Seismic Performance of Confined Masonry Buildings in the February - - PowerPoint PPT Presentation

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Seismic Performance of Confined Masonry Buildings in the February - - PowerPoint PPT Presentation

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Seismic Performance of Confined Masonry Buildings in the February 27, 2010 Chile Earthquake Svetlana Brzev British Columbia Institute of Technology, Vancouver, Canada Maximiliano Astroza Maria Ofelia Moroni Yadlin Universidad de Chile,

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Svetlana Brzev

British Columbia Institute of Technology, Vancouver, Canada

Maximiliano Astroza Maria Ofelia Moroni Yadlin

Universidad de Chile, Santiago, Chile

Seismic Performance of Confined Masonry Buildings in the February 27, 2010 Chile Earthquake

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Background Background

  • Magnitude 8.8 earthquake

Magnitude 8.8 earthquake

  • 521 deaths

521 deaths

  • 5 collapsed buildings

5 collapsed buildings

  • 100 severely damaged buildings

100 severely damaged buildings

  • Approximately 1% of the total building

Approximately 1% of the total building stock in the earthquake stock in the earthquake-

  • affected area either

affected area either damaged or collapsed damaged or collapsed

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Earthquake Earthquake Rupture Zone Rupture Zone

EERI Newsletter, June 2010

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Seismic Intensity Seismic Intensity Map (MSK Scale) Map (MSK Scale)

Santiago Rancagua MSK 6.5 Talca MSK 8.0 Constitucion MSK 9.0 Cauquenes MSK 8.0 Santa Cruz MSK 7.5

Paper by Astroza et al. EERI web site Chile eq.

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Over 12 million people were estimated to have experienced shaking of MMI intensity VII or stronger (about 72% of the total population of Chile) Source: PAGER (USGS)

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Confined Masonry (CM) Construction in Chile

Widely used for construction of low-rise single

family dwellings (up to two-storey high), and medium-rise apartment buildings (three- to four- storey 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.

The area affected by the Maule earthquake was

exposed to several major earthquakes in the past, including the 1985 Llolleo earthquake (M 7.8).

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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). Modern masonry codes first issued in 1990s – prior to that, a 1940 document “Ordenanza General de Urbanismo y Construcción” had been followed

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Seismic Performance of Confined Seismic Performance of Confined Masonry Construction Masonry Construction

By and large, confined masonry buildings performed

well in the earthquake.

Most one- and two-storey single-family dwellings

did not experience any damage, except for a few buildings which suffered moderate damage.

Large majority of three- and four-storey buildings

remained undamaged, however a few buildings suffered severe damage, and two three-storey buildings collapsed.

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Confined Masonry Confined Masonry Buildings

Buildings:

: Key Components Key Components

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M

Masonry walls asonry walls – built using a variety of masonry units with a typical thickness of 140 mm

  • T

Tie ie-

  • columns

columns - vertical RC confining elements at 3 to 3.5 m spacing

  • T

Tie ie-

  • beams

beams - horizontal RC confining elements provided at the floor/roof level (typical floor height 2.2 to 2.3 m)

Confined Masonry: Key Components Confined Masonry: Key Components

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Confined Masonry: Key Design Provisions Confined Masonry: Key Design Provisions

Source: Seismic Design Guide for Masonry Buildings (EERI, 2010)

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Masonry Units

Hollow clay blocks Clay bricks Concrete blocks

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Confined Masonry: Construction Sequence Confined Masonry: Construction Sequence Foundation construction, showing RC tie-column reinforcement

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Confined Masonry: Construction Sequence Confined Masonry: Construction Sequence Masonry wall construction in progress

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Confined Masonry Construction: Confined Masonry Construction: Toothing Toothing at the Wall to Tie at the Wall to Tie-

  • Column Interface

Column Interface Toothing enhances interaction between masonry walls and RC confining elements

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Steel Reinforcement

Common steel grades:

A44-28H: yield strength 280 MPa A63-42H: yield strength 420 MPa AT56-50H: high-strength steel used for tie-beam

and tie-column prefabricated reinforcement cages and ladder reinforcement (yield strength 500 MPa)

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Steel Reinforcement Cages: Examples

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Floor Systems

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)

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“Tralix” Floor System

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“Tralix” Floor System (Cont’d)

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Timber Roof Trusses (Typical)

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Low Low-

  • Rise Confined Masonry Construction

Rise Confined Masonry Construction

Single-storey rural house

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Low Low-

  • Rise Confined Masonry Construction

Rise Confined Masonry Construction

Two-storey townhouses (semi-detached): small plan dimensions (5 m by 6 m per unit)

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Typical Damage Patterns in Low Typical Damage Patterns in Low-

  • Rise

Rise Buildings Buildings

Horizontal crack at the timber gable-to-masonry wall interface

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Typical Damage Patterns in Low Typical Damage Patterns in Low-

  • Rise

Rise Buildings Buildings

In-plane shear cracking in masonry piers (note absence of tie-columns at the openings)

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Medium Medium-

  • rise Confined Masonry Buildings

rise Confined Masonry Buildings

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Damage Patterns Damage Patterns

Typical damage patterns: Typical damage patterns:

  • in

in-

  • plane shear failure of masonry walls, and

plane shear failure of masonry walls, and

  • damage to the RC confining members

damage to the RC confining members (particularly tie (particularly tie-

  • columns)

columns)

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In In-

  • Plane Shear Cracking: a Case

Plane Shear Cracking: a Case Study from Santiago Study from Santiago

Typical four-

storey buildings in Santiago

Recorded PGA

  • approx. 0.3g
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In In-

  • Plane Shear Cracking

Plane Shear Cracking (ground floor level) (ground floor level)

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In In-

  • Plane Shear Cracking

Plane Shear Cracking (third floor level) (third floor level)

Another building in the same complex (damage occurred at the third floor level only)

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In In-

  • Plane Shear Cracking: Damage

Plane Shear Cracking: Damage Pattern at the Third Floor Level Pattern at the Third Floor Level

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In In-

  • Plane Shear Cracking

Plane Shear Cracking – – the Effect the Effect

  • f Confinement
  • f Confinement

Non-confined openings Confined openings

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In In-

  • plane shear failure of masonry

plane shear failure of masonry walls at the base level walls at the base level -

  • hollow clay

hollow clay blocks ( blocks (Cauquenes Cauquenes) )

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In In-

  • plane shear failure of masonry

plane shear failure of masonry walls at the base level (cont walls at the base level (cont’ ’d) d)

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In In-

  • plane shear failure: hollow clay

plane shear failure: hollow clay block masonry block masonry

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In In-

  • plane shear failure: clay brick masonry

plane shear failure: clay brick masonry

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In In-

  • plane shear failure: hollow

plane shear failure: hollow concrete blocks concrete blocks

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Out Out-

  • of
  • f-
  • Plane Wall Damage

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

Damage at the 2nd floor level

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Out Out-

  • of
  • f-
  • Plane Damage

Plane Damage (cont (cont’ ’d) d)

Damage at the 3rd floor level

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Buckling of a RC Tie Buckling of a RC Tie-

  • Column due to the

Column due to