Evaluation of dynamic properties of site and Response of Motion Si mulator Foundation
Author: P. Anbazhagan * , T.G. Sitharam + , G.L. Sivakumar Babu and More Ramulu | Size: 122 KB | Format:PDF | Quality:Unspecified | Publisher: Department of Civil Engineering, Indi an Institute of Science, Bangalore | pages: 10
Geotechnical parameters such as shear wave velocity and shear modulus are very important parameters in ground response analysis. The dynamic properties of foundation material below the three axes motion simulator are evaluated using the Block vibration test, Multichannel Analysis of Surface Waves (MASW) and a seismograph. This paper presents the measurements of dynamic properties using Block vibration test and MASW. Paper also present the response of foundation material due to local site condition using SHAKE2000 and vibration measurements for a passive source. Vibration characteristics of foundation material have been monitored by a seismograph with tri-axial sensors to measure the peak particle velocity in all the three directions from the passive sources such
as generator, pump house and industrial Buildings which are located at about 70m to 200m from the proposed motion simulator.
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Foundation impedance ordinates are identified from forced vibration tests conducted on a large-scale model test structure in
Garner Valley, California. The structure is a steel moment frame with removable cross-bracing, a reinforced concrete roof, and a nonembedded
square slab resting on Holocene silty sands. Low-amplitude vibration is applied across the frequency range of 5–15 Hz with a uniaxial
shaker mounted on the roof slab. We describe procedures for calculating frequency-dependent foundation stiffness and damping for horizontal
translational and rotational vibration modes.We apply the procedures to test data obtained with the structure in its braced and unbraced
configurations. Experimental stiffness ordinates exhibit negligible frequency dependence in translation but significant reductions with
frequency in rotation. Damping increases strongly with frequency, is stronger in translation than in rocking, and demonstrates
contributions from both radiation and hysteretic sources. The impedance ordinates are generally consistent with numerical models for a
surface foundation on a half-space, providing that soil moduli are modestly increased from free-field values to account for structural weight,
and hysteretic soil damping is considered.
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Vibrations of machine foundations and surrounding soil
Author: H. van Koten, Zoetermeer, 2 e Stationsstraat 223, the Netherlands 1 P.C.J. Hoogenboom, Delft University of Technology, Delft, the Netherlands | Size: 1.5 MB | Format:PDF | Quality:Unspecified | Publisher: HERON Vol. 57 (2012) No. 1 | Year: 2012 | pages: 26
Rotating or pulsing machines are often placed on concrete foundations supported by soil. The machines cause vibrations in the building and in the surrounding soil. This paper provides information, formulas and calculation examples to predict these vibrations. The formulas have been experimentally tested for both soil foundations and pile foundations. In addition, criteria are provided for evaluating the vibrations.
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Analysis of machine foundation vibrations: state of the art
Author: GEORGE GAZETAS Rensselaer Polytechnic lnstitute, Troy, New York, USA | Size: 3.9 MB | Format:PDF | Quality:Unspecified | Publisher: Soil Dynamics and Earthquake Engineering, 1983, Vol. 2, No. 1 | Year: 1981 | pages: 41
The paper reviews the state-of-the-art of analysing the dynamic response of foundations subjected to machine-type loadings. Following a brief outline of the historical developments in the field, the concepts associated with the definition, physical interpretation and use of the dynamic impedance functions of foundations are elucidated and the available analytical/numerical methods for their evaluation are discussed. Groups of crucial dimensionless problem parameters related to the soil
prot~ile and the foundation geometry are identified and their effects on the response are studied. Results are presented in the form of simple formulae and dimensionless graphs for both the static and dynamic parts of impedances, pertaining to surface and embedded foundations having circular,strip, rectangular or arbitrary plan shape and supported by three types of idealized soil profdes: the halfspace, the stratum-over-bedrock and the layer-over-half space. Consideration is given to the effects of inhomogeneity, anisotropy and non-linearity of soil. The various results are synthesized in a case study referring to the response of two rigid massive foundations, and practical recommendations are made on how to inexpensively predict the response of foundations supported by actual soil deposits.
