Intro to Confined Masonry


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Intro to Confined Masonry

  1. 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. 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. 3. TopicsTopics 33  Confined masonry: key conceptsConfined masonry: key concepts Lessons learned from the pastLessons learned from the past earthquakesearthquakes
  4. 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. 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. 6. Confined Masonry Construction: An Alternative to RC Frame Construction 66
  7. 7. Confined Masonry Construction: An Alternative to Unreinforced Masonry Construction 77
  8. 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. 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. 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. 11. Confined Masonry Design Codes 1111Available at
  12. 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. 13. Components of a Confined Masonry Building: 1313
  14. 14. 1414 Reinforced Concrete Frame ConstructionReinforced Concrete Frame Construction
  15. 15. 1515 Confined Masonry Construction
  16. 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. 17. Confined Masonry: Construction Process 1717 Source: TomSource: Tom SchacherSchacher
  18. 18. Confined Masonry vs RC Frames with Infills – Key Differences 1818
  19. 19. A comparison: confined masonry and RC frames with infills Youtube videos developed by a Calpoly student, USA No.No. 1919
  20. 20. Location of Confining Elements is Very Important! 2020
  21. 21. Key Elements – Layout Rules 2121
  22. 22. Typical Floor Plans – Examples from Chile 2222 Source: O. Moroni and M.Source: O. Moroni and M. AstrozaAstroza
  23. 23. Confined Masonry Panel Under Lateral Loading: Shear Failure 2323
  24. 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. 25. Confined Masonry Panel – Bending Stress Distribution Source: EERI Guide (2011) 2525
  26. 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. 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. 28. Mechanism of Seismic Response in a Confined Masonry Building 2828 Masonry walls Critical region Diagonal cracking Source: M. Astroza lecture notes, 2010
  29. 29. Failure Mechanism: Key Stages 2929 Masonry walls Damage in critical regions Onset of Diagonal cracking
  30. 30. 3030 This condition should be avoided!
  31. 31. Confined Masonry Construction: Toothing at the Wall-to-Tie-Column Interface 3131 Toothing enhances interaction between masonry walls and RC confining elements
  32. 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. 33. 3333 ecomán earthquake,ecomán earthquake, January 2003January 2003 Oaxaca quake,Oaxaca quake, September 1999September 1999
  34. 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. 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. 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. 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. 38. Low-Rise Confined Masonry Construction 3838Single-storey rural house
  39. 39. Low-Rise Confined Masonry Construction 3939 Two-storey townhouses (semi-detached): small plan dimensions (5 m by 6 m per unit)
  40. 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. 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. 42. In-plane shear failure of masonry walls at the base level - hollow clay blocks (Cauquenes) 4242
  43. 43. In-plane shear failure of masonry walls at the base level (cont’d) 4343
  44. 44. In-plane shear failure: hollow clay block masonry 4444
  45. 45. Same failure mechanism as infill masonry in RC frames! 4545 Diagonal Tension (INPS-2), FEMA 306 p.207
  46. 46. In-plane shear failure: clay brick masonry 4646
  47. 47. Same failure mechanism as infill masonry in RC frames! 4747 Bed Joint Sliding (INPS-3), FEMA 306 p.208
  48. 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. 49. Out-of-Plane Damage (cont’d) 4949 Damage at the 3rd floor level
  50. 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. 51. Discussion on Out-of-Plane Wall Failure 5151 Source: EERI Confined Masonry Guide
  52. 52. Tie-Column Failure 5252
  53. 53. Buckling of a RC Tie-Column due to the Toe Crushing of the Masonry Wall Panel 5353
  54. 54. Shear Failure of RC Tie-Columns 5454
  55. 55. Same failure mechanism as columns in RC frames with infills! 5555 Column Snap Through Shear Failure (INF1C1), FEMA 306 p.211
  56. 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. 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. 58. Inadequate Anchorage of Tie-Beam Reinforcement 5858
  59. 59. Inadequate Anchorage of Tie-Beam Reinforcement (another example) 5959
  60. 60. Tie-Beam Connection: Drawing Detail 6060 Tie-Beam Intersection: Plan ViewTie-Beam Intersection: Plan View
  61. 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. 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. 63. Deficiencies in Tie-Beam-to-Tie-Column Joint Reinforcement Detailing 6363
  64. 64. RC Tie-Columns: Absence of Ties in the Joint Area 6464
  65. 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. 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. 67. Absence of Confining Elements at the Openings 6767
  68. 68. In-Plane Shear Cracking – the Effect of Confinement Unconfined openings Confined openings 6868
  69. 69. Recommendation… 6969 Unconfined and confined openings - criteria specified in the Guide
  70. 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. 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. 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. 73. Haiti Blocks 7373 Block D (215 psi) Block C (1000 psi)
  74. 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. 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. 76. A Possible Collapse Mechanism for Multi-storey Confined Masonry Buildings 7676
  77. 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. 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. 79. Three Building Blocks: A, B and C 7979 collapsedcollapsed A B C damageddamaged
  80. 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. 81. Building C Collapse 8181 Building C collapsed at the first floor level and moved by approximately 1.5 m towards north
  82. 82. Building C Collapse (cont’d) 8282 C
  83. 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. 84. Building #2: A Three-Storey Building in Santa Cruz 8484
  85. 85. Collapsed Three-Storey Building 8585
  86. 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. 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. 88 Prescriptive international guide endorsed by EERI and IAEE Available online at