Experimental and Numerical Study on Seismic Response ... Cost base isolator_S.K.Deb.pdf ·...
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Prof. S.K. Deb
Experimental and Numerical Study on Seismic Response Control of Unreinforced Masonry
Test Model using U-FREI
Department of Civil EngineeringIndian Institute of Technology Guwahati
IITG-IITK Workshop: 25-06-2016
Other Members of the Research Group:
Prof. Anjan Dutta, IITG Mr. Ngo Van Thuyet, Research
Scholar (R/S) Dr. Animesh Das, BHEL (former R/S) Mr. A. Hazarika, former PG student Mr. K. Reddy, former UG student
Industry Partner: M/S METCO Pvt. Ltd., Kolkata
Outline of the presentation
Basic Concepts of Base Isolation
Design and detailing issues
Brief Literature Review
FE Simulation of Isolator
Comparison of Experimental and FE Results
Shake Table Testing of unreinforced masonry test model
Prototype Implementation
Advantages of Base Isolation System
Reduced floor acceleration and inter-story drift
Less (or no) damage to structural members
Better protection of secondary structural systems
Prediction of response is more reliable
Philosophy of base isolation
Lengthening of time period
Enhancement of damping
Fixed Base
Base IsolatedPeriod
Significantly Increase the Period of the Structure and the Damping so that the Response is Significantly Reduced
The Concept of Base Isolation
Idealized force-displacement hysteretic behavior of isolation system
Laminated Rubber bearing: Design Concept
Conventional Laminated Rubber Seismic Isolation Bearings
Estimation of Displacement [ASCE / SEI: 7-05]
Construction Details
Construction Details
Literature Review
Experimental and Analytical Study on FREI
Kelly(2001), Tsai (2005), Moon(2008), Nezhad et al. (2008)
FE Analysis
Mordini (2008), Nezhad (2011), Kelly(2012), Osgooei (2014),
Spizzuoco (2014), Das et al. (2014)
Shake Table Testing of Base Isolated building
Nezhad (2009), Das et al. (2016)
The main objectives of this study are:
(i) To carry out numerical simulation of FREI
(ii) To develop lightweight, low cost FREI
(iv) To carry out experimental study on U-FREI
(v) To carry out shake table testing of base isolated TestModel
(vi) Prototype implementation
The simple single degree-of-freedom natural frequency(fn) of the base isolated model structure is given by
𝑓𝑓𝑛𝑛 =1
2𝜋𝜋𝐾𝐾𝐻𝐻𝑚𝑚𝑡𝑡
Horizontal stiffness of bearing
𝐾𝐾ℎ = 𝐾𝐾𝐻𝐻Number of bearings
= 60.217 ⁄kN m
Designs of Seismic Isolator
For (SREI), the horizontal stiffness is given by simple shear
formula
𝐾𝐾ℎ =𝐺𝐺𝐺𝐺𝑡𝑡𝑟𝑟
From above equation, 𝑡𝑡𝑟𝑟=95 mm. To achieve high stiffness
of the bearings, 19 layers of elastomer, each of 5 mm thick,
is selected. The elastomer layers are separated by 0.55 mm
thick fiber reinforcement.
𝐾𝐾𝑣𝑣 =𝐸𝐸𝐶𝐶𝐺𝐺𝑡𝑡𝑟𝑟
The vertical stiffness is given by,
The compression modulus EC modulus for square isolator isgiven by:
𝐸𝐸𝑐𝑐 = 96𝐺𝐺𝑆𝑆2
𝜋𝜋2 𝛼𝛼𝛼𝛼 2 ∑𝑛𝑛=1∞ 2𝑛𝑛−1/2 2
𝑡𝑡𝛼𝛼𝑛𝑛ℎ𝛾𝛾𝑛𝑛𝛼𝛼𝛾𝛾𝑛𝑛𝛼𝛼
− 𝑡𝑡𝛼𝛼𝑛𝑛ℎ𝛽𝛽𝑛𝑛𝛼𝛼𝛽𝛽𝑛𝑛𝛼𝛼
𝐸𝐸𝑐𝑐= 101212.6 kN/m2. 𝐾𝐾𝑣𝑣 = 10653.96 kN/m. Therefore,ratio of the compressive stiffness to shear stiffness is equal173.
