Seismic response of earth dams: some recent developments
Author: George Gazetas Rensselaer Polytechnic Institute, Troy, New York, USA, and National Technical University, Athens, Greece | Size: 3.8 MB | Format:PDF | Quality:Unspecified | Publisher: Soil Dynamics and Earthquake Engineering, 1987, Vol. 6, No. 1 | Year: 1987 | pages: 46
The paper focuses on theoretical methods for estimating the dynamic response of earth dams to earthquake ground excitation. Following an outline of the historical developments in this field, the basic concepts/models for response analysis are introduced and their salient features, advantages and limitations are elucidated. The major phenomena associated with, and factors influencing, the response are identified and studied. Particular emphasis is accorded to inhomogeneity due to dependence of soil stiffness on confining pressure, nonrectangular canyon geometry, and nonlinear-inelastic soil behaviour. Several new formulations that have evolved over the last five years are outlined and characteristic results provide considerable insight into the problem. The simplicity of some of these formulations is underlined and attempts are made to compare their predictions with measurements from full-scale, natural and man-made, forced vibration tests. The basic validity as well as the limitations of the proposed analysis methods is demonstrated and topics of needed further research are suggested.
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GUIDELINES FOR EVALUATING AND MITIGATING SEISMIC HAZARDS IN CALIFORNIA
Author: CALIFORNIA GEOLOGICAL SURVEY JOHN G. PARRISH, PH.D, STATE GEOLOGIST | Size: 1.2 MB | Format:PDF | Quality:Unspecified | Year: 2008 | pages: 108
This document contains several important revisions to the 1997 edition of Special Publication 117, ―Guidelines for Evaluating and Mitigating Seismic Hazards in California‖, and supersedes that version. This release also supersedes a previous 2008 update of Special Publication 117 that was released electronically in portable document format. Changes in ground motion requirements for foundation design, and, for assessments of liquefaction and slope stability hazards in the latest edition of the California Building Code, have necessitated additional changes for consistency. To avoid confusion with the previous 2008 release, this document carries the designation ―Special Publication 117A.‖ More than ten years have passed since these Guidelines were first published, during which time there have been significant changes in practice as a result of continuing research in geotechnical earthquake engineering and soil mechanics, and from investigations of several significant earthquakes such as the 1999 Chi-Chi Earthquake in Taiwan and the 1999 Kocali Earthquake in Turkey. This has prompted the need to revise these Guidelines in several areas.
New tools for the screening and evaluation of slope stability and liquefaction hazards have been developed, and new and improved attenuation relations for the estimation of future ground motions have emerged from analysis of numerous new near-field strong motion recordings of recent large earthquakes. These advancements are already finding their way from the professional literature into practice, and the revised Special Publication 117A includes references to them. In addition, mitigation of ground failure hazards has been consolidated into a new chapter that includes the role of grading in hazard mitigation. These changes will improve the utility of these Guidelines in the evaluation of seismic hazards for proposed development within California‘s regulatory ―zones of required investigation‖ pursuant to the Seismic Hazards Mapping Act of 1990. Future revisions to the Guidelines may be more frequent because of rapid developments in this field, and for efficiency the revisions will be downloadable from the following web site:
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Seismic vulnerability in wide areas is usually assessed in the basis of inventories of structural parameters of the building stock, especially in high hazard countries like USA or Italy. France is a country with moderate seismicity so that it requires lower-cost methods. Ambient vibrationsn analyses seem to be an alternative way to determine the vulnerability of buildings. The modal parameters we extract from these recordings give us a 1D model for each class of building found in the study area. We then study the response of these models to realistic seismic excitations (scenarios) including site effects in order to determine a threshold acceleration sustained by this class of building which we interpret as a vulnerability index. The distribution of the classes in the city will lead to a vulnerability map. In order to validate this method, we compare the modal parameters of a building in Grenoble (France) determined under ambient noise and during a stronger excitation: the demolition of a nearby bridge. A statistical study of recordings using time windowing gives uncertainties and leads us to conclude that the modal parameters are equal.
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Mitigation of earthquake induced vibrations by Tuned Mass Dampers
Author: Alexander Tributsch , Christoph Adam , Thomas Furtmüller | Size: 2.4 MB | Format:PDF | Quality:Unspecified | Publisher: Proceedings of the 8th International Conference on Structural Dynamics, EURODYN 2011 Leuven, Belgium, 4-6 July 2011 | Year: 2011 | pages: 08
This paper addresses the assessment of the performance of Tuned Mass Dampers (TMDs) to mitigate seismic induced structural vibrations. Two different sets of recorded ground motions are employed: the first set contains far-field records, the second one near-field records with strong pulse characteristics. The evaluation of the TMD efficiency and of its
optimal parameters is based on reduction coefficients, which are derived from the ratio of the structural response with and without attached TMD. These response quantities are evaluated statistically, and the difference between the outcomes for both ground motion sets is quantified. Numerous combinations of parameters are consulted to predict the effect of detuning from optimal TMD parameters. It is verified that a TMD damping coefficient larger than the optimal one reduces the peak deflection of the TMD spring significantly, while the response reduction of the main structure remains almost unaffected.
