Design of neck welds of welded I-sections and box sections
The RF-/STEEL EC3 add-on module can perform the design of fillet welds for all parametric, welded cross-sections of the cross-section library. For this, the option must be activated in the detail settings of the module. Alternatively, a surface model can also be used for the design.
Loading of the neck fillet welds
The neck fillet welds of welded I-sections or the flank fillet welds of welded box girders are subjected to a shear force parallel to the weld axis when the beam is bent. The cause of this longitudinal shear force is that the welds prevent the flanges and the web from being displaced against each other. Only in this way can the cross -section act as a composite cross -section.
The resulting shear stress in the weld can be determined from the shear force distribution. The following formula is used for this:
|τ∥, Vz||Longitudinal shear stress in the neck seams from shear force|
|Sy||Static moment of the connected cross -section part|
|Iy||second moment of area|
|∑a||Sum of all weld thicknesses connected to the considered part of the cross -section|
In the case of box girder cross -sections, the flank fillet welds are additionally stressed by an acting torsional moment. Here, the shear stress in the welds is determined as follows:
|τ∥, Mx||Longitudinal shear stress in the flank fillet welds from torsional moment|
|[LinkToImage02]w||Thickness of a flank fillet weld|
Checking on the surface model in RFEM
Another method is the design of the neck welds on a surface model in RFEM. By using line releases, the shear flow in the connection can be efficiently read and then used for the evaluation. Alternatively, you can evaluate the shear stress on the web.
In the following example, the neck welds of the welded I-beam are designed under bending. For this, the stresses determined on the surface model are compared with the results of the calculation in RF-STEEL EC3.
The neck seams are each selected with 5 mm and thus a maximum longitudinalshear stress of τ ∥ = 266 kN/m/(2 · 5 mm) = 2.66 kN/cm² results from the surface model.
An alternative evaluation results from the shear stresses τxy in the web. In this case, it is necessary to convert the stresses from the web thickness of 8 mm to the effective weld thickness of 10 mm. In the example, the distribution of the shear stress is evaluated over a section at the bottom weld.
τ∥ = 3.34 kN/cm² · 8 mm/10 mm = 2.67 kN/cm²
The design in RF-STEEL EC3 provides a comparable shear stress of τ∥ = 2.72 kN/cm².
Unfortunately, the design of the neck welds in the RF-/STEEL EC3 add-on module is not possible for user-defined cross-sections created with SHAPE-THIN.
The loading of the welds due to a concentrated load introduction (e.g. wheel loads on crane runways) must be considered separately.
Dipl.-Ing. Oliver Metzkes
Product Engineering & Customer Support
Mr. Metzkes is responsible for the development of the add-on modules for steel structures and provides technical support for our customers.
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In RF-/FOUNDATION Pro, the foundation design requires the definition the corresponding loading (load cases, load combinations, or result combinations) for the different design situations (STR, GEO, UPL or EQU).
SHAPE-THIN determines the effective cross-sections according to EN 1993-1-3 and EN 1993-1-5 for cold-formed sections. You can optionally check the geometric conditions for the applicability of the standard specified in EN 1993‑1‑3, Section 5.2.
The effects of local plate buckling are considered according to the method of reduced widths and the possible buckling of stiffeners (instability) is considered for stiffened sections according to EN 1993-1-3, Section 5.5.
As an option, you can perform an iterative calculation to optimize the effective cross-section.
You can display the effective cross-sections graphically.
Read more about designing cold-formed sections with SHAPE-THIN and RF-/STEEL Cold-Formed Sections in this technical article: Design of a Thin-Walled, Cold-Formed C-Section According to EN 1993-1-3.
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