This study investigates the influence of isolation damping on the response of multi-storey steel moment frames isolated by lead–rubber bearings (LRB) and high damping rubber bearings (HDRB) subjected to near-fault ground motions. The LRB is modeled as a bilinear system and the HDRB is modeled as an equivalent linear system with viscous damping. The structures meet the gravity and seismic requirements of IBC 2006 and are analyzed in SAP2000 by the Fast Non-linear Analysis method. Past studies have shown that although the base response decreases effectively with increasing isolation damping, the super-structure response is not steadily decreased; there exists a value of damping for which the superstructure response, displacement and acceleration, of a given system attains a minimum and then starts increasing. As the isolation damping is increased, the imposed ground acceleration increasingly influences the dynamic modes of the structural response via the interaction terms. The results of this study show that the significance of the modal interaction terms is almost singularly dependent on the characteristics of the ground-motion. Some ground motions coupled with increasing damping in the isolation significantly increase the super-structure response, other ground motions coupled with increasing damping in the isolation effectively decrease the super-structure response, and still others show a combination of both behaviors. Further studies are necessary to characterize the specific traits of the ground-motions that adversely effect the interaction terms. Important precautionary steps can be taken in the interim to lessen the negative impact that certain ground motions present to heavily damped base isolated structures. For lead-rubber bearings the damping should not exceed 25%. For a range of near fault ground motions, hysteretic damping in the isolators up to 25% can show significant benefits in lowering the base response as well as the response in the superstructure; exceeding this magnitude can exacerbate the unfavorable behavior some ground motions present to any hysteretic damping. HDRB or LRB with a low value of the post-yield stiffness ratio with stiffening measures in the super-structure are strongly recommended to reduce the floor accelerations and inter-storey drifts respectively. In addition, a low value of the effective stiffness is one of the most effective ways to minimize the increase in floor acceleration and inter-storey drift due to high isolation damping. An effective strategy to moderate the base displacement and the isolation damping is to select the lowest value of the effective stiffness, which will allow the base displacement to stay within necessary limits, for the damping levels recommended.
Advisor: Professor Sashi Kunnath
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Mechanics is one of the oldest and at the same time newest disciplines, in the sense that there are methods and principles developed first in mechanics but now widely used in almost all branches of physics: electrodynamics, quantum mechanics, classical and quantum field theory, special and general theory of relativity, etc. More than that, there are some formalisms like Lagrangian and Hamiltonian approaches, which represent the key stone for the development of the above-mentioned disciplines. During the last 20-25 years, classical mechanics has undergone an important revival associated with the progress in non-linear dynamics, applications of Noether’s theorem and the extension of variational principles in various interdisciplinary sciences (for instance, magnetofluid dynamics). Thus, there ought to exist a book concerned with the applied analytical formalism, first developed in the frame of theoretical mechanics, which has proved to be one of the most efficient tools of investigation in the entire arena of science.The present book is an outcome of the authors’ teaching experience over many years in different countries and for different students studying diverse fields of physics. The book is intended for students at the level of undergraduate and graduate studies in physics, engineering, astronomy, applied mathematics and for researchers working in related subjects. We hope that the original presentation and the distribution of the topics, the various applications in many branches of physics and the set of more than 100 proposed problems, shall make this book a comprehensive and useful tool for students and researchers. The present book is an outcome of the authors’ teaching experience over many years in different countries and for different students studying diverse fields of physics. The book is intended for students at the level of undergraduate and graduate studies in physics, engineering, astronomy, applied mathematics and for researchers working in related subjects. We hope that the original presentation and the distribution of the topics, the various applications in many branches of physics and the set of more than 100 proposed problems, shall make this book a comprehensive and useful tool for students and researchers.
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Nonlinear Torsional Behavior of Buildings under Earthq Ground Motions (PhD Thesis)
Author: Jorge H. C. Gomez | Size: 3.1 MB | Format:PDF | Quality:Original preprint | Publisher: Illinois Institute of Technology | Year: 2009 | pages: 263
ABSTRACT
This research studies the dynamic torsional response of buildings to seismic actions. The focus is on framed buildings with non linear behavior of their components. One and three story buildings are studied, and they are idealized using simplified models made of four plane frames. The research is divided in two stages. First, the response of single buildings to a single seismic action is evaluated to find their patterns of behavior. The instant eccentricity is compared with the static eccentricity, and the instant effective torsional moment with the nominal torsional moment, to evaluate the usefulness of the static eccentricity to predict the maximum torsional moment. For the studied cases, a poor correlation and unconservative predictions are found. Responses using unidirectional and bidirectional seismic actions are compared, and instant eccentricities on X and Y direction are induced for buildings with static eccentricity only on the X direction. In the second stage, a set of ten seismic events prepared for Los Angeles area is used to evaluate the maximum demands induced in sets of one story and three story buildings. Twelve angles of incidence are used with each seismic event. The demands are calculated for different values of static eccentricity, induced by the location of the center of mass, the location of the static center of rigidity, and the strength asymmetries of frames.
