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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenSat, 13 Apr 2024 01:23:55 +0000Vibration Tests of a Multistory Building
https://resolver.caltech.edu/CaltechETD:etd-09302002-101427
Authors: {'items': [{'id': 'Kuroiwa-Julio-Horiuchi', 'name': {'family': 'Kuroiwa', 'given': 'Julio Horiuchi'}, 'show_email': 'NO'}]}
Year: 1967
DOI: 10.7907/NW3D-FE77
<p>Vibration tests were performed on a 9 story reinforced concrete building with basement, in order to investigate its dynamical characteristics, by exciting the building with 2 vibration generators installed on its 9th floor.</p>
<p>The natural periods of vibration, the value of the damping, and the mode shapes, in the N-S and E-W directions and in torsion, were determined by measurement. Before the main part of the testing was carried out, some preliminary tests were made to check the correctness of some assumptions which would simplify the main test procedure.</p>
<p>It was possible to investigate in detail only the first mode of each type of motion, because of the relatively high rigidity of the building and a limitation on the maximum frequency at which the shakers could be driven.</p>
<p>The periods measured were quite short for a 9 story building, 0.505 sec in the N-S direction, 0.662 sec in the E-W direction, and 0.346 sec in torsion, and their values increased by about 3 per cent when the tests were performed at the highest force levels.</p>
<p>The damping, which consistently increased as the exciting force increased, varied between 0.70 and 2.00 per cent of the critical viscous damping. The periods and damping values were also determined at very low force levels by exciting the building with a rhythmical movement of the operator's body. The periods measured in this way were slightly smaller than those found using the shakers, and the damping varied between 0.6 and 0.9 per cent of the critical viscous damping.</p>
<p>The mode shape did not seem to be well defined for the lower force levels, but after the force level reached a certain minimum value, the normalized mode shape remained unchanged, both with further increases in the forces, and with changes in the frequency of excitation. However, in both the N-S direction and in torsion, the horizontal displacements of the first and basement floors consistently increased, on the order of 3 per cent with respect to the displacements of the upper floors as the exciting force increased.</p>
<p>Some aspects of the dynamical behavior of buildings, which have not been studied by other investigators in previous tests, were examined. It is a common practice in the seismic analysis of structures to assume that the floor systems act as rigid diaphragms when the building is acted upon by horizontal forces, and also to assume that the structure is fixed at the ground level. It was found that the first assumption was correct, but instead of the second it is more accurate to assume that the building is fixed at the foundation, and not at ground level.</p>
<p>The vibration of the ground in the vicinity of the building was also measured, together with the vibrations of the basement and first floor. It was also possible to measure the acceleration at the top of one of the units of the air conditioning equipment located on the roof. The acceleration at the top of this unit was about 8.5 times that of the roof.</p>https://thesis.library.caltech.edu/id/eprint/3825Gravity Effects on the Earthquake Response of Yielding Structures
https://resolver.caltech.edu/CaltechETD:etd-09202002-143339
Authors: {'items': [{'id': 'Husid-Raúl', 'name': {'family': 'Husid', 'given': 'Raúl'}, 'show_email': 'NO'}]}
Year: 1967
DOI: 10.7907/9XAB-6V59
The effect of gravity on the earthquake response of one degree of freedom yielding structures is studied by subjecting them to earthquake-like excitation. Interest is centered on the time required for yielding to progress to the point of collapse. The results show that the effect of gravity is to increase significantly the development of permanent set over that occurring when gravity is ignored. Because the gravity effect increases as the deflection grows, the permanent set increases rapidly just prior to failure.
A statistical study of the time to failure for elasto-plastic structures indicates that the average time to failure is inversely proportional to the square of the ratio of the earthquake strength to the lateral yield level of the structure, implying that an earthquake of short duration would have to possess significantly higher accelerations than a longer earthquake in order to cause failure of a given structure.
It was found that for the range of periods considered the average time to collapse for the yielding structures was independent of period. For the bilinear hysteretic structure the results show a large increase in the time of failure when the second slope increases from zero.
Calculations made with simultaneous vertical and horizontal excitation, and with recorded strong earthquake accelerograms, indicate that the thesis results, obtained from artificial earthquakes, should be applicable for strong earthquake excitation.
