P 1456 - Influence of realistic boundary conditions and structural systems on the stability behaviour of steel structures

P 1455 - Development of normative principles for the consideration of prestressing force losses in prestressed bolted joints in steel construction with surfaces coated on all sides In steel construction, bolted connections are prestressed for reasons of serviceability or load-bearing capacity. A distinction is made between target level I and target level II. Target level I (load-bearing capacity relevant) describes slip-resistant connections of categories B/C as well as tensile connections subject to fatigue loading of category E. In the case of prestressed connections of target level I, the prestressing force is included in the mathematical verification. As a result, it must be ensured that the prestressing force remains in the designed connections over the service life of a structure. Target level II (serviceability) is used for categories A and D to avoid slippage and deformation. Immediately after assembly, there is a drop in the applied prestressing forces due to the effects of settlement and creep or cyclic loading. In this research project, the influences of selected tightening methods and coating systems on bolted prestressed connections according to DIN EN 1993-1-8 were specifically investigated, which can be assigned to categories B/C and category E and thus to target level I, but can also be prestressed for serviceability reasons and thus be assigned to target level II (connections of categories A and D). In order to be able to evaluate the influences of settlement effects, relaxation tests were carried out, whereby the results were extrapolated to a service life of 50 years. The influence of cyclic loading on the static friction of the paired contact surfaces was investigated by means of static-drag GV tests, both before and after cyclic loading. By means of quasi-static tests as well as cyclic loading, preload losses on category E connections were determined, extrapolated to 2-109 load cycles and evaluated. The test specimens were designed with M16 HV fittings, lockbolt systems and M20 IHF bolt fittings and analysed using various tightening methods, clamping length ratios and coating systems. The test results provided fundamental insights into the influence of coating systems commonly used in steel construction on the initial prestressing forces, the resulting system reserves and the loss of prestressing force. It was shown that the prestressing force losses also increase with increasing coating thickness. Furthermore, the selected tightening methods had a non-negligible influence on the achievable initial prestressing forces (and thus system reserves) and on the resulting prestressing force losses. The knowledge gained can be used to formulate recommendations for the further handling of the coating systems investigated and the selected tightening methods. The objective of the research project was achieved. Publication: 2024 Authors: Univ.-Prof. Dr.-Ing. habil. N. Stranghöner, Dr.-Ing. L. Makevičius, P. Werner M.Sc, Univ.-Prof. Dr.-Ing. W. Flügge, Dr.-Ing. M. Schwarz

P 1454 - Safeguarding the process chain for the application of higher-frequency hammering processes in offshore wind turbines The aim of the research project is to investigate the influence of HFH processes on the service life extension of offshore wind turbines. Offshore steel structures are predominantly subject to non-stationary stresses, whereby the fatigue analysis is generally decisive. To date, there have been no comprehensive investigations into the effect of HFH treatment on the fatigue strength of offshore-relevant construction details such as T-joints and longitudinal welds, which need to be investigated. The aim is also to test the surface requirements for corrosion protection and to analyse the influence of shot blasting on the fatigue strength of HFH-treated weld seams. Furthermore, the research project includes experimental and numerical investigations into the effect of varying HFH parameters on the indentation depth and the resulting fatigue strength of weld seams in offshore-typical construction details. In this context, quality requirements are to be developed and corresponding assurance measures derived. The results will be used to develop validated notch case recommendations, especially for monopiles, and their inclusion in the DASt guideline 026 should enable a more economical design of corresponding structures. Publication: October 2024 Authors: Prof. Dr.-Ing. T. Ummenhofer, Prof. Dr.-Ing. Engelhardt, Dr.-Ing. P. Weidner, Dr.-Ing. St. Gkatzogiannis, D. Löschner, D. Kopic

P 1458 - Optimisation of free steel construction geometries under arbitrary loading conditions with the aid of damage mechanics In this research project, the load-bearing behaviour of free steel construction geometries, in particular with high-strength steels, was initially investigated experimentally. Damage mechanics simulations were then carried out in order to be able to numerically model the arbitrary stress states and different types of failure. Extensive investigations and calibrations were carried out in advance, whereby an approach was developed to take into account the mesh size dependency in order to be able to draw conclusions from the damage parameters determined on a laboratory scale to the component scale. The developed approach was prepared for application so that it can be used with commercial FE software. The numerical models were then successfully validated in laboratory and component tests. Further geometric and material influences on the load-bearing behaviour were investigated in additional numerical studies. Based on the experimental and numerical results, the design rules according to Eurocode 3 for various details, in particular bolted connections and beams with web openings, could be checked and optimised. The greatest potential for optimisation was identified in the design of the bearing resistance of the holes. The knowledge gained also offers great potential for reviewing and deriving further design rules based on damage mechanics simulations in the future. The project results will favour the use of high-strength steels in the future, which will primarily benefit planning companies, e.g. engineering offices, as well as manufacturers, which are predominantly SMEs. Germany will also be strengthened as a business location, as a great deal of expertise in the production and use of high-strength steels is available here. Furthermore, the results allow for more economical steel constructions, which can save costs and resources. By saving important resources and realising removable (bolted) connections, the sustainable use of steel in particular is promoted. The objective of the research project was achieved. Publication: February 2024 Authors: F. Eyben, Dr.-Ing. H. Bartsch, Dr.-Ing. S. Schaffrath, Univ.-Prof. Dr.-Ing. M. Feldmann, V. Göksu, D. Lenz, Dr.-Ing. M. Könemann, Univ.-Prof. Dr.-Ing. S. Münstermann

P 1438 - Development and testing of a modelling framework for the predictive investigation of erosive wear in pneumatic conveyors As part of the research project, wear in pneumatic conveyors was analysed by means of numerical and experimental investigations both on the microscopic length scale of individual particle impact events and on the macroscopic scale of pipe bends. A total of four steel grades - three stainless steels and one structural steel - and one plastic were experimentally analysed with regard to their wear resistance in contact with round and angular bulk material particles in different wear situations. This enabled the materials to be assessed in terms of their wear resistance in different applications and the significant influence of the shape of the bulk material particles to be identified. The relevance of the particle shape for erosive wear was confirmed by detailed numerical simulations using SPH. Based on the simulation results, an established, analytical erosion model, which quantifies the wear per impact, was successfully extended by two parameters that characterise the particle shape. This has created a model that is suitable both for rapid estimations of the wear behaviour of a specific bulk material and can also be integrated directly into CFD-DEM simulations for process analysis. Experiments were carried out to characterise the particles used in order to obtain contact parameters for CFD-DEM simulations. These include, for example, particle-particle and particle-wall contact parameters, with the help of which contact phenomena of the materials to be analysed could later be validly represented. Furthermore, experimental investigations have shown that typical wear patterns on paint coatings can be generated and are reproducible. In addition, methods for measurement were investigated with which a quick and simple evaluation should be possible. The method shows new possibilities for realising material-friendly wear tests within the shortest possible time or not necessarily requiring special measurement technology. The implementation of a validation simulation using CFD-DEM showed that experimental results could be reproduced with a high level of agreement, which opens up the possibility of varying system and process parameters and investigating the influences on wear. In addition to the variation of velocities and mass loadings, these parameters also include the use of different wear-reducing pipe bend geometries and their influence on wear rates, pressure loss and particle loading. This showed that, depending on the application, wear rates can be significantly reduced without a disproportionate increase in pressure loss. The objective of the research project was achieved. Publication: August 2022 Authors: Prof. Dr.-Ing. H. Kruggel-Emden, M. Sc. E. Drescher, Dr C. Bierwisch, Dr Sh. Mohseni-Mofidi