Reinforcement_Article_Mohanad_2019

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Jordan Journal of Civil Engineering Volume 13 No. 2 2019 - 197 - © 2019 JUST. All Rights Reserved. Reinforcement of the Seismic Interaction of Soil-Damaged Piles-Bridge by Using Micropiles Mohanad Talal Alfach Faculty of Science and Engineering School of Architecture and Built Environment University of Wolverhampton UK. E-Mail: mohanad.alfachwlv.ac.uk ABSTRACT This paper presents a three-dimensional numerical model of soil-damaged piles-bridge interaction under seismic loading. This study focuses on the effect of developing plastic hinges in piles’ foundation on the seismic behavior of the system. Several field investigations on seismic damages due to recent strong earthquakes have confirmed the decisive role of the plastic hinges in the piles in the seismic behavior of the system. In particular this study is interested in evaluating the proposed approach for strengthening the system of soil-damaged piles- bridge. The proposed approach is based on using micropiles significantly promoting the flexibility and ductility of the system. This study was carried out using a three-dimensional finite differences’ modeling program FLAC 3D. The results confirmed the considerable effect of developing concrete plasticity in the piles’ foundation which reflects in changing the distribution of internal forces between the piles. Results show the efficiency of using micropiles as a reinforcement system. The detailed analysis of the micropiles’ parameters shows a slight effect of pile-micropile spacing. The use of inclined micropiles leads to attenuation of internal forces induced in the piles and the micropiles themselves. KEYWORDS: Interaction Piles Concrete Seismic design Plasticity Three-dimensional modeling Micropiles. INTRODUCTION Often piles ensure the stability of structures located in seismic zones but under strong seismic loadings they are subject to efforts exceeding the allowable limit of seismic resistance. These efforts are particularly dangerous when the piles are installed in nonlinear soil. Post-seismic observations and analysis showed the fundamental role of soil-foundation-superstructure in determining the seismic damage suffered by piles and structures Kagawa 1980 Mizuno 1987 Boulanger et al. 1998-1999 Miura 2002 …. In case of strong seismic loading nonlinearities of the soil and the structure can play a decisive role. During seismic loading with high intensity plastic hinges probably develop in the piles. In the literature there are several models of concrete behaviour particularly the elastic- perfectly plastic model other damage models may take into account the reduction in elastic rigidity and development of irreversible deformations. In seismic design the development of plastic hinges is allowed in specific locations in heads as example. In fact these plastic hinges will absorb the oscillation induced by the seismic loading and thereby limit the resultant stresses. In this study we analyze the influence of these plastic hinges on the seismic response of the system. The plasticity of the concrete piles is governed by a plastic Received on 15/6/2018. Accepted for Publication on 8/1/2019.

