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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.
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