P 1458 - Optimisation of free structural steel geometries under arbitrary loading conditions with the aid of damage mechanics

P 1456 - Influence of realistic boundary conditions and structural systems on the stability behaviour of steel structures The use of slender steel profiles promotes the competitiveness of steel structures in building construction and industrial construction, but requires efficient design, especially for the often daunting stability verification of lateral-torsional buckling in construction practice. The simplified verification method with reduction factors, i.e. the well-known "equivalent member method", has its significance here. Despite increasing computer support and the use of numerical methods, it is frequently used in engineering practice and is therefore also familiar to planners from areas outside steel construction. However, practical connection designs in structural engineering, such as typical main and secondary beam connections, often deviate from the idealisations on which the method is based, especially the fork-supported single-span beam. Depending on the connection type, the torsional stiffness varies significantly and a significant difference in load-bearing behaviour between idealised and real structures can be assumed. For end plate connections, the restraining effect on the warping is known, but is generally not taken into account. And finally, single-span beams are rarely present at system level; continuous beams or frame beams are far more common. The aim of the research project is therefore to extend the range of application of simplified verification methods for lateral-torsional buckling both for practical bearing conditions and for structural systems. Initially, the results of research work already completed on the influence of connection types and multi-span beam and frame systems were analysed. The currently valid design methods and those included in the next generation of the Eurocode were summarised and explained. As part of an extensive test programme, experimental investigations were carried out at the University of Stuttgart on practical bearing conditions and at the Ruhr University Bochum on two-span beam systems. The results at the University of Stuttgart show the influence of different shear force connections on the profile deformations at the beam connection and the associated influence on the component load-bearing capacities achieved. The results of the Ruhr University Bochum show the stability behaviour of two-span beams as well as the influence of centre bearing design, torsional loading and normal compressive force on the component load-bearing capacity. The experimental investigations carried out served as the basis for supplementary numerical investigations. Numerical models validated in the tests were used to carry out numerous parameter studies. This made it possible to investigate the influence of parameters that were not covered by the test programme. Among other things, the torsion spring values of various practical bearing conditions were determined and requirements for the design of two-span beams on the centre bearing were defined for the mathematical consideration of ideal fork bearings. Based on the parameter analyses, analytical and numerical equivalent models were derived for practical bearing conditions, which enable the torsional softness to be taken into account compared to an ideal fork bearing when determining the elastic lateral-torsional buckling moment. The modified lateral-torsional buckling slenderness can then be used to conservatively and economically determine the lateral-torsional buckling resistance of various practical support conditions using the analytical design model from EN 1993-1-1:2023 para. 8.3.2.3. The scope of the stability verification from EN 1993-1-1:2023 Annex C.2 was extended so that practically relevant two-span beam systems with double-symmetrical and -ݕ-axis single-symmetrical (U-)cross-sections can also be designed. The objective of the research project was achieved. Publication: January 2024 Authors: Prof. Dr. sc. techn. M. Knobloch, Dr.-Ing. R. Winkler, A.-L. Bours, Prof. Dr.-Ing. U. Kuhlmann, F. Jörg

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 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