Base Isolation

© 2005 IST Group. All rights reserved

Seismic Isolation Project for Seismic Isolation Project for Mitchell HallMitchell Hall

Supervised by:Prof. Dr. Oral Büyüköztürk

Graduate Students:Leonardo Duenas

John KellyTai Chieh Wu

May 2001

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PRESENTATION OVERVIEW

PART 1INTRODUCTION, INVESTIGATION, REHABILITATION OPTIONS

PART 2ANALYSIS OF EXISTING FIXED BASE STRUCTURE

PART 3DESIGN OF BASE ISOLATION

PART 4 ANALYSIS OF ISOLATED STRUCTURE

COMPARISON (PART 2)

PART 5 REALISATION

CONSTRUCTION SEQUENCE AND COST ESTIMATION

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MMISSION ISSION SSTATEMENTTATEMENT

To repair and retrofit Mitchell Hall for seismic upgrade.

It is required that it remain SERVICEABLE - 100 year period of returnand INTACT – 475 period of return.

Superstructure restored aesthetically and functionally.

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Elevation of Mitchell Hall

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TYPICAL FLOOR PLAN

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BBUILDING UILDING DDESCRIPTIONESCRIPTION

• 30 x 15 m footprint

• Exterior walls : 0.6 m thick un-reinforced concrete

• Columns : Concrete encased I-Sections

• Floor Slabs : Structural slabs resting on mild steel beams

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IINVESTIGATIONNVESTIGATION

Visual InspectionInitial assessment of internal and external members/surfaces

Non-Destructive TestingDetection of faults not visible to the naked eye

Voids, DiscontinuitiesMeasure of material propertiesExtent of internal crack propagation

Historical Research and Analysis Supported by Photographic records

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CCAUSES AUSES OOF F DDETERIORATIONETERIORATION

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PPREVIOUS REVIOUS SSEISMIC EISMIC AACTIVITYCTIVITY

Magnitude 7.4 on the Richter Scale, near Izmit, at 15.9 km depth, August 1999

Multiple shocks; 125 – 200 km surface rupture, up to 4.9m right lateral offset, up to 2m vertical offset

Tectonic subsidence or landsliding (in addition to liquefaction and settlement)

Urban earthquake

- fault displacements beneath buildings and bridges

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NNORTH ORTH AANATOLIAN NATOLIAN FFAULTAULT

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SSTRUCTURAL TRUCTURAL DDAMAGEAMAGE

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RREHABILITATION EHABILITATION OOPTIONSPTIONS

Structural Stiffening vs. Base IsolationStructural Stiffening vs. Base Isolation

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SSTRUCTURAL TRUCTURAL SSTIFFENINGTIFFENING

• Cement Injections

• Use of Composite Materials to improve existing

infrastructure

e.g. Composite wrapping/confinement of columns

• Conduit tying (Building Confinement)

• Installation of Shear Walls

• Post Tensioning of external walls

• Gunite / Shotcrete

• Diagonal Bracing Systems

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CCONCRETE ONCRETE RREPAIR EPAIR MMETHODSETHODS

Grout Injections in a Grout Injections in a structural floor slab.structural floor slab.

Wrapping of concrete Wrapping of concrete column with composite column with composite materialmaterial

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CCONCRETE ONCRETE RREPAIR EPAIR MMETHODSETHODS

Use of Shear Walls to resist induced Use of Shear Walls to resist induced seismic loadingseismic loading

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SSTRUCTURAL TRUCTURAL SSTIFFENING TIFFENING

Post-Tensioning Internal Outriggers=>Stiffening System

Ground-Anchors

Induced Moments

3 ft thickmasonry wall (unreinforced)

Building Section

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SSTRUCTURAL TRUCTURAL SSTIFFENING TIFFENING •Advantages

-Most economic and widely used method in Europe.

-Involves repair of existing infrastructure.

e.g. Composite wrapping of columns

Shotcrete walls

•Disadvantages-Involves major intrusion upon existing infrastructure.

-May not be a sufficient solution in itself.

-Restricted building access during construction.

-Irreversible.

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BBASEASE IISOLATIONSOLATION

Concept - Isolate the superstructure from the foundation.Two ways to approach - Install rubber bearings or friction sliding system

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σ σσf

σf

σf

σy

εy εu

A AA*

εε ε

Elastic strategy Plastic strategy Base Isolation

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Advantages- Isolates Building from ground motion.

=> Minimal repair of superstructure

- Building can remain serviceable throughout construction.

- Does not involve major intrusion upon existing superstructure.

Disadvantages- Costly. Is challenging to implement in an efficient manner.

- Costly to connect utilities to building (flexible connections).

- Must allow for building displacements.