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Reinforcement of the Seismic Interaction… Mohanad Talal Alfach - 198 - moment M p which is the maximum allowable bending moment of the pile. Cakir and Mohammed 2013 studied the seismic retrofitting of historical masonry bridges using micropiles and the seismic performance of this technique. Likewise Momenzadeh et al. 2013 confirmed the micropiles’ seismic retrofit efficiency in poor soil conditions with high structural load demands of the San Francisco Bay area bridge. Furthermore Doshi et al. 2017 have analyzed the seismic behavior of soil-piles-micropiles-bridge and confirmed the beneficial effect of the added micropiles in reducing settlement bending moment and shear force. Ousta and Shahrour 2001 studied the seismic behavior of micropiles in saturated soils. Sadek and Shahrour 2003 showed that the inclination of micropiles results in an improvement of lateral stiffness bending moment and axial force. Alsaleh and shahrour 2006 confirmed that nonlinearities of the soil and micropile-soil interface have a significant effect on the seismic response of the micropiles’ group as well as that of the structure. The research conducted in this study provides a thorough analysis of the soil-pile-bridge under seismic loading. Particular attention is paid to the influence of nonlinearity of concrete piles and the behavior of soil- pile-bridge reinforced by adding a group of micropiles. The study is carried out using a three-dimensional model by means of the calculation code Flac 3D. Soil-Pile Structure System and Numerical Model The model consists of a group of piles implanted in soil. The modeling of the behavior of such system under seismic loading requires specific methods to take into consideration the interaction between those different components namely the soil-piles pile-pile piles –cap interaction and all piles-cap-soil with the structure. The boundaries of the model should be put sufficiently away from the structure to minimize the effect of wave reflection which leads to a dense mesh. To overcome this difficulty we use specific borders which prevent the waves from reflecting on the model. FLAC 3D is used in this study. This code uses the Lagrangian representation of movement. It is based on the explicit finite difference method to solve the equations of dynamic equilibrium. Reference Example Elastic The reference example consist of a group of 23 floating piles with length L p 10.5 m. The group is implanted into a layer of homogeneous soil with a depth of 15 m and embedded in a cap of 1 m thickness Figure 1. The characteristics of soil piles and superstructure are given in Tables 1 and 2. The mechanical and geometrical characteristics of the reference example are plotted in Figure 1.a. The pile heads D p 80 cm are embedded in a cap of thickness e c 1m with rigid contact spacing between piles is S 3.75D p 3 m. To avoid the complexity of soil-cap interaction the cap was placed 0.5 m above the soil. In this reference example the behavior of soil-pile- structure is assumed to be elastic with Rayleigh damping for the soil the factor of damping used is 5 for the soil and 2 for the structure. The fundamental frequency of soil is 0.67 Hz. The superstructure is modeled by a column which supports a lumped mass in its head M350 tons. The rigidity of the superstructure and its frequency assumed fixed at the base are equal to K st 86840 kN/m and F st 2.5 Hz. They were determined by the following expressions: The frequency of the superstructure taking into consideration the soil-structure interaction is f st flex 1.1 Hz including SSI.

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Jordan Journal of Civil Engineering Volume 13 No. 2 2019 - 199 - Table 1. The elastic property of the soil and piles’ materials Table 2. The elastic property of the superstructure  E and  are the density Young modulus and coefficient of Poisson. ζ is the factor of damping. D p is the pile diameter. EA and EI are the axial and bending stiffness. The used mesh shown in Figure 1.b includes 3856 zones of 8 nodes and 138 three-dimensional beams of 2 nodes. The mesh was refined around the piles and near the superstructure where inertial forces induce high stresses. a System geometry Seismic loading S375 Dp3 m S 4 m 10 m 1 m 1 m Mst350 T f st flexible 1 Hz Superstructure 05 m Pile Cap Dp80 cm x y z

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Reinforcement of the Seismic Interaction… Mohanad Talal Alfach - 200 - b 3D numerical mesh with absorbing boundaries 138 beam elements and 6978 nodes Figure 1: Problem under consideration Seismic Loading Real The seismic loading chosen in this research is the one recorded in Kocaeli Turkey on 17/08/1999 Station AMBARLI KOERI source. The seismic loading is applied as a speed at the base of the soil as shown in Figure 2. The maximum amplitude of this loading is 40 cm/s maximum acceleration 0.247 g. The spectrum of Fourier corresponds to the used seismic loading illustrated in Figure 2. We note that the frequencies involved are less than 3 Hz with a maximum peak for F 0.9 Hz which is between the fundamental frequency of the soil F1 0.67 Hz and the frequency of the structure Fss 1.1 Hz. Also note that a first peak is observed for frequency F 0.6 Hz which is very close to the fundamental frequency of the soil. Figure 2: Kocaeli earthquake record 1999 a displacement b velocity c acceleration d Fourier spectra of velocity component 15  60 m   40  m

