Books / Conferences / Workshops / Papers

 

Copyright of the papers below rests with a variety of different parties.
They are made available solely on the same basis that I would supply a single copy of a paper to an individual. It is up to you to ensure that your use of a paper does not infringe copyright law.

B80.
Kokkali P., Abdoun T., Anastasopoulos I., Kourkoulis R., Gelagoti F., Gazetas G. (2014), “Experimental Investigation of The Rocking Response of SDOF Systems on Sand”, Proc. 8th Int. Conf. on Physical Modelling in Geotechnics 2014 (ICPMG2014), Perth, Australia, 14–17 January.

[ABSTRACT]

Highly inelastic foundation response is inevitable in a strong earthquake event. Shallow foundations supporting bridge piers or building columns and frame walls may experience sliding and/or uplifting from the supporting soil or bearing capacity failure. However, such non-linear foundation response may be beneficial for the overall system performance since high energy dissipation occurs at the foundation level, thus limiting the ductility demands exerted on the structural components. This paper presents an experimental investigation of the rocking response of surface foundations on dry sand. A comparison between centrifuge tests and equivalent reduced scale 1g slow cyclic tests is presented in order to explore the effects associated with the low confining stresses prevailing at 1g test conditions. (Full Text)

B79.
Loli M., Anastasopoulos I., Knappett J.A., Brown M.J. (2014), “Use of Ricker wavelet ground motions as an alternative to push-over testing”, Proc. 8th Int. Conf. on Physical Modelling in Geotechnics 2014 (ICPMG2014), Perth, Australia, 14–17 January.

[ABSTRACT]

When conducting studies of seismic soil-structure interaction, it is useful to be able to define the pseudo-static ‘push-over’ response of the structure under static horizontal loads representing structural in-ertia. Normally, this would require separate centrifuge experiments with horizontal actuators attached. This paper describes an alternative procedure, using a specific type of ground motion (a Ricker wavelet) to obtain the push-over response, thereby allowing both this and the response to conventional earthquake shaking to be determined using the same (earthquake) actuator. Application of this technique to a 1:50 scale model highway bridge pier with two different shallow foundations is presented. The moment rotation (‘backbone’) behaviour of the footings was accurately determined to large rotations, as verified though independent 3-D non-linear fi-nite element modelling. Ricker wavelet ground motions are therefore shown to be a useful tool for the identi-fication of push-over system behaviour without requiring additional actuators. (Full Text)

B78.
Anastasopoulos I., Drosos V., Antonaki N. (2014), “Shaking Table Testing of Retrofitted 3-storey Building”, Proc. 8th Int. Conf. on Physical Modelling in Geotechnics 2014 (ICPMG2014), Perth, Australia, 14–17 January.

[ABSTRACT]

The paper investigates the seismic performance of an existing 3–storey structure, built in the 70’s. Not complying with capacity design principles, the structure is prone to soft-storey collapse, calling for retrofit through addition of shear walls. Two alternatives are considered with respect to the foundation of the latter: (a) conventional design; and (b) rocking isolation. In the latter case, the foundation is intentionally “un-der-designed” to fully mobilize its capacity acting as a “fuse”. A reduced-scale model of the soil–structure system is tested in the shaking table of the Laboratory of Soil Mechanics. At reduced-scale, it is practically impossible to maintaining similarity in terms of stiffness, and achieve the desired bending moment capacity of structural members at the same time. Therefore, each beam–column connection is modeled with artificial plastic hinges. It is shown that the rocking–isolated structure outperforms the conventional, when subjected to very strong seismic shaking. (Full Text)

B77.
Gazetas G., Ishihara Lecture (2013).“Soil–Foundation–Structure Systems Beyond Conventional Seismic “Failure Thresholds”, 18th ICSMGE International Conference on Soil Mechanics and Geotechnical Engineering , 2-6 September, Paris, France.

[ABSTRACT]

A new paradigm has now emerged in performance–based seismic design of soil-foundation-structure systems. Instead of imposing strict safety limits on forces and moments transmitted from the foundation onto the soil (aiming at avoiding pseudo-static failure), the new dynamic approach “invites” the creation of two simultaneous “failure” mechanisms: substantial foundation uplifting and ultimate-bearing-capacity slippage, while ensuring that peak and residual deformations are acceptable. The paper shows that allowing the foundation to work at such extreme conditions not only may not lead to system collapse, but it would help protect (save) the structure from seismic damage. A potential price to pay: residual settlement and rotation, which could be abated with a number of foundation and soil improvements.  Numerical studies and experiments demonstrate that the consequences of such daring foundation design would likely be quite beneficial to bridge piers and building frames.  It is shown that system collapse could be avoided even under seismic shaking far beyond the design ground motion. (Full Text)

B76.
Sapountzakis E., Kampitsis A.(2013). “Cyclic Inelastic Response of Beam-Foundation Systems using the Boundary Element Method”, Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, B.H.V. Topping and P. Iványi, (Editors),Civil-Comp Press, Stirlingshire, Scotland.

[ABSTRACT]

Institute of Structural Analysis and Antiseismic Research School of Civil Engineering, National Technical University of Athens, Greece Keywords: inelastic analysis, cyclic loading, beam on foundation, inelastic Winkler model, distributed plasticity, boundary element method. In this paper a boundary element method (BEM) is developed for the inelastic analysis of beams of arbitrarily shaped constant cross section having at least one axis of symmetry, resting on a nonlinear inelastic foundation. The beam is subjected to arbitrarily distributed or concentrated vertical cyclic loading along its length, while its edges are subjected to the most general boundary conditions. A displacement based formulation is developed and inelastic redistribution is modelled through a distributed plasticity model exploiting material constitutive laws and numerical integration over the cross sections. An incremental – iterative solution strategy is adopted to resolve both the plastic part of stress resultants and the foundation reaction along with an efficient iterative process to integrate the inelastic rate equations. The arising boundary value problem is solved employing the BEM. (Full Text)

B75.
Psycharis I., Fragiadakis M., Stefanou I. (2013). “Seismic Reliability Assessment of Classical Columns Subjected to Near Source Ground Motions”, COMPDYN 2013, Proceedings of the 4th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering,(ECCOMAS) June, Kos, Greece.

[ABSTRACT]

A methodology for the performance-based seismic risk assessment of classical columns is presented. Classical columns are articulated structures, made of several discrete bulgy stone blocks (drums) put one on top of the other without mortar. Despite its apparent instability, this structural system is, in general, earthquake resistant, as proven from the fact that many classical monuments have survived many strong earthquakes over the centuries. Nevertheless, due to the fundamental non-linear character and the sensitivity of their response, the quantitative assessment of their reliability and the understanding of their dynamic behaviour are not easy. Consequently, the derivation of general remarks regarding their seismic risk is not trivial. In order to understand the dynamic behaviour and estimate the capacity of multidrum columns, a seismic risk assessment methodology is performed using Monte Carlo simulation with synthetic ground motions. The ground motions adopted contain a high and a low frequency component, combining the stochastic method and a simple analytical pulse model in order to simulate the directivity pulse contained in near source ground motions. Fragility curves are produced first conditional on magnitude and fault distance and then using a scalar intensity measure. The deterministic model for the numerical analysis of the system is three dimensional and is based on the Discrete Element Method (3D DEM). Fragility analysis demonstrates some of the salient features of these spinal systems and provides useful results regarding their reliability and decision-making during restoration process. (Full Text)

B74.
Kampitsis A., Sapountzakis E., Giannakos S., Gerolymos N., (2013). “Seismic Soil-Pile Interaction – Influence of Soil Inelasticity”, COMPDYN 2013, Proceedings of the 4th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering,(ECCOMAS) June, Kos, Greece.

[ABSTRACT]

The main purpose of this study is to investigate the influence of soil p-y nonlinearity in soil–pile–structure kinematic and inertia interaction. Within this context, a beam on nonlinear Winkler foundation model is adopted based on the Boundary Element Method (BEM), accounting for the effects induced by geometrical nonlinearity, rotary inertia and shear deformation, employing the concept of shear deformation coefficients. The soil nonlinearity is taken into consideration by means of a hybrid spring configuration consisting of a nonlinear (p-y) spring connected in series to an elastic spring–damper model. The nonlinear spring captures the near–field plastification of the soil while the spring–damper system represents the far–field viscoelastic character of the soil. An extensive case study is carried out on a pile–column–deck system of a bridge, founded in two cohesive layers of sharply different stiffness and subjected in various earthquake excitations. (Full Text)

B73.
Kampitsis A., Sapountzakis E.(2013).”Elastoplastic Dynamic Analysis of Beam-Foundation Systems Employing BEM”, BETEQ, International Conference on Boundary Element and Meshless Techniques, July,Paris-France.

[ABSTRACT]

In this investigation a Boundary Element Method (BEM) is developed for the elastoplastic dynamic analysis of an Euler-Bernoulli beam of simply or multiply connected constant cross section having at least one axis of symmetry, resting on inelastic foundation. (Full Text)

B72.
Sapountzakis E., Kampitsis A.(2012). “Inelastic Analysis of Beams on Two Parameter Elastoplastic Foundation”, 13th International Conference on Boundary Element and Meshless Techniques, BeTeq, September, Prague.

[ABSTRACT]

In this investigation the inelastic analysis of beams of doubly symmetric simply or multiply connected constant cross section resting on two-parameter elastoplastic foundation is presented employing the boundary element method. (Full Text)

B71.
Sapountzakis E., Kampitsis A.(2012). “Nonlinear Seismic Response Analysis of Piles in Nonlinear Viscoelastic Foundation”, European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2012), September, Austria.

[ABSTRACT]

Dynamic response of piles has been the subject of extensive investigations during the past few decades as in high seismicity regions pile foundation is widely used to support superstructures such as buildings, bridges and offshore platforms. In this investigation, a boundary element method is developed for the nonlinear kinematic seismic interaction of piles of arbitrary doubly symmetric simply or multiply connected constant cross section, embedded in viscoelastic foundation, undergoing moderate large deflections under general boundary conditions, taking into account the effects of rotary inertia and shear deformation by employing the concept of shear deformation coefficients. The soil deposits are modeled as a layered Winkler-type medium, while the seismic excitation motion is obtained by means of one dimensional wave propagation analysis. Five boundary value problems are formulated with respect to the transverse displacements, to the axial displacement and to two stress functions and solved using the Analog Equation Method, a BEM based method. Application of the boundary element technique yields a system of nonlinear Differential – Algebraic Equations, which is solved using an efficient time discretization scheme, from which the transverse and axial displacements are computed. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress functions using only boundary integration. The proposed model takes into account the coupling effects of bending and shear deformations along the member as well as the shear forces along the span induced by the applied axial loading. Numerical examples employing recorded accelerograms of well-known earthquakes are worked out in order to illustrate the efficiency, the range of applications and wherever possible the accuracy of the developed method. (Full Text)

B70.
Gazetas G. (2012). “Should elastic response Spectra be the basis of designing strongly and SSI systems? ”, Proceedings of the 3rd International Symposium on Advances in Urban Safety, 24-25 November, Nadjing, China.

