Dynamics of structures

The dynamic behavior of rigid-block structures resting on a rigid foundation subjected to horizontal harmonic excitation is examined. For slender structures, the nonlinear equation of motion is approximated by a piecewise linear equation. Using this approximation for an initially quiescent structure, safe or no-toppling and unsafe regions are identified in an excitation amplitude versus excitation frequency plane. Furthermore, several possible modes of steady-state response are detected, and analytical procedures are developed for determining the amplitudes of the predominant modes and for performing stability analyses. It is shown that the produced stability diagrams can be beneficial to assessing the toppling potential of a rigid-block structure under a given amplitude-frequency combination of harmonic excitation; in this manner the integration of the equation of motion is circumvented.

Closure of "Rocking of Rigid Blocks Due to Harmonic Shaking"

SynOptics Communications Inc.

Written by a leader on the subject, Introduction to Geotechnical Engineering is first introductory geotechnical engineering textbook to cover both saturated and unsaturated soil mechanics. Destined to become the next leading text in the field, this book presents a new approach to teaching the subject, based on fundamentals of unsaturated soils, and extending the description of applications of soil mechanics to a wide variety of topics. This groundbreaking work features a number of topics typically left out of undergraduate geotechnical courses.

Geotechnical Engineering: Unsaturated and Saturated Soils

Automatic detection of atrial fibrillation using stationary wavelet transform and support vector machine

Since the earthquakes of Niigata (Japan, 1964) and Alaska (USA, 1964), the dangers of liquefaction have been highlighted and research into liquefaction has been actively performed. Particularly, as part of the provision and verification of liquefaction data through physical modeling by using centrifuge and numerical prediction, the Liquefaction Experiments Analysis Project (LEAP) was launched. The purpose of the recent LEAP-UCD-2017, in which nine facilities participated, was to evaluate the uncertainty and repeatability of response in a previous study for LEAP-GWU-2015. The ground models were prepared in a rigid box with a 5° sloping model with relative densities of 85 and 50% by using Ottawa sand. The models were subjected to nondestructive and destructive motions based on a ground motion consisting of a tapered 1 Hz sine wave. This paper describes not only the experimental procedure in detail but also the difference in the sensor response of the ground model corresponding to the relative density of 85 and 50% during liquefaction. Moreover, it provides data for permanent horizontal–vertical displacement through liquefaction and for validation of the numerical model.

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LEAP-UCD-2017 Centrifuge Test at KAIST

The lateral deflection of a cylindrical diaphragm wall and the associated ground movement induced by deep excavation are analyzed by performing site instrumentations and numerical analyses in the coastal area of Korea. Wall lateral deflection, rebar stress, and pore water pressure were measured and analyzed in eight directions. Variations of soil properties with the decrease of confining pressure are compared by performing various in situ tests before ad after excavation. To calculate the wall lateral deflection accurately, the effects of small strain nonlinearity, confining pressure, and the hysteresis loading/unloading loop developed during excavation are considered in the proposed numerical analysis. By comparing numerical results with measured ones, the importances of considering small strain nonlinearity and confining pressure reduction in the nonlinear (FEM) are emphasized. Also, the effects of wall stiffness on the performance of cylindrical diaphragm walls are studied for future similar e...

Instrumentation and Numerical Analysis of Cylindrical Diaphragm Wall Movement During Deep Excavation at Coastal Area

Improved load capacity of a hybrid bucket foundation for offshore structures in sand

Liquefaction evaluation using frequency characteristics of acceleration records in KAIST centrifuge tests for LEAP

To eliminate the source of errors in deformational measurements at small to intermediate strains (0.01% to 1.0%), a local strain measurement system inside the triaxial cell has been adopted in the resilient modulus (M sub R) test. However, because of complexities inherent in the local measurement, there are difficulties in using this technique in routine tests. As an alternative solution, external M sub R measurement with the specimen grouted to the end platens with hydrostone paste was used. The effects of specimen grouting and the stiffness range on reliable external M sub R measurements were investigated using six synthetic specimens of known stiffnesses ranging from that approximating a soft subgrade to that approximating stiff base material [from 20.7 MPa (3 ksi) to 552 MPa (80 ksi)]. For stiffness below about 345 MPa (50,000 psi), M sub R values determined by external measurements with grouted specimens are identical to the known values from torsional testing. However, for the stiffer specimens, M sub R values of the grouted specimens are less than those from torsional testing, and the deviation increases with the increasing stiffness of the specimen. The secant static moduli determined by both loading and unloading curves closely matched the cyclic M sub R at the same strain rate (or loading frequency), proving the feasibility of using the static testing scheme instead of the more expensive cyclic test. Finally, the effects of specimen grouting were investigated using compacted subgrade soils.

Dong-Soo Kim

Papers

LEAP-UCD-2017 Centrifuge Test at KAIST

Instrumentation and Numerical Analysis of Cylindrical Diaphragm Wall Movement During Deep Excavation at Coastal Area

Improved load capacity of a hybrid bucket foundation for offshore structures in sand

Liquefaction evaluation using frequency characteristics of acceleration records in KAIST centrifuge tests for LEAP

Accuracy improvement of external resilient modulus measurements using specimen grouting to end platens