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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The interaction between a surface foundation and the supporting inelastic soil under the action of monotonic, cyclic, and seismic
loading is studied numerically. The foundation supports an elastic tall system, the horizontal loading of which induces primarily an
overturning moment and secondarily a shear force. Starting from linear elastic behavior, the footing eventually uplifts from the soil,
provoking strong inelastic soil response culminating in development of a bearing–capacity failure mechanism and progressive
settlement. The substantial lateral displacement of the pier mass induces an additional aggravating moment due to P–δ effect. The
paper outlines the moment–rotation–settlement relations under monotonic loading at the mass center, under cyclic loading, and under
seismic excitation at the base.
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SEISMIC BEHAVIOR OF DAMAGED BUILDINGS: A COMPARISON OF STATIC AND DYNAMIC NONLINEAR APPROACH
Author: Maria Polese , Marco Gaetani d’Aragona , Andrea Prota and Gaetano Manfredi | Size: 1 MB | Format:PDF | Quality:Unspecified | Publisher: COMPDYN 2013 4th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering M. Papadrakakis, V. Papadopoulos, V. Plevris (eds.) | Year: 2013 | pages: 18
Seismic behavior of damaged buildings may be expressed as a function of their REsidual Capacity (RECag), that is a measure of seismic capacity “reduced” due to damage and represented in terms of peak ground acceleration ag. RECag may be estimated through pushover analyses. In fact, adopting a lumped plasticity model, the plastic hinges may be suitably modified to account for the damage level of the single elements [1]; as shown in [2] nonlinear static analyses of the modified damaged models yield pushover curves that, depending on the number of elements involved in the damaged mechanism and on their damage level, may differ significantly with respect to original ones. The applicability of Pushover Analyses (PA) has been demonstrated for regular structures [3, 4], with their significance being generally supported by the comparison of the results obtained by these “simplified” analyses with Nonlinear dynamic Time-History (NTH) analyses. However, the usability of pushover analysis
for the assessment of the behavior of damaged buildings has not been verified yet, and the study presented in this paper aims at contributing in the evaluation of this issue. The results of PA are confronted with those of NTH for Multi Degree Of Freedom (MDOF) systems representative
of existing R.C. building typologies in the Mediterranean regions. In particular, the response (and damage) of each one of the original “intact” MDOF systems for earthquakes of increasing intensity is studied with either the PA and NTH. Next, applying the methodology described in [2], damage dependent behavior is estimated for varying levels of initial seismic (damaging) intensity. The maximum inter-storey drift and shape along the height, as well as the “modified” RECag are compared to the ones that could be obtained with NTH by subsequent application of suitably scaled pairs of accelerograms. The results of this study suggest that degree of approximation that is obtained by PA applied to damaged structures
with respect to NTH does not vary with respect to the approximation of standard PA compared to NTH.
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PROCEEDINGS OF THE 43RD JOINT MEETING OF U.S.-JAPAN PANEL ON WIND AND SEISMIC EFFECTS UJNR
Author: Keiichi Tamura, Secretary-General Japan-side Panel on Wind and Seismic Effects | Size: 12.5 MB | Format:PDF | Quality:Unspecified | Publisher: August 29 - 30, 2011 TSUKUBA, JAPAN | Year: 2011 | pages: 230
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