dynamic soil structure interaction analysis...

DYNAMIC SOIL STRUCTURE INTERACTION ANALYSIS FOR

AYMMETRICAL BUILDING

by

Pallavi Ravishankar, Neelima Satyam

in

50th INDIAN GEOTECHNICAL CONFERENCE

College of Engineering (Estd. 1854), Pune, India

Report No: IIIT/TR/2015/-1

Centre for Earthquake EngineeringInternational Institute of Information Technology

Hyderabad - 500 032, INDIADecember 2015

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INDIAN GEOTECHNICAL CONFERENCE

17th

– 19th

DECEMBER 2015, Pune, Maharashtra, India

Venue: College of Engineering (Estd. 1854), Pune, India

DYNAMIC SOIL STRUCTURE INTERACTION ANALYSIS FOR AYMMETRICAL

BUILDING

Pallavi Badry1, Neelima Satyam D.

2

ABSTRACT

All of the civil engineering structures involve some type of structural element which is in direct contact

with soil. To estimate the accurate response of the superstructure it is necessary to consider the response

of the soil supporting the structure and is well explained in the soil structure interaction analysis. Many

attempts have been made to model the SSI problem numerically, but have been found that the soil

nonlinearity, and foundation interfaces, application of boundary element makes analysis more complex

and computationally costlier. To overcome this problem the attempt has been made to optimize the

computational efficiency by applying an equivalent pier method for the deep foundation system. In this

research paper the L-shape 11 storey building supported by a pile foundation with homogeneous local soil

condition is analyzed for dynamic loading including the SSI effect. A new approach has been proposed to

provide simplicity in SSI modeling and reduce the computational cost (memory wise). The approach

includes the applicability of the equivalent pier method for the asymmetrical pile group system, including

SSI effect of the pile foundation system. The approach is validated for group effect and study has been

found that the extended equivalent pile method can successfully be adopted and helps to reduce the

computational cost of SSI problem. The study has been extended to understand the effect of wave

propagation through soil mass. In this regards the SSI analysis has been carried out for different soil

type including cohesive, cohesionless and the combination of both with specific bearing capacity

consideration. It has been observed that the kinematic interaction is governed primarily by bearing

capacity that the soil stiffness.

Keywords: DSSI, Asymmetrical building, Soil pile interaction, Asymmetrical pile group, Equivalent pier

The seismic response of structure is influenced by the medium on which the structure is founded. The

dynamic response of the superstructure founded on the rock is different from soil and even varies with the

soil type and its state at that particular instant. When the interaction effect included in the analysis the

responses of the superstructure is found to more than the fixed base analysis [1,3]. As the asymmetrical

buildings are one of common and unavoidable construction the more attention must be given towards the

precise analysis which included the interaction effect. But once the interaction effect included in the

1PhD student, Geotechnical Engineering laboratory, International Institute of Information Technology, Hyderabad, INDIA,

[email protected] 2Assistant Professor , Geotechnical Engineering laboratory, International Institute of Information Technology, Hyderabad,

INDIA, [email protected]

mailto:[email protected]

mailto:[email protected]

Pallavi Badry & Neelima Satyam D.

numerical analysis the modeling becomes very complex and the time of analysis also increases

exponentially due to consideration of soil element and up to the infinite domain.

Thus, it is significantly needed to suggest the approach which simplifies the modeling of SSI system and

reduce the time of analysis. This study aimed to suggest the approach for reducing the complexity in SSI

modeling and reducing the analysis time by implementing the Equivalent Pier Method (EPM) for the

asymmetrical building supported by piles.

The finite element program developed for the DSSI analysis includes the two types of finite elements viz.

2 noded 3-D beam elements and 3-D 8 noded brick element. In the present study the soil structure

interaction analysis for asymmetrical building has been considered for a homogenous soil condition.

