Madan Kumar, PhD submission PPT

RESPONSE OF BUILDING FRAME MODELS
SITUATED ON DIFFERENT FOUNDATION
SYSTEMS USING SHAKE TABLE TEST
By
MADAN KUMAR
Roll no.- 155CE13
Enrolment no.- 151017
Under the Guidance of
Dr. S. S. MISHRA
Professor & Head
Department of Civil Engineering
NIT Patna, Patna-5 1

OVERVIEW
 Introduction
 Literature Review
 Objectives
 Methodology used in Experiments
 Response of Models with different Foundations
 Effect of Excavation with different Foundations
 Numerical Modelling
 Results and Discussions
 Conclusions and Future Recommendations
 References
2

INTRODUCTION
 Most of the mega cities in India are in seismically active
zones.
 By design engineers, any foundations such as shallow, pile, or
pile-raft foundation have been considered.
 Many high rise buildings in India are supported on pile
foundations in seismically active areas.
 Many mid rise and tall buildings have been built in EQ prone
areas employing different types of foundation systems.
3

Contd…
 When an earthquake occurs, structures and the ground vibrate
together influencing response of each other. This phenomenon
is called soil-structure interaction.
 The response of a structure to earthquake shaking is affected
by interactions between three linked systems viz.,
 structure,
 foundation and
 soil.
4

Why? Soil-Structure Interaction (SSI)
 Seismic input motion acting on structure-soil system affect the
response of the building.
 Presence of soil mass  makes the system more flexible.
 Radiation of energy of propagating waves increase of the
effective damping.
 The dynamic soil–structure interaction consists of two parts
(i) Kinematic Interaction
(ii) Inertial Interaction
5

Control motion
Modified free-field
motion
Kinematic interaction
Inertial interaction
Effect of soil
Effect of base (foundation)
Effect of structure
Figure 2: Flow Chart of Effect of SSI
9

Contd…
 In urban areas where land is limited and buildings are closely
spaced, deep excavation for construction are necessary.
 Soil excavations resulting in a ditch or a trench adjacent to a
building may adversely affect the nearby buildings in the event
of earthquakes.
 The effect of the earthquake on super structures have been
studied before construction of the underground and has been
compared with those induced after excavation of the adjacent
soil.
10

Literature Gap
 Limited study has found in performance of different type of
foundations under the effect of SSI.
 Very limited study was found showing the performance of
frame buildings of different heights standing on different
foundations system in proximity to a parallel trench.
 It is very necessary to determine experimentally the minimum
spacing of a trench from a building line so that the building is
least affected.
 It is also very much desired to obtained empirical formulas to
estimate the damping and natural frequencies of building frame
models on different type of foundations.
11

OBJECTIVE
The key objectives of the experimental investigations are:
To develop empirical relation of natural frequency and damping
ratio for different heights of frame structures.
Investigating the behaviour and response of conventional building
frame models resting on various foundation systems (i.e. shallow
and deep foundation) subjected to earthquake excitation
considering the influence of SSI.
 To examine the response of the experimental model for different
length of deep piles using the shake table test.
 Response of the building frames in proximity to excavations
under earthquake.
12

Author Year
Methodolo
gy used
Measure findings
Hokmabadi,
et. al
2014 shake
table test
• tests on 5, 10, and 15 story model structures.
• they investigate base shear, floor deformation, and
inter-storey drifts
Saha, et. al 2012 FEM • soil-structure interaction leads to considerable
increase of period though the lateral shear in
columns was not significantly changed
Tabatabaiefar
and Massumi
2010 Numerical • consideration of SSI effect is important for higher
buildings
Sekhar and
Koushik
2004 FEM • increase in the natural period will increase or
decrease the response of the structure depending on
the locations of the natural period in the design
response spectrum.
Vivek and
Raychowdhury
2017 Impact
hammer
tests,
Experimen
tal
• conducted on a 3-story and a 6-story model steel
frame.
• Experimental results were compared with FEMA
provisions.
• The period and damping amplifications are more
prominent in the case of the 3-story building than in
that of the 6-story building.
LITERATURE REVIEW
13

