Journal of Engineering Mechanics

This work has a twofold objective. First, a new method to separate incident and reflected wave components, using measurements from one wave probe, is presented. This technique is based on local variations in amplitude and phase of the measured wave and uses wavelet analysis. Second, the method is applied to perform a parametric study to compare the reflection and transmission characteristics of flexible and rigid breakwaters. Results are discussed for different depths of submergence of the models, different internal pressures in the case of the flexible breakwater, and a wide range of wave steepnesses. The results show that, in general, the rigid model has a higher reflection coefficient than the flexible model. On the other hand, the flexible model has a much higher energy-loss coefficient. Optimal breakwater widths for reflection, transmission, and energy-loss coefficients for waves with different wavelengths are also presented.

In this paper the elastic stability analysis of X-bracing systems is performed. Special attention is focused on the effect of midspan (center) connection on the out-of-plane buckling load of these systems. Commonly, in practice, one of the diagonal members is discontinuous at the midspan intersection and a gusset plate is used to connect the members. So the center connection is modeled as partly pinned or semirigid. In this study the closed-form relationships are obtained for the evaluation of effective length factor of X-bracing with pinned end connections and either pinned or semirigid (discontinuous) midconnection. The tension and compression diagonals are assumed to have different section properties and axial loading. The results are graphically displayed for some practical cases. Three types of double angles X-bracing with different detailing for midconnection are compared. The numerical results show that the discontinuous center connection can affect the buckling load and effective length factor of diagonal members and it should be considered in the design of X-bracing systems.

This paper is concerned with the continuous and discontinuous contact problem of two elastic layers resting on an elastic semi-infinite plane. The top layer is subjected to a uniform pressure applied over a finite portion of its top surface. It is assumed that the contact between all surfaces is frictionless. The problem is solved using the theory of elasticity, and body forces are taken into account. Separation may occur between the top and the bottom layers or between the bottom layer and the half-plane or between both interfaces. The problem is formulated in terms of singular integral equations obtained from the discontinuous contact positions and is numerically solved by the Gauss-Chebyshev integration method. Furthermore, numerical results for the separations and the loads corresponding to these separations and the stress distribution on the contact interfaces are given in graphical forms.

A refined global approximation theory of thin multilayered anisotropic shells is developed. The effects of the laminated material response, transverse shear, and transverse normal strains are included. The material of each layer of the shell is assumed to be linearly elastic, anisotropic, homogeneous, or fiber reinforced. As unknown functions the tangential displacements of the face surfaces and transverse displacements of the face or middle surfaces of the shell are chosen. It is an important feature of the proposed theory. This fact simplifies, for example, an analysis of the contact problems and allows to elaborate universal numerical algorithms. An exact solution for the problem of the bending of homogeneous isotropic rectangular plates subjected to a sinusoidal load has been found. Numerical solutions for the problem of the bending of multilayered composite plates and cylindrical shells have been also obtained. The influence of anisotropy, and transverse shear and transverse normal deformation response of the stress state of the shell is examined.

Since concrete members with fiber-reinforced polymer (FRP) reinforcement are not as ductile as conventional structures, and since concrete in retrofitted members is often covered and not readily available for visual inspection, development of nonintrusive and nondestructive damage assessment tools is essential. Ultrasonic pulse velocity (UPV) can provide such an assessment tool, and help quantify the extent and progression of damage in concrete. Continuous UPV monitoring of a number of concrete cylinders and concrete-filled FRP tubes showed the concrete-filled tubes to have higher sensitivity at lower stress ratios as compared to plain concrete. When compared with the axial strain energy, the UPV damage index has a much better resolution for stress ratios up to about 50% of ultimate strength. This ratio depends on the thickness of the jacket. It was also shown that the UPV has a strong correlation with volumetric strains after confinement is activated. Therefore, at high levels of axial loads when the confining pressure of the jacket results in volumetric compaction, the UPV increases by about 6% of the initial pulse velocity. Repeated loading generally induces the same rate of change of UPV damage index as that of the initial loading on the virgin specimen. This phenomenon occurs irrespective of the stress ratio at which the specimen is unloaded or reloaded. A comparison of the UPV damage index with the normalized acoustic emission counts reveals that the two methods have different sensitivities at different stages of loading and could potentially complement each other as a hybrid damage assessment tool.

