Journal: Journal of Engineering Mechanics

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American Society of Civil Engineers

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0733-9399
1943-7889

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Publications 1 - 10 of 20
  • Dynamics of the Vertically Restrained Rocking Column
    Item type: Journal Article
    Vassiliou, Michalis F.; Makris, Nicos (2015)
    Journal of Engineering Mechanics
    This paper investigates the rocking response of a slender column that is vertically restrained with an elastic tendon that passes through its centerline. Following a variational formulation, the nonlinear equation of motion is derived, in which the stiffness and the prestressing force of the tendon are treated separately. In this way, the post-uplift stiffness of the system can be anywhere from negative to positive depending on the axial stiffness of the vertical tendon. This paper shows that vertical tendons are effective in suppressing the response of smaller columns subjected to long-period excitations. As the size of the column or the frequency of the excitation increases, the effect of the vertical tendon becomes immaterial given that most of the seismic resistance of large rocking columns originates primarily from the mobilization of their rotational inertia.
  • Kirchhoff-Love Plate Deformations Reinterpreted
    Item type: Journal Article
    Marti, Peter; Kaufmann, Walter; Seelhofer, Hans; et al. (2022)
    Journal of Engineering Mechanics
    The deformations of Kirchhoff–Love plate elements are usually characterized by three components describing the strains in the middle plane and three components describing the bending of the plate element. It is shown that alternatively onemay consider pure bending deformations about two neutral axes that generally are not in the same plane and skew to each other. This interpretation provides an intuitive understanding of the plate deformations and is particularly useful when analyzing the behavior of reinforced concrete plate elements subjected to combined bending moments and membrane forces. After a recapitulation of the conventional interpretation of Kirchhoff–Love plate deformations and their implications on the strain distribution in plate elements, this paper presents the alternative interpretation and illustrates its application for a special case with orthogonal neutral axes.
  • Training of a Classifier for Structural Component Failure Based on Hybrid Simulation and Kriging
    Item type: Journal Article
    Abbiati, Giuseppe; Marelli, Stefano; Ligeikis, Connor; et al. (2022)
    Journal of Engineering Mechanics
    Hybrid simulation is a tool for investigating the dynamic response of a structural prototype subjected to realistic loading. Hybrid simulation is conducted using a hybrid model that combines physical and numerical substructures interacting with each other in a feedback loop. As a result, the tested substructure interacts with a realistic assembly subjected to a credible loading scenario. In the current practice, experimental results obtained via hybrid simulation support conceptualization and calibration of computational models for structural analysis. Instead, this paper extends the scope of hybrid simulation in constructing a safe/failure state classifier for the tested substructure by adaptively designing a sequence of parametrized hybrid simulations. Such a classifier is intended to compute the state of any physical-substructure-like component within system-level numerical simulations. It follows that the main contribution of this paper lies in the way experimental results are aggregated and integrated with structural analysis. The proposed procedure is experimentally validated for a three-degrees-of-freedom hybrid model subjected to Euler buckling.
  • Unconfined expansion of supercritical water flow
    Item type: Journal Article
    Hager, Willi H.; Yasuda, Youchi (1997)
    Journal of Engineering Mechanics
    The spread of supercritical free-surface flow on a smooth horizontal plane is considered. Experiments with selected approach Froude numbers are presented indicating that the effect of the Froude number may be dropped for hypercritical flow, that is, for values larger than 3. Also, a simple relation between local streamline direction and local flow depth is established. For sufficiently large approach flow depth, the Froude similarity law governs the phenomenon. Assuming that the streamwise velocity component is constant yields a system of equations identical to the one-dimensional simple wave problem. The solutions are compared with observations, and reasonable agreement is noted. Further particularities of hypercritical channel flow are established that are important for the numerical simulation of such currents. The features of expansion flow are documented with selected photographs. Supercritical unconfined expansion flow on a horizontal plane is studied. The governing equations can be shown to simplify considerably for hypercritical flow. A complete description is given based on both computations and experiments.
  • Robust-to-uncertainties optimal design of seismic metamaterials
    Item type: Journal Article
    Wagner, Paul-Remo; Dertimanis, Vasilis; Chatzi, Eleni; et al. (2018)
    Journal of Engineering Mechanics
    Metamaterials, which draw their origin from a special class of structured (periodic) materials characterized by a dynamic filtering effect, have recently emerged as a prospective means for structural seismic protection. This paper explores such a periodic arrangement in the form of local adaptive resonators buried in the soil, serving as a seismic protection barrier. As a starting point, a simplistic representation is chosen herein that comprises chains of mass-in-mass unit cells. A robust-to-uncertainties optimization of such a chain, addressing uncertainties at the level of the excitation, the system properties and the model structure itself, is conducted. The optimization problem is formulated within the context of reliability assessment, where the objective function is the failure probability of the structure to be protected against seismic input. The problem is solved through adoption of the subset optimization algorithm enhanced through the simultaneous implementation of a stochastic approximation algorithm. It is demonstrated that not all parameters of the chain model require optimization, because the failure probability proves to be a monotonic function of a subset of the parameters. A primary objective herein lies in optimizing the internal unit-cell stiffness properties. It is further demonstrated that the effectiveness of the protection offered by the metamaterial is improved for spatially varying unit-cell properties. The optimization procedure is carried out in the frequency domain, with an example application confirming that a time domain optimization is expected to yield similar optimal configurations. A parametric study using a nonlinear model is also presented, offering a starting point for more refined future investigations.
