SOIL-PILE KINEMATIC INTERACTION: NEW PERSPECTIVES FOR EC8 IMPROVEMENT

Transcription

1 E. Cosenza (ed), Eurocode 8 Persectives from the Italian Standoint Worksho, , 2009 Doiavoce, Naoli, Italy SOIL-PILE KINEMATIC INTERACTION: NEW PERSPECTIVES FOR EC8 IMPROVEMENT Roberto Cairo a, Enrico Conte a, Giovanni Dente a, Stefania Sica b, Armando Lucio Simonelli b a University of Calabria, Rende (CS), Italy, cairo@dds.unical.it b University of Sannio, Benevento, Italy, alsimone@unisannio.it ABSTRACT Kinematic interaction between soil and structure originates from the incomatibility of the seismic free-field motion and the dislacements of a more rigid embedded foundation. Foundation iles will actually exerience deformations not only due to the loads directly transmitted by the suerstructure, but also due to the assage of the seismic waves through the surrounding soil. In articular, bending moments may reveal quite imortant and, under certain circumstances, should be taken into account in the design, as rescribed by recent seismic codes (EN 998-5; D.M ). In this aer, the main results of a theoretical study are illustrated and some reliminary elements to be considered for seismic building codes are suggested. KEYWORDS Piles, kinematic interaction, code, simlified aroach, bending moment. INTRODUCTION During strong earthquakes foundation iles tend to significantly modify soil deformations, since they oose to the seismic motion of the ground. The interlay between soil and structure makes the motion at the base of the suerstructure to deviate from the free-field motion, and the iles to be subjected to additional bending, axial and shearing stresses. The bending moments, usually referred to as kinematic ones, may result somewhat imortant even in the absence of the suerstructure. The kinematic interaction between soil and iles has been studied by many researchers (Fan et al., 99; Gazetas et al., 992; Kaynia and Mahzooni, 996; Poulos and Tabesh, 996; Mylonakis, 200; Nikolaou et al., 200; Saitoh, 2005; Cairo and Dente, 2007; Sica et al., 2007; Simonelli and Sica, 2008; Maiorano et al., 2009, and others). In site of the big effort on such a toic, kinematic interaction is rarely accounted for in ractical design. Modern seismic codes have, however, acknowledged the imortance of kinematic interaction and demand iles to be designed also accounting for soil deformations arising from the assage of seismic waves. Two main issues should be also addressed by a building code: - when has kinematic interaction to be considered (or, conversely, when can it be neglected)?; - how has kinematic interaction to be analysed?

2 264 R. Cairo, E. Conte, G. Dente, S. Sica, A.L. Simonelli At resent, the evidence collected is far from roviding a definitive answer to the former question, but it is adequate to indicate what has still to be done for this issue. Eurocode 8 (EN 998-5) suggests that kinematic effects should be taken into account when all the following conditions simultaneously exist: ) seismicity of the area is moderate or high (secifying that moderate or high-seismicity areas are characterized by a eak ground acceleration a g S>0.g, where a g is the design ground acceleration on tye A subsoil and S is the soil factor); 2) subsoil tye is D or worse, characterized by sharly different shear moduli between consecutive layers; 3) the imortance of the suerstructure is of III or IV class (e.g. schools, hositals, fire stations, ower lants, etc). The recent Italian building code (D.M ) rovides quite similar indications concerning the kinematic bending moments in iles. The toic of this aer is to illustrate the key asects of ile kinematic interaction and to individuate some reliminary elements to be considered for technical codes. 