states, it is essential to ensure that local load introductions do not cause undesirable effects such as compression, web crippling, or local buckling in the web of the profiles. Such effects can occur both from the load introduction through the flange into the web and from support forces at the support points. Section 6.1.7 of EN 1993-1-3 describes how to determine the bearing capacity of the web R_w,Rd under local load introduction.

The Steel Design Add-On allows for an analysis of local load introduction for unstiffened webs according to Section 6.1.7 [1]. In cases of combined actions from bending and local load introduction, it is also checked whether the conditions stated in [1] 6.1.11 are met.

An example of the corresponding verifications is presented below using a bending beam made of a cold-formed C-profile. The beam is subjected to a concentrated load.

System and Load

The considered beam has a length of 2 meters and consists of a cold-formed C-profile (C 2020) made from steel S235JR according to EN 10025-2. The support width is 110 mm each, and the beam does not extend beyond the support. The beam is loaded with a concentrated load of 10 kN at a distance of 50 cm from the support. The concentrated load is introduced over a length of 100 mm onto the flange and acts at the shear center. The self-weight of the beam is not considered in this calculation.

Structural System and Load

Data Entry

In the ultimate limit state configuration, the checkbox "Determine web bearing capacity under local load introduction according to 6.1.7" must be checked to enable verification of the local load introduction.

Ultimate Configuration

The necessary boundary conditions must be defined in the "Design Supports and Deflection" tab. At every location where local load introduction verification needs to be conducted, a design support of the type "Steel" must be defined. The length of the stiff load introduction s_s is entered in the "Support Width w" input field. However, the "Support Depth d" has no influence on the verification.

The local load introduction is investigated when the support is defined at the edge that is directed opposite to the action force. The directions "+z/z'-axis" and "-z/z'-axis" refer to the orientation of the local z/z'-axis of the member. When the concentrated load acts in the +z direction, the edge "-z/z'-axis" must be selected for the support.

For the supports, a design support with a length of the stiff load introduction of 110 mm at the edge of the "+z/z'-axis" is defined as an end support with an overhang length of 0 mm.

Design Support Type for Design at Support Location

For the concentrated load, a design support with a length of the stiff load introduction of 100 mm at the edge of the "-z/z'-axis" is defined.

Design Support Type for Design at Location of Concentrated Load

The support type for the supports is assigned to the member start and end, while the support type for the concentrated load is defined at the intermediate node at the location of the concentrated load.

Assigning Design Support Types

The design supports can also be graphically displayed. In the Navigator - Display, the display of the design supports can be activated or deactivated under Types for Members → Design Supports.

Navigator – Display of Design Supports

Results

The verification for the local load introduction is conducted at the defined design support locations – both at the supports and at the load introduction point. At the position x = 0.00 m, the highest utilization occurs. The verification is conducted at this point for illustration below.

Design of Local Load Introduction in Steel Design Add-on

There is a support reaction at a cross-section that has only one web. The C-profile with a plate thickness of t = 2.0 mm has stiffened flanges due to its lips. The distance of the support from the free end is 0.00 m and is thus less than 1.5 times the web height h_w = 198 mm. Thus, [1] Equation (6.15a) is decisive for determining the web bearing capacity R_w,Rd.

According to [1], 6.1.7.2 (3), the following coefficients are to be applied:

This results in the following web bearing capacity under local load introduction:

The verification condition according to [1] Equation (6.13) is satisfied:

The verification for the other two design locations is conducted analogously. It is also checked whether the conditions according to [1], 6.1.11 are met.

Summary

With the Steel Design Add-On, verifications for local load introduction according to [1] Section 6.1.7 can be conducted. Design supports must be defined at the design-relevant locations for this purpose. The verification for local load introduction is conducted according to [1] 6.1.7.2 for cross-sections with one unstiffened web or according to [1] 6.1.7.3 for cross-sections with two or more unstiffened webs. It is also checked whether the conditions according to [1], 6.1.11 are satisfied.