Papers by Silvano Erlicher
Lecture notes in civil engineering, 2023
Computer-aided Civil and Infrastructure Engineering, Aug 8, 2022
This paper aims to study the seismic mitigation of a typical nuclear small modular reactor (SMR) ... more This paper aims to study the seismic mitigation of a typical nuclear small modular reactor (SMR) where extreme loading conditions are considered by the safe shutdown earthquake. For this purpose, to reproduce the main dynamic properties of the reactor's reinforced concrete system, a detailed structural model was synthetized, also taking into account the presence of the reactor pools. Thus, to protect the reactor from strong earthquakes, finite locally resonant multiple degrees of freedom metafoundations were developed; and resonator parameters were optimized by means of an improved frequency domain multivariate and multiobjective optimization procedure. Also, the stochastic nature of the seismic input was taken into account. It is proposed: (i) a linear metafoundation endowed with multiple cells, linear springs, and linear viscous dampers; and (ii) a foundation equipped with additional nonlinear vertical quasi‐zero stiffness (QZS) cells. QZS cells were obtained by horizontally precompressed springs in an unstable state with vertical springs in parallel. With this arrangement, additional flexibility and dissipation against nonsymmetrical modes of the SMR and vertical seismic loadings are proposed. It was shown in both cases, how each metafoundation was successfully optimized via a sensitivity‐based parameter grouping strategy and a hybrid grid searching algorithm. Thus, the performance of the optimized metafoundations was assessed by means of frequency and time history analyses; and finally, results were compared with an SMR endowed with both rigid foundation and conventional base‐isolation solutions.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 29, 2008
Tires are made of viscoelastic materials with stiffness quite dependent on the frequency. General... more Tires are made of viscoelastic materials with stiffness quite dependent on the frequency. Generally, two causes of the stiffness increase are distinguished : a frequency dependence complex modulus and a geometrical stiffness. In this paper, an experimental and theoretical study on the relaxation and frequency dependence of complex moduli of the tire constitutive materials are presented and validated. Expressions of the viscoelastic behavior are presented in time and frequency domains. The results show that the real part of the Young's modulus is monotonic according to the frequency. It contributes to an important part of the stiffening. A numerical approach simulating the experimental results of the contact area of Cesbron is also presented. The tire is modeled with a real material distribution in the tire section. The geometrical stiffness also increases with the rotational velocity and it varies with the vibration frequencies. Static and dynamic computations for different rolling velocities are done. The results show that the contact area depends on the velocity of the rolling tire. Comparisons between the measurements and the computations show a good agrement and a decrease of about 20% in the contact areas when the tire rolls compared to a static tire. This difference can be explained by the viscoelastic properties of the materials
Annals of Solid and Structural Mechanics, Mar 26, 2016
One of the main objectives of crowd modeling is to optimize evacuation and improve the design of ... more One of the main objectives of crowd modeling is to optimize evacuation and improve the design of pedestrian facilities. In this work, a sensitivity analysis is performed to study the effect of the parameters of a 2D discrete crowd movement model on the nature of pedestrian's collision and on evacuation times. After presenting the proposed model in its full version (three degrees of freedom for each individual), a pedestrian-pedestrian collision is considered. We identified the parameters that govern this type of collision and studied their effects on it. Then an evacuation experiment of a facility with a bottleneck exit is introduced and its configuration is used for numerical simulations. It is shown that without introducing a social repulsive force, the obtained flow rate values are much higher than the experimental ones. For this reason, we introduced the social force as defined by Helbing and performed a parametric study to find the set of optimized values of this force's parameters that enables us to achieve simulation results close to the experimental ones. Using the values of the parameters obtained from the parametric study, the evacuation simulations give flow rate values that are closer to the experimental ones. The same optimized model is then used to find the density in front and inside the bottleneck and to reproduce the lane formation phenomenon as was observed in the experiment. Finally, the obtained results are analyzed and discussed.
