Out-of-Plane Bending Moment-Induced Hotspot Stress Evaluation Using Advanced Numerical Technique

There have been various studies to predict out-of-plane bending (OPB) moment-induced stresses in mooring chain links. Recently, the BV guideline as one of the deliverables from OPB JIP reported empirical formulas to predict the nominal OPB moment-induced stress with suitable concentration factors (SCFs) so that prediction of the OPB moment-induced hotspot stresses can be available. A non-linear finite element analysis technique has been developed to more accurately estimate the OPB moment-induced hotspot stress. There has been no choice but to apply prescribed rotation to generate the OPB moment in this numerical technique (existing approach). Pointing out some disadvantages in the BV guideline and existing approach, an advanced numerical was proposed to simulate more realistic tension-induced OPB mechanism. In the present paper, basic differences were presented in terms of numerical simulation techniques, nominal OPB moments, and hotspot OPB stresses. In order to show differences of the stress distributions and the hotspot OPB stresses between existing and advanced approaches, a benchmark chain link model was constructed in which the nominal diameter was 107mm. From the comparison of stress distributions in straight parts of the link, significant differences were found between the existing and advanced approaches. The existing approach more developed the compressive stresses due to the prescribed rotation-induced OPB moment than the advanced approach. This also led to more increased hotspot OPB moments.

Fatigue assessment of a high-speed railway composite steel-concrete bridge by the hot-spot stress method

PurposeThe purpose of this paper is to investigate the fatigue performance of a welded detail from a composite steel-concrete railway twin girder bridge caused by a passenger train circulating at varying speeds, by identifying the dynamic amplification scenarios induced by resonance. For this purpose, the hotspot stress method is used, instead of the traditional nominal stress methods.Design/methodology/approachThis paper assesses the fatigue behavior of a welded connection considering critical stress concentration locations (hotspot). Finite element analysis (FEA) is applied, utilizing both a global and a local submodel, made compatible by displacements field interpolation. The dynamic response is obtained through the modal superposition method. Stress cycles are extracted with the rainflow counting method and the fatigue damage is calculated with Palmgren-Miner’s rule. The feasibility of five submodels with different mesh densities, i.e. 1, 2, 4, 8 and 20 mm is verified.FindingsAn increase in the fatigue damage due to the resonance effect was found for the train traveling at a speed of 225 km/h. A good agreement between the computed fatigue damage for the submodels is achieved. However, a non-monotonic hotspot stress/fatigue damage vs mesh density convergence was observed with a peak observed for the 4 mm model, which endorses the mesh sensitivity that could occur when using the surface stress extrapolation detailed rules specified in the standards for the hotspot stress method.Originality/valueAdvanced dynamic analyses are proposed to obtain local stresses in order to apply a local method for the fatigue assessment of a bridge’s structure subjected to high-speed railway traffic on the basis of the mode superposition technique resulting in much less computing times.