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Jordan Journal of Civil Engineering Volume 13 No. 2 2019 - 201 - Table 3 shows the efforts induced in the piles under Kocaeli earthquake loading. In order to compare the obtained results the induced efforts are normalized to inertial forces of the superstructure as follows: Table 3. Reference example: response of a group of 23 piles under Turkey loading 1999 Seismic Loading ɑst m/s² ɑCap m/s² Internal Forces Normalized Forces Central Piles Corner Piles Corner Piles Tmax kN Mmax kN.m Tmax kN Mmax kN.m Tmax Mmax Turkey 11.28 8.385 675.8 954.4 1016.1 1099 0.196 0.05 ∗ ∗ where: m st : the bending moment at the base of the superstructure. T cap and  st denote the shear force induced at the cap and the acceleration of the superstructure mass. H st : superstructure height. Influence of Nonlinearity of Concrete Piles Results The numerical simulations were carried out for the case of frictional soil C2 kPa φ30° 20° under seismic loading recorded in Turkey 1999 with maximum amplitude V max 0.4 m/s. The results obtained in the case of linear behavior of concrete piles were compared with the results obtained for elasto- plastic behavior of the piles and plastic bending moment M p 500 kN.m which is the maximum moment the piles can support. The results show a significant decrease in the internal forces induced in the piles with the nonlinear behavior of the piles. This result is confirmed in Figure 3 and Table 4. The acceleration of the superstructure for elastic pile behavior is 23.5 higher than that obtained for elastoplastic behavior. The comparison of elastic and elastoplastic responses Table 4 reveals a reverse trend for the acceleration at the cap. The profile of bending moment shows that plasticity has attained over a large part of the pile and is not located only in the pile head plastic hinge. This result shows that the collapse of the structure is very probable with the elastoplastic behavior of the piles. On the other hand we note that only in case of nonlinear behavior of the piles we obtain a reduction of maximum normal forces by about 24.6 and 34 for maximum shear forces in external piles. Also there is an attenuation in the spectral amplitude of the structure velocity as shown in Figure 4. This is due to the damping induced by the plasticity of the piles. It is important to note that the presence of plasticity in the piles influences the distribution of the maximum shear forces between the central and external piles. Table 4. Influence of nonlinear behavior of concrete pile on dynamic forces in piles frictional soil earthquake of Turkey Vg 40 cm/s Model Concrete ɑst m/s 2 ɑCap m/s 2 Dynamic Forces Normalized Forces Central Piles Corner Piles Corner Piles Nmax kN Tmax kN Mmax kN.m Nmax kN Tmax kN Mmax kN.m Tmax Mmax Elastic 9.567 6.592 38.2 511.7 897.9 1840.2 917.3 1140 0.211 0.062 Plastic Mp500 kN.m 7.744 8.327 38.8 450.8 500 1386.2 604.1 500 0.154 0.033

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Reinforcement of the Seismic Interaction… Mohanad Talal Alfach - 202 - Figure 3: Influence of nonlinear behavior of concrete pile on dynamic forces in the corner piles frictional soil earthquake of Turkey Vg 40 cm/s Figure 4: Influence of nonlinear behavior of concrete pile on the superstructure head spectral velocity Fourier spectra diagram frictional soil earthquake of Turkey Vg 40 cm/s 0 0.01 0.02 0.03 0.04 0.05 0.06 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Fréquence HZ Amplitude béton élastique béton p Mp500 KN.m Elastic Behavior of Concrete Plastic Behavior of Concrete pile Mp500 KN.m Frequency Hz 0 2 4 6 8 10 12 0 200 400 600 800 1000 1200 M KN.m H m béton élastique béton p Mp500 KN.m Elastic behavior of concrete Plastic behavior of concrete Mp 500 KN.m 0 2 4 6 8 10 12 0 200 400 600 800 1000 T KN H m béton élastique béton p Mp500 KN.m Elastic Behavior of Concrete Plastic Behavior of Concrete Mp 500 KN.m a Bending Moment b Shear Force

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Jordan Journal of Civil Engineering Volume 13 No. 2 2019 - 203 - Piles’ Interaction Reinforcement The site observations of Lizzi and Carnevale 1981 Pearlman et al. 1993 Mason 1993 Herbst 1994 as well as recent research have demonstrated that the micropiles’ system constitutes a reliable tool as reinforcement technique for existing structures. The facility of installation especially in difficult access locations represents its main asset. The use of such system in seismic sites provides great benefits because this system of foundations is characterized by good flexibility and ductility which are very appreciated properties for structures exposed to seismic risks. In the field of numerical modeling the main research on the seismic behavior of micropiles focused on their use as foundation of new structures Sadek 2003 Al Saleh 2006. In this part we examine the response of soil-pile- structure system reinforced by a group of micropiles. The model used is an identical system to that previously studied with a foundation of 6 piles that will be reinforced by a group of 4 micropiles 22. The micropiles’ diameter is D m 0.25 m Figure 5. The implementation of the reinforcement solution used takes place by enlarging the existing cap in which the micropiles will be built in order to rigidify the foundation system. The interface between the piles or micropiles and the soil is supposed elastic. The calculations were carried out with assuming the value of piles’ plastic moment M p 500 kN.m. The applied loading is the record of Turkey 1999 but with a maximum amplitude V max 0.6 m/sec. This amplitude was chosen in order to induce the development of plasticity over a large part of the piles which justifies the reinforcement. The soil characteristics are identical to those used in the previous sections frictional soil: C2 kPa φ30° 20°. In order to limit the number of reinforcement elements 4 elements and perform a qualitative analysis the behavior of the micropiles will be assumed to be linear elastic even if the induced forces exceed their bearing capacity. For a real study the number of micropiles must be optimized according to applied seismic loading. Figure 5: Micropile reinforcement scheme S375 D3 m Superstructure Dp80 cm 4 m 10 m 05 m 05 m x Seismic Loading Piles 1m S375D3 m Mst350 T Cap y 3m Sm Dm025 m 15 m Micropiles

