PSI - Issue 19

Jennifer Hrabowski et al. / Procedia Structural Integrity 19 (2019) 267–274 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

268

2

manufacturing. So, for example for high strength steels as well as for sections with large thickness only little information about the fatigue behavior is available. In addition, today's software and hardware solutions offer a much wider range of possibilities. Associated with this, there is often a great uncertainty in the design and calculation of hollow section joints. Preliminary investigations have shown, that in several cases this could lead to very conservative and uneconomic design on the one hand, or to unsafe constructions on the other hand (Herion et al. 2014). So, fatigue tests as well as extensive numerical parameter studies are carried out to establish a base for the extension of the application range of common design rules.

Fig. 1. Hollow section K-joint with gap (Zhao et al. 2001)

2. Recent Research

2.1. General

Since the release of the CIDECT Design Guide 8 in 2001 (Zhao et al., 2001), nearly no further research on the fatigue behavior of K-joints with gap have been published. To the fatigue behavior of K-joints with normal or higher strength steel grades only few publications are available, mostly based on finite-element analysis (FEA) (Herion 2018). To close the lack of knowledge concerning the use of high strength steels, CCTH initiated and coordinated a joint research project of KIT Steel and Lightweight Structures with TNO Structural Dynamics lab in Delft, Netherlands as an additional project partner (FOSTA P1132 / CIDECT 7AB). As part of this project TNO performed fatigue tests on hollow section K-joints on a custom produced test frame with single acting jacks at the two braces and at the chord, see Fig. 2. The tests are carried out load and frequency controlled using constant amplitude loads with a stress ratio of R = +0.2 or R = +0,1. Within the experimental investigations K-joints with gap made of RHS or CHS are examined. All K-joints have a brace opening angle of 45°. Hereby, the main emphasis is on fatigue tests with constant amplitudes and axially loaded braces (load case AX). The failure criterion for the tests is a through thickness crack, as usually defined for hollow sections. To enable the verification of subsequent finite-element analysis (FEA), statically loaded tests on specimens prepared with strain gauges are carried out, too.

Fig. 2. Test set-up at TNO for K-joints.