Journal of Engineering Mechanics

An interstory drift-estimation method using structural acceleration measurements is presented in this study. In this method, the structural system, generally modeled with multiple-degree-of-freedom (MDOF) and Bouc–Wen hysteretic models, is decomposed into a series of single-degree-of-freedom (SDOF) substructures for interstory drift prediction. A virtual linear structural model, representing the linear behavior of the designed substructure, is used to generate reference response signals to obtain the tracking error of acceleration. The tracking error of displacement is subsequently estimated with the implementation of a robust Kalman-filtering approach, and the corresponding interstory drift of the objective substructure is then predicted accordingly. The prediction performance of interstory drift, in terms of peak drift and time history, is numerically investigated with two SDOF models and a four-story shear-beam model adopting different hysteretic characteristics. Results obtained by the present numerical simulations for the illustrative examples are further validated by experimental investigations using a base-isolated three-story structure. The numerical simulation results are found to be in favorable correlation with some representative experimental data. Influences of the time interval of the tracking-error signals on the prediction performance is further studied and discussed.

In the present study, the discrete singular convolution (DSC) method is used to analyze the dynamic stability of beams subjected to different boundary conditions under periodic axial forces. A unified DSC algorithm is established to solve the governing equations of beam motion under different boundary conditions. The regularized Shannon’s delta kernel is selected as singular convolution to illustrate the present algorithm. The matched interface and boundary method is applied to the treatment of elastic restraint boundary conditions. The effects of a constant term in the periodic axial force and damping on dynamic instability regions are also investigated. The obtained numerical results are compared with those of Bolotin’s method. Numerical results indicate that the DSC method is a reliable method for dynamic stability analysis of beams.

Most behaviors of granular materials have been studied under the limit conditions of stress paths such as cyclic triaxial compression and extension tests. Furthermore, the macrobehavior and micromechanical response of granular materials under more comprehensive cyclic loading tests in the generalized stress condition are not well understood. The objectives of this paper are to ensure the ability of the Discrete Element Method (DEM), to simulate the macrobehavior of granular materials under various cyclic stress paths of the generalized stress condition, and to explore the micromechanical response. To this end, four different cyclic stress paths under generalized stress simulations, following the stress-controlled method on a sample of spheres, were conducted. To check the validity of DEM results, the experimental results of the real sand under cyclic stress programs were used. The macrobehaviors, indicated by the stress–strain–dilation relationship and the directions of principal strain increment vectors, are described. A qualitative comparison of the stress–strain–dilation between the DEM and experimental results under triaxial cyclic loading shows a similarity tendency. Furthermore, micromechanical responses, which are indicated by coordination number and sliding contact fraction, are used to explain the macrobehavior in cyclic loading. Additionally, the macro–micro relationship is explained using the relationship between the stress ratio and the fabric structures of all contacts, and of only the strong contacts. The result shows that the unique macro–micro relationship does not depend on the generalized cyclic stress path or the number of cycles.

A generic crack bridging model for short fiber-reinforced cementitious composites is developed aiming to analytically account for fiber tensile rupture at the pullout stage and two-way fiber pullout induced by both the slip-hardening interface behavior and the chemical bond and fiber tensile rupture at the debonding stage. Explicit solutions to the current model have been given in this paper. The predicted composite bridging-stress versus crack-opening relations as well as concerned composite characteristics such as the tensile strength and mean postfailure crack opening are shown to reasonably agree with the experimental results for a series of polyvinyl alcohol fiber-based engineered cementitious composites. The influence of slip-hardening interface behavior on fiber rupture and crack bridging is clarified by comparing current model with a previous model. It is found that the slip-hardening interface behavior-induced fiber rupture can significantly govern the crack bridging behavior, and it is essential to take this effect into account. A parametric study based on the current model identifies the critical value of the slip-hardening coefficient for the optimal composite properties.

