Showing papers in "Journal of Engineering Mechanics-asce in 2015"
TL;DR: An algorithm for the implementation of BUS is proposed, which can be interpreted as an enhancement of the classic rejection sampling algorithm for Bayesian updating, and its efficiency is not dependent on the number of random variables in the model.
Abstract: Bayesian updating is a powerful method to learn and calibrate models with data and observations. Because of the difficulties involved in computing the high-dimensional integrals necessary for Bayesian updating, Markov chain Monte Carlo (MCMC) sampling methods have been developed and successfully applied for this task. The disadvantage of MCMC methods is the difficulty of ensuring the stationarity of the Markov chain. We present an alternative to MCMC that is particularly effective for updating mechanical and other computational models, termed Bayesian updating with structural reliability methods (BUS). With BUS, structural reliability methods are applied to compute the posterior distribution of uncertain model parameters and model outputs in general. An algorithm for the implementation of BUS is proposed, which can be interpreted as an enhancement of the classic rejection sampling algorithm for Bayesian updating. This algorithm is based on the subset simulation, and its efficiency is not dependent on the number of random variables in the model. The method is demonstrated by application to parameter identification in a dynamic system, Bayesian updating of the material parameters of a structural system, and Bayesian updating of a random field–based finite-element model of a geotechnical site.
186 citations
TL;DR: In this paper, the unscented Kalman filter is used to estimate unknown material parameters in frame-type structures, such as a cantilever steel column representing a bridge pier and two-dimensional steel frame.
Abstract: This paper proposes a novel framework that combines high-fidelity mechanics-based nonlinear (hysteretic) finite-element (FE) models and a nonlinear stochastic filtering technique, referred to as the unscented Kalman filter, to estimate unknown material parameters in frame-type structures. The proposed identification framework updates nonlinear FE models using spatially limited noisy measurement data, and it can be further used for damage identification purposes. To validate its effectiveness, robustness, and accuracy, this framework is applied to a cantilever steel column representing a bridge pier and two-dimensional steel frame. Both structures are modeled using beam-column elements with distributed plasticity and are subjected to a suite of earthquake ground motions of varying intensity. The results indicate that the material parameters of the nonlinear FE models are accurately estimated provided that the loading intensity is sufficient to exercise the parts (branches) of the nonlinear material...
98 citations
TL;DR: In this article, single-lap direct-shear tests were carried out on FRCM strips, comprised of one layer of fiber net embedded within two layers of matrix, bonded to a concrete block.
Abstract: Fiber-reinforced cementitious matrix (FRCM) composites represent a newly developed promising technique for strengthening RC structures. The FRCM composites are comprised of high-strength fibers applied to the concrete substrate through an inorganic cementitious matrix. In this work, single-lap direct-shear tests were carried out on FRCM strips, comprised of one layer of fiber net embedded within two layers of matrix, bonded to a concrete block. The weakness of FRCM-concrete joints was observed to be the debonding at the matrix-fiber interface. The experimental results indicated that the role of each matrix layer is different. The stress-transfer mechanism between the fiber filaments and the matrix layers on either side of the fiber net was studied by means of a fracture mechanics approach, and three models of the interfacial cohesive material law were proposed for each matrix-fiber interface.
94 citations
TL;DR: In this article, a novel outlier-resistant extended Kalman filter (OR-EKF) is proposed for outlier detection and robust online structural parametric identification using dynamic response data possibly contaminated with outliers.
Abstract: Structural health monitoring (SHM) using dynamic response measurement has received tremendous attention over the last decades. In practical circumstances, outliers may exist in the measurements that lead to undesirable identification results. Therefore, detection and special treatment of outliers are important. Unfortunately, this issue has rarely been taken into systematic consideration in SHM. In this paper, a novel outlier-resistant extended Kalman filter (OR-EKF) is proposed for outlier detection and robust online structural parametric identification using dynamic response data possibly contaminated with outliers. Instead of definite judgment on the outlierness of a data point, the proposed OR-EKF provides the probability of outlier for the measurement at each time step. By excluding the identified outliers, the OR-EKF ensures the stability and reliability of the estimation. In the illustrative examples, the OR-EKF is applied to parametric identification for structural systems with time-varyin...
