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# Ongoing research projects

IMMC

### Ongoing research projects in iMMC (November 2021)

This a short description of research projects which are presently under progress in iMMC.

Hereunder, you may select one research direction or choose to apply another filter:

### List of projects related to: Civil and environmental engineering

WholeTrackResearcher: Nicolas Docquier Supervisor(s): Paul Fisette The project aims at improving railway track lifecycle by improving its components such as the ballast, the sleeper, elastic pads, ... It consists in developing computer models coupling multi-body system dynamics (MBS) and granular modelling method (the discrete element method, DEM). Full scale experiments are conducted in parallel to validate the numerical models and assess the developed solutions. |

Optimization of tensegrity bridges based on morphological indicatorsResearcher: Jonas Feron Supervisor(s): Pierre Latteur Tensegrity structures are composed of struts and tendons in such way that the compression is “floating” inside a net of tension in a stable self-equilibrated state. Although tensegrity forms have inspired artists and architects for many years, there exist very few real construction projects across the world. The main reasons are, among others, the complex construction processes and the lack of design guidelines. This research, performed in collaboration with the company BESIX, aims at proving the feasibility of a first pure tensegrity bridge around the world. When the structure is externally loaded, large displacements occur and require non-linear calculation before reaching an equilibrium. Indeed, in tensegrity structures more than in conventional ones, form and forces are intrinsically correlated. This phenomenon is due to their intern mechanism, unless appropriate pre-stressing is applied. An allowable stiffness can be possible, but at a certain material cost, which in turn justifies the relevance of the optimization of the weight. While designing a tensegrity structure, optimization and form finding are often great challenges. Indeed, the large amount of parameters (span, height, shape, cross sections, materials, loads, pre-stress, etc) makes the search for the structure with the best performances cumbersome. A solution to this problem is to reduce the number of degrees of freedom to consider, by grouping them into dimensionless numbers, the morphological indicators. In 2014, R.E. Skelton et al were pioneers in using a similar approach for optimizing planar tensegrity bridges uniformly loaded. In 2017, P. Latteur et al adapted the morphological indicators methodology, used so far to optimize mainly trusses and arches, to 3D non-linear and pre-stressed lattice structures such as tensegrity structures. In 2019, J. Feron et al used this methodology to investigate the performances of different 3D forms of uniformly loaded tensegrity footbridges. This research focus on the required checks to ensure the practicality, the constructability and the economical and structural efficiency of a pure tensegrity footbridge thanks to non linear finite element analysis, experimental validation, parametric design, prestress optimization and dynamic behavior assessment |

Morphological impact of dam-flushingResearcher: Robin Meurice Supervisor(s): Sandra Soares Frazao An important number of dams worldwide face sedimentation issues, leading to a decrease in their reservoir capacity and hence, many difficulties to properly satisfy to their different functions (e.g. water distribution, flood management, hydroelectricity production). To overcome these problems, we can proceed to dam flushing operations, transporting huge amounts of sediment downstream of the dam. Nevertheless, these operations can be harmful to the environment, the living organisms and the human infrastructures if not properly handled. For that reason, this thesis aims at developing a numerical model capable of accurately predicting the sediment deposition downstream of a dam after flushing operations. In order to do so, several mathematical models shall be implemented, among which a two-phase two-layer model, and laboratory experiments shall be run. The numerical model will then be confronted with the data collected from the experiments. Finally, the model will be tested with real-case data collected in situ near Lyon, France. |

Evaluation of alternative damping approaches for nonlinear time history analysis, and their influence on the development of fragility curves used in seismic risk, for low-to-moderate seismicity regions.Researcher: Jose Baena Urrea Supervisor(s): Joao Saraiva Esteves Pacheco De Almeida One of the major sources of uncertainty in dynamic non-linear time history analysis (THA) of structures is modelling of damping as this parameter is not easy to measure and continues largely misunderstood. Damping simulates energy dissipation on structural and nonstructural elements that is not explicitly modelled. Although it is known to be frequency-independent and amplitude-dependent, these features are not typically considered by practicing engineers. The classical and most used model is Rayleigh damping, developed in the XIX century as a mathematic convenient representation of friction effects in acoustic waves transmission. During the last decades, engineers have accepted this model in linear THA because the damping forces are relatively small compared with the other resisting forces in the structures and due to efficiency, simplicity and low computational cost. Contrary to this, when nonlinear THA are performed, several numerical pathologies appear such as spurious damping forces in the massless degrees of freedom and other issues resulting from stiffness decay during the analysis. Over the years researchers have developed damping models to overcome these challenges, but the scientific community still did not reach a generalised agreement. The most suitable model will depend, to a certain degree, on the specific structural problem. Unfortunately, one major concern with damping modelling is that the structural response can change drastically depending on the model used. Nonlinear THA are commonly used to define fragility functions, which are statistical curves of performance relating demands (accelerations and displacements, typically) versus probability of exceedance of reaching a specific level of damage. They are used in the context of seismic risk analyses and will depend on the damping model employed. This research focus on evaluating current models and proposing an alternative approach better matching experimental evidence of the response at the element level. Subsequently, the influence of these damping models on the development of fragility curves will be assessed. Finally, their impact on the final outcome of seismic risk assessment for low-to-moderate seismicity regions, such as Belgium, will be computed and interpreted. |