The vibration response of piled foundations to inertial and underground railway induced loadings
Author: Pieter COULIER | Size: 5.1 MB | Format:PDF | Quality:Unspecified | Publisher: ENGINEERING DEPARTMENT MECHANICS, MATERIALS AND DESIGN DYNAMICS AND VIBRATION TRUMPINGTON STREET CB2 1PZ CAMBRIDGE UK | pages: 123
Vibrations and re-radiated noise in buildings induced by (underground) railway traffic are a major environmental concern. Vibrations are generated at the wheel-rail interface and propagate through the soil into buildings, where they cause annoyance to inhabitants. During the last decades, a lot of research has been performed to search for efficient and cost-effective vibration countermeasures. This dissertation is concerned with the dynamic behaviour of piled foundations. A model for piled foundations which accounts for the fundamental behaviour of each pile and the interaction between neighbouring piles, through wave propagation in the soil, is developed. It is a boundary element
model, formulated in the frequency domain, based on an existing single pile model.
The model is used to validate the Pipe-in-Pipe (PiP) model for piles, a computationally efficient model
for piled foundations based on the homonymic model for vibrations from underground railways. The
models are found to be in good agreement, which offers great perspectives to use the PiP model as an
engineering tool.
The influence of adjacent piles on the response of a certain pile is investigated by means of a power
flow analysis. It will be demonstrated that the effect is strongly dependent on the relative positions
of the piles compared to the position of the load applied. Moreover, a tendency to wave scattering is
revealed when the wavelength approaches the distance between piles and load.
Ultimately, the response of piled foundations to underground railway induced loadings is investigated.
Uncoupling of source (railway track) and receiver (piled foundations) is assumed, resulting in a two-step approach. The model is once more used to validate the PiP model for piles. Several aspects, such as the effect of the foundation design, the contribution of horizontal and rotational motion, the importance of pile-soil-pile interactions and the isolation performance of base isolation are examined. Results suggest that steel springs are preferred to rubber bearings, as the isolation frequency can be lowered more significantly. Moreover, it will become clear that the current boundary element model has the ability to reveal the complexity of the situation, which cannot be achieved by means of simplified
models.
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Size: 3.4 MB | Format:PDF | Quality:Unspecified | Publisher: SP Swedish National Testing and Research Institute Acoustics SP REPORT 2000: 25 Borås 2000 | Year: 2000 | pages: 103
Field measurements were carried out at two sites in southwest Sweden. Three, 3-directional accelerometers were used at three different distances from the middle of the railway track. All the accelerometers were mounted 50cm below the ground surface. Each accelerometer for the three directional accelerometers was mounted to represent one direction, the X direction is perpendicular to the railway track, the Y direction is parallel to the railway track and the Z direction is the vertical direction on the ground. The signal generated due to the passing trains were recorded by Sony Digital Recorder (DAT). Due to the fact that, this DAT has eight input channels and we used three 3-directional accelerometers, which
means nine accelerometers, one channel had to be omitted.
MATLAB was used to analyse the signals. The vibration levels were analysed using time weighting Sand the acceleration values were converted to velocity values. These measurements were carried out on three different types of trains: X2000, intercity, and freight trains.
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VIBRATION SERVICEABILITY OF FOOTBRIDGES UNDER HUMAN-INDUCED EXCITATION: A LITERATURE REVIEW
Author: STANA ŽIVANOVIĆ, ALEKSANDAR PAVIC and PAUL REYNOLDS | Size: 854 MB | Format:PDF | Quality:Unspecified | Publisher: Živanović, S., Pavić, A. and Reynolds, P. (2005) Vibration serviceability of footbridges under human-induced excitation: a literature review. Journal of Sound and Vibration, Vol. 279, No. 1-2, pp. 1-74. ( | pages: 69
Increasing strength of new structural materials and longer spans of new footbridges, accompanied with aesthetic requirements for greater slenderness, are resulting in more lively footbridge structures. In the past few years this issue attracted great public attention. The excessive lateral sway motion caused by crowd walking across the infamous Millennium Bridge in London is the prime example of the vibration serviceability problem of footbridges. In principle, consideration of footbridge vibration serviceability requires a characterisation of the vibration source, path and receiver. This paper is the most comprehensive review published to date of about 200 references which deal with these three key issues.
