PSI - Issue 19

Helen Bartsch et al. / Procedia Structural Integrity 19 (2019) 395–404 Helen Bartsch, Benno Hoffmeister, Markus Feldmann / Structural Integrity Procedia 00 (2019) 000 – 000

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flexible connection panels. Modified nominal stresses must be determined for these connections. However, there is no criterion in (Eurocode 3-1-9, 2005) for the deformability of the connection plate, i.e. there are also no regulations as to when Detail 1 and when Detail 2 is to be applied. Additionally, in Table 8.5, no classification is given for a crack in the connection plate, which is especially in a flexible case subjected to large bending stresses. 3. Fatigue tests of endplate connections with prestressed bolts In the context of the present study, investigations on the fatigue behavior of end plate connections with prestressed bolts are carried out in form of large-scale and small-scale tests. As outlined in section 1 and 2, the stress determination of this detail currently requires expensive efforts and is incorporated into the code rather user unfriendly. On the basis of the fatigue tests in combination with numerical simulations, the global fatigue behavior of the prestressed bolt as the first and the weld as the second element at risk of fatigue failure in the bolted end plate connection is analyzed in order to give design requirements. Three different types of connections have been tested in terms of two large-scale and six small-scale tests each. The test specimens vary in the weld shape (fillet welds or butt welds) and the geometry of the end plate (overlapping or flush). The connection consists of two identical HEA 240 beams made of S355 with welded 30 mm end plates. The two welded beams are connected to each other with M24 bolts of grade 10.9 using a prestressing force of 220 kN according to (Eurocode 3-1-8, 2005). Fig. 2 depicts the layout of the specimens. For detailed information on the specimens, see (Enhancement detail catalouge, 2019).

Fig. 2. Layout of tested large- and small-scale specimens

The large-scale specimens have been tested in a four-point-bending test rig, while the small-scale specimens in terms of L-joints and T-joints have been investigated under pure tension in a four-column testing machine. In all cases a stress ratio of 0.1 has been applied. The failure criterion of the fatigue tests was the complete loss of strength (N4), resulting in a total fracture of the small scale specimens and a fracture of tension flange and web of large scale specimens. In order to record local magnitudes, apart from force and displacement measurements, strain gauges have been applied to all specimens to end plate and beam, especially for subsequent comparisons with numerical simulations. Also, at least one bolt per specimen has been applied with a strain gauge in the centre in order to measure tension bolt stresses. Failure in the large-scale specimens A and small-scale specimens LA occurred at first in the bolts. In the small scale tests, a failure of the weld could not be obtained. The second most critical detail after changing bolts during the test proofed to be the plate, which underlid a large amount of bending. Regarding specimens B and TB, the most critical detail was found to be the weld root. However, in some cases a combination of weld root and weld toe failure could be observed. All specimens of kind C and TC failed, as presumed, at the weld toe. Fig. 3 shows examples of fatigue fractures of the investigated large-scale and small-scale tests.