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Reinforcement of the Seismic Interaction… Mohanad Talal Alfach - 204 - Effect of Pile-Micropile Spacing In order to analyze the influence of pile-micropile spacing on the seismic response of the system numerical simulations were carried out for several values of pile-micropile spacing S m 1.5 2 and 3 m. Tables 5 and 6 and Figure 6 give the results of the comparison between system response before and after reinforcement for several pile-micropile spacings. Firstly it is noted that reinforcement with micropiles can constitute an effective reinforcement solution. In fact there is a strong reduction in the internal forces in the piles after reinforcement. Figure 6 compares the bending moment envelopes in the piles with and without reinforcement. After reinforcement we note that the plasticized area of the pile is reduced to a point located at the head of the pile which can be accepted by seismic codes and does not jeopardize the structure. Furthermore it can be seen that the maximum bending moment decreases with the increase of pile-micropile spacing. A similar tendency is observed for the shear force envelope in the pile. The reinforcement incites a reduction of the normal force by about 45 in the pile head. The influence of pile-micropile spacing is not very significant despite a small decrease of the internal forces with the spacing increase. In terms of the normal forces induced in the piles the reinforcement was very beneficial in reducing the forces taken by the piles. In fact a 75 attenuation of the maximum normal force in the piles after reinforcement is obtained. However the influence of pile-micropile spacing on the normal force in the piles is not important but it incites a significant attenuation of normal force in the micropiles. By examining the spectral response of the velocity at the top of the superstructure Figure 7 we note a decrease in the maximum amplitude with the increase of pile- micropile spacing. This reflects an increase in the stiffness of the structure and explains the reduction of the dynamic forces in the piles. This result agrees with those obtained by Sadek 2003 concerning the increase in the rigidity of the system and the reduction of the lateral amplification with the spacing. Figure 8 shows the envelope of the bending moment and shear force induced in the micropiles under seismic loading. It can be seen that the spacing does not have a significant effect on the distribution of these forces. These results confirm the measurements performed in centrifuges by Fukui et al. 2001. Table 5. Influence of nonlinear behavior of concrete pile on dynamic forces in piles Model Concrete Mp 500 kN.m Acc mass m/s 2 Acc Cap m/s 2 Dynamic Forces Central Piles Corner Piles Nmax kN Tmax kN Mmax kN.m Nmax kN Tmax kN Mmax kN.m Before reinforcement 8.712 14.25 36.3 489.1 500 1553.2 691.5 500 After reinforcement S1.5 m 8.432 8.4 8.6 289.1 500 376 359.6 500 After reinforcement S2 m 8.358 8.759 0.5 281.9 500 422.6 339.7 500 After reinforcement S3 m 7.608 8.131 0.4 247.2 500 331 291 500

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Jordan Journal of Civil Engineering Volume 13 No. 2 2019 - 205 - Table 6. Influence of pile-micropile spacing on the dynamic forces in the reinforcing micropiles Model Dynamic Forces Micropile Nmax kN Tmax kN Mmax kN.m S1.5 m 984 602.7 1090 S2 m 841.3 596.6 1080 S3 m 594 491.4 926.8 Figure 6: Influence of pile-micropile spacing on dynamic forces in the corner piles 0 2 4 6 8 10 12 0 100 200 300 400 500 600 M KN.m H m avant le renforcement aprèsS1.5 m après S2 m après S3 m Before reinforcement After After After 0 2 4 6 8 10 12 0 100 200 300 400 500 600 700 800 T KN H m avant le renforcement après S1.5 m après S2 m après S3 m After After After Before Reinforcement a Bending Moment b Shear Force