HAL (Le Centre pour la Communication Scientifique Directe), Dec 1, 2013
International audienceConvex analysis is very useful to prove that a material model fulfills the ... more International audienceConvex analysis is very useful to prove that a material model fulfills the second law of thermodynamics. Dissipation must remains non-negative and an elegant way to ensure this property is to construct an appropriate pseudo-potential of dissipation. In such a case, the corresponding material is said to be a Standard Generalized Material and the flow rules fulfill a normality rule (i.e. the dissipative thermodynamic forces are assumed to belong to an admissible domain and the flow of the corresponding state variables is orthogonal to the boundary of this domain). The sum of the pseudo-potential with its Legendre-Fenchel conjugate fulfills the Fenchel's inequality and as the actual value of the dual pair forces-flows minimizes this inequality, this can be used as a convergence criterium for numerical applications. Actually, some very commonly used and effective models do not fit into that family of Standard Generalized Materials. A procedure is here proposed which permits to retrieve the normality assumption and to construct a pair of dual pseudo-potentials also for these non-standard material models. This procedure was first presented by the authors for non-associated plasticity. Now it is extended to a large range of mechanical problems
Lecture notes in civil engineering, Oct 21, 2017
The purpose of this article is to present the methodology used to define the soil-structure inter... more The purpose of this article is to present the methodology used to define the soil-structure interaction under multiple static loads of a nuclear power plant. Nuclear facilities are characterized by their geometrical complexity and by the large size of the buildings. This has induced the need for robust numerical tools and the need to develop a specific methodology. Actually, in structural calculations the soil is usually represented by linear springs defined at each node of the model by iterative process. When the stiffness computed at two subsequent iterations are almost identical, iteration is stopped. The obtained stiffness values depend on the load case. To simplify this process, and under condition of linearity of the soil behavior, it is proposed to compute the soil flexibility matrix which is finally integrated as a “superelement” within the software ANSYS for the structural computation. The soil flexibility matrix is an intrinsic representation of the soil, which is totally independent from the stiffness, loading, geometry of structures. Then, any modification of structures does not require the reconsideration of the boundary condition (soil). The effectiveness and accuracy of this procedure is discussed with reference to the case study of a nuclear power plant
HAL (Le Centre pour la Communication Scientifique Directe), Jun 22, 2009
For the serviceability analysis of civil engineering structures under human induced vibrations, a... more For the serviceability analysis of civil engineering structures under human induced vibrations, a correct modelling of the pedestrian-structure interaction is needed. The proposed approach consists in thinking the human body as a Single Degree of Freedom oscillator: the force transmitted to the floor is the restoring force of this oscillator. In rigid floor conditions, such an oscillator must be able to reproduce two experimentally observed phenomena: (i) the time-history of lateral force can be approximated by a periodic signal with a "natural" frequency related with the single pedestrian characteristics; (ii) the motion of a pedestrian is self-sustained, in the sense that the pedestrian produces by itself the energy needed to walk. Accounting for these aspects, a modified Van der Pol (MVdP) oscillator is proposed here to represent the lateral pedestrian force. The suitable form of its nonlinear restoring force is inferred from experimental data concerning a sample of twelve pedestrians. The experimental and model lateral forces show an excellent agreement. For a laterally moving floor, the MVdP oscillator representing a pedestrian becomes non-autonomous. It is well-known that self-sustained oscillators in the non-autonomous regime are characterized by the so-called entrainment phenomenon. It means that under certain conditions, the vibration frequency switches from the "natural" value to that of the external force: the response frequency is entrained by the excitation frequency. According to the physical interpretation considered here, the entrainment corresponds to the situation where the pedestrian changes its natural walking frequency and synchronizes with the floor oscillation frequency. The steady response of the MVdP oscillator subjected to a harmonic excitation is discussed in terms of non-dimensional amplitude response curves, obtained using the harmonic balance method truncated at the first harmonic. The model predictions are compared with some experimental results concerning pedestrians available in the literature and a good agreement is obtained.
