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Seismic Protection of Masonry Seismic Protection of Masonry BuildingsBuildings

20 years later…20 years later…

Dr. Svetlana BrzevDr. Svetlana Brzev

Department of Civil EngineeringBritish Columbia Institute of Technology

Vancouver, Canada

TopicsTopics

Background

Seismic Isolation: Key Concepts

Practical ApplicationsPractical Applications

Seismic Performance

Energy Dissipation Devices

BACKGROUND BACKGROUND

Why seismic protection for masonry buildings?

Damage of Unreinforced Masonry Damage of Unreinforced Masonry Buildings in Past Earthquakes Buildings in Past Earthquakes

February 28, 2001 Nisqually (Washington) earthquake

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Seismic Protection – How?

In different ways: by reinforcing or retrofitting masonry buildings using conventional approachespp

orBy means of custom-designed systems intended to absorb seismic energy and limit damage in a masonry structure -> passive seismic control systems

Passive Seismic Control Systems

Seismic isolation devices

Passive energy dissipation devices

Seismic Isolation

Reduces seismic response of building structures by “decoupling” the structures from the ground;

In many applications installed beneath the structure and referred to as base isolation

Passive Energy Dissipation DevicesPassive Energy Dissipation Devices

Reduce response of the superstructure by

providing supplemental damping (and also

stiffness in some cases)

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Common Features

May provide superior seismic

protection of building structures than

alternative seismic design approaches

Innovative technologies (structural

engineering applications since mid-

1980’s, research since 1970’s)

SEISMIC SEISMIC ISOLATION:ISOLATION:

KEY CONCEPTSKEY CONCEPTS

Source: Charleson (2008)Source: Charleson (2008)

Why is Seismic Isolation Suitable for

Masonry Buildings?

Low- to medium-rise masonry buildings are

typically rigid and characterized by lowtypically rigid and characterized by low

fundamental periods and high spectral

accelerations (and seismic forces) during an

earthquake

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Base Isolated Versus Conventional Base Isolated Versus Conventional FixedFixed--Base BuildingBase Building

Conventional

Fixed-Base Building

Forces reduced by 3 to 6 across the isolators

Forces reduced by 8 to 12 at the roof

Deformation occurs

Base Isolated StructureBase Isolated Structure

across the isolators rather in the frame

Both the contents and the structure are protected

Seismic Isolation Systems for Masonry Seismic Isolation Systems for Masonry

BuildingsBuildings

1. Sliding joint (non-commercial)

2. Friction Pendulum System (commercial)

3. Rubber-based devices with/without lead core

(commercial)

Sliding Joint ConceptSliding Joint Concept

Sliding Sliding jointjoint

The basic concept is to

enable sliding of the

structure during an

earthquake

Adapted from Charleson (2008)

q

The structure is likely not

expected to return to the

original position after the

earthquake

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Sliding Joint Isolation Concept

Also known as Pure Friction (P-F) isolation system

Based on the Coulomb’s Law (friction)

The shear force transmitted to the structure across

the sliding joint is limited by the coefficient of g j y

friction (μ)

The μ value must be kept as low as practical;

however, it must be sufficiently high to sustain

strong winds and small earthquakes without sliding

Base Isolation for a Single-Storey Building gm ⋅

)(

gxm &&⋅

)( gm ⋅μ

Rigid bodysystem

Two-mass spring and dashpot system

Sliding starts when gxg ⋅= μ&&

Sliding stops when gxg ⋅< μ&&

Base Isolation for a MultiBase Isolation for a Multi--Storey BuildingStorey Building

Nikolic-Brzev (1993), Trajkovski (2010)

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MultiMulti--Level Seismic IsolationLevel Seismic Isolation

Nikolic-Brzev (1993), Trajkovski (2010)

Practical ApplicationPractical Application

Sliding joint can be placed at the location of Damp-Proof Course (DPC) at plinth level of a ( ) pbuilding

Key challenge: finding suitable material(s) for sliding joint construction

Multi-Level Seismic Isolation

Continuous sliding system

Discrete sliding system

Nikolic-Brzev (1993) – research at the University of Roorkee, India

Experimental Model(Nikolić(Nikolić--Brzev 1993, University of Roorkee, India)Brzev 1993, University of Roorkee, India)

Three-storey brick masonry building, scale 1:3, dimensions 213 cm length x 165 cm width x 331 cm heightTh t t fi t t t dThe structure first tested as fixed-base structure (PGA of 0.12 to 0.21g)Base isolated model tested at peak ground accelerations of0.20 to 0.38g13 test runs in total (6 fixed-base and 7 sliding)