[ABSTRACT]

Elastic Design Response Spectra (EDRS) have been adopted all over the world as the basic description of the seismic threat at a particular site, corresponding to its specific seismicity and soil conditions. Originally utilized directly in modal response analyses, today such EDRS are being used to derive compatible artificial time histories, i.e. whose response spectra closely match the EDRS. One of the main dogmas in earthquake engineering is that these EDRS and the artificial motions compatible with them completely and rationally describe the seismic excitation for all possible structures to be built on the particular site even for highly inelastic systems. The presentation will demonstrate the fallacy of this presumption by showing that the critical motions which lead to maximum response of elastic and inelastic systems are fundamentally different. Highly inelastic-nonlinear structures in particular, such as sliding and rocking systems, are shown to be sensitive to motion characteristics that are not reflected at all in the elastic spectra. The concept of “equivalent” spectra is developed to to illustrate this point
Another presumption entrenched in earthquake engineering practice with severe consequences when assessing soil-structure interaction (SSI) effects refers to the shape of the EDRS for soft soil categories. In general, the design spectra have a constant maximum acceleration plateau, max SA 2.5A to 3.0A where A = the effective ground acceleration, followed by a monotonically descending branch at higher periods. For soil categories the constant Sa plateau extends to higher periods. In other words : the softer the soil, the flatter the spectrum. Thus SSI effects are always beneficial. The presentation will illustrate the fallacy of this presumption and will propose the adoption of so-called “Bi-normalized” Spectra for (nearly) elastic design. (Full Text)

B69.
Gazetas G. (2012). “Some presumptions on the nature of base excitation may erroneously affect the response of strongly inelastic systems”, Proceedings of the 15th World Conference on Earthquake Engineering (WCEE), 24-28 September, Lisbon, Portugal.

[ABSTRACT]

Three presumptions on how the design base ground motion is defined are entrenched in earthquake engineering codes of practice: (a) elastic Design Response Spectra (consisting of a horizontal constant-acceleration branch from very low to medium periods and a descending branch at higher periods) adequately describe the seismic threat at a site; hence they must be closely respected from the selected accelerograms–excitations, even for highly inelastic systems; (b) for relatively soft and medium soil categories (as broadly defined in the codes) the shape of the acceleration design spectra, Sa /A, is flatter than for the stiffer soil categories, with its horizontal plateau extending to higher periods — “the softer, the flatter”; and (c) the vertical component of ground shaking can be very important in all cases and, for geotechnical systems, its effect is best accounted for by vectorially combining the vertical and horizontal effective ground accelerations. Severe limitations of the above concepts (which most often lead to unsafe results) are shown in the presentation, along with alternatives that largely avoid some of the detrimental consequences. (Full Text)

B68.
Manoledaki A., Drosos V., Anastasopoulos I., Vintzileou E. & Gazetas G. (2012). “Experimental assessment of the seismic response of three-leaf stone masonry walls, with due consideration to soil–structure interaction”, Proceedings of the 15th World Conference on Earthquake Engineering (WCEE), 24-28 September, Lisbon, Portugal.

[ABSTRACT]

The out-of-plane seismic response of historic stone masonry walls is investigated herein, with due consideration to soil–foundation–structure interaction (SFSI). A series of pushover tests were performed on reduced scale (1:3) wall specimens, which consisted of a three-leaf stone masonry built on top of a spread footing. The walls were subjected to out-of-plane displacement, imposed at mid-height. Initially, a set of experiments were conducted ignoring SFSI. Then, the specimens were founded on a sand layer to examine the role of SFSI. Two idealized soil deposits were modelled: (a) dense sand of relative density Dr = 92%, and (b) loose sand of relative density Dr = 33%. The results are discussed in terms of force–displacement response, failure modes (crack patterns, soil deformation), and footing settlement–rotation response. It is shown that the performance of the walls is substantially affected by SFSI effects, as well as by the boundary conditions. (Full Text)

B67.
Tasiopoulou P., Smyrou E., Bal I., Gazetas G. (2012). “Bridge pile−abutment−deck interaction in laterally spreading ground: Lessons from Christchurch “, Proceedings of the 15th World Conference on Earthquake Engineering (WCEE), 24-28 September, Lisbon, Portugal.

[ABSTRACT]

Liquefaction-induced lateral spreading caused extensive damage to bridges during September 2010 Darfield and the following February 2011 Christchurch earthquake. The majority of bridges in the Central Business District (CBD) and the eastern/southern suburbs crossing Avon riverconsists of single to three−span continuous concrete deck and is founded on piles. Bridge damage assessment sheds light to the deformation mechanism, initiated by the riverward displacement of abutment−pile and pier−pilesystems along with the spreading ground. This typical deformation pattern comprises the back rotation of abutments around their contact point with the deck, accompanied by subsequent settlement of the fill behind the abutment and additional distress of the piles. Despite the localized damage, the deck remained intact acting like a strut, thus reducing the displacement demand imposed on the bridge. Therefore, most of these bridges were repairable and held open to traffic after the earthquake events. Three characteristic case histories (Ferrymead Bridge, South Bridge Road Bridge and Anzac Bridge)are described to obtain a deeper insight on how the axial stiffness of the deck controls the overall performance of the bridge by restraining the movement of abutment-pile system. An analytical estimation of the contribution of the superstructure constraint on the stiffness of the abutment−pile system is attempted. (Full Text)

B66.
Anastasopoulos I., Drosos V., Antonaki N., Rontogianni Ag. (2012). “The Role of Soil–Foundation–Structure Interaction on the Seismic Performance of a n Existing 3-storey Building : Numerical Simulation and Shaking Table Testing “, Proceedings of the 15th World Conference on Earthquake Engineering (WCEE), 24-28 September, Lisbon, Portugal.

[ABSTRACT]

This paper investigates experimentally the seismic performance of an existing building, with emphasis on the effects of nonlinear soil–foundation–structure interaction (SFSI). An idealized 3-storey structure is considered, inspired from the large-scale tests of the SPEAR project. The seismic performance of the original structure is simulated in a first step, confirming its vulnerability. Then, the building is retrofitted with the equivalent of a RC shear wall, following the provisions of modern seismic codes. A reduced-scale physical model of the soil-structure system is tested in the shaking table of the Laboratory of Soil Mechanics of NTUA. It is shown that SFSI may substantially alter the collapse capacity of the structure. Moreover, it is concluded that mobilization of foundation bearing capacity may be beneficial for the performance of the rehabilitated structure, and should therefore be considered in design. (Full Text)

B65.
Kourkoulis R., Gelagoti F., Kaynia A. (2012). “Seismic Response of offshore wind turbine foundations”, Proceedings of the 15th World Conference on Earthquake Engineering (WCEE), 24-28 September, Lisbon, Portugal.

[ABSTRACT]

This paper investigates the response of wind turbines founded on suction caissons with due account of non-linear soil-structure interaction. The models are subjected to static cyclic and earthquake loading in order to parametrically explore the role of potential non-linear interface behavior materialized through sliding between the caisson skirt and the soil or gap formation. It is shown that interface failure may substantially reduce the capacity of such foundations, while the effect becomes more intense as the caisson depth decreases. When subjected to earthquake shaking, imperfect interface conditions may limit the tower bending but produces irrecoverable displacement on the nacelle level; a direct result of the accumulated rotation at the foundation. This undesirable rotation may be more effectively prevented by increasing the caisson diameter rather than its depth of embedment. (Full Text)

B64.
Tasiopoulou P., Gerolymos N. (2012). “Development of a modified elastoplasticiy model for sand”, Proceedings of the First Bulletin of the Second International Conference on Performance–Based Design in Earthquake Geotechnical Engineering, 28-30 May, Taormina (Italy).

[ABSTRACT]

The key prerequisite to performance based design of geotechnical structures is the reliable estimation of the induced displacements. Thus, the need for advanced yet practical constitutive modeling of soil behavior continuously becomes more profound and demanding. This paper presents a new simple effective stress model for drained and undrained behavior of sand under monotonic and cyclic loading conditions, with emphasis on liquefaction. The model is formulated in the framework of classical elastoplasticity, and combines features of: (a) the bounding surface plasticity, (b) the critical state concept, and (c) a hardening evolution law and unloading-reloading rule of the modified Bouc-Wen type. The predictive capabilities of the model are demonstrated through simulations of loading tests in p-q space. (Full Text)

B63.
Zafeirakos Ath., Gerolymos N. (2012). “Seismic performance of caisson supported piers”, Proceedings of the First Bulletin of the Second International Conference on Performance–Based Design in Earthquake Geotechnical Engineering, 28-30 May, Taormina (Italy).

[ABSTRACT]

Incremental dynamic analysis (IDA) of caisson supported structures is carried out with due consideration to material and interface nonlinearities. Two base systems are examined: a heavily loaded and a lightly loaded. Two alternative designs are considered for each system: (a) conventional capacity design with over-designed foundation (the plastic hinge on the column); (b) un-conventional capacity design with under-designed foundation (the plastic “hinge” into the soil). IDA curves are produced for a variety of earthquake demand parameters (EDP) describing the response of the system. The results emphasize the beneficial role of foundation nonlinearities on reducing the seismic demands of the superstructure. (Full Text)

B62.
Gerolymos N., Zafeirakos A. , Souliotis Ch. (2012). “Insight to failure mechanisms of caisson foundations under combined loading : a macro-element”, Proceedings of the First Bulletin of the Second International Conference on Performance–Based Design in Earthquake Geotechnical Engineering, 28-30 May, Taormina (Italy).

[ABSTRACT]

The undrained response of massive caisson foundations to combined horizontal, vertical and moment loading is investigated through a series of three-dimensional finite element analyses. The ultimate limit states are presented by failure envelopes in normalized form. The effects of embedment ratio and vertical load on the bearing capacity are investigated in detail. Closed-form expressions are proposed for (a) the yield surface in M-Q-N space, and (b) the lateral capacity under pure horizontal and moment loading. Finally, the use of an associated flow rule to define the plastic deformation of the caisson at near failure conditions is parametrically examined. The results of the analysis could serve as a basis for a macro-element approach.
(Full Text)

B61.
Anastasopoulos I., Loli M., Gelagoti F., Kourkoulis R., Gazetas G. (2012). “Nonlinear soil-foundation interaction : numerical analysis”, Proceedings of the First Bulletin of the Second International Conference on Performance–Based Design in Earthquake Geotechnical Engineering, 28-30 May, Taormina (Italy).

[ABSTRACT]

Modern theoretical studies and experimental investigations of the dynamic response of soil–footing–structure systems have revealed the fallacy behind the prohibition of nonlinear foundation response, which is currently one of the cornerstones of a seismic design. Shallow foundations have been found to unavoidably respond non-linearly, experiencing uplifting and/or bearing capacity failure mechanisms when subjected to seismic episodes of significant magnitude. What is more, such nonlinear behavior appears to have a beneficial role in the performance of the supported structure. Yet, before allowing foundation nonlinearity in engineering practice, it is essential to develop valid and comprehensible tools for modeling the nonlinear rocking behavior and predicting the associated foundation permanent displacements with sufficient accuracy. To this end, a numerical methodology has been formulated — which makes use of a simplified but fairly comprehensive constitutive soil model — and implemented within the ABAQUS FE code. The methodology is rigorously validated through the reproduction of a variety of physical model tests conducted on different soils (sand and clay) and at different modeling scales (making use of both large scale and reduced scale experiments). The paper presents the results of this validation procedure, showing that the numerical method is capable of reliably reproducing the details (ultimate capacity, stiffness degradation with increasing rotation, hysteretic response, settlement–uplifting behavior in relation to the rotation amplitude and the number of loading cycles) of cyclic foundation response. (Full Text)

B60.
Anastasopoulos I. (2012). “Effectiveness of shallow soil improvement on the performance of rocking-isolated bridge piers : monotonic and cyclic pushover testing ”, Proceedings of the First Bulletin of the Second International Conference on Performance–Based Design in Earthquake Geotechnical Engineering, 28-30 May, Taormina (Italy).