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GARAGE STRUCTURE VIBRATION TRANSMISSION TO HUMAN OCCUPIED SPACES
Author: Jack B. Evans* | Size: 1.9 MB | Format:PDF | Quality:Unspecified | pages: 08
Parking garages designed to be separate, stand-alone structures are often very limber, longerspan structures with low resonant frequencies. They exhibit vibration characteristics ill suited for office, residential, hospital or other human occupancies. Expansion or extension of the garage structure for a proposed human occupancy should recognize differences between occupancies or usages and incorporate acceptable floor vibration design parameters. Three case studies are presented about investigations garage vibration, one for an office expansion above the parking level and two for continuous slab extension from garage to horizontally adjacent residential spaces. . Measurements were conducted to determine
resonant frequencies of driveway and parking areas and to determine vibration amplitude spectra for ambient and vehicle pass disturbance conditions. Ambient and disturbed
conditions are compared with human perception criteria (re: ISO 2631). Differences between garage driveway “sources” and parking “receiver” locations indicate transmission losses.Apparent resonant frequency (narrow band) and 1/3 octave amplitude spectra for ambient and disturbed condition are shown. Garage plans and photos are incorporated. Design implications for structural continuity between garage driveway and parking slabs and adjacent floor slabs for human occupancy are discussed with conceptual methods of reducing vibration amplitudes on receiver slabs for continuous and discontinuous slabs.
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Author: R. N. Mortimore | Size: 6.6 MB | Format:PDF | Quality:Unspecified | Publisher: Geological Society of London | Year: 2006 | pages: 173 | ISBN: 1862391505
Most of the rocky coastlines around the world are subject to active erosion processes. Because of the growing hazard to local communities from coastal cliff retreat, it is necessary to investigate where, when and how cliffs collapse. The results of these studies are vital for the planners and local authorities responsible for safety and access to cliffs and beaches.
This volume focuses on the coastal chalk cliffs of the English Channel, where a multidisciplinary approach has been used to understand active coastal cliff recession. The book is organized around three main themes: the geological factors controlling cliff instability, the marine parameters influencing coastal erosion and the use of some new tools for hazard assessments. This book will be of use to academics and professionals working on rocky shores, with an interest in sedimentary geology, stratigraphy, tectonics, geomorphology, engineering geology, coastal engineering and GIS.
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3D Periodic Foundation-based Structural Vibration Isolation
Author: Z.B. Cheng, Y.Q. Yan, Farn-Yuh Menq, Y.L. Mo, H.J. Xiang, Z.F. Shi and Kenneth H. Stokoe, II | Size: 938 MB | Format:PDF | Quality:Unspecified | Publisher: Proceedings of the World Congress on Engineering 2013 Vol III, WCE 2013, July 3 - 5, 2013, London, U.K. | Year: 2013 | pages: 06
Guided by the recent advances in solid-state
physics research, a 3D periodic foundation-based structural
vibration isolation is studied. Using construction materials,
concrete, rubber and steel, the three-component periodic
foundation is developed. Frequency band gaps for the specimens
are found to be in low-frequency region (<20Hz). A parametric
study is also conducted to illustrate the influences of the
geometrical and material parameters on the frequency band
gaps. Based on the frequency band gaps analysis, numerical
simulations are performed to verify the efficiency of the periodic
foundation. Harmonic analysis results show periodic foundation
can reduce vibrations in the frequency band gap. Further, a
transient analysis shows that 3D periodic foundations can also
isolate seismic wave effectively.
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Practical Methods for Vibration Control of Industrial Equipment
Author: Andrew K. Costain, B.Sc.Eng. and J Michael Robichaud, P.Eng. Bretech Engineering Ltd | Size: 444 KB | Format:PDF | Quality:Unspecified | pages: 8
The generally accepted methods for vibration control of industrial equipment include; Force Reduction, Mass Addition, Tuning, Isolation, and Damping. This paper will briefly introduce each method, and describe practical methods for their application. Several scenarios and case studies will be presented, with emphasis on pragmatic solutions to industrial vibration problems.
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Vibration from Underground Railways: Considering Piled Foundations and Twin Tunnels
Author: Kirsty Alison Kuo King’s College University of Cambridge | Size: 6.8 MB | Format:PDF | Quality:Unspecified | Publisher: King’s College University of Cambridge | Year: September 2010 | pages: 208
Most engineering courses on vibration begin with a mass on a spring, and then move on to continuous systems such as strings, columns and membranes. These simple systems provide students with a good understanding of the fundamentals of vibration theory, and the physical behaviour of such systems is represented by using well-known equations. However, many vibration problems do not involve such simple systems.
In the past, to solve these problems, engineers would turn to experimental investigations, or would construct simple models that could capture the essential physical behaviour and yet be solved using the available computational techniques. Nowadays, many engineers use commercial software packages that make use of powerful numerical methods such as finite-element or boundary-element methods as their primary tool in constructing models. The difficulty that may arise from the use of such software (that is specially designed to have a user-friendly interface) is that many practitioners lack an awareness of the limitations of these numerical models, and the uncertainty that may be present in the results is often poorly understood
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In this paper mechanical system containing four horizontal blowers with separate frame each is analyzed. The system is fixed on one general foundation. The high level of vibrations is dominating during the work of the system. The results of experimental investigation of mechanical system are represented here. The finite element model of the operation investigated system gives possibility to investigate natural frequencies. The reasons of high level vibrations were identified by comparing the results of experimental data and theoretical calculations. The concept of vibrations reduction based on the results of this investigation was proposed as well.
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