Simon Schaffrath

Ultra-Low-Cycle Fatigue Behaviour of Full-Scale Elbows

This paper presents an investigation concerning the ultra-low-cycle fatigue (ULCF) characterization of large-scale elbows produced from line pipes subjected to hot bending process. Two distinct pipes were used in this process: a 16” (w.t. 9.5 mm) X60 and an 8 5/8” (w.t. 5.59 mm) X65 pipes that were bent to 45 and 90° elbows (8 tests). Cyclic external loading was applied to the elbows, combined with internal pressure, until failure was observed. The failure was preceded by a local plastic instability (bucking) and resulted due to intense cyclic plastic deformation. In general, the number of cycles to failure was lower than 100 cycles which typifies this failure mechanism as ultra-low-cycle fatigue. Besides the full-size tests, the plain material was investigated under ULCF conditions using both smooth and notched specimens. The thermal process used in the hot bending manufacturing process was also accounted for in the material testing in order to understand the effect of this process on pipe material. Non-linear finite element models of the elbows were constructed to simulate the cyclic behaviour of the elbows using the actual loading histories applied to the elbows. Damage models (e.g. Coffin-Manson, Xue) identified using material test data are applied to simulate the failure cycles of the tested elbows. Besides the use of damage models available in the literature and identified with generated materials experimental data, current ASME VIII Div.2 procedures are also used to compute the failure cycles of the elbows to allow an assessment of these existing procedures.Copyright

Seismic Design of Steel Frames with Fuseis Beam Link Energy Dissipation Systems

Within the EU funded project INNOSEIS different seismic devices developed in earlier projects are worked up with the aim to provide information sheets and design guidelines for an easy practical implementation of these systems. One of these seismic protection systems is the FUSEIS beam link concept. The main idea is to use two closely spaced strong columns rigidly connected by several beams, resulting in a Vierendeel girder in upright position. Energy dissipation is originated by plastification of the connecting girders, similar as in seismically designed moment resisting frames. Forming the lateral load resisting system but not taking part intentionally in the vertical load transfer, the girders can be inspected and replaced much more easily after a strong earthquake. In this paper, first the FUSEIS beam link system is described in detail supported by results of experimental tests. Behaviour and main mechanical principles are outlined. Further on, three case studies consisting of steel office buildings of different heights are designed for seismic loads using the FUSEIS beam link solution. 878 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 878-890

Prediction of Ductile Damage in Case of Seismic Action using Innovative Damage mechanics

Abstract. An approach to investigate the true behaviour of dissipative elements utilising numerical simulations is presented. By way of example dissipative members in terms of beamcolumn connections of moment-resisting frames are considered. Material failure in terms of crack formation is taken into account by incorporating a damage mechanics model into the numerical analyses. By means of a phenomenological damage mechanics model, which is based on critical strains depending on the stress state, an efficient simulation of large scale components is enabled. To validate this approach, an extensive testing program has been performed. Subsequently, numerical simulations of the experimental investigations have been conducted.