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ROSE SCHOOL

Homework # 0Masonry construction in Chile

Francisco Figueroa3/18/2013


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Francisco Figueroa

Homework # 0 Masonry construction Chile

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1 Use and relevance of masonryThe masonry as structural material on Chile is used on two ways, confined masonry and

reinforcement masonry, however still can be found some mud houses or unreinforced masonry

but this kind of constructions have been disappearing over the time, due to earthquakes.

Figure 1: left: Mud House (Casa de Adobe) Los Angeles Chile right: Most common new masonry house

The most common use of masonry is on residential building of one or two story, predominate the

combination of masonry on the first floor and some other light material on the second floor

(wood or light steel). Usually for these cases, the floor is made it with wood or a slab of concrete

(usually the slab of 12-15 cm for a two stories building), when is one story building the roof will

be of wood.

Also can be found 3 or 4 story masonry building, usually for these cases is used a concrete slab.

The connection between the walls and the slab is monolithic.

In term of volume of new masonry building, information of the last decade is presented because

was the only available, never the less this data is helpful to understand the materials used on

new constructions.


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According to INE (National Statistics Institute, Chile, 2000) the wall materials on residential

building of 1 or 2 stories are given by the next chart:

Figure 2: Wall materials on residential buildings

Note: Inside of the 52% of masonry are reinforced and confined masonry.

2 Design codes of masonryIn the early 20

thcentury, considering the observed poor seismic behavior of the unreinforced

masonry in Chile and abroad (San Francisco -1906, Tokio-1923, New Zealand 1931, among

others), arises the need of reinforced the building with masonry in order to improve the behavior

on futures earthquakes. With this purpose arises the first ordinance of masonry buildings (ex:

earthquake Building ordinances for small towns in the Earthquakes Districts of Italy, 1927).

On Chile, after Talca earthquake (1928) the first technical documents with the provisions and

limits to fulfill on masonry building according with the reinforcement technic (Ordenanza General

sobre Construcciones y Urbanizacin, General Ordinances about constructions and urbanization,

1931)

Usually the codes on Chile are based on foreign codes and then have been calibrated due to the

experience over the earthquakes. For the masonry code, the experience of Chillan earthquake

(1939) is really important and worthwhile to mention.

Masonry

52%

RC28%

Wooden

14%

other

6%

Materiales de muro en la edificacin habitacional (datos 2000)


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At 23:33, the earth began to shake strongly underneath Chilln, destroying more than half of it,

at around 3,500 homes (including the recently constructed Casa Rabi) which then was the city.

After this quake, others came, which, although they were less intense, left the city completely

destroyed. Until then, the Cathedral of Chilln had been one of the principal buildings of the

area, but it was completely destroyed by the earthquake. The church that was built to replace

the one destroyed in the earthquake was designed specifically to withstand future earthquakes.

Figure 3: Left: Old Chillan Church Right: Actual Chillan Church.

A memorial cross next to the cathedral in Chilln commemorates the earthquake victims 50

years later.

It is currently the single earthquake that has caused the most deaths in

Chile. (Ms=8.3). The death toll was around 28000 compare to the 2000death of the great Chilean earthquake of 1960.

Amid collapsed buildings and desolation due to the earthquake, there

was a contribution of the ordinance of 1931, the few confined masonry

houses built it using this code resisted the earthquake with some minor

damage. This new technique to build confined masonry (put first the

units before casting the concrete of the beam and columns) was

successfully tested on the earthquake of Mesina (1908) Italy.

Chillan 1939 earthquake showed the inefficiency of unreinforced

masonry to resist seismic excitation and the goodness of the confinedmasonry.

To give an idea of the damage of the city after the earthquake, is

showed a table according to the observation of 3482 residencial

buildings.


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Material% over

Total

% in

good

condition

%

deteriorated

% partial

collapse

% total

collapse

Mud 62.6 - 35 8 59

URM 24.2 - 43 13 44

Wood 3.0 4 88 8 -

RM 4.5 53 31 5 11

RC 0.2 80 - 20 -

Mud and

wood5.5 86 6

This experience shows to the constructor the need to follow the provisions of the code and get

real importance to the technique inspection.