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Reinforcement of the Seismic Interaction… Mohanad Talal Alfach - 206 - Figure 7: Influence of pile-micropile spacing on the superstructure head spectral velocity Figure 8: Influence of pile-micropile spacing on the dynamic forces in the reinforcing micropiles 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0 0.5 1 1.5 2 2.5 3 Fréquence Hz Amplitude avant le renforcement après S1.5 m après S2 m après S3 m Before reinforcement After After After Frequency Hz 0 2 4 6 8 10 12 0 200 400 600 800 1000 1200 M KN.m H m S1.5 m S2 m S3 m 0 2 4 6 8 10 12 0 100 200 300 400 500 600 700 T KN H m S1.5 m S2 m S3 m a Bending Moment b Shear Force

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Jordan Journal of Civil Engineering Volume 13 No. 2 2019 - 207 - Effect of Micropile Connection In this section we propose to analyze the effect of the micropile-cap connection on the seismic response of the system. Two types of connection are studied: fixed and articulated. The analysis is carried out for pile- micropile spacing S2 m. Figures 9 and 10 and Tables 7 and 8 present the results obtained for the two studied cases. By checking the induced forces in the piles we note that reinforcement by fixed micropiles reveals better efficiency in comparison with articulated micropiles. For articulated micropiles the plastic moment has attained the upper quarter of the pile. Furthermore the maximum shear force of the piles obtained in the case of articulated micropiles is higher by 25-35 than the one obtained in the case of reinforcement by fixed micropiles. This result is accompanied by the increase of cap acceleration which reflects lower rigidity for the system in the case of reinforcement with articulated micropiles. The normal effort shows comparable maximum values in both cases fixed articulated. Concerning the internal forces developed in the micropiles the presence of articulation permits to relieve the induced internal forces in the pile head. In that case the maximum moment obtained at a depth of 2 m of the micropile is considerably less than that developed at the top of the fixed micropiles M1080 kN.m. This result is consistent with the results found by Sadek 2003. The profile of the shear force also shows a decrease in the case of articulated micropiles which is not in favor of the internal forces induced in the existing piles. Table 7. Influence of micropile/shear connection on the dynamic forces in the piles frictional soil φ30° C2 kPa ψ20° earthquake of Turkey Vg 60 cm/s Model Concrete Mp 500kN.m Acc mass m/s 2 Acc Cap m/s 2 Dynamic Forces Central Piles Corner Piles Nmax kN Tmax kN Mmax kN.m Nmax kN Tmax kN Mmax kN.m Fixed Micropiles 8.358 8.759 0.5 281.9 500 422.6 339.7 500 Articulated Micropiles 8.179 14.28 18.7 381.2 500 406.1 499.4 500 Table 8. Influence of micropile/shear connection on the dynamic forces in the micropiles frictional soil φ30° C2 kPa ψ20° earthquake of Turkey Vg 60 cm/s Model Dynamic Forces Nmax kN Tmax kN Mmax kN.m Fixed 841.3 596.6 1080 Articulated 655.8 359 529.7

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Reinforcement of the Seismic Interaction… Mohanad Talal Alfach - 208 - Figure 9: Influence of micropile/shear connection on the dynamic forces in the corner piles frictional soil φ30° C2 kPa ψ20° earthquake of Turkey Vg 60 cm/s Figure 10: Influence of micropile/shear connection on the dynamic forces in the micropiles frictional soil φ30° C2 kPa ψ20° earthquake of Turkey Vg 60 cm/s 0 2 4 6 8 10 12 0 100 200 300 400 500 600 M KN.m H m avant le renforcement micropieux encastrés micropieux articulés Before reinforcement Fixed micropiles Articulated micropiles Before reinforcement Fixed micropiles Articulated 0 2 4 6 8 10 12 0 100 200 300 400 500 600 700 800 T KN H m avant le renforcement micropieux encastrés micropieux articulés Before reinforcement Fixed micropiles Articulated micropiles a Bending Moment b Shear Force 0 2 4 6 8 10 12 0 100 200 300 400 500 600 700 T KN H m micropieux encastrés micropieux articulés Fixed micropiles Articulated micropiles 0 2 4 6 8 10 12 0 200 400 600 800 1000 1200 M KN.m H m micropieux encastrés micropieux articulés Fixed micropiles Articulated micropiles a Bending Moment b Shear Force