[ABSTRACT]

An alternative seismic design philosophy, in which soil failure is used as a “fuse” for the superstructure has recently been proposed, in the form of “rocking isolation”. Within this context, foundation rocking may be desirable as a means of bounding the inertia forces transmitted onto the superstructure, but incorporates the peril of unacceptable settlements in case of a low static factor of safety FSv . Hence, to ensure that rocking is materialized through uplifting rather than sinking, an adequately large FSv is required. Although this is feasible in theory, soil properties are not well-known in engineering practice. However, since rocking-induced soil yielding is only mobilized within a shallow layer underneath the footing, “shallow soil improvement” is considered as an alternative approach to release the design from the jeopardy of unforeseen inadequate FSv. For this purpose, this paper studies the metaplastic rocking response of SDOF structures, with emphasis on the effectiveness of shallow soil improvement stretching to various depths below the foundation. A series of reduced-scale monotonic and slow-cyclic pushover tests are conducted on relatively slender SDOF systems lying on a square surface foundation. It is shown that shallow soil improvement may, indeed, be quite effective provided that its depth is equal to the width of the foundation. (Full Text)

B59.
Kourkoulis R., (2012). “Rocking of Foundations on Improved Soil: Application to 1-dof and Frame Structures”, Proceedings of the First Bulletin of the Second International Conference on Performance–Based Design in Earthquake Geotechnical Engineering, 28-30 May, Taormina (Italy).

[ABSTRACT]

Rocking isolation has recently been proposed as an alternative foundation design scheme, in which inelastic footing response is used as a means of protecting the superstructure. Such a response, may be desirable as it bounds the inertia forces transmitted onto the superstructure. Yet it incorporates the peril of unacceptable settlements in case of a low static factor of safety FSV. Therefore an adequately large FSV must be achieved in order to ensure that rocking is materialized through uplifting rather than footing settlement. Given that soil properties are seldom well known in engineering practice, guaranteeing a target FSV value may constitute a tedious task. Therefore, this paper investigates the use of “shallow soil improvement” as an alter-native approach in order to release the design from the jeopardy caused by an unforeseen inadequate FSV. The paper studies the response of a simple 1-dof oscillator and a rocking-isolated 1-bay 2-storey frame on two-layered soil profile consisting of a stiff surface layer overlying a weak homogeneous soil stratum. Analyses were conducted employing the finite element method and involved monotonic and cyclic push-over tests and dynamic time-history analyses. It is shown that the existence of even a shallow surface layer enhances the seismic performance of the system by reducing its residual settlements. (Full Text)

B58.
Gelagoti F., (2012). “Rocking Isolation of Frames on Shallow Footings : Design Limitations”, Proceedings of the First Bulletin of the Second International Conference on Performance–Based Design in Earthquake Geotechnical Engineering, 28-30 May, Taormina (Italy).

[ABSTRACT]

Taking advantage of mobilization of inelastic foundation response has been recently proposed as a novel seismic protection scheme. Such a design concept has been termed ―rocking isolation, and consists of intentionally under-dimensioning of the footings in order to respond to strong seismic shaking through rocking, thus bounding the inertia forces transmitted to the superstructure. This paper attempts to shed light in the possible limitations of rocking isolation, mainly caused by the unavoidable uncertainties regarding the estimation of soil properties and ground motion characteristics. It is shown that even a gross overestimation of the soil properties may not cancel the favorable role of rocking–isolation, although at the cost of increased residual deformations of the structure. In contrast, its effectiveness may be limited in case of un-symmetric structures although the prevailing rocking. (Full Text)

B57.
Drosos V., Georgarakos T., Loli M., Anastasopoulos I., Gazetas G. (2012). “Nonlinear soil – foundation interaction : an experimental study on sand”, Proceedings of the First Bulletin of the Second International Conference on Performance–Based Design in Earthquake Geotechnical Engineering, 28-30 May, Taormina (Italy).

[ABSTRACT]

Recent studies have highlighted the beneficial role of foundation uplifting and the potential effectiveness of guiding the “plastic hinge” into the foundation soil by allowing full mobilization of bearing capacity during strong seismic shaking. With the inertia loading transmitted onto the superstructure being limited by the capacity of the foundation, such concept may provide an alternative method of “in-ground” seismic isolation: the so called rocking isolation. Attempting to unravel the effectiveness of such alternative design method, this paper investigates experimentally the nonlinear response of a surface foundation on sand and its effect on the seismic performance of an idealized slender 1-dof structure. Using a bridge pier as an illustrative prototype, three foundation design alternatives are considered, representing three levels of design conservatism. Their performance is investigated through static (monotonic and slow-cyclic “pushover”) loading, and reduced-scale shaking table testing. It is shown that foundation rocking isolation may provide a valid alternative for the seismic protection of structures and encouraging evidence is presented in favor of the innovative idea of moving foundation design towards a less conservative, even unconventional, treatment. (Full Text)

B56.
Garini E., Gazetas G. (2012). ” Destructiveness of earthquake ground motions : “Intensity measures” versus sliding displacement “, Proceedings of the First Bulletin of the Second International Conference on Performance–Based Design in Earthquake Geotechnical Engineering, 28-30 May, Taormina (Italy).

[ABSTRACT]

The scope is to estimate qualitatively and quantitatively the potential destructiveness of earthquakes on structures characterized by inelastic response. To this end, earthquake records are utilized studying several seismological parameters as destructiveness indices of earthquake shaking. We employ twenty six widely acknowledged indices, such as the Arias intensity, the Housner intensity, the destructiveness potential factor, the acceleration spectrum intensity, the specific energy density etc. A large number (eighty nine) of earthquake records are selected, paying particular attention to include ground motions with strong near-fault characteristics: forward directivity and fling. Apart from the seismological parameters, sliding displacement on an inclined plane is utilized as an additional destructiveness index representative of the inelastic response of structural systems. In particular, we adopt the Newmark’s model of a rigid block resting on an inclined surface (governed by the Coulomb friction law) subjected to seismic excitation. The results are presented in form of sliding displacement versus each one of the seismic indexes. By comparison we conclude to specific indices which can describe satisfactorily the inelastic response. (Full Text)

B55.
Garini E., Gazetas G. (2012). ” The Christchurch 2011 Earthquake : Elastic and perfectly-plastic response potential of ground motions”, Proceedings of the First Bulletin of the Second International Conference on Performance–Based Design in Earthquake Geotechnical Engineering, 28-30 May, Taormina (Italy).

[ABSTRACT]

The 22 February 2011 Mw 6.3 Earthquake produced a number of unique accelerograms in the city of Christchurch and the port of Lyttelton. Four of these records are analyzed in this paper. Their elastic response spectra are discussed and associated with some salient characteristics of the motions. Also, symmetric and asymmetric sliding of a block resting through Coulomb friction on horizontal or inclined planes, when excited at their base by these records, offer a strong indication of their “destructiveness potential” in terms of perfectly-plastic response. For strongly inelastic systems the paper introduced two new spectra to serve as indices of the “destructiveness” potential of a motion: the sliding spectra for symmetric and asymmetric slippage of a rigid block. (Full Text)

B54.
Gazetas G. (2012). “Can we design in Geotechnics with seismic factors of safety less than 1 ?” Proceedings of the XV European Conference on Soil Mechanics & Geotechnical Engineering, 12-15 September 2011, Athens.

[ABSTRACT]

The paper outlines the key points of the lecture given in September 2011. Its goals are to demonstrate that: (a) in seismic geotechnical design it is not always feasible to achieve factors of safety (FS) greater than one ; (b) under seismic base excitation an “engineering” apparent FS less than 1 does not imply failure of the system ; and (c) in many cases it may be beneficial to under-design the foundation by accepting an engineering FS < 1 (even an FS well below 1). Five examples from slopes and foundations illustrate the above points. (Full Text)

B53.
Anastasopoulos I., Loli M., Bransby F., Gazetas G. (2012). “Caisson Foundation Subjected to Normal Faulting : Experiment vs. analysis”, Proceedings of the XV European Conference on Soil Mechanics & Geotechnical Engineering, 12-15 September 2011, Athens.

[ABSTRACT]

Dramatic failures have occurred in large magnitude earthquakes due to the interplay of surface structures with outcropping fault ruptures. Employing both centrifuge testing and numerical analysis, this paper explores the mechanisms of normal fault rupture interaction with rigid caisson foundations. First, a series of centrifuge tests were conducted to study the response of a 5m x 5mx 10 m caisson founded on a layer of dry dense sand. Nonlinear 3-D numerical modelling of the problem was then developed and adequately validated against the centrifuge tests results. Depending on its position relative to the fault, the caisson is found to interact with the fault rupture, sometimes modifying spectacularly the free field rupture path. Acting as a kinematic constraint, the caisson causes the rupture to divert on either one, or both, of its sides. The numerical study was subsequently extended to a parametric investigation of the effect of the exact position of the caisson relative to the fault outcrop. Different mechanisms taking place for different caisson positions are identified, and their effect on the response of the soil–foundation system is discussed. (Full Text)

B52.
Sapountzakis E.J. and A.E. Kampitsis (2011). ”Nonlinear Vibrations of Piles in Viscoelastic Foundation” Proc. of the Eighth International Conference on Earthquake Resistant Engineering Structures, ERES2011, Chianciano Terme, Italy, 07-09 September.

[ABSTRACT]

In this paper, a boundary element method is developed for the nonlinear dynamic analysis of piles of arbitrary doubly symmetric simply or multiply connected constant cross section, partially embedded in viscoelastic foundation, undergoing moderate large deflections under general boundary conditions, taking into account the effects of shear deformation and rotary inertia. The pile is subjected to the combined action of arbitrarily distributed or concentrated transverse loading and bending moments in both directions as well as to axial loading. To account for shear deformations, the concept of shear deformation coefficients is used. Five boundary value problems are formulated with respect to the transverse displacements, to the axial displacement and to two stress functions and solved using the Analog Equation Method, a BEM based method. Application of the boundary element technique yields a nonlinear coupled system of equations of motion. The solution of this system is accomplished iteratively by employing the average acceleration method in combination with the modified Newton Raphs on method. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress functions using only boundary integration. The proposed model takes into account the coupling effects of bending and shear deformations along the member as well as the shear forces along the span induced by the applied axial loading. Numerical examples are worked out to illustrate the efficiency, wherever possible the accuracy and the range of applications of the developed method. (Full Text)

B51.
Sapountzakis E.J. and A.E. Kampitsis (2011) “Nonlinear Inelastic Analysis of Beams on Nonlinear Foundation”, Proc. of the Thirteenth International Conference on Civil, Structural and Environmental Engineering Computing CC2011, Chania, Crete, Greece,06-09 September.

