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000229473 005__ 20190317000748.0
000229473 0247_ $$2doi$$a10.5075/epfl-lchcomm-69
000229473 022__ $$a1661-1179
000229473 037__ $$aBOOK
000229473 245__ $$aInfluence of geometrical imperfections and flaws at welds of steel liners on fatigue behavior of pressure tunnels and shafts in anisotropic rock
000229473 269__ $$a2017
000229473 260__ $$aLausanne$$bEPFL-LCH$$c2017
000229473 336__ $$aBooks
000229473 490__ $$aCommunication (Laboratoire de constructions hydrauliques, Ecole polytechnique fédérale de Lausanne)$$v69
000229473 520__ $$aHigh-head steel lined pressure tunnels and shafts may be considered as critical infrastructures especially when rock overburden is small. In the case of lining failure, catastrophic damages can occur when a large amount of water can reach the steep valley slopes and induce dangerous mud and debris flow. In the last decades, high-strength steel has been used more frequently for such high-head pressure tunnels and shafts mainly for economic and construction reasons. Under the more and more rough operation conditions of storage hydropower plants, high-strength steels, which are generally thinner than lower grade steels, are more prone to fail by fatigue. Design guidelines for the application of high-strength steel for steel liners are still missing. With his research project, Dr Alexandre Pachoud made an important and novel contribution for the design of pressure tunnels and shafts considering the influence of anisotropic behavior of rock as well as the geometrical imperfections and flaws at welds on the fatigue resistance of the steel liners. For the first time, Dr Pachoud studied systematically the influence of rock anisotropy on the deformation of the lining system comprising steel liner, backfill concrete and near as well as far field rock mass. He performed an extensive parametric study with the finite element method (FEM) over a wide range of geometrical and material parameters. Normalized stresses and displacements were analyzed in the steel liner and the far-field rock mass and correction factors to be included in the analytical solution for isotropic rock conditions could be derived. For transversely anisotropic rock mass the analytical solution allows a simple and fast estimation of the maximum stresses in the steel liner by a correction applied to the isotropic analytical solution with a high accuracy. Based on extensive FEM simulations Dr Pachoud derived in a further step parametric correction factors, which allow estimating stress concentrations and structural stresses in steel liners considering geometrical imperfections. Dr Pachoud obtained also Stress Intensity Factors (SIF) for axial cracks in the weld material of the longitudinal joints by means of computational Linear Elastic Fracture Mechanics (LEFM) and could propose new parametric equations for the weld shape correction. For fatigue assessment, a probabilistic model for steel liner crack growth and fracture was developed by using the above mentioned new parametric equations for considering geometrical imperfections. Finally, Dr Pachoud illustrated the implementation of all the developed parametric equations in a probabilistic model for crack growth in the steel liner under dynamic loading with a case study for a high-head power plant. The probabilistic model allows determining the acceptable undetected initial crack sizes in the steel liner depending on the choice of the steel grade, which is crucial for engineering practice using high-strength steels for pressure tunnels and shafts.
000229473 6531_ $$asteel liners
000229473 6531_ $$apressure tunnels and shafts
000229473 6531_ $$afinite element method
000229473 6531_ $$aanisotropy
000229473 6531_ $$awelded joints
000229473 6531_ $$astress concentration factors
000229473 6531_ $$astress intensity factors
000229473 6531_ $$alinear elastic fracture mechanics
000229473 6531_ $$avariable amplitude loading
000229473 6531_ $$aprobabilistic fatigue crack growth
000229473 700__ $$0246915$$aPachoud, Alexandre Jean$$g179222
000229473 720_1 $$0241228$$aSchleiss, Anton$$eed.$$g112841
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