Journal of Engineering Mechanics

This paper presents a theory for the buckling of short beams considering cross-sectional distortions due to transverse shear (i.e., shear warping), based on the consistent linearization of a geometrically nonlinear planar beam. The proposed deformation field considers the warping amplitude as an independent kinematic field, and the hyperelastic material assumes that the stresses normal and tangent to the deformed cross section are linear with respect to their work-conjugate finite strains. An approximate closed-form solution to the resulting quartic equation for the critical load is provided to facilitate practical implementation. Theoretical differences giving rise to distinct buckling theories for higher-order shear beams are discussed in terms of (1) the assumed deformation field, (2) variational consistency, and (3) material constitutive relation. The proposed formulation is applied to evaluate the stability of infinite strip unbonded fiber-reinforced elastomeric isolators (FREIs) with moderate-to-high shape factor, for which shear warping is expected to have a major influence due to the flexural flexibility of the fiber reinforcement. A homogenization procedure is described to obtain effective isolator rigidities considering rubber compressibility and fiber extensibility. Next, a finite element parametric study of the buckling of unbonded infinite strip FREIs is presented, and the results are used as a benchmark to evaluate the adequacy of the proposed and existing formulations. The theory presented herein and its approximate solution exhibit the best match with the numerical results, and the latter is deemed adequate for practical application.

This paper presents a discrete element method (DEM) numerical model to elucidate mechanical behavior, particle crushing, and anisotropy evolution within a pressurized sand damper (PSD) subjected to cyclic loading. Computational simulations of the PSD under different initial pressures and stroke amplitudes were conducted and compared to experimental results. Good agreement was achieved between the DEM model and experimental results for the different cases. Force–displacement, particle crushing, shear, and normal stresses along with geometric and mechanical anisotropy degrees were closely monitored in different areas of the PSD. Dissipated energy was also monitored and used to calculate the specific damping capacity. Employing spherical particles, crushable clusters, and uncrushable clumps as sand particles revealed that the closest results to the experiments are obtained when using crushable clusters. The results show that the majority of crushing occurs in the vicinity of the center of the PSD and within the first loading cycle. Increasing stroke amplitude significantly influenced particle crushing, whereas increasing initial pressure was less considerable. In addition, a direct relationship between the PSD’s direction of movement with shear and normal stresses and anisotropy degree was observed. Moreover, the contribution of mechanical anisotropy was more considerable than the geometric anisotropy to the overall anisotropy degree. Regarding dissipated energy, an increase in stroke amplitude resulted in higher dissipated energy whereas an increase in initial pressure had a minor influence on the dissipated energy. Based on the dissipated energy, it was found that the specific damping capacity was nearly equal to one for all cases studied.

Currently, finite-element (FE) simulation is ubiquitous in engineering research and practice as a tool for solving a wide variety of problems. In steel structures, high-fidelity continuum FE (CFE) analysis is often used to characterize the mechanical behavior of structural members and geometrically complex components such as connections. Accurate description of the material constitutive behavior lies at the heart of these CFE simulations, and over the years, many phenomenologically-based rate-independent constitutive models have been proposed, and a select few have been incorporated in commercially available FE software. In this study, we examine the effect of constitutive model selection on the accuracy of FE analysis predictions of structural steel component responses. Models were selected to have a gradual progression in complexity; some are well-established, widely available in commercial FE software, and extensively used by researchers and practitioners, whereas others, despite being more advanced, have so far been limited in application. Given the difficulties in accurately accounting for extraneous variables common to full-scale experimental testing of realistic structural steel components such as, residual stresses, geometric imperfections, complex boundary conditions, and material inhomogeneities, a set of small-scale configured component experiments were designed to economically minimize these sources of uncertainty and establish a benchmark for critically examining the accuracy of model predictions. Data from these experiments, which included the accurate measurement of local strains that were as high as 75%, facilitated detailed comparisons between model predictions and experiment results, revealing both strengths and limitations of various models.

The permeability evolution of lining fracture is of great significance for the safety evaluation of tunnel engineering in service. To date, there are few reports on the evolution in concrete fracture permeability when arbitrary seepage differential pressures are applied under the coupled hydraulic–mechanical processes. In this work, long-term water flow-through experiments on concrete single fractures are conducted to examine the permeability evolution during simulating the fractured lining concrete in service. Five seepage differential pressures from 0 to 350 kPa were experimentally designed, and it was found that the permeability of the fracture slightly increases by 13% at 0 kPa and decreases by 31%–77% at 70–350 kPa. The mineral dissolution of fracture surfaces during the flow-through experiments was analyzed using X-ray diffraction, X-ray fluorescence, scanning electron microscopy with energy-dispersive spectroscopy, and inductively coupled plasma mass spectrometry. Additionally, the distribution of water flow pressure within the fractures was investigated using computational fluid dynamics, and the potential occurrence of hydrodynamic impact was proposed. These studies reveal the evolution mechanism of the permeability of concrete fractures under the coupled processes, which provides an important help to the long-term safety evaluation of tunnel engineering.