A technical theory for pretwisted beams that accounts for variable twist (constrained warping) is based on an approximate displacement field that is defined completely in terms of two unknown functions: the axial displacement $w_1(z)$ and the rotation $\varphi (z)$ of the cross section about the centroidal axis of the beam, $z$ being the coordinate along the axis of the beam. The primary unknowns are determined by minimizing the potential energy of the beam. The problem is then formulated in terms of $w_1(z)$, and an analogue between the technical theory and a one-dimensional dipolar gradient elasticity model is presented. The application of the theory to textile materials is discussed.

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 capabilities of this framework, the scope of this investigation is extended to incorporate various sources of uncertainty into the predictive models. For this purpose, the most influential parameters that represent material properties, geometric characteristics, exposure conditions, and limit state criteria are considered as random variables and their corresponding probability distributions are identified. Multidimensional Gaussian and non-Gaussian stochastic fields are generated to evaluate the spatial variation of each of these parameters. The generated fields are introduced to the computational framework and the probabilistic measures of the vulnerability of structural components to the attack of deteriorating agents are presented.

Two distinct groups of bond models were developed on the basis of dominant concrete splitting and rebar–concrete interfacial failures, respectively. Their accuracy highly depended on the specific test data sets selected in analysis and validation. In this study, a unified model of local bond is proposed and developed on the basis of the indentation analogy at the rib front of the deformed rebar and on the concrete plastic deformation around the rebar. Unlike existing models, the unified model is completely validated with all sets of test data available in the literature. It can accurately predict the transition mechanism of failure modes from concrete splitting to rebar pullout. The predicted bond strength is in excellent agreement with experimental results as the rib spacing-to-height ratio changes in practical range.

A hysteretic plate finite element for inelastic, static and dynamic analysis is presented and its performance is compared with currently used methods. A smooth, 3D hysteretic rate-independent model is utilized generalizing the uniaxial Bouc–Wen model. This is expressed in tensorial form, which incorporates the yield criterion and hardening law. The elastic mixed interpolation of tensorial components with four nodes (MITC4) element is extended by considering as additional hysteretic degrees of freedom the plastic strains at the Gauss points of each layer interface, which evolve following Bouc–Wen equations. Incorporating hysteretic relations directly into the element’s formulation is proved computationally advantageous and enables a better identification of the involved parameters in cyclic loading. The solution advances by establishing the equilibrium of external and internal forces on the basis of the initially computed stiffness and hysteretic structural matrices, thereby avoiding Gauss integration at every iteration of Newmark’s method steps, over the volume of each element. The additional evolution equations decoupled at every Gauss point are integrated tracing the elastoplastic path. Numerical results are presented that validate the proposed method, demonstrating the efficacy, accuracy and generality of the proposed approach.

Characterizing dynamic failure is critically important to a number of applications, among others including armor, material fragmentation, and structural blast. In brittle materials, this failure is driven by crack growth from pre-existing flaws in the material microstructure. Structural scale models that explicitly address the cracks associated with each individual flaw are computationally infeasible; therefore, a model that accurately links flaw population to dynamic failure strength provides a much-needed connection between the microscale and macroscale. The current paper introduces a micromechanical model that addresses the effects of both air-entrained pores and slit-like flaws on the strain-rate dependent uniaxial compressive strength of the material. In particular, four variants of the model are addressed: a two-dimensional (2D) model with only pore flaws, a 2D model with both pores and slit-like flaws, a pseudo-three-dimensional (3D) model with only pore flaws, and a pseudo-3D model with both pores and slit-like flaws. To demonstrate the relative success of each of these approaches, the model is based on microstructural characterization and subsequent Kolsky bar tests on air-entrained mortar. Air-entrained mortar provides an excellent model material for this study, since the pore population introduced by air-entrainment is characterized relatively easily and the slit-like flaw population is deduced from the sand gradation. Furthermore, the sample sizes used in the Kolsky bar set-up are larger than the length scale of the microstructure of mortar, so that the samples are reasonably representative and provide a good basis of comparison with the micromechanics model. The micromechanics model is shown to provide reasonable agreement with experimentally obtained uniaxial compressive dynamic strength of air-entrained mortar.