Journal of Engineering Mechanics

Analytic solution methods are developed that can be used to evaluate dynamic response characteristics of partially filled flexible rectangular fluid containers under horizontal or vertical ground excitation. Fluid-structure interaction effects on the dynamic responses of partially filled fluid containers are taken into account incorporating wall flexibility. The containers are assumed fixed to the rigid ground. Solutions based on three-dimensional modeling of the rectangular containers are obtained by applying the Rayleigh-Ritz method using assumed vibration modes of rectangular plate with suitable boundary conditions as admissible functions. Solutions by the present two-dimensional analysis method are compared well with those by a coupled boundary-element/finite-element method. Dynamic responses of twoand three-dimensional models are calculated by the proposed methods in time domain and the effects of three-dimensional geometry on the responses are investigated. Variation of dynamic response characteristics with respect to the length to height ratio of the flexible wall is studied. The effect of wall flexibility on the sloshing response is investigated.

Two analytical models are presented for the identification of the actual static scheme and tensile force of metallic tie-rods included in masonry arches and vaults. The reference structural system consists of a moment-resistant tie-beam with elastic rotational springs at the extremities. Symmetrical restraint conditions are initially hypothesized, thus obtaining a two-parameter model in which the unknowns are the springs' rigidity along with the axial force. The preceding assumption is then removed by defining a more general, three-parameter model in which two different spring rigidities are considered. The mutual experimental data are the middle-section vertical displacement under a concentrated load and the fundamental vibration frequency; the second vibration frequency is adjunctively assumed for the three-parameter model. Closed-form equations are formulated in both cases. Laboratory tests show a notable agreement between analytical estimates and experimental measures. A statistical balance of the application of the proposed models to over 200 rods belonging to several Italian monumental as well as common ancient buildings is presented along with more-detailed information about a significant case study.

The buckling behavior of elastic space rods under torsional moment is studied theoretically. A consistent method is developed to identify the buckling torsional moment as well as to trace the postbuckling path. Since this buckling phenomenon accompanies a nonlinear interaction between flexural deformation and torsional deformation, a special consideration has to be made in the treatment of finite rotations in three-dimensional space. First, a buckling analysis based on a rigorous nonlinear beam theory is developed to identify the bifurcation moment. This analysis precisely takes into account the prebuckling torsional deformations as well as the effect of axial compressive force. Next, the postbuckling behavior is analyzed by the transfer matrix technique, which was previously presented by the writers. With this method, the buckling and postbuckling behavior of space rods under torsional moment are examined with an emphasis on the effect of cross-sectional shapes as well as axial compressive force.

A random-vibration analysis is performed for the torsional response of symmetric structural systems subjected to spatially varying earthquake ground motion. Torsional effects are assessed by means of an equivalent eccentricity that can be expressed in terms of the system lateral displacement and rotation variances. Two case studies of systems consisting of a rigid slab supported by columns and walls are presented. A parametric analysis is conducted to evaluate the influence of local soil conditions and incoherence effects on the torsional responses of these systems. The results show that depending on the aspect ratio of the system, the soil conditions, and the times for seismic waves to travel across the base of the system, torsional effects can be significant especially for structural systems with fundamental periods close to the predominant period of the ground.

A consistent finite-element formulation is presented in order to analyze the spatial stability of shear deformable thin-walled space frames and circular arches. The displacement field of unsymmetric thin-walled cross sections is introduced based on the inclusion of second-order terms of Rodriguez's finite rotations, and the potential energy corresponding to the semitangential moments is consistently derived. For finite-element analysis, cubic Hermitian polynomials including shear deformation effects due to flexural and restrained warping shear stress are utilized as shape functions. Load correction stiffness matrices for the different types of moments and off-axis loadings are taken into account. For spatial buckling behaviors of space frames and circular arches, finite-element solutions using the two-noded straight frame element are presented and compared with the analytical solutions and the results in the literature.

The objective of this research is to provide an approximate but reliable method of assessing various fiber configurations in a metallic composite structure with the intent of achieving optimal resistance to creep failure. The approximate method, envisioned as an early design tool, is based on an upper bound on the creep rupture time and an associated representative failure stress. The latter is evaluated and compared for different fiber configurations, thereby identifying the configuration with optimal creep rupture resistance. A substantial saving in computational time is realized by avoiding a detailed analysis of the actual failure process. Application is made to reinforced thinand thick-walled cylindrical vessels under interior pressure.