Nowadays Chile has two codes for masonry structures, these codes are based on the experience

of Via (1985) and modified on 2003 due to several experimental test running on Chile as a part

of the project FDI (Quality of constructions, Technique update of official Chilean codes), this

update was due the need to include new dimensions of unit for the constructions of masonry

buildings.

Figure 4: Tested walls on the frame of the project FDI


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2.1 Nch169 UnitsThis code assigns classifications of units according some requirement of the units.

MqM brick without perforations2.1.1Most common use is for confined masonry

MqH less than 50% perforations2.1.2

Used for reinforcement masonry

MqP2.1.3

Normally used for non-structural walls

Concrete blocks2.1.4


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Note: Resistencia a la compression = compression resistance

Absorcion de agua = water absorption

adherencia = cohesion force.

2.2 NCh433 Earthquake resistance design of buildingsThe demand and the factor R (q on Eurocode) are defined on this code. Here will shows some

values related to masonry.

The zoning of Chile is showed on the topic 3, which shows the seismic hazard of Chile, this zoning

is on the code NCh433.

The lateral force of a building is defined by: Where Seismic coefficientI: important coefficient (normal buildings equal to 1): Seismic weight


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The R factor is defined on the next table:

Translation of table 5.1:

Confined masonry is equal to 4.

Reinforced masonry with unit or concrete block on which all the perforations had been filled and

also for double layers walls is equal to 4.

Reinforced masonry with unit or concrete block on which not all the perforations had been filled

is equal to 3.

Homever, is important to mentions that on Chile there is an upper bound for the lateral force Q,defining a Cmax to use on the equation Q=C*I*P.


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For obtain this Cmax value, also is included the table with the parameters related to the soil. Soil

I is (approx.) rock. Concepcion is on soil 3 and is considered the worst soil on the Code. On soil 4

is need it a specified study of the seismic hazard of the place.

So for soil 3 on Zone 3, with confined masonry Cmax=0.55*1.2*0.4*g= 0.264g.

Usually masonry buildings are stiff and the force is over this limit, so if the elastic spectra is

considered with a 0.4 g, the R factor considering this upper boundary limit will be bigger than 4.

Note: For reinforced concrete building on zone 3, soil 3, (R=7 -> Cmax =0.35*1.2*0.4*g=0.168g)

2.3 NCh1928 Reinforced MasonryNCh1928 of 1993 Modified on 2003: Reinforced Masonry Design requirements and

calculations.

This code use the admissible stress approach and assuming this:

o The masonry work as a homogenous materialo Sections planes remains planeso Elastic modulus of masonry and steel remains constant.o Masonry doesnt resist traction stress.o The steel is bounded and fixed to the masonry.

This code also defined two admissible stresses, one with and one with-out special technique

inspection, in order to have a conservative design with-out inspection.

o The minimum wall thickness is 14 cm.o The minimum steel bar are with a diameter 8 mmo The minimum steel bar on the corner of the walls is 12 mmo On the infill of the holes is not allow to use mortar, shut be concrete.


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2.4 NCh2123 Confined MasonryNCh2123 of 1997 Modified on 2003: Confined Masonry Design requirements and calculations.

Note: All the strengths are referred to the gross area.

Strength compression (fm)2.4.1

For defined the compression resistance (fm) shut be used a set of experimental test, or the unit

compression strength (some limit values due to the uncertantains) or a value given by the code

(really slow value, 1.5 MPa)

Shear strength and traction resistance due to flexion.2.4.2

Could be computed by a set of experimental results or related to a table with conservatives

values. (Example: handmade unit m=0.25 MPa Fbt=0.1 MPa).

Elastic modulus and Shear Modulus2.4.3

Level of Confined masonry:2.4.4

Shut be confined all the walls on building on the seismic zone 2 and 3. For zone 1 all the

perimeter shut be confined, at least an amount of walls who carried the 70% of the shear force

of the level and any wall who carried 10% or more of the shear of the level.