2 METHODS OF ANALYSIS 2. Overview of existing methods Available methods for the analysis of kinematic soil-ile interaction may be classified into three grous: numerical aroaches (FEM, BEM), Winkler methods (BDWF), simlified formulations. The finite element method (Wu and Finn, 997; Cai et al., 2000; Kimura and Zhang, 2000; Maheshwari et al., 2004) rovides a owerful and versatile technique, since some imortant effects such as soil nonlinearity and heterogeneity may be directly accounted for. Nevertheless, this method is generally very exensive from a comutational viewoint, since it requires suitable boundaries conditions being introduced to simulate the radiation daming effect. In such a context, a more attractive aroach is reresented by the boundary element technique (Kaynia and Kausel, 982; Mamoon and Banerjee, 990; Cairo and Dente, 2007). It only needs the discretization of the interfaces and ermits the condition of wave roagation towards infinity to be automatically satisfied. This technique is generally formulated in the frequency domain and, in rincile, is valid only under the assumtion of material linear behaviour. The methods based on the Winkler foundation model (Novak, 974; Flores-Berrones and Whitman, 982; Kavvadas and Gazetas, 993) rove quite accurate and comutationally time saving. They allow nonlinear behaviour of the soil to be easily incororated if solution is envisaged in the time domain (Boulanger et al., 999; El Naggar et al., 2005; Maheshwari and Watanabe, 2006; Cairo et al., 2008). According to this method, the ile is modelled as a linearly elastic beam, with length L and diameter d, discretized into segments connected to the surrounding soil by srings and dashots, which rovide the interaction forces in the lateral direction (Figure ). As a first aroximation, the sring stiffness k may be considered to be frequencyindeendent and exressed as a multile of the local soil Young s modulus E s (Kavvadas and Gazetas, 993). The dashot coefficient c reresents both material and radiation daming. The latter one may be comuted using the analogy with one-dimensional wave roagation in an elastic rismatic rod of semi-infinite extent (Gazetas and Dobry, 984). For harmonic vertically roagating S-waves, the governing differential equation of the ile resonse is: E I u 4 4 z + m u 2 2 t = ( k + iωc)( u ff u ) ()

3 Soil-Pile Kinematic Interaction: New Persectives for EC8 Imrovement 265 Seismic free-field motion P i, E i, v i, ß i Seismic ile motion, Y(z) U ff (z) P i, E i, v i, ß i Y(z) k(z) c(z) Vertical shear waves Figure. Beam on Dynamic Winkler Foundation model (BDWF). where E I is the ile flexural rigidity, m the ile mass er unit length, u is the amlitude of the ile lateral dislacement, u ff the free-field soil dislacement, ω the circular frequency of the motion, z is the deth, t the time and i=(-) 0.5. Pile resonse in the time domain is then attained through standard Fourier transformations. Some results obtained using the Winkler aroach (BDWF), as roosed by Mylonakis et al. (997), will be resented in a subsequent section of the aer. 2.2 Aroximate methods Closed-form exressions (Dobry and O Rourke, 983; Nikolaou and Gazetas, 997; Mylonakis, 200; Nikolaou et al., 200) are available in literature for aroximately comuting the maximum steady-state bending moment at the interface between two layers. These aroaches have been derived by modelling the ile as a beam on a Winkler foundation and are based on the following simlified assumtions: each soil layer is homogeneous, isotroic and linearly elastic; the soil is subjected to a uniform static shear stress field; the ile behaves as a linear-elastic semi-infinite beam; the embedded length of the ile in each layer is greater than the so-called active length. This latter is usually exressed by the equation (Randolh, 98): 0.25 E.5 L a = d (2) Es The simlified design rocedure roosed by Dobry and O Rourke (983) ermits to comute the bending moment at the interface between two layers as: M 3 / 4 / 4 =.86( E I ) ( G ) γ F (3) where G and γ are the shear modulus and shear strain in the uer soil layer, resectively; F is a function of the ratio c=(g 2 /G ) 0.25, with G 2 being the shear modulus of the lower layer, and exressed by: F ( c ( + c) ( c 4 = 3 ) ( + c ) + + c + c 2 ) (4)

