Prediction of the measured response of a scaled soil-pile-superstructure system   总被引：1，自引：0，他引：1  

N. Makris  T. Tazoh  X. Yun  A.C. Fill 《Soil Dynamics and Earthquake Engineering》1997,16(2):113-124

The validity of the Winkler foundation model is investigated by predicting the experimentally measured displacement transfer functions and strain spectra of a single pile embedded in a sandbox and supporting a single-degree-of-freedom superstructure. The foundation-superstructure system is a scale model and was subjected to shake table excitations. The distributed springs and dashpots of the Winkler foundation model are frequency dependent and the calibrated model predicts satisfactorily the displacement transfer function at different depths for both fixed- and free-tip pile conditions. On the other hand, the pile-axial-strains are substantially underestimated when expressed in terms of the second derivative of the computed elastic line of the pile. It is shown that a much more dependable prediction is achieved when pile-axial-strains are expressed in terms of the inertial forces acting along the pile-superstructure system.  相似文献   

Microseismicity and active deformation of Messinia,SW Greece     

J. Papoulia  J. Makris 《Journal of Seismology》2004,8(4):439-451

By deploying a 30 3-component digital seismic array in the Messiniakos gulf and the surrounding region, we recorded for a period of 45 days the microseismic activity. With a minimum of six records per event, we located 1121 earthquakes corresponding to an average of 20 events per day. For the hypocenter location we used a local velocity model adopted to two controlled source seismic experiments. Within the array, traveltime residuals were within ± 0.2 s and the epicentral accuracy in the order of ± 2 km, while the hypocentral one is twice this value. Correlation of the seismicity with the tectonic elements indicated that most of the NW-SE oriented faults are active with strike-slip movement along this orientation and extension perpendicular to it. The neogene basins of Messini, Meligalas and Megalopolis are seismically very active and their eastern flanks are delineated by higher seismic activity than their western ones. This indicates that the basins are asymmetric with master faults defining their eastern-northeastern flanks. This hypothesis is supported by the asymmetric structure mapped at the offshore Messiniakos basin as densely spaced high resolution reflection seismic profiles have revealed. The western margins of the basins are less deformed and the seismic activity is dispersed over several minor NW-SE faults. Since the NW-SE striking faults onshore are truncated by major NE-SW oriented ones, their overall length is shortened, reducing their seismic potential and capacity to store large stresses that could produce events above Ms6.1. Offshore western Messinia, in the Ionian Sea, the size and activity of the faults is significantly larger and prone to develop events of larger magnitudes. Subcrustal seismicity indicates a deepening of the foci to the east-northeast.Part of this work was presented at the CIESM Conference, Monaco, 2001, and in the EGS General Assembly, Nice, 2001.  相似文献   

Seismic response analysis of multidrum classical columns     

Dimitrios Konstantinidis  Nicos Makris 《地震工程与结构动力学》2005,34(10):1243-1270

This paper presents a numerical investigation on the seismic response of multidrum classical columns. The motivation for this study originates from the need to understand: (a) the level of ground shaking that classical multidrum columns can survive, and (b) the possible advantages or disadvantages of retrofitting multidrum columns with metallic shear links that replace the wooden poles that were installed in ancient times. The numerical study presented in this paper is conducted with the commercially available software Working Model 2D?, which can capture with fidelity the sliding, rocking, and slide‐rocking response of rigid‐body assemblies. This paper validates the software Working Model by comparing selected computed responses with scarce analytical solutions and the results from in‐house numerical codes initially developed at the University of California, Berkeley, to study the seismic response of electrical transformers and heavy laboratory equipment. The study reveals that relative sliding between drums happens even when the g‐value of the ground acceleration is less than the coefficient of friction, µ, of the sliding interfaces and concludes that: (a) typical multidrum classical columns can survive the ground shaking from strong ground motions recorded near the causative faults of earthquakes with magnitudes M_w=6.0–7.4; (b) in most cases multidrum classical columns free to dislocate at the drum interfaces exhibit more controlled seismic response than the monolithic columns with same size and slenderness; (c) the shear strength of the wooden poles has a marginal effect on the sliding response of the drums; and (d) stiff metallic shear links in‐between column drums may have an undesirable role on the seismic stability of classical columns and should be avoided. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Seismic response of pile groups under oblique-shear and Rayleigh waves     

