“CONFINED MASONRY BUILDINGS: THE CHILEAN EXPERIENCE”

_____________________________________

M. Astroza, F. Andrade , M.O. Moroni

Santiago, january 2017

Universidad de Chile

Facultad de Ciencias Físicas y Matemáticas

Introduction

Reinforced concrete and confined masonry are the most used materials for housingconstruction.

The use of confined masonry started in the 30s.

01

23

45

67

8

m2

*106

1980 1984 1994 1998 2005 2010 2014

stoneAdobe

steelOthers

concrete Blocktimber

reinforced concretemasonry

year

material

Main components of confined masonry buildings

Unreinforced masonry panels are constructed first

Cast-in-place RC tie-columns follows

Some key events in the use of confined masonry in Chile

1928 Talca earthquake. A draft to regulate the seismic design of buildings and the way to approve building projects is proposed.

1936 Ordenanza General de Construcciones y Urbanización (OGCU) is published.1939 Low rise confined masonry buildings showed good seismic behavior during Chillan earthquake.1945 For the first time a moderate earthquake (M= 7.1) is recorded in Santiago.1959 A committee was constituted in INDITECNOR (Now INN) to prepare a Chilean code for Seismic

Design of Buildings.1972 NCH 433-Seismic Design of Buildings (first edition) is published.1975 Massive construction of multifamily masonry buildings of three and four-story starts at Metropolitan

Region.1985 Records of a severe earthquake (M = 7.8) are obtained at the epicenter area (Llolleo, Valparaiso, Viña

del Mar, Melipilla).1989 A committee was constituted to prepare NCh2123, Design of Confined Masonry Buildings.1995 Multifamily masonry building three and four stories high are built in Regions V, VI, VII VIII.1997 The first edition of NCH-2123: Design and Calculation of Confined Masonry is published.2003 NCH 433-Seismic Design of Buildings and NCh2123 (second editions) are published2005/2007/2010 Tarapacá, Tocopilla and Maule Earthquakes tested the confined masonry buildings

designed with NCh2123 Chilean codes.

Design requirements evolution

Subject OGCU-1949 NCh433Of.1972 NCh433.Of2011

Base shear coefficient

Rigid buildings (T

Main requirements NCh2123

(a) the allowable shear load capacity of a confined masonry wall isbased on the basic masonry shear strength of the masonry and thevertical load applied on it,(b) the size and the minimum quantity of concrete elementsreinforcement (tie-column and tie-beam),(c) the amount and spacing of stirrups in confining elements (Criticalzones),(d) the minimum wall thickness,(e) the tie-column spacing,(f) the required reinforcement elements around the panel openings(windows and doors).

The allowable shear load capacity is about fifty percent of the diagonalcracking panel load.

Earthquake performance previous to publication of NCh2123 code

Old confined masonry house currently in use in Chillan

Concrete block masonry panel during 1965 La Ligua earthquake

One story house, 1971 Papudo earthquake 4-story building, 1985 Llolleo earthquake

Earthquake performance after publication of NCh2123 code (Partially confined masonry)

One-story house damaged during 1997 Punitaqui earthquake , bad masonry quality (hollow concrete block masonry)

Basic masonry shear strength (τM) ≤ 0.5 MPa

Collapsed Buildings, Maule Earthquake, 2010 (partially confined masonry, low wall density)

Constitución

Santa CruzIMSK = VII -VIII

IMSK = IX

Specific observed damage:

Crushing of masonry units, with large percentageof voids and thin shells and webs, in the moststressed zones of the masonry panel.

Hollow or multi-perforated units:

Recommendation: Ratio net to gross area ≥ 70%

Specific observed damage:

Lack of tie-columns around doors and window openings.

vertical

Specific observed damage:

Tie-column width (dp) = 150 mm

Critical zone

Advisable: Size of tie-column in critical zone, dp ≥ 200 mm

Inadequate reinforcement detailing

Anchorage length

Tie-beam-Tie-column connection (Joint)

Splice of tie-beam reinforcement

Inadequate Reinforcement detailing

Amount and spacing of stirrups

Wall density index per unit floor(Jaramillo, 2011)

dni = Wall density index per unit floor in direction “i”.

nm = number of walls in direction “i”.

