Basic Concept of Base Isolation System for Buildings Dr. Taiki SAITO Japan Society of Seismic Isolation Chief Research Engineer, Building Research Institute, Japan Email: tsaito@kenken.go.jp
Contents • Introduction – Basic Idea of BI system
• Design procedure of BI building – Response spectrum method – Time history analysis – Ultimate capacity of isolators
• International activity of JSSI
1
Basic Idea of BI system • Isolation from ground
By Magnetic force?
By balloon?
Introduction • Seismic isolation
Friction
Stopper Rolling?
Sliding?
2
Introduction • Restoring position?
Sliding?
Introduction • Restoring system
By spring?
By sliding on a curved plate?
3
Introduction Gravity Force and Inertia Force Resisting Force
T = 2π
m k
(m: mass, k: stiffness) Effective for heavy building
T = 2π
L g
(L: curvature, g: gravity acceleration) Effective for light building
Introduction • Damping system T d0 d0
With Damper
time ダンパー
Damper
4
Introduction • Requirement of BI devices 1. Isolating the building from the ground 2. Supporting the weight of building ダンパー
3. Damping of response amplitude 4. Restoring the original position after an earthquake
Rubber Block
Introduction
Rocking Weight of building
• Isolators Rubber bearing
Large axial deformation
Laminated Rubber Weight of building Rubber
Earthquake Load
Steel Stiff
Soft
5
High damping rubber Reinforcing steel plate Cover rubber
2 2
500 400 300 200 100 0 -100 -200 -300 -400 -500 -300
Shear stress (N/mm )
Force (kN)
Flange plate
-200
-100
0
100
200
300
1 0 -1 -2
Displacement (mm)
Natural Rubber Bearing (NRB)
-3
-2
0
-1
1
2
3
High-damping Rubber Bearing (HRB)
800 600 Force (kN)
400 200 0 -200 -400 -600 -800 -300
Lead Rubber Bearing (LRB)
-200
-100
0
100
200
300
Displacement (mm)
Sliding bearing Force (kN)
Introduction • Isolators
50 40 30 20 10 0 -10 -20 -30 -40 -50 -150
-100
-50
0
50
100
150
Displacement (mm)
Curved plane sliding bearing
Sliding bearing or Roller bearing 200 150 Force (kN)
100 50 0 -50 -100 -150 -200 -400 -300 -200 -100
0
100 200 300 400
Displacement (mm)
Linear Rail
Rail roller bearing 12
Linear Block Rubber Shim Flange Plate
CLB2000F (P =19 6MN)
6
0
-6 P/P =0 98
-12 -600
-300
0 変位（ mm）
300
600
6
Introduction
Cast Lead
Steel Flange Plate
• Dampers Lead damper Stud
Steel Flange Plate
Steel Damper Rod ダンパー
Steel damper (kN) 800
F = 1150 (kN·s/m) V
600
0.38
400 200 0 -200 -400 -600 -800 -20
-15
-10
-5
0
5
10
15
20 (cm)
Viscous damper
Introduction • Response of BI building
STERA 3D
7
Introduction • Response of BI system X
Upper structure (rigid mass) Base Isolation level (spring)
Y"
Introduction • Response of BI system Vibration model
Equilibrium of forces
Equation of motion M X” + CX’ + Ke X = - MY”
X
- m(X"+Y")
X” + 2hωX’ + ω2 X = - Y” ω = √(2π/T) = √(Ke/M)
Q=keX c X'
X Y’’
T: natural period h : damping factor
Y"
X’ X’’
Numerical integration
8
Introduction • Effect of natural period
Y’’: JMA-Kobe NS component h = 0.05 T Æ longer Acceleration Æsmaller
X’’
T Æ longer Displacement Æ larger
X
Introduction • Response spectrum X
Y
Response of SDOF system with natural period of T & viscous damping of h
Time history of acceleration
T Æ longer Acceleration Æsmaller
Response spectrum of acceleration for JMA Kobe-NS wave, h=0.05
9
Introduction JMA Kobe-NS wave
• Effect of damping
Acceleration response spectrum
Introduction
Displacement response spectrum
Reduction of applied lateral forces to super structure
Increase of displacement response of isolated story
10
Contents • Introduction – Idea of BI system
• Design procedure of BI building – Response spectrum method – Time history analysis – Ultimate capacity of isolators
• International activity of JSSI
Design procedure of BI building • Statistics Number of buildings 350 300 250
Private house
200 150 100
Apartment building
50
1995 The Great HanshinAwaji Earthquake Disaster
19 87 19 88 19 89 19 90 19 91 19 92 19 93 19 94 19 95 19 96 19 97 19 98 19 99 20 00 20 01 20 02
19 83 19 84 19 85 19 86
0
2000 Revision of Building Standard Law
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Design procedure of BI building • Building Standard Law, Japan NO
Need for Structural Calculation?