Comparison of the results with those of a one-dimensional random walk indicates that on the average a yielding structure will collapse after the input of a certain amount of energy.https://thesis.library.caltech.edu/id/eprint/3653Dynamic Analysis of Coupled Shear Walls and Sandwich Beams
https://resolver.caltech.edu/CaltechThesis:10192017-151943526
Authors: {'items': [{'id': 'Skattum-Knut-Sverre', 'name': {'family': 'Skattum', 'given': 'Knut Sverre'}, 'show_email': 'NO'}]}
Year: 1971
DOI: 10.7907/SMJ0-W112
<p>A study is made of the free vibration of planar coupled shear walls, a common lateral load-resisting configuration in building construction where two walls are coupled together by a system of discrete spandrel beams. The differential equations and boundary conditions are obtained by the variational method, and by assuming that the spandrels can be replaced by a continuous system of laminae, or small beams.</p>
<p>Natural frequencies and mode shapes are determined, and the results are presented in a number of figures from which the natural frequencies of any coupled shear wall can be extracted. The importance of including vertical displacement in the analysis is discussed, and a study of the effect of neglecting the vertical inertia term is given. These cases are illustrated with graphs and with one specific example. Investigations are also made of the asymptotic behavior of the system as the spandrels become weak, as they become stiff, and as the frequencies become large.</p>
<p>Finally, the theory of sandwich beams is presented and compared to that for coupled shear walls. It is observed that for most cases of constant properties, the differential equations (and boundary conditions) reduce to the same mathematical form for both theories.</p>https://thesis.library.caltech.edu/id/eprint/10532Modal Coupling and Earthquake Response of Tall Buildings
https://resolver.caltech.edu/CaltechThesis:10192017-153501109
Authors: {'items': [{'id': 'Hoerner-John-Brent', 'name': {'family': 'Hoerner', 'given': 'John Brent'}, 'show_email': 'NO'}]}
Year: 1971
DOI: 10.7907/0H45-NM32
<p>The major dynamic features of tall buildings are within the scope of a shear beam model. Herein the usual one-dimensional model is extended to three dimensions to include modes with translational and rotational components. The analysis is restricted to the continuous model with linear response.</p>
<p>A class of models for tall buildings is presented which possesses three sets of mutually orthogonal coupled modes. The amount of modal coupling is related to the eccentricities divided by the translational-torsional frequency differences. Strong modal coupling can occur if the eccentricities and frequency differences are small, as in a rectangular building with a smooth distribution of columns. A perturbation scheme is developed for buildings almost in this class. The perturbation method is applicable to buildings with nearly vertical mass and rigidity centers and with ith-modes of nearly the same shape.</p>
<p>Rotational components of earthquake response in buildings primarily results from modal coupling, and it is shown that modal coupling can increase response on the building's perimeter. Furthermore, rectangular buildings with modal coupling can show a beating-type frequency response, for which the more usual r.m.s. combination should be replaced by an absolute sum. These effects can significantly increase certain response parameters. The corners of a rectangular building can have a 95% increase in shear, as compared with 30% implied by a 5% eccentricity in the codes. Base shears and overturning moments can be increased by 40%.</p>
https://thesis.library.caltech.edu/id/eprint/10533Earthquake Response of Building-Foundation Systems
https://resolver.caltech.edu/CaltechTHESIS:12062017-133056313
Authors: {'items': [{'id': 'Bielak-Jacobo', 'name': {'family': 'Bielak', 'given': 'Jacobo'}, 'show_email': 'NO'}]}
Year: 1971
DOI: 10.7907/YEAJ-FN27
<p>The influence of a deformable foundation on the response of
buildings to earthquake motion is examined. The study is divided into
two parts; the vibration of the base of the building on the foundation
medium, and the response of the whole building-foundation system.</p>
<p>Studied first are the forced horizontal, rocking and vertical
harmonic oscillations of a rigid dis c bonded to an elastic half-space, which
is considered as a mathematical model for the soil. The problem,
formulated in terms of dual integral equations, is reduced to a system
of Fredholm integral equations of the second kind. For the limiting
static case these equations yield a closed form solution in agreement
with that obtained by others.</p>
<p>Using the force-deflection relations for the base, the equations of
motion of linear building-foundation systems are solved by both direct
and transform methods. It is shown that, under assumptions which
appear to be physically reasonable, the earthquake response of the interaction
system reduces to the linear superposition of the responses of
damped, linear one-degree-of-freedom oscillators subjected to modified
excitations. This result is valid even for systems that do not possess
classical normal modes. Explicit approximations in terms of the parameters
of the system are obtained for the dynamic properties of
the one-degree-of-freedom oscillator which is equivalent to a single story
building-foundation system. For multi-story buildings it is shown that the