[ABSTRACT]

In this investigation the inelastic analysis of beams of doubly symmetric simply or multiply connected constant cross section resting on inelastic foundation is presented employing the boundary element method. The beam is subjected to arbitrarily distributed or concentrated bending loading along its length, while its edges are subjected to the most general boundary conditions. A displacement based formulation is developed and inelastic redistribution is modelled through a distributed plasticity model exploiting material constitutive laws and numerical integration over the cross sections. An incremental – iterative solution strategy is adopted to restore global equilibrium along with an efficient iterative process to integrate the inelastic rate equations. The arising boundary value problem is solved employing the boundary element method. Numerical results are worked out to illustrate the method, demonstrate its efficiency and wherever possible its accuracy. (Full Text)

B50.
Sapountzakis E.J. and A.E. Kampitsis (2011) “Shear Deformable Beamson Nonlinear Viscoelastic Foundation under Moving Loading”, Proc. of the IV International Conference on Computational Methods for Coupled Problems in Science and Engineering -COUPLED PROBLEMS, Kos, Greece, 20-22 June.

[ABSTRACT]

In this paper, a boundary element method is developed for the nonlinear response of shear deformable beams of simply or multiply connected constant cross section, traversed by moving loads, resting on tensionless nonlinear viscoelastic foundation, undergoing moderate large deflections under general boundary conditions. The beam is subjected to the combined action of arbitrarily distributed or concentrated transverse moving loading as well as to axial loading. To account for shear deformations, the concept of shear deformation coefficients is used. Three boundary value problems are formulated with respect to the transverse displacement, to the axial displacement and to a stress functions and solved using the Analog Equation Method, a BEM based method. Application of the boundary element technique yields a system of nonlinear differential – algebraic equations (DAE), which is solved using an efficient time discretization scheme, from which the transverse and axial displacements are computed. The evaluation of the shear deformation coefficient is accomplished from the aforementioned stress function using only boundary integration. Analyses are performed to investigate the effects of various parameters, such as the load velocity, load frequency, shear rigidity, foundation nonlinearity, damping, on the beam displacements and stress resultants and to examine how the consideration of shear and axial compression affect the response of the system. (Full Text)

B49.
Smyrou E., Tasiopoulou P., Bal I.E., Gazetas G., and Vintzileou E. (2011) “Structural and Geotechnical Aspects of the Christchurch (2011) and Darfield (2010) Earthquakes in N. Zealand”, Proceedings of the Seventh National Conference on Earthquake Engineering, 30 May-3 June, Istanbul, Turkey.

[ABSTRACT]

The city of Christchurch, New Zealand, was hit by two severe earthquakes in September 2010 and February 2011. Both earthquakes were generated by faults which were completely unknown. The first earthquake, centred in sparsely-populated countryside, inflicted serious damage but no life losses, whilst the second earthquake in close proximity to the city caused 181 fatalities. The damage and some collapses observed during Darfield and Christchurch earthquakes can be attributed to the structural characteristics of the existing building stock in the region, as well as to the widespread manifestation of liquefaction. This paper aims to investigate aspects of these two earthquakes and their effects on soil and structure. An effort is made to relate the extensive structural damage to the observed soil behaviour and the particular features of the recorded motions. Certain structural types are examined with respect to the acceleration and displacement demands imposed by the two events, in an attempt to explain their behaviour and thus their performance. Bridge structures, which suffered significantly as result of soil liquefaction and lateral spreading, are also studied comparing their behaviour in the two consecutive earthquakes. (Full Text)

B48.
Zafeirakos A., Gerolymos N., Gazetas G. (2011), “The Role of Soil and Interface Nonlinearities on the Seismic Response of Caisson supported Bridge Piers”, Proceedings of the 5th International Conference on Earthquake Geotechnical Engineering, Santiago, Chile, 10-13 January.

[ABSTRACT]

The present paper examines the seismic performance of caisson foundations under a new design philosophy, where soil “failure” is allowed to protect the superstructure. To investigate the effectiveness of such an approach, a caisson–column supported bridge structure is used as an example. Two alternatives are compared: one complying with conventional capacity design, with over-designed foundation so that the soil is marginally plastified; the other following the new design philosophy, with under-designed foundation, “inviting” the plastic “hinge” into the soil (Anastasopoulos et al. 2010). The two alternatives are then subjected to an artificial accelerogram appropriately calibrated so that both systems would exhibit the same spectral response in a linear elastic regime, allowing thus the seismic performance of the two systems to be achieved on a “fair” basis. Key performance measures of the systems are then compared, such as: accelerations, spectral response, displacements, pier base rotation sand settlements. It is shown that separation of the caisson from the supporting soil and extensive soil plastification contribute beneficially to the seismic performance of both the foundation and the superstructure. (Full Text)

B47.
Drosos V., Gerolymos N., Gazetas G. (2011), “Seismic Response of Bridge Pile-Columns”, Proceedings of the 5th International Conference on Earthquake Geotechnical Engineering, Santiago, Chile, 10-13 January.

[ABSTRACT]

While seismic codes do not allow plastic deformation of piles, the Kobe earthquake has shown that limited structural yielding and cracking of piles may not be always detrimental. As a first attempt to investigate the consequences of pile yielding in the response of a pile–column supported bridge structure, this paper explores the soil–pile–bridge pier interaction to seismic loading, with emphasis on structural nonlinearity. The pile-soil interaction is modeled through distributed nonlinear Winkler-type springs and dashpots. Numerical analysis is performed with a constitutive model (Gerolymos and Gazetas, 2005a; 2005b;2006a) materialized in the Open Sees finite element code (Mazzoni et al. 2005) which can simulate: the nonlinear behaviour of both pile and soil; the possible separation and gapping between pile and soil; radiation damping; loss of stiffness and strength in pile and soil. The model is applied to the analysis of pile-column supported bridge structures, focusing on the influence of soil compliance, intensity of seismic excitation, pile diameter, above–ground height of the pile, and above or below ground development of plastic hinge, on key performance measures of the pier as is: the displacement (global) and curvature (local) ductility demands and the maximum drift ratio. It is shown that kinematic expressions for performance measure parameters may lead to erroneous results when soil–structure interaction is considered. (Full Text)

B46.
Gelagoti F., Kourkoulis R., Anastasopoulos I., Gazetas G. (2011), “ Effect of Soil Non-Linearity on the Seismic Response of a Very Soft Alluvial Valley”, Proceedings of the 5th International Conference on Earthquake Geotechnical Engineering, Santiago, Chile, 10-13 January.

[ABSTRACT]

To develop insight into the sensitivity of 2D wave effects to soil non-linearity, a numerical study is conducted, utilizing a shallow soft valley in Japan (the Ohba Valley) as a test case. Overall, soil nonlinearity may modify the 2D valley response to a substantial extent. The Aggravation Factor (AG) at the center of the valley is significantly reduced with increasing soil nonlinearity while, quite remarkably, AG at the valley edges may increase due to the trapping of multi-refracted waves into a narrow plastified zone. The analyses revealed the generation of a quite important parasitic vertical acceleration component close to valley edges. The latter, being a direct result of 2D wave refractions, is well correlated and of similar frequency content with the horizontal component and could therefore be very detrimental to structures. (Full Text)

B45.
Giannakos S., Gerolymos N., Gazetas G., (2011), “On the Lateral Response of Piles : Numerical Analysis Against Centrifuge Experiments”, Proceedings of the 5th International Conference on Earthquake Geotechnical Engineering, Santiago, Chile, 10-13 January.

[ABSTRACT]

To gain insight into the inelastic behavior of piles, the response of a vertical pile embedded in a dry sand of 75% relative density and subjected to cyclic lateral loading was studied experimentally in centrifuge tests conducted in Laboratoire Central des Ponts et Chaussees. Three types of cyclic loading were applied, two asymmetric and one symmetric with respect to the unloaded pile. The model pile (scale 1/40) was aluminum hollow cylinder of 18 mm external diameter, 3 mm wall thickness, and 365 mm length. The objective of the tests was to investigate the influence of certain nonlinear features of cyclic loading such as strength relaxation and stiffness hardening on pile response. Comparison is given with results from three-dimensional finite element analysis. (Full Text)

B44.
Kourkoulis R., Gelagoti F., Anastasopoulos I., Gazetas G. (2011), “Stabilization of Seismically Unstable Slopes Using Piles: Parametric Analysis”, Proceedings of the 5thInternational Conference on Earthquake Geotechnical Engineering, Santiago , Chile, 10-13 January.

[ABSTRACT]

A recently developed and validated simplified numerical model for the investigation of the response of slope stabilizing piles is utilized to explore the parameters determining the effectiveness of such systems. Pile diameter and spacing, depth of pile embedment, soil strength and stiffness are the key problem parameters investigated. It is shown that a pile spacing of 4 diameters is the most cost-effective being able to generate soil arching between the piles. For relatively small pile embedment, pile response is dominated by rigid-body rotation, without substantial flexural distortion: The critical embedment depth to achieve fixity conditions at the base of the pile is found to range depending on the relative strength of the unstable ground compared to that of the stable ground (i.e. the soil below the sliding plane). (Full Text)

B43a.
Pecker A. (2011), “Influence on non linear soil structure interaction on the seismic demand in bridge” Proceedings of the International Conference, Innovations on Bridges and Soil-Bridge Interaction, 13-15 October, Athens.

[ABSTRACT]

Examination of the seismic behavior of bridge foundations during earthquake points out that even at low shaking level permanent displacements, i.e. nonlinear soil structure interaction, takes place. Nonlinear soil structure interaction is usually not considered in design although it may have a beneficial effect as illustrated in this paper. Results of incremental dynamic analyses (IDA) of a simple structural bridge pier for a fixed base system or the same system with consideration of linear and nonlinear soil structure interaction, including uplift and soil plasticity, are presented. The results highlight the beneficial role of foundation nonlinearities in decreasing the ductility demand in the superstructure but point out the need to carefully assess the variability of the response when non linearity is allowed at the foundation design. (Full Text)

B43.
Tsatsis A., Kourkoulis R., Anastasopoulos I., Gazetas G. (2011), “Bridge Pier Founded on Pile-Group Ductile Design Against Faulting”, Proceedings of the International Conference, Innovations on Bridges and Soil-Bridge Interaction, 13-15 October, Athens.

[ABSTRACT]

This paper explores the feasibility of ductility design for bridge pile group foundations subjected to tectonic deformation. Its potential effectiveness is investigated utilizing a typical bridge structure as an illustrative example. It is shown that allowing plastic hinging at the piles can be an effective way of obtaining vertical offsets of greater magnitude. The penalty to pay is larger rotation at pier base due to pile yielding. (Full Text)

B42.
Gerolymos N., Zafeirakos Th., Gazetas G. (2011) “Some new Thoughts on the Performance-based Design of Caisson Supported Bridges”, Proceedings of the International Conference, Innovations on Bridges and Soil-Bridge Interaction, 13-15 October, Athens.

