research details

Fatigue of K joints


CIDECT 7AB "Fatigue behaviour of hollow sections joints and high strength steel"

Within the last few years the need for lightweight structures made of steels with yield strengths of 355 MPa and higher is increasing, not only for statically, but also for fatigue loaded structures. Welded plates made of S460 and S700 has been widely investigated and are now successfully used in the fields of machine building, plant and crane construction.

Besides that, also new application fields become important, such as use of hollow sections in the area of e.g. wind energy, bridges and roller coasters and amusement rides. The type of joint most frequently used is the K-joint with gap as generally used in lattice girders.

For high strength steels as well as for sections with large wall thickness only isolated information about the fatigue behavior of such joints is available. The rules given in CIDECT Design Guide 8 are mainly based on experimental investigations on joints with small wall thicknesses (rectangular hollow sections RHS with maximum wall thickness
of 12 mm, circular hollow sections with maximum wall thickness of 16 mm) made of S235 or S355.

Preliminary studies have shown that existing design rules are not necessarily applicable to the mentioned application fields and parameter ranges, since this might lead on the one hand to very conservative and uneconomic or on the other hand also to unsafe solutions.

This research will form the basis for an expansion of the parameter range of the existing design rules to a larger wall thickness and high strength steel grades or a reformulation of the design rules for a safe and also economic design of fatigue loaded K-joints.

This project  is supported by CIDECT and coordinated and elaborated by KoRoH. The experimental investigations on smaller specimens are subcontracted to TNO, Delft. In the scope of the cooperation project FOSTA P1132, with financial support of Stiftung Stahlanwendungsforschung, large scale tests will be carried out at KIT Steel & Lightweight Structures, Karlsruhe. 

Competence Center

Thanks to the many years of experience of our employees and the active participation in standardization and international committees, we have been able to build up solid and extensive competences in hollow profile applications.


Engineering services

Our services include verification of stability, fatigue design, dimensioning and optimization of steel structures including offshore constructions. We carry out investigations to clarify damages and residual life and prepare damage analyzes and expert opinions.



Konzept, Layout und Programmierung von