effect of an elastic foundation, as measured by the change in
the natural frequencies of the building, is negligible for modes
higher than the first for many types of building structures.</p>
https://thesis.library.caltech.edu/id/eprint/10591Studies in the Statics and Dynamics of Simple Cable Systems
https://resolver.caltech.edu/CaltechThesis:10162019-164456880
Authors: {'items': [{'id': 'Irvine-Hilary-Max', 'name': {'family': 'Irvine', 'given': 'Hilary Max'}, 'show_email': 'NO'}]}
Year: 1974
DOI: 10.7907/K4Y4-8H02
<p>An investigation is made of the static and dynamic response of simple cable systems to applied load. Both the single, suspended cable and the counterstressed double cable system (the cable truss) are treated. More complicated systems, such as cable nets, are not treated. The geometry of the simple cable systems is such that the c able slopes are, and remain, small. For example, the ratio of sag to span of the suspended cable must be about 1:8, or less.</p>
<p>Closed form solutions are given to a variety of cable problems which have important applications in practice. The work is divided into two chapters.</p>
<p>In the first chapter solutions are given for the response of a single, suspended cable to static loading, and a comprehensive theory is presented for the free, linear vibrations of the suspended cable. Where necessary, in the static analyses, the solutions are given accurate to the second order of small quantities. The results of simple experiments are reported.</p>
<p>The second chapter deals with the cable truss and, again, static analyses are given and a theory is presented for the free, linear vibrations of the cable truss. The possible lateral instability of the cable truss under applied load is investigated.</p>
<p>An attempt is made to give static solutions which are of general significance. In the part this has rarely been done. It is shown that a parameter which involves cable elasticity and geometry has a very important bearing on several of the theories presented. The parameter does not appear to have been given before and, for this reason, most previous works are of limited applicability and in some cases they are wrong. For example, the linear in-plane vibrations of these simple cable systems can be analyzed correctly only if this parameter is included. The lateral instability of the cable truss is important, not only because previously it appears that it has been ignored, but also because it opens up a new field of buckling problems which are unlike any others.</p>https://thesis.library.caltech.edu/id/eprint/11820Engineering Studies of the San Fernando Earthquake
https://resolver.caltech.edu/CaltechThesis:08112021-192505383
Authors: {'items': [{'id': 'Crouse-Charles-Brian', 'name': {'family': 'Crouse', 'given': 'Charles Brian'}, 'show_email': 'NO'}]}
Year: 1974
DOI: 10.7907/17yn-bc14
<p>A number of accelerograms obtained during the San Fernando earthquake were analyzed to investigate the nature of the strong motion. The particular features studied were soil-structure interaction and the relative influence of local site conditions versus the source mechanism and travel paths of earthquake waves.</p>
<p>Evidence of soil-structure interaction in the EW fundamental mode of the Hollywood Storage building is seen in the earthquake data. General agreement exists up to ~ 5 c.p.s. in both lateral directions between theoretical, base to free field transfer functions and transfer functions derived from accelerograms obtained in the basement and adjacent parking lot. There was no evidence of soil-structure interaction in the Millikan Library and Athenaeum buildings on the Caltech campus, and this effect could not account for the major differences in their accelerograms.</p>
<p>Accelerogram, Fourier Amplitude Spectra, and Response Spectra data were compared from a group of six tall buildings close together near Wilshire Blvd. and Normandie Ave. in Los Angeles and from seven surrounding buildings, two to three miles away. The data indicated that local site conditions and soil-structure interaction were not major contributors to the observed differences in the response at these sites. There was correlation between the degree of similarity in the response at two sites and their distance apart. A simple wave superposition model with numerical examples confirms this correlation.</p>https://thesis.library.caltech.edu/id/eprint/14321Dynamic Soil-Structure Interaction
https://resolver.caltech.edu/CaltechTHESIS:05242023-213627945
Authors: {'items': [{'id': 'Wong-Hung-Leung', 'name': {'family': 'Wong', 'given': 'Hung Leung'}, 'show_email': 'NO'}]}
Year: 1975
DOI: 10.7907/yqyx-mg56
<p>The dynamic response of a structure placed on a deformable soil medium subjected to seismic excitation is studied. The basic phenomena of soil-structure interaction was investigated by several analytical models supplemented by experimental observations; a brief review of literature in this discipline is also included.</p>
<p>Among the physical phenomena investigated: the effects caused by local topography, the interaction with other structures, and the dissipation of dynamic energy through the soil medium were described by exact series solutions. Foundations of arbitrary shape, however, were modeled by using an approximate integral representation. This latter method utilizes the principle of superposition and provides flexibility in analyzing numerically the three-dimensional disc foundations placed on the soil surface. The results indicate that the detailed description for the shape of a rigid foundation placed on a deformable soil medium is not essential in the overall response of the superstructure, but the stress distribution under the disc foundation is quite sensitive to these changes in detail.</p>