4 266 R. Cairo, E. Conte, G. Dente, S. Sica, A.L. Simonelli An imrovement of the Dobry and O Rourke (983) solution has been achieved by Mylonakis (200). Using more suitable dynamic arameters, the following exression has been derived: E I ε M = 2 γ (5) d γ in which ε indicates the ile eak bending strain and γ denotes the soil shear strain at the layer interface. The ratio of these arameters reresents a sort of strain transmissibility function, which is strongly frequency-deendent. If this asect is neglected, the strain transmissibility function takes into account only ile-soil interaction effects and is exressed as: ε γ ω= 0 = c 2 c + 4 2c E 4.7 E 9 / 32 H H d d c( c ) (6) where H and E are the thickness and the Young s modulus of the uer layer, resectively. The effect of frequency may be introduced in terms of the ratio: ε Φ = γ ε γ ω= 0 (7) which is a function of H /d, G /G 2, E /E. Nevertheless, in the range of frequencies of interest Φ is generally less than.25. A fitted formula has been roosed by Nikolaou et al. (200) for harmonic excitation. It is based on the maximum shear stress τ c induced at the layer interface by the free-field motion. The resulting exression is: L E Vs2.042 τc d d E Vs M = (8) where V s and V s2 are the shear wave velocities in the uer and lower layer, resectively. In order to account for the transient nature of the seismic excitation, the authors have introduced a reduction factor deending on the duration of the accelerograms in terms of the effective number N c of cycles in the record, the relative frequency characteristics between earthquake and soil deosit, the effective daming of the soil-ile system. Two simlified exressions are given: 0.04N c η = 0.05N c for T for T T T (9) where T reresents the redominant eriod of the ground motion and T the fundamental eriod of the deosit. A crucial issue in the use of these aroximate aroaches is the evaluation of the uniform soil shear strain γ in the uer layer and the maximum shear stress τ c at the interface. As

5 Soil-Pile Kinematic Interaction: New Persectives for EC8 Imrovement 267 suggested by Mylonakis (200), if the seismic eak acceleration a maxs is secified at the soil surface, γ can be comuted using the exression suggested by Seed and Idriss (982) for liquefaction roblems: ρh γ = ( 0.05H) amax s (0) G where, in addition to the soil arameters already defined, the mass density of the uer layer ρ has been introduced. Equivalently, the maximum shear stress τ c at the interface may be roughly estimated as (Nikolaou and Gazetas, 997; Nikolaou et al., 200): max s τ = a ρ H () c In the next section, the accuracy of these simlified aroaches will be investigated. 3 MAIN RESULTS Several analyses have been erformed referring to a fixed-head ile with length L=20 m, diameter d=0.6 m, Young s modulus E = kn/m², and mass density ρ =2.5 Mg/m³ (Figure 2). The ile is embedded in a two-layered subsoil which is 30 m thick and underlined by a stiffer bedrock. Soil shear stiffness contrast has been changed as a function of the shear wave velocities V s and V s2 of the two layers, in order to reroduce a subsoil of tye D or C (D.M ). Poisson s ratio and mass density of the soil are: ν s =0.4, ρ s =.9 Mg/m³. The shear wave velocity of the rock is 200 m/s. The analyses have been erformed by adoting 8 Italian accelerograms (Table ) scaled in amlitude to rovide a rock eak acceleration consistent with the seismic zone considered. These records are rovided by the database SISMA (Scasserra et al., 2008). In Table, the frequency content of the inut motion is quantified through the redominant eriod T, corresonding to the maximum sectral acceleration in an acceleration resonse sectrum (comuted for 5% viscous daming) and through the mean eriod, T m, as defined by Rathje et al. (998) on the basis of the Fourier sectrum of the signal. Actually, T m should rovide a better indication of the frequency content of the recordings because it averages the sectrum over the whole eriod range of amlification. Figure 2. Reference scheme adoted in the analyses.