Author Year
Metho
dology
used
Measure findings
Chaallal and
Ghlamallah
1998 • SSI effects resulted in a lengthening of the period of the
building.
S. S. Mishra 2017 FEM • base shear and displacement of a multi-storeyed building
on flexible soil considering the effects of soil stiffness are
presented in terms of its time period.
• RC framed buildings with different fundamental time
periods and with different foundation soil stiffnesses have
been analysed.
Rodriguez
and Montes
2000 param
etric
study
• in most cases of inelastic response, SSI effects can be
evaluated considering the rigid-base case and the SSI
period.
Chu and
Truman
2004 3D
FEM
• studied the effects of pile group configurations on seismic
soil-pile kinematic interaction.
• pile foundation system with different soil properties and
due to El-Centro earthquake excitation.
• observed that the soil properties affect seismic interaction
of the soil-pile system greatly.
14
Contd…

STEPS OF METHODOLOGY USED
The investigation of the structural response conducted are briefly
pointed out in the following steps:
 fabrication of three-dimensional geometrically scaled framed
building models of different storeys,
 preparation of a flexible soil container,
 determination of the properties of the soil,
 determination of dynamic properties of test models such as
natural frequency, damping ratio.
15

Contd…
 conducting a series of shake table tests for investigating the
different characteristics of SSI and its influence of the seismic
response of superstructure with respect to the different types of
foundations.
 conducting a series of shake table tests on the building frame
models standing adjacent to excavations.
 Acquiring the response data and analysing it for different
response behaviours.
16

The research work consists of four parts
Preparation of frame model
Preparation of soil container
Experiment
Analysis
Figure 3: Flow chart of steps used in study
17

Instrumentation and Data Acquisition System
• For the study, Shake Table Test is used to
perform the experiment.
• The shake table is of BISS make having 3 axes,
6 degree of freedom for imparting motion as
shown in Figure 4.
 Technical specifications of Shake table
 Displacement Range: ± 200 mm
 Simulator table size:
 Fully digitally controlled with servo loop
update 2-5 Hz and DAQ rate of 0.5-2 Hz.
 capable of carrying a maximum payload
of one ton.
Figure 4: Shake Table Test setup
1.5m×1.5m
18

Accelerometer
Technical specification:
• Frequency range (Hz) : 50± 5%
• Measurement range: ± 490 m/s-2
• Measurement accuracy:
• Operating temperature:
Figure 5: Accelerometer
54 121
to C
  
2
0.006 /
m s

19

Building Frame for the study
 Three types of conventional moment
resisting frame models are used as
prototype superstructure of four, six
and eight storeys.
 The slender frame building models
are assumed to be a residential
building and it has a plan dimension
of 3m x 3m and the height of 12 m,
18m and 24 m from the ground level,
respectively.
 Each frame model consists of one
span with a total width of 3m.
 The plan and elevation of the test
models are shown in Figure 6.
Figure 6: Plan and elevation of
building frame models
20

Contd…
21
 The size of the isolated footing of the actual building was 2m x
2m.
 The size of mat footing was 6m x 6m.
 In this study, two separate depths of piles were considered.
 In the first case, the depth of piles was 9m (abbreviated as
Pile#1) and in the second case the depth of piles was 11.75m
(abbreviated as Pile#2).

Soil Container
 In the shake table test,
the soil cannot be placed
in an infinite dimension
box.
 Due to variation of
system vibration and
wave reflection on the
boundary, the error is
bounded to occur in test
results.
22
Figure 7: Soil Container

Contd….
 The ideal soil container should simulate the free field soil behaviour as
it exists in the prototype, by minimising the boundary effects.
 The flexible soil container was designed and prepared at the Heavy
Structure Lab, NIT Patna.
 The dimension of flexible soil container is 650mm X 650mm X
650mm as shown in Figure 7.
 Due to limitations in container size, a laminar soil container was
designed to simulate the flexible boundary (Hokmabadi et al. 2015; Lu
et al. 2002; Luzhen et al. 2010; Turan et al. 2009b).
 To minimise the boundary effects the inner sides of soil container were
laminated with foam layer of thickness 20mm (Chen et al. 2012;
Guobo et al. 2018; Hokmabadi et al. 2015; Qian et al. 2018).
 The base of the container was made of steel plate.
23

