Journal of Engineering Mechanics

This study examined the inelastic seismic behavior of low-rise systems with varying story eccentricities (i.e., general class of eccentric systems). Seismic demands of such systems were found to be potentially high relative to those obtained from single-story or regularly asymmetric models, particularly for flexible-side elements of torsionally stiff systems and stiff-side elements of torsionally flexible systems. This appears to be a consequence of the complex participation of higher torsion–dominated modes in multistory systems with general class of asymmetry, unlike the predominant participation of single torsional mode in its regularly asymmetric counterpart. The study also indicates that the degrading features of RC structural elements may cause a significant increase in inelastic demands. Summarizing elastic range response, coefficients $\alpha$ and $\delta$ are proposed to predict seismic demand through equivalent static analysis. Further, a design envelope was outlined to predict inelastic seismic demand. This may prove useful in the selection of the appropriate response reduction factor in practical design. Observations highlighting the dynamics of multistory systems with generalized asymmetry establish the conceptual framework for envisioning the seismic response.

This paper proposes a new constrained viscoelastic (VE) layer treatment as a distributed supplemental damping mechanism for structural members. A steady-state solution of a cantilevered column utilizing this system is formulated under harmonic loading and validated with experimental shake table tests. Parametric studies indicated that the new treatment can reduce the elastic response of a $1/5$ -scale square column up to 20%, or increase the damping ratio of the column from 2% to 2.5%. They remain effective as the column begins rocking at the column-footing construction joint. The numerical results were found to be in general agreement with the shake table test data of two column specimens with and without VE layers. On the basis of the validated model, applying two VE layers of 2.38 mm-thick to cover the lower 50–90% height of a cantilevered column appears the most efficient, and can increase the damping ratio up to 12% for a full-scale column. The significant reduction in peak responses indicates that the proposed new constrained-layer system is promising for civil engineering applications.

Application of spline element and state-space approach in analyzing dynamic response of rectangular plates is presented in this paper. The proposed method is on the basis of state-space theory of control systems and spline element interpolation procedure to take advantage of both the time domain and the space domain analysis methods. A state-space recursive scheme is developed for analyzing the dynamic response, such as displacement and internal forces in the structure. The application of the proposed method is demonstrated by two numerical examples.

The fatigue-crack growth (FCG) behavior of 14MnNbq bridge steel was experimentally investigated in this paper. The fatigue-crack growth rate and threshold under different stress ratios ( $R$ ) are given for 14MnNbq base metal (BM), heat affected zone (HAZ), and weld metal (WM), respectively. Using the test results, an approach to determine the fatigue-crack closure factor by threshold values is proposed and a uniform expression of fatigue crack growth rate including stress ratio $R$ is presented. Furthermore, the prediction of surface-crack growth is presented and the results are compared with the test results obtained from surface-crack growth tests under tensile/bending loading. Finally, a damage tolerance design method based on the condition of no crack growth is proposed, and suggestions about the fatigue design technique and accuracy requirement of nondestructive testing are proposed.

In this work, a beam element is proposed for the nonlinear dynamic analysis of frame structures. The classical Euler-Bernoulli formulation for the elastic beam is extended by implicitly defining new hysteretic degrees of freedom, subjected to evolution equations of the Bouc-Wen type with kinematic hardening. A linear interpolation field is employed for these new degrees of freedom, which are regarded as hysteretic curvatures and hysteretic axial deformations. By means of the principle of virtual work, an elastoplastic hysteretic stiffness relation is derived, which together with the hysteretic evolution equations fully describes the behavior of the element. The elemental stiffness equations are assembled to form a system of linear global equations of motion that also depend on the introduced hysteretic variables. The solution is obtained by simultaneously solving the entire set of governing equations, namely the linear global equations of motion with constant coefficient matrices, and the nonlinear local constitutive equations for every element converted into a state-space form. Numerical results are presented to demonstrate the efficiency of the method as compared to existing methods.

Identifying properties of civil engineering structures is an important task for their condition assessment, damage diagnosis, maintenance and repair, and life-cycle management. These structures usually contain a large number of degrees of freedom and exhibit some time-varying or nonlinear behavior, especially under extreme excitation or when damaged. In this study, an offline substructure method based on wavelet multiresolution approximation (WMRA) is proposed for the identification of arbitrary time-varying parameters in a shear-beam building. Assuming that the possible damage location of the building can be identified a priori, a substructural model containing both interface and internal restoring forces can be formulated. The WMRA can then be used to approximate the time-varying damping and stiffness parameters and convert a time-varying parametric identification problem into a time-invariant coefficient estimation problem. To obtain accurate estimation and minimize the computational effort, Akaike’s information criterion is used for the selection of a resolution level and the pruning of insignificant terms. Numerical and experimental results show that the proposed technique can locate and quantify the time-varying parameters in the substructure. The method inherits the wavelet’s excellent capability in the approximation of arbitrary functions and provides a flexible approach for identifying various types of time-varying parameters in shear-beam buildings.