1 or 2 story wooden house 1 story S or RC building
YES Height>60m
YES
Specification code NO
Time History Analysis
Response Spectrum Method
Reviewed by special committee
Reviewed by local government official
Design procedure of BI building • Response Spectrum Method Design earthquake is defined as the response spectrum at the bedrock level. 1500
cm/s2
Hard soil Medium soil Soft soil
1000
Engineering Bedrock
500
s
0 0
1
2
3
4
5
Soil amplification 1500
cm/s2
5% damping 1000
Bedrock
500
Vs > 400 cm/sec s
0 0
1
2
3
4
5
12
Design procedure of BI building • Response Spectrum Method Building is modeled by SDOF nonlinear hysteresis system. Upper structure (elastic range) Base Isolation level (inelastic range) Force
Drift
Design procedure of BI building • Response Spectrum Method Responses are obtained by equivalent linearization. Response evaluation Upper structure (elastic range)
cm/s2
1500
h=0.05
1000
Base Isolation level (inelastic range)
500
he
s
0 0
Equivalent linear system
Nonlinear system Force
1
2
Te
4
5
Acceleration response
Force
Ke
cm
100
h=0.05
80 60
Drift
3
Drift he Ke: equivalent stiffness he : equivalent damping
40
he
20 0 0
1
2
3
Te
4
s 5
Displacement response
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Design procedure of BI building • Time History Analysis Artificial earthquake compatible with design spectrum 1500
2
cm/s2
cm/s 400
5% damping
200
1000
0
Bedrock
500
s
-200 -400 0
s
0 0
1
2
3
4
5
20
40
60
80
100
120
Three different phase models
Historical earthquake scaled to have the max. velocity 50cm/s 2
cm/s 600 400 200 0 -200 -400 -600
Earthquake response is obtained by time history analysis (numerical integration method) using design earthquake ground motions.
s
0
20
40
60
80
100
120
El Centro1940NS, Taft 1952EW, Hachinohe1968EW, etc.
Site specific artificial earthquake 2
cm/s 1000 500
s
0 -500 -1000 0
20
40
60
80
100
120
Wave generation from the nearest Fault, etc.
Design procedure of BI building • Time History Analysis 800
2,860 600 600
Building is modeled by MDOF nonlinear hysteresis system. Responses are obtained by numerical integration method. RFL
RFL
Living
10F
Kitchen
10FL
9FL
9FL 29,99
8FL 7FL
7FL
6FL
6FL
5FL
4FL
5FL
3FL
2,860
4FL 2FL
3,550
30,79
8FL
Isolator
Isolator
3FL
Isolator
1FL GL
2FL 6,800 960 Y1
Y2
Sway
Rocking
2,700
6,000
950
15,500 Y3
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Design procedure of BI building • Confirmation of ultimate limit state a. Allowable deformation of isolation device b. Compressive and tensile load of isolator c. Isolation gap (horizontal and vertical) Example. LRB
Isolation gap
Compression stress (N/mm2)
Diameter: 800mm Rubber sheet: 5.1mm Number of sheets: 33 Rubber height: 168mm
Design criteria 21N/mm2 Design criteria 240%×168 = 403mm = Shear strain (%)
Design procedure of BI building • Ultimate capacity of isolators
Ultimate Compression Test
Ultimate Shear Test
(from Prof. Nishi, Tokyo Institute of Technology, Japan)
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Design procedure of BI building • Architectural planning 9 Isolators must support superstructure without losing supporting capacity of vertical loads subjected to fires expected to happen in or in the vicinity of isolation interface. 9 Piping and wiring must have flexible joints and slacks between superstructure and substructure, so as to follow the displacement at isolation interface during earthquakes. 9 It must be planned that entrances, connecting bridges, stairs, elevators and etc. do not pound to other facilities or injure humans. 9 Information panels, which show that the building is seismically isolated and deforms largely during earthquakes, must be set up on noticeable place in the building.
