Basic Concept of Base IsolationSystem for Buildings

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

13

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

14

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)

15

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/

17

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

19

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

20

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

21

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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