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Configuration of the Test StructureConfiguration of the Test Structure ConstructionConstruction

Teflon sliderTeflon slider

Discrete Sliding Isolation System – Base Level Discrete Isolation Discrete Isolation System: ConstructionSystem: Construction

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Continuous Sliding System: Floor-Level Isolation Continuous Continuous Sliding System: ConstructionSliding System: Construction

Maximum Base Shear for the FixedMaximum Base Shear for the Fixed--Base and Isolated StructureBase and Isolated Structure Earthquake Input Energy Earthquake Input Energy vsvs PGAPGA

Sliding system Fixed-base system

Sliding system is more effective at higher PGA levels

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Numerical Simulations

PGAPGA== 00..379g379gCompliance with Compliance with the experimental the experimental response within response within 5%5%ce

lera

tion

5%5%Sliding at the Sliding at the base levelbase level

Abso

lute

roo

f ac

c

Time (s)

Nikolic-Brzev (1993), Trajkovski (2010)

Key Challenges

1. Selection of appropriate materials for

sliding joint

2. Restoring force

Materials for Sliding JointsMaterials for Sliding Joints

Ideally, materials used for base isolation of low-strength masonry buildings should be characterized by a frictional coefficient ranging from 0 05 to 0 15coefficient ranging from 0.05 to 0.15 Several researchers studied frictional properties of materials for sliding joints (Nikolic-Brzev, 1993; Page and Griffith, 1998; Trajkovski, 2010)

Materials for Sliding Joints Materials for Sliding Joints ––Frictional CoefficientsFrictional Coefficients

Lowest frictional coefficients obtained for Teflon (PTFE) sliding against stainless steel (0.05-0.10)All th t i l t t d f hAll other materials tested so far have significantly higher coefficient of friction:– Bitumen coated aluminum (DPC) > 0.5– Polythene > 0.25

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Sliding Joint Materials Test Setup

Sliding materialsSliding materials

Trajkovski (2010)

Restoring Force

P-F isolation system usually does not

have a restoring force

A restoring force may be provided by g y p y

means of high-tension springs or

laminated rubber bearings, or by

making the sliding surface curved e.g.

Friction Pendulum system

STAINLESS STEELSTAINLESS STEELCONCAVE SURFACECONCAVE SURFACE

HOUSINGHOUSINGPLATEPLATE

Commercial Product: Friction Pendulum System (FPS)

SECTIONSECTION

SELF LUBRICATINGSELF LUBRICATINGCOMPOSITE LINERCOMPOSITE LINER

ARTICULATINGARTICULATINGSLIDERSLIDER

PLATEPLATECONCAVECONCAVE

Friction Pendulum System: How Does it Work ?

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Friction Pendulum Device Friction Pendulum System – An Animation

Source: Maurer Söhnewww.maurer-soehne.de

Friction Pendulum System – Testing Under EqLoading

Source: Maurer Söhnewww.maurer-soehne.de

Energy Dissipation CoreEnergy Dissipation Core

Steel Reinforcing PlatesSteel Reinforcing Plates

(Top Mounting Plate Not Shown)(Top Mounting Plate Not Shown)

Provides vertical load Provides vertical load capacitycapacityConfines lead coreConfines lead core

Reduces earthquake forces &Reduces earthquake forces &displacements by energydisplacements by energydissipationdissipation

Provides wind resistanceProvides wind resistance

LeadLead--Rubber Seismic Isolation Rubber Seismic Isolation Device (Isolator)Device (Isolator)

Cover RubberCover Rubber

InternalInternal RubberRubber LayersLayers

Bottom Mounting PlateBottom Mounting PlateIntegral with IsolatorIntegral with IsolatorConnects to structure Connects to structure above above and below isolatorand below isolator

Protects steel platesProtects steel plates

Provides lateral flexibilityProvides lateral flexibility

Source: Dynamic Isolation Systems (DIS)

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Lead core yieldsLead core yields

Idealized Hysteretic ForceIdealized Hysteretic Force--Displacement Relation Displacement Relation of a Leadof a Lead--Rubber Rubber DeviceDevice

Idealized Hysteretic ForceIdealized Hysteretic Force--Displacement Relation for Displacement Relation for a High Damping Rubber a High Damping Rubber Device Device (no lead core)(no lead core)

Testing of Lead-Rubber Devices

Source: Maurer Söhnewww.maurer-soehne.de

Research Studies - Masonry BuildingsUniversity of Illinois, Urbana-Champaign

Source: Paulson, Abrams and Mayes (1991)Source: Paulson, Abrams and Mayes (1991)