This paper presents an advanced elastic formulation intended for modeling imperfect beam-columns subject to thermal loading using only one element per member. The new formulation is derived in a local Eulerian (convected) system, where the effects of large displacements and rotations in three-dimensional space are accounted for through transformations between the local and global systems. In the Eulerian system, the proposed formulation utilizes quartic shape functions for the transverse displacements and linear shape functions for the rotational twist, whereas no shape functions are required for the axial displacement since the constant axial force criterion is used. The paper proceeds with the formulation details, where particular emphasis is placed on the modeling of thermal effects. This is followed by a discussion on the modeling of distributed element loads which require special treatment in the context of the large-displacement Eulerian approach. Finally, verification of the new formulation is undertaken using the nonlinear analysis program ADAPTIC, where several examples are presented to illustrate the accuracy and efficiency of the quartic formulation.

“Ground response” in geotechnical earthquake engineering refers to the response of level ground subjected to seismic loading originating from the underlying rock formation. Catering to this special loading condition, the stresses and strains in soil can be sufficiently represented by four-component vectors instead of second-order tensors. Correspondingly, the order of a “full-fledged” soil model can be reduced, resulting in a great improvement in the efficiency and robustness of computation. This paper presents a simplified and reduced-order version of a bounding surface hypoplasticity model that captures the essential behavior of granular soils under the ground response loading conditions. To make the model well behaved under nearly-zero mean normal stress conditions, a curved phase transformation surface is proposed. An attempt has been made to minimize the number of model parameters, and most of the parameters are associated with commonly used engineering properties. The model has been integrated into a fully-coupled effective stress procedure and has shown its effectiveness and robustness in analysis.

Higher-order nonlinear transfer functions are applied to model the computed nonlinear responses obtained from the dynamic analysis of a tension leg platform (TLP). Under the nonlinear wave-loading condition considered in the present study, the horizontal motion of TLP exhibits a significant amount of response components at frequencies that are outside the range of the excitation frequencies, but which are near the natural frequency of the TLP. Higher-order nonlinear transfer functions based on a Volterra series representation are used to model these nonlinear responses that cannot be properly represented with a linear transfer function only. The transfer function model clearly shows the degrees of nonlinearity of these responses as strongly quadratic. To examine the applicability of the nonlinear transfer functions, both the quadratic transfer functions obtained from a wave spectrum and the corresponding responses were applied to other wave spectra with different magnitude of wave power, and the results are discussed.

Axisymmetric laminar blood flows in a stenotic model vessel are calculated by using a finite-difference scheme of the Navier-Stokes equations. The wavy lumen are transformed to a rectangular region with fine and irregular meshes mapped to regular ones in the computational domain. The pulsating flow is controlled by a time-dependent von Kármán number. At the upstream and downstream ends, the local acceleration is employed to replace the Neumann boundary condition for solving the pressure field from the divergence of the Navier-Stokes equations, resulting in a new treatment on the inlet and outlet conditions for transient flow problems. The kinematic and dynamic characteristics of vortices in the pulsating flow processes are analyzed along with the pressure and shear fields.

In this paper physically motivated and nonparametric models are investigated that predict within some tolerance the response of a semiactive electrorheological (ER) damper that was designed, constructed, and tested. The electrorheological damper is a hydraulic device that was designed for applications in vibration control of civil structures. The simplest possible physically motivated phenomenological models are first considered to predict the damper response without and with the presence of electric field. Subsequently, the performance of a multilayer neural network constructed and trained by an efficient algorithm known as the dependence identification algorithm is examined to predict the response of the ER damper. The performance of the neural network is compared to that of the phenomenological models and some conclusions are provided.

To date, most of the current active structural control strategies for aseismic protection have been based on either full-state feedback (i.e., all structural displacements and velocities) or on velocity feedback. However, accurate measurement of displacements and velocities is difficult to achieve directly in full-scale applications, particularly during seismic activity, since the foundation of the structure is moving with the ground. Because accelerometers can readily provide reliable and inexpensive measurement of accelerations at strategic points on the structure, development of control methods based on acceleration feedback is an ideal solution to this problem. The purpose of the present paper is to demonstrate experimentally that acceleration feedback-control strategies are effective and robust, and they can achieve performance levels comparable to full-state feedback controllers.