78 citations
TL;DR: In this paper, the authors investigated the seismic response of a rocking frame with columns unequal in height (asymmetric), which are either freestanding or hybrid, and established the equations of motion following the principles of analytical dynamics.
Abstract: Unlike conventional seismic design, the columns of a rocking frame are designed to uplift and pivot during earthquake excitation. This paper investigates, analytically and numerically, the seismic response of a rocking frame with columns unequal in height (asymmetric), which are either freestanding or hybrid, i.e., enhanced with supplemental damping and recentering capacity. The paper establishes the equations of motion following the principles of analytical dynamics. Throughout the study, the deformation of the structural members is considered negligible. The analysis considers both pulse-type and non-pulse-type (historic) ground motions. It shows that the effect of asymmetry on the seismic stability of the rocking frame is marginal compared with the symmetric configuration, despite the very different kinematics of the corresponding rocking mechanisms. In contrast, the seismic stability of the hybrid rocking frame is very sensitive to fracture elongation of the supplemental restoring (tendons) an...
77 citations
TL;DR: In this article, bottom-standing and surface-piercing porous structures of finite width placed at a finite distance from a vertical rigid wall were analyzed based on the small-amplitude water wave theory in water of finite depth.
Abstract: The current study deals with the oblique wave trapping by bottom-standing and surface-piercing porous structures of finite width placed at a finite distance from a vertical rigid wall Using the Sollitt and Cross model for wave motion within the porous structure, the problems are analyzed based on the small-amplitude water wave theory in water of finite depth The solutions of the associated boundary value problems are obtained analytically using the eigenfunction expansion method and numerically using a multidomain boundary-element method In the boundary-element method, the boundary value problems are converted into integral equations over the physical boundaries The physical boundaries are discretized into a finite number of elements to obtain a system of linear algebraic equations Various aspects of structural configurations, in trapping surface gravity waves, are analyzed from the computed results on the reflection coefficients and the hydrodynamic forces Suitable arrangements of the rigid
76 citations
TL;DR: In this paper, a 3D elastoviscoplastic (EVP) constitutive model for both normally consolidated and overconsolidated clays is presented, which combines a logarithmic creep function with the reloading function of the unified hardening (UH) model.
Abstract: A new three-dimensional (3D) elastoviscoplastic (EVP) constitutive model for both normally consolidated and overconsolidated clays is presented In developing the new model, first the time effects on clays were connected with the change of overconsolidation degree according to the concepts of aging time and the instant normal compression line This made it convenient to combine a logarithmic creep function with the reloading function of the unified hardening (UH) model (a model for overconsolidated clays), and, thus, an isotropic EVP relationship was built Second, a time variable derived from the isotropic EVP relationship was embedded into the current yield function of the UH model, and, thereby, a time-dependent current yield function is proposed Based on the time-dependent current yield function and the flow rule, an EVP model for triaxial compression stress states was built The EVP model for triaxial compression stress states then was extended to a 3D EVP model for general stress states thr
65 citations
TL;DR: In this paper, the authors investigated the rocking response of a column that is vertically restrained with an elastic tendon that passes through its centerline and derived a nonlinear equation of motion, in which the stiffness and the prestressing force of the tendon are treated separately.
Abstract: 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.
64 citations
TL;DR: In this paper, an anisotropic plasticity model is proposed to describe the fabric effect on sand behavior under both monotonic and cyclic loading conditions within the framework of critical state theory, which employs a cone-shaped bounding surface in the deviatoric stress space and a yield cap perpendicular to the mean stress axis to describe sand behavior in constant mean stress shear and constant stress ratio compression.
Abstract: An anisotropic plasticity model is proposed to describe the fabric effect on sand behavior under both monotonic and cyclic loading conditions within the framework of anisotropic critical state theory. The model employs a cone-shaped bounding surface in the deviatoric stress space and a yield cap perpendicular to the mean stress axis to describe sand behavior in constant mean stress shear and constant stress ratio compression, respectively. The model considers a fabric tensor characterizing the internal structure of sand associated with the void space system and its evolution with plastic deformation. The fabric evolution law is assumed to render the fabric tensor to become codirectional with the loading direction tensor and to reach a constant magnitude of unit at the critical state. In constant stress ratio compression, the final degree of anisotropy is proportional to a normalized stress ratio. An anisotropic variable defined by a joint invariant of the fabric tensor and loading direction tensor...
