Journal of Engineering Mechanics

A theory is developed to demonstrate the effects of sorptive exchange on the transport of a chemical in a sediment-laden open-channel flow. Based on the multiple-scale method of homogenization, a depth-averaged transport equation is deduced up to a long time-scale. The dispersion coefficient is the sum of a modified Taylor dispersion coefficient and a dispersion coefficient due to a finite rate of mass exchange between dissolved phase in the water column and sorbed phase on suspended particles. These coefficients are functions of the suspension number and the bulk solid-water distribution ratio. It is shown that, for sufficiently large particles and solid fractions, enhancement of the longitudinal dispersion coefficient due to the sorptive exchange can be significant and should be included in a comprehensive model.

In this study, the Green's function of a point dislocation for the mixed boundary value problem of a thin plate is derived and then employed to analyze the interaction problem between a partially bonded rigid inclusion and a line crack in an infinite plate under uniform bending moments at infinity. A rational mapping technique and the complex stress function approach are used in the derivation. Based on the method of analytical continuation, the problem of obtaining the stress functions is reduced to a Riemann-Hilbert problem. Without loss of generality, the numerical results are demonstrated for a square rigid inclusion with a debonding. The stress intensity factors of crack tips and the stress intensities of debonding tips are shown for various parameters.

This paper presents the results of a study to evaluate the performance of a number of recently proposed semiactive control algorithms for use with multiple magnetorheological (MR) dampers. Various control algorithms used in recent semiactive control studies are considered including the Lyapunov controller, decentralized bang-bang controller, modulated homogeneous friction algorithm, and a clipped optimal controller. Each algorithm is formulated for use with the MR damper. Additionally, each algorithm uses measurements of the absolute acceleration and device displacements for determining the control action to ensure that the algorithms could be implemented on a physical structure. The performance of the algorithms is compared through a numerical example, and the advantages of each algorithm are discussed. The numerical example considers a six-story structure controlled with MR dampers on the lower two floors. In simulation, an El Centro earthquake is used to excite the system, and the reduction in the drifts, accelerations, and relative displacements throughout the structure is examined.

Efficient simplified models are available for reinforced concrete beams and columns, with the assumption of a perfectly rigid connection. However, interior beam/column joints have been shown to be the area of strong deformation and degradation mechanisms, involving mainly the cyclic behaviors of concrete under shear and of bond under push-pull loading. In this paper, a global component-based model is proposed for the beam/column connections of reinforced concrete frame structures that can be directly connected to beam elements. This model incorporates explicitly the modeling of concrete, steel, and steel/concrete bond. Thus, the key mechanisms of deformation and degradation of the connection, as well as various interactions can be taken into account naturally. In particular, the effect of push-pull-type loading on the flexural steels can be captured. On the basis of a local finite-element modeling of the connection, simplifying assumptions are proposed and implemented leading to the component-based model. Both approaches (local and component-based) are compared on an application example.

A method for the probabilistic failure analysis of laminated composite plates with random system parameters subject to transverse loads is presented. System parameters such as material properties, plate thickness, and lamina strengths of a laminated composite plate are treated as baseline random variables. The statistics of the baseline random variables obtained from experiments are used in a stochastic finite-element analysis for computing the statistical moments of stresses in the laminated composite plate. An appropriate failure criterion from which the statistical moments of first-ply failure load are derived via a first-order second moment method is used to construct the limit state equation of the plate in the probabilistic failure analysis. The reliability of the laminated plate is then computed using an assumed probability distribution function of the first-ply failure load. The feasibility and accuracy of the present method are validated by the experimental data of centrally loaded laminated composite plates with different layups. The suitability of several commonly used failure criteria for reliability analysis of laminated composite plates is also investigated by means of several examples.

Constitutive equations based upon stress dependent moduli, like K-θ and Uzan-Witczak, are widely used to characterize the resilient response of granular materials for the analysis and design of pavement systems. These constitutive models are motivated by the observation that the granular layers used in pavement structures shake down to (nonlinear) elastic response under construction loads and will, therefore, respond elastically under service loads typically felt by these systems. Due to their simplicity, their great success in organizing the response data from cyclic triaxial tests, and their success relative to competing material models in predicting the behavior observed in the field, these resilient modulus constitutive models have been implemented in many computer programs used by researchers and design engineers. This paper provides an analysis of the nonlinear solution algorithms that have been used in implementing these models in a conventional nonlinear 3D finite-element framework. The analysis shows that these conventional algorithms are destined to fail at higher load levels. The paper offers two competitive methods for global analysis with these models. A comparative study of eight possible implementations of the algorithms described in the paper is made through two simulation examples.