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Experimental Program

Two scaled models of a 3-storey reinforced concrete block masonry building tested on a shaking table (1/4 g g ( /scale)One test structure was fixed-base and the other was base isolated using natural rubber elastomeric bearings

Configuration of Test StructureEach structure was

subjected to 3 ground motions with increasing intensity

P k d l tiPeak ground accelerations (PGA):

Run 1: 0.34 g (0.34 g)Run 2: 0.49 g (0.75 g)Run 3: 0.70 g (1.07 g)Values in brackets = base-isolated structure

Base Isolation DevicesBase Isolation Devices

Elastomeric (rubber) bearings – no lead core

Results: Relations between Results: Relations between Frequencies and Lateral DriftFrequencies and Lateral Drift

The first-mode frequency of the isolated structure =isolated structure = 17 to 25% of the frequency for the fixed-base structure

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Acceleration Amplification EnvelopesAcceleration Amplification Envelopes

Acceleration amplification for the fixed-base structure was around 2.0 while for base isolated structure it was only 0.5The ratio of amplification factors (fixed-base/isolated) was 0.36 for the Run 3

Displacement Profile Displacement Profile –– Run 3Run 3

Drift ratio: - fixed-base structure 1.9% - isolated structure 0.9%

SEISMIC ISOLATION OF MASONRY SEISMIC ISOLATION OF MASONRY

BUILDINGS BUILDINGS ––

PRACTICAL PRACTICAL APPLICATIONSAPPLICATIONS

Seismic Protection of New Unreinforced Masonry Buildings Using Base Isolation

Technique

Latur, Maharashtra, India, 1999

Design: S. Brzev

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Maharashtra Emergency Earthquake Maharashtra Emergency Earthquake Rehabilitation ProjectRehabilitation Project

Post-earthquake rehabilitation project (after the M 6.4 September 1993 earthquake in Maharashtra) sponsored by the World Bank creditcredit

Two demonstration base isolated buildings, a school building and a shopping complex

Unreinforced masonry with concrete bond beams; typical for approx. 60% of the Indian housing stock

Design HighlightsDesign Highlights

Design based on the 1994 UBC seismic provisions

for base isolated buildings, Zone 2B

Rubber isolators installed beneath the wallRubber isolators installed beneath the wall

intersections

Special reinforced concrete ring beams

constructed below and above the isolators

Twin buildings (one conventional and the other

isolated) constructed at the same site to compare

seismic performance of fixed-base vs. isolated

structure

Buildings located approximately 10 km away

from the 1993 earthquake epicentre

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The first design application of base isolation technology in India

The world’s first reported application of base isolation technology in a rural area, installed using local (low-skilled) labour

New Zealand Parliament Building, Wellington, NZ – a seismic retrofit project

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SEISMIC PERFORMANCE OF BASE SEISMIC PERFORMANCE OF BASE

ISOLATED MASONRY BUILDINGS ISOLATED MASONRY BUILDINGS ––

2010 Maule, Chile Earthquake2010 Maule, Chile Earthquake

Edificio Comunidad Andalucía, Santiago, Chile - Project Summary

Two identical four-storey buildings, one isolated and the other conventionalThe buildings were built in 1992 (first application of base isolation in Chile)First storey level RC walls, and upper floors confined

RC fl l bmasonry; RC floor slabs Eight high damping rubber bearings (313 mm diameter and 320 mm high)Fundamental period approx. 0.6 secEstimated modal damping ratio 15% for any isolated buildingThese buildings did not experience damage during the 2010 earthquake

Source: M.O. Moroni

Base isolated building

Conventional (non-isolated) building

Typical Building -Elevation

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Base Isolation Layout and Instrument Location

Roof PGA=0.22 gIsolated building

North-South Direction

Ground PGA=0.31 g

Roof PGA=0.19 gIsolated building

East-West Direction

Isolated building

Ground PGA=0.21 g

PGA=1 11 g

North-South Direction

PGA=1.11 gConventional building

PGA=0.22 gIsolated building

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PGA 0 79

East-West Direction

PGA=0.79 gConventional building

PGA=0.19 gIsolated building

Note damaged contents in the conventional (non-isolated) building!