The DSSI model has been reduced by using the Equivalent Pier Methodology suggested by Paulos &

Davis (1980). In this method, the pile group is replaced by a pier of similar length to the piles in the group

and with an equivalent diameter (Deq), estimated as follows [13]. The responses of the superstructure

have been compared to the Equivalent Pier Model and General pile layout system for the applied Bhuj

(2001) Ground motion (Fig.2). The responses have been checked for the different soil type conditions

including cohesive and non cohesive soil with the various bearing capacity values.

Fig. 2 Floor wise response comparison for

EPM and General pile layout system under dynamic loading in X,Y and Z direction

The study concluded that the complexity in modeling the integrated soil structure problem has been

reduced with considerable extent. It has been observed that the time required to get the solution is reduced

to 68 % for all EPM configuration than the general pile layout, the EPM approach is satisfactory for the

SSI problems where the numerical cost and CPU memory is required very high.

The peak displacement varies w.r.t the soil type since the material properties of the soil, including

Young’s modulus, Poisson’s ratio contributes to the response. In the S1soil (Ø soil) the response is lesser

as Young’s modulus and bearing capacity are much more than the soil type S3 (C soil S3). Hence the soil

having more bearing capacity gives lesser displacement values. From this the study concludes that the

responses of the superstructure govern primarily by the bearing capacity of the supporting strata than its

young’s modulus.

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DYNAMIC SOIL STRUCTURE INTERACTION ANALYSIS FOR

AYMMETRICAL BUILDING

Pallavi Badry1 , PhD Student, International Institute of Information Technology,

[email protected]

Neelima satyam D. 2, Assistant Professor, Institute of Information Technology, [email protected]

ABSTRACT: All of the civil engineering structures involve some type of structural element which is in direct

contact with soil. To estimate the accurate response of the superstructure it is necessary to consider the response of

the soil supporting the structure and is well explained in the soil structure interaction analysis. Many attempts have

been made to model the SSI problem numerically, but have been found that the soil nonlinearity, and foundation

interfaces, application of boundary element makes analysis more complex and computationally costlier. To

overcome this problem the attempt has been made to optimize the computational efficiency by applying an

equivalent pier method for the deep foundation system. In this research paper the L-shape 11 storey building

supported by a pile foundation with homogeneous local soil condition is analyzed for dynamic loading including

the SSI effect. A new approach has been proposed to provide simplicity in SSI modeling and reduce the

computational cost (memory wise). The approach includes the applicability of the equivalent pier method for the

asymmetrical pile group system, including SSI effect of the pile foundation system. The approach is validated for

group effect and study has been found that the extended equivalent pile method. The evaluated that EPM method

can successfully be adopted and helps to reduce the computational cost of SSI problem.

The study has been extended to understand the effect of wave propagation through soil mass. In this regards the

SSI analysis has been carried out for different soil type including cohesive, Cohisionless and the combination of

both with specific bearing capacity consideration. It has been observed that the kinematic interaction is governed

primarily by bearing capacity that the soil stiffness.

INTRODUCTION

The seismic response of structure is influenced

by the medium on which the structure is founded.

The dynamic response of the superstructure

founded on the rock is different from soil and

even varies with the soil type and its state at that

particular instant. When the interaction effect

included in the analysis the responses of the

superstructure is found to more than the fixed

base analysis [1].

Thus, it is highly recommended that, the effect of

soil structure interaction is needed to consider in

the analysis in order to get the more precise

response of the superstructure. In Soil structure

Interaction (SSI) analysis the structural response

is governed by the interplay between the

characteristics of the soil, the structure and the

input motion. It determines the actual loading

experienced by the soil–structure system

resulting from the free-field seismic ground

motions. According to Chandler et al. (2010),

Mid-rise buildings are aggregations of dwelling

buildings ranging from 5 to 15 stories [17]. With

respect to this definition, to cover this range the

G +10 pile supported L-shape R.C.C. building is

considered .The initial configuration of the pile is

decided depending upon the critical load case of

earthquake and frame gravity load. The selected

span width conforms to architectural norms and

construction practices of the conventional

buildings in mega cities.