Advisor: Professor Jie Hua Shen
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Analysis and Modeling of SSI in Bridge Support Structures (PhD Thesis)
Author: Payman K. Tehrani | Size: 3.6 MB | Format:PDF | Quality:Original preprint | Publisher: University of California, Los Angeles | Year: 2009 | pages: 231
ABSTRACT
The p-y method is an established analysis tool for lateral response of piles. Existing soil lateral load-displacement (or p-y) backbone curves have been calibrated with tests on small-diameter, linearly elastic piles. The first portion of this study is devoted to obtaining several new p-y curves by using data from three solitary reinforced concrete shafts embedded in stiff clay and tested to failure under lateral loading. These new curves are shown to differ from the standard curves, primarily in capacity: For a 6ft-diameter free-head specimen, the new curve reaches a load capacity that is 60% higher than the standard curve; for a 2ft-diameter free-head shaft, the new curve is 20% weaker; and for a 2ft-diameter fixed-head shaft, the new curve is 100% stronger than the existing standard.
In the second part of this study, the calibrated p-y model of the 2ft-diameter fixed-head specimen, and a validated finite element model of a group of nine piles are utilized to determine "group efficiency factors." These scaling factors are found to depend on the magnitude of lateral pile-cap displacement. The efficiencies are less than unity when the passively resisting soil wedges in front of the piles interfere with each other—for the same lateral displacement, a pile in the group generates a resisting force that is less than that of a solitary pile. Usually dubbed as the "shadowing effect," this behavior is observed up to intermediate levels of lateral pile-cap displacement. The group efficiencies tend to unity as the displacement increases.
The third part explores abutment-backfill interaction in bridges. This effect can significantly influence the seismic response of a bridge. Both log-spiral hyperbolic (LSH) and finite element models are validated using data from several abutment tests. Extensive parametric studies are carried out using the LSH model, which is more amenable for this task than the finite element model because of its computational efficiency. Results are used to devise hyperbolic equations to represent the lateral load-displacement backbone curves of abutments as an explicit function of wall height and the backfill soil's physical parameters. This physically parameterized hyperbolic formula is amenable for routine seismic response simulations of bridges.
Advisor: Professor Ertugrul Taciroglu
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SSI and Its Roles in Performance-Based Seismic Analysis of Shear Wall Structures (PhD Thesis)
Author: Yuchuan Tang | Size: 3.2 MB | Format:PDF | Quality:Original preprint | Publisher: University of California, Los Angeles | Year: 2009 | pages: 287
ABSTRACT
In order to systematically assess the complex soil-structure interaction (SSI) effects on the seismic responses of shear wall structures, this dissertation deals with several critical and inter-related topics under the framework of performance-based earthquake engineering. Firstly, the study develops improved pulse representations for earthquake ground motions that govern the peak structural responses. Based on rigorous dimensional analysis, the dimensionless Il-response spectra are derived for both linear and bilinear SDOF systems. They are shown to be congruent with the corresponding (dimensional) response spectrum in bi-logarithmic plotting. This leads to a novel approach to identify pulse parameters that match simultaneously the kinematic characteristics and the response spectrum of the original ground motion. The improved pulse representations can potentially be used as the intensity measures of earthquake ground motions. Secondly, the SSI effects of lumped soil-foundation-structure interacting (SFSI) systems are investigated through the dimensional analysis with pulse motions as input.
The dimensionless terms that govern the interactive behavior of SFSI systems are derived. The SSI effects are related explicitly and directly to the characteristics of input ground motions and the properties of SFSI systems. The conditions under which the SSI effects amplify or reduce the structural responses are also identified. Subsequently, dynamic responses of strip foundations bonded on linear or nonlinear soil half-space are investigated using the finite element method. The dynamic foundation responses are found to depend on the amplitude and frequency of input motion, foundation geometry, and soil properties. The energy dissipation through radiation damping for nonlinear soil case is reduced and can be quantified with two alternative factors related to the yielding of soil medium.
Finally, the SSI effects are evaluated for a realistic shear wall structure using the probabilistic seismic demand analysis where the nonlinear hysteretic behavior of shear walls and foundations are accurately modeled. Either the inelastic spectral displacement or the pulse representation is adopted as the intensity measure of input ground motions. The damage probability of the shear wall generally decreases when the SSI effects are considered for this case study.
Advisor: Professor Jian Zhang
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The purpose of this study is to investigate the P-Delta effect on bridge piers with consideration of soil-structure interaction effect. The traditional P-Delta effect was calculated assuming the base of the structure is fully fixed. However, all structures in real life are supported by soil, and soil is deformable. Therefore, under wind or earthquake loads, the additional lateral deflection of a bridge pier
caused by the deformation of the soil, which supports the pier, should be considered. The traditional method regarding the computation of the deflection of a pier caused by wind or earthquake loads does not take soil-structure interaction effects into account. In this study finite element analysis method will be used to investigate the additional overturning moment introduced by the soil-structure interaction effect.
Advisor: Assoc.Prof. Dr. J. Kent Hsia
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Dear Friends
i need paper
"Settlemet of Raft Foundations"
by Kay.J.N and Cavagano.R.L
Journal of Geotechnical Engineering division of ASCE 1983
vol 109 pp 1367-1382
could anyone share it?
thanks in advance
with best regards
mz55
This book is an introduction to surgery theory: the standard classification method for high-dimensional manifolds. It is aimed at graduate students, who have already had a basic topology course, and would now like to understand the topology of high-dimensional manifolds.
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Author: Romeyn Henry Rivenburg | Size: 5.2 MB | Format:PDF | Quality:Scanner | Publisher: American Book Company | Year: 1914 | pages: 80 | ISBN: B006CN21OW
The object of this book is to provide a thorough and effective review that is necessary in order to prepare college candidates for the entrance examinations and for effective work in the freshman year in college. This is the 1914 edition.
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