PASSIVE ENERGY PASSIVE ENERGY

DISSIPATION DEVICESDISSIPATION DEVICESDISSIPATION DEVICESDISSIPATION DEVICES

Passive Energy Dissipation Devices for Passive Energy Dissipation Devices for

Masonry BuildingsMasonry Buildings

1. Anchoring device for retrofit of existing masonry

buildings (Paganoni and D’ Ayala)

2. Fuses for hybrid masonry construction (Abrams)

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Anchor Device ‐ Research Rationale and Significance

Cat 1Cat 1 Cat 2Cat 2

Problem: Out‐of‐plane damage of wall panels of heritage masonry structuresDevelopment of anchoring device for:

• Control of displacement• Reduction of acceleration• Reduction of stress concentration NaybandNayband, Iran, Iran

Cat 3Cat 3 Cat 4Cat 4

Validation by dynamic tests with earthquake‐like 

input signal

Characterisation by monotonic/cyclic 

static/dynamic tests

Validation of Prototypes

Design of prototypes

Final design

1) Yielding device1) Yielding device 1) Frictional device1) Frictional deviceElement with reduced:• Cross sectional area

Mechanism based on Coulomb friction:Cross sectional area

• Material strength

‐300

‐200

‐100

0

100

200

300

400

‐2000 0 2000 4000 6000 8000

Stress [M

Pa]

Strain [10e‐6]

Anchorage

Dissipative element

Test of prototypes in masonry specimensExperimental programme:

• Pull‐out tests;• Cyclic tests of T‐shape walls;• Shaking table tests within the FP7‐SERIES framework

Standard Anchors: performance variesdepending on the bond grout/masonry.

Friction anchors: the sliding mechanismactivates for a load lower than pull‐out;

Locking is a “source” of capacity BUTthere is large scattering in performance

relative displacements are possible andanchorage failure prevented

steel steel connector connector plate or fuseplate or fuse

Hybrid Masonry Fuses

figure from IMIfigure from IMI

gapgap

slotted hole slotted hole and through and through boltbolt

reinforcing barSource: Abrams (2013)

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Tapered Fuse Developed at UHTapered Fuse Developed at UHSS--P6_T4_FT2.4P6_T4_FT2.4--0101

Torsional buckling initiated during the ±1.25 inch cycleFailure at 2.5 inch displacement after 55 total cycles

LargeLarge--Scale Test StructureScale Test Structure

Test VideoTest VideoConclusionsConclusions

Base isolation is an effective approach for achieving seismic protection of masonry buildingsThe main obstacles for broader application of this technology are relatedapplication of this technology are related to prohibitive costs of devices Several simple non-commercial isolation schemes (e.g. sliding joint) have been developed, but none of them has seen a practical application to date

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ReferencesReferences

Paulson,T.J., Abrams,D.P., and Mayes,R.L. (1991). Shaking-Table Study of Base Isolation for Masonry Buildings, Journal of Structural Engineering, ASCE, Vol. 117, No.11, pp. 3315-3336.

Abrams, D. (2013). NEES Research on Hybrid Masonry Structural Systems, Proceedings of the 12th Canadian Masonry Symposium, Vancouver, Canada.

Arya A S (1984) Sliding Concept for Mitigation of Earthquake DisasterArya, A.S. (1984). Sliding Concept for Mitigation of Earthquake Disaster to Masonry Buildings, Proceedings, Eighth World Conference On Earthquake Engineering, San Francisco, Vol. 5, pp.951-958.

Charleson, A. (2008), Seismic Design for Architects, Architectural Press, Elsevier, United Kingdom, 281 pp.

Nikolic-Brzev, S. (1993). Seismic Protection of Multi-storey Brick Buildings by Seismic Isolation Technique, Thesis submitted in the fulfillment of the Degree of Doctor of Philosophy, Department of Earthquake Engineering, University of Roorkee, India.

ReferencesReferencesNikolic-Brzev, S., and Arya, A.S. (1996). Seismic Isolation of Masonry

Buildings - An Experimental Study, Proceedings, Eleventh World Conference On Earthquake Engineering, Paper No.1338, Acapulco, Mexico.

Paganoni, S., D’Ayala, D. (2012). Numerical Simulation of Dissipative Anchor Devices in Historic Masonry. Proceedings of the 15th World Conference on Earthquake Engineering, Lisbon, Portugal.

Page,A.W. and Griffith,M.C. (1998). A Preliminary Study on the Seismic Behaviour of Slip Joints and Joints Containing Membranes inBehaviour of Slip Joints and Joints Containing Membranes in Masonry Structures, Research Report No. 160.02.1998, The University of Newcastle, Australia.

Sarrazin,M., and Moroni,M.O. (1992). Design of a Base Isolated Confined Masonry Building, Proceedings, 11th World Conference on Earthquake Engineering, Madrid, Spain, pp.2505-2508.

Trajkovski, S. (2010). Analysis of Masonry Buildings with Sliding Seismic Isolation Subjected to Earthquake Excitations, Thesis submitted in the fulfillment of the Degree of Doctor of Philosophy, University of Ljubljana, Slovenia.