The field of (practical) data-driven approaches that utilize the vibration signature of target systems for developing mathematical models (for computational purposes, control, or anomaly detection for structural health monitoring) is still an active research area, despite the fact that several powerful system identification techniques have been developed in the system dynamics field to analyze such measurements. However, there is still a paucity of comprehensive experimental studies that investigate the range of validity of such identification techniques, particularly those applicable to realistic situations encountered in the structural engineering field, with the focus on detecting, quantifying, locating, and classifying observed changes, especially when there are significant inherent nonlinearities in the reference (undamaged) complex target structure, and where there are unavoidable sources of errors and uncertainties in the measurements and the attendant data analysis procedures. The research team constructed a well-instrumented, reconfigurable test apparatus (resembling a tall building) that allows the introduction of quantifiable levels of composite changes at various locations, orientations, and types of linear and/or nonlinear changes, with the aim of investigating a subset of the aforementioned challenges facing researchers who are interested in assessing the utility of some practical system identification approaches. The primary focus of the identification approach is on a decomposition procedure that is ideally suited for certain types of structures that possess some topological features that can be exploited to enhance the detectability of small changes. A companion paper provides a detailed description of the testbed features and its instrumentation. The present paper focuses on the analysis of some of the very extensive data sets that were created to study the usefulness of some practical dimensionless probabilistic measures that not only provide normalized change indices but also simultaneously attach a confidence level to each of these indices.

Understanding the response of sand to drained cyclic loading is relevant to the design of abutments of integral bridges and foundations of wind turbines among other applications. In this study, the discrete element method (DEM) was applied to simulate drained triaxial element tests. The simulations were able to reproduce trends observed in physical laboratory experiments. The loading amplitude determined the observed material behavior during cyclic loading. Specifically, similar behavior was observed at different mean effective stresses when applying the same ratio of loading amplitude to mean effective stress. A key question is how the application of drained low-amplitude load cycles can influence the mechanical response of the material. A number of monotonic drained and undrained shearing tests were carried out on digital snapshots that recorded the sample state at various instances during cyclic loading. While there was systematic variation in the response as a function of the number of load cycles with monotonic undrained shearing, the responses in drained shearing were less sensitive to the number of load cycles applied. Clear correlations between the maximum deviatoric stress, the void ratio, mechanical coordination number, and degree of anisotropy were confirmed by the DEM simulations. These links were previously hypothesized in laboratory experiments.

Abstract

In this scientific investigation, the impact of mechanical vibrations, precisely the vibration time ($t$), vibration amplitude ($A$), and external normal stress ($\sigma$), on the packing density ($\rho$) of wheat is thoroughly examined and analyzed. The findings reveal that both normal stress and vibration amplitude substantially affect wheat packing density, with increased normal stress and vibration amplitude resulting in higher packing density. Moreover, the utilization of normal stress accelerates the attainment of wheat’s final stable bulk density and yields a higher value than freeloaded testing. The validity of the proposed approach, which employs normal stress and vibration amplitude as predictors for wheat packing density, was confirmed using an exponential model. This method holds considerable promise for optimizing wheat handling and storage operations, facilitating more accurate estimation of transportation expenses and storage needs, and minimizing wastage by ensuring optimal packing density during storage and transport. Moreover, the implications of this study have broader applicability to other granular materials, including pharmaceuticals, chemicals, and mining commodities, where packing density serves as a vital determinant of transport and storage efficiency, thereby underscoring the potential significance of the findings beyond the context of wheat. In summary, this study sheds light on the factors that influence wheat packing density, proposing a novel method for predicting packing density and providing insights into the potential applications of this method in agriculture and related industries.

Practical Applications

This study investigates the impact of mechanical vibrations, precisely the vibration time ($t$), vibration amplitude ($A$), and external normal stress ($\sigma$), on the packing density ($\rho$) of wheat particles. The findings demonstrate that both normal stress and vibration amplitude significantly influence wheat packing density, with higher stress and amplitude leading to increased density. Additionally, applying normal stress accelerates the attainment of stable bulk density in wheat, surpassing freeloaded testing. The study proposes an exponential model to predict wheat packing density based on vibration amplitude, offering promising prospects for optimizing wheat handling and storage operations. The implications extend to various granular materials in pharmaceuticals, chemicals, and mining industries, where packing density determines transport and storage efficiency. The investigation highlights the relevance of sensitivity analysis for precise data interpretation and paves the way for practical applications in agriculture and related sectors.

Computing the response power spectral densities (PSDs) of structures from the excitation PSDs has always been a classical problem in structural random vibration. Conventional analytical methods ignore the frequency characteristics of the transient response and therefore yield an incomplete solution. An analytical solution is needed for the structural response PSDs induced by nonstationary excitations with slow-varying time modulation functions considering the transient response. Decomposing nonstationary stochastic excitation as a series of single-frequency excitations, the analytical solutions of the transient and the steady-state responses are derived. The total analytical solutions of the response PSDs are therefore established for single-degree-of-freedom (SDOF) and multidegree-of-freedom (MDOF) systems. Numerical examples validate that the proposed method can yield response PSDs with both the transient-state and the steady-state components. The proposed method can accurately compute time-varying response PSDs of structures subjected to short-duration nonstationary excitations.