[ABSTRACT]

The present paper examines the seismic performance of caisson foundations under a new design philosophy, where soil “failure” is allowed to protect the superstructure. To investigate the effectiveness of such an approach, a caisson–column supported bridge structure is used as an example. Two alternatives are compared: one complying with conventional capacity design, with over-designed foundation so that the soil is marginally plastified; the other following the new design philosophy, with under-designed foundation, “inviting” the plastic “hinge” into the soil. Key performance measures of the systems are then compared, such as: accelerations, spectral response, displacements, pier base rotations and settlements. It is shown that separation of the caisson from the supporting soil and extensive soil plastification contribute beneficially to the seismic performance of both the foundation and the superstructure. (Full Text)

B41.
Zafeirakos A., Gerolymos N. (2011), “The effect of soil and interface nonlinearities on the response of caisson supported bridge piers”, Proc. 4th Japan–Greece Workshop on Seismic Design of Foundations, Innovations in Seismic Design, and Protection of Cultural Heritage, Kobe, Japan, 6–7 October.

[ABSTRACT]

The seismic response of caisson supported bridge piers is numerically investigated with due consideration to soil and interface nonlinearities. Evaluation of system performance is carried out under the prism of a new capacity design paradigm where soil “failure” mechanisms are mobilized to protect the superstructure. To investigate the effectiveness of such an approach, a caisson–column supported bridge structure is used as an example. Two alternatives are compared: one complying with conventional capacity design, with over-designed foundation so that the soil is marginally plastified; the other following the new design philosophy, with under-designed foundation, “inviting” the plastic “hinge” into the soil (Anastasopoulos et al. 2010). The two alternatives are then subjected to an artificial accelerogram appropriately calibrated so that both systems would exhibit the same spectral response in a linear elastic regime, allowing thus the seismic performance of the two systems to be achieved on a “fair” basis. Key performance measures of the systems are then compared, such as: accelerations, spectral response, displacements, pier base rotations and settlements. It is shown that separation of the caisson from the supporting soil and extensive soil plastification contribute beneficially to the seismic performance of both the foundation and the superstructure. (Full Text)

B40.
Garini E., Gazetas G. (2011), “Destructiveness of Earthquake Ground Motions: “Intensity Measures” versus Sliding Displacement” Proceedings of the 4th Japan – Greece Workshop, Seismic Design of Foundations, Innovations in Seismic Design, and Protection of Cultural Heritage, 6-7 October, Kobe, Japan.

[ABSTRACT]

The scope is to estimate qualitatively and quantitatively the potential destructiveness of earthquakes on structures characterized by inelastic response. To this end, earthquake records are utilized studying several seismological parameters as destructiveness indices of earthquake shaking. We employ twenty six widely acknowledged indices, such as the Arias intensity, the Housner intensity, the destructiveness potential factor, the acceleration spectrum intensity, the specific energy density etc. A large number (eighty nine) of earthquake records are selected, paying particular attention to include ground motions with strong near-fault characteristics: forward directivity and fling. Apart from the seismological parameters, sliding displacement on an inclined plane is utilized as an additional destructiveness index representative of the inelastic response of structural systems. In particular, we adopt the Newmark’s model of a rigid block resting on an inclined surface (governed by the Coulomb friction law) subjected to seismic excitation. The results are presented in form of sliding displacement versus each one of the seismic indexes. By comparison we conclude to specific indices which can describe satisfactorily the inelastic response. (Full Text)

B39.
Kourkoulis R., Gelagoti F., Founta V. (2011), “Rocking of Inelastic Frame on Two-Layered Inelastic Soil”, 4th Japan-Greece Workshop on Seismic Design of Foundations and Innovations in Seismic Protection, 2-9 September, Kobe, Japan.

[ABSTRACT]

The paper studies the response of a simple rocking-isolated I-bay 2-storey frame on two-layered soil profile consisting of a stiff surface layer overlying a weak homogeneous soil stratum. Analyses were conducted employing the finite element code ABAQUS and involved monotonic and cyclic push-over tests and dynamic time-history analyses. It was shown that the existence of even a shallow surface layer of depth equal to the footing width enhances the seismic performance of the frame-foundation system by reducing the residual settlements and limiting the extent of damage in the structural members. (Full Text)

B38.
Gelagoti F. and Kourkoulis R. (2011), “A simplified Method to Assess the Toppling Potential of Ground Motions: Application in Rocking–Isolated Frame Structures”, 4th Japan-Greece Workshop on Seismic Design of Foundations and Innovations in Seismic Protection, 2-9 September, Kobe, Japan.

[ABSTRACT]

This paper aims to explore the limitations associated with the design of “rocking – isolated” frame structures. According to this novel seismic design concept the foundation is intentionally under-designed (so as to present lower moment capacity than the corresponding column), with the intention to bOlU1d the inertia loading that may be transmitted to the superstructure. Yet, decreasing footing dimensions increases the risk of toppling. Motivated by the need to address this issue in design, this paper proposes the peak spectral displacement of an earthquake record as a conservative upper-bound estimate of displacement demand. The adequacy of the measure is validated through comparison with published analytical and numerical results. Finally the paper attempts an investigation on the record characteristics affecting the overturning potential of ground motions, concluding that the impact pulse velocity and the number of cycles exceeding the toppling acceleration play prominent role. (Full Text)

B37.
Kourkoulis R. and Kokkali P. (2011), “Parametric Dimensional Analysis on Rocking of 1-dof Systems”, 4th Japan-Greece Workshop on Seismic Design of Foundations and Innovations in Seismic Protection, 2-9 September, Kobe, Japan.

[ABSTRACT]

This paper investigates the metaplastic rocking response of single degree of freedom oscillators that are founded through surface square footings on inelastic soil. Dimensional analysis has been performed in an attempt to produce results pertaining to a group of cases that exhibit common characteristics which are here after termed as equivalent systems. The system response has been found to be depending on non-dimensional parameters such as: the factor of safety against vertical load, the imposed acceleration amplitude, the frequency ratio between the soil and the rocking oscillator, the dimensionless flexibility of the oscillator, the ratio of the available shear strength over the earthquake-induced stress, and the “rigidity ratio” which is the ratio of the soils hear modulus (at small strains) over the undrained shear strength. Systems exhibiting equality between their respective non-dimensional terms are shown to respond equivalently for the same type of imposed shaking. A parametric analysis has been performed to reveal the impact of each dimensionless term on the overall system response. It was shown that dimensionless toppling rotation θult/θc (where θc is the toppling rotation of the equivalent rigid block) is a function of the factor of safety against vertical loads FS” and the slenderness ratio hlB :the toppling rotation decreases with FS”. while the role of the hlB becomes increasingly important for low values of FSv. A simplified “empirical” equation that approximately captures these phenomena is proposed. (Full Text)

B36.
Tasiopoulou P., Smyrou E., Bal I.E., Gazetas G. (2011), “Correlation of Ground Motion Characteristics with Liquefaction: Christchurch 2011 Earthquake”, Proceedings of the 4th Japan – Greece Workshop, Seismic Design of Foundations, Innovations in Seismic Design, and Protection of Cultural Heritage, 6-7 October, Kobe, Japan.

[ABSTRACT]

Hit by two severe earthquakes in September 2010 and February 2011, the city of Christchurch and its environs have sut’t’ered extensive damage that has been augmented by phenomena of widespread soil liquefaction and associated ground deformations. This paper has been aimed to find out the quantifiable parameters that could provide a better insight to seismologists and engineers who try to systematically investigate the reasons behind soil failures that occurred in the February shaking correlating the soil behavior to the particular features of the recorded ground motions. (Full Text)

B35.
Tasiopoulou P., Gazetas G., “Seismic Analysis of Reinforced Earth Wall on Precarious Soil Improved with Stone Columns”, Proceedings of the 4th Japan – Greece Workshop, Seismic Design of Foundations, Innovations in Seismic Design, and Protection of Cultural Heritage, 6-7 October, Kobe, Japan, 2011.

[ABSTRACT]

The seismic response of a 15m high reinforced-earth retaining wall on top of a soil deposit containing liquefiable soil layers is explored with effective-stress dynamic time history analyses. The simultaneous generation and dissipation of seismic excess pore-water pressures (EPWP) is reproduced in the analysis. The need for, and effectiveness of, soil improvement with 60 cm stone columns placed in a triangular configuration is demonstrated with a series of graphs. Improvement results from both the increased rate of EPWP dissipation and, mainly, the increased stiffness/strength of the system. (Full Text)

B34.
Garini E., Gazetas G. (2011) “The Christchurch 2011 Earthquake: Elastic and Perfectly-Plastic Response Potential of Selected Ground Motions”, Proceedings of the 4th Japan –Greece Workshop, Seismic Design of Foundations, Innovations in Seismic Design, and Protection of Cultural Heritage, 6-7 October, Kobe, Japan.

[ABSTRACT]

The 22 February 2011 Mw 6.3 Earthquake produced a number of unique accelerograms in the city of Christchurch and the port of Lyttelton. Four of these records are analyzed in this paper. Their elastic response spectra are discussed and associated with some salient characteristics of the motions. Also, symmetric and asymmetric sliding of a block resting through Coulomb friction on horizontal or inclined planes, when excited at their base by these records, offer a strong indication of their “destructiveness potential” in terms of perfectly plastic response. (Full Text)

B33.
Giannakos S., Gerolymos N. , Gazetas G. (2011), “Single Pile versus Pile Group Lateral Response under Asymmetric Cyclic Loading”, Proceedings of the 4th Japan – Greece Workshop, Seismic Design of Foundations, Innovations in Seismic Design, and Protection of Cultural Heritage, 6-7 October, Kobe, Japan.

[ABSTRACT]

To gain insight into the inelastic behavior of piles, the response of a vertical pile embedded in a dry dense sand and subjected to cyclic lateral loading was studied experimentally in centrifuge tests conducted in Laboratoire Central des Ponts et Chaussees, in Nantes, France. A three-dimensional finite element analysis with the use of a new constitutive model for the cyclic behavior of sand was performed in order to capture the cyclic response of the single pile. Performance measure parameters were introduced to evaluate the overall response of the pile soil system indicating that the proposed model is suitable for the prediction of the lateral response of a pile under cyclic loading and the domination of the mechanism of “system densification” upon soil densification in cyclic loading. The response of an 1×2 pile group under cyclic lateral loading is also investigated showing that the model is capable of representing the shadow effect of the pile group. (Full Text)

B32.
Anastasopoulos I., Loli M., Drosos V., Gazetas G. (2011), “Cyclic Pushover and Shake Table Testing of Bridge Pier with Foundation Uplifting and Soil Yielding”, Proceedings of the 4th Japan–Greece Workshop, Seismic Design of Foundations, Innovations in Seismic Design, and Protection of Cultural Heritage, 6-7 October, Kobe, Japan.

