Journal of Engineering Mechanics

A real-valued random field $\left\{Z_{i,j}\right\}$ with piecewise constant samples and defined on a lattice $L$ in ${\mathbb{R}}^2$ is developed to characterize two-dimensional metallic polycrystals. The subsets defined by constant values of $\left\{Z_{i,j}\right\}$ are virtual grains and the values of $\left\{Z_{i,j}\right\}$ give Euler angles at the nodes of $L$ . The field $\left\{Z_{i,j}\right\}$ is completely defined by its marginal distribution and conditional probabilities associated with the nearest neighbor model. The defining probabilities of $\left\{Z_{i,j}\right\}$ need to be estimated from measurements of atomic lattice orientation. Random fields $\left\{Z_{i,j}\right\}$ calibrated to the measurements of crystallographic texture in two AA7075 aluminum plates have been used to generate virtual polycrystals. Virtual and actual polycrystals are similar.

In this paper, a description of inherent anisotropy of soil, based on micromechanics framework, is presented. The problem is formulated by assuming that sliding of two contact particles governed by Coulomb criterion in which the friction angle is a function of the orientation of the interparticle contact. The orientation distribution of these parameters is described by a set of symmetric second-order tensors. The formulation of the problem is illustrated by simulations of Santa Monica Beach Sand under true triaxial tests. In particular, the directional dependence of the strength characteristics is examined for samples with inherent cross anisotropy. The orientations of failure planes between particles are also examined.

Measuring displacement for large-scale structures has always been an important yet challenging task. In most applications, it is not feasible to provide a stationary platform at the location where its displacements need to be measured. Recently, image-based technique for three-dimensional (3D) displacement measurement has been developed and proven to be applicable to civil engineering structures. Most of these developments, however, use two or more cameras and require sophisticated calibration using a total station. In this paper, we present a single-camera approach that can simultaneously measure both 3D translation and rotation of a planar target attached on a structure. The intrinsic parameters of the camera are first obtained using a planar calibration board arbitrarily positioned around the target location. The obtained intrinsic parameters establish the relationship between the 3D camera coordinates and the two-dimensional image coordinates. These parameters can then be used to extract the rotation and translation of the planar target using recorded image sequence. The proposed technique is illustrated using two laboratory tests and one field test. Results show that the proposed monocular videogrammetric technique is a simple and effective alternative method to measure 3D translation and rotation for civil engineering structures. It should be noted that the proposed technique cannot measure translation along the direction perpendicular to the image plane. Hence, proper caution should be taken when placing target and camera.

This paper presents a new numerical procedure for the determination of the viscoelastic compliance properties of a matrix phase from a simple three-point bending test on a composite beam. The composite is modeled as elastic inclusions randomly dispersed throughout a viscoelastic matrix. It is also assumed that the spatial distribution of the inclusions in the composite is known or can be determined. Zevin’s method of iterative functions is proposed for the determination of the matrix properties. Following a detailed explanation of the proposed scheme, a numerical verification is performed using three-dimensional finite-element (FE) analysis simulations. The proposed scheme was applied to the experimentally obtained creep compliance of the asphalt concrete beam. The obtained viscoelastic properties of the asphalt binder matrix phase were used as input into the FE model to simulate the behavior of the composite beam. An excellent comparison between the experimental data and the predicted beam deflections was observed. This shows that the proposed method is robust and it can be implemented to solve identification problems for viscoelastic composite materials.

A full-scale blast test was conducted on eight masonry walls reinforced with two and four layers of carbon fibers and two types of polymer matrices. The walls were then subjected to a 0.45-kg pentolite booster suspended from the ceiling of a test structure. The pressure-time history caused by the blast and the resulting displacement response were measured during the test. This paper presents a summary of the test program and the corresponding results from a nonlinear single degree of freedom analysis. The results provide a basis for determining effective means of retrofitting existing masonry walls and designing new structures to withstand blast loads. The paper also outlines a fiber-reinforced polymer retrofit design procedure for walls subjected to blast loading.