63 citations
TL;DR: In this article, a new type of nonlinear energy sink (NES), termed a track NES, is proposed, where the shape of the track over which the auxiliary mass moves determines the character of the nonlinear restoring force for the NES.
Abstract: A new type of nonlinear energy sink (NES), termed a track NES, is proposed in this paper. The shape of the track over which the auxiliary mass moves determines the character of the nonlinear restoring force for the NES. After deriving the equations of motion for the track NES, numerical optimization is carried out for the system implemented in a two-degree-of-freedom primary structure. The optimization results are in the track shape of a fourth-order polynomial. The performance of the track NES is compared with an equivalent tuned mass damper (TMD) and the Type I NES, which utilizes a cubic restoring force. The results of this comparison show that the attenuation observed with the track NES is competitive with the Type I NES and is more robust against changes in the underlying structure than the TMD. Moreover, the track NES is more scalable and offers greater flexibility in prescribing the associated nonlinear restoring force.
59 citations
TL;DR: In this paper, the first moments of the steady-state response of a dynamical random system are determined through a polynomial chaos expansion (PCE) and a Monte Carlo simulation that gives the reference solution.
Abstract: The first two moments of the steady-state response of a dynamical random system are determined through a polynomial chaos expansion (PCE) and a Monte Carlo simulation that gives the reference solution. It is observed that the PCE may not be suitable to describe the steady-state response of a random system harmonically excited at a frequency close to a deterministic eigenfrequency: many peaks appear around the deterministic eigenfrequencies. It is proved that the PCE coefficients are the responses of a deterministic dynamical system—the so-called PC system. As a consequence, these coefficients are subjected to resonances associated to the eigenfrequencies of the PC system: the spurious resonances are located around the deterministic eigenfrequencies of the actual system. It is shown that the polynomial order required to obtain some good results may be very high, especially when the damping is low. These results are shown on a multidegree-of-freedom (DOF) system with a random stiffness matrix. A 1-D...
TL;DR: In this article, an in-house-built rheological device, made of assemblies of custom-made nickel titanium-Naval Ordnance Laboratory (Nitinol) strands, wires, and steel wire ropes, is experimentally tested in different configurations corresponding to three distinct constitutive behaviors: a strong hardening pinched hysteresis, a quasi-linear-softening behavior, and an intermediate behavior in the range of interest.
Abstract: An in-house–built rheological device, made of assemblies of custom-made nickel titanium-Naval Ordnance Laboratory (Nitinol) strands, wires, and steel wire ropes, is experimentally tested in different configurations corresponding to three distinct constitutive behaviors: a strong hardening pinched hysteresis, a quasi-linear–softening behavior, and an intermediate behavior in the range of interest. The nonlinear features of the hysteretic rheological device are the result of geometric hardening of the ropes, interwire friction, and dissipation caused by the phase transformations of the Nitinol wires. These different mechanisms determine a pinching at the origin of the hysteresis force-displacement loops. A phenomenological representation of the experimentally acquired constitutive responses is obtained by an extension of the Bouc-Wen model incorporating a pinching function that depends on two parameters. The responses of the Nitinol wires and strands under uniaxial tension are instead well identifie...
TL;DR: In this article, the authors presented a description and results from validation studies for the Karagozian & Case (K&C) concrete (KCC) model, which is primarily intended for modeling the dynamic responses of RC structural components.
Abstract: A description and results from validation studies for the Karagozian & Case (K&C) concrete (KCC) model are presented in this paper. This material model is primarily intended for modeling the dynamic responses of RC structural components. It is based on a partially associative plasticity theory and has proven itself capable of replicating most of the key behaviors of concrete, such as those related to hardening, softening, rate effects, confinement, shear dilatancy, and fracture. Three pressure-sensitive, independent strength surfaces are used by the KCC model to capture the variations in hardening and softening behaviors exhibited by concrete. These three strength surfaces are used to compute a failure surface that reflects the influence on the concrete’s behavior of the current stress and strain states at a material point. This dynamic form of the failure surface is realized by interpolating between pairs of fixed-strength surfaces on the basis of the value of a damage parameter computed by the K...
TL;DR: In this paper, the effect of soil grading on the stress-strain and the critical-state behavior of granular materials from idealized spheres to natural soils as well as from discrete to continuous modeling was investigated.