Nicos Makris  Deepak Badoni 《地震工程与结构动力学》1995,24(4):517-532

A simple analytical solution is presented to calculate the pile-soil-pile interaction and eventually the dynamic response of pile groups when excited by the passage of Rayleigh waves and obliquely incident SH-waves. A dynamic Winkler model, with realistic frequency-dependent ‘springs’ and ‘dashpots’ in conjunction with physically motivated approximations is utilized to compute the wave field radiating from an oscillating pile and the effect of this field on an adjacent pile. The coupled rocking motion of the pile group resulting from Rayleigh waves and the torsional motion of the pile group resulting from SH-waves is accurately predicted by a simple mathematical expression. The results of the presented method can be obtained with ‘hand calculations’ and are in excellent agreement with results from ‘rigorous’ solutions based on integral equation formulations. It is found that the group response is primarily affected from the phase difference of the input seismic motion at the location of each pile (wave-passage effect). Pile-soil-pile interaction has insignificant effect and can be neglected.  相似文献   

Nonlinear response of single piles under lateral inertial and seismic loads   总被引：1，自引：0，他引：1  

Deepak Badoni  Nicos Makris 《Soil Dynamics and Earthquake Engineering》1996,15(1):29-43

A macroscopic model that consists of distributed hysteretic springs and frequency dependent -pots is utilized to model the lateral soil reaction and a practical method based on one-dimensional finite element formulation is developed to compute the nonlinear response of single piles under dynamic lateral loads. The model is physically motivated, adequate for cohesive and cohesionless soils, and involves standard geotechnical parameters. Only two parameters have to be calibrated by fitting experimental data. Hysteretic and radiation damping are modeled realistically within the practical range of amplitudes and frequencies. The model is calibrated and validated against five well instrumented full-scale experiments and typical values for the range of the model-parameters are provided. Subsequently, the developed model is utilized to study the nonlinear seismic response of single piles. Finally, the developed method and the calibrated model are used to predict the inertial and seismic response of one of the piles used in the foundation of the Ohba bridge near Tokyo, Japan.  相似文献   

Planar rocking response and stability analysis of an array of free‐standing columns capped with a freely supported rigid beam     

Nicos Makris  Michalis F. Vassiliou 《地震工程与结构动力学》2013,42(3):431-449

This paper investigates the planar rocking response of an array of free‐standing columns capped with a freely supported rigid beam in an effort to explain the appreciable seismic stability of ancient free‐standing columns that support heavy epistyles together with the even heavier frieze atop. Following a variational formulation, the paper concludes to the remarkable result that the dynamic rocking response of an array of free‐standing columns capped with a rigid beam is identical to the rocking response of a single free‐standing column with the same slenderness yet with larger size, that is a more stable configuration. Most importantly, the study shows that the heavier the freely supported cap beam is (epistyles with frieze atop), the more stable is the rocking frame regardless of the rise of the center of gravity of the cap beam, concluding that top‐heavy rocking frames are more stable than when they are top light. This ‘counter intuitive’ finding renders rocking isolation a most attractive alternative for the seismic protection of bridges with tall piers, whereas its potential implementation shall remove several of the concerns associated with the seismic connections of prefabricated bridges. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Dimensional analysis of the earthquake-induced pounding between inelastic structures     

Elias G. Dimitrakopoulos  Nicos Makris  Andreas J. Kappos 《Bulletin of Earthquake Engineering》2011,9(2):561-579