Contd…
 To avoid over-deformation during lifting, the container corners
were braced with steel sheets.
 To avoid the slippage of container the base of the soil container
was fixed with shake table platform by using steel fasteners
and bolts.
 Container was filled in with 5 layers of soil and properly
compacted.
 The filled in soil was left for some days to simulate its natural
condition approximately and thereafter the properties of the
soil were determined.
24

Soil and its Property
 Soil parameters were derived from laboratory tests to get a
broad view of the geotechnical properties.
 The specific gravity, dry density, and plasticity index of the soil
obtained from the tests were 2.69, 16.8 kN/m3 and 15%,
respectively.
 This soil is classified as silty-sand soil as per the Indian
Standard Soil Classification.
25

Foundation Models used for this study
 The size of isolated, mat and pile foundations were considered
judiciously as shown in Figure 8.
26
Figure 8: Foundation system considered (a) isolated footing, (b) mat footing and (c) pile foundation
(a) (b) (c)

Contd…
 The isolated footings of the steel frame model were of
steel plates of dimensions 200mm x 200mm x 8mm.
 The dimensions of mat footing were 340mm x 340mm x
8mm.
 The piles were of 25mm dia. reinforced concrete
containing 6 nos. 2mm dia. steel rods (by cycle spokes).
 The lengths of Pile#1 and Pile#2 were 300mm and
375mm respectively.
27

Physical quantity Dimension Scaling factors
Length L λ
Mass Density ML-3 1
Acceleration LT-2 1
Time T λ1/2
Force MLT-2 λ3
Stiffness ML-1T-2 λ2
Frequency T-1 λ-1/2
Stress ML-1T-2 λ
Strain - 1
Table 2: Prototype Model Scaling Factors
28
Scaling Factors used for the study

Input Motion
Figure 9: El-Centro N-S earthquake input excitation (a) acceleration, (b) displacement
• In this study, the acceleration time history and response values of the N-S
component of El-Centro earthquake (California 1940) was used.
• The frequency of this earthquake input motion is 2.92 Hz.
• The absolute maximum amplitude of El-Centro N-S component
earthquake is 0.319g.
• Input motions for the shake table tests are filtered with a 50 Hz low-pass
filter to filter out the frequency component above 50 Hz.
29

Assumptions of Experiment
Following are the assumptions were considered which apply
uniformly during the entire experimental program:
 The properties of soil remain the same during the entire
experimental process.
 The dimension of the soil container was considered the
same during the entire experiment.
 The flexible boundary of the container represent the soil
continuity.
30

Limitations of the Experimental Study
Following limitations apply to the contemplated experimental
investigation study:
 The entire study was conducted for one bay symmetrical building frame
models. Asymmetrical building models have not been considered in this
study.
 During experiments, the properties of soil remain the same.
 In the entire experiment, the N-S component of El-Centro earthquake
excitation is considered.
 Excavations of finite dimensions and their offset distance are considered.
 The excess pore water pressure of the soil mix was not measured during the
shake table tests in this study.
31

Free Vibration Test: Determination of
Natural Frequency and Damping Ratio
 In free vibration method the structure
is suddenly released from an imposed
initial displacement and the resulting
free vibration digital data are
recorded.
 The natural frequencies and damping
ratio of frame models are computed.
 For free vibration test, the structural
model was directly fixed on shake
table platform and a horizontal pull
was applied by using non-extensible
rope as shown in Figure 10.
32
Figure 10: Experimental setup for free vibration test

Contd…
 From the several free vibration acceleration records natural
frequencies and damping ratios of the frame models were
determined by counting the number of cycles and using
Equation 1.
 Free Vibration Test (Ref: Chopra, 1985)
33
1
ln
2
i
i j
u
j u

 

 
th
i
th
i+j
where,
j=number of cycles,
u = acceleration at i peak,
u = acceleration at i+j peak.
….. (1)

Contd…
34
• Free vibration analysis is conducted for each frame model
taking two cases:
i) by fixing the frame model legs directly on the shake
table platform and
ii) by properly securing the frame models legs with each
foundation on the soil-filled in the container.
• The values of natural frequency and damping ratio for each
case are presented in Table 3 to 5 for four, six and eight storey
frame models and for different types of foundation systems,
respectively.

