PSI - Issue 19

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

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The designation of the test series follows the rules “Joint_  _b 0 _t 0 _b i _t i _g_steel grade” with “K” for K -joint, brace opening angle  chord width b 0 and wall thickness t 0 , brace width b i and wall thickness t i , gap size g and steel grade. For the evaluation the nominal stress range is determined using the section of the loaded member, here the axially loaded brace (AX). This is general practice (Zhao et al, 2001), although the failure usually occurs at the chord section.

2.2. Fatigue Tests on RHS K-joints

Eighteen fatigue tests on K-joints with rectangular hollow sections made of steel grade S500 and S700 have been carried out in three different test series to investigate the influence of steel grade, see Table 1.

Table 1. Dimensions of RHS K-joints for fatigue testing.

Series

No. of

Chord [mm]

Brace [mm]

Gap g Brace Angle Material

tests

Width b 0 Thickness t 0 Width bi Thickness t i [mm]



K45_100_6_80_4_g25_S700 K45_130_4_80_4_g25_S500 K45_130_4_80_4_g25_S700

9 4 5

100 130 130

6 4 4

80 80 80

4 4 4

25 25 25

45 45 45

S700 S500 S700

The test results include the secondary bending effects resulting by pure axial load in the braces. As the joint geometry influences the secondary bending moments, a rough assumption for this influence is given in EN 1993-1-9 (2010) and by Zhao et al (2001). Accordingly, for braces of K-joints with gap made of RHS, the nominal stress range in the braces must be multiplied by a magnification factor MF = 1.5. The test results are compared to the standard S-N-curves for detail categories (DC) according to EN 1993-1-9 (2010) in Fig. 3. Outliers or run outs are marked with an arrow in the evaluation.

Fig. 3. Fatigue test results of RHS K-joints.