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Jordan Journal of Civil Engineering Volume 13 No. 2 2019 - 209 - Effect of inclination of the micropiles In this section we are interested in the analysis of the effect of the inclination of the micropiles which can be beneficial as already reported by Sadek 2003 and Al Saleh 2006 for micropiles used as new foundations. We study the influence of inclination on the response of the existing structure superstructure + piles as well as on the response of the micropiles themselves. The soil- pile and soil-micropile connections are assumed to be perfectly rigid. Figures 11 and 12 and Tables 9 and 10 present the results of numerical simulations carried out for two inclinations of the micropiles α 0° and α 15° in the case of frictional soil C2 kPa φ30° ψ20°. In the case of inclined micropiles we note a considerable decrease in the shear force accompanied by an attenuation in the lateral acceleration at the superstructure and the cap. This decrease in the shear force is in the order of 30 compared with the vertical reinforcement. Concerning the bending moment in the piles the plastic moment has attained at the pile heads in both cases In the case of inclined micropiles a significant attenuation is observed in the upper half of the piles. The inclination is also very beneficial for the normal force induced in the piles where a considerable reduction of the normal force is obtained. This beneficial effect of the inclination confirms the results of the tests carried out in centrifuges by Fukui et al. 2001. By examining the forces induced in the reinforcing micropiles it can be seen that the inclination of the micropiles results in a significant reduction in the maximum shear force and bending moment. This reduction attains 53 for the shear force and 42 for the bending moment which significantly improves the strength of the reinforcement elements without jeopardizing the existing piles. It should be noted that the inclination of the micropiles leads to a moderate increase 15 of the normal force in the micropiles. Table 9. Influence of inclination of the micropiles on the dynamic forces in the piles frictional soil φ30° C2 kPa ψ20° earthquake of Turkey Vg 60 cm/s α ° Acc mass m/s 2 Acc Cap m/s 2 Dynamic Forces Central Piles Corner Piles Nmax kN Tmax kN Mmax kN.m Nmax kN Tmax kN Mmax kN.m 0 8.358 8.759 0.5 281.9 500 422.6 329.7 500 15 6.473 6.897 0.3 206.5 500 126 231.9 500 Table 10. Influence of inclination of the micropiles on the dynamic forces in the micropiles frictional soil φ30° C2 kPa ψ20° earthquake of Turkey Vg 60 cm/s α ° Dynamic Forces Nmax kN Tmax kN Mmax kN.m 0 841.3 596.6 1080 15 978.5 276 624

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Reinforcement of the Seismic Interaction… Mohanad Talal Alfach - 210 - Figure 11: Influence of inclination of the micropiles on the dynamic forces in the corner piles frictional soil φ30° C2 kPa ψ20° earthquake of Turkey Vg 60 cm/s Figure 12: Influence of inclination of the micropiles on the dynamic forces in the micropiles frictional soil φ30° C2 kPa ψ20° earthquake of Turkey Vg 60 cm/s 0 2 4 6 8 10 12 0 100 200 300 400 500 600 M KN.m H m α 0° α 15° 0 2 4 6 8 10 12 0 50 100 150 200 250 300 350 T KN H m α 0° α 15° 0 2 4 6 8 10 12 0 100 200 300 400 500 600 700 T KN H m α 0° α 15° 0 2 4 6 8 10 12 0 200 400 600 800 1000 1200 M KN.m H m α 0° α 15°