Types of foundations Fixed Isolated Mat Pile#1 Pile#2
Natural frequency (rad/sec) 14.00 13.00 12.54 10.75 9.87
Damping ratio (%) 5.00 4.58 4.24 4.12 3.98
Table 3: Natural frequency and damping ratio of four storey frame model
Damping ratio (%) 3.95 3.10 3.58 2.84 2.46
Table 4: Natural frequency and damping ratio of six storey frame model
Damping ratio (%) 2.67 2.40 2.51 2.29 2.05
Table 5: Natural frequency and damping ratio of eight storey frame model
35
Contd…

Contd…
 For isolated footing the formula obtained from best fit curve
can be given as:
 For mat footing the formula obtained from best fit curve can be
given as:
 For pile#1 foundation the formula obtained from best fit curve
can be given as:
 For pile#2 foundation the formula obtained from best fit curve
can be given as:
….. (2)
….. (3)
….. (4)
….. (5)
36
0.94
47.77
Iso h
 

0.67
23.3
Mat h
 

0.86
#1 35.31
Pile h
 

1.08
#2 50.51
Pile h
 


Contd…
 From above equations for different building height
founded on different types of foundation system, empirical
formula gives good result with minimum error.
 The equations (2 to 5) are only valid for square
symmetrical type scaled steel frame model and taken soil
conditions.
37

38
2
2.5
3
3.5
4
4.5
5
12 18 24
Damping
ratio
(%)
Building height, h (m)
Isolated footing
Experimental
Emperical
Empirical
2
2.5
3
3.5
4
4.5
5
12 18 24
Damping
ratio
(%)
Mat footing
Experimental
Empirical
2
2.5
3
3.5
4
4.5
12 14 16 18 20 22 24
Damping
ratio
(%)
Pile#1
Experimental
Empirical
1
2
3
4
5
12 14 16 18 20 22 24
Damping
ratio
(%)
Pile#2
Experimental
Empirical
Figure 11: Comparison of experimental and best fit curve for (a) Isolated footing, (b) Mat footing, (c) Pile#1 and (d) Pile#2

Seismic Response of Building Frame Models due to El-Centro
Earthquake
The main outcomes acquired from the experimental study of the
frame models with and without SSI effects is observed.
 All output responses have been presented here for 50 s due to
space limitation and also due to insignificant response
characteristics after 50 s.
 The output responses of frame models to El-Centro earthquake
input motion for fixed base, isolated footing, mat footing, and
pile foundations were obtained.
39
RESPONSE OF MODELS WITH DIFFERENT
FOUNDATIONS

Shake Table Tests on Model Structure
supported by Shallow Foundation
 The second set of the shake table tests was to study the effects of
the SSI under the shallow foundations (viz. isolated footing, mat
footing) under the influence of El-Centro earthquake.
40

Figure 12: Experimental setup of (a) four (G+3), (b) six (G+5) and (c) eight storey (G+7) frame models
41
Experimental set-up
(a) (b) (c)

Shake Table Tests on Model Structure
supported by Pile Foundation
 The third case of the shake table tests was to consider the pile
foundations.
42

Figure 13 Top floor acceleration and displacement responses of eight storey
frame model due to El-Centro for fixed base condition
43
Seismic Response of Building Frame Models
• Figure 13 to 15 shows the acceleration vs. time and displacement
vs. time curves when structural models were of fixed base
condition.

Figure 15: Top floor acceleration and displacement responses of four storey frame
model due to El-Centro for fixed base condition
44
Figure 14: Top floor acceleration and displacement responses of six storey
frame model due to El-Centro for fixed base condition
Seismic response contd…

45
• For isolated footing, mat footing and pile foundations
(Pile#1 and Pile#2), the response plots in terms of
displacement vs. time are presented in Figures 16 to
19, respectively.