Abstract: The aim of this paper is to investigate the effect of soil grading on the stress-strain and the critical-state behavior of granular materials from idealized spheres to natural soils as well as from discrete to continuous modeling. The three-dimensional discrete-element method has been applied to study the mechanical behavior of idealized granular materials. The results confirm that the critical-state line (CSL) shifts downward as grading broadens with an increase of the coefficient of uniformity Cu. An exponential relationship between the critical-state parameters and the coefficient of uniformity Cu can then be established. Furthermore, experimental investigations on an artificial material (glass beads) and a natural material (Hostun sand) were carried out. The experimental results confirm the grading dependency of the critical-state behavior, and a similar relationship between CSL and Cu, for both glass beads and natural sand, extending previous literature results for high Cu values up to 20. Mo...
TL;DR: In this paper, a vehicle-bridge coupled (VBC) system was first theoretically derived in a system consisting of a simply supported beam and a single-degree-of-freedom vehicle, and a numerical study was conducted to investigate the feasibility of detecting bridge damages using the vehicle transmissibility.
Abstract: Research on damage detection is commonly carried out in the frequency domain using methods based on the modal data, transfer function or frequency response function, and transmissibility. The motivation for using transmissibility to detect damages relies on the fact that transmissibility measurements are local quantities that suggest high sensitivity. Nevertheless, the measurement of transmissibility requires external harmonic forces as the known input and sensors directly attached to the structure. There is a need for methods that can perform damage detection without attaching sensors and knowing the details of the input excitations. In a vehicle-bridge coupled (VBC) system the vehicle can serve as a force exciter and its dynamic response can be easily measured. In this paper, to make use of the vehicle response the transmissibility of a VBC system was first theoretically derived in a system consisting of a simply supported beam and a single-degree-of-freedom vehicle. Then, a numerical study was conducted to investigate the feasibility of detecting bridge damages using the vehicle transmissibility of the VBC system. In the numerical analysis, several damage indicators were constructed based on the transmissibility from both the bridge and vehicle responses, and compared to each other to select a proper one for damage detection. A parametric study was conducted on factors such as the measurement numbers, road roughness, and vehicle speeds and numbers to analyze the effectiveness of using such indicators for damage detection. To make use of the mobility of moving vehicles, two methods were finally proposed to measure the transmissibility of vehicle responses by using two vehicles. Method I used one reference vehicle and one moving vehicle; Method II used two moving vehicles at a constant distance in the longitudinal direction along the bridge. Using these two methods, the modal information such as natural frequencies and modal shape squares was successfully extracted for damage detections.
TL;DR: In this paper, an unscented Kalman filter with unknown input (UKF-UI) is proposed for structural health assessment, which does not need the information on the time history of the excitation to identify structural systems represented by finite elements and can identify defects in them using only a limited amount of noise-contaminated nonlinear response information.
Abstract: A novel procedure for structural health assessment, denoted as unscented Kalman filter with unknown input (UKF-UI), is proposed using the nonlinear system identification concept. To increase its implementation potential, a substructure concept is introduced, producing a two-stage approach. It integrates the unscented Kalman filter concept and an iterative least-squares technique. The two most important features of the method are that it does not need the information on the time history of the excitation to identify structural systems represented by finite elements, and that it can identify defects in them using only a limited amount of noise-contaminated nonlinear response information. The proposed method is robust enough to detect the locations and severity of defects at different locations in the structure. The defect detection capability increases significantly if the defective member is in the substructure or close to it. The method is conclusively verified with the help of two examples using ...
TL;DR: In this article, a coupled wave-vegetation model for simulating the interaction between water waves and submerged flexible plants is presented, where vegetation-induced drag and inertia are introduced into the wave model as a source term in the momentum equation.
Abstract: This paper presents a coupled wave–vegetation model for simulating the interaction between water waves and submerged flexible plants. The balance of forces for the vegetation motion includes buoyancy, damping, stiffness of the vegetation, and gravity as restoring forces, and drag and inertia as driving forces. The governing equation for vegetation motion is solved by the high-order finite element method (FEM) together with an implicit time differencing scheme. The results of the vegetation model exhibit a fourth-order convergence rate. The vegetation-induced drag and inertia are introduced into the wave model as a source term in the momentum equation. This coupled model is rigorously verified by comparing numerical results with theoretical solutions for single swaying vegetation cases and with experimental data for large-scale swaying vegetation cases. Excellent agreement is achieved. A scaling analysis is performed on the governing equation for vegetation motion to understand the importance of ea...
