Ultimate Limit State Design of Rail Welds of Crane Girders According to EN 1993-6

Technical Article

If crane runway girders are designed with flat steel rails, the welding of these rails is always a detail for the design. As a rail fixing, you can generally select between continuous and intermittent fillet weld. The following article provides an overview of the design processes and their specific features, especially when using the EN 1993‑6.

Arrangement Options of Rail Fillet Welds

There are two variants of intermittent fillet welded connections. These are shown in the following figure from [2].

Figure 01 - Arrangement Options

Weld sections can be arranged either on opposite sides or staggered. The staggered arrangement is disadvantageous for the design since only one weld can be used for the transfer of horizontal loads. The third option that is not shown in the figure above, is a continuous fillet weld along the entire rail length, of course.

Figure 02 - Continuous Weld

Effective Loaded Length

The determination of the corresponding weld stresses requires the calculation of effective loaded lengths. EN 1993‑6 [3] differentiates between three options and provides the corresponding formulas for the calculation of leff in Table 5.1.

Figure 03 - EN 1993-6, Table 5.1

In this case, leff refers to the underside of the top flange. However, the upper surface of the top flange is governing for the weld design. Therefore, leff is reduced by double flange thickness tf.

Figure 04 - Effective Loaded Length

Ultimate Limit State Designs

Rail weld stresses are calculated according to Directional Method specified in [2]. In this case, the stresses refer to the bisecting surface of the fillet weld. According to [2], (NA) Section 4.5.2, the minimum structural thicknesses must be kept for the weld. The standard requires a weld the minimum thickness of at least 3 mm or the application of the following formula:

$$\mathrm a\;\geq\;\sqrt{\max\;\mathrm t}\;-\;0.5$$

The eccentric wheel load of 1/4 of the rail head width is not taken into account at the ultimate limit state according to [3]. Therefore, the design due to wheel loading is always performed.

Case 1: Continuous Rail Weld

Figure 05 - Stresses at Ultimate Limit State

For intermittent rail fillet welds, it is necessary to check whether the weld length lw is smaller than the calculated loaded length leff. Generally, the minimum of both values is governing for the design.

Figure 06 - Fillet Weld

Case 2: Intermittent Rail Weld on Opposite Sides

Figure 07 - ULS Stresses of Intermittent Rail Weld on Opposite Sides

Case 3: Staggered Intermittent Rail Weld

Since the horizontal load is only applied to a weld section in the case of the staggered arrangement of welds, Divisor 2 is omitted in terms of HEd.

Figure 08 - ULS Stresses of Staggered Intermittent Rail Weld

Reference

[1]   Seeßelberg, C. (2016). Kranbahnen: Bemessung und konstruktive Gestaltung nach Eurocode (5th ed.). Berlin: Bauwerk.
[2]   Eurocode 3: Design of steel structures - Part 1‑8: Design of joints; EN 1993‑1‑8:2005 + AC:2009
[3]   Eurocode 3: Design of steel structures - Part 6: Crane supporting structures; EN 1993‑6:2007

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