Analytical solutions to the geometrically nonlinear boundary value problems of laminated-composite plate undergoing moderately large deformations and subjected to various boundary conditions are presented in this paper. The nonlinear coupled partial differential equations are linearized using a quadratic extrapolation technique. The spatial discretization of the linear differential equations is carried out using fast-converging Chebyshev polynomials. A convergence study reveals that 8–10 terms of expansion of the function is sufficient to yield quite accurate results. The results for uniformly loaded, moderately thick laminated-composite plates with simply supported immovable edges, clamped immovable edges, free edges, and their combinations are presented. Some new results are presented, and it is observed that the present method is efficient and less expensive.

Increasing interest has focused on applying active control systems to civil engineering structures subjected to dynamic loading. This study presents an active pulse control algorithm, termed the adaptive neural structural active pulse (ANSAP) controller, to control civil engineering structures under dynamic loading. The ANSAP controller minimizes structural cumulative responses during earthquakes by applying active pulse control forces. The effect of pulses is assumed to be delayed until just before the next sampling time so that the control force can be calculated in time and applied; the newly developed control strategy circumvents the effect of time delay due to the computation time. The ANSAP controller also circumvents the difficulty of obtaining system parameters of a real structure for the algorithm for active structural control. Illustrative examples reveal significant reductions in cumulative structural responses, which demonstrates the feasibility of using the adaptive artificial network for controlling civil engineering structures under dynamic loading.

The effect of joint geometry parameters and the size of jointed rock block on the hydraulic properties of jointed rock, including the equivalent continuum behavior, was investigated through numerical experimentation. The chance to reach equivalent continuum behavior for a rock mass having a certain joint configuration increases with the increase of block size. The REV (representative elementary volume) size to show hydraulic equivalent continuum behavior for a jointed rock system was found to depend on the orientation of the joint sets; the REV size seems to decrease with increasing joint density and joint size. The REV does not seem to exist for some rock masses having joint systems with low relative orientation angles (systems with two joint sets) and low densities. The average block permeability (K₀) value at the REV size for a joint system increases with increase in joint size and joint density. The equivalent continuum behavior of a joint system can be expressed with respect to a cut-off value for the first invariant of fracture tensor (F₀). The block size corresponding to the aforementioned cut-off F₀ (between 10 and 30 for the joint systems investigated in this study) can be considered to provide the REV size for a given joint configuration. A threshold value for F₀ (a joint network having two perpendicular joint sets produced 2.75) can be used to find the chance for a given joint network to have nonzero block permeability. A strong power functional relation seems to exist between the directional permeability and the fracture tensor component for the connected joint configuration when rock blocks contain minor discontinuities.

The inclusion of the higher order terms in the Taylor's series expansion of the status variable is presented in the formulation for stochastic analysis with the weighted integral method. Generally, in almost all the numerical formulations, omission of the higher order terms is introduced due partly to the complexities of deriving the appropriate simple equations for stochastic analysis or due to the large amount of additional computation time and memory requirement. In this study, the Lagrangian remainder is included in the expansion of the status variable with respect to the mean value of the random variables, which results in simple and efficient formulas for stochastic analysis in the weighted integral method. In the resulting equation, only the “proportionality coefficients” are introduced; thus, no additional computation time or memory requirement is needed. Various examples are investigated to show the efficiency and appropriateness of the suggested formula. The results obtained by the improved weighted integral method equations proposed in this study are reasonable and are in good agreement with those of the Monte Carlo simulation.

This paper suggests a method for obtaining closed-form solutions for a reinforced Timoshenko beam on an elastic foundation subjected to any pressure loading. A particular solution is obtained for uniform pressure loading at any location of the beam. This solution can be used to calculate settlement, rotation, tension, bending moment, and shear force of the beam. A parametric study is carried out to investigate the effects of geosynthetic shear stiffness and tension modulus and the location of the pressure loading. Results are presented and discussed.

The main purpose of the present article is to exhibit the power and potential of the initial values method by means of the solution of a crucial problem. First, the initial values method is presented and a general carryover matrix is obtained for plane rods loaded perpendicular to their plane. Then an example is solved and the advantages of the method are depicted.

We present a procedure for estimating peaks of non-Gaussian processes representing fluctuating internal forces induced by wind in low-rise building frames. The procedure is designed for inclusion in computer programs that use surface pressure databases to obtain peak internal forces in frames. In general, the processes of interest are non-Gaussian, and we apply translation models to estimate the distribution of their peaks. To illustrate the procedure we calibrate a translation model to the record of a 1 h time history of the bending moment at the upwind bent of a low-rise frame.

An asymptotic theory is presented for the analysis of laminated annular spherical shells by the perturbation method. By means of proper nondimensionalization, asymptotic expansion, and then successive integration of the basic equations through the thickness direction, we obtain the recursive sets of governing equations for the bending analysis of annular spherical shells. The method of differential quadrature is adopted for solving the problems of various orders. Illustrative examples are given to demonstrate the performance of the present asymptotic theory.