TL;DR: In this paper, the dynamic response of a simply supported viscously damped double-beam system under moving harmonic loads is investigated, where two coupled governing equations describing the vibration of those two beams are decoupled by a simple change of variables, so that the analytical solutions for the dynamic deflections of both beams can be given.
Abstract: In this paper, the dynamic response of a simply supported viscously damped double-beam system under moving harmonic loads is investigated. The double-beam system consists of two elastic homogeneous isotropic beams, which are identical, parallel, and connected continuously by a layer of elastic springs provided with viscous damping. Two coupled governing equations describing the vibration of those two beams are decoupled by a simple change of variables, so that the analytical solutions for the dynamic deflections of both beams can be given. Numerical examples are employed to investigate the effects of moving speed and frequency of load, as well as the damping and the elasticity of the layer, on the dynamic responses of the beams. The deflections for the double-beam system are also compared to these of a single-beam system.
TL;DR: In this paper, an innovative method to estimate the forces within stay cables with complex boundary conditions is presented. But the method is not suitable for estimating the cable forces in cable-stayed bridges when using conventional modelbased force identification methodologies.
Abstract: The presence of unknown complex boundary conditions usually imposes difficulties in estimating the cable forces in cable-stayed bridges when using conventional model-based force identification methodologies. Therefore, there exists a need for new methodologies that can overcome these challenges while achieving acceptable force identification accuracy. This paper presents an innovative method to estimate the forces within stay cables with complex boundary conditions. The proposed approach transforms the cable force estimation problem from the common procedure of constructing and solving the equation of motion of the cable to a simpler problem of finding the zero-amplitude points of its mode shapes. Ultimately, the presented methodology yields accurate cable force estimations regardless of the complexity of the boundary conditions. An equivalent segmental model whose length is given by the distance between these points is used next to find an estimate of the cable tension force. A stay cable under a...
TL;DR: In this paper, Eringen's small length-scale coefficients are presented for the vibration and buckling of nonlocal rectangular plates with simply supported edges, and the coefficients are calibrated by comparing the vibration frequency and bearing loads obtained from a nonlocal plate and a microstructured beam-grid model with the same characteristic length.
Abstract: For the nonlocal theory of structures, Eringen's small length-scale coefficient e0 may be identified from atomistic modeling or experimental tests. In this study, Eringen's small length-scale coefficients are presented for the vibration and buckling of nonlocal rectangular plates with simply supported edges. The coefficients are calibrated by comparing the vibration frequency and buckling loads obtained from a nonlocal plate and a microstructured beam-grid model with the same characteristic length. The beam-grid model is composed of rigid beams connected by rotational and torsional springs. It is found that the small length-scale coefficient e0 varies with respect to the initial stress, rotary inertia, mode shape, and aspect ratio of the rectangular plate.
TL;DR: In this paper, a nonuniform Timoshenko beam model of a building, with piecewise constant properties along the height, is presented, along with an algorithm for structural system identification from earthquake records.
Abstract: A nonuniform Timoshenko beam model of a building, with piecewise constant properties along the height, is presented, along with an algorithm for structural system identification from earthquake records. The model accounts for shear and flexural deformation, rotatory inertia, and variation of building properties with height. The model stiffness parameters are identified by matching (in the least-squares sense) propagating pulses in impulse response functions. To minimize the effects of soil–structure interaction, the fit is performed on a band excluding the fundamental mode of vibration. This algorithm is a new development in a wave method for structural health monitoring of buildings, intended for use in seismic alert systems to facilitate decision making on evacuation immediately after the earthquake, and for general condition monitoring. The model can also be used with an earthquake early warning system for quick linear response prediction to decide on safe shutdown of sensitive equipment in adv...
TL;DR: The paper discusses the benefits of applying such machine-learning methods to strong-motion databases for PSHA and ground motion simulation, particularly in large urban areas where dense instrumentation is available or expected.
