1. Short Course on Seismic Design of Reinforced and Confined MasonryShort Course on Seismic Design of Reinforced and Confined Masonry
BuildingsBuildings
February 17-21, 2014, IIT Gandhinagar, IndiaFebruary 17-21, 2014, IIT Gandhinagar, India
Confined Masonry Buildings: Key Components
and Performance in Past Earthquakes
11
Dr. Svetlana BrzevDr. Svetlana Brzev
BCIT, Vancouver, CanadaBCIT, Vancouver, Canada
IIT Gandhinagar, IndiaIIT Gandhinagar, India

2. Acknowledgments
22
• Earthquake Engineering Research Institute
(SPI Projects Fund)
• Maximiliano Astroza and Maria Ofelia
Moroni, Professors, Department of Civil
Engineering, Universidad de Chile
(members of the EERI team)
• Roberto Meli and 12 other co-authors of
the EERI’s Confined Masonry Guide

3. TopicsTopics
33
 Confined masonry: key conceptsConfined masonry: key concepts
Lessons learned from the pastLessons learned from the past
earthquakesearthquakes

4. Why Confined Masonry?Why Confined Masonry?
44
 Poor performance of unreinforced masonry andPoor performance of unreinforced masonry and
nonductile reinforced concrete (RC) framenonductile reinforced concrete (RC) frame
construction caused unacceptably high human andconstruction caused unacceptably high human and
economic losses in past earthquakeseconomic losses in past earthquakes
 This prompted a need for developing and/orThis prompted a need for developing and/or
promoting alternative building technologiespromoting alternative building technologies
The goal is to achieve enhanced seismic performance using
technologies which require similar (preferably lower) level of
construction skills and are economically viable

5. an opportunity for improved seismic performance
both for unreinforced masonry and reinforced
concrete frame construction in low- and medium-rise
buildings
55
CONFINED MASONRY:CONFINED MASONRY:

6. Confined Masonry Construction:
An Alternative to RC Frame Construction
66

7. Confined Masonry Construction: An Alternative
to Unreinforced Masonry Construction
77

8. Confined Masonry: Beginnings
 Evolved though an informal process based on its
satisfactory performance in past earthquakes
 The first reported use in the reconstruction after the 1908
Messina, Italy earthquake (M 7.2) - death toll 70,000
 Practiced in Chile and Columbia since 1930’s and in
Mexico since 1940’s
88
Currently practiced in several countries/regions with high
seismic risk, including Latin America, Mediterranean Europe,
Middle East (Iran), South Asia (Indonesia), and the Far East
(China).

9. Confined Masonry and RC Frame Construction:
Performance in Recent Earthquakes
99
January 2010, HaitiJanuary 2010, Haiti
M 7.0M 7.0
300,000 deaths300,000 deaths
February 2010, ChileFebruary 2010, Chile
M 8.8 521 deathsM 8.8 521 deaths
(10 due to confined(10 due to confined
masonry construction)masonry construction)

10. Global Confined Masonry Initiative
An International Strategy Workshop on the
Promotion of Confined Masonry organized in
January 2008 at Kanpur, India
Confined Masonry NetworkConfined Masonry Network established as a project
of the World Housing Encyclopedia with two major
objectives:
 To improve the design and construction quality of
confined masonry where it is currently in use; and
 To introduce it in areas where it can reduce seismic
risk.
1010

11. Confined Masonry Design Codes
1111Available at www.confinedmasonry.org

12. Key Components of a Confined Masonry
Building :
 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 elements
which resemble beams in reinforced concrete
frame construction.
1212

13. Components of a Confined Masonry Building:
1313

14. 1414
Reinforced Concrete Frame ConstructionReinforced Concrete Frame Construction

15. 1515
Confined Masonry Construction

16. Confined Masonry versus Infilled RC frames:
1616
Confined Masonry
– Walls first
– Concrete later
Reinforced Concrete Infilled
Frame
– Concrete first
– Walls later
Source: Tom Schacher
-construction sequence
- integrity between masonry and frame