Cross section of isolator
Geometrical properties of square and circular isolator
Description Square Circular
Width (2a) or radius (R) of isolator = 100 mm 112 mmThickness of fiber layer (tf) = 0.55 mm 0.55 mmNumber of fiber layer = 18 18Thickness of single rubber layer (te) = 5 mm 5 mmNumber of rubber layer = 19 19Total height of isolator (h) = 104.9 mm 104.9 mm
Hardness IRHD = 60Shear modulus of elastomer (G) = 0.7 MPaElongation at break > 400%Young’s modulus of fiber reinforcement (Ef) = 4400 MPaPoisson’s ratio of rubber (ϑf) = 0.20
Material properties of elastomer
Buckling load of Square Isolator
sl No. Investigator Buckling Load (kN)1 Gent 43.992 Koh and Kelly 42.773 Kelly 40.50
FE Simulation of Isolator Behaviour
Finite Element Modeling
Element Type for Finite Element Model
Element type of fiber reinforcement
SOLID46, 8-Node Layered Structural Solid is used to model thereinforcement.
Element type of ElastomerSOLID185, 8-Node Structural Solid element isused to model the elastomer
Contact, Target Elements
This modeling is done using 3-D surface-to-surface contact elements CONTA173 andTARGE170.
Material Model
Ogden 3-terms model
Loading History
A vertical load of 12.0kN ±3.0kN
02468
10121416
0 10 20 30 40 50 60 70 80 90 100
Ver
tical
Loa
d (k
N)
Time (s)
-70
-50
-30
-10
10
30
50
70
0 3 6 9 12 15 18
Horiz
ontal
Disp
lacem
ent (
mm
)
Time (s)
Three cycles ofspecific displacementup to 60 mm isapplied on the top ofisolator with constantvertical load
FE Analysis of Square Isolator
X axis aligned with fibersoriented along 0°, while Yaxis aligned with fibers along90°. The orientation ofhorizontal loading 00 and 450
are along X-axis and 450 toX-axis respectively
The top and bottom surfaces can roll off the support surfacesand no tension stresses are produced in un-bonded FREI. Tensilestresses are not transferred to the contact surfaces of un-bondedapplication
Free body diagram in laterally deformed FREI with different boundary condition
Stress and Strain of Square Isolator
Square isolator with 00 loading direction
Distribution of normalized stress S33/Pn.
(a) 60mm horizontal displacement
(b) 40mm horizontal displacement (c) 20mm horizontal displacementPeak stress is 44% higher for bonded.
-6
-4
-2
0
2
0 0.2 0.4 0.6 0.8 1No
rmal
ized
stre
ss S
33/P
nNormalized width of isolator
Square Unbonded (0)Square Bonded (0)
-6
-4
-2
0
2
0 0.2 0.4 0.6 0.8 1
Nor
mal
ized
stre
ss S
33/P
n
Normalized width of isolator
Square Unbonded (0)Square Bonded (0)
-6
-4
-2
0
2
0 0.2 0.4 0.6 0.8 1
Nor
mal
ized
stre
ss S
33/P
n
Normalized width of isolator
Square Unbonded (0)Square Bonded (0)
Contour of normal stress S33 (kN/m2) in mid rubber layer of theisolator at horizontal displacement 60mm (00 loading direction &positive value indicate tension)
(a) Un-bonded isolator at 60mm displacement
(b) Bonded isolator at 60mm displacement
Contour of shear strain in therubber layer of isolator athorizontal displacement 60mm(00 loading direction) and strainalong mid height of elastomer
(a) Un-bonded