Aj = cross-sectional area of wall “j”.

Fj = reduction factor by wall “j” slenderness.

Ap = plan area.

n = number of stories.

Fc = reduction factor by masonry type1.0, machine made clay bricks

0.5, hand-made clay bricks

0.4, hollow concrete blocks

Recommendation: dni ≥ 0.85%

Wall density vs damage grade

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5

Damage Grade

Wal

l den

sity

Inde

x [d

n %]

MSK VI-VI1/2

MSK VII-VII1/2

MSK VIII-IXRecommendation: dni ≥ 0.85%

Gráfico2

003

044

245

224

42

20

30

20

20

35

04

00

00

00

00

20

30

0.350

40

00

40

20

23

40

40

00

00

00

00

00

00

00

00

0

0

0

0

0

0

0

MSK VI-VI1/2

MSK VII-VII1/2

MSK VIII-IX

Damage Grade

Wall density Index [dn %]

0.81

0.71

0.75

0.59

0.52

0.56

0.42

0.74

0.69

0.42

0.6

0.52

0.5

0.73

0.71

0.84

0.49

0.77

0.58

0.48

0.83

0.53

0.76

0.31

0.91

0.48

0.82

0.72

0.63

0.77

0.69

0.77

0.52

0.47

0.28

0.47

0.31

0.8

0.67

0.57

0.5

0.76

0.26

0.54

0.2

0.74

0.53

0.16

0.46

0.4

0.51

0.48

0.38

0.68

0.9

0.48

0.75

0.78

0.51

0.45

0.51

0.52

0.38

0.74

0.7

0.59

0.55

0.58

0.69

0.62

0.85

0.47

0.7

0.53

Hoja1

old

new

Hoja1

003

044

245

224

224

403

30

20

20

35

00

00

0.760

00

00

20

30

0.820

40

00

40

20

20

40

40

00

00

00

00

00

00

0

0

0

0

0

0

0

0

Int 6-6.5

Int7-7.5

Int8-9

Damage Grade

dn [%]