In this paper the seismic response of inelastic structures with unilateral contact is revisited with dimensional analysis. All physically realizable contact types are captured via a non-smooth complementarity approach. The implementation of formal dimensional analysis leads to a condensed presentation of the response and unveils remarkable order even though two different types of non-linearity coexist in the response: the boundary non-linearity of unilateral contact and the inelastic behaviour of the structure itself. It is shown that regardless the intensity and frequency content of the excitation, all response spectra become self-similar when expressed in the appropriate dimensionless terms. The proposed approach hinges upon the notion of the energetic length scale of an excitation which measures the persistence of ground shaking to impose deformation demands. Using the concept of persistency which is defined for excitations with or without distinct pulses, the response is scaled via meaningful novel intensity measures: the dimensionless gap and the dimensionless yield displacement. The study confirms that contact may have a different effect on the response displacements of inelastic structures depending on the spectral region. In adjacent inelastic structures, such as colliding buildings or interacting bridge segments, contact is likely to alter drastically the excitation frequencies’ at which the system is most vulnerable. Finally, it is shown that the proposed approach yields maximum response displacements which correlate very well with the persistency of real earthquakes for a bridge system with considerably complex behaviour.  相似文献   

Interpretation of shallow refraction seismic data by reflection/refraction tomography     

Pavel Ditmar  Jan Penopp  Rainer Kasig  & Jannis Makris 《Geophysical Prospecting》1999,47(6):871-901

A new algorithm for tomographic inversion of traveltimes of reflected and refracted seismic waves is developed. The inversion gives interface configurations and velocity distributions in layers. The important features of the algorithm are: (a) the inclusion of shot time delays in the list of unknown parameters; (b) the regularization is applied in such a way that the most probable model is characterized by the similarity of neighbouring interfaces. As the problem under consideration is non-linear, several iterations are necessary in order to obtain the final model. In the case of a very inexact initial model, a 'layer-by-layer' inversion strategy is recommended as a first inversion step. The inversion program is supplied with a user interface, thanks to which one can: (a) pick interactively and identify seismic traveltimes; (b) build and edit depth/velocity models; and (c) display calculated traveltime curves and compare them with picked traveltimes as well as with the original seismic sections. The efficiency of the inversion software developed is illustrated by a numerical example and a field example in which shallow seismic data are considered. Application to wide-aperture reflection/refraction profiling (WARRP) data is also possible.  相似文献   

The Photogrammetric Survey of a Prehistoric Site Undergoing Removal     

A. Georgopoulos  G. E. Karras  & G. N. Makris 《The Photogrammetric Record》1999,16(93):443-456

For the construction of the new Athens International Airport, it was imperative that a hill, obstructing air traffic, be lowered by approximately 40 m. Unfortunately, a fortified prehistoric settlement was situated on top of that hill. In order to carry out this task, it was required: (a) to produce a model of the site at a scale of 1;50; and (b) to monitor and document every single stone during the dismantling of the most important parts of the site, so that its rebuilding elsewhere and at a later time would be possible.
The Laboratory of Photogrammetry, National Technical University of Athens, undertook to provide the necessary metric data. By using low altitude aerial photographs from a helicopter, a specialized tripod and terrestrial photogrammetric techniques, the following products were created, all at a scale of 1;50: contour lines and DTM of the site; digital orthophotograph of the site; graphic drawing of the development of the exterior of the surrounding wall; and graphic drawings of the upper (initial) and the lower (last) levels of the parts to be removed. In this paper, both the fieldwork and the final products are presented and evaluated.  相似文献   

Effect of viscous,viscoplastic and friction damping on the response of seismic isolated structures     

Nicos Makris  Shih‐Po Chang 《地震工程与结构动力学》2000,29(1):85-107

In this paper the efficiency of various dissipative mechanisms to protect structures from pulse‐type and near‐source ground motions is examined. Physically realizable cycloidal pulses are introduced, and their resemblance to recorded near‐source ground motions is illustrated. The study uncovers the coherent component of some near‐source acceleration records, and the shaking potential of these records is examined. It is found that the response of structures with relatively low isolation periods is substantially affected by the high‐frequency fluctuations that override the long duration pulse. Therefore, the concept of seismic isolation is beneficial even for motions that contain a long duration pulse which generates most of the unusually large recorded displacements and velocities. Dissipation forces of the plastic (friction) type are very efficient in reducing displacement demands although occasionally they are responsible for substantial permanent displacements. It is found that the benefits by hysteretic dissipation are nearly indifferent to the level of the yield displacement of the hysteretic mechanism and that they depend primarily on the level of the plastic (friction) force. The study concludes that a combination of relatively low friction and viscous forces is attractive since base displacements are substantially reduced without appreciably increasing base shears and superstructure accelerations. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献