BACKGROUND


Seismic damage surveys and analyses conducted

on modes of failure of building structures during

past, severe earthquakes concluded that most

vulnerable building structures are those, which

are asymmetric in nature. However, the

destruction of numerous asymmetric buildings in

the 1985 Mexico earthquake made researchers

focus on soil–structure interaction effects and on

the response behavior of such systems [1]. So

far, several researchers have attempted to

incorporate the flexibility of foundation in

asymmetric system models. Among them,

Balendra (1982) used simple springs to represent

frequency-independent values and to

approximate the frequency-dependent foundation

impedance functions in an asymmetric multistory

building [17]. Subsequently Tsicnias and

Hutchinson (1985) extensively investigated the

steady-state response of flexibility supported

torsionally coupled buildings subjected to

harmonic ground motions by using frequency-

independent springs and dashpots [5].

The response of the asymmetrical building has

been investigated by Lin (2009) and Olariu

(Olariu 2014) by analytical approaches like

arithmetic sum method and spectral acceleration

method to understand the behavior of shallow

foundation by incorporating the interaction effect

by spring and dashpot [20,2]. Mason (Mason

2013) and Bui (2014) carried out the

experimental study with scaled down model of

the asymmetrical dwarf building to study the soil

structure interaction effect on the structural

response under earthquake [6]. Still the

approaches not extended for the pile supported

asymmetrical buildings. Chopra and Gutierres

(1978) highlighted out that the numerical

methods are most appropriate and accurate

methods for soil structure interaction analysis

[1]. Followed by this several researchers,

including Wegner, Yao and Bhullar (2009),

Maridan and Tsai (2009), Sharma and Pandey,

(2011) carried out the study for SSI analysis of

the asymmetrical building supported by the

isolated, raft and shallow foundation system by

considering the 3-D and the 2-D nonlinear

analysis [14,11,17]. Venkatesh (2012), Yigit

(2013), Tehrani and Khoshnoudian (2014),

Isbiliroglu and Taborda ( 2014), Irfan (2014)

attempted to analyze the nonlinear dynamic SSI

system of an asymmetrical building supported by

shallow foundation and effect of interaction has

been modeled by the spring and dashpot

[17,12,16]. As the asymmetrical buildings are

one of common and unavoidable construction the

more attention must be given towards the precise

analysis which included the interaction effect.

But once the interaction effect included in the

numerical analysis the modeling becomes very

complex and the time of analysis also increases

exponentially due to consideration of soil

element and up to the infinite domain.

Thus, it is significantly needed to suggest the

approach which simplifies the modeling of SSI

system and reduce the time of analysis. This

study aimed to suggest the approach for reducing

the complexity in SSI modeling and reducing the

analysis time by implementing the Equivalent

Pier Method (EPM) for the asymmetrical

building supported by piles.

METHODS FOR ESTIMATION

SETTLEMENT OF PILE GROUP

Many methods have been presented in the

literature for estimating the settlement of pile

foundations, ranging from empirical methods,

through simple hand calculation methods, to

sophisticated numerical finite element and finite

difference analyses. The importance of

appropriate estimation of Geotechnical

parameters will be emphasized, and finally, it

will be demonstrated that misleading results can

arise from the imprudent application of group

settlement analysis. In this way, an attempt will

be made to narrow some of the gaps that have

developed between research and practice.

The soil pile interaction effect can be

implemented with more preciseness in equivalent

pier method than the other empirical methods

(Paulos, 1983). Thus, in the present study the

dynamic dipacement of pile group and

superstructure has been estimated by reducing

the pile group in to single pier of equivalent

stiffness.

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DSSI MODEL OF T-SHAPE

ASYMETRICAL BUILDING

In the present study the finite element program

using C++ has been developed to analyze the SSI

system. The Program can perform nonlinear

static and dynamic analysis, including node to

node contacts. The input need to be provided

through the text files in the specified format. The

program takes the input, including geometry, i.e.

nodes and elements, contact information,

boundary conditions, material data, constraints

and Load data with respect to the DOFs.