<p>In this thesis, several methods for the calculation of foundation compliances for several types of foundation models were discussed, some of which have direct practical practical applications. The importance of the base input motion induced by incident seismic waves is also stressed, because the seismic input, along with the foundation compliances, are necessary for a complete analysis of this problem.</p>https://thesis.library.caltech.edu/id/eprint/15207A Study of the Vibrational Characteristics of Two Multistory Buildings
https://resolver.caltech.edu/CaltechTHESIS:03312017-102214623
Authors: {'items': [{'id': 'Foutch-Douglas-Allen', 'name': {'family': 'Foutch', 'given': 'Douglas Allen'}, 'show_email': 'NO'}]}
Year: 1977
DOI: 10.7907/X944-SG43
<p>Forced vibration tests and associated analysis of two multistory
buildings are described. In one case, the dynamic properties of the
building measured during the tests are compared to those predicted by
simple analytical models. A three-dimensional finite element model
of the second building was constructed for the purpose of evaluating
the accuracy of this type of analysis for predicting the observed
dynamic properties of the structure.</p>
<p>Forced vibration tests were performed on Millikan Library, a
nine-story reinforced concrete shear wall building. Measurements of
three-dimensional motions of approximately 50 points on each of six
floors (including the basement) were taken for excitation in the N-S and
E-W directions. The results revealed a complex interaction between
lateral and vertical load carrying systems in both directions. The
results also suggest that a significant change in the foundation response
of the structure occurred in the stiffer N-S direction during the San
Fernando earthquake. This phenomenon was investigated through the
use of two analytical models of the building which included the effects
of soil-structure interaction.</p>
<p>The Ralph M. Parsons world Headquarters building, a twelve-story
steel frame structure, was also tested. The natural frequencies,
three-dimensional mode shapes, and damping coefficients of nine modes
of vibration were determined. Other features of this investigation
included the study of nonlinearities associated with increasing levels
of response and the measurement of strain in one of the columns of the
structure during forced excitation. The dynamic characteristics of
the building determined by these tests are compared to those predicted
by a finite element model of the structure. The properties of primarily
translational modes are predicted reasonably well; but adequate predictions
of torsional motions were not obtained. The comparison
between measured and predicted strains suggests that estimates of
stress obtained from finite element analyses of buildings should be
within 25 percent of those experienced by the structure for a known
excitation.</p>https://thesis.library.caltech.edu/id/eprint/10122Determining Models of Structures from Earthquake Records
https://resolver.caltech.edu/CaltechETD:etd-11212003-110242
Authors: {'items': [{'email': 'jimbeck@caltech.edu', 'id': 'Beck-James-Leslie', 'name': {'family': 'Beck', 'given': 'James Leslie'}, 'show_email': 'NO'}]}
Year: 1979
DOI: 10.7907/JP7R-KF57
<p>The problem of determining linear models of structures from seismic response data is studied using ideas from the theory of system identification. The investigation employs a general formulation called the output-error approach, in which optimal estimates of the model parameters are obtained by minimizing a selected measure-of-fit between the responses of the structure and the model. The question of whether the parameters can be determined uniquely and reliably in this way is studied for a general class of linear structural models. Because earthquake records are normally available from only a small number of locations in a structure, and because of measurement noise, it is shown that it is necessary in practice to estimate parameters of the dominant modes in the records, rather than the stiffness and damping matrices.</p>
<p>Two output-error techniques are investigated. Tests of the first, an optimal filter method, show that its advantages are offset by weaknesses which make it unsatisfactory for application to seismic response. A new technique, called the modal minimization method, is developed to overcome these difficulties. It is a reliable and efficient method to determine the optimal estimates of modal parameters for linear structural models.</p>
<p>The modal minimization method is applied to two multi-story buildings that experienced the 1971 San Fernando earthquake. New information is obtained concerning the properties of the higher modes of the taller building and more reliable estimates of the properties of the fundamental modes of both structures are found. The time-varying character of the equivalent linear parameters is also studied for both buildings. It is shown for the two buildings examined that the optimal, time-invariant, linear models with a small number of modes can reproduce the strong-motion records much better than had been supposed from previous work using less systematic techniques.</p>https://thesis.library.caltech.edu/id/eprint/4611Frequency Domain Identification of Structural Models from Earthquake Record
