406A SURFACE STRUCTURES:DYNAMIC LOADS

The general time-domain boundary dement in cylindrical co- ordinates developed for the study of wave propagation in a layered half-space is extended to the response analysis of single piles under horizontal trauisient excitations. The pile is treated as a beam, and therefore, only the bending stiffness has to be considered in the analysis. The soil is modelled by boundary (cylindrical) elements with the vertical, radial and tangential displacements as well as their corresponding tractions as independent variables. The characteristic matrices for the two different types of element are combined to form the equation of motion for the whole system by virtue of compatibility and equilibrium conditions along the pile-soil interface. The transient responses of a pile under Heaviside loads are found to converge to the static values. Parametric studies are carded out to reveal the influences of pile-soil stiffness ratio (Ep/Es) and soil layering. (Authors)

958363 Horizontal translation and rocking rotation of a rigid tubular foundation F. Abedzadeh & R. Y. S. Pak, Geotechnique, 45(1), 1995, pp 83-94.

An exact formulation is presented for the lateral loading of a rigid tube of finite length embedded in a semi-infinite medium. The asymmetric mechanical interaction problem, which is relevant to the analysis of anchors and caissons in foundation engineering, is shown to be reducible to three coupled Fredholm integral equations. By analysis of the kernels involved, the fundamental singular characteristics of the radial, angular and vertical interfacial reactions acting on the foundation are explored. The results are incorporated into a computational scheme which permits the efficient evalua- tion of the contact loads and other structural responses. (Authors)

958364 Modification of Mononobe-Okabe theory Y.-S. Fang & T.-J. Chen, Geotechnique, 45(1), 1995, pp 165- 167.

The earliest method for determining the dynamic lateral pressure on a retaining structure was developed by Mono- nobe (1924) and Okabe (1924). In this method, Coulomb's earth pressure equation was modified to take account of the additional vertical and horizontal forces induced by an earthquake. The Mononobe-Okabe analysis was developed for dry cohesionless backfill. The technical note investigates the influences of the direction of inertia forces on dynamic earth pressure. Based on the reasoning in this study, a more rational approach is introduced. (from Authors)

958366 Solution of random structural system subject to nonsta- tionary excitation: transforming the equation with random coefficients to one with deterministic coefficients and random initial conditions H. U. Koyluogh, S. R. K. Nielsen & A. S. Cakmak, Soil Dynamics & Earthquake Engineering, 14(4), 1995, pp 219- 228.

The method of analysis is based on a Markov approach using stochastic differential equations (SDE). The linear SDE are transformed to an equivalent nonfinear SDE with determi- nistic coefficients and random initial conditions subject to random excitation. In this precedure, new SDE with random initial conditions, deterministic coefficients and zero forcing functions are introduced to represent the random variables. General formulation is given for multi-degree-of-freedom systems and the performance of the method in problems with nonstationary excitations and large variabilities is illustrated for a single-degree-of-freedom oscillator. (from Authors)

958367 Active control of nonlinear base4solated bufldiags A. H. Barbat, J. Rodellar, E. P. Ryan & N. Molinares, Journal of Engineering Mechanics - ASCE, 121(6), 1995, pp 676-684.

A hybrid seismic control system for building structures is considered, which combines a class of passive nonlinear base isolator with an active control system. The global behavior of the structure-hase-isolator system is such that the absolute base displacement is significantly reduced, the price paid being a slight increase of the response of the structure. (Authors)

958368 Reduction of steady-stnte forced vibrations of structures with dynamic absorbers M. Klasztorny, Earthquake Engineering & Structural Dy- namics, 24(8), 1995, pp 1155-1172.

The problem of reduction of the steady-state response of a tightly damped structure to periodic excitation is considered. A general formulation of the dynamic absorber design methodology is presented, based on independent design of conventional absorbers, taking into account the selected modal systems of the original structure and the selected harmonic components of the excitation. In order to cover the losses in the vibration reduction, resulting from the couplings in the primary structure - the set of absorbers system and from the remaining harmonic components of the excitation, the mass of modal dynamic absorbers is increased properly. (from Author)

958365 Control algorithm for estimating future responses of active variable stiffness structure K. Yamada & T. Kobori, Earthquake Engineering & Structural Dynamics, 24(8), 1995, pp 1085-1099.

A response controlled structure that actively and artificially alters its stiffness is one possible means of suppressing structural responses against seismic excitations and strong winds. The authors call it the Active Variable Stiffness (AVS) structure. A control algorithm has been developed for controlfing these AVS structures. This algorithm analyses information of an observed seismic excitation, estimates the future structural responses and determines how to alter the structure stiffness. The effectiveness of the induced algorithm is confirmed by numerical experiments on a model of a three- storey building under sine and seismic excitations. (Authors)

958369 Seismic response of segmental bnildings Tso-Chien Pan, Shih-Fu Ling & Wei Cui, Earthquake Engineering & Structural Dynamics, 24(7), 1995, pp 1039- 1048.

Proposes an aseismic design concept in which the super- structure of a hase-isolated building is divided into several segments. Each segment may comprise a few storeys and is interconnected by additional vibrational isolation systems. The optimum parameters of the vibration isolation systems are determined by minimizing the mean square acceleration response. The seismic response of a typical segmental building is evaluated and compared with the responses of the corresponding fixed-base and conventional base-isolated buildings. The comparisons show that, when the super- structure is segmented the displacement across the base isolation system at foundation level is substantially reduced. (from Authors)