Shear force allowed:2.4.5 = basic shear resistance of the masonry measured over the gross area.= average stress on the section= gross area, included the columns

Axial force allowed:2.4.6

=basic compression resistance of the masonry measured over the gross area.= slenderness factor. [ ( )

]= thickness of the wall


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=less value of the distance between columns or the distance between beam.

Flexion and compression due to in-plane forces2.4.7

a) Simple Flexion: =longitudinal steel area on each columns on the edge of the wall.= distance between the centroid of columns edge of the wall.= admissible stress on the steel, assumed = yield stress on the steel

b) Composite Flexion ( ) = axial force on the wall

= allowed axial force on the wall= distance between the centroid of the longitudinal steel bar on the tensile side of the walluntil the edge of the compressive side of the wall.


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3 Earthquake Hazard on ChileChile is on the subduction zone between the pacific plate and South American plate, due this all

the country is subjected to several earthquakes generated by the interactions of these plates.

The earthquake hazard of Chile is high. The seismic demand for buildings is on the code

NCh433of93mod2009 (these means Chilean code number 433 formalized on 1996 and modified

on 2009) and divided the country on 3 zones, which zone 3 means the zone with the highest

seismicity.


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Zoning on Chile, maps on

NCh433.

Zone Ao

1 0.20 g

2 0.30 g

3 0.40 g


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4 References- NCh433 Chilean Code Building design Code- NCh1928 Chilean Code Reinforced Masonry Code- NCh2123 Chilean Code Confined Masonry Code- NCh169 Chilean Code Clay Brick Code- http://en.wikipedia.org/wiki/1939_Chill%C3%A1n_earthquake#Gallery- http://chillanantiguo.blogspot.it/2010/10/catedral-de-chillan.htmlhttp://earthquake.usgs.gov/earthquakes/world/chile/gshap.phphttp://www.confinedmasonry.org/performance-of-confined-masonry-buildings-in-the-

february-27-2010-chile-earthquake

- Manual del albail de ladrillos ceramicoswww.ich.cl- M. Astroza Design of structural masonry Handout Universidad de Chile- Seismic engineering on Chile Rodrigo Flores- Interview with Eng. Luis Mendieta [email protected]
http://en.wikipedia.org/wiki/1939_Chill%C3%A1n_earthquake#Galleryhttp://en.wikipedia.org/wiki/1939_Chill%C3%A1n_earthquake#Galleryhttp://chillanantiguo.blogspot.it/2010/10/catedral-de-chillan.htmlhttp://chillanantiguo.blogspot.it/2010/10/catedral-de-chillan.htmlhttp://earthquake.usgs.gov/earthquakes/world/chile/gshap.phphttp://earthquake.usgs.gov/earthquakes/world/chile/gshap.phphttp://www.confinedmasonry.org/performance-of-confined-masonry-buildings-in-the-february-27-2010-chile-earthquakehttp://www.confinedmasonry.org/performance-of-confined-masonry-buildings-in-the-february-27-2010-chile-earthquakehttp://www.confinedmasonry.org/performance-of-confined-masonry-buildings-in-the-february-27-2010-chile-earthquakehttp://www.confinedmasonry.org/performance-of-confined-masonry-buildings-in-the-february-27-2010-chile-earthquakehttp://www.confinedmasonry.org/performance-of-confined-masonry-buildings-in-the-february-27-2010-chile-earthquakehttp://www.ich.cl/http://www.ich.cl/http://www.ich.cl/http://www.ich.cl/http://www.confinedmasonry.org/performance-of-confined-masonry-buildings-in-the-february-27-2010-chile-earthquakehttp://www.confinedmasonry.org/performance-of-confined-masonry-buildings-in-the-february-27-2010-chile-earthquakehttp://earthquake.usgs.gov/earthquakes/world/chile/gshap.phphttp://chillanantiguo.blogspot.it/2010/10/catedral-de-chillan.htmlhttp://en.wikipedia.org/wiki/1939_Chill%C3%A1n_earthquake#Gallery

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