Figure 16: Top floor displacement responses of (a) eight, (b) six and (c) four storey
frame due to El-Centro for isolated footing
due to El-Centro for mat footing
46

Figure 19: Top floor displacement responses of (a) eight, (b) six and (c) four
storey due to El-Centro for pile#2 foundation
Figure 18: Top floor displacement responses of (a) eight, (b) six and (c) four
storey due to El-Centro for pile#1 foundation
47

Types of frame
models
Foundation
type
Maximum
displacement
(mm)
Occurrence time
for maximum
displacement
(sec)
Maximum
acceleration
(g)
Occurrence time
for maximum
acceleration
(sec)
Four storey
Fixed base 9.18 9.51 0.1612 16.74
Isolated 12.58 9.62 0.2248 16.89
Mat 12.11 9.47 0.2207 16.88
Pile#1 11.79 9.78 0.2181 17.66
Pile#2 11.26 9.65 0.2045 17.32
Six storey
Fixed base 10.04 9.39 0.1568 16.81
Isolated 12.89 10.46 0.2787 7.84
Mat 12.41 9.51 0.2616 16.91
Pile#1 11.95 10.10 0.2401 17.67
Pile#2 11.48 10.31 0.2460 17.66
Eight storey
Fixed base 10.68 9.65 0.1425 16.95
Isolated 13.15 10.76 0.2875 8.17
Mat 12.78 9.62 0.2651 17.06
Pile#1 12.01 10.10 0.2408 17.92
Pile#2 11.67 9.76 0.2345 17.48
Table 6: Peak displacement and maximum acceleration and their occurrence time
48

 The values in Table 6 have been plotted also in Figure 20 for
more clarity.
 It is seen from Figure 20 that all the building models with mat
footing reach their maximum displacements earlier as
compared to the models on the other footings.
49
6
8
10
12
14
16
18
20
Four Six Eight
Time
of
occurence
of
max
acceleration
(sec)
Storey
Isolated
Mat
Pile#1
Pile#2
9
9.5
10
10.5
11
Four Six Eight
Time
of
occurence
of
max
displacement
(sec)
Storey
Isolated
Mat
Pile#1
Pile#2
Figure 20: Peak displacement and maximum acceleration and their occurrence time experienced by frame models resting on different foundations

EFFECT OF EXCAVATION ON THE RESPONSE
OF FRAME MODELS
Shake Table Tests on Model Structure due to Nearby
Excavation
 The aim is to predict the deformation pattern of the frame models
supported on foundations and close to deep surface excavations.
 Trenches were made of different widths and depths.
 All the trenches are of the same length, which is equal to the
lateral dimension of the scaled model structure.
 For this study same earthquake excitation were used as described
earlier.
50

Size of the trenches and its offset from the edge of the building
Trench No.
Offset from Building Edge
(m)
Width
(m)
Depth
(m)
Length
(m)
1
0.150 0.075
0.075
0.300
2 0.150
3 0.225
4
0.075 0.150
0.075
5 0.150
6 0.225
7
0.000 0.225
0.075
8 0.150
9 0.225
Table 7: Description of trench and their respective dimension for frame building
51

Series
Foundation type
Details of test parameters
No of Storey Depth of trench (m) Width of trench (m) Offset distance (m)
Fixed
G+3 0.000 0.000 0.000
G+5 0.000 0.000 0.000
G+7 0.000 0.000 0.000
Isolated
G+3 0.000 0.075 0.150
G+5 0.000 0.075 0.150
G+7 0.000 0.075 0.150
Mat
G+3 0.000 0.075 0.150
G+5 0.000 0.075 0.150
G+7 0.000 0.075 0.150
Pile#1
G+3 0.000 0.075 0.150
G+5 0.000 0.075 0.150
G+7 0.000 0.075 0.150
Pile#2
G+3 0.000 0.075 0.150
G+5 0.000 0.075 0.150
G+7 0.000 0.075 0.150
Table 8: Description of foundation condition and their respective trench dimension
52

Figure 21: A typical variation of trench size with width for different depths of excavation
53

54
Figure 23: Top floor responses of four storey frame model due to El-Centro earthquake for fixed base condition with trench size
0.225m
Figure 22: Top floor responses of six storey frame model due to El-Centro earthquake for fixed base condition with trench size
0.225m

Displacement of Frame Models situated on
Foundation systems in Proximity to Excavation
frame due to El-Centro earthquake for isolated footing with excavation size 0.225m
due to El-Centro earthquake for mat footing with excavation size 0.225m 55

due to El-Centro N-S component of earthquake for pile#1 foundation with excavation
size 0.225m
Figure 27: Top floor displacement responses of (a) eight, (b) six and (c) four storey due
to El-Centro N-S component of earthquake for pile#2 foundation with excavation size
size 0.225m
56