6 268 R. Cairo, E. Conte, G. Dente, S. Sica, A.L. Simonelli The main results of the whole arametric study, described elsewhere (Sica et al., 2007; Simonelli and Sica, 2008), are reorted in the following. It is worth noting that the behaviour of the soil-ile system is assumed to be linearly elastic. Table. Seismic records rovided by the database SISMA and used in the analyses. Label Station name Earthquake Com. Date (d/m/y) T (s) T m (s) A-TMZ270 Tolmezzo-Diga Ambiesta Friuli EW A-TMZ000 Tolmezzo-Diga Ambiesta Friuli NS A-STU270 Sturno Camano Lucano EW A-STU000 Sturno Camano Lucano NS A-AAL08 Assisi-Stallone Umbria Marche NS E-NCB090 Nocera Umbra-Biscontini Umbria Marche (aftershock) EW E.NCB000 Nocera Umbra-Biscontini Umbria Marche (aftershock) NS R-NCB090 Nocera Umbra-Biscontini Umbria Marche (aftershock) EW J-BCT000 Borgo-Cerreto Torre Umbria Marche (aftershock) NS J-BCT090 Borgo-Cerreto Torre Umbria Marche (aftershock) EW E-AAL08 Assisi-Stallone Umbria Marche (aftershock) EW B-BCT000 Borgo-Cerreto Torre Umbria Marche NS B-BCT090 Borgo-Cerreto Torre Umbria Marche EW TRT000 Tarcento Friuli (aftershock) NS C-NCB000 Nocera Umbra-Biscontini Umbria Marche (aftershock) NS C-NCB090 Nocera Umbra-Biscontini Umbria Marche (aftershock) EW R-NC2090 Nocera Umbra 2 Umbria Marche (aftershock) EW R-NC2000 Nocera Umbra 2 Umbria Marche (aftershock) NS Figure 3 resents the enveloes of the maximum kinematic bending moments with deth, as comuted in the time domain using the Winkler aroach by Mylonakis et al. (997), for each of the selected 8 accelerograms (scaled to the same eak ground acceleration of 0.35g). The thickness of the layers is assumed to be H =H 2 =5 m; the shear wave velocities of the uer and the lower layers are V s =00 m/s and V s2 =400 m/s, resectively. On the basis of the average shear wave velocity V s,30 =60 m/s, the soil rofile under consideration can be classified as tye D. The daming ratio of the soil is β s =0.0. Three grey zones are also dislayed corresonding to the range of reinforced concrete ile yielding moments for tyical reinforcements of the cross section (8φ6, 24φ2 and 2φ30) and magnitude of the axial force in the ile. For each reinforcement the lower limit of the grey zone reresents the cross section yielding moment corresonding to zero axial force while the higher one to an axial force equal to 200 kn. From the results of this study, the following remarks may be made: - the maximum kinematic bending moment generally occurs at the soil layer interface; - at the soil layer interface, the kinematic bending moment dramatically increases when the shear wave velocity contrast between the bottom and to layer Vs 2 /Vs increases from 2 to 4, for subsoil tyes D and C; - for subsoil rofiles corresonding to class D, the comuted kinematic bending moments may be well above the assumed yielding moments of the ile cross section.

7 Soil-Pile Kinematic Interaction: New Persectives for EC8 Imrovement 269 z (m) M kin (KN*m) V S =00 m/s; V S2 =400 m/s A-AAL08 A-STU000 2 A-STU270 ATMZ φ 6 2 φ 24 ATMZ270 B-BCT090 C-NCB090 E-NCB000 J-BCT000 R-NC2000 R-NCB090 B-BCT000 C-NCB000 E-AAL08 E-NCB090 J-BCT090 R-NC2090 Figure 3. Kinematic bending moments for two-layer soil rofile of tye D and with H =H 2 =5 m. 3. Effect of the frequency content of the earthquake As a further interretation of the results reviously shown, the ratio between the eriod T inut of the inut motion (in terms of T and T m ) and the fundamental eriod T soil of the subsoil in hand (in the secific case, T soil =0.62 s) is resented in Figure 4, for all the considered seismic records. It is worth noting that the accelerograms characterized by values of T /T soil or T m /T soil close to unity rovide the higher kinematic moments in Figure 3, due to the occurrence of a resonance henomenon. This confirms what ointed out by Nikolaou et al. (200) by frequency domain analyses: maximum effects of kinematic bending in iles occur at the fundamental eriod of the subsoil. Conversely, all accelerograms having T /T soil or T m /T soil below 0.5, induce lower kinematic moments in the ile. These results suggest that a critical band of the ratio T inut /T soil in which kinematic effects could be imortant, may be individuated (Figure 4). This observation could be a ossible criterion to select significant records from a database of local seismic events. Therefore, if the acceleration time-histories are rovided for a given seismic zone (in addition to the eak ground acceleration), the suscetibility of the site with the associated waveforms to induce significant kinematic bending in iles may be established on the basis of the following criterion: - if the ratio T inut /T soil is external to the critical band, site suscetibility is low, and only inertial interaction should be accounted for; - if the ratio T inut /T soil is internal to the critical band, site suscetibility is high, and kinematic interaction should be analysed in addition to inertial interaction. In the latter case, the analysis tool should be consistent to the one adoted in the design of the overall structure. 2 φ 30 TRT000