Several methods have been developed to identify forces moving on a beam from measured responses. The results from all of them exhibit fluctuations at the beginning and end of the time history, and they are results of the ill-conditioned inverse problem. This paper includes a regularization method in the solution of the problem with the aim to explore the feasibility of collecting vehicle weight in the weigh-in-motion application. The improvements through regularization to the identified forces using different measured responses are studied with simulation, and the identified forces in the laboratory study obtained from two different existing moving force identification methods are compared. The studies show that the indirect estimation of vehicle weight from dynamic responses is feasible, and further improvements could be achieved with preprocessing of the measured data to reduce the measurement noise.

A direct BEM (boundary element method) formulation and its numerical implementation for steady-state elastodynamic analysis of two-dimensional problems involving orthotropic and nonorthotropic solids of arbitrary shape is presented. The present formulation is developed by incorporating isoparametric quadratic boundary elements, a rigorous self-adapting numerical integration scheme, and the Green's functions of Wang and Rajapakse for two-dimensional orthotropic solids. The full-space as well as the half-space Green's functions have been implemented. The formulation is capable of treating multidomain problems by substructuring and satisfying the equilibrium and displacement compatibility at the interfaces. Thus, problems related to the layered media and soil-structure interaction can all be analyzed. The accuracy and reliability of the present BEM analysis are demonstrated through comparison of results obtained for a few example problems with published solutions. Finally, the applicability of this methodology is demonstrated by analyzing three types of problems, a rigid strip footing embedded in an orthotropic half-space, a strip footing resting on an orthotropic stratum overlaying an orthotropic half-space, and a rigid strip footing embedded in a nonorthotropic half-space.

The mechanical behavior of saturated geomaterials is largely governed by the interaction of the solid skeleton with the fluids present in the pore structure. Traditional geotechnical analyses, commonly based on simplified effective stress theories, fail to fully describe the behavior of saturated porous materials. Hence, it has become necessary to use more robust and complete formulations. In this context, the use of multiphase theories appears to be an alternative and more appropriate approach. In this work, the governing equations of a porous media interacting with immiscible porous fluids are presented in the light of the theory of mixtures. A generalized Galekin procedure is devised to establish the coupled mixed finite-element equation set with u-p-U form. An unconditionally stable implicit solution procedure is used for the time domain numerical solution. Finally, a recently developed constitutive model based on the fuzzy set plasticity concept is described and implemented in the finite-element tool. A companion paper focuses on applications of this theory, and case studies are used to evaluate the proposed formulation.

It is widely accepted that the mechanical behavior of saturated geomaterials is largely governed by the interaction of the solid skeleton with the fluids present in the pore structure. This interaction is particularly strong in quasi-static and dynamic problems and may lead to the catastrophic loss of strength known as liquefaction, which frequently occurs under earthquake loading. In this work, numerical simulations of saturated granular deposits under transient loads are presented to illustrate the performance of a u-p-U finite-element method formulation and the versatility of the numerical implementation. Closed-form solutions based on both a Biot formulation and modern theories of mixtures are compared with numerical results. In addition, centrifuge experimental results are correlated with numerical simulations. A companion paper presents the details of the theoretical formulation and the numerical implementation within the finite-element method.

The contact pressure arising when a flat-ended punch is loaded against an elastic half-plane with a thin, rigid-ideally plastic interlayer is found under adhesive conditions. Slip line field theory is employed, and the local stress state in the substrate deduced in order to assess the brittle fracture strength of the material beneath the contact.

The crushing response of a polycarbonate circular cell honeycomb to inplane biaxial loading under displacement control is analyzed. The study involves a combination of experiment and numerical simulation. Experiments corresponding to several different biaxial loading conditions are carried out. In the first phase of the response, the material deforms in a uniform fashion. Next, a nonlinear phase caused by the progressive localization of deformation is characterized by the variation of overall (macroscopic) stiffness. The progressive localization causes the walls of each cell to contact. These periodic honeycomb materials show different collapsed modes under different biaxial loading histories. Experimental measurements indicate how the magnitude of the collapse load varies and how the load-displacement response changes as a function of load biaxiality. The experimental results are simulated through numerical analysis using the finite-element method.

This paper develops a new representation scheme for random fields, which can be used in a variety of mechanics applications, based upon the projection onto a biorthogonal wavelet basis. The merits of such a scheme can be shown to result from the relaxation of the condition of orthonormality, while still requiring compact support of the basis functions. Earlier methods have relied on the diagonalization properties of wavelets to demonstrate how the Daubechies family of orthonormal wavelets is effective in weakening the correlation across scales for a large class of random processes. It is shown that biorthogonal processes achieve better decorrelation owing to the fact that fewer filter coefficients are needed to maintain the same support of basis functions when compared to the Daubechies family. Numerical examples of fields encountered in earthquake engineering and other applications are given.