Journal of Engineering Mechanics

The influences of couplers on wave propagation and mode localization in simply supported multispan beams with couplers consisting of lumped rotational stiffness and mass on supports are studied. A transfer matrix equation governing the vibrational wave propagation in the simply supported multispan beams with couplers is newly derived and simplified. The eigenvalue of the simplified transfer matrix shows that the larger stiffness or the larger mass of the coupler makes the internal coupling between spans weaker and so it makes the system more sensitive to mode localization. As the wave frequency or the eigenvalues of the system increases, the mass effect is increased while the stiffness effect is decreased. In a case considering the large stiffness and mass at the same time, there is a region with relatively wider passbands and narrower stop bands having small attenuation rates and the normal modes in it become delocalized ones. As an example structure, a simply supported two span beam with a coupler at the midspan is considered.

This paper demonstrates how system identification techniques can be successfully applied to a soil–structure interaction system using the earthquake response data. The parameters identified are the shear moduli of several near-field soil regions and Young’s moduli of the shell sections of the structure. The soil–structure interaction system is modeled by the finite element method combined with the infinite element formulation for the unbounded layered soil medium. The simulated earthquake responses using the identified parameters are shown to be in excellent agreement with the observed response data. Prediction of the responses is also carried out for a larger earthquake event using the identified parameters as the initial properties in the equivalent linearization procedure. It has been found that the predicted responses are also compared very well with the measured responses.

A unified mixed, higher-order analytical formulation is presented to evaluate the buckling of laminated composite struts. The formulation can also be used to evaluate the overall buckling and wrinkling loads of a general multilayer, multicore sandwich strut having any arbitrary sequence of stiff layers and cores. The usual assumptions of thin stiff layers and antiplane core are advantageously eliminated. Displacements as well as transverse stress continuities are enforced in the formulation by incorporating them as the degrees of freedom, thus avoiding separate calculations of the modal transverse stresses. Two sets of mixed models are proposed, based on individual layer and equivalent single layer theories, by selectively incorporating nonlinear components of Green’s strain tensor. Limitations of the equivalent single-layer theories and typical simplifying assumptions are highlighted. A parametric investigation is presented, concerning the influence of the material and geometric properties on the buckling behavior of a sandwich strut. A few recommendations are also made for the stability analysis of laminated composite struts.

A method for performing discrete element simulations of granular flow and pressures within industrial silos is presented. Special attention is devoted to complex problems involving large numbers of particles and sophisticated boundary conditions due to the presence of inserts. The proposed method consists of partitioning the silo into layers that are analyzed sequentially, and in determining stresses and velocities at the virtual interlayer boundaries. The method is first validated by simulating the discharge of a single insert hopper containing 20,000 particles, performing both a simulation of the whole silo and a multilayer partition. The results show a small discrepancy in the displacement fields produced by the two simulations. Then the discharge of an industrial silo containing 170,000 particles with several inserts of different size and shape is simulated. The relevance of the stress and velocity fields obtained confirms the feasibility and the efficiency of the procedure. The method allows for managing huge numbers of particles with a limited memory capacity and a gain of computational time that may be significant depending on each particular case.

Since cash flow of asset in the long run is generally subject to economic fluctuation, and also to potential damage due to seismic hazard risk, asset pricing is more relevantly evaluated, provided that uncertainties of both cash flow and seismic risk are properly taken into account. This study will propose a discounted cash flow method to evaluate asset pricing, in which incomes gained from asset are modeled as a Markov process and seismic loss is modeled due to only one earthquake event during the service time. A numerical example is demonstrated for an 11 story steel reinforced commercial building considering the service time of 50 years. Various risk–asset price curves are numerically obtained in the form of probability of excess versus asset price with discount rate as a parameter for cases with and without earthquake loss taken into account, and for a case in which earthquake strengthening measure is implemented. These curves contribute information to decision makers in charge of risk and investment management.

This paper proposes a combined feedback–feedforward control algorithm for reducing structural response of buildings to seismic excitations. The controller contains both feedback and feedforward components. The feedback component is assumed to be the same as that found from traditional linear quadratic regulator design. The feedforward component is obtained by estimating the external excitation as a series of step functions at each time increment. This feedforward gain varies with the duration of the step function used for estimation and converges as the time duration increases. Thus, a finite number of precalculated gains can be used to represent the potential feedforward gain profile. At any instant in time, the excitation is measured and by using the past measurements, the most effective feedforward gain for the recorded excitation values can be selected from the set of precalculated gains. This value is used as the feedforward gain for the current time step. Numerical examples are presented to show the effectiveness of this adaptive control scheme. The effects of varying the control objectives, the updating time for the feedforward gain, and the number and location of actuators are studied.

We introduce a simple model of gas–particle flow in a pipeline, which can be used as a tool in engineering design. A chaotic particle motion due to the particle–particle and particle–wall collisions is modeled by analogy with the motion of gas molecules. The pressure gradient is calculated as a sum of particles drag forces per unit volume. As a result, the problem of pressure losses is reduced to the solution of one nonlinear algebraic equation. The gas viscous friction losses are found by the Colebrook–White approximation. The model is validated by testing it against the experimental data and other, more sophisticated, models known in the literature.

