FATIGUE ASSESSMENT OF SHIP SUPERSTRUCTURE AT EXPANSION JOINT

Despite the long history of application of subdivided superstructures and deckhouses, and efforts of ship designers and researchers a sensible solution in design of reliable details at the cut endings was not found yet. It may be explained as consequence of controversial requirements in design of the cut endings. Fatigue design of the superstructure details is addressed to solution of the problem. Presented is an example of fatigue design of the cut ending in a fast ship superstructure based on application of modified «Strain-Life» criterion for fatigue and subsequent approach which utilizes Neuber’s formula and material cyclic properties. To realize the approach a procedure of the long-term stress distribution transformation to the block-type format is developed. Efficiency of the developed technique is illustrated by comparing the results with those of application standard S-N criteria based techniques. The results of analysis allowed selection of the expansion joint detail of the superstructure geometry and construction procedure providing necessary reliability.

Fatigue strength of normal and high strength steel joints improved by weld profiling

While some post-weld treatment techniques increase the fatigue life mainly due to induced compressive residual stress others are trying to create a smooth transition at weld toes. One of the latter is weld profiling. This study investigates the effect of weld profiling for four different steel types from S355 to S900 including one duplex stainless-steel and performs a comparison with high frequency mechanical impact treatment. The observed fatigue strength improvement is significantly higher than typically assumed for such techniques and comparable to increases observed for HFMI treatment. The fatigue strength further increases with parent material strength and is only slightly below the estimated fatigue strength of the parent material. Finally, fatigue design curves are proposed for weld profiling that include an increasing fatigue strength improvement for higher strength materials, but that are still conservative for low weld quality.

Research on anti-fatigue design method of welded structure oriented to stiffness coordination strategy

PurposeIn order to obtain the relationship between the geometry and stress concentration of load-bearing welded joints, the fatigue design method of welded structures based on stiffness coordination strategy is studied.Design/methodology/approachBased on the structural stress theory, a new method for anti-fatigue design of welded structures oriented to stiffness coordination strategy is proposed, and the detailed implementation process of this method is given. This method is also called the three-stage anti-fatigue design method for welded structures, which includes three stages, namely, identification, analysis and relief of stress concentration.FindingsThrough the experimental analysis of welded joints in IIW standard, the effectiveness of stiffness coordination in welded joint design is proved. The method is applied to the design of welded parts and products, and the feasibility of the method in alleviating the phenomenon of stress concentration and improving the fatigue resistance of welded structures is verified.Originality/valueIn this study, based on the principle of coordinated design of weld stiffness, a three-stage anti-fatigue design method of welded structure is proposed. The method has practical value for the optimization design and anti-fatigue performance improvement of welded structure in engineering products.

Fracture Mechanics and Fatigue Design in Metallic Materials

Devices, working structures and their elements are subjected to the influence of various loads [...]

Investigations on Interface Shear Fatigue of Semi-Precast Slabs with Lattice Girders

Due to their high cost efficiency and flexibility, semi-precast concrete slabs with lattice girders are widely used in constructions all over the world. Prefabricated concrete slabs, combined with in situ concrete topping, exhibit a quasi-monolithic structural behavior in which lattice girders serve as vertical shear reinforcement and ensure the transfer of longitudinal shear within the interface, acting in combination with concrete-to-concrete bonding mechanisms. To be applicable in industrial and bridge construction, semi-precast slabs need to have sufficient resistance against fatigue failure. To improve and expand the limits of application, theoretical and experimental investigations are conducted at the Institute of Structural Concrete (IMB), RWTH Aachen University. To investigate the fatigue behavior of lattice girders, small size tests with lattice girder diagonals were carried out. These test results have been used to derive an S–N curve (S: stress, N: number of load cycles) for lattice girders for a more refined fatigue design. Subsequently, the fatigue behavior of semi-precast slabs with lattice girders was investigated by fatigue tests on single-span slab segments. The fatigue design regulations of lattice girders according to technical approvals can generally be confirmed by this test program; however, they tend to be conservative. The use of the derived S–N curve leads to significantly improved agreement of fatigue behavior observed in tests and design expressions.

Statical Evaluation Of The Europe Bridge Between Kehl And Strasbourg According To The “Guideline For The Recalculation Of Existing Road Bridges” With Specific Mathematical And Structural Examination Of The Cracks In The Superstructure

<div>This master´s project re-evaluates the Europe Bridge after 60 years of service. The framework for the calculations is provided by the “Guideline for the Recalculation of Existing Road Bridges”. With the help of a computer model, generated by the program SOFiSTiK, and the prescribed loads of the guideline, the required checks in the ULS were performed at the main load bearing system. As the results indicate a high exceedance of the capacity, different alternatives were evaluated to restore the structural safety.</div><div><br></div><div>A specific focus was laid on the assessment of the cracks in a connection of the lateral load bearing system. Initially, a literature research on the crack formation in the superstructure of steel bridges was conducted. The gathered information points towards category three fatigue cracks that were caused by poor fatigue design and a discrepancy between static modelling and execution on site. These conclusions were confirmed by the fatigue checks of the affected connections. However, an analysis of the crack detail with a FE-model of the lateral system shows that the crack has no significant impact on the load bearing behaviour of other components. </div>