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Nonlinear Analysis of a Collapsed Reinforced Concrete Chimney
Author: Phillip L. GOULD * , Wei HUANG a, | Size: 859 KB | Format:PDF | Quality:Unspecified | Publisher: Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2009, Valencia Evolution and Trends in Design, Analysis and Construction of Shell and Spatial Structures 28 September – 2 October 2009, Universidad Politecnica de Valencia, Spain Alberto DOMINGO and Carlos LAZARO (eds.) | pages: 08
During the Ismit (Kocaeli) Earthquake of August 17, 1999, a 115 m. High reinforced concrete chimney or heater stack, located at the Tüpras Refinery, collapsed. The falling debris cut 63 pipes, which contributed to interrupted production for more than 14 months. This stack was designed and constructed according to international standards and is representative of similar structures at refineries throughout the world, including those in earthquake-prone regions. It was distinguished from similar stacks at the site by a much larger rectangular opening for a flue duct, circumscribing a horizontal arc of about 50º. The opening was located about 1/3 of the height above the base and appeared to be the region of initiation of the collapse. The investigation is focused on the dynamic response of the stack due to anearthquake motion recorded at a nearby site. In this study, the results of a response spectrum analysis of the Tüpras stack and a generic U.S. stack are summarized. Then, a two dimensional nonlinear static pushover analysis of the collapsed Tüpras stack is presented using a demand-collapse comparison. Different pushover methods for the consideration of the higher mode effects, including traditional pushover procedures as well as the newly developed Modal Pushover Analysis (MPA) procedure, are evaluated. In order to consider three dimensional interaction effects, a new 3-D pushover analysis procedure is proposed and applied to the Tüpras stack. Finally, a full nonlinear dynamic analysis of the Tüpras stack is introduced to verify the pushover analysis and show more clearly the failure mechanism of the stack during the earthquake. Results are presented that show the effects of the opening and the orientation of the motion with respect to the opening. Higher mode contributions and three dimensional interaction effects are considered. The results confirm that the stack could readily fail under the considered earthquake and are also consistent with the debris pattern.
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Estimation of hysteretic energy demand using concepts of modal pushover analysis
Author: Tholen Prasanth , Siddhartha Ghosh , d Kevin R. Collins | Size: 235 KB | Format:PDF | Quality:Unspecified | Publisher: EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS Earthquake Engng Struct. Dyn. 2008; 37:975–990 Published online 17 March 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/eqe.802 | Year: 2008 | pages: 16
Hysteretic energy dissipation in a structure during an earthquake is the key factor, besides maximum displacement, related to the amount of damage in it. This energy demand can be accurately computed
only through a nonlinear time-history analysis of the structure subjected to a specific earthquake ground acceleration. However, for multi-story structures, which are usually modeled as multi-degree of freedom
(MDOF) systems, this analysis becomes computation intensive and time consuming and is not suitable for adopting in seismic design guidelines. An alternative method of estimating hysteretic energy demand on MDOF systems is presented here. The proposed method uses multiple ‘generalized’ or ‘equivalent’ single
degree of freedom (ESDOF) systems to estimate hysteretic energy demand on an MDOF system within the
context of a ‘modal pushover analysis’. This is a modified version of a previous procedure using a single ESDOF system. Efficiency of the proposed procedure is tested by comparing energy demands based on
this method with results from nonlinear dynamic analyses of MDOF systems, as well as estimates based on the previous method, for several ground motion scenarios. Three steel moment frame structures, of 3-, 9-, and 20-story configurations, are selected for this comparison. Bias statistics that show the effectiveness of the proposed method are presented. In addition to being less demanding on the computation time and
complexity, the proposed method is also suitable for adopting in design guidelines, as it can use response spectra for hysteretic energy demand estimation.
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Mid- to high-rise buildings are often braced by slender reinforced concrete (RC) walls, which are coupled by RC floor diaphragms. In design it is typically assumed that the walls act independently and the design base shear demand is computed neglecting any compatibility forces between the walls. Pushover analysis of systems
comprising walls of different lengths have, however, shown that large compatibility forces can develop between walls of different length, which should be considered in design, but also that the magnitude of the computed forces is very sensitive to the modelling assumptions. The paper explores by means of a case study of an eight storey structure with two walls of different lengths the shear forces developing at the base of the wall. It compares and discusses the analysis results from different models including simple hand calculations, a lumped plasticity beam element model and a complex shell element model. It concludes that numerical and analytical approaches which are based on the lumped plasticity model tend to overestimate the shear force demand on the shorter wall.
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Comparison of Static and Dynamic Pushover Analysis in Assessment of the Target Displacement
Author: Fayaz R. Rofooei1, Nader K. Attari , Ali Rasekh , Amir H. Shodja | Size: 237 KB | Format:PDF | Quality:Unspecified | Publisher: International Journal of Civil Engineerng. Vol. 4 , No. 3, September 2006 | Year: 2006 | pages: 14
Pushover analysis is a simplified nonlinear analysis technique that can be used to estimate the dynamic demands imposed on a structure under earthquake excitations. One of the first steps taken in this approximate solution is to assess the maximum roof displacement, known as target displacement, using the base shear versus roof displacement diagram. That could be done by the so-called dynamic pushover analysis, i.e. a dynamic time history analysis of an equivalent single degree of freedom model of the original system, as well as other available approximate static
methods. In this paper, a number of load patterns, including a new approach, are considered to construct the related pushover curves. In a so-called dynamic pushover analysis, the bi-linear and tri-linear approximations of these pushover curves were used to assess the target displacements by performing dynamic nonlinear time history analyses. The results obtained for five different special moment resisting steel frames, using five earthquake records were compared with those resulted from the time history analysis of the original system. It is shown that the dynamic pushover analysis approach, specially, with the tri-linear approximation of the pushover curves, proves to have a better accuracy in assessing the target displacements. On the other hand, when nonlinear static procedure seems adequate, no specific preference is observed in using more complicated static procedures (proposed by codes) compared to the simple first mode target displacement assessment.
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