17. Confined Masonry: Construction Process
1717
Source: TomSource: Tom
SchacherSchacher

18. Confined Masonry vs RC Frames with Infills – Key Differences
1818

19. A comparison: confined masonry and RC frames with
infills
Youtube videos developed by a Calpoly student, USA
http://www.youtube.com/watch?v=zv_q8saRZfQ
http://www.google.co.in/url?sa=t&rct=j&q=confined%
No.No. 1919

20. Location of Confining Elements is Very
Important!
2020

21. Key Elements – Layout Rules
2121

22. Typical Floor Plans – Examples from Chile
2222
Source: O. Moroni and M.Source: O. Moroni and M.
AstrozaAstroza

23. Confined Masonry Panel Under
Lateral Loading: Shear Failure
2323

24. Confined Masonry Panel Under
Lateral Loading: Shear Failure
Three stages:Three stages:
1- Onset of diagonal1- Onset of diagonal
crackingcracking
2 – Cracking propagated2 – Cracking propagated
through RC tie-columnsthrough RC tie-columns
3 – Failure3 – Failure
Note: internal stress redistribution starts at Stage 1Note: internal stress redistribution starts at Stage 1
2424

25. Confined Masonry Panel – Bending
Stress Distribution
Source: EERI Guide (2011)
2525

26. Strut-and-Tie Model for a Confined
Masonry Panel
BB
AA
CC
DD
BB
AA
CC
DD
nono
dede
strstr
utut
tietie
2626

27. Seismic Design Objectives
 RC confining elements must be designed to
prevent crack propagation from the walls into
critical regions of RC 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.
2727

28. Mechanism of Seismic Response in a Confined
Masonry Building
2828
Masonry walls
Critical region
Diagonal cracking
Source: M. Astroza
lecture notes, 2010

29. Failure Mechanism: Key Stages
2929
Masonry walls
Damage in critical
regions
Onset of
Diagonal
cracking

30. 3030
This condition should be avoided!

31. Confined Masonry Construction: Toothing at
the Wall-to-Tie-Column Interface
3131
Toothing enhances interaction between masonry walls and
RC confining elements

32. Seismic Performance
3232
 Confined masonry construction is found in
countries/regions with very high seismic risk, for
example: Latin America (Mexico, Chile, Peru,
Argentina), Mediterranean Europe (Italy, Slovenia),
South Asia (Indonesia), and the Far East (China).
 In some countries (e.g. Italy) for almost 100 years
 If properly built, shows satisfactory seismic
performance
EXTENSIVE ENGINEERING INPUT NOTEXTENSIVE ENGINEERING INPUT NOT
REQUIRED!REQUIRED!

33. 3333
ecomán earthquake,ecomán earthquake,
January 2003January 2003
Oaxaca quake,Oaxaca quake,
September 1999September 1999

34. Earthquake Performance
3434
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 earthquake (magnitude 8.8)
 2010 Haiti earthquake (magnitude 7.0)
Confined masonry buildings performed very well in these
major earthquakes – some buildings were damaged, but
no human losses

35. 3535
Confined Masonry Performed Very Well in Past
Earthquakes
A six-storey confined
masonry building
remained undamaged in
the August 2007 Pisco,
Peru earthquake
(Magnitude 8.0) while
many other masonry
buildings experienced
severe damage or
collapse

36. Seismic Performance of Confined Masonry Buildings in
the February 27, 2010 Chile Earthquake
3636
 Confined masonry (CM) used for construction of low-rise
single family dwellings and medium-rise apartment buildings
(up to four-story high).
 CM construction practice started in the 1930s, after the 1928
Talca earthquake (M 8.0).
 Good performance reported after the 1939 Chillan
earthquake (M 7.8) and this paved the path for continued use
of CM in Chile.