[ABSTRACT]

Recent studies have highlighted the beneficial role of foundation uplifting and full mobilization of bearing capacity during strong seismic shaking. With the inertia loading transmitted onto the superstructure being limited by the capacity of the foundation, such concept may provide an alternative method of “in-ground” seismic isolation: the so called rocking isolation. Attempting to unravel the effectiveness of such alternative design method, this paper investigates experimentally the nonlinear response of a surface foundation on sand and its effect on the seismic performance of an idealized slender 1-dof structure. Using a bridge pier as an illustrative prototype, three foundation design alternatives are considered, representing three levels of design conservatism. Their performance is investigated through static (monotonic and slow-cyclic “pushover”) loading, and reduced-scale shaking table testing. It is shown that rocking isolation may constitute a valid alternative for the seismic protection of structures, providing encouraging evidence in favor of the innovative idea of moving foundation design towards a less conservative, even unconventional, treatment. (Full Text)

B31.
Anastasopoulos I., Kourkoulis R., Papadopoulos E. (2011), “1-g Experimental Investigation of the Metaplastic Rocking Response of 1-dof Oscillators on Shallow Footings”, Proc. 4th Japan–Greece Workshop on Seismic Design of Foundations, Innovations in Seismic Design, and Protection of Cultural Heritage, Kobe, Japan, 6–7 October

[ABSTRACT]

This paper experimentally investigates the effect of shallow soil improvement layer on the rocking response of 1-dof systems. A series of 1-g horizontal monotonic and slow cyclic pushover tests were conducted in the laboratory of soil mechanics of the National Technical University of Athens (NTUA) with the depth of the soil improvement layer being varied parametrically. It is shown that due to the very nature of foundation rocking which mobilizes only a shallow stress bulb within the soil underneath the foundation, the presence of a shallow zone of mitigation acts very effectively towards limiting the shaking-induced settlement of the foundations. (Full Text)

B30.
Loli M., Anastasopoulos I. (2011), “Normal and Reverse Fault Rupture Interaction with Caisson Foundations : Centrifuge Modeling and Numerical Simulation”, Proc. 4th Japan–Greece Workshop on Seismic Design of Foundations, Innovations in Seismic Design, and Protection of Cultural Heritage, Kobe, Japan, 6–7 October.

[ABSTRACT]

Owing to their rigidity, caisson foundations are believed to be less sensitive to fault induced loading compared to other foundation types. This paper investigates experimentally and numerically the response of a caisson foundation subjected to dip slip (normal and reverse)fault rupture. A series of centrifuge tests were conducted focusing on the effect of the caisson position with reference to the free field fault outcrop. The fault rupture was found to develop preferentially around the margins of the rigid caisson body, which acted as a kinematic constrain, altering sometimes dramatically the free field rupture pattern. Depending on the caisson position, the fault diverted towards the hanging wall or the footwall side of the caisson, or bifurcated, spreading the soil failure at a wider area on both sides. 3-D nonlinear numerical simulation of the problem was also developed and validated through comparison with the experimental results. (Full Text)

B29.
Anastasopoulos I., Georgarakos T., Kourkoulis R., Gazetas. G. (2010), “Design of Bridges Against Seismic Faulting : Methodology and Applications”, Proceedings of the Fifth International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, May 24-29, San Diego (available in Cd rom).

[ABSTRACT]

This paper presents a methodology for design of bridge–foundation systems against seismic faulting. The problem is decoupled in two steps. Step 1 deals with the response of a single bridge pier and its foundation subjected to faulting–induced deformation ; Step 2 deals with the detailed model of the superstructure, which is subjected to differential displacements computed in Step 1. We analyze typical viaduct and underpass bridges, founded on piles or caisson foundations. Piled foundations are found to be vulnerable to faulting– induced deformation. While end–bearing piles cannot really sustain any appreciable bedrock offset, floating piles may perform better, especially if combined with hinged pile–to–cap connections. Statically–determinate superstructures are shown to be less sensitive to faulting– induced differential displacements and rotations. Finally, an application of the method is shown for a major bridge, demonstrating the feasibility of design against seismic faulting. (Full Text)

B28.
Gerolymos N., Drosos V., Gazetas. G., (2010), “Seismic Response of Inelastic Pile Foundations : A New Performance Based Design Philosophy”, Proceedings of the Fifth International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, May 24-29, San Diego (available in Cd rom).

[ABSTRACT]

While seismic codes do not allow plastic deformation of piles, the Kobe earthquake has shown that limited structural yielding and cracking of piles may not be always detrimental. This paper focuses on the influence of soil compliance, pile-to-pile interaction, intensity of seismic excitation, pile diameter, above–ground height of the pile, location of plastic hinges (above or below ground development), on the seismic response of pile supported bridge structures. Evaluation of the bridge pier behaviour is achieved through key performance measure indices, as is: the displacement (global) and curvature (local) ductility demands and the maximum drift ratio. It is shown that the ductility demand of a bridge pier decreases with both (a) increasing soil compliance, and (b) below-ground location of plastic hinges development. By exploiting the results, a new performance based design method is developed that allows for soil and pile yielding instead of over-designing the foundation to behave nearly elastically and forcing the potentially developed plastic hinges to occur in the pier (as with conventional capacity design). (Full Text)

B27.
Tasiopoulou P., Gerolymos N., Gazetas G. (2010). “Numerical Simulation of Pile Response due to Liquefaction based on Centrifuge Experiment”, 6th Greek Conference on Geotechnical and Environmental Engineering, 29 September-1 October, Volos, Greece (in Greek).

[ABSTRACT]

The kinematic soil-pile interaction under conditions of soil liquefaction consists one of the most complex and particularly damaging phenomena. This paper presents the dynamic numerical simulation of the abovementioned mechanism in two dimensions, using appropriate springs, based on a centrifuge experiment (Abdoun et al. 2003). (Full Text)

B26.
Zarzouras O., Gerolymos Ν., Gazetas G. (2010). “ Seismic response of caisson quay-wall in a liquefied environment: Analysis of a case history”, 6th Greek Conference on Geotechnical and Environmental Engineering, 29 September-1 October, Volos, Greece (in Greek).

[ABSTRACT]

A simplified constitutive model for the development of pore water pressure in the soil, due to cyclic loading is applied to analyze a quay-wall undergoing soil flow due to liquefaction. The great advantage of this model against other more sophisticated is the use of one and only parameter, the SPT numbers. A parametric study sheds light on the role of critical parameters, such us the lateral stress, Ko, relative density, interface conditions, seismic excitation, on the seismic response of the quay-wall. (Full Text)

B25.
Gelagoti F., Kourkoulis R., Anastasopoulos Ι., & Gazetas G. (2010). “Non-Linear Inelastic Behavior of Foundations: Application on the Seismic Protection of Frame Structures”, 6th Greek Conference on Geotechnical and Environmental Engineering, 29 September-1 October, Volos, Greece (in Greek).

[ABSTRACT]

The paper explores the effectiveness of a new approach for the earthquake design of foundations: intentional under-design of the foundation in order to activate the mechanism of uplifting and mobilization of the soil bearing capacity. Hence, a “plastic hinge” will be formed in the foundation-soil interface thus limiting the earthquake inertia that may be transmitted to the superstructure. This paper presents non-linear numerical analyses of a simple frame structure founded on stiff clay and subjected to an ensemble of strong ground motions. The results show that when designed according to the new concept the frame sustains the strong shaking with serious damage but avoids collapse. (Full Text)

B24.
Gelagoti F., Kourkoulis R., Anastasopoulos Ι., & Gazetas G. (2010). “Seismic Soil-Foundation-Frame Interaction under Valley-affected Ground Motion”, 6th Greek Conference on Geotechnical and Environmental Engineering, 29 September–1 October, Volos, Greece (in Greek).

[ABSTRACT]

Although the 2-dimensional wave propagation in alluvial valleys has been extensively studied in the literature, only limited attention has been drawn to the generation of a “parasitic” vertical component of ground motion near the valley edges. Being a direct result of geometry, this component is expected to be correlated with the horizontal one and hence much more detrimental to structures. The validity of the above statements is confirmed in this non-linear numerical study of the response of a frame structure founded near the edges of different valley formations subjected to strong ground shaking. (Full Text)

B23.
Kourkoulis R., Gelagoti F., Anastasopoulos I., Gazetas G. (2010). “Piles Effectiveness for Slope Stabilization: 3D Numerical Investigation”, 6th Greek Conference on Geotechnical and Environmental Engineering, 29 September-1 October, Volos, Greece (in Greek).

[ABSTRACT]

The study presents a parametric investigation of the factors controlling the effectiveness of slope stabilization piles. A 3D numerical model is utilized to perform parametric analyses of piles embedded in an unstable slope undergoing lateral soil movement. Pile diameter and spacing, depth of pile embedment, soil layering and stiffness are the key problem parameters. Dimensionless Design Charts are developed from the compilation of numerical results. (Full Text)

B22.
Gazetas G., Ziotopoulou A. (2010). “Bi-normalized Responses Spectrum for a Rational Soil Structure Interaction Analysis”, Workshop on Soil Structure Interaction (SSI) Knowledge and Effect on the Seismic Assessment of NPPS Structures and Components, Otawa, Canada, 6-8 October.

[ABSTRACT]

Seismic codes have universally adopted smooth design acceleration spectra, on the basis of averaging of a large number of elastic response spectra of actual recordings. Such spectra have, for each soil category, an essentially-constant acceleration plateau, Sa, usually equal to 2.5A, followed by a descending acceleration branch. The period range of the constant acceleration plateau is larger for softer soils. However, such a flat shape of spectra has little resemblance to an actual soil-amplified spectrum. The unrealistic shape stems basically from the fact that the spectra of motions recorded on soft soils belonging to one soil category attain their maxima at different well-separated periods; thereby, averaging them eliminates their peaks and leads to a (spurious) flat spectrum. An extensive analytical parametric study is summarized here to demonstrate that by normalizing the period of the spectra with the predominant period of motion, and then averaging, results in a bi-normalized spectrum (Sa/A : T/Tp) which has a sharp peak at T/Tp = 1. It is found out that this spectrum has peak value Sa/A  3.75 (rather than 2.5), for a narrow range of normalized periods. The effect of such a spectrum especially on SSI studies may be drastically different from the beneficial effect of a (conventional) code spectrum. (Full Text)

B21.
Ziotopoulou A., Gazetas G. (2010), “Are Current Design Spectra sufficient for Soil-Structure Systems on Soft Soils?”, Advances in Performance-Based Earthquake Engineering, M.N. Fardis Editor, Springer Verlag : Berlin pp.79-87.

[ABSTRACT]

Seismic codes have largely adopted smooth design acceleration response spectra on the basis of statistical processing of a large number of elastic response spectra of actual recordings. Such spectra have, for each soil category, a constant acceleration Φe = 2.5A branch and a declining acceleration branch. The period range of the constant–acceleration plateau is larger for softer soils. However, the flat shape of the spectra has no resemblance to actual soil-amplified spectra. An extensive parametric study covering several types of soil profile and seismic excitation sheds light on the shape of normalized spectra, as they result from both equivalent–linear and truly–inelastic soil response analyses. It then explores the effect of dividing the period, T, with the dominant period, Tp, of motion and thus normalizing the period-axis of each spectrum. This results in a bi-normalized spectrum which has a peak at T / Tp = 1. The average bi-normalized spectra for each soil category are nearly identical to each other, leading to a unique spectrum which has a peak of Φe/A ≈ 3.75 for a very narrow range of normalized periods, and is thus quite different from the conventional design spectra of the seismic codes. (Full Text)

B20.
E.J. Sapountzakis, A.E. Kampitsis and Α.D. Koroneou (2010) «Nonlinear Dynamic Analysis of Beam – Columns of Bridge Piers – Application in Valley bridges of Metsovo and in Metsovitikos River Bridge.», Proc. of 6th Interscientific Interuniversity Conference, “The Integrated Development of Highland Areas”, Μetsovo, Greece, September.

