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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1. Introduction Many types of steel structures, such as cranes, crane runways and bridges, are subjected not only to static but also to time-varying loads which can lead to failure due to fatigue of the construction. For the fatigue check in EC 3-1-9 (Eurocode 3-1-9, 2005) detail category tables are given indicating the fatigue strength of specific components. Current research works concern the re-evaluation of the detail catalogue of the Eurocode (Enhancement detail catalouge, 2019). End plate connections with prestressed bolts are nowadays indispensable as an economical and easy-to-assemble connection. However, the existing regulations for the use of end plate connections with prestressed bolts when the load is not predominantly static, e.g. on crane runway girders, are inadequate. In EC 3-1-9 (Eurocode 3-1-9, 2005), the notch details of the end plate connection with prestressed bolts are not specified in a user-friendly way. Within a component, notches of any kind lead to a disturbance of the force flow. As a result, strong local stress peaks occur which must also be taken into account when determining weld stresses for the fatigue check of the T joint (Detail 2, Table 8.5, EC 3-1-9). This requires complex numerical simulations. Another problem is the verification of prestressed bolt connections (Detail 14, Table 8.1, EC 3-1-9). The tables to be used require knowledge of the true bolt force, which in turn can only be taken into account by finite element simulations. In order to be able to include the fatigue details of the end plate connection more practically in a future, revised version of the Eurocode, experimental and numerical investigations of their fatigue behavior are necessary. After a short literature review, the third chapter deals with the experimental tests carried out on end plate connections with fillet as well as butt welds, overhanging and flush endplates and prestressed bolts. The tests performed on three series with small and large scale specimens are then described and the test results are shown. Chapter 4 presents the numerical simulations of the tests using local fatigue design concepts. First, the developed finite element (FE) model is described in detail. Subsequently, the model verification by comparing simulations to test results is outlined. Using the numerical model a parametric study is carried out, as presented in Chapter 5, to investigate the influence of geometry on the fatigue behavior of end plate joints. The influences of end plate thickness, bolt diameter, hole spacing and the dimensions of the girder on the bolt and weld stresses are investigated separately. Standardized joints are also examined. The outcome of these simulations may lead to design recommendations. 2. Literature review 2.1. Fatigue design according to EC 3-1-9 The verification procedure against fatigue according to (Eurocode 3-1-9, 2005) is based on fatigue strengths in terms of S-N curves. Determined by the fatigue detail with its metallurgical and geometric notch effects, the fatigue strengths are specified in FAT classes by the detail category tables in (Eurocode 3-1-9, 2005). For standard cases, the tables are based on nominal stresses Δσ c at N C = 2 · 10 6 load cycles. Previous investigations have shown (Sedlacek, G. et al., unpublished), however, that the bases of the current detail catalogue are incomplete and that some details must have been categorized without an experimental basis. Therefore, within the framework of current research activities (Feldmann, et al., 2019 (yet unpublished)), a re evaluation as well as an extension of the fatigue detail catalogue is carried out (Bartsch, et al., 2018). Since global verification methods such as the nominal stress concept are only applicable to a limited extent due to the required stress values, a fatigue strength evaluation with local stress concepts is often necessary. The advantage of these local concepts lies in the exact determination of the decisive fatigue stress, independent of the detail to be investigated. Also in combination with fatigue test results, these concepts can be very useful in the context of fatigue detail classifications. In contrast to nominal stress concept, the effective notch stress concept additionally takes into account local stresses at the weld toe and the weld root (Fricke, 2008). Thus, the detail shape of a weld is integrated into the evaluation. The effective notch stresses depict maximum principle stresses at the weld toe or root, which can be determined by means of finite element method (FEM). For the depiction of the exact weld geometry, a filleting of