The motion of spherical particles (diameter 1.58 mm, specific gravity 2.5) on 2 and 3% plane slope was studied in a laboratory wave flume for shoaling wave conditions. The range of wave-height-to-water-depth ratio was $0.24<H/h<0.82$ , the range of Keulegan-Carpenter number was $128<\text{KC}<500$ , and the maximum particle Reynolds number was 240. The instantaneous sediment particle position and the associated fluid velocity field were measured simultaneously in the bottom boundary layer using a particle image velocimetry (PIV) system. The measurement plane was parallel to the bed and located at a height of 1/2 particle diameter above the bed. Morphological image processing techniques were used to separate the fluid (tracers) and solid (glass spheres) phases from the same PIV images based on their signature sizes. The separated image files were processed to determine the displacement, velocity, and acceleration of the individual sediment particles and the corresponding fluid velocity and total acceleration. These measurements were used to calculate the individual terms (inertia, gravity, pressure gradient, added mass, drag, lift, and friction) in the equation of motion for the sediment particle. It was found that the drag force was the largest force in the equation of motion. The equation of motion could not be balanced when bottom friction was modeled as dry or rolling friction. The equation was balanced approximately by introducing a viscous friction term of the form $F_F=\mu U_s\delta$ , where $\mu =\text{dynamic}$ viscosity; $U_s=\text{sediment}$ particle velocity; and $\delta =\text{viscous}$ length scale. Much of the drag force was canceled out by this frictional force, resulting in increased importance of the pressure gradient force. The study also evaluated several commonly used formulas for calculating the drag coefficient. It was found that the formula developed for steady motion in an infinite fluid described the measured data better than other formulas. It was also found that using the free-stream local fluid acceleration instead of the total fluid acceleration in the vicinity of the particle had negligible effects on the calculated total resultant force.

The influence of seepage (lateral flow) on the turbulence characteristics in free-surface flows over an immobile rough boundary is investigated. Steady flows having zero-pressure gradient over an immobile rough boundary created by uniform gravels of 4.1 mm in size were simulated experimentally with injection (upward seepage) and suction (downward seepage) applied through the boundary. A Vectrino (acoustic Doppler velocimeter) was used to measure the instantaneous velocities, which are analyzed to explore second- and third-order correlations, turbulent kinetic energy, turbulent energy budget, and conditional Reynolds shear stresses. It is observed that the second-order correlations decrease in presence of injection and increase in suction. The turbulent diffusivity and mixing length increase in presence of injection and decrease in suction. The third-order correlations suggest that the ejections are prevalent over the entire flow depth. The near-boundary flow is significantly influenced by the existence of upward seepage, which is manifested by a reduction in streamwise flux and the vertical advection of streamwise Reynolds normal stress. In addition, the upward flux and the streamwise advection of vertical Reynolds normal stress are also affected. The streamwise flux of turbulent kinetic is found to migrate upstream, while the vertical flux of turbulent kinetic energy is transported upward. The fluxes increase in presence of injection and decrease in suction. Energy budget evidences a lag between the turbulent dissipation and production and an opposing trend in the turbulent and pressure energy diffusions. A quadrant analysis for the conditional Reynolds shear stresses reveals that the ejection and sweep events are the primary contributions toward the total Reynolds shear stress production, with ejections dominating over the entire flow depth. The effect of seepage is shown to affect the magnitude of such events. However, in case of sweeps, this phenomenon is the opposite. The mean-time of occurrence of ejections and that of sweeps in suction are more persistent than those in no-seepage and injection.