[ABSTRACT]

In this paper, a boundary element method is developed for the nonlinear dynamic analysis of beam-columns of arbitrary doubly symmetric simply or multiply connected constant cross section, partially supported on tensionless Winkler foundation, undergoing moderate large deflections under general boundary conditions, taking into account the effects of shear deformation and rotary inertia. The beam-column is subjected to the combined action of arbitrarily distributed or concentrated transverse loading and bending moments in both directions as well as to axial loading. To account for shear deformations, the concept of shear deformation coefficients is used. Five boundary value problems are formulated with respect to the transverse displacements, to the axial displacement and to two stress functions and solved using the Analog Equation Method, a BEM based method. Application of the boundary element technique yields a nonlinear coupled system of equations of motion. The solution of this system is accomplished iteratively by employing the average acceleration method in combination with the modified Newton Raphson method. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress functions using only boundary integration. The proposed model takes into account the coupling effects of bending and shear deformations along the member as well as the shear forces along the span induced by the applied axial loading.The proposed model can be easily applied to the Valleybridges of Metsovo and in Metsovitikos River Bridge. (Full Text)

B19.
E.J. Sapountzakis and A.E. Kampitsis (2010d) “Nonlinear Analysis of Shear Deformable Beam-Columns Partially Supported on Tensionless Winkler Foundation”, Proc. of the BeTeq10 International Conference on Boundary Element Techniques, July 12-14, Berlin, Germany.

[ABSTRACT]

In this paper, a boundary element method is developed for the nonlinear analysis of shear deformable beam-columns of arbitrary doubly symmetric simply or multiply connected constant cross section, partially supported on tensionless Winkler foundation, undergoing moderate large deflections under general boundary conditions. (Full Text)

B18.
E.J. Sapountzakis and A.E. Kampitsis (2010c) “Nonlinear Analysis of Shear Deformable Beam-Columns Partially Supported on Tensionless Three-Parameter Foundation”, Proc. of the CST – Tenth International Conference on Computational Structures Technology , September 14-17, Valencia Spain.

[ABSTRACT]

In this paper, a boundary element method is developed for the nonlinear analysis of shear deformable beam-columns of arbitrary doubly symmetric simply or multiply connected constant cross section, partially supported on tensionless three parameter foundation, undergoing moderate large deflections under general boundary conditions. The beam-column is subjected to the combined action of arbitrarily distributed or concentrated transverse loading and bending moments in both directions as well as to axial loading. To account for shear deformations, the concept of shear deformation coefficients is used. Five boundary value problems are formulated with respect to the transverse displacements, to the axial displacement and to two stress functions and solved using the Analog Equation Method, a BEM based method. Application of the boundary element technique yields a system of nonlinear equations from which the transverse and axial displacements are computed by an iterative process. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress functions using only boundary integration. The proposed model takes into account the coupling effects of bending and shear deformations along the member as well as the shear forces along the span induced by the applied axial loading. Numerical examples are worked out to illustrate the efficiency, wherever possible the accuracy and the range of applications of the developed method. (Full Text)

B17.
E.J. Sapountzakis, A.E. Kampitsis (2009b), “Nonlinear Dynamic Analysis of Partially Supported Beam-Columns on Nonlinear Elastic Foundation Including Shear Deformation Effect “, 3rd Greece – Japan Workshop on Seismic Design, Observation and Retrofit of Foundations, September 22-23, Santorini, Greece.

[ABSTRACT]

In this paper, a boundary element method is developed for the nonlinear dynamic analysis of beam-columns of arbitrary doubly symmetric simply or multiply connected constant cross section, partially supported on tensionless Winkler foundation, undergoing moderate large deflections under general boundary conditions, taking into account the effects of shear deformation and rotary inertia. The beam-column is subjected to the combined action of arbitrarily distributed or concentrated transverse loading and bending moments in both directions as well as to axial loading. To account for shear deformations, the concept of shear deformation coefficients is used. Five boundary value problems are formulated with respect to the transverse displacements, to the axial displacement and to two stress functions and solved using the Analog Equation Method, a BEM based method. Application of the boundary element technique yields a nonlinear coupled system of equations of motion. The solution of this system is accomplished iteratively by employing the average acceleration method in combination with the modified Newton Raphson method. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress functions using only boundary integration. The proposed model takes into account the coupling effects of bending and shear deformations along the member as well as the shear forces along the span induced by the applied axial loading. Numerical examples are worked out to illustrate the efficiency, wherever possible the accuracy and the range of applications of the developed method.

B16.
E.J. Sapountzakis, A.E. Kampitsis (2009a), “Nonlinear Dynamic Analysis of Timoshenko Beam-Columns Partially Supported on Elastic Foundation”, Computational Modeling and Advance Simulation, June 30- July 3, Bratislava, Slovak Republic

[ABSTRACT]

In this paper, a boundary element method is developed for the nonlinear dynamic analysis of beam-columns of arbitrary doubly symmetric simply or multiply connected constant cross section, partially supported on elastic foundation, undergoing moderate large deflections under general boundary conditions, taking into account the effects of shear deformation and rotary inertia. The beam-column is subjected to the combined action of arbitrarily distributed or concentrated transverse loading and bending moments in both directions as well as to axial loading. To account for shear deformations, the concept of shear deformation coefficients is used. Five boundary value problems are formulated with respect to the transverse displacements, to the axial displacement and to two stress functions and solved using the Analog Equation Method, a BEM based method. Application of the boundary element technique yields a nonlinear coupled system of equations of motion. The solution of this system is accomplished iteratively by employing the average acceleration method in combination with the modified Newton Raphson method. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress functions using only boundary integration. The proposed model takes into account the coupling effects of bending and shear deformations along the member as well as the shear forces along the span induced by the applied axial loading. Numerical examples are worked out to illustrate the efficiency and the range of applications of the developed method.

B15.
Panagiotidou A.I., Gerolymos N., Gazetas G. (2010), “Pushover and inelastic-seismic response of shallow foundations supoorting a slender structure”, Proc. 6th Greek National Conference on Geotechnical Engineering. Volos, Greece, September 2010 (in greek).

[ABSTRACT]

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 the above three types of loading. (Full Text)

B14.
Panagiotidou A.I., Gerolymos N., Gazetas G. (2010), “Pushover and inelastic-seismic response of shallow foundations supoorting a slender structure”, Proc. 5th International Conference on Recent Advances in Earthquake Engineering and Soil Dynamics. San Diego, California, May 2010.

[ABSTRACT]

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: 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. Prominent among the key problem parameters are : (a) the static factor of safety, FSv, against vertical bearing capacity failure ; (b) the distance, R, of the mass centre of gravity from the base edge ; (c) the slenderness ratio h/b ; (d) the intensity, frequency content and sequence of pulses of the seismic excitation ; (e) the vibrational characteristics (natural period) of the structure. The results reveal a remarkable sensitivity of the system response to the above parameters and particularly to the static factor of safety. For large static factors of safety (FSv > 2) the dominant nonlinearity in the response is in the form of foundation uplifting, whereas for small static factors of safety (FSv ≤ 2) the bearing capacity mechanisms are fully developed leading to additional settlement of the foundation with permanent rotation. Another surprising conclusion is the non–symmetric overcapacity of the ultimate moment of the footing, observed only in the cases of heavily loaded systems for the cyclic and seismic analyses. This is due to the development of uni–directional bearing capacity type of failure in the preceding steps. (Full Text)

B13.
Loli M., Anastasopoulos I., Bransby M.F, Gazetas G. (2010b). ” Caisson foundation subjected to normal faulting: Experimental and analytical study.” 5th National Conference on Geotechnical Engineering, 29September – 1 October, 2010, Volos, Greece (in Greek).

[ABSTRACT]

This paper explores the mechanisms of normal fault rupture interaction with caisson foundations through an integrated approach, using both experiments and analysis. First, a series of centrifuge tests were conducted to study the response of a 5m x 5m x 10 m caisson founded on a layer of dry dense sand. Nonlinear 3-D numerical modelling of the problem was then developed and adequately validated against the centrifuge tests results. Τhe caisson is found to interact with the fault rupture modifying, sometimes spectacularly, the free field rupture path. The observed failure pattern and the consequent caisson response are shown to vary significantly, depending on the caisson position with reference to the fault. (Full Text)

B12.
Loli M., Anastasopoulos I., Bransby M.F, Gazetas G. (2011). “Normal and Reverse Fault Rupture Interaction with Caisson Foundations: Centrifuge modelling and Numerical Simulation.” 5th International Conference on Earthquake Geotechnical Engineering, January 10-13, San Diago, Chile.

[ABSTRACT]

Permanent ground displacements due to faulting constitute a secondary, yet not less destructive, earthquake associated hazard, in addition to shaking. In fact, a great variety of structures suffered extensive deformation loading, and even failed, when crossed by the outcropping fault rupture in recent large magnitude earthquakes. Owing to their rigidity, caisson foundations are believed to be less sensitive to fault induced loading compared to other foundation types. This paper investigates experimentally and numerically the response of a caisson foundation subjected to dip slip (normal and reverse) fault rupture. A series of centrifuge tests were conducted to explore the mechanisms of fault rupture–caisson interaction, focusing on the effect of the caisson position with reference to the free field fault outcrop. The fault rupture was found to develop preferentially around the margins of the rigid caisson body, which acted as a kinematic constrain, altering sometimes dramatically the free field rupture pattern. Depending on the caisson position, the fault diverted towards the hanging wall or the footwall side of the caisson, or bifurcated, spreading the soil failure at a wider area on both sides. 3-D nonlinear numerical simulation of the problem was also developed and validated through comparison with the experimental results. A further numerical parametric investigation was finally carried out, showing the strong effect of the exact caisson position on the response of the system. (Full Text)

B11.
Kourkoulis R., Gelagoti F., Anastasopoulos I., Gazetas G. (2009b), “Piles for Stabilising Seismically Precarious Slopes. Part B: Parametric Analyses and Design Charts”, Proc. 3rd Greece–Japan Workshop : Seismic Design, Observation, Retrofit of Foundations, Santorini 22–23 September, pp. 520-533.

[ABSTRACT]

The simplified numerical model formulated and validated in the companion paper is utilized to perform parametric analyses of piles embedded in an unstable slope undergoing lateral soil movement. Pile diameter and spacing, depth of pile embedment, soil layering and stiffness are the key problem parameters investigated. Dimensionless Charts are developed for guiding the design of piles for slope stabilization. (Full Text)

B10.
Kourkoulis R., Gelagoti F., Anastasopoulos I., Gazetas G. (2009a), “Piles for Stabilising Seismically Precarious Slopes. Part A: Development and Validation Charts”, Proc. 3rd Greece–Japan Workshop : Seismic Design, Observation, Retrofit of Foundations, Santorini 22–23 September, pp. 506-519.