8 270 R. Cairo, E. Conte, G. Dente, S. Sica, A.L. Simonelli Tm/Tsoil T/Tsoil Tinut/Tsoil critical band A-AAL08 A-STU000 A-STU270 ATMZ000 ATMZ270 B-BCT000 B-BCT090 C-NCB000 C-NCB090 E-AAL08 E-NCB000 E-NCB090 J-BCT000 J-BCT090 R-NC2000 R-NC2090 R-NCB090 TRT000 Accelerogramma Figure 4. Ratio among the redominant eriod of the inut motion and the fundamental eriod of the soil. 3.2 Kinematic moments comuted with simlified methods The simlified methods rovided by Dobry and O Rourke (983), Mylonakis (200), and Nikolaou et al. (200) have been alied to comute the kinematic moments at the interface of the above secified two-layered subsoil, in order to comare their redictions to those obtained numerically by the BDWF aroach of Mylonakis et al. (997). The formulas by Dobry and O Rourke (983) and Mylonakis (200) have been alied by adoting both the shear strain at the bottom of the first layer γ rovided by Eq. (0) (Figure 5a) and the value of γ directly comuted with SHAKE (Schnabel et al., 972) or EERA (Bardet et al., 2000) for each selected accelerogram (Figure 5b). At the same way, the equation derived by Nikolaou et al. (200) has been alied by adoting both the shear stress at the interface using Eq. () as suggested by the authors (Figura 5a), and the value directly rovided by EERA (Figura 5b). The formula of Nikolaou et al. (200) has been alied without introducing any corrective factor η. From Figure 5a and 5b, it emerges that if literature closed-form solutions - Dobry and O Rourke (983), Mylonakis (200), and Nikolaou et al. (200) - are adoted with the values of γ and τ c rovided by the simlified aroaches, all formulas overestimate the kinematic moments with resect to the values comuted numerically by BDWF analyses. Conversely, if γ or τ c are derived from a free-field analysis, carried out with SHAKE or EERA, the kinematic moments rovided by the literature formulas are quite close to those comuted numerically (Figure 5b). Similar results have been obtained also by Maiorano et al. (2009). In short, it seems well-established that it is more suitable to aly the literature formulas for estimating ile kinematic moment at the interface in combination with free-field analyses (with SHAKE or EERA) in order to get the roer value of γ or τ c, esecially when the interface is quite dee. As well-known, in such case the formula rovided by Seed & Idriss (982) for comuting γ (or, equivalently, τ c ) is no longer reliable.

9 Soil-Pile Kinematic Interaction: New Persectives for EC8 Imrovement 27 Mkin (KN*m)l Numerical analyses BDWF (D=0%) Nikolaou et al. (200) Dobry&O'Rourke (983) Mylonakis (200) Mkin (KN*m)l 400 a) b) Numerical analyses BDWF (D=0%) Nikolaou et al. (200) Dobry&O'Rourke (983) Mylonakis chart (200) A-AAL08 A-STU000 A-STU270 ATMZ000 ATMZ270 B-BCT000 B-BCT090 C-NCB000 C-NCB090 E-AAL08 E-NCB000 Earthquake E-NCB090 J-BCT000 J-BCT090 R-NC2000 R-NC2090 R-NCB090 TRT A-AAL08 A-STU000 A-STU270 ATMZ000 ATMZ270 B-BCT000 B-BCT090 C-NCB000 C-NCB090 E-AAL08 E-NCB000 Earthquake E-NCB090 J-BCT000 J-BCT090 R-NC2000 R-NC2090 R-NCB090 TRT000 Figure 5. Kinematic moment at the interface comuted with aroximate formulas and the BDWF model. 3.3 An alternative simlified aroach Recently, Cairo et al. (2009) have suggested an alternative rocedure that may be romtly used in current ractice. This rocedure (that is fully analytical) is very simle to use and needs only two arameters for defining the seismic motion: the eak ground acceleration and the mean eriod of the excitation. The former is directly rovided by the code; the latter may be assumed on the basis of some suitable regression equations available in the literature (Rathje et al., 2004; Ausilio et al., 2007). In the roosed rocedure, Eq. (8) by Nikolaou et al. (200) has been considered the most suitable, and a corrective factor δ has been introduced. This latter is defined as the ratio of the maximum ile bending moment in the time domain, calculated using the BEM aroach develoed by Cairo and Dente (2007), to the kinematic moment obtained by Eq. (8), in which the eak ground acceleration is comuted by site resonse analyses. The results of Figure 6 show the factor δ, calculated with reference to the case-studies reviously documented, versus the ratio T /T m of the fundamental eriod of the soil deosit to the mean eriod of the seismic excitation. A linear relationshi between δ and T /T m can be obtained with reference to the 95 th ercentile of the distribution. This line is described by the following exression: T δ = (2) T m This relation may be considered to evaluate the exected maximum bending moment. As a first aroximation (Mylonakis, 200) the fundamental eriod of the deosit may be evaluated by the equation: 4H T = (3) where H and V s are the first layer thickness and shear wave velocity, resectively. Therefore, the maximum ile bending moment M kin at the interface between two soil layers may be comuted by: V s M kin = δ M (4) with δ and M rovided by Eq. (2) and Eq. (8), resectively.