0.81

0.71

0.75

0.59

0.74

0.75

1.06

0.89

0.69

0.85

0.52

0.7

0.91

0.66

0.84

0.77

0.49

0.77

0.83

0.48

0.78

0.48

0.76

0.68

0.91

0.72

0.95

0.77

0.77

0.69

0.47

0.52

0.47

0.61

0.68

0.98

0.83

0.67

0.9

0.5

0.76

0.66

0.91

0.49

0.72

0.51

0.4

0.38

0.4

0.9

0.75

0.51

0.68

0.51

1.11

0.38

0.91

0.55

0.74

0.55

0.89

0.79

0.83

0.85

0.47

0.7

0.53

Hoja2

013

024

025

024

024

003

004

005

004

254

003

043

0.494

02

02

20

20

0.550

10

05

20

10

00

40

30

00

00

00

00

00

00

00

00

0

0

00

00

00

00

00

00

00

00

20

20

20

40

30

20

20

30

00

00

0.440

00

00

20

30

0.550

40

00

40

2

2

4

4

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Int 6-6.5

Int 7-7.5

Int 8-9

Damage Grade

Ig

0.54

0.49

0.81

0.54

0.49

0.73

0.43

0.61

0.5

0.67

0.63

0.5

0.49

0.63

0.49

0.49

0.9

0.4

0.44

0.81

0.47

0.44

0.5

0.53

0.44

0.45

0.49

0.49

0.65

0.61

0.54

0.45

0.49

0.49

0.5

0.61

0.54

0.63

0.54

0.63

0.49

0.68

0.49

0.55

0.4

0.4

0.4

0.49

0.73

0.39

0.81

0.73

0.52

0.72

0.41

0.65

0.49

0.61

0.81

0.49

0.65

0.61

0.81

0.61

0.72

0.49

0.72

0.54

0.81

0.55

0.9

0.81

0.9

0.44

0.81

0.44

0.9

0.49

0.72

0.54

0.81

0.54

0.72

0.55

0.81

0.49

0.64

0.54

0.58

0.67

0.58

0.49

0.81

0.49

0.72

0.4

0.65

0.47

0.58

0.48

0.58

0.49

0.65

0.61

0.72

0.44

0.72

0.65

0.55

0.58

0.49

0.81

0.49

0.72

0.49

0.72

0.65

0.58

0.4

0.81

0.9

0.49

0.52

0.41

0.49

0.61

0.49

0.68

0.49

0.61

0.55

0.48

0.5

0.44

0.55

0.49

Hoja3

003

044

245

224

42

20

30

20

20

35

04

00

00

00

00

20

30

0.350

40

00

40

20

23

40

40

00

00

00

00

00

00

00

00

0

0

0

0

0

0

0

MSK VI-VI1/2

MSK VII-VII1/2

MSK VIII-IX

Damage Grade

Wall density Index [dn %]

0.81

0.71

0.75

0.59

0.52

0.56

0.42

0.74

0.69

0.42

0.6

0.52

0.5

0.73

0.71

0.84

0.49

0.77

0.58

0.48

0.83

0.53

0.76

0.31

0.91

0.48

0.82

0.72

0.63

0.77

0.69

0.77

0.52

0.47

0.28

0.47

0.31

0.8

0.67

0.57

0.5

0.76

0.26

0.54

0.2

0.74

0.53

0.16

0.46

0.4

0.51

0.48

0.38

0.68

0.9

0.48

0.75

0.78

0.51

0.45

0.51

0.52

0.38

0.74

0.7

0.59

0.55

0.58

0.69

0.62

0.85

0.47

0.7

0.53

013

024

025

024

023

004

005

004

00

25

00

04

04

02

02

20

20

0.550

10

05

24

10

00

40

30

00

00

00

00

00

00

00

03

0

0

00

00

00

00

00

00

00

00

04

20

20

40

20

30

20

20

30

00

00

00

03

00

20

30

0.550

40

00

40

20

20

40

4

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

MSK VI-VI1/2

MSK VII-VII1/2

MSK VIII-IX

Damage Grade

Gallegos Index [Ig]

0.54

0.49

0.81

0.54

0.49

0.73

0.43

0.61

0.5

0.67

0.53

0.5

0.49

0.54

0.9

0.49

0.49

0.81

0.4

0.44

0.454

0.47

0.4

0.45

0.56

0.4

0.44

0.49

0.55

0.54

0.49

0.49

0.49

0.61

0.54

0.53

0.54

0.54

0.49

0.61

0.49

0.55

0.4

0.44

0.4

0.4

0.49

0.44

0.39

0.73

0.81

0.49

0.73

0.41

0.72

0.49

0.65

0.61

0.49

0.81

0.61

0.65

0.61

0.81

0.49

0.72

0.54

0.72

0.55

0.45

0.64

0.58

0.44

0.58

0.55

0.81

0.49

0.72

0.44

0.65

0.49

0.58

0.49

0.58

0.49

0.65

0.55

0.72

0.49

0.65

0.54

0.81

0.67

0.9

0.49

0.81

0.49

0.9

0.4

0.81

0.47

0.56

0.9

0.49

0.72

0.61

0.81

0.44

0.72

0.44

0.81

0.55

0.5

0.49

0.72

0.49

0.65

0.49

0.58

0.81

0.4

0.72

0.4

0.72

0.49

0.65

0.49

0.58

0.81

0.49

0.9

0.41

0.49

0.61

0.49

0.68

0.68

0.49

0.61

0.55

0.48

0.61

0.49

0.5

0.39

0.55

0.49

Analytical and Recorded Response:Comunidad Andalucia building

A local acceleration network was installedin 1992.

4 stories, first story RC.