https://resolver.caltech.edu/CaltechThesis:08232021-222545352
Authors: {'items': [{'id': 'McVerry-Graeme-Haynes', 'name': {'family': 'McVerry', 'given': 'Graeme Haynes'}, 'show_email': 'NO'}]}
Year: 1980
DOI: 10.7907/bpab-qq32
<p>The usefulness of simple linear mathematical models for representing the behaviour of tall buildings during earthquake response is investigated for a variety of structures over a range of motions including the onset of structural damage. The linear models which best reproduce the measured response of the structures are determined from the recorded earthquake motions. In order to improve upon unsatisfactory results obtained by methods using transfer functions, a systematic frequency domain identification technique is developed to determine the optimal models. The periods, dampings and participation factors are estimated for the structural modes which are dominant in the measured response.</p>
<p>The identification is performed by finding the values of the modal parameters which produce a least-squares match over a specified frequency range between the unsmoothed, complex-valued, finite Fourier transform of the acceleration response recorded in the structure and that calculated for the model. It is possible to identify a single linear model appropriate for the entire response, or to approximate the nonlinear behavior exhibited by some structures with a series of models optimal for different segments of the response.</p>
<p>The investigation considered the earthquake records obtained in ten structures ranging in height from seven to forty-two stories. Most of the records were from the San Fernando earthquake. For two of these structures, smaller-amplitude records from more distant earthquakes were also analyzed. The maximum response amplitudes ranged from approximately 0.025 g to 0.40 g.</p>
<p>The very small amplitude responses were reproduced well by linear models with fundamental periods similar to those measured in vibration tests. Most of the San Fernando responses in which no structural damage occurred (typically 0.2g-0.3g maximum accelerations) were also matched closely by linear models. However, the effective fundamental periods in these responses were characteristically 50 percent longer than in vibration tests. The average first mode damping identified from these records was about 5 percent of critical. Only those motions which produced structural damage could not be represented satisfactorily by time-invariant linear models. Segment-by-segment analysis of these records revealed effective periods of two to three times the vibration test values with fundamental mode dampings of 15 to 20 percent.</p>
<p>The systematic identification technique generally achieves better matches of the recorded responses than those produced by models derived by trial-and-error methods, and consequently more reliable estimates of the modal parameters. The close reproductions of the measured motions confirm the accuracy of linear models with only a few modes for representing the behaviour during earthquake response of tall buildings in which no structural damage occurs.</p>https://thesis.library.caltech.edu/id/eprint/14335Silent Boundary Methods for Transient Wave Analysis
https://resolver.caltech.edu/CaltechThesis:08132021-221014507
Authors: {'items': [{'id': 'Cohen-Martin', 'name': {'family': 'Cohen', 'given': 'Martin'}, 'show_email': 'NO'}]}
Year: 1981
DOI: 10.7907/xrgh-ag46
<p>This thesis sets forth a dynamic model, designed to absorb infinitely radiating waves in a finite, computational grid. The analysis is primarily directed toward the problem of soil-structure interaction, where energy propagates from a region near a structure, outward toward the boundaries.</p>
<p>The proposed method, called the extended-paraxial boundary, is derived from one-directional, wave theories that have been propounded by other authors. In this thesis, the theory is presented from a more general viewpoint and is studied for its stability properties. This work suggests some modifications to the method as it was first presented. Innovations are also put forward in the boundary's implementation for finite element calculations. These alterations render the boundary an effective wave absorber.</p>
<p>The extended-paraxial boundary is then compared, both analytically and numerically, with two other transmitting (or silent) boundaries currently available -- the standard-viscous and unified-viscous methods. The analytical results indicate that the extended-paraxial boundary enjoys a distinct advantage in cancelling wave reflections; actual numerical tests revealed a small superiority over the viscous approaches.</p>
<p>Various issues are also discussed as they relate to the silent boundaries. These include Rayleigh waves, spherically symmetric and axially symmetric waves, nonlinear waves, anisotropic media, and numerical stability.</p>https://thesis.library.caltech.edu/id/eprint/14322Dynamic Behavior of Rocking Structures Allowed to Uplift
https://resolver.caltech.edu/CaltechTHESIS:05162018-151856693
Authors: {'items': [{'id': 'Psycharis-Ioannis-N', 'name': {'family': 'Psycharis', 'given': 'Ioannis N.'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/jexq-jr68