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COMPARISON (PART 2)

PART 5 REALISATION


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FUNDAMENTAL PERIOD

Ct = Coefficient of structural systemhn = Height [m]

Ct = 0.018 Weak seismic resistance

System

hn = 15 m Height

From the bottom of top floor

Ta = 0.1372 s

4/3* nta hCT =

© 2005 IST Group

BASE SHEAR FORCE

Z = Seismic Zone Factor S = Site coefficientI = Importance coefficient W = Seismic dead load

S = 1.2 Medium-dense to dense soil

C = 2.75

I = 1 Special ocupation

Z = 0.4 Seismic zone factor

Rw = 4 Shear walls masonry

M = 1,800,000 kg Seismic load

Vs = 4,950 kN

3/2*25.1

TSC =W

RCIZV

ws ***

=

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WIND LOAD

F = Wind Force [kN] qs = Dynamic wind pressureCq = Pressure Coefficient Iw = Importance factorCe = Coefficient of exposure Ae = Effective area

qs = 0.786 kN/m2 10 - 20 m Height range

130 kph Wind Velocity

Ae = 450 m2 30 m Length

15 m HeightCq = 1.2 Prismatic structure

H <= 2b

Ce = 1.73 Exposure D

Iw = 1 Special occupancy structures

F = 734 kN

ewsqe AIqCCF ****=

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FLOOR DISTRIBUTION

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NODE DEFINITION

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FIXED CONDITION

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Station Peak Ground Acceleration Max-Horizontal Max-Vertical

ARÇELÝK(ARC)

AMBARLI(ATS)

BOTAÞ (BOT)

ÇEKMECE(CNA)

HAVA ALANI(DHM)

YAPI KREDÝ(YKP)

YARIMCA(YPT)

FATÝH (FAT)

HEYBELÝADA(HAS)

BURSA (BUR) 100.891 mg

57.678 mg

55.115 mg

27.100 mg

241.089 mg

131.714 mg

143.494 mg

48.218 mg

41.07 mg

322.205 mg

189.392 mg

110.230 mg

98.877 mg 23.560 mg

177.307 mg

90.210 mg

211.365 mg 83.252 mg

252.564 mg 80.078 mg

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[North - South] Yarimca Sacaled Record

-500

-400

-300

-200

-100

0

100

200

300

-20 0 20 40 60 80 100 120 140

Seconds

mg

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FFT N-S

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

0 2 4 6 8 10 12 14 16

Frequency [Hz]

Am

plitu

de [

H(w

) ]

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[Vertical] Yarimca Sacaled Record

-400

-300

-200

-100

0

100

200

300

400

-20 0 20 40 60 80 100 120 140

Seconds

mg

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FFT UP

0

2000

4000

6000

8000

10000

12000

14000

16000

0 2 4 6 8 10 12 14 16

Frequency [Hz]

Am

plitu

de [

H(w

) ]

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Max Displacement:

0.60 m

Max Displacement:

0.43 m

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SPECTRAL ACCELERATION [N-S]

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Stresses in Z direction - Compression

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Stresses in X direction - Compression

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Shear Stresses in Y-Z direction

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END ZONE END ZONE

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COMPRESSIONAL FORCES

Maximum Displacement:

0.084 m

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COMPARISON (PART 2)

PART 5 REALISATION


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FIXED BASE vs. ISOLATED

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CONCEPT OF BASE ISOLATION

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BBASE ASE IISOLATIONSOLATION

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THEORY OF BASE ISOLATION SYSTEM

Base Isolation system can be modifiedas a 2-DOF system

Kb, Cb

Mb

M

Ks, Cs

Us+Ub+Ug

Ub+Ug

Ug

© 2005 IST Group

THEORY OF BASE ISOLATION SYSTEM (Cont.)

Governing Equation:

)(.......

bgsss uumkuucum +−=++

1.000

Us

1.000

Us

First Mode Second Mode

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RUBBER BEARINGS

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FRICTION PENDULUM SYSTEM

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DEFINE GUIDELINES

OBTAIN PROPERTIES

ESTIMATE DESIGN

PARAMETERS

SET UP TARGET BUILDING PERIOD AND

BUILDING DISPLACEMENT

COMPUTE EFFECTIVE

STIFFNESS & BASE SHEAR BACK

CALCULATE AND CHECK RESULT

SELECT OPTIMAL

ISOLATORS

PRELIMINARY DESIGN PROCEDURE

© 2005 IST Group

PRELIMINARY DESIGN

References: Uniform Building Code (UBC), 1997 Edition.Design of Seismic Isolated Structures, J. M. Kelly, 1999.