A method to carry out reliability-based optimization of uncertain structural systems under stochastic excitation is presented in this paper. The approach is based on a nonlinear interior point algorithm and a line search strategy. The associated reliability problems to be solved during the optimization process are high-dimensional (thousands or more random variables). An advanced Monte Carlo simulation is adopted for the purpose of estimating the corresponding failure probabilities. The gradients of the failure probability functions needed during the design process are estimated by an approach based on the local behavior of the normalized demand functions that define the failure domains. Numerical results show that only a small number of reliability estimates has to be performed during the entire design process. By construction, the design scheme is monotonically convergent; that is, it generates a sequence of steadily improved feasible designs. Example problems that consider a resistant element of a shear building model under ground motion and a nonlinear 11-story building model under earthquake excitation are presented to illustrate the effectiveness and feasibility of the approach reported in this paper.

Finite-element (FE) model updating aims at the parametric identification of a structure by correcting model parameters in an initial FE model of the structure to reconcile FE predictions with experimental counterparts. However, experimental data inevitably contain a certain level of measurement noise, and the measurement noise will further generate error and uncertainty in updating results. This paper presents a Monte Carlo (MC) simulation study of the effect of measurement noise on updating parameters in FE models updating with regularization, attempting to quantify the distribution functions of updating parameters in face of measurement noise, and evaluating the adequacy of moment-based stochastic FE model updating algorithms. Taking a numerical study of model updating of a simple truss bridge as an example, a series of artificial measurement noise generated with the normal distribution of zero mean and varying variance is introduced into the simulated modal parameters to quantify the effect of measurement noise on updating parameters. The results indicate that the coefficients of variation of the updating parameters are quite different in magnitude, implying different sensitivities of the updating parameters to measurement noise in modal data. In the case of a low level of measurement noise, the updating parameters also comply with normal distributions; in the case of a high measurement noise level, however, the updating parameters are largely nonnormal. The significant deviation from the normal distribution warrants that the low-order, moment-based stochastic FE model updating algorithms may be inadequate in the presence of severe measurement noise.

The steady two-dimensional laminar forced magneto-hydrodynamic (MHD) Hiemenz flow against a flat plate with variable wall temperature in a porous medium is analyzed. The transformed nonlinear boundary-layer equations are solved analytically by homotopy analysis method (HAM). Results for the velocity and temperature profiles are presented for various values of Prandtl number $\mathsf{P}\mathsf{r}$ , the Hartmann number ( $M$ ), exponent of wall temperature ( $\lambda$ ), the permeability parameter ( $\Omega$ ), and suction and injection parameter ( $f_w$ ). Increments in $f_w$ , $M$ , and $\Omega$ increase the velocities profiles but decrease the temperature profiles. Contrarily, the increment in the $\mathsf{P}\mathsf{r}$ decreases the velocity profiles and increases the temperature profiles. The convergence of the obtained series solutions is explicitly studied and a proper discussion is given for the obtained results. Comparison between the HAM and numerical solutions showed excellent agreement.

This paper presents a tailored extended finite-element model (XFEM) to predict crack propagation and fracture properties within idealized and digital cementitious material samples. The microstructure of the idealized cement-based materials includes the cement paste, particles, and interfacial boundaries. The tailored XFEM was developed to allow crack propagation within finite elements by using discontinuous enrichment functions and level-set methods. The Heaviside jump and the elastic asymptotic crack-tip enrichment functions were used to account for the displacement discontinuity across the crack-surface and around the crack-tip. The maximum fracture energy release rate was used as a criterion for determining the crack growth. The shielding effects within the interfacial zone were addressed with a numerical search scheme. The tailored XFEM was implemented with a MATLAB program to simulate the compact tension (CT) and the single-edge notched Beam (SEB) tests. For a homogeneous CT testing sample, the XFEM prediction on stress intensity factors was verified with the fracture mechanics analysis. The idealized samples of cement-based materials were generated with varied microstructures, including particle locations, orientations, and shape factors. The tailored XFEM was applied to investigate the effects of these microparameters on the fracture patterns of the idealized samples under CT loading. The XFEM simulation was also conducted on a homogeneous offset-notched SEB sample to predict the mixed-mode crack propagation. The predicted crack path matches well with refined cohesion fracture modeling from a recent study. Further validation of the tailored XFEM was conducted with fracture simulation of a digital SEB sample generated from the actual tested specimen. The predicted crack path was favorably compared with the fracture pattern of the tested concrete specimen with a middle notch. These simulation results indicated that the tailored XFEM has the ability to accurately predict the crack propagation and fracture properties within idealized and digital cementitious material samples.