(b) Bonded
0.00
0.10
0.20
0.30
0.40
0.50
0 0.2 0.4 0.6 0.8 1
Shea
r str
ain
Normalized width of isolator
Square unbondedSquare Bonded
0.00
0.10
0.20
0.30
0.40
0.50
0 0.2 0.4 0.6 0.8 1
Shes
r str
ain
Normalized width of isolator
Square unbondedSquare Bonded
0.00
0.10
0.20
0.30
0.40
0.50
0 0.2 0.4 0.6 0.8 1
Shea
r str
ain
Normalized width of isolator
Square unbondedSquare Bonded
20mm horizontal displacement
40mm horizontal displacement
60mm horizontal displacement
Hysteresis of square isolator with 00 loading direction
-3
-2
-1
0
1
2
3
-80 -60 -40 -20 0 20 40 60 80
Shea
r For
ce (k
N)
Horizontal Displacement (mm)
-5
-3.75
-2.5
-1.25
0
1.25
2.5
3.75
5
-80 -60 -40 -20 0 20 40 60 80
Shea
r For
ce (k
N)
Horizontal Displacement (mm)
Shear force vs horizontal displacement for un-bonded isolator at 0° loading
Un-bonded isolator at 60mm displacement (0°Loading)
Shear force vs horizontal displacement for bonded isolator at 0°
Bonded isolator at 60mm displacement (0°Loading)
un-bonded bonded Displac-ement(mm)
Effective Horizontal
Stiffness (𝑲𝑲𝒆𝒆𝒆𝒆𝒆𝒆𝒉𝒉 )
(kN/m)
Damping (β) (%)
Effective Horizontal
Stiffness (𝑲𝑲𝒆𝒆𝒆𝒆𝒆𝒆𝒉𝒉 )
(kN/m)
Damping (β) (%)
10 88.3 12.3 89.7 12.120 76.5 12.8 86.4 12.330 66.2 13.1 83.2 12.340 56.9 13.9 79.3 12.550 46.2 15.2 74.7 12.860 39.3 16.1 70.7 13.1
Computation Effective Stiffness and Damping
Kheff = (Fmax – Fmin)/(dmax – dmin) and β = Wd/(4πWs)
Hysteresis of square isolator with 450 loading direction
Shear force vs horizontal displacement for un-bonded isolator at 45° loading
Un-bonded isolator at 60mm displacement (45°Loading)
Shear force vs horizontal displacement for bonded isolator at 45° loading
Bonded isolator at 60mm displacement (45°Loading)
-4
-3
-2
-1
0
1
2
3
4
-80 -60 -40 -20 0 20 40 60 80
Shea
r For
ce (k
N)
Horizontal Displacement (mm)
-5
-3.75
-2.5
-1.25
0
1.25
2.5
3.75
5
-80 -60 -40 -20 0 20 40 60 80
Shea
r For
ce (k
N)
Horizontal Displacement (mm)
Lateral load vs displacement of the bonded & un-bonded square isolator
-5000
-3750
-2500
-1250
0
1250
2500
3750
5000
-60 -40 -20 0 20 40 60
Shea
r For
ce (N
)
Horizontal displacement (mm)
Unbonded FREIBonded FREI
Analytical (𝐾𝐾ℎ = 𝐺𝐺𝐺𝐺𝑡𝑡𝑟𝑟
) From Eq. (3.1) FE Analysis
73.68 73.65 70.7
Horizontal stiffness (N/mm) of bonded square FREI
Horizontal Stiffness of un-bonded is 70% less than bonded
Effect of Vertical Load on Shear Capacity
-3
-2
-1
0
1
2
3
-80 -60 -40 -20 0 20 40 60 80
Shea
r For
ce (k
N)
Horizontal Displacement (mm)
Analysis (100% Vertical load)Analysis (75% Vertical load)
100% and 75% of total vertical load
-3
-2
-1
0
1
2
3
-80 -60 -40 -20 0 20 40 60 80
Shea
r For
ce (k
N)
Horizontal Displacement (mm)
Analysis (100% Vertical load)Analysis (125% Vertical load)
100% and 125% of total vertical load
Vertical Load (%)
Maximum shear force (kN)
Minimum shear force (kN)
75 2.37 -2.37100 2.42 -2.41125 2.52 -2.50
Lateral Load Testing Arrangement and Instrumentation
Total weight arrangement consists of a two storied frame structureplaced on a steel plate, concrete slabs and beams.