Two Approach to Seismic Hazard:Design Basis Earthquake (DBE)Maximum Capable Earthquake (MCE)

Isolation Design Data:Building Weight : 1,800,000 (Kg) = 4,000 (Kips)Estimate All Dynamic Parameters

© 2005 IST Group

DEFINE GUIDELINES

OBTAIN PROPERTIES

ESTIMATE DESIGN

PARAMETERS

SET UP TARGET BUILDING PERIOD

AND BUILDING DISPLACEMENT

COMPUTE EFFECTIVE



SELECT OPTIMAL

ISOLATORS

PRELIMINARY DESIGN Procedure

© 2005 IST Group

DESIGN RESPONSE SPECTRA

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Period (sec)

Spec

tral

Acc

erla

tion

(g)

Ca/T

To Ts

Fixed-Based Period

Design Period

Target Building Period : TD = 2.5 (s)TM = 3.0 (s)

© 2005 IST Group

PRELIMINARY DESIGN PROCEDUREDEFINE

GUIDELINES

OBTAIN PROPERTIES

ESTIMATE DESIGN

PARAMETERS



COMPUTE EFFECTIVE



SELECT OPTIMAL

ISOLATORS

© 2005 IST Group

DDESIGN DATAESIGN DATA

Effective Stiffness & Base Shear Keff = 70 kips/in (12,000 kN/m)Base Shear Below Interface = 940 kips (4200 kN)Above Isolation Interface = 470 kips (2100 kN)

Loading Condition:80% of the weight – Taken by the external wall20% of the weight – Taken by the internal columns

Design Parameters:Max. Displacement – 18 in. (46 cm)Effective Stiffness – average 3 kips/in (500 kN/m) per isolator

© 2005 IST Group


GUIDELINES

OBTAINPROPERTIES

ESTIMATE DESIGN

PARAMETERS



COMPUTE EFFECTIVE



SELECT OPTIMAL

ISOLATORS

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CENTER ZONE

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DETAIL OF ISOLATORS

Information Resources : DIS Incorporated Description – Select same size of IsolatorsDiameter : 29.5 (in)Height : 18 (in)

Isolator Properties C29.5-18-L0-S C29.5-18-L1-SDisplacement (in) 20 20

Effective Stiffness (kips/in) 2.2 3.5Energy Dissipation per Cycle (kips-in) 0 1520

Damping Ratio β 0.02 0.23Load Capacity (kips) 230 223

Numbers 16 8

© 2005 IST Group


GUIDELINES

OBTAIN PROPERTIES

ESTIMATE DESIGN

PARAMETERS



COMPUTE EFFECTIVE



SELECT OPTIMAL

ISOLATORS

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ISOLATORS LOCATION

Natural Rubber Bearing

Lead-Plug Rubber Bearing

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ISOLATOR HYSTERESIS LOOP

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COMPARISON (PART 2)

PART 5 REALISATION


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FIXED BASE VS. ISOLATED

Fixed Base IsolatedFixed Base Isolated

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3D – ISOLATED MODEL

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Stresses in Z direction – Compression FIXED

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Stresses in Z direction – Compression ISOLATED

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MOAT EXCAVATION

Insert Lateral Supports

Place Ring BeamsLateral constraintLongitudinal ConstraintProvide for connectiondetailing

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PROVISION OF RIGID LAYERA rigid layer is required directly above and below the soft (isolation) layer.Insert hydraulic jacks

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SITE LOGISTICS4.5 ft

57 ft

50 ft

100 ft

105 ft

Isolator unit

Section from W est side to enable access

R ails

D esired Location

C rane

C ut C olum ns

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INSTALLATION TEAMSTEAM TASK

Demolition: Concrete cutting, and chipping from columns to expose steel (2 days)

Steel: Welding/bolting of collars and corbels to columns /walls to facilitate jacking, and setting up of temporary bracing system (1 – 3 days)

Jacking: Operation of jacks and maintaining correct pressure distributionover building (1/2 day)

Craning: Lower isolators into building and manipulate into place (1 – 3 days)

Grouting: Connect the isolators to the building as specified by manufacturers (1 – 2)

Concrete: Finish on cut outs and columns, ensure good connection and stability against future cracking. (1 – 2 days)

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FLAT JACKING THE ISOLATORS

••Standard jacksStandard jacks

••Oil transfusion jacksOil transfusion jacks

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COST DISTRIBUTION

20%

10%

10%36%

14%

10%

Isolators

Excavation

Demolition

Instalation

Structuralimprovement

Sundries$1,269,050$1,269,050

(New Structure – US$4,000,000)

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Low Cost Strategies

WallsColumns

Matrix of Rubber bearings Connecting beams

Longitudinal rubber bearings in matrix configuration

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Low Cost Strategies

Continuous phase(Matrix)

Interphase

Dispersed phase(Reinforcement)

Multidirectional continuous fiber composite

Composite plates

Reinforcing scheme

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Low Cost Strategies

Set of independent isolators

Columns in charge of single floors.

Internal space is never restricted at any floor

Columns placed in the same external or internal wall-axes

Load distribution to independent sets of isolatorsLocal Fabrication

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BBASEASE IISOLATIONSOLATION (Ball System)(Ball System)mg

2r

N N N

Rigid ballSpherical groove

mg

P

F F

N N

Base Isolation

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