[ABSTRACT]

This is the first in a series of two papers presenting a decoupled methodology for the design of slope stabilising piles. The proposed methodology combines the widely accepted analytical calculations to obtain the required stabilising force, with non-linear finite elements analysis to obtain the ultimate lateral capacity of piles. The soil and pile constitutive model is validated against experimental and observational data. The simplified numerical model results are compared satisfactorily with 3D Finite Elements analyses and theoretical studies. (Full Text)

B9.
Gerolymos N., Drosos V., Gazetas G. (2010). ” Alternative design of rafts with structurally unconnected piles.” 6th Greek Conference on Geotechnical and Environmental Engineering, 29 September – 1 October, Volos, Greece (in Greek).

[ABSTRACT]

A new foundation method is presented as an alternative to conventional pile foundations. It consists of piles which are structurally unconnected to the raft, with the intervention of a well-compacted coarse grained layer. Since the structural considerations of such piles are no longer critical in the design, the proposed foundation method might be economically more efficient while improving the response of the superstructure to both static and seismic loading. Our main goal is to investigate the role of key parameters such as: soil stiffness and strength, thickness of gravel layer, pile configuration and bonding conditions at the pile-soil interface on the foundation response, in terms of the subgrade modulus coefficient of the raft. (Full Text)

B8.
Gazetas G., Anastasopoulos I., Loli M., Gerolymos N. (2009), “Nonlinear Inelastic Seismic Response of Slender Bridge Pier on Surface Foundation”, Proc. 2nd International Conference on Computational Dynamics and Earthquake Engineering – COMPDYN-2009, 22-24 June, Rhodes, Greece.

[ABSTRACT]

The paper highlights the results of a numerical study of the seismic response of a tall bridge-pier type structure supported on surface foundation. Both the structure and the soil are treated as inelastic materials – the former capable of developing plastic hinging at its column base, the latter capable of mobilizing bearing-capacity type “failure” mechanisms. Moreover, the geometric nonlinearity arising from the uplifting of the foundation due to the large overturning transmitted moment is treated rigorously. Exciting a typical such system with two actual earthquake records, it is shown that whereas a conventionally-designed sys-tem may suffer substantial structural plastic permanent rotation at the column base (and thereby even collapse in a very strong event), a more-daring unconventional design which specifically allows inelasticity/nonlinearity in the soil and the soil–foundation interface to take place suffers only permanent settlement and in some cases permanent tilt of the founda-tion without suffering any structural distress. (Full Text)

B7.
Garini E., Gazetas G., Gerolymos N. (2010), ” Effect of Pre-Yielding Elasticity on Sliding Triggered by “Near-Fault” Wavelets “, 6th Greek Conference on Geotechnical and Geoenvironmental Engineering, Volos, 29 September –1 October, Paper No.290300.

[ABSTRACT]

The influence of elastic pre-yielding on the response of a mass resting on an inclined plane is investigated in this paper. The ultimate shearing capacity of the interface obeys Coulomb’s friction law. The slope is subjected to near-fault triggering by two types of idealized wavelets: (i) a Ricker wavelet, representative of forward directivity affected motions, and (ii) an one-cycle sinusoidal wavelet, representative of fling-affected motions. The asymmetric sliding response is analyzed and the effect of a number of parameters is explored. They include: the critical acceleration ratio, aC /aH, the excitation frequency, fo, and the magnitude of elastic pre-yielding displacement, dy. (Full Text)

B6.
Drosos V., Gerolymos N., Gazetas G. (2010b). “Seismic Response of Pile-columns: Numerical Investigation.” 5th National Conference on Geotechnical Engineering, 29September – 1 October, 2010, Volos, Greece (in Greek).

[ABSTRACT]

Preliminary investigation of the influence of pile nonlinearity on the soil-pile-structure response is conducted through parametric non-linear analyses. Eight different structure configurations founded on four different soil materials are excited by seismic strong motions. The analyses results indicate that the increased soil deformability and the potentiality of plastic hinge formation on pile may reduce the local ductility demand and consequently lead to a more economic design of the structure. (Full Text)

B5.
Drosos V., Georgarakos P., Anastasopoulos I., Gazetas G. (2010a). “Experimental Validation of Bridge Pier Seismic Design Employing Soil Ductility.” 5th National Conference on Geotechnical Engineering, 29 September – 1 October, 2010, Volos, Greece (in Greek).

[ABSTRACT]

A new methodology for the dynamic design of bridges is experimentally investigated using the shaking table of the Soil Mechanics Laboratory of NTUA. The proposed methodology, reversing the conventional capacity design, takes advantage of soil ductility and allows a plastic hinge in the ground to develop. It is observed that superstructure straining reduces to the elastic range, contrary to the conventionally designed collapsible structure. Nevertheless, the inevitable penalty for this beneficial behavior is the increased settlements and rotation of the foundation. (Full Text)

B4.
Anastasopoulos I., Georgarakos T., Drosos V., Giannakos S., Gazetas G. (2009b), “Towards a Reversal of Seismic Capacity Design : Part B. Shaking-Table Testing of Bridge Pier–Foundation System”, Proc. 3rd Greece–Japan Workshop : Seismic Design, Observation, Retrofit of Foundations, Santorini 22–23 September, pp. 407-418.

[ABSTRACT]

This paper investigates experimentally the effectiveness of a new seismic design philosophy, in which soil failure is “utilized” to protect the superstructure. A physical model of a simple bridge pier is used as an example. Two alternatives are considered: one in compliance with conventional capacity design, with over-designed foundation so that the plastic “hinge” will develop at the bridge pier ; and one following the new philosophy, with under-designed foundation, moving the plastic “hinging” will develop in the soil or the soil foundation interface. The seismic performance of the two alternatives is investigated through 1-G shaking table testing using real records and synthetic motions as base excitation. It is shown that the performance of the new design concept can be advantageous : in cases where the conventionally designed system collapses, the new concept can survive the seismic motion with the “damage” being limited to residual deck drift and increased settlement. (Full Text)

B3.
Anastasopoulos I., Loli M., Gerolymos N., Apostolou M., Gazetas G. (2009a), “Towards a Reversal of Seismic Capacity Design. Part A : Analysis of Bridge Pier–Foundation System”, Proc. 3rd Greece–Japan Workshop : Seismic Design, Observation, Retrofit of Foundations, Santorini 22–23 September, pp. 393-406.

[ABSTRACT]

The paper illuminates a new seismic design philosophy, which takes advantage of soil “failure” to protect the superstructure. A reversal of conventional “capacity design” is introduced, through intentional under-designing of the foundation. A simple but realistic bridge is used as an illustrative example of the effectiveness of the new philosophy. Two alternatives are compared : one in compliance with conventional capacity design, with over-designed foundation so that the plastic “hinge” develops in the superstructure ; and one with under-designed foundation, so that the plastic “hinge” may occur in the soil. The seismic performance of the two alternatives is investigated through nonlinear dynamic time history analysis, using a variety of seismic excitations. It is shown that the performance of both alternatives is totally acceptable for moderate seismic motions. For large intensity seismic motions, the performance of the new scheme is proven advantageous, not only avoiding collapse but hardly suffering any inelastic structural deformation. The penalty to pay is a substantial foundation settlement. (Full Text)

B2.
Anastasopoulos I., P. Georgarakos, V. Drosos, Gazetas G. (2010). “Experimental soil–foundation–bridge pier interaction: towards a reversal of capacity design.” 5th International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, May 24-29, 2010, San Diego, California.

[ABSTRACT]

This paper presents a new seismic design philosophy, which under-designs the foundation to act as a “fuse” in case of strong seismic shaking. A simplified bridge pier is used to illustrate the advantages and disadvantages of this new philosophy compared to conventional capacity design. For this purpose, two alternatives are compared : one with an over-designed foundation, in accordance with conventional capacity design (so that the plastic “hinge” develops in the superstructure), and one with under-designed foundation. The performance of the two alternatives is investigated through shaking table testing of reduced scale models, using real accelerograms and artificial sinusoidal motions. It is shown that the performance of both alternatives is acceptable for moderate seismic shaking. For larger intensity ground motions, that clearly exceed the design limits, the performance of the new design concept is advantageous, not only avoiding collapse but hardly suffering any inelastic structural deformation. The price to pay is mainly the increase of seismic settlements, and in some cases of permanent foundation rotation. (Full Text)

B1.
Anastasopoulos Ι. (2010), “Beyond conventional capacity design : towards a new design philosophy”, In : Soil–Foundation–Structure Interaction, Pender M. and Davies M.C.R. (editors), CRC Press, Taylor & Francis Group : New York .

[ABSTRACT]

The paper illuminates a new seismic design philosophy, which takes advantage of soil “failure” to protect the superstructure. A reversal of conventional “capacity design” is introduced, through intentional under-designing of the foundation. A simple but realistic bridge is used as an illustrative example of the effec-tiveness of the new philosophy. Two alternatives are compared : one in compliance with conventional capacity design, with over-designed foundation so that the plastic “hinge” develops in the superstructure ; and one with under-designed foundation, so that the plastic “hinge” may occur in the soil. The seismic performance of the two alternatives is investigated through numerical (finite element) and experimental (shaking table) simulation. It is shown that the performance of both alternatives is totally acceptable for moderate seismic motions. For large intensity seismic motions, the performance of the new scheme is shown to be advantageous, not only avoiding collapse but hardly suffering any inelastic structural deformation. Naturally, there is always a price to pay, which is none other than increased foundation settlement and residual rotation. (Full Text)

B01.
Stavropoulou E., Anastasopoulos I., Gazetas G., (2009). “Preliminary SFSI Studies for the Messina Bridge Foundations”, Proc. 3rd Greece–Japan Workshop : Seismic Design, Observation, Retrofit of Foundations, Santorini 22–23 September, pp. 438-448.

[ABSTRACT]

The Messina Bridge in Italy, when completed will be the longest suspension bridge ever built, having a central span of 3300 m. In this paper, a generic study of the soil–pier–foundation interaction of the Calabrian-side pier of the preliminary Bridge design is examined. The massive concrete foundation of this pier is to be founded in a gravelly deposit, after the latter has been subjected to improvement by jet grouting. A parametric elastic study is first conducted to investigate the influence of the width and depth of soil improvement beneath the foundation. Then, the response of an alternative less conservative” foundation is investigated and compared to the “original” design. Non–linear features of material (soil) and geometry (uplifting, sliding, and second order effects), , as well as the flexibility of the tower, are taken into account. (Full Text)

B02.
Tasiopoulou P., Gerolymos N., Tazoh T., Gazetas G. (2009). “ Piles in Liquefaction- Induced Soil Flow behind Quay Wall : A Simple Physical Method Versus Centrifuge Experiments”, Proc. 3rd Greece–Japan Workshop, Seismic Design, Observation, Retrofit of Foundations, Santorini 22–23 September, pp. 114 -127

[ABSTRACT]

The paper presents a new physically simplified methodology for computing displacements and internal forces on piles under conditions of lateral spreading. The results compare well with results from centrifuge tests. To this end, 2D effective stress dynamic analysis of a cross-section of the wall-soil system without the presence of the piles is combined with an also 2D quasi-static analysis of a horizontal slice of the system with the group of piles. (Full Text)