  • A Kriging–NARX Model for Uncertainty Quantification of Nonlinear Stochastic Dynamical Systems in Time Domain
    Item type: Journal Article
    Bhattacharyya, Biswarup; Jacquelin, Eric; Brizard, Denis (2020)
    Journal of Engineering Mechanics
    A novel approach, referred to as sparse Kriging–NARX (KNARX), is proposed for the uncertainty quantification of nonlinear stochastic dynamical systems. It combines the nonlinear autoregressive with exogenous (NARX) input model with the high fidelity surrogate model Kriging. The sparsity in the proposed approach is introduced in the NARX model by reducing the number of polynomial bases using the least-angle regression (LARS) algorithm. Sparse KNARX captures the nonlinearity of a problem by the NARX model, whereas the uncertain parameters are propagated using the Kriging surrogate model, and LARS makes the model efficient. The accuracy and the efficiency of the sparse KNARX was measured through uncertainty quantification applied to three nonlinear stochastic dynamical systems. The time-dependent mean and standard deviation were predicted for all the numerical examples. Instantaneous stochastic response characteristics and maximum absolute response were also predicted. All the results were compared with the full scale Monte Carlo simulation (MCS) results and a mean error was calculated for all the numerical problems to measure the accuracy. All the results had excellent agreement with the MCS results at a very limited computational cost. The efficiency of the sparse KNARX also was measured by the CPU time and the required number of surrogate model evaluations. In all instances, sparse KNARX outperformed other state-of-the-art methods, which justifies the applicability of this model for nonlinear stochastic dynamical systems.
  • Guided Wave–Based Defect Localization via Parameterized FRF-Based Reduced-Order Models
    Item type: Journal Article
    Sieber, Paul; Agathos, Konstantinos; Soman, Rohan; et al. (2024)
    Journal of Engineering Mechanics
    The use of Lamb waves within a guided wave (GW)–based scheme holds promise toward monitoring and nondestructive evaluation (NDE) of plate structures. Their short wavelength enables interaction with small defects and they can travel long distances, thus offering extensive spatial coverage. In boosting the performance of these schemes for more advanced damage identification tasks, such as precise damage localization and quantification, the fusion of measurement data with models is advantageous. Such a hybrid scheme, which relies on the inclusion of engineering models, is hampered by the short wavelengths of GW-based schemes. Short wavelengths require a fine discretization of numerical models in space and in time, which results in high computational costs. In alleviating this issue, we propose a reduced-order model (ROM) relying on exploitation of the frequency response function (FRF) principle, which is parameterized with respect to the positioning of local defects. Through appropriate coordinate transformations, the surrogate, constructed based on the matching pursuit (MP) algorithm, can exploit the mechanical properties of the wave so that only a small amount of training simulations are needed. The efficacy of the proposed surrogate is demonstrated in a synthetic inverse setting, using a particle swarm optimization (PSO) strategy.
  • Mode II Fracture Localization in Concrete Loaded in Compression
    Item type: Journal Article
    van Mier, Jan G.M. (2009)
    Journal of Engineering Mechanics
    As an alternative to a series-coupling model for localization of deformations under uniaxial and confined compression, an approach based on Mode II crack growth is proposed. Such a model appears to be in closer agreement to experimental observations than the presently used series-coupling model, and has the advantage that both material and structural aspects of softening are incorporated directly. Similarities to tensile fracture exist that would make the approach universal.
  • Progressive Collapse Mechanisms of Brittle and Ductile Framed Structures
    Item type: Journal Article
    Masoero, Enrico; Wittel, Falk K.; Herrmann, Hans Jürgen; et al. (2010)
    Journal of Engineering Mechanics
    In this paper, we study the progressive collapse of three-dimensional framed structures made of reinforced concrete after the sudden loss of a column. The structures are represented by elastoplastic Euler-Bernoulli beams with elongation-rotation failure threshold. We performed simulations using the discrete element method considering inelastic collisions between the structural elements. The results show what collapse initiation and impact-driven propagation mechanisms are activated in structures with different geometric and mechanical features. Namely, we investigate the influence of the cross sectional size and reinforcement α and of the plastic capacity β of the structural elements. We also study the final collapse extent and the fragment size distribution and their relation to α, β, and to the observed collapse mechanisms. Finally, we compare the damage response of structures with symmetric and asymmetric reinforcement in the beams.
  • Assessment of Uncertainty Propagation in the Dynamic Response of Single-Degree-of-Freedom Structures Using Reachability Analysis
    Item type: Journal Article
    Scacchioli, Annalisa; Bayen, Alexandre M.; Stojadinovic, Bozidar (2014)
    Journal of Engineering Mechanics
    A novel method to compute the bounds of the response of structures to dynamic loads, including earthquakes, is presented. This method, based on reachability analysis, deterministically predicts the sets of states an elastic structural system can reach under uncertain dynamic excitation starting from uncertain initial conditions, where deterministic uncertainty ranges describe uncertainties. Ellipsoidal approximations of these reachable sets for three canonical dynamic problems are presented to demonstrate the applicability of this method to singledegree-of-freedom (SDOF) systems. The principle of superposition is formulated as a concatenation of ellipsoidal reachable sets using their semigroup properties. Using this extension, computation of the external (worst-case) ellipsoidal approximation of reachable sets for a SDOF system under earthquake excitation is presented. Possible applications of this method for software validation and hybrid simulation are discussed. © 2014 American Society of Civil Engineers.
Publications 1 - 10 of 20