Especially in railway vehicles like wagons and locomotives pre-loaded (pre-stressed) bolted joints are applied in purpose of maintenance or repair. Those bolted joints offer the opportunity to demount and reinstall components and assemblies e. g. accumulators and drive units.

The configurations of the bolted joints mostly lead to a ratio between clamp length and diameter of lk/d ≈ 1. This fact is caused by the low thickness of the sheet metal and the necessary diameter of the bolt for prestressing with their mandated property class. To execute pre-stressed bolted joints with such small ratios between clamp length and diameter is prohibited by standards and regulations, e. g. DIN 25201-2 which is a national standard for bolted railway joints. Therein clamp length diameter ratios lk/d ≈ 3...5 are recommended. In consequence, this recommendation leads to usage of long extension sleeves in the bolted joint to raise the clamp length diameter ratio up to the mentioned range. The extension sleeves can induce an additional of weight up to 200 kg in total for a single wagon. With the aim of lightweight design for the approval for railway vehicles, additional weight has to be principally avoided. The following article deals with the comparison of overlapped shear stressed bolted joints with and without extension sleeves. The experimental results are evaluated in respect of the necessary proof of load bearing capacity of shear joints.

In the construction concept for railway vehicles pre-loaded bolted joints are not allowed to slip or gap under working stress except in crash load scenarios. Therefore the frictional engaged load capacity to be obtained by the preload respectively the clamp load in the pre-stressed bolt. With the actual durability approvals e. g. according to VDI 2230 or DIN 25201-2 the computation with small clamp length diameter ratios deliver a tremendous loss of preload in respect of embedding. This loss has to be taken appropriately into consideration by subtraction from the preload. The friction coefficient in combination with the residual preload respectively clamp load returns the limiting slip load. To avoid an utilization of the cutting load in relation to the slip load > 1 extension sleeves are applied.

In the studies, slip loads are experimentally determined for joints with and without extension sleeves in pre-loaded bolted joints. Furthermore, two different tightening procedures are taken into account. At the one hand, the conventional torque-controlled tightening method is used, on the other hand yield-controlled tightening procedures are evaluated. The results of the investigations doubt the necessity of expansion sleeves for pre-loaded bolted joints in railway vehicles.