The literature survey identified humans as the most important source of vibration for footbridges. However, modelling of the crowd-induced dynamic force is not clearly defined yet, despite some serious attempts to tackle this issue in the last few years. The vibration path is the mass, damping and stiffness of the footbridge. Of these, damping is the most uncertain but extremely important parameter as the resonant behaviour tends to govern vibration serviceability of footbridges. A typical receiver of footbridge vibrations is a pedestrian who is quite often the source of vibrations as well. Many scales for rating the human perception of vibrations have been found in the published literature. However, few are applicable to footbridges because a receiver is not stationary but is actually moving across the vibrating structure.
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Seismic wave propagation in granular soils can induce large strain amplitudes in case of strong earthquakes. Seismic motions are irregular in frequency content and in amplitude, and have three different components in orthogonal directions. In this context, the main objective of this PhD research deals with nonlinear effects observed in granular soils under such complex loadings. The assumptions and simplifications usually considered for representing seismic loadings are evaluated, focusing on two main aspects: (i) cyclic stress frequency applied to the sample (ii) superposition of two
independent stresses. For that purpose, the nonlinear behaviour of two different sands, Leman Sand and Fonderie Sand, is explored with cyclic and seismic triaxial tests. These tests are performed with
unidirectional or bidirectional loadings, at medium to high strain amplitude, and in the earthquake frequency range. A dynamic triaxial press was developed to perform such tests, with dry and undrained saturated sand
samples. Axial and lateral stresses can be applied independently with large amplitudes for various loading shapes. An innovative non-contact measurement technique was developed to continuously
monitor the sample radius; this testing equipment is based on three laser sensors, set up around the triaxial cell, which detect the position of the sample surface thanks to optical triangulation. The obtained data are processed through a complex calibration system to provide the radial strain evolution at mid-height of the sample. The mounting structure supporting the sensors allows precise positioning and is equipped for manual vertical scanning of the sample profile.
The first triaxial tests are performed with classical cyclic loadings, to characterize the behaviour of the two sands in pseudo-dynamic conditions. These dry and undrained saturated tests allow to describe the
decrease of stiffness which leads to failure of the sand sample. Failure of undrained saturated sand occurs by liquefaction. Dry and undrained cyclic tests performed on Leman Sand at various frequencies from 0.1 to 6.5 Hz
show that the behaviour of this granular material is frequency-dependent at medium to large strains.
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A Dynamic Response Study on Optimal Piling Depth with respect to Ground Vibrations
Author: ERIK OLSSON Department of Civil and Environmental Engineering Division of Applied Acoustics Vibroacoustics Group | Size: 1.3 MB | Format:PDF | Quality:Unspecified | Publisher: CHALMERS UNIVERSITY OF TECHNOLOGY Göteborg, Sweden 2014 | Year: 2014 | pages: 74
Dynamic response of a piled foundation in soil has lately received much attention in research areas such as civil engineering and seismic engineering. The goal of this thesis is to learn more about the dynamic response of a single pile in clay and in particular to study if there is an optimal piling depth. The clay types investigated are an idealized isotropic clay and a case-specific for Gamla Ullevi, Gothenburg, Sweden. The motion and forces are small and the soils are considered as linear elastic materials. A solid finite element model is built in one case-specific and one idealized version. The idealized version is validated by mechanical response theory of a elastic half-space and also by comparison to a semi-analytical wavenumber model published 2013 by Kuo & Hunt. The response results show perfect agreement with half-space response theory and good agreement with the wavenumber model. The point mobility of a vertically loaded pile, and the transfer mobility at surface and in depth, are studied for different pile lengths for frequencies below 20 Hz. The results from both finite element model and the wavenumber model show convergence piling
depth at about 30 meters for both soil types. The transfer function results are reciprocal which allows to consider the foundation as the recipient of ground vibrations.
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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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