Proceedings of the 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2019
Non-linear calculation results can be significantly different when considering monotone or cyclic... more Non-linear calculation results can be significantly different when considering monotone or cyclic analyses. The crack opening and re-closing phenomena are quite difficult to represent with non-linear constitutive models using finite elements methods. The comparison between seismic time-history and pushover analyses is performed in this paper using GLRC HEGIS non-linear global model for reinforced concrete mono-layer shell elements. It takes into account four different dissipative phenomena: concrete cracking, concrete damage, steel-concrete slip and steel yielding, by means of an analytical multi-scale analysis. This stress-resultant model is formulated for cyclic calculations in the framework of the thermodynamics of irreversible processes, in order to allow efficient numerical computations of earthquake engineering applications of RC buildings. This paper explores the validity range of this constitutive law through cyclic time-history analyses (that consider the crack opening and reclosing phenomena) and monotone pushover static analyses on asymmetric structures of CASH and SMART benchmarks. Pushover analysis is a nonlinear static procedure for evaluating the seismic margin of buildings accounting for their non-linear behavior. The pushover method used in this paper is the so-called Enhanced Direct Vectorial Addition (E-DVA) which defines the load pattern for the pushover analysis as a linear combination of load patterns proportional to the mode shapes. As this method is based on the application of a static force field with constant shape and increasing amplitude, only monotone non-linear phenomena are taken into account. The pushover and time-history analyses are performed (i) on the CASH benchmark model representing a multi-storey shear wall of a real nuclear power plant building structure and (ii) on the SMART benchmark mock-up representing a typical RC building of a nuclear facility. Several numerical comparisons are made at both global and Gauss points levels and are focused on the global mechanical behaviour and the computation of crack opening.
An emerging problem for civil engineering in the field of dynamics is the modelling of dynamic ef... more An emerging problem for civil engineering in the field of dynamics is the modelling of dynamic effects due to crowdstructure interaction. We are particularly concerned with structures such as footbridges, which oscillate due to the crossing of a group of pedestrians. The objective of this study is double: to model the movement of pedestrians with consideration of pedestrian-pedestrian and pedestrian-obstacle interactions and to include a pedestrian-structure coupling in the proposed model. This 2D discrete model would be able to study the problem of synchronization between pedestrians and structure on footbridges. Our idea is to extend the modelling of particles movements to study the movements of a crowd. The non-smooth discrete model of Frémond initially proposed to simulate a granular assembly, is chosen. It applies a rigorous thermodynamic framework in which the local interactions between particles are managed by the use of dissipation pseudo-potentials. Social forces as well as a desired direction/ velocity are introduced in order to simulate the behaviour of pedestrians. Concerning the pedestrian-structure coupling, a differential equation of Kuramoto allows one to manage the evolution of the pedestrians' phase. Two cases are studied depending on the sensitivity of pedestrians to the footbridge's oscillations. Numerical simulations on the Millenium Bridge are performed and discussed.
Strain, 2016
This paper describes the use of Digital Image Correlation (DIC) techniques for the cracking asses... more This paper describes the use of Digital Image Correlation (DIC) techniques for the cracking assessment of reinforced concrete (RC) massive beams and walls. DIC is known to provide accurate and detailed information on displacement and strain fields. Non‐contact measurements can be used to evaluate concrete cracking of destructive tests carried out on a wide range of specimen scales. When applied to large RC structures tested outdoors or in difficultly controllable conditions, DIC‐based methods may lead to erroneous results. In this study a post‐processing procedure is presented to cope with noisy full‐field measurements. The proposed cracking assessment approach is validated on a large experimental campaign. Four points bending tests are carried out on RC beams: firstly on full‐scale rectangular beams and then on mock‐ups scaled down by 1/3. In addition, fours RC walls are tested under in‐plane cyclic shear up to failure. Digital images taken throughout the tests are processed by DIC...
Pijaudier-Cabot/Electrohydraulic Fracturing of Rocks, 2016
Procedia Structural Integrity
Control of Cracking in Reinforced Concrete Structures, 2016
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Papers by Silvano Erlicher