37. Confined Masonry Construction in Chile (Cont’d)
 Good performance track record in past earthquakes based on
single family (one- to two-storey) buildings.
 Three- and four-storey confined masonry buildings exposed to
severe ground shaking for the first time in the February 2010
earthquake (construction of confined masonry apartment
buildings in the earthquake-affected area started in 1990s).
3737
Modern masonry codes first issued in 1990s – prior
to that, a 1940 document “Ordenanza General de
Urbanismo y Construcción” had been followed

38. Low-Rise Confined Masonry Construction
3838Single-storey rural house

39. Low-Rise Confined Masonry Construction
3939
Two-storey townhouses (semi-detached): small plan dimensions (5 m by 6 m per unit)

40. Performance of Confined Masonry Construction
 By and large, confined masonry buildings performed well in
the earthquake.
 Most one- and two-story single-family dwellings did not
experience any damage.
 Large majority of three- and four-story buildings remained
undamaged
4040
A few buildings suffered severe damage, and twoA few buildings suffered severe damage, and two
three-story buildings collapsedthree-story buildings collapsed

41. Damage Observations: Topics
 Masonry damage (in- and out-of-plane)
 RC tie-columns
 Tie-beam-to-tie-column joints
 Confining elements around openings
 Construction materials
 Collapsed buildings
4141

42. In-plane shear failure of masonry walls at the
base level - hollow clay blocks (Cauquenes)
4242

43. In-plane shear failure of masonry walls at
the base level (cont’d)
4343

44. In-plane shear failure: hollow clay
block masonry
4444

45. Same failure mechanism as infill masonry in
RC frames!
4545
Diagonal Tension (INPS-2), FEMA 306 p.207

46. In-plane shear failure: clay brick masonry
4646

47. Same failure mechanism as infill masonry
in RC frames!
4747
Bed Joint Sliding (INPS-3), FEMA 306 p.208

48. Out-of-Plane Wall Damage
 An example of out-of-plane
damage observed in a three-
storey building
 The damage concentrated at the
upper floor levels
 The building had concrete floors
and timber truss roof
 The same building suffered
severe in-plane damage
4848
Damage at the 2nd
floor level

49. Out-of-Plane Damage
(cont’d)
4949
Damage at the 3rd
floor level

50. Floor and Roof Diaphragms
 Wood floors in single-family buildings (two-storey
high)
 Concrete floors in three-storey high buildings and
up (either cast-in-situ or precast)
 Precast concrete floors consist of hollow masonry
blocks, precast RC beams, and concrete overlay
(“Tralix” system)
5050

51. Discussion on Out-of-Plane Wall Failure
5151
Source: EERI Confined Masonry Guide

52. Tie-Column Failure
5252

53. Buckling of a RC Tie-Column due to the Toe
Crushing of the Masonry Wall Panel
5353

54. Shear Failure of RC Tie-Columns
5454

55. Same failure mechanism as columns in RC
frames with infills!
5555
Column Snap Through Shear Failure (INF1C1), FEMA
306 p.211

56. How to prevent buckling and shear failure
of RC tie-columns?
5656
 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)

57. How to Prevent Shear Failure?
5757
Must check shear capacity of tie-
columns!
Vp ≥ Vr/2
Vr = wall shear resistance
Same approach like RC frames with
infills!
Note: an increase of tie-column length
may be required in some cases!
Vr

58. Inadequate Anchorage of Tie-Beam
Reinforcement
5858

59. Inadequate Anchorage of Tie-Beam Reinforcement
(another example)
5959

60. Tie-Beam Connection: Drawing Detail
6060
Tie-Beam Intersection: Plan ViewTie-Beam Intersection: Plan View

61. Tie-Column-to-Tie-Beam
Connection: Drawing Detail
(prefabricated reinforcement)
6161
Note additional reinforcing
bars at the tie-beam-to-tie-
column joint
(in this case, prefabricated
reinforcement cages were
used for tie-beams and tie-
columns)Tie-columnTie-column
Tie-beamTie-beam

62. Tie-Column-to-Tie-Beam Reinforcement: Anchorage
6262
Alternative anchorage details involving 90°
hooks (tie-column and tie-beam shown in an
elevation view) – note that no ties in the joint
area were observed

63. Deficiencies in Tie-Beam-to-Tie-Column Joint
Reinforcement Detailing
6363

64. RC Tie-Columns: Absence of Ties in the Joint
Area
6464

65. Tie-column Vertical Reinforcement & Tie-Beam
Longitudinal Reinforcement
6565
It is preferred to place beam reinforcement outsideIt is preferred to place beam reinforcement outside
the column reinforcement cagethe column reinforcement cage
NONO YEYESS

