Post on 06-Jul-2020
transcript
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Svetlana Brzev, Ph.D., P.Eng.
British Columbia Institute of Technology, Vancouver, Canada
Confined Masonry Buildings: Construction Practice and Seismic
Design Concepts
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…and they can be very destructive
EARTHQUAKES HAPPEN
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Recent Deadly Earthquakes in the World
➢ 1993 Latur, Maharashtra, India – 8000 deaths
➢ 1999 Ducze, Turkey – 20000 deaths
➢ 2001 Bhuj, Gujarat, India – 14000 deaths
➢ 2003 Boumerdes, Algeria – 3000 deaths
➢ 2004 The Great Sumatra Earthquake and Tsunami in Indonesia, Thailand, Sri Lanka, and India -270,000 deaths
➢ 2005 Kashmir Earthquake in Pakistan and India -100000 deaths
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CONFINED MASONRY:
an opportunity for improved seismic
performance both for unreinforced
masonry and reinforced concrete
frame construction in low- and
medium-rise buildings
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Confined Masonry Construction: An
Alternative to Reinforced Concrete Frame
Construction
An example from Chile (Source: Ofelia Moroni)
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Confined Masonry Construction: An Alternative
to Unreinforced Masonry Construction
An example from Indonesia (Source: C. Meisl, EERI)
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Earthquake Performance
Confined masonry construction has been practiced in countries/regions with very high seismic risk, such as
➢ Latin America (Mexico, Chile, Peru, Argentina),
➢Mediterranean Europe (Italy, Slovenia), ➢ South Asia (Indonesia), ➢Middle East (Iran) and ➢ the Far East (China).
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Earthquake Performance (cont’d)Confined masonry construction has been exposed to several destructive earthquakes:
➢ 1985 Lloleo, Chile (magnitude 7.8)➢ 1985 Mexico City, Mexico (magnitude 8.0)➢ 2001 El Salvador (magnitude 7.7)➢ 2003 Tecoman, Mexico (magnitude 7.6)➢ 2007 Pisco, Peru (magnitude 8.0)➢ 2003 Bam, Iran (magnitude 6.6)➢ 2004 The Great Sumatra Earthquake and Tsunami, Indonesia (magnitude 9.0)➢ 2007 Pisco, Peru (magnitude 8.0)➢ 2010 Maule, Chile (magnitude 8.8)
Confined masonry buildings performed very well in these major earthquakes – some buildings were damaged, but no human losses
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Confined Masonry and RC Frame Construction: Performance in Recent
Earthquakes
January 2010, Haiti
M 7.0
300,000 deaths
February 2010, Chile
M 8.8
521 deaths
(10 due to confined masonry construction)
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Confined Masonry Construction: a Definition
Confined masonry is a construction system
where the walls are built first, and RC
columns and beams are cast afterwards.
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A difference between the confined masonry and reinforced concrete frames = construction
sequence
Confined Masonry
– Walls first
– Concrete later
Reinforced Concrete Frame
– Concrete first
– Walls later
Source: Tom Schacher
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Reinforced Concrete Frame Construction
15Confined Masonry Construction
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Key Components of a Confined Masonry Building
Key structural components of a confined masonry building are:
➢Masonry walls made either of clay brick or concrete block units
➢Tie-columns = vertical RC confining elements which resemble columns in reinforced concrete frame construction.
➢Tie-beams = horizontal RC confining elementswhich resemble beams in reinforced concrete frame construction.
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Components of a Confined Masonry Building
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Confined Masonry: Construction PracticeAn example from Chile
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Indonesia
Mexico
Pakistan
Peru
Confined Masonry Under Construction in Earthquake-Prone Regions of the World
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Location of Confining Elements is Very Important!
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Location of Confining Elements is Very Important!
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Wall Density
➢ A key parameter influencing the seismic performance of confined masonry
buildings - confined masonry buildings with adequate wall density were
able to sustain the effects of major earthquakes without collapse
➢ Wall density index (d) is a ratio of the total wall area in each orthogonal
direction and the floor plan area
➢ The required d value depends on seismic hazard, soil type, number of
stories, building weight, and masonry shear strength.
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How to Determine Wall Density?
d= Aw/Ap
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Recommended Wall Density
The Guide recommends d values from 1 to 9.5%
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How to Distribute Seismic Forces to Walls ?
Wall i
(area Ai)
Vi
V = Total seismic force
at a floor level
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Seismic Force Distribution
F= 1 if H/L1.33
OR
F=(1.33 L/h)2
if H/L>1.33
This is based on the Mexican Code NTC-M 2004
=
=N
i
ii
iii
AF
AFVV
1
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Mechanism of Seismic Response in a Confined Masonry Building
Masonry walls
Critical region
Diagonal cracking
Source: M. Astroza lecture notes, 2010
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Mechanism of Seismic Response in a Confined Masonry Building
Masonry walls
Damage in critical regions
Onset of Diagonal cracking
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Seismic Design Objectives
➢RC confining elements must be designed to prevent crack propagation from masonry walls into critical regions of confining elements.
➢This can be achieved if critical regions of the RC tie-columns are designed to resist the loads corresponding to the onset of diagonal cracking in masonry walls.
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This seismic performance should be avoided!
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Seismic Design of Confined Masonry Components = Wall + RC Confining
Elements
Wall + RC confining elements
Wall
= shear
due to V
= +Confining elements
=tension/compression due to M
V
V M
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Seismic Design of Walls for Shear
V
Use CSA S304.1 Cl.10.10.1.1
Vr=Vm
Consider masonry shear resistance only
See page 2-11 of Seismic Masonry Guide (Anderson and Brzev)
Diagonal crack is caused by shear stresses (same as beams)!
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Design Walls for Shear
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In-plane shear failure: hollow clay block masonry
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In-plane shear failure of masonry walls at the base level - hollow clay
blocks (Cauquenes)
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In-plane shear failure of masonry walls at the base level (cont’d)
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Design of RC Confining Elements
Find T and C forces due to M and design according to CSA A23.3 concrete code (same as RC columns)
MT C
d1
Mr=0.9*As*s*Fy*d1
As= total steel area in a tie-column
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Tie-Column Failure
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Buckling of a RC Tie-Column due to the Toe Crushing of the Masonry Wall Panel
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How to prevent buckling and failure of RC tie-columns?
➢All surveyed buildings in Chile had uniform tie spacing 200 mm
➢Tie size 6 mm typical, in some cases 4.2 mm (when prefabricated cages were used)
Closer tie spacing at the ends of tie-columns (200 mm regular and 100 mm at ends)
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How to prevent buckling failure of RC tie-columns?
Source: Confined Masonry Guide, Jan 2011 draft
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Shear Failure of RC Tie-Columns
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How to Prevent Shear Failure?
Vp Vr/2
Vr = wall shear resistance
Same approach like RC frames with infills!
Vr
Source: M. Astroza lecture notes, 2010
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Confined Masonry: Construction Details
Good connections are of critical importance!
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Inadequate Anchorage of Tie-Beam Reinforcement
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Inadequate Anchorage of Tie-Beam Reinforcement (another example)
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Tie-column Vertical Reinf and Tie-Beam Longitudinal Reinforcement
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Draft guide available online at
www.confinedmasonry.org