The program produces nodal displacement,

element stresses at integration points as output.

All required output data has been created in the

text files. The program also produces binary files

in LS-PP format for creating the evectional and

sectional views.

The modeling of the DSSI system for G+10 L-

shape a symmetrical building with generalized

pile layout has been explained in detail. The

finite element program developed for the DSSI

analysis includes the two types of finite elements

viz. 2 noded 3-D beam elements and 3-D 8

noded brick element. In the present study the

soil structure interaction analysis for

asymmetrical building has been considered for a

homogenous soil condition. Table 1 explains the

engineering properties of the various modeling

parameters of superstructure, soil and the piles

and interface/contact considered.

Table 1 Engineering properties of soil and

structure considered

Soil

type

Uni

t

Wt.

(kN

/m3)

Fric

tion

ang

le,

(0)

Pois

son’

s

Rati

o

E

(kN/m2

)

Vs

(m/s)

sand 18 35 0.35 445,87

2

300

Super

structu

24 0 0.15 2.0x

107

120

0

re

Pile 24 0 0.15 2.0x

107

120

0

Raft 24 0 0.15 2.0x

107

120

0

Materi

al

model

parame

ters

Poisson’s

ratio =

0.35

Friction angle = 35°

Interfa

ce data

Friction angle (δ)= 1/3 ɸ' = 11.4°

The G+10 superstructure components, including

beams and column have been modeled with 2

noded 3-D beam elements. The joints between

beam and column are considered to be rigid. The

connection between the raft and first storey

column is modeled as the rigid connections. Half

space of size 20 x 20 x 20 m is modeled using as

sandy silt and the engineering properties of the

soil domain has been explained in detail in Table

1. The nonlinear behavior of the supporting soil

is captured using Drucker –Prager material

model.

The 0.5 m thick L-shape raft with the 1.0 m

offset from all the sides of the base of the

superstructure have been modeled with the 3-D

brick elements. The circular piles with 0.45 m

and 9.0 m length have been modeled with the 3-

D brick elements. The L-shape layout of piles

accommodates the 21 piles spaced at 1.5 m c/c.

The joints between the raft and pile have been

modeled with the rigid contacts. The meshing of

the finite element model has been created by

using GSA 2-D mesher.

The SSI effect has been incorporated in the

analysis by modeling the interfaces between soil

and pile and viscous boundary soil mass

considered. The finite element model of L-shape

SSI system developed to understand the coupled

response of the soil and structure is shown in

figure 1.


a. Plan b. Isometric view c. Meshed

model

Fig. 1 General finite element model for G + 10

building for DSSI

The interface between the pile and soil has been

modeled as a node to the node friction contact

using Lagrange multiplier method. These

interface elements replicated the penetration and

sliding effect under loading. All four sides of the

sole domain has been modeled with the viscous

boundary where the nodes of the extreme

elements provided with the extra force which is

equal to the force estimated at the of each time

step to nullify the forces at the node. The bottom

element of the soil domain is considered with the

earthquake boundaries which provide the

displacement in the same direction of earthquake

given in the analysis and the rest of the DOF of

the elements will be assigned as zero. In present

study E-W (x-direction) component of Bhuj

earthquake (2001, 0.31g) has been given to study

the response of SSI system. The finite element

model of the SSI system is given

SEISMIC ANALYSIS OF SSI SYSTEM

The model is analyzed for both static and

dynamic loading conditions. Initially the SSI

system is analyzed for static load in order to get

the initial stress condition which includes the self

weight of the superstructure and the foundation

system. The static analysis has been carried out

by applying the fixed boundary condition in

normal direction i.e. constraining the

displacements only in the normal direction to

surface to the nodes of the extreme element of

the soil volume considered.