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Jordan Journal of Civil Engineering Volume 13 No. 2 2019 - 211 - CONCLUSIONS This study was devoted to global numerical modeling of soil-pile-bridge interaction problem under seismic loading. Attention was particularly given to the influence of soil nonlinearity and development of plastic hinges in piles. The research within the domain of this study was conducted using a three-dimensional finite differences’ modeling program FLAC 3D. The consideration of non-linear behavior of concrete is important especially if the bearing capacity of the concrete is likely to be exceeded. It permits better prediction of system failure under any load. The development of plastic hinges leads to an attenuation of the overall response of the system. It is found that the plasticizing of the piles changes the report of distribution of shear and normal forces between the central and external piles. This type of behavior permits to predict the failure of the system in the case of plasticity extension in the concrete piles which is not the case with a linear behavior. On the other hand it permits an analysis of the behavior of an existing structure requiring reinforcement. The results confirm the efficiency of the reinforcement system with micropiles for existing piles. The implantation of reinforcement elements plays a decisive role in the response of the system. Parametric study of the reinforcement system pile-micropile spacing micropile connection and micropile inclination was carried out. The results reveal a slight effect of pile-micropile spacing on the response of the system. The fixing of micropiles in the cap allows a better attenuation of the forces in the piles and the structure. Similarly the use of inclined micropiles as reinforcing elements is very beneficial to existing piles and micropiles themselves. These conclusions confirm the results of recent centrifuge tests on groups of piles reinforced by micropiles REFERENCES Alsaleh H. and Shahrour I. 2009. “Influence of plasticity on the seismic soil-micropiles-structure interaction”. Soil Dynamics and Earthquake Engineering 29 3 574- 578. Cakir F. and Mohammad J. 2013. “Micropiles’ applications for seismic retrofitting of historical bridges”. International Journal of Engineering and Applied Sciences 5 2 1-8. Chen W.F. and Scawthorn C. 2003. “Earthquake engineering handbook”. CRC Press LLC. Chin B.H. and Aki K. 1991. “Simultaneous study of source path and site effects on strong ground motion during the 1989 Loma Prieta earthquake: a preliminary result on pervasive nonlinear site effects”. Bulletin of Seismological Society of America 81 5 1859-1884. Doshi D. Desai A. and Solanki C. 2017. “Bridge foundation restoration with retrofitting technique”. International Journal of Civil Engineering and Technology Japan 8 6 856-866. Fan K. Gazetas G. Kaynia A. Kausel E. and Ahmad S. 1991. “Kinematic seismic response of single piles and pile groups”. J. Geotech. Engng. Div. ASCE 117 12 1860-1879. Field E.H. Johnson P.A. Beresnev I.A. and Zeng Y. 1997. “Nonlinear ground-motion amplification by sediments during the 1994 Northridge earthquake”. Nature 390 6660 599-602. Finn W.D.L. 2005. “A study of piles during earthquakes: issues of design and analysis”. Bulletin of Earthquake Engineering 3 2 141-234. Doi: 10.1007/s10518-005- 1241-3. FLAC: Fast Lagrangian Analysis of Continua vol. I. Users Manual vol. II. 2005. “Verification problems and example applications”. Second Edition FLAC3D Version 3.0 Minneapolis Minnesota 55401 USA.

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Reinforcement of the Seismic Interaction… Mohanad Talal Alfach - 212 - Gazetas G. 1991. “Foundation vibrations”. Foundation Engineering Handbook. In: Fang Y. Editor. 2 nd Edn. New York Van Nostrand Reinhold 553-593. Gazetas G. and Mylonakis G. 1998. “Seismic soil- structure interaction: new evidence and emerging issues”. Emerging Issues Paper. Geotechnical Special Publication no. 75. vol. III. New York ASCE 1119- 1174. Gazetas G. Fan K. Kaynia A.M. and Kausel E. 1991. “Dynamic interaction factors for floating pile groups”. Journal of Geotechnical Engineering ASCE 117 10 1531-1548. Gazioglu S.M. and O’Neill M.W. 1984. “An evaluation of p–y relationships in cohesive soils”. J.R. Meyer Ed.. Proceedings of the ASCE Symposium on Analysis and Design of Pile Foundations ASCE National Convention San Francisco California Oct. 1-5. Gerolymos N. Escoffier S. Gazetas G. and Garnier J. 2009. “Numerical modeling of centrifuge cyclic lateral pile load experiments”. Earthquake Engineering and Engineering Vibration 8 1 61-76. Gerolymos N. Giannakou A. Anastasopoulos I. and Gazetas G. 2008. “Evidence of beneficial role of inclined piles: observations and summary of numerical analyses”. Bulletin of Earthquake Engineering 6 4 705-722. Lokmer I. Herak M. Panza G.F. and Vaccari F. 2002. “Amplification of strong ground motion in the city of Zagreb Croatia estimated by computation of synthetic seismograms”. Soil Dynamics and Earthquake Engineering 22 105-113. Maheshwari B.K. Truman K.Z. El-Naggar M.H. and Gould P.L. 2004. “3D nonlinear analysis for seismic soil-pile-structure interaction”. Soil Dynamics and Earthquake Engineering 24 4 343-356. Makris N. and Gazetas G. 1992. “Dynamic pile-soil-pile interaction. Part II: Lateral and seismic response”. Earthq. Eng. Struct. Dyn. 21 2. Momenzadeh M. Nguyen T. Lutz P. Pokrywka T. and Risen C. 2013. “Seismic retrofit of 92/280 I/C foundations by micropile groups in San Francisco Bay area California”. Chicago Apr. 29 th -May 4 th 2013 Seventh International Conference on Case Histories in Geotechnical Engineering Paper No. 2.58 2013. Murchison J.M. and O’Neill. M.W. 1984. “An evaluation of p–y relationships in cohesionless soils”. J.M. Meyer Ed. Proceedings of the ASCE Symposium on Analysis and Design of Pile Foundations ASCE National Convention San Francisco California Oct. 1-5 174- 191. Nikolaou S. Mylonakis G. Gazetas G. and Tazoh T. 2001. “Kinematic pile bending during earthquakes: analysis and field measurements”. Géotechnique 51 5 425-440. Ousta R. and Shahrour I. 2001. “Three-dimensional analysis of the seismic behavior of micropiles used in the reinforcement of saturated soils”. International Journal for Numerical and Analytical Methods in Geomechanics 25 183-196. Paolucci R. 2002. “Amplification of earthquake ground motion by steep topographic irregularities”. Earthquake Engineering and Structural Dynamics 31 1831-1853. Parish Y. Sadek M. and Shahrour I. 2009. “Review article: numerical analysis of the seismic behavior of earth dams”. Natural Hazards and Earth System Sciences 9 2 451-458. Rabin T. Takeshi M. and Hiroshi M. 2008. “Cyclic behavior of laterally loaded concrete piles embedded into cohesive soil”. Earthquake Engineering and Structural Dynamics 37 1 43-59. Sadek M. and Shahrour I. 2004. “Three-dimensional finite element analysis of the seismic behaviour of inclined micropiles”. Soil Dynamics and Earthquake Engineering 24 473-485. Sadek M. and Shahrour I. 2006. “Influence of the head and tip connection on the seismic performance of micropiles”. Soil Dynamics and Earthquake Engineering 26 6 461-468.

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Jordan Journal of Civil Engineering Volume 13 No. 2 2019 - 213 - Satoh T. Sato T. and Kawase H. 1995. “Nonlinear behavior of soil sediments identified by using borehole records observed at the Ashigara Valley Japan”. Bulletin of Seismological Society of America 85 6 1821-1834. Sen R. Davies T.G. and Banerjee P.K. 1985. “Dynamic analysis of piles and pile groups embedded in homogeneous soils”. Earthquake Engrg. and Struct. Dyn. 13 53-65. Shahrour I. Sadek M. and Ousta R. 2001. “Seismic behavior of micropiles used as foundation support elements: three-dimensional finite element analysis”. Transportation Research Record No. 1772 84-91. Trifunac M.D. and Todorovska M.I. 1996. “Nonlinear soil response - 1994 Northridge California earthquake”. Journal of Geotechnical and Geoenvironmental Engineering 122 9 725-735. Wilson D.W. 1998. “Soil-pile superstructure interaction in liquefying sand and soft clay”. PhD Thesis Department of Civil and Environmental Engineering University of California Berkeley CA. Wu G. and Finn W.D.L. 1997a. “Dynamic elastic analysis of pile foundations using the finite element method in the frequency domain”. Canadian Geotechnical Journal 34 1 34-43. Wu G. and Finn W.D.L. 1997b. “Dynamic nonlinear analysis of pile foundations using the finite element method in the time domain”. Canadian Geotechnical Journal 34 1 44-45.

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