Lock gates, penstocks, valves, turbines and storage tanks: many hydromechanical systems rely on metallic structures that are subjected to repeated loading year after year. These movements do not cause visible damage in the short term. Yet, after millions of loading cycles, steel gradually weakens. Cracks may initiate, propagate over time and eventually compromise the reliability and safety of the structure.<\/p>\n\n\n\n
In the hydraulic, energy and civil engineering sectors, many infrastructures built after World War II are still in operation today. Asset managers are therefore faced with a critical question: How can the remaining useful life of these structures be assessed reliably in order to anticipate maintenance, inspection and replacement needs?<\/strong><\/p>\n\n\n\n This is the challenge addressed by the PhD research of Kamal Harb<\/a>, conducted within the Medelia Chair<\/a>, with the objective of developing new analysis methods to improve the durability, safety and performance of metallic hydromechanical structures.<\/p>\n\n\n\n Bend and unbend a paper clip repeatedly. Eventually, it breaks, even though none of the individual movements would have been sufficient to cause failure. Hydromechanical steel structures are subjected to a similar phenomenon. Exposed to repeated loads over several decades, they may develop cracks that appear progressively, often in welded joints. Engineers refer to this process as fatigue degradation.<\/p>\n\n\n\n This degradation is not distributed uniformly throughout the structure. It tends to concentrate at structural discontinuities, particularly at welds. While essential for joining steel plates, welds also create geometric variations, residual stresses and localized material modifications. These areas are therefore common sites for crack initiation, with defects evolving from imperceptible to detectable and eventually critical.<\/p>\n\n\n\n An inspection can identify a crack once it exists. However, it cannot accurately predict when the next crack will appear, nor how quickly it will propagate.<\/p>\n\n\n\n Two structures that are identical on paper never age in exactly the same way. The mechanical properties of steel vary from one plate to another, no weld is perfectly identical to another, and loading conditions depend on operating regimes, vibrations and hydrodynamic effects. These parameters evolve over time and remain only partially known, particularly after several decades of service.<\/p>\n\n\n\n Traditional approaches often respond to this complexity with a single value: an estimated service life. Yet this figure gives an impression of certainty that does not fully reflect the actual behaviour of the structure.<\/p>\n\n\n\n Probabilistic fatigue analysis adopts a different perspective.<\/strong> Instead of defining a single end-of-life date, it evaluates multiple scenarios and produces risk indicators such as probability of failure, probability of survival, risk level and reliability index. The method explicitly incorporates uncertainties related to materials, loading conditions and the actual condition of the structure.<\/p>\n\n\n\n For asset managers, the difference is significant: rather than relying on a single number, they can assess risk levels and make informed decisions regarding inspection, strengthening, replacement or continued operation.<\/p>\n\n\n\n This PhD research develops a probabilistic fatigue assessment methodology for welded structures, with a particular focus on hydromechanical gate components. Its objective is to better account for the uncertainties that influence damage evolution and structural service life.<\/p>\n\n\n\n The approach is built on three complementary pillars:<\/p>\n\n\n\n The methodology is validated through case studies based on real structures provided by the project's industrial partners. This field validation ensures that the developed tools address practical needs related to inspection, maintenance and decision support.<\/p>\n\n\n\n For operators and asset managers :<\/strong><\/p>\n\n\n\n For society:<\/strong><\/p>\n\n\n\n This project is conducted in close collaboration with several industrial and academic partners: Artelia<\/a> \/ SPRETEC<\/a>, la Compagnie Nationale du Rh\u00f4ne (CNR)<\/a>, EDF<\/a> \u2013 EDF Hydro<\/a>, TEC21<\/a>, as well as the laboratories 3SR<\/a> and SIMaP<\/a>.<\/p>\n\n\n\n These collaborations make it possible to confront scientific developments with real operational cases using field data, feedback from operators and practical engineering challenges. They ensure that the methodologies developed meet the concrete needs of infrastructure owners and operators in the areas of inspection, maintenance and decision support.<\/p>\n\n\n\nFatigue: wear that cannot be seen<\/strong><\/h2>\n\n\n\n
Uncertainty at the heart of the analysis<\/h2>\n\n\n\n
A scientific approach<\/strong>th<\/h2>\n\n\n\n
Expected impacts<\/strong><\/h2>\n\n\n\n
Research grounded in real-world challenges<\/strong><\/h2>\n\n\n\n
Making research accessible: Kamal Harb, PhD Candidate within the medelia chair<\/strong><\/h2>\n\n\n\n