10 272 R. Cairo, E. Conte, G. Dente, S. Sica, A.L. Simonelli As an examle, this rocedure has been alied to a case-study roosed by Nikolaou and Gazetas (997) and recalled by Cairo and Dente (2007). A concrete ile is embedded 9.5 m into a to layer of soft clay and 6 m into a dee layer of dense sand. The shear wave velocities for the uer and lower layers are 80 and 330 m/s, resectively. The soil deosit is 30 m thick and rests on a rigid bedrock. The ile has E =25 GPa, d=.3m, L=5.5 m, ρ =2.5 Mg/m 3. Two actual accelerograms, scaled to 0.0g eak acceleration, have been used as excitation at the rock level. In Figure 7 the results obtained by Eq. (4) are comared with the enveloes of the eak moments comuted by Nikolaou and Gazetas (997) and by Cairo and Dente (2007) using different methods. As can be seen, the agreement between the results is quite satisfactory. δ T /T m Figure 6. Corrective factor δ as a function of the ratio of the fundamental eriod T of the soil deosit to the mean eriod T m of the earthquakes. M (MNm) 0 2 M (MNm) JMA, Kobe 0 Anderson, Loma Prieta 4 4 z (m) z (m) this study Cairo and Dente (2007) Nikolaou and Gazetas (997) Figure 7. Enveloes of time-domain moments in a ile and eak kinematic moments at the interface. 4 CONCLUSIONS In the aer some of the results from a comrehensive arametric study erformed on a single fixed-head ile, embedded in two-layered soil deosits, have been illustrated. The analyses have been carried out using the Winkler-tye model rovided by Mylonakis et al. (997), the

11 Soil-Pile Kinematic Interaction: New Persectives for EC8 Imrovement 273 BEM formulation develoed by Cairo and Dente (2007), and some simlified closed-form exressions available in the secific literature for evaluating, in an aroximate manner, the maximum kinematic moment in the ile at the interface between two soil layers. Italian seismic records have been used as inut motion for the numerical analyses. From the obtained results, the following conclusions may be drawn: - in high seismicity zones and esecially for subsoil tye D, kinematic bending moments may be very high deending on the stiffness contrast between consecutive layers; - the maximum effects of kinematic ile bending generally occur for inut motions having the fundamental eriod close to that of the subsoil; - the simlified methods here examined (Dobry and O Rourke, 983; Mylonakis, 200; Nikolaou et al., 200) tend to redict conservative moments at the subsoil interface, esecially when the interface is dee. In such case it is better their use in combination with free-field resonse analyses to get redictions closer to the ones obtained from more rigorous aroaches. On the basis of these observations, a simle criterion has been suggested to roughly estimate site suscetibility to induce significant kinematic bending in iles, and a simlified rocedure for crudely evaluating kinematic moment has been resented. Yet, caution is required before roosing suggestions to be incororated into seismic building codes. The theoretical evidence derived from the analysis needs to be extended to a wider selection of schemes, and to be comared with further exerimental evidence. 5 ACKNOWLEDGEMENTS The work resented in this aer is art of the ReLUIS Research Project Innovative methods for the design of geotechnical systems, romoted and funded by the Deartment of Civil Protection (DPC) of the Italian Government and coordinated by the AGI (Italian Geotechnical Association). The contribution of the Italian Ministry of University, through the research roject Seismic resonse of ile foundations and seismic sloe stability (PRIN 2007) is also acknowledge. 