Hand-made bricks e=15 cm.

NCh433. Of72.

Conjunto de viviendas Comunidad Andalucía

Comuna Santiago Centro, Región Metropolitana

End of construction: March1992

February 27, 2010 earthquake effects:

Peak acceleration larger than 1 [g] in the longitudinal direction Diagonal crack at the 2º floor

“Deformations were closed to the elastic limit”

Building Characteristics

Axis 1

Axis 3

Axis A Axis C

1

3

A C

Damaged wall

Plan 10 x 6 m RC slab. e=10 cm Roof: wood

February 27, 2010 records

Dynamics properties

Fundamental frequency v/s ground peak acceleration

Microtremors frecuencies

Analytical lineal response

Mode Period FFT [s]Period model

[s]

N-S - 0.216E-O 0,179 0.180

Torsional - 0.149

Response for different damping

β[%] Acel NS [cm/s²] Acel EO [cm/s²]

2 1542.7 1133.45 1094.1 724.6

10 794.0 505.8

0 20 40 60 80 100 120 140 160 180 200-6

-4

-2

0

2

4

6Desplazamiento EO 4° piso

Tiempo [s]

Despl

azamie

nto [cm

]

SAP2000Registro

Displacements

Lessons Learnt From Chilean Earthquakes

Confined masonry buildings show a good performance if therecommendations of the Chilean Code NCh2123 are satisfied ,

A wall density per unit floor plan equal to or larger than 0.85% on eachdirection of building plan is recommended.

Key factors that contributed to the presence of severe damages are:the local site conditions, a low wall density in one or both horizontaldirections, limited robustness of masonry units, absence ofreinforcement (tie-column) around openings, reinforcement detailing,and construction of RC confining elements. In recent years, it hasbecome evident that the effect of the focal mechanism of theearthquake also plays an important role.

Lessons Learnt From Chilean Earthquakes

The confining elements must be located close enough to avoid out-of-plane damage, especially when wall thickness is less than orequal to 150 mm.

Lack of tie-columns around window opening decreases the shearstrength and the post-shear cracking displacement capacity.

It is recommended to include closer stirrups at both ends of tie-columns and a minimum cross sectional area of tie-column to avoiddiagonal crack propagation that may appear at the masonry panel.

The detailing of reinforcement bars is essential in the zones whereconfinement elements concur and has been the cause of badbehavior observed in many masonry houses since 1958.

The vertical reinforcement bars placed inside vertical holes locatedat the ends of the masonry panels, in replacement of externalconcrete tie-column, has been ineffective.

The misbehaviour of masonry walls built with hollow concreteblocks during all the Chilean earthquakes, since 1965, suggeststhat its use should be avoided

Conclusions about analytical model

To reproduce the recorded behavior of the AndaluciaBuilding, material properties, modal damping and rigidityof the support were determined.

The damaged wall was subjected to a shear stress closeto its nominal cracking shear strength.

Fortunately the building over-strength was important, ifnot more damage would be expected.

¡ GRACIAS !

“CONFINED MASONRY BUILDINGS: THE CHILEAN EXPERIENCE”�_____________________________________IntroductionMain components of confined masonry buildingsSome key events in the use of confined masonry in ChileDesign requirements evolutionMain requirements NCh2123Earthquake performance previous to publication of NCh2123 codeEarthquake performance after publication of NCh2123 code (Partially confined masonry)Collapsed Buildings, Maule Earthquake, 2010 (partially confined masonry, low wall density)Specific observed damage:Specific observed damage: Specific observed damage:Inadequate reinforcement detailing Inadequate Reinforcement detailingWall density index per unit floor�(Jaramillo, 2011) Wall density vs damage gradeAnalytical and Recorded Response:� Comunidad Andalucia buildingSlide Number 18Building CharacteristicsFebruary 27, 2010 recordsDynamics propertiesAnalytical lineal responseLessons Learnt From Chilean EarthquakesLessons Learnt From Chilean Earthquakes Conclusions about analytical modelSlide Number 26