Design procedure of BI building • Maintenance Designer must draw up maintenance plans and inform owners, managers and others so that seismic isolation keep demanded performance during the building’s lifetime. 9 Large relative displacement at isolation interface occurs during strong earthquake. Thus, obstacles in or in the vicinity of isolation interface spoil efficient seismic performances. 9 Some isolation devices deteriorate by aging. Aged deteriorations must be considered by heat accelerated tests and others at design stage. 9 Rubber bearings creep subjected to long term loads. Unexpected creeps and external damages must be found out by regular examinations. 9 Breaks, water leakage and others may happen when piping and wiring have insufficient deformation capacities.
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Contents • Introduction – Idea of BI system
• Design procedure of BI building – Response spectrum method – Time history analysis – Ultimate capacity of isolators, etc.
• International activity of JSSI
International Activity of JSSI • CIB/W114 As one of the working commissions in CIB (International Council for Research and Innovation in Building and Construction), W114: Earthquake Engineering and Buildings has been established since November 2006 . Headquarter: JSSI Coordinator: Taiki SAITO
http://www.cibw114.net/
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International Activity of JSSI • CIB/W114 The first CIB/W114 meeting, "International Workshop on Response Control and Seismic Isolation of Buildings," was held in Guangzhou, China on 27 November 2006.
International Activity of JSSI • CIB/TG44 book published in November 2006
Contents 1. 2.
Introduction Devices for Seismic Isolation and Response Control 3. A Comparative Study of Seismic Isolation Code Worldwide 4. Observed Response of Seismically Isolated Buildings 5. World Report 5.1 China 5.2 Italy 5.3 Japan 5.4 Korea 5.5 New Zealand 5.6 Taiwan 5.7 The United of America 6. Conclusions
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China
from Dr. Zhou Fulin adn Dr. Wen Liuhan
Around 600 base isolation buildings have been constructed. The one was constructed in 1991.
35 base isolation buildings are constructed on the two-story reinforced concrete platform of subway station in Beijing, China.
Base isolators at the large span structure of the Shanghai F1 circuit.
Italy
Miniature building models for shaking table test
from Mauro Dolce, Massimo Forni and Alessandro Martelli 60 50 40 30 20 10 0 1981 1986 1991 1996
2001 2006
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Korea
from Dong Guen Lee
Currently, there are only two seismically isolated buildings in Korea, with a third to be built soon. The Unison Research and Development Center building, constructed in 1997, was the first seismically-isolated building.
Korea
from Dong Guen Lee
The second was Traum Hous III, a 12story apartment building in Seoul
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New Zealand
from John X. Zhao
The first seismically isolated structure in New Zealand was the Motu Bridge in the North Island completed in 1974.
Rocking Seismic Isolation System The isolation mechanism is provided by stepping action of each of the two feet of the piers. Steel dampers are used for energy dissipation.
USA
from Ian Aiken and Andrew Whitaker
Construction of the first seismically-isolated building in the USA was completed in 1985, and by mid-2005 there were approximately 80 seismically-isolated buildings in the USA The first building in the USA is the Foothill Communities Law & Justice Center, in Rancho Cucamonga, California, was completed in 1985,with 98 highdamping rubber bearings located below the basement level
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USA
from Ian Aiken and Andrew Whitaker
The second building application in the USA was the City and County Building, in Salt Lake City, Utah, completed in 1989 with 208 lead-rubber and 239 natural rubber bearings. This project was the first in the world to use isolation for retrofit, completed in 1989.
USA
from Ian Aiken and Andrew Whitaker The USC University Hospital in Los Angeles, completed in 1991, was the first hospital in the world to use seismic isolation with 68 leadrubber isolators and 81 naturalrubber isolators.
Roof 6th
4th
Lower Foundation
The 1994 Northridge earthquake
22
Macedonia
from Garevski A. Mihai and James M. Kelly
Primary School Pestalozzi" in Skopje, the first structure in the world base isolated by means of rubber bearings constructed in 1969
Thank you for your attention.
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