Nathanaël SavalleUniversity of Minho · Institute for Sustainability and Innovation in Structural Engineering (ISISE)
Post-doctoral fellow working on the seismic behaviour of masonry structures
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PhD at University of Lyon, France. Working on drystone retaining walls. Especially interested in their seismic behaviour: analytical, experimental and numerical approaches (using UDEC (Itasca) DEM numerical model).
March 2020 - present
April 2016 - October 2019
- PhD Student
- Seismic behaviour of Drystone Retaining Walls, with the aim at providing recommendations for their design. Analytical (pseudo-static), Numerical (real dynamic DEM simulations) and Experimental (tilting tests and shaking-table tests) approchaes.
April 2015 - August 2015
- Master's Student
- SEMA Project: Statistical model to predict the most probable stuctural state of sewer canalizations. Database management and analysis - study of the uncertainty associated with the canalisation inspection (structural evaluation) process.
Dry-stone retaining walls can be found worldwide and constitute critical assets of the built heritage for many sloped territories, holding cultural and economic value. Their design currently follows empirical rules, though the first steps towards a static safety assessment have recently been proposed in the scientific and engineering literature. Ho...
Heritage masonry structures are often modelled as dry-jointed structures. On the one hand, it may correspond to the reality where the initial mortar was weak, missing, or has disappeared through time because of erosion and lixiviation. On the other hand, this modelling approach reduces complexity to the studied problem, both from an experimental an...
Masonry structures have been observed to display a high vulnerability to failure under seismic action. This stems from the fact that their structural configurations usually lack adequate connections among the distinct elements, resulting in the formation of local mechanisms experiencing Out-Of-Plane (OOP) collapse. In this context, rocking dynamics...
Modelling masonry bond pattern is still challenging for the scientific community. Though advanced Laser Scanning methods are available and allow to extract blocks sizes and shapes of actual masonry structures, they are up to now very time-consuming and complex to set up. Therefore, modelling masonry as an ideal and regular assemblage of regular uni...
The observation of damages caused by past seismic events demonstrated the high vulnerability of masonry systems, which represent intrinsically diverse and complex structures with resistance to horizontal forces highly dependent on the capacity of ensuring a monolithic behaviour. In this framework, tilting tests represent a low-cost and effective st...
A two-step strategy for the mechanical analysis of unreinforced masonry (URM) structures, either subjected to in- and out-of-plane loading, is presented. At a first step, a semi-automatic digital tool allows the parametric modeling of the structure that, together with an Upper bound limit analysis tool and a heuristic optimization solver, enables t...
In this paper, an experimental study aiming at understanding the seismic behaviour of dry stone retaining walls is presented. Harmonic shaking table tests have been carried out on scaled-down dry-joint retaining walls involving parallelepiped bricks. It is found that a thicker wall is more resistant and that a given retaining wall is less sensitive...
This erratum is published due to vendor overlooked corrections related with Table 6 during proofing. The original article has been thus corrected with the corrected references and thus updated. A pseudo-static study on dry-joint brick retaining walls has been carried out as part of a preliminary work aiming at designing actual dry stone retaining...
In this paper, an experimental study aiming at understanding the behaviour of dry stone retaining walls to shakings is presented. Harmonic shaking table tests have been carried out on scaled-down dry-joint retaining walls involving parallelepiped bricks. It is found that a thicker wall is more resistant and that a retaining wall is less sensitive t...
Slope Dry Stone RetainingWalls (DSRWs) are vernacular structures made of rubble stones assembled without mortar. DSRWs are present worldwide and may have been built hundreds and even thousands years ago. They have always played a key role in economic sectors like agriculture, transportation and at present tourism. However, the lack of scientific kn...
Dry stone retaining walls (DSRWs) are vernacular structures, which consist in a specific assemblage of individual rubble stones. Herein, we propose some recommendations to achieve a correct modelling of the mechanical behaviour of DSRWs towards failure with the use of the Discrete Element Method (DEM). There are two kinds of DSRWs, those that just...
A pseudo-static study on dry-joint brick retaining walls has been carried out as part of a preliminary work aiming at designing actual dry stone retaining walls located in seismic areas. First, scaled-down dry-joint brick retaining walls have been tilted towards failure and the influence of the wall geometry has been analysed. Then, numerical simul...
Dry stone retaining walls (DSRWs) are vernacular structures which can be found all over the world. Most of them have been built in the 19th century but they can be as old as two hundred years. Because of decades of neglect, many of these walls are highly damaged; however, in the absence of national rules for this peculiar heritage, any intervention...
Dry stone retaining walls (DSRWs) are vernacular structures, present worldwide, and made of rubble stones assembled with a precise know-how without any mortar. As many of them were built in the XIX th century and have not been maintained for decades, they need today some repairs or even sometimes whole reconstruction. However, the lack of national...
Dear RG members,
I'm carrying dynamic analysis on retaining walls using UDEC software (DEM).
I'm asking myself what kind of damping should be used (Rayleigh damping, local damping, no damping) for my analysis.
In fact, it seems that Rayleigh damping is more appropriate for dynamic analysis. However, on an identical model, changing the damping (from no damping to rayleigh damping or from local damping to rayleigh damping) led to an decrease of the timestep from 1e-5 to 1e-7 (depending on the values (freq, damping) chosen for the rayleigh damping). This new value of timestep make the simulations hundred times longer which is not satisfactory.
Do you have any ideas to deal with this problem? Do you know why the timestep is decreasing?
I've read the UDEC manual and the described methodology to compute the timestep in dynamic analysis, but it does not match the values given by UDEC.
Thank you !
Dear RG members,
I'm carrying dynamic analysis on retaining walls using UDEC. Concerning boundary conditions (especially the input motion boundary), I would like to use a stress input motion (as described in the UDEC Manual). However, at the end of the shakings, the whole model still move, with a constant velocity.
Maybe, it's not a problem since the whole model is moving, but it seems that even during the shakings, the whole model moves (see attached picture).
Do you have any idea to deal with this problem ?
I've succeeded in using the velocity input motion but want to use the stress input in order to add quiet boundaries.
Thank you !
Built historic masonry structures are important cultural assets in Europe, playing a key role in the economy, through tourism. Their correct maintenance/assessment is thus unavoidable, while they are very sensitive to out-of-plane loading through earthquake motions. The present project aims at defining new standards for the out-of-plane performance assessment of masonry structures. It follows a very complete process, from the study of the seismic input, to the seismic capacity of masonry structures and the occurence of specific damage limit state. 1) Sampling of realistic earthquake motions generated from real earthquakes, parameter representative variation and Monte-Carlo simulations 2) Extensive shaking-table testing of masonry specimens (plastered, mortared, dry-stack, rocking blocks) under various input signals. Use of state-of-art Non-Damaging-Testing methods (DIC, sonic tests, infrare thermography, ...) 3) Development and validation of intermediate numerical approaches (Rocking dynamics, Macro-element models) against the extensive experimental dataset in a probabilistic way. Incremental Dynamic Analysis used to build up the response statistics. 4) Definition of specific limit state for built heritage (e.g associated to the safeguard of mural paintings) in terms of out-of-plane displacement. Extraction of guidelines for performance assessment of heritage buildings.
Give some clues of the seismic behaviour of drystone retaining walls. Produce recommandations for the seismic design of these vernacular structures to repair and rebuild old (over 100 years) and damaged ones.