Abstract: This paper presents a novel method of data-based probabilistic seismic hazard analysis (PSHA) and ground motion simulation, verified using previously recorded strong-motion data and machine-learning techniques. The procedure consists of three parts: (1) selection of an orthonormal set of basis vectors called eigenquakes to represent characteristic earthquake records; (2) estimation of response spectra for the anticipated level of shaking for a scenario earthquake at a site using Gaussian process regression; and (3) optimal combination of the eigenquakes to generate time series of ground acceleration consistent with the response spectral ordinates obtained in the second part. The paper discusses the benefits of applying such machine-learning methods to strong-motion databases for PSHA and ground motion simulation, particularly in large urban areas where dense instrumentation is available or expected. The effectiveness of the proposed methodology is exhibited using four scenario examples for downtown Los Angeles. Advantages, disadvantages, and future research needs for this machine-learning approach to PSHA are discussed.
TL;DR: In this paper, the behavior of pipelines is investigated through analytical and numerical analyses, and it is shown that the initial negative pipeline displacement is a threat to pipeline safety because of the large increase in bending moment.
Abstract: The damage to pipelines from submarine landslides or debris flows has been vastly reported. In this paper, the behavior of pipelines is investigated through analytical and numerical analyses. A refined analytical method is first brought forward by improving the tension assumption. The pipeline is divided into different segments based on loading conditions, and the continuity of displacement, inclination angle, bending moment, and shear are all preserved. Then numerical analysis by vector-form intrinsic FEM is carried out by further considering the axial soil resistance at the sliding zone. The numerical analysis demonstrates that the initial negative pipeline displacement is a threat to pipeline safety because of the large increase in bending moment. The axial tension is closely related to the location of the landslide impact and the initial pipeline configuration. The variations in displacement and tension with time are also investigated in the parametric analysis.
TL;DR: In this article, a spectral representation method was proposed for the generation of spatially correlated nonstationary ground motion time histories that are compatible with a prescribed response spectrum using spectral representation.
Abstract: A new methodology is presented for the generation of spatially correlated nonstationary ground motion time histories that are compatible with a prescribed response spectrum using the spectral representation method. The method introduces two important improvements over the current state of the art in that it preserves the coherence among the ground motion histories and enables the incorporation of both time and frequency modulation by upgrading the evolutionary power spectral density function with random pulse-like perturbations. An example is provided for the simulation of design spectrum–compatible, uniformly modulated nonstationary acceleration time histories at three locations on the ground, and the results are compared directly with an existing state-of-the-art methodology.
TL;DR: In this article, a two-dimensional hybrid truss-continuum topology optimization scheme was developed to overcome these challenges with the goal of reconfiguring traditional reinforcement layouts to automatically follow principal tensile stresses, reducing cracking at service loads and increasing strength and ductility at an ultimate limit state.
Abstract: Strut-and-tie models (STMs) are widely used by RC designers. However, selection of a viable model is a challenging task, especially in complex three-dimensional (3D) design domains with irregular cutouts, which are common in building cores and shear walls. Therefore, topology optimization has been promoted as a means of automating the development of minimum strain energy STMs, which can lead to improved structural behavior. Current drawbacks of such methods are that solutions may be difficult to construct and may fail to properly account for tensile stresses resulting from force spreading. A two-dimensional hybrid truss-continuum topology optimization scheme was recently developed to overcome these challenges with the goal of reconfiguring traditional reinforcement layouts to automatically follow principal tensile stresses, reducing cracking at service loads and increasing strength and ductility at an ultimate limit state. That work is generalized and extended herein to 3D domains and mechanics mo...
TL;DR: In this paper, the authors developed a computational framework that examines the time-dependent effects of multiple environmental stressors on the integrity of structural components and provided a reliable estimate of the extent of penetration of deteriorating agents into concrete.
Abstract: Deterioration of reinforced concrete structures has been a subject of interest for the researchers, practicing engineers, and decision makers who work on the reliability assessment and safety evaluation of civil infrastructure systems. Over the last two decades, several studies have approached this subject and developed numerical and experimental methods to quantify the extent of deterioration over time. The studies completed to date, however, lack the comprehensive probabilistic approach needed to consider the uncertainties involved in the deterioration of structural components during their service life. To address this issue, the current study develops a computational framework that examines the time-dependent effects of multiple environmental stressors on the integrity of structural components. This framework takes into account the mutual interactions of all exposure factors and provides a reliable estimate of the extent of penetration of deteriorating agents into concrete. Given the capabiliti...