Front view of the experimental set up for lateral loading test
Top cross sectional view of the experimental set up
Comparison of Numerical and Experimental Results
Result of Loading along 00 Orientation
-3
-2
-1
0
1
2
3
-12 -9 -6 -3 0 3 6 9 12
Shea
r Fo
rce
(kN
)
Horizontal Displacement (mm)
Test ResultAnalysis Result
-3
-2
-1
0
1
2
3
-25 -20 -15 -10 -5 0 5 10 15 20 25
Shea
r Fo
rce
(kN
)Horizontal Displacement (mm)
Test ResultAnalysis Result
10mm displacement 20mm displacement
-3
-2
-1
0
1
2
3
-35 -28 -21 -14 -7 0 7 14 21 28 35
Shea
r For
ce (k
N)
Horizontal Displacement (mm)
Test ResultAnalysis Result
-3
-2
-1
0
1
2
3
-45 -36 -27 -18 -9 0 9 18 27 36 45
Shea
r For
ce (k
N)
Horizontal Displacement (mm)
Test ResultAnalysis Result
-3
-2
-1
0
1
2
3
-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60
Shea
r For
ce (k
N)
Horizontal Displacement (mm)
Test ResultAnalysis Result
-3
-2
-1
0
1
2
3
-70 -56 -42 -28 -14 0 14 28 42 56 70Sh
ear F
orce
(kN
)
Horizontal Displacement (mm)
Test ResultAnalysis Result
30mm displacement 40mm displacement
50mm displacement 60mm displacement
Displaced Shape of Isolator (00 loading direction)
at 10mm maximum displacement
at 20mm maximum displacement
at 30mm maximum displacement
at 40mm maximum displacement
at 50mm maximum displacement
at 60mm maximum displacement
Concluding Remarks on Isolator Testing
Horizontal stiffness as obtained from numerical solutionshows close agreement with those obtained from experiment.
Horizontal stiffness of un-bonded isolator corresponding to450 loading is observed to be slightly higher than that for 00
loading.
Experimentally observed displaced shapes of the isolatorsare matching with analytically obtained shapes.
Shake Table Testing of Test ModelThe experiment carried out on a 1/5th scaled two storey unreinforcedmasonry building supported on four square un-bonded fiber reinforcedelastomeric isolator (U-FREI)
A scale factor of 1:5 is considered shake table size and its payloadcapacity
The laws of similitude are as follows
Parameters Scale Prototype 1/5-scale model
Length S 5 Mass S2 25 Displacement S 5 Time 𝐒𝐒 2.236 Acceleration S 5
Model building and its details
Parameter Prototype Building
Model Building
Length (m) 7.5 1.5Width (m) 5.5 1.1Height of storey (m) 3 0.6Thickness of slab (m) 0.15 0.08Base beam (m x m) 0.625x0.7
500.125x0.15
0Total weight of building (kg)
12140 971
Sample Ground Motions for Shake Table Test(1) Koyna (1967): Comp - Longitudinal, (2) Parkfield (1966): Comp - C02065, (3) El Centro (1940): Comp - 180, (4) Victoria (1980): Comp - CPE045 transverse earthquakes.
Earthquake Components Peak Ground Acceleration (g)
Frequency Range (rad/sec)
Koyna (1967): Comp - Longitudinal 0.63 0-12Parkfield (1966): Comp - C02065 0.48 0-40El Centro (1940): Comp - 180 0.32 0-65Victoria (1980): Comp - CPE045 0.62 0-160
Table: Characteristics of selected earthquake records
(a) Koyna (1967): Comp - Longitudinal (b) Parkfield (1966): Comp - C02065
(c) El Centro (1940): Comp - 180 (d) Victoria (1980): Comp - CPE045
Time scaled representation of the four selected earthquakesacceleration histories are shown in following figures
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0 1 2 3 4 5
Acc
eler
atio
n (g
)
Time (sec)-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0 5 10 15 20
Acc
eler
atio
n (g
)
Time (sec)
-0.4
-0.2
0
0.2
0.4
0 3 6 9 12 15
Acc
eler
atio
n (g
)
Time (sec)-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0 2 4 6 8 10 12A
ccel
erat
ion
(g)
Time (sec)
Displaced shape of isolator during shake table test for Parkfield input earthquake
(a) Parkfield (for 100% acceleration amplitude of earthquakes along X-axis).
(b) Parkfield (for 70% acceleration amplitude of earthquakes along 450 to X-axis.)