66. Tie-Column Reinforcement:
Drawing Detail (Chile)
6666
 Note prefabricated tie-
column reinforcement: 8
mm longitudinal bars and
4.2 mm ties at 150 mm
spacing
 Additional ties to be placed
at the site per drawing
specifications

67. Absence of Confining Elements at the Openings
6767

68. In-Plane Shear Cracking – the Effect of
Confinement
Unconfined openings Confined openings
6868

69. Recommendation…
6969
Unconfined and confined openings - criteria specified in
the Guide

70. Building Materials: Hollow Concrete
Blocks ???
7070
 Concrete blocks are widely used for masonry
construction in North America and
 The quality is very good due to advanced
manufacturing technology
 Quality of blocks in other countries often not
satisfactory due to low-tech manufacturing
technology and an absence of quality control

71. A severely damaged confined masonry concrete
block wall in Chile
7171
In spite of poor seismic performance, it is impossible
to avoid the use of concrete blocks for masonry
construction in many countries…

72. Masonry Units – Confined Masonry Guide
7272
The guide permits the use of concrete blocks, but restricts the
percentage of perforations and minimum compressive
strength: 4 MPa (bricks) and 5 MPa (blocks-gross area)

73. Haiti Blocks
7373
Block D
(215 psi)
Block C
(1000 psi)

74. Engineered Confined Masonry Buildings –
Evidence of Collapse
 Two 3-storey confined masonry buildings
collapsed in the February 2010 Chile earthquake
(Santa Cruz and Constitución)
 Most damage concentrated in the first storey level
7474

75. Simulated Seismic Response:
Shake-Table Testing
Questions:
1. Which analysis approach is able to simulate seismic response in the
most accurate manner?
2. Which approach is most suitable for practical design applications?
Sources:Sources:
Alcocer, Arias, andAlcocer, Arias, and
Vazquez (2004)Vazquez (2004)
Juan Guillermo AriasJuan Guillermo Arias
(2005)(2005)
7575

76. A Possible Collapse Mechanism for Multi-storey
Confined Masonry Buildings
7676

77. Seismic Performance of Confined Masonry
Buildings: Shake-Table Studies
777777
Shake-Table Testing of a 3-storey Confined Masonry Building at UNAM,
Mexico (Credit: Sergio Alcocer and Juan Arias)

78. Building #1: Building Complex in Constitución (Cerro O’
Higgins)
7878
A
BC
N
Note a steep slope on the west
and north sides!

79. Three Building Blocks: A, B and C
7979
collapsedcollapsed
A B C
damageddamaged

80. 8080
Building Plan – Collapsed Building
RC Tie-
Columns:
P1= 15x14 cm
P2 = 20x14 cm
P4 = 15x15 cm
P5 = 70x15 cm
P6 = 90x14 cm

81. Building C Collapse
8181
Building C
collapsed at
the first floor
level and
moved by
approximately
1.5 m towards
north

82. Building C Collapse (cont’d)
8282
C

83. Probable Causes of CollapseProbable Causes of Collapse
8383
1. Geotechnical issues: a localized influence of the
unrestrained slope boundary and localized
variations in sub-surface strata caused localized
variations of horizontal (and possibly vertical)
ground accelerations
2. Inadequate wall density (less than 1% per floor)

84. Building #2: A Three-Storey Building in
Santa Cruz
8484

85. Collapsed Three-Storey Building
8585

86. 8686
Probable Causes of Collapse
 Poor quality of
construction (both brick
and concrete block
masonry)
 Low wall density (less
than 1% per floor)
Note: only one (out of 28) buildings in the
same complex collapsed !

87. Key Causes of DamageKey Causes of Damage
8787
1. Inadequate wall density
2. Poor quality of masonry materials and
construction
3. Inadequate detailing of reinforcement in confining
elements
4. Absence of confining elements at openings
5. Geotechnical issues

88. 88
Prescriptive
international guide
endorsed by EERI
and IAEE
Available online at
www.confinedmasonry.org