<p>Strong shaking of structures during large earthquakes may result in some cases in partial separation of the base of the structure from the soil. This phenomenon of uplifting, which can affect the dynamic behavior of the structure significantly, even if the amount of uplift is small, is examined in this thesis. First the case of a rocking rigid block is investigated and then more complicated, flexible superstructures are introduced. Two foundation models which permit uplift are considered: the Winkler foundation and the much simpler "two-spring" foundation. Several energy dissipating mechanisms are also introduced into these models. It is shown that an equivalence between these two models for the foundation can be established, so that one can always work with the much simpler two-spring foundation. In this way complete analytical solutions can be derived in most cases. Moreover, simple approximate methods for the calculation of the apparent fundamental period of the rocking system are developed and simplified methods of analysis are proposed.</p>
<p>In general, uplift leads to a softer vibrating system which behaves nonlinearly, although the response is composed of a sequence of linear responses. As a result, the apparent fundamental resonant frequency of the uplifting system is always less than the fundamental resonant frequency of both the soil-structure interacting system, in which lift-off is not allowed, and the superstructure itself. The second and higher resonant frequencies of the superstructure, however, are not affected significantly by lift-off. For damped foundations, the ratio of critical damping associated with the apparent fundamental mode decreases, in general, with the amount of lift-off. These effects of uplift on the dynamic properties of the rocking system can alter the response of the structure significantly during an earthquake. Nevertheless, it cannot be said a priori whether they are favorable to the behavior or not; this depends on the parameters of the system and the time history of the excitation.</p>https://thesis.library.caltech.edu/id/eprint/10901Experimental Observations of the Effect of Foundation Embedment on Structural Response
https://resolver.caltech.edu/CaltechTHESIS:05162018-100416743
Authors: {'items': [{'id': 'Lin-Albert-Niu', 'name': {'family': 'Lin', 'given': 'Albert Niu'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/ksr8-pf30
<p>Ambient, ring-down, and forced vibration tests were used to determine the effect of foundation embedment on the response of a one-story model structure 10 ft square in plan and 11.4 ft high. The tests, conducted at the full-, half- and unembedded foundation conditions, led to the identification of the fundamental translatory mode in the primary (east-west) and secondary (north-south) directions, and two torsional modes. The forced vibration consisted of horizontally incident SH-waves generated at an excitation structure located 47.5 ft (center-to-center) away. During these tests, detailed measurements of the near-field ground motion and modal displacement ratios were obtained at the fundamental mode in the primary direction. The displacement ratios were used to calculate the structural and foundation-soil stiffnesses and damping coefficients for comparison to theoretical results. Foundation embedment increased the model frequencies and decreased the contribution of the foundation motion to the overall displacement of the superstructure. For the fundamental mode response, which consisted of translatory and rocking motions, the resonant frequency predicted by lumped parameter analysis was higher than that measured experimentally by 25% for the unembedded case. While the experimental and theoretical fundamental mode shapes were in close agreement, the calculated effect of embedment on the response was less than that measured. These results were consistent with the comparison of the impedances and embedment factors. Serious discrepancies between analytical and experimental results were found for the case of torsion; a simple two-degree-of-freedom model was consistent only with the first of the two measured resonant frequencies.</p>https://thesis.library.caltech.edu/id/eprint/10896Analytical Models for the Dynamics of Buildings
https://resolver.caltech.edu/CaltechTHESIS:08162019-113014700
Authors: {'items': [{'id': 'Jain-Sudhir-Kumar', 'name': {'family': 'Jain', 'given': 'Sudhir Kumar'}, 'show_email': 'NO'}]}
Year: 1983
DOI: 10.7907/4k04-ca84
<p>This thesis investigates the significance of in-plane floor flexibility on the dynamics of buildings, and develops analytical models for structures that have flexible floor diaphragms. Experience with past earthquakes demonstrates that this feature is particularly important for long, narrow buildings and buildings with stiff end walls. In the method developed in this study, the equations of motion and appropriate boundary conditions for various elements of the structure are written in a single coordinate system and then are solved exactly.</p>
<p>One- and two-story buildings with end walls are analyzed by treating their floors and walls as bending and shear beams, respectively. The resulting equations of motion and the boundary conditions are solved to obtain the dynamic properties of the structure. The expected low torsional stiffness of the end walls or frames is confirmed by analysis of a single-story example structure. Study of a similar two-story building showed that the first two modes, dominated by the floor and the roof vibrations, make the largest contributions to the total base shear in the structure.</p>
