Journal of Engineering Mechanics

It is a well‐known paradox in the theory of plastic plate buckling that the discredited deformation theory of plasticity predicts the buckling stress well, whereas the generally accepted incremental theory predicts a buckling stress which is too high. The paradox is traced to the fact that prior analytical approaches neglect the effect of friction acting on the loaded edges during tests. The method of analysis makes use of finite element techniques based on incremental theory. Numerical computations were carried out on a digital computer. The shear stresses introduced by the edge frictional have the effect of substantially lowering the buckling stress. The numerical results compare well with the experimental data obtained by Pride and Heimerl (1948). It is indicated that the inclusion of frictional effects is crucial to obtain realistic results for plate buckling in the plastic range.

A finite element method of analysis is developed and applied to the study of global and local pressures generated on a cylindrical indenter during sea‐ice deformations in the creeping mode. Numerical simulations are performed under plane stress conditions to assess the influence of interface adfreeze and friction, material constants for a multiaxial power‐law creep model, indenter diameter, and ice‐sheet velocity on predicted pressures. The results are compared with those based on approximate methods of analysis. Stress, strain rate, and strain contours are obtained in addition to the distribution of interface pressures.

The self‐consistent energy method is used to develop a model for determining the effective moduli of a transversely isotropic cracked solid. To apply the technique, the three‐dimensional crack distributions within the solid must be known. Results are presented for a series of transversely isotropic cracked solids using crack distributions in which all orientations are represented. This type of distribution is typical of crack distributions in cement paste and mortar. The sensitivity of the model to variations in crack size and orientation is discussed. The crack‐induced variations in moduli depend primarily on a parameter representing the volume density of the cracks and on the degree of anisotropy.

A differential equation model is proposed for true bilinear hysteretic systems. The stationary distribution of the response process is obtained using the stochastic averaging technique. Explicit analytical expressions are developed for various response statistics. The validity of the theoretical results is established through digital simulations.

The on‐line computer test control method (the on‐line test) is a new experimental technique to directly simulate the earthquake response behavior of structural systems without using a shake table device. This paper presents a review of Japanese activities in the development and application of the on‐line test. First, the history of the development of the on‐line test and its software and hardware algorithms are described, and 27 previous on‐line tests conducted by Japanese researchers are summarized. Second, the reliability of the on‐line test is discussed. Sources that may bring errors in the response are defined, and efforts to examine their effects on the response and to control the response error growth are introduced. Third, two extensions of the on‐line test concept are presented: the fast on‐line test and the substructure on‐line test.

This investigation concerns the mechanical behavior of plastic pipes buried in a trench and subjected to gravitational loading by the trench fill. The pipe materials of interest, particularly in regard to sewers and drains, are polyvinylchloride and high‐density polyethylene. The analysis is confined to inplane behavior and is carried out with a two‐dimensional finite element model of the pipe‐trench system, taking kinematical nonlinearities fully into account. The pipe materials are modeled as linear viscoelastic, and trench materials as linear elastic, although plastic and viscous effects are estimated. For a realistic range of material parameters, stresses and deformations arising in the system with time are determined, and the risk of final failure through excessive deformation is discussed.

AS a simpler alternative to a previous microplane model, a new microplane model is presented, in which the relative slipping of clay platelets is characterized by normal rather than shear strains on the microplanes. As is the case for Batdorf and Budianski's slip theory of plasticity, the microplanes are constrained statically, i.e., the stress components on a microplane are the resolved components of the macroscopic stress, while the previous model used a kinematic constraint. This different type of constraint is needed to model correctly material anisotropy. The distribution function of normal strain rate intensity for microplanes of various orientations is calculated from the frequency distribution function of clay platelet orientations, which was approximately determined by other authors from X‐ray diffraction measurements. The 6×6 fluidity matrix is calculated from the principle of complementary virtual work on the basis of deformations of individual microplanes and the current values of the stress components. The activation energy approach, validated in previous works, is used to quantify the dependence of the normal strain rates on the microplanes of all orientations as a function of the stress level and temperature. A numerical algorithm to calculate the fluidity matrix is given, and typical test data from the literature are analyzed. With only two free material parameters, good fits of the data are achieved, including their anisotropic features. The modeling is limited to deviatoric creep, and volumetric response is left for subsequent work. The proposed model could be used in finite element programs.

Interaction between piles, known as pile‐soil‐pile interaction or group effect, modifies both group stiffness and damping and, consequently, affects the dynamic properties and behavior of the offshore tower. The formulation of the pile group stiffness by means of dynamic interaction factors is outlined, frequency dependent dynamic interaction factors are presented for piles with separation (gapping), and examples of pile group stiffness and damping are given. Then, the pile group properties are included in the dynamic analysis of an offshore tower. The effects of pile‐soil‐pile interaction on tower modal properties, i.e., natural frequencies, mode shapes, and damping, as well as response to wave action, are demonstrated.

The matrix function method is applied to the dynamic stability problems of initially imperfected columns and plates under time‐dependent axial compression in elastic and elastic‐plastic regions. Matrix functions are derived from the solution of ordinary differential equation systems in a manner similar to that for scalar equations. The rigid body spring mode (RBSM) is adopted for presenting the spatial properties of the structural members. In this model, each element consists of rigid bodies with a rotational spring, which allows the restoring forces to be taken into consideration. In the numerical examples in the elastic and elastic‐plastic regions, the propoosed method, based on the reanalysis technique, is compared with other methods based on the incremental procedure. It is concluded that the proposed method is numerically efficient, general, and practical for the dynamic stability analysis of structural systems.

The dynamic response of a finite flexible pile, partially embedded in an elastic half‐space and under transverse loadings, is discussed. The loadings are applied at the unembedded end of the pile and may, in general, be a combination of time‐harmonic lateral shear force and moment. By treating the pile as a one‐dimensional structure and the half‐space as a three‐dimensional elastic continuum, the interaction problem is formulated as a Fredholm integral equation of the second kind, which is solved by an appropriate numerical procedure. Selected results are presented to illustrate the basic features of the solution. Examples of the compliance functions of the system are also included.