A new class of scheduled controllers is presented for improving the response of seismic-excited buildings under actuators with limited capacity. The controller is scheduled based on the response of the system on-line, to take full advantage of the inevitably limited actuation. While the controller is nonlinear, the overall approach relies on a variety of techniques from linear designs, which makes it possible to generalize the approach to a variety of systems and control objectives. For example, sufficient conditions for feasibility of a feedback controller are expressed in terms of linear matrix inequalities, thus solvable with standard software. Both state feedback and observer-based controllers are discussed. Performance of the proposed technique is illustrated through simulations of a six-story building subject to earthquake ground motion.

This paper presents experimental and numerical results of the elastic–plastic response and buckling of $S3\times 5.7$ steel and aluminum I-beams subjected to cyclic pure bending. A special four-point bending device was designed and built for this purpose. The emphasis of the work is on the description of the response and buckling of the beams. The numerical results were obtained using a commercial finite element program that implements the nonlinear kinematic hardening plasticity model. The results indicate that the beams considered, most of which had length-to-height ratio of 5, buckled first in a global mode involving either twisting or lateral deflections of the beams. The prevailing deflection mode seems to be determined by the nature of the initial geometric imperfections. The deformations induced by the global deflections could induce a local buckle at mid-span. The finite element predictions yield results that qualitatively reproduce the development of most of the aspects of the response of the beams, but generally at a slower rate.

The paper deals with the theoretical investigation of the postbuckling of laminated composite rectangular plates subjected to uniform in-plane temperature. An analytical method based on Chebyshev polynomial is employed. The formulation is based on Reissner–Mindlin plate theory and von Kármán nonlinear kinematics. The resulting nonlinear coupled differential equations are linearized using quadratic extrapolation technique. Double Chebyshev finite series is used to discretize the differential equations. An incremental iterative approach is employed for the solution. The effects of temperature dependent mechanical and thermal properties on the limiting/critical temperature and the postbuckling response are studied. The numerical results for different boundary conditions and lamination schemes are presented. Analysis results indicate that temperature dependent properties reduce the critical/limiting temperature and postbuckling strength.

The paper presents a definition of rolling between a pair of two-dimensional or three-dimensional particles with a compliant contact. The definition of rolling movement is based upon the shapes of the objects’ surfaces as described with differential geometry. A pseudoinverse of the surface curvatures is used for producing a rolling vector that is tangent to the two objects at their contact. Matrix expressions are presented for the efficient computation of the vector. The rolling vector is objective and is independent of the reference points that are used to track the particle motions. The definition of rolling is applied in a discrete element method simulation of the triaxial compression of three large, dense cubic assemblies: one packing of spherical particles and two packings of nonspherical particles. At small strains, particle rolling was slightly less with the nonspherical particles, but the packing with the greatest coordination number had much less rolling.

The research results are presented of the joint project of the National Center for Research on Earthquake Engineering (Taiwan) and Stanford University on the pseudodynamic testing of a three-story full-scale reinforced concrete steel moment frame. Nonlinear stress–strain relations, corresponding to oscillations in the frame, were estimated for successive time intervals from a pseudodynamic test of strong ground motion excitation. Numerical models of the behavior of the frame under the pseudodynamic loading of four levels of input ground motion were constructed and used for estimating changes in the shear moduli in the frame during its loading and for the nonlinear identification of the frame behavior. The contents of linear and nonlinear quadratic and cubic components in the response of the frame were estimated. It was found that the frame possesses mostly odd-order nonlinearities, such as the third, fifth, seventh, etc. order nonlinearities, whereas, even-order nonlinearities, such as, quadratic, the fourth, sixth, eighth, etc. order nonlinearities, are weak. Temporal changes in the behavior of the frame were observed during the test, indicating a substantial decrease in the elastic shear moduli, increase in the absorption of seismic waves and in the contents of the nonlinear part in the response of the frame.

A geometrically nonlinear buffeting analysis of a cable-stayed bridge in the time domain is described. The bridge structure is modeled with three-dimensional thin-walled beam elements and three-dimensional elastic catenary cable elements. Spatially correlated wind velocity fluctuations are modeled and simulated using an algorithm for generating sample functions of a stationary, multivariate stochastic process according to its prescribed cross-spectral density matrix. Aerodynamic damping and aerodynamic stiffness are formulated based on experimentally determined flutter derivatives. The focus of this paper is on the effect of fluctuating components of the spatially correlated wind velocity on the geometrically nonlinear buffeting response for an 870 m cable-stayed bridge.

This paper presents a technology for detecting invisible damage inside concrete, which is based on reconstruction of dielectric profile (image) of the concrete illuminated with microwaves sent from and received by antenna arrays controlled by specialized software. The imaging system developed in this study consists of an 8×8 transmitting and an 8×8 receiving arrays, an innovative numerical bifocusing operator for improving image resolution, and imaging software for reconstructing a two-dimensional image from the scattered field. The effectiveness of the developed technology in detecting steel and voids inside concrete has been demonstrated through numerical simulation and experiments.