Displacement of Frame Models due to Different Depths of
Excavations and Foundation Types
13
14
15
16
17
0 0.075 0.15 0.225
Maximum
displacement
(mm)
Trench depth (m)
four storey
six storey
eight storey
Figure 28: Maximum deflection vs. trench depth for Isolated footing
57
Isolated Footing

12.5
13
13.5
14
14.5
0 0.075 0.15 0.225
Maximum
displacement
(mm)
Trench depth (m)
four storey
six storey
eight storey
Figure 29: Maximum deflection vs. trench depth for mat footing
58
Mat Footing

11
12
13
14
15
16
17
0 0.075 0.15 0.225
Maximum
deflection
(mm)
Trench depth (m)
four storey
six storey
eight storey
Figure 30: Maximum deflection vs. trench depth for pile#1
59
Pile#1

10
11
12
13
14
15
16
0 0.075 0.15 0.225
Mximum
displacement
(mm)
Trench depth (m)
four storey
six storey
eight storey
Figure 31: Maximum deflection vs. trench depth for pile#2
60
Pile#2

0
2
4
6
8
10
12
0 0.075 0.15 0.225
%
increment
in
maximum
displacement
Depth (m)
raft 0.075
raft 0.150
raft 0.225
isolated 0.075
isolated 0.075
isolated 0.075
pile#1 0.075
pile#1 0.150
pile#1 0.225
pile#2 0.075
pile#2 0.150
pile#2 0.225
Figure 32: Percentage (%) increment in maximum deflection at top floor vs depth
for raft, isolated footing and pile systems
61
Comparison of maximum displacement

Influence of Height on Frame Displacement
Adjacent to Excavation
 It is seen that irrespective of the building size of the frame
models, the value of seismic response varies in accordance with
trench size and their dimension.
 Figure 28 to 31 show that:
 the increasing trench depth increases the deflections of the buildings in
all types of foundations.
 isolated and mat footings produce almost equal deflections at the top
floor.
 After a certain depth of excavation equal to approximately a
quarter of the lateral dimension of the building, it is observed
that the model is getting excessively deflected.
 The pile foundations show a linear increment of deflections in
the building with increasing trench depth.
62

Numerical Modelling
 A 3D numerical analysis have been attempted to perform the
seismic behaviour of building frame model.
 The shake table experimental results were used to verify the
developed numerical model.
 ABAQUS is used to simulate building frame model using
various foundation types and different element behaviour.
63

Modeling in ABAQUS
64
Figure 33: Flowchart of steps used in ABAQUS for modeling a structure
Defining the material and section properties
Assembling of model parts
Configuring the model analysis
Assigning interaction properties
Applying boundary conditions and applied loads
Designing the mesh
Creating, running, and monitoring the job
Creating a part/defining the model geometry

Contd…
65
 In this study, the finite element mesh is generated with 8-noded
element.
 C3D8R was used for beams-columns-soil and soil container.
 For slab and foundation, S4R elements were used.
 A master surface is an element-based surface.
 Slave surfaces, on the other hand, can be either element or node
based.
 The option for selecting master and slave surfaces depends on
the types of problem given.
 In this study, relatively rigid surface were selected as master
surface.
 In this analysis geostatic stress is not considered to the finite
element mesh because of problems related to static boundary
conditions for the dynamic model.

Contd…
66
 Viscous boundary condition has been defined at the side
boundary of soil by providing dashpot to avoid wave reflection
from lateral surface of soil (Deeks and Randolph 1994; Fenza
2011; Li and Lü 2004).
• For better wave transmission through a model, the element
size must be
l

…6
…7
…8

Structural Models
67
Figure 34: 3D model of (a) four, (b) six and (c) eight storey model

Properties used in the FE models
68
Table 9: Properties used in the FE models in validation of model size analysis.