6 REFERENCES Ausilio E., Costanzo A., Silvestri F., Troeano G. (2009). Valutazione della stabilità sismica di endii naturali mediante un aroccio semlificato agli sostamenti, XIII Convegno ANIDIS, L Ingegneria Sismica in Italia, Bologna (in Italian; in ress). Bardet J.P., Ichii K., Lin C.H. (2000). EERA: A comuter rogram for equivalent-linear earthquake site resonse analyses of layered soil deosits, Deartment of Civil Engineering, University of Southern California. Boulanger R.W., Curras C.J., Kutter B.L., Wilson D.W., Abghari A. (999). Seismic soil-ile-structure interaction exeriments and analyses, Journal of Geotechnical Engineering, ASCE, 25, ASCE, 25: Cai Y.X., Gould, P.L. Desai C.S. (2000). Nonlinear analysis of 3-D seismic interaction of soil-ilestructure systems and alication, Engineering Structures, 22: Cairo R., Conte E., Cosimo V.A., Dente G. (2009). Analisi dell interazione cinematica alo-terreno, XIII Convegno ANIDIS, L Ingegneria Sismica in Italia, Bologna (in Italian; in ress). Cairo R., Conte E., Dente G. (2008). Nonlinear seismic resonse of single iles, Seismic Engng. Conf. commemorating the 908 Messina and Reggio Calabria Earthquake (MERCEA 08), Reggio Calabria, AIP, Melville, N.Y., Vol.,

12 274 R. Cairo, E. Conte, G. Dente, S. Sica, A.L. Simonelli Cairo R., Dente G. (2007). Kinematic interaction analysis of iles in layered soils, ISSMGE-ERTC 2 Worksho Geotechnical Asects of EC8, Madrid, Pàtron Editore, Bologna, aer No. 3. D.M del Ministero delle Infrastrutture. Nuove norme tecniche er le costruzioni. S.O. n. 30 alla G.U. del , No. 29. Dobry R., O Rourke M.J. (983). Discussion on Seismic resonse of end-bearing iles by Flores- Berrones R. and Whitman R.V., Journal of Geotechnical Engineering, ASCE, 09. El Naggar M.H., Shayanfar M.A., Kimiaei M., Aghakouchak A.A. (2005). Simlified BNWF model for nonlinear seismic resonse analysis of offshore iles with nonlinear inut ground motion analysis, Canadian Geotechnical Journal, 42: EN Eurocode 8: Design of structures for earthquake resistance Part 5: Foundations, retaining structures and geotechnical asects. CEN Euroean Committee for Standardization, Bruxelles, Belgium. Fan K., Gazetas, G., Kaynia, A., Kausel, E., Ahmad, S. (99). Kinematic seismic resonse of single ile and ile grous, Journal of Geotechnical Engineering, ASCE, 7(2): Flores-Berrones R., Whitman R.V. (982). Seismic resonse of end-bearing iles, Journal of Geotechnical Engineering, ASCE, 08(4): Gazetas G., Dobry R. (984). Simle radiation daming model for iles and footings, Journal of Engineering Mechanics, ASCE, 0(6): Gazetas G., Fan K., Tazoh T., Shimizu K., Kavvadas M., Makris N. (992). Seismic ile-grou-structure interaction, Piles under dynamic loads, Geotechnical secial ublication No. 34, ASCE: Kavvadas M., Gazetas G.. (993). Kinematic seismic resonse and bending of free-head iles in layered soil, Géotechnique, 43(2): Kaynia A.M., Kausel, E. (982). Dynamic behavior of ile grous, 2 nd Int. Conf. on Numerical Methods in Offshore Piling, Austin, Texas, Kaynia A.M., Mahzooni S. (996). Forces in ile foundations under seismic loading, Journal of Engineering Mechanics, ASCE, 22(): Kimura M., Zhang F. (2000). Seismic evaluation of ile foundations with three different methods based on 3D elasto-lastic finite element analysis, Soils and