Recently, blind source separation (BSS) methods have gained significant attention in the area of signal processing. Independent component analysis (ICA) and second-order blind identification (SOBI) are two popular BSS methods that have been applied to modal identification of mechanical and structural systems. Published results by several researchers have shown that ICA performs satisfactorily for systems with very low levels of structural damping, for example, for damping ratios of the order of 1% critical. For practical structural applications with higher levels of damping, methods based on SOBI have shown significant improvement over ICA methods. However, traditional SOBI methods suffer when nonstationary sources are present, such as those that occur during earthquakes and other transient excitations. In this paper, a new technique based on SOBI, called the modified cross-correlation method, is proposed to address these shortcomings. The conditions in which the problem of structural system identification can be posed as a BSS problem is also discussed. The results of simulation described in terms of identified natural frequencies, mode shapes, and damping ratios are presented for the cases of synthetic wind and recorded earthquake excitations. The results of identification show that the proposed method achieves better performance over traditional ICA and SOBI methods. Both experimental and large-scale structural simulation results are included to demonstrate the applicability of the newly proposed method to structural identification problems.

Experimental data have shown that vibratory roller compactors often exhibit rotational kinematics in addition to translation during operation. This rotation is not considered in roller-integrated measurement systems that estimate soil stiffness based on drum vibration. To model and explore the effect of rotation, a lumped parameter roller/soil model was developed. The machine parameters for this model were tuned from suspended drum testing that isolated the drum from the ground. The model was then verified using field data collected over a range of excitation frequencies on spatially homogenous soil, and over transversely heterogeneous soil using one excitation frequency. Rotational motion was found to significantly influence roller-integrated measurement of soil stiffness based on single position drum vibration data. Rotational motion causes single position measurement system results to be nonunique and to vary depending on the direction of roller travel. Using the model, various alternative measurement schemes were investigated. The directional dependence was eliminated by deriving a measurement at the drum’s center of gravity, and dual-sided measurement is proposed to gain a measure of heterogeneity. A more theoretical approach was also created wherein the contact force between the drum and soil are measured rather then being calculated.

In the present paper the mechanical and acoustic emission (AE) behaviors of full-scale reinforced concrete beams are evaluated. One of the beams was constructed in two parts, which were assembled later in order to evaluate the effect of the joints in the structural behavior. The load was applied by means of a four-point-bending configuration. It is revealed that at initial stages of loading, the conventional measurements of strain and deflection, as well as pulse velocity, do not show any discrepancy, although the structural performance of the two beams is eventually proven to be quite different. On the contrary, AE parameters, even from early load steps, indicate that the damage accumulation is much faster in the assembled beam. This is confirmed by the calculated sources of AE events which are close to the construction joints. The results show that the AE technique is suitable to monitor the deterioration process of full-scale structures and yields valuable information that cannot be obtained at the early stages of damage by any other way.

Vertical vibration of a rigid circular disc attached to the surface of a transversely isotropic half-space is considered in such a way that the axis of material symmetry is normal to the surface of the half-space and parallel to the vibration direction. By using Hankel integral transforms, the mixed boundary-value problem is transformed to a pair of integral equations termed dual integral equations in the literature, which generally can be reduced to a Fredholm integral equation of the second kind. With the aid of complex variable or contour integration the governing integral equation is numerically solved in the general dynamic case. The reduced static case of the dual integral equations is solved analytically and the vertical displacement, the contact pressure, and the static impedance/compliance function are explicitly solved. The dynamic contact pressure under the disc and the impedance function are numerically evaluated, and it is shown that the singularity that exists at the edge of the disc is the same as the one obtained for the static case. In addition, the impedance functions evaluated here are identical to the solution given by Luco and Mita for the isotropic domain. To show the effect of different material anisotropy, the numerical evaluations are given for some different transversely isotropic materials and compared.

This technical note presents explicit formulas for calculating the response moments of stochastic systems by polynomial dimensional decomposition entailing independent random input with arbitrary probability measures. The numerical results indicate that the formulas provide accurate, convergent, and computationally efficient estimates of the second-moment properties.

A mathematical model has been presented for the mechanism of interfacial slip damping in layered and jointed cantilever beams with continuous and tack welds. The pressure distribution at the interfaces, number of contacting layers, techniques of welding, length and thickness of the beam specimen, and amplitude and frequency of vibration are found to be the dominating factors influencing the damping capacity of such welded structures. The results can be exploited positively in the design of machine tools, aircraft, spacecraft, satellites, automobiles, missile systems, etc. for maximizing their damping capacity.