Inverse Laplace transform methods have a long history in the development of time-domain fluid line models. This paper presents a study combining the new Laplace-domain input/output (I/O) model derived from the network admittance matrix with the Fourier series expansion numerical inverse Laplace transform (NILT) to serve as a time-domain simulation model. A series of theorems are presented demonstrating the stability of the I/O model, which is important for the construction of the NILT method. In the previous work by the first author, the Fourier series expansion algorithm was studied, where qualitative relationships between the parameters and numerical errors were analyzed, and reliable parameter heuristics were developed. These heuristics are used for a series of numerical examples dealing with networks of 11, 35, 51, and 94 pipes by using five different pipe models. The examples are used as the basis from which the accuracy and numerical efficiency of the proposed NILT are compared to the standard method of characteristics (MOCs) model for transient pipeline networks. Findings show that, for all case studies considered, the proposed NILT is numerically efficient for the pipe types involving convolution operations, and it is accurate for networks composed of both linear and nonlinear pipe types.

Direct numerical simulation (DNS) and large eddy simulation (LES) with a dynamic Smagorinsky subgrid model are performed to investigate the flow past a square cylinder under the influence of velocity shear at the inlet at moderate Reynolds numbers ( $\mathsf{R}=150–1,000$ ). The shear rate is expressed by a dimensionless shear parameter $\beta$ , which is based on the velocity gradient, side length of the cylinder, and upstream velocity at the center plane of the cylinder. Shear parameter varies from 0 to 0.2 in this study. Several Reynolds numbers are considered to study the Reynolds number dependence and the Strouhal number were found to have no significant variation with the shear parameter. The peak frequency of drag coefficient fluctuation becomes identical with that of the lift force coefficient when $\beta >0.1$ . The vortices on the low-velocity side disappear in the far wake under the strong shear condition. The stagnation point moves to the high-velocity side and the movement increases with an increase in shear parameter. An interesting finding is that the lift force acts from the low-velocity to the high-velocity side, which is opposite to the case of a circular cylinder under the same inflow situation, whereas the drag force shows little variation with shear parameter.

The estimation of the elastic soil modulus from many in situ field test devices currently rely on the continuum theory and assumptions about linear elasticity that are somewhat ill-posed. To improve the understanding of in situ field measurement of elastic modulus using intelligent roller compactors and light-weight deflectometers (LWDs), a complete understanding of the contact problems formed through the use of these devices is needed for a wide range of soils. The varying material properties of cohesionless and cohesive soils can have dramatic effects on the assumed stress distributions, contact areas, and surface deformations. Investigations are conducted by using the discrete-element method (DEM) to investigate the relationships between soil properties and the mechanical responses for both plate (simulated LWD) and drum-roller loading. Simulations of purely cohesionless granular soils are shown to exhibit substantially different stress and strain fields compared to simulations of cohesive soils. This paper demonstrates the ability of DEM to accurately model macroscale features from variable microstructure and interactions. Comparisons between finite element models and predictions are made for soils with varying abilities to transmit tensile forces.

The meshfree edge-based smoothed point interpolation method (ES-PIM) is extended to the simulation of transient heat transfer problems for concrete dams in the construction process. The present ES-PIM consists of the following ingredients: (1) a novel cell death and birth technique is proposed to deal with the existence or nonexistence of the concrete layers, and hence the construction process of dams can be easily simulated; (2) a lumped diagonalization procedure for specific heat matrix is implemented to improve the stability and efficiency of transient computations; and (3) the triangular background cells are used to construct the nonoverlapping smoothing integral subdomains, and the cell-based T3- and T6/3-schemes are adopted for the node selection in the formation of PIM shape functions. On the basis of the weakened weak formulation, the ES-PIM is spatially stable and convergent to the exact solution. The ES-PIM can achieve better results in accuracy and convergence rate, in comparison with the finite element method using the same meshes.

To analyze the thermal stress distribution of ceramic-coated pistons, the wavelet finite-element was constructed by using the Daubechies wavelet scale function as the interpolating function. The thermal stress distributions of the conventional and ceramic-coated diesel engine pistons were obtained, respectively. The calculated results obtained by wavelet finite-element method were compared with test results and the simulation results gained by ANSYS software. Through analyzing the calculation results, the wavelet finite-element method was convergent and had higher analysis precision than the traditional finite-element method. The wavelet finite-element method avoids the numerical oscillation during analysis of the transient-state thermal stress fields of the piston. The wavelet finite-element method showed advantages for analyzing the high gradient problems. The wavelet finite-element method provides a preferable theoretical basis for optimizing the design of the ceramic-coated diesel piston.