Foundations, 40: Maheshwari B.K., Truman K.Z., El Naggar M.H., Gould P.L. (2004). Three-dimensional finite element nonlinear dynamic analysis of ile grous for lateral transient and seismic excitations, Canadian Geotechnical Journal, 4: Maheshwari B.K., Watanabe H. (2006). Nonlinear dynamic behavior of ile foundations: effects of searation at the soil-ile interface, Soils and Foundations, 46: Maiorano R.M.S., de Sanctis L., Aversa S., Mandolini A. (2009). Kinematic resonse analysis of iled foundations under seismic excitation, Canadian Geotechnical Journal, 46(5): Mamoon S.M., Banerjee P.K. (990). Resonse of iles and ile grous to travelling SH waves, Earthquake Engineering and Structural Dynamics, 9(4): Mylonakis G. (200). Simlified model for seismic ile bending at soil layer interfaces, Soils and Foundations, 4(4): Mylonakis G., Nikolaou A., Gazetas G. (997). Soil-ile-bridge seismic interaction: kinematic and inertial effects. Part : soft soil, Earthquake Engineering and Structural Dynamics, 26: Nikolaou A., Gazetas G. (997). Seismic design rocedure for kinematically stressed iles, Seismic behaviour of ground and geotechnical structures, Seco & Pinto (eds.), Balkema, Rotterdam, Nikolaou S., Mylonakis G., Gazetas G., Tazoh T. (200). Kinematic ile bending during earthquakes: analysis and field measurements, Géotechnique, 5(5): Novak M. (974). Dynamic stiffness and daming of iles, Canadian Geotechnical Journal, : Poulos H.G., Tabesh A. (996). Seismic resonse of ile foundations Some imortant factors, th WCEE, Acaulco, aer No Randolh M.F. (98). The resonse of flexible iles to lateral loading, Géotechnique, 3(2): Rathje M., Abrahamson N.A., Bray J.D. (998). Simlified frequency content estimates of earthquake ground motions, Journal of Geotechnical Engineering, ASCE, 24(2):

13 Soil-Pile Kinematic Interaction: New Persectives for EC8 Imrovement 275 Rathje M., Faraj F., Russell S., Bray J.D. (2004). Emirical relationshis for frequency content arameters of earthquake ground motions, Earthquake Sectra, Earthquake Engineering Research Institute, 20(): Saitoh M. (2005). Fixed-head ile bending by kinematic interaction and criteria for its minimization at otimal ile radius, Journal of Geotechnical Engineering, ASCE, 3(0): Scasserra G., Lanzo G., Stewart J.P., D Elia B. (2008). SISMA (Site of Italian Strong-Motion Accelerograms): a web-database of ground motion recordings for engineering alications, Seismic Engng. Conf. commemorating the 908 Messina and Reggio Calabria Earthquake, Reggio Calabria, AIP, Melville, N.Y., Vol. 2, ; htt://sisma.dsg.uniroma.it. Schnabel P.B., Lysmer J., Seed H.B. (972). SHAKE: A comuter rogram for earthquake resonse analysis of horizontally layered sites, Reort No. EERC 72-2 Earthquake Engineering Research Center, University of California, Berkeley, California. Seed H.B., Idriss I.M. (982). Ground motions and soil liquefaction during earthquakes, Earthquake Engineering Research Institute, Berkeley, California. Sica S., Mylonakis G., Simonelli A.L. (2007). Kinematic bending of iles: analysis vs. code rovisions, 4 th Inter. Conf. on Earthquake Geotechnical Engineering, Greece, aer No Simonelli A.L., Sica S. (2008). Fondazioni rofonde sotto azioni sismiche, Oere Geotecniche in Condizioni Sismiche, Pàtron Editore, Bologna, Italy, Chater, (in Italian). Wu G., Finn W.D.L. (997). Dynamic nonlinear analysis of ile foundations using finite element method in the time domain, Canadian Geotechnical Journal, 34():