TL;DR: In this article, the stochastic distribution characteristics of fluctuating wind pressures for the super-large hyperbolic cooling towers (SCTs) in the Jiangxi nuclear power plant with aeroelastic effect based on synchronous pressure and vibration wind tunnel test were investigated, then the formation mechanism of non-Gaussian fluctuated wind pressures was further revealed.
Abstract: Super-large hyperbolic cooling towers (SCT) are typical cylinder-like structures and feature spatial, three-dimensional (3D), circumferential motion characteristics, wherein the non-Gaussian probability distribution characteristics of local fluctuating wind pressures involved with vortex shedding or reattachment phenomena are excessive compared with the traditional wind load theoretical system based on Gaussian assumption. In this paper, the stochastic distribution characteristics of fluctuating wind pressures for the SCT (H=215 m) in the Jiangxi nuclear power plant with aeroelastic effect based on synchronous pressure and vibration wind tunnel test were investigated, then the formation mechanism of non-Gaussian fluctuating wind pressures was further revealed. According to the formation mechanism, the probability distribution characteristics, spatial correlation, criterion, and division of non-Gaussian fluctuating wind pressures were discussed in detail. Finally, the prediction method and distrib...
TL;DR: In this article, an efficient, almost accurate, and straightforward algorithm is developed for the simulation of the multivariate nonstationary process, where an evolutionary spectral matrix is decomposed via Cholesky method, and then proper orthogonal decomposition (POD) is used to factorize decomposed spectra as the summation of the products of time and frequency functions.
Abstract: The classic spectral representation method (SRM)-based nonstationary process simulation algorithm is used extensively in the engineering community. However, it is less efficient owing to the unavailability of fast Fourier transform (FFT). In this paper, an efficient, almost accurate, and straightforward algorithm is developed for the simulation of the multivariate nonstationary process. In this method, an evolutionary spectral matrix is decomposed via Cholesky method, and then proper orthogonal decomposition (POD) is used to factorize decomposed spectra as the summation of the products of time and frequency functions. Because original time-dependent decomposed spectra are decoupled via factorization, FFT can be used to significantly expedite the simulation efficiency. This POD-based factorization is totally data-driven and optimal, and fewer items are required in matching decomposed spectra. Therefore, the accuracy and efficiency of the factorization can be guaranteed at the same time. Another att...
TL;DR: In this article, the authors presented a new and novel approach that uses complex variables to estimate derivatives within an incremental-iterative procedure for the solution of nonlinear finite-element equations.
Abstract: The complex variable FEM (ZFEM) has been enhanced in this research to compute derivatives with respect to shape, material properties (elastic modulus, yield stress, plastic modulus, hardening parameters), and loads for a nonlinear solid mechanics model undergoing plastic deformation. This method presents a new and novel approach that uses complex variables to estimate derivatives within an incremental-iterative procedure for the solution of nonlinear finite-element equations. ZFEM offers significant advantages over real-valued finite-element analysis in that highly accurate derivative information may be obtained from a single analysis. The method has been implemented within a commercial finite-element software package using the user element and user material options. A strategy was developed to allow the software’s solver algorithm to handle complex variable operations needed by ZFEM to perform sensitivity analysis. Numerical results confirm the high accuracy of the method through the analysis of ...
TL;DR: In this article, a nonlinear constitutive model was proposed to characterize axial strain and circumferential strain in reinforced portland-cement concrete, where the linearized strain can be a non-linear function of the stress.
Abstract: Unreinforced portland-cement concrete exhibits a nonlinear relationship between applied stress and observed strain, even though the strains are at magnitudes that warrant the infinitesimal strain approximation (i.e., the norm of the displacement gradient is appropriately small). Previous efforts to model this nonlinear response of concrete express a dependence of stress on the deformation gradient (via the infinitesimal strain). However, models derived from the class of Cauchy elastic bodies do not allow a nonlinear relationship between the stress and linearized strain. Nonlinear constitutive relations that are implicit relations between the stress and a proper measure of strain, or nonlinear expressions of an appropriate measure of strain as a function of stress, lead to a logical linearization procedure wherein the linearized strain can be a nonlinear function of the stress. Using such a constitutive model, the authors accurately characterize both axial strain and circumferential strain in concr...