<p>Floors of multistory buildings with end walls (or frames) are idealized as equivalent, distributed beams while the walls or frames are treated as bending or shear beams. Analysis of a nine-story building showed that the structure possesses several lower modes in which floors vibrate essentially as pinned-pinned beams.</p>
<p>Buildings with large numbers of uniform stories and frames (or walls) are treated as vertically-oriented anisotropic plates. It is concluded that the floors in such buildings can be assumed rigid for seismic analysis, since the modes involving floor deformations are not excited by uniform ground motion.</p>
<p>The approach can be generalized further to study more complex structures. An example is the Imperial County Services Building, which has two end walls in the upper stories and several walls in the ground story. The analytical model of this building predicts several important features of the complex dynamic behavior of the structure.</p>
https://thesis.library.caltech.edu/id/eprint/11761Analysis of the Observed Earthquake Response of a Multiple Span Bridge
https://resolver.caltech.edu/CaltechTHESIS:11262018-124513833
Authors: {'items': [{'id': 'Wilson-John-Charles', 'name': {'family': 'Wilson', 'given': 'John Charles'}, 'show_email': 'NO'}]}
Year: 1984
DOI: 10.7907/5321-6p57
<p>Accelerograms obtained during the 1979 Coyote Lake, California earthquake are used to examine the response of a multiple-span, steel girder bridge to strong earthquake loading. The structure studied, the San Juan Bautista 156/101 Separation Bridge, is typical of many highway bridges in seismic regions of the United States. Although the bridge was not damaged, the strong-motion records are of significant engineering interest as they are the first to be recorded on such a structure.</p>
<p>An engineering seismology study suggests that long-period ground displacements at the bridge site were caused by Rayleigh waves. A three-second period, pseudostatic response of the superstructure is attributed to small amounts of differential support motion induced by the surface waves.</p>
<p>A time-domain technique of system identification is used to determine linear models which can closely replicate the observed bridge response. Using time-invariant models, two structural modes at 3.50 and 6.33 Hz, are identified in the horizontal direction. Each mode, having approximately ten-percent damping, involves coupled longitudinal and transverse motions of the superstructure. Time-variations of frequency and damping in the horizontal response are also identified using a moving-window analysis.</p>
<p>A three-dimensional finite element model which includes soil-structure interaction predicts several important features of the dynamic response of the bridge. The first two computed horizontal frequencies are found to be in excellent agreement with the observed responses provided the model's expansion joints are locked, preventing relative translational motions from occurring across the joints. Locking is confirmed by the observed deformations of the structure in the fundamental mode. Fundamental vertical frequencies of the individual spans, predicted by the finite element model, are in very good agreement with ambient vibration test data. Results of the strong-motion data analysis and the finite element modeling are used to recommend a plan for expansion of the strong-motion instrumentation array on the bridge.</p>https://thesis.library.caltech.edu/id/eprint/11283A Model for the Rigid Body Motions of Skew Bridges
https://resolver.caltech.edu/CaltechTHESIS:02132019-102055741
Authors: {'items': [{'id': 'Maragakis-Emmanuel', 'name': {'family': 'Maragakis', 'given': 'Emmanuel'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/YWES-NJ36
<p>This thesis investigates the rigid body motions of skew bridges, concentrating on the in-plane translational and rotational displacements of the bridge deck induced by impact between the deck and the abutments. Experience in the San Fernando Earthquake of February 9, 1971 demonstrates that this feature is particularly important for skew bridges.</p>
<p>A simple model, in which the bridge deck is represented by a rigid rod restricted by column and abutment springs is examined first. This model illustrates the mechanism by which in-plane rotational vibrations is triggered after the closure of the gap between the bridge deck and the abutment. It also shows that the force-deflection relations of the columns and the abutments are particularly important features for the response of the bridge. Methods for the exact and approximate estimation of the elastic stiffness of elastically founded, tapered bridge columns with octagonal cross section are presented next. The methods are applied to a bridge used later as an example. In addition, the yielding of the columns is examined and the force-deflection relations for bending about two orthogonal axes are estimated.</p>
<p>The abutments are treated as rigid bodies and the soil embankments as Winkler Foundations with elastic spring constants increasing with depth. For the examination of the yielding of soil the Rankine theory is used. Based on these assumptions an approximate force deflection relation for the abutments is constructed.</p>