Peak Responses of Base Isolated Model
Fig: Acceleration response at shake table level and base level subjected to four earthquakes (full intensity) applied along X-axis
(a) Koyna (b) Parkfield
(c) El Centro (d) Victoria
-0.8
-0.4
0
0.4
0.8
0 1 2 3 4 5
Acc
eler
atio
n (g
)
Time (sec)
Shake TableBase of bldg
-0.8
-0.4
0
0.4
0.8
0 5 10 15 20
Acc
eler
atio
n (g
)
Time (sec)
Shake TableBase of bldg
-0.4
-0.2
0
0.2
0.4
0 3 6 9 12 15
Acc
eler
atio
n (g
)
Time (sec)
Shake TableBase of bldg
-0.8
-0.4
0
0.4
0.8
0 3 6 9 12
Acc
eler
atio
n (g
)
Time (sec)
Shake TableBase of bldg
Peak Responses of Base Isolated Model
Fig: Comparison of acceleration responses at base level, first floor and roof level subjected to four earthquakes (full intensity) applied along X-axis
(a) Koyna (b) Parkfield
(c) El Centro (d) Victoria
-0.12
-0.06
0
0.06
0.12
0 1 2 3 4 5
Acc
eler
atio
n (g
)
Time (sec)
Base levelFirst floorRoof level
-0.3
-0.15
0
0.15
0.3
0 5 10 15 20
Acc
eler
atio
n (g
)
Time (sec)
Base levelFirst floorRoof level
-0.2
-0.1
0
0.1
0.2
0 3 6 9 12 15
Acc
eler
atio
n (g
)
Time (sec)
Base levelFirst floorRoof level
-0.2
-0.1
0
0.1
0.2
0 3 6 9 12A
ccel
erat
ion
(g)
Time (sec)
Base levelFirst floorRoof level
Peak Responses of Base Isolated Model
Fig: Displacement at base level and first floor level subjected to four earthquakes (full intensity) applied along X-axis
(a) Koyna (b) Parkfield
(c) El Centro (d) Victoria
-10
-5
0
5
10
0 1 2 3 4 5
Disp
lacem
ent (
mm
)
Time (sec)
Base levelFirst floor
-60
-30
0
30
60
0 5 10 15 20
Disp
lace
men
t (m
m)
Time (sec)
Base levelFirst floor
-22.5
-15
-7.5
0
7.5
15
22.5
0 3 6 9 12 15
Disp
lace
men
t (m
m)
Time (sec)
Base levelFirst floor
-30
-20
-10
0
10
20
30
0 3 6 9 12
Dis
plac
emen
t (m
m)
Time (sec)
Base levelFirst floor
Peak acceleration and displacement at different levels of model subjected to four earthquakes (full intensity) along X-axis
EarthquakePeak Accelerations (g) Peak Displacement
(mm) At Shake
Table At Base At First Floor
At Roof Level
At Base level
At First Floor
Koyna 0.632 0.0873 0.0700 0.0867 6.326 7.240
Parkfield 0.476 0.2145 0.2081 0.2463 36.199 39.920
El Centro 0.319 0.1524 0.1601 0.1686 17.789 19.409
Victoria 0.615 0.1230 0.1310 0.1459 19.452 21.251
The following conclusions are drawn from the scaled model study:
U-FREIs are observed to be very effective in reducing seismic responses of model structure.
The effectiveness in seismic isolation increases with increased displacement, where U-FREI maintains a stable rollover configuration within the estimated displacement limit.
The U-FREIs are observed to be effective irrespective of loading directions.
Inertia forces, shear forces and bending moment of the test model supported on U-FREI are substantially lesser than the fixed base structure.
The designed U-FREIs used in this study are applicable to the scaled model building only. The isolators for this model building are slender because of lesser vertical load. This constraint would not be encountered in the design of prototype U-FREIs, and hence higher aspect ratio for prototype bearings is achievable.
Experimental study demonstrated potential of U-FREI in reducing the seismic vulnerability of un-reinforced masonry buildings . Introduction of U-FREI at the interface of superstructure and substructure of an un-reinforced masonry building would be simple and hassle free.
Base Isolated Masonry Building at TawangArunachal Pradesh (under-construction)
Isolation System: Un-bonded Fiber Reinforced Isolator (U-FREI) R&D and design: IIT Guwahati and Manufacturee: M/s METCO Pvt. Ltd. Kolkata
Testing of prototype FREIs
Validation of Numerical Model
IITG CAMPUS: SPRING 2016
Thank you for your kind attention