Contd…
69
 For this study, Rayleigh viscous damping coefficient is
considered.
 The Rayleigh viscous damping coefficient for a given
frequency can be expressed in terms of critical damping
as:
where, α and β are the Rayleigh damping coefficients.
• For calculation of the value of α and β first two modes of
natural frequencies of building system were considered.
• The peak displacement experienced on the top-left corner
node of the structure is compared with the experimental
results of the model structures.
…9

Experimental vs. numerical results
70
Figure 36: Maximum displacement of
experimental and analytical results for G6 model
Figure 35: Maximum displacement of
experimental and analytical results for G4
model

71
 Maximum displacement of experimental and
analytical results for G8 model
Figure 38: Maximum acceleration response of
Figure 37: Maximum displacement
of experimental and analytical results
for G8 model

72

73
Figure 41: Change (%) in variation for experimental and analytical for acceleration response

74
Figure 42: Change (%) in variation for experimental and analytical for displacement response

75
 It is observed that some differences in experimental and
numerical results occur.
 The reason can be attributed to different limitations in
experimental setup.
 During experiment it is very difficult to replicate actual test
model.
 For example, replicating the field soil with the soil mass in the
container, boundary conditions, frame model, experimental
measurements and human errors are some of the plausible
factors.
 In majority of the cases, the percentages difference is less than
10%. Only in few cases the difference is slightly exceeds 10%.
Therefore, results are in agreement.

Conclusions based on the Shaking Table
Tests
Based on the experimental study the following conclusions made:
 Both the natural frequency and the damping ratio depend
on the foundation systems of the frame models.
 The natural frequency of frame models situated in fixed
condition is maximum as compared to other end
conditions.
 The time period of frame models increases with the
increase in height of model, irrespective of foundation
type.
 The pile foundation gives the least damping ratio as
compared to all other foundation systems irrespective of
the heights of buildings.
76

Contd…
77
 When compared to other foundations, the damping
ratio of fixed base foundations is also higher.
However, the fixed base condition seldom exists.
 The taller building frame model standing on a given type
of footing is found to have lower damping ratio.
 Fixed base offers least lateral displacement as compared to
all other types of foundations.
 Pile foundation offers least lateral displacement of the
frame models as compared to isolated and mat
foundations.
 Deeper pile (Pile#2) gives the least displacement for a
particular height of frame models.

Contd…
78
 In case of isolated footing system the frame model
experiences maximum acceleration response.
 The maximum displacement takes place in the case of
isolated footing system for all frame height.
 The maximum displacement for all building heights tends to
decrease in the order of isolated-mat-pile foundation system.
 The structure supported by the shallow foundation has a 55
% more maximum lateral deflection as compared to the
maximum lateral deflection for the fixed-base building.
 Comparing with fixed base type of foundation, pile
foundations give larger lateral displacements of the
superstructure.

Contd…
79
 Irrespective of the building height of frame model the
value of seismic response varies in accordance with trench
size and their dimension.
 Increasing the trench depth increases the deflection of the
buildings in all types of foundation systems.
 When the trench depth is more than quarter of the lateral
dimension of the building, the top floor deflection of the
building with isolated footing is more as compared to mat
footing.

Contd…
80
 Deep pile as compared to isolated footing is found to
produce lesser deflection of the building adjacent to a
trench.
 The depth of the excavation should be limited upto the
quarter width of the building.

Main significant points and applications
81
Main significant points and applications are highlighted as :
 By using proposed empirical formula the damping and
frequency of the buildings can be estimated quickly.
 The depth of the trench should be limited up to the quarter
width of the building to prevent excessive deflection.

Recommendations for Future Works
 Extend the numerical and physical shake table models to account
for foundations with varying parameters.
 The current results of study can be applied to a broader range of
earthquake experiments in engineering practice.
 Perform future studies on cases when frame models are
embedded.
 Adopt the findings of this study and related studies to create a
new design procedure that fills a gap in the existing design codes.
 Various scale factors can also be selected to extend this study to
determine the effect of scale factor.
82

References
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Seismic Excitation”. Ph. D Thesis Queensland University of Technology Brisbane, Australia
 A. S. Hokmabadi, B. Fatahi and B. Samali (2014) “Physical Modeling of Seismic Soil-Pile-Structure
Interaction for Buildings on Soft Soils”. Int. J. Geomech., 2015, 15(2): 04014046
 Tabatabaiefar SHR, Fatahi B, Samali B (2014) Numerical and Experimental Investigations on Seismic
Response of Building Frames under Influence of Soil-Structure Interaction. Adv Struct Eng 17:109–130 .
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10.1016/j.jseaes.2016.03.014.
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10.1080/19648189.2015.1110057
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Structure Interaction System. J Asian Archit Build Eng 55–64
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