<p>The response of a more complicated bridge model applied to a bridge near Riverside, California is examined at the end of the thesis and examples of the results are given. This model, in which the bridge deck is still represented as a rigid rod, has three in-plane degrees of freedom: two orthogonal displacements and a rotation, and is capable of capturing many of the more important features of the nonlinear, yielding response of skew bridges during strong earthquake shaking.</p>https://thesis.library.caltech.edu/id/eprint/11391System Identification of Hysteretic Structures
https://resolver.caltech.edu/CaltechTHESIS:12192018-105342164
Authors: {'items': [{'id': 'Cifuentes-Arturo-O', 'name': {'family': 'Cifuentes', 'given': 'Arturo O.'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/p43n-j428
<p>This thesis is concerned with the earthquake response of hysteretic structures subjected to strong ground acceleration. Several earthquake records corresponding to different instrumented buildings are analyzed. Based on these observations, a new model for the dynamic behavior of reinforced concrete buildings is proposed. In addition, a suitable system identification algorithm to be used with this new model is introduced. This system identification algorithm is based upon matching the restoring force behavior of the structure rather than the time history of the response. As a consequence, the new algorithm exhibits significant advantages from a computational point of view. Same numerical examples using actual earthquake data are discussed.</p>https://thesis.library.caltech.edu/id/eprint/11322Dynamic Response of a Partially Embedded Bar Under Transverse Excitations
https://resolver.caltech.edu/CaltechTHESIS:01222019-152401456
Authors: {'items': [{'id': 'Pak-Ronald-Y-S', 'name': {'family': 'Pak', 'given': 'Ronald Y.S.'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/pp2r-fc10
<p>This dissertation is concerned with the dynamic response of a finite flexible bar partially embedded in a half-space, under transverse loadings. The loadings are applied at the unembedded end of the bar and may, in general, be a combination of time-harmonic shear and moment. The problem is intended to serve as a fundamental idealization for the dynamic analysis of piles or other embedded foundations whose flexibilities are not negligible.</p>
<p>By treating the bar 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. The essential tool required in the formulation is a group of Green's functions which describe the response of an elastic half-space to a finite, distributed, buried source which acts in the lateral direction. By means of a technique developed for a class of three-dimensional asymmetric wave propagation problems, the Green's functions are derived as integral representations. A numerical procedure for the computation of the semi-infinite Hankel-type integrals involved is presented which is free of the basic difficulties commonly encountered in such problems. Owing to the special nature of the kernel function, a numerical scheme which contains the essence of quadrature and collocation techniques is developed for the solution of the governing integral equation. Selected results for the interaction problem are presented to illustrate various basic features of the solution. In addition to furnishing the compliance functions commonly used in soil-structure interaction studies, the solution should prove useful in providing a basis for the assessment and improvement of approximate and numerical models currently employed for such analyses.</p>https://thesis.library.caltech.edu/id/eprint/11355Analysis of Unanchored Liquid Storage Tanks under Seismic Loads
https://resolver.caltech.edu/CaltechTHESIS:10232019-110854163
Authors: {'items': [{'id': 'Peek-Ralf', 'name': {'family': 'Peek', 'given': 'Ralf'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/w43k-hj54
<p>Because of cost, cylindrical, ground supported liquid storage tanks are often not fixed to their foundation, even in seismic areas. For such an unanchored tank made of steel, the weight of the cylindrical shell is mostly insufficient to prevent local uplift due to seismic overturning moments. Although, for properly designed connecting pipes, uplift itself is not a problem, it results in larger vertical compressive stresses in the tank wall at the base, opposite to where the uplift occurs. These compressive stresses have often caused buckling, even in earthquakes which did not cause much damage to other structures.</p>
<p>Various investigators have studied the behavior of unanchored tanks experimentally, but, due to the complexity of the problem, so far very little theoretical work has been done. Two methods of analysis for static lateral loads are presented: An approximate one in which the restraining action of the base plate is modeled by nonlinear Winkler springs, and a more comprehensive one in which the two dimensional nonlinear contact problem is solved by the finite difference energy method. The theoretical results are compared with existing experimental results and with the approach from current U.S. design standards. The theoretical peak compressive stresses are in good agreement with the experimental results, but in some cases exceed those calculated by the code method by more than 100%.</p>
<p>Finally, a new design concept, by which the tank wall is preuplifted all around its circumference by inserting a ring filler is described. It will be shown theoretically and experimentally that this preuplift method substantially improves the lateral load capacity.</p>https://thesis.library.caltech.edu/id/eprint/11848