The stresses and displacement so obtained at the

end of static analysis has been considered as the

initial response for the dynamic analysis. The

2001 Bhuj ground motion (PGA= 0.31G, E-W)

has been applied at the bottom nodes of the soil

domain and the analysis has been carried out for

the peak response which lies in the 15 Sec (Fig.

2).

Fig. 2 Bhuj ground motion and Part of

ground motion considered for study

FE MODEL OF SSI SYSTEM USING

EQUIVALENT PIER METHOD

The dynamic soil structure interaction problem is

a very huge size problem as includes the

structure elements, foundation elements and

supporting soil domain which need to extend in

all 3 directions depending upon the base size of

the structure and the depth of deep foundation

system to avoid the effect of wave reflection.

Thus, there is tremendous need to reduce the

interaction problem to optimize the

computational cost, efforts, accuracy in results

and reality in the model simulation.

In the present study, an attempt has been made to

reduce the computational cost by applying an

equivalent pier method for the existing pile group

of the structure and interfaces has been applied to

the equivalent pile which gives the ease in the

modeling of the huge domain problem.

THEORY OF EQUIVALENT PIER

METHOD

Paulos & Davis (1980) proposed an Equivalent

Pier method for heavy and large superstructures

where a large pile group needs to analyze.

Horikoshi & Randolf (1999) adopted this method

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to find out the settlement analysis for the huge

pile group [13]. In this method the pile groups as

a whole pier to simplify the procedure for

estimating the settlement of pile groups which

equals that of single pile by means of load-

transfer functions. In this method, the pile group

is replaced by a pier of similar length to the piles

in the group (Fig. 3), and with an equivalent

diameter (Deq), estimated as follows (Poulos,

1993).

Fig. 3 Concept of equivalent pier method

The diameter of the equivalent pier is given by

the following equation

or (1)

Where, Ag plan area of pile group, including the

soil between the piles.

The lower value in Eq.1 is more relevant to

predominantly end bearing piles, while the

largest value is more applicable to predominantly

friction or floating piles.

As in equivalent pier includes the soil entrapped

in the pile spacing it is needed to modify the

Young’s modulus in the analysis. The Young’s

modulus of the equivalent pier is given by the

following formula

(2)

Where, Ep is the Young’s modulus of the pile,

Es is the Young’s modulus of the soil

penetrated by the piles

Anp is the total cross sectional area of the

piles in a group

Ag is the plan area of pile group,

including the soil between the piles.

Poulos (1993) and Randolph (1994) have

examined the accuracy of the equivalent pier

method for predicting group settlements, and

have concluded that it gives good results [13].

Poulos (1993) has examined group settlement as

a function of the number of piles, for a group of

end bearing piles. Solutions from the computer

program DEFPIG, the equivalent raft method and

the equivalent pier methods were compared, and

for more than about 9 piles, the settlements given

by all three methods agreed reasonably well.

Thus the applicability of EPM has been validated

for the symmetric pile group, but there is no

attempt has been made for the asymmetrical pile

group.

In the present study the entire pile group is

replaced by the single equivalent pier of with

equivalent diameter and stiffness (Table 2).

Table 2 Details of an equivalent pier (EPM)

configurations considered in the study

Deq

(m)

Es

(kN/m2

)

Eeq

(kN/m2)

Location

(x,y) (m,m)

5.8 445872 3.67 x 106 (2.5,2.5)

The finite element model has been developed by

taking the engineering properties associated with

the equivalent pier for the same configuration of

superstructure and soil type (Fig.4).

Fig. 4 Finite element model for different EPM

configuration.

RESULTS

Lp

Eeq , Aeq

Eeq, Deq


The G+10 R.C.C. L-shape asymmetrical building

supported by the pile foundation system in a

homogenous soil strata analyzed for Bhuj ground

motion (2001, PGA =0.31g). The results are

estimated with the view of the applicability of

the Equivalent Pier Method to reduce the

computational efforts and the complexity in

modeling, effect of the supporting soil type on

the superstructure response. The preceding

sections explain the analysis results with

considering each issue independently.

Response of building, including SSI for

general pile layout

The response of the system, including

superstructure and foundation system has been

estimated for a general pile layout at the different

corners of the building. The figure shows the X,

Y and Z direction response obtained at the

leftmost corner of the L layout for the general

pile system (Fig. 5).

Fig. 5 Superstructure response for general pile

system.

The effect of EPM on building response

In the present study the existing pile group is

replaced by the equivalent pier with modified

diameter and the modulus of elasticity (Table 2).

The method is good enough for the symmetric

pile group but need to extend its applicability in

an asymmetrical pile group. The displacements

obtained at each storey level and at different pile

locations are compared with the response

obtained from the general pile configuration. In

finite element model the interaction effect is

included by introducing the interfaces at pile soil

nodes and structure raft location.

The CPU time required to obtain the converged

nonlinear dynamic solution has been noted for

each EPM and general pile system to check the

numerical expense lies with each model. The

Figure 6 shows the comparative storey wise

response obtained responses of superstructure

obtained for the general pile layout and EPM

system in X, Y and Z direction.

Fig. 6 Floor wise response comparison for

EPM and General pile layout system under

dynamic loading in X,Y and Z direction

The numerical adaptability of the proposed

approach for soil structure interaction of the pile

supported building has been checked by

measuring the CPU running time to get the

converged solution. The table 3 and 4 shows the

quantitative metric for each configuration to

understand the numerical expense lies with each

model in details.

Table 3 Peak response at the top of

superstructure for different EPM configuration

Configuration

Gen

EPM

Percentage

deviation

(%)

X-Disp. (cm) 6.29 6.16 2.09

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Y-Disp. (cm) 4.91 3.72 19.58

Z -Disp. (cm) 8.87 9.13 -2.89

Table 4: Expense comparison

Numerical attributes General EPM

Dof s 73,927 30,653

Element 22515 8872

No. of Nodes 24665 10227

No. of Nodes in

Contact 1505 328

Least element size in

FE model (m) 0.11 0.15

Critical time step

taken (Sec.) 5 x 10

-5 8 x 10

-5

CPU time to get the

response (Hrs) 51.17 15.35

The study has been further extended to

understand wave propagation in the soil mass

which shows the kinematic interaction in the

system. In this regards in the present study the

effect of different soil, including Sandy soil (S1),

Sandy clay (S2) and clay (S3) on the G+10

building response to L shape supported by the

pile group has been estimated.

the bearing capacity has been assumed with the

recommendations given by the IS IS 1904-1978

for the type of soils which has been used in the

analysis of the parametric study (Table 5).

Table 5 Engineering properties of the soil

considered for parametric study.

Soil

Type

Young’s

Modulus

(kN/m2)

,

Density

(kN/m3)

Shear

wave

velocity

(m/s)

Angle of

friction

(°),Cohesion

(kN/m2)

Bearing

capacity

(kN/m2)

S1 645,872

; 20

300 42, 0 240

S2 545,872

;20

200 30, 20 350

S3 445,872

; 18

100 0, 30 150

The displacements in X directions for top floor

of the superstructure have been compared for

each type of soil type for T shape structure in

order to study the influence of soil type on the

behavior of the superstructure (Fig.7).

Fig. 7: Displacement time history of various soil

types in X direction of T- Shape building at the

top storey

CONCLUSIONS AND DISUSSIONS

The soil structure analysis is complex research

problem and need much computational capability

and time. Especially in direct method it is

essential to model superstructure and foundation

along with the soil half space, in such case the

analysis become very numerically expensive and

sometimes the solution goes out of the bond of

the computer memory. Another challenge lies

with the complexity in SSI modeling. To

overcome this complication present research

work, an attempt has been made to reduce the

size of the problem numerically by applying the

Equivalent Pier Method for the existing pile

group. With this the no. of piles get reduced and

the time of computation and the complexity in

modeling has been reduced.


The Dynamic soil structure analysis has been

carried out and following are the conclusions

drawn from the present study.

Applicability of EPM for asymmetrical pile

group

The pile group has been reduced to 4 different

configurations by dividing the asymmetrical area

into multiple symmetrical areas. For each EPM

configuration the response of the superstructure

including interaction effect has been estimated at

each floor level. The displacement in X, Y and Z

directions have been estimated for all EPM

models.

It has been found than superstructure responses

in X and Z directions are found to have good

agreement with the responses of the

superstructure with general pile configuration

with the deviation of +-2%.

Coming to the Y direction response the deviation

in responses for EPM and general pile layout is

observed at 20%. Thus, this EPM configuration

is found to be more conservative as compared to

the general pile layout system configuration and

thus promises the more safety of the structure

during earthquakes.

Effect of Complexity and Numerical Expense

It has been observed that the no. of contact nodes

has been greatly reduced from 1505 to 328 which

gives the measure of reducing the complexity

and time reduction in iterating the contact

displacements. This is found to be the countable

advantage to EPM approach.

The no. of elements and DOFs are the key

parameters which impacts the numerical cost. In

EPM approach the no. of elements reduces to

8872 from 22,515 and DOF s reduces 30,653

from 73,000 which prove the numerical

efficiency of the approach.

In this study the solution has been obtained by

the explicit solver where the time step is needed

to be taken very small and depends upon the least

element size in the finite element model. In EPM

approach the equivalent piers gives the larger

diameter, which gives the bigger size elements

after mashing. This facilitates to take the larger

time step which is one of the prime factors which

reduces the solution time.

In general pile layout the critical time step is

needed to be taken as 5 x 10 -5

sec. For the 0.11 m

element size of the pile (with pile dia 0.45 m)

which is average least element size in models.

When the dynamic load (duration 15 Sec.)

applied to the system the solution obtained is in

51 hours for the general pile configuration. But

when the EPM configuration facilitates to take

critical time step 8 x 10 -5

sec as the minimum

element size is found to 1.5 m (where the

equivalent diameter is 5.0 m), thus gives the

results in average 15 hours for the same dynamic

loading duration. Thus, all EPM configurations

give the solution in quicker than the original pile

layout which proves the EPM is one of the

reliable approaches which reduces the analysis

time of the huge size problem like SSI.

It has been observed that the time required to get

the solution is reduced to 68 % for all EPM

configuration than the general pile layout, the

EPM approach is satisfactory for the SSI

problems where the numerical cost and CPU

memory is required very high.

Effect of supporting soil type

In dynamic analysis the propagation of the wave

and the attenuation effect of the wave amplitude

when it travels through the solid media plays

important role in transferring the vibration to the

structure.

In the present study among the three types of soil

considered as the supporting stratum the soil type

S3 (C soil) shows more transfer of vibration to

the superstructure than the S2 (C- Ø) and S1 (Ø)

respectively. Thus the floor wise peak

displacement values are found to be more in case

of soil type S3 as a supporting strata than the

other two types of soil S1 and S2. It has been

observed that the % difference in the peak

displacement values lies in the range of 12 to 15

%.

The peak displacement varies w.r.t the soil type

since the material properties of the soil, including

Young’s modulus, Poisson’s ratio contributes to

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the response. The Young’s modulus which

governs the strength of soil also contribution has

more effect on the superstructure response. In the

S1soil (Ø soil) the response is lesser as Young’s

modulus and bearing capacity are much more

than the soil type S3 (C soil S3). But it has been

observed that though Young’s modulus of soil

type S2 (C-Ø soil) is lesser than S1 (Ø soil ), the

responses of the superstructure with supporting

soil condition than that of the soil type S2 (Ø) is

lesser than S1. The reason for this is the bearing

capacity of the strata. Thus the soil type S2 has

more bearing capacity than soil type S1 and S3.

Hence the soil having more bearing capacity

gives lesser displacement values. From this the

study concludes that the responses of the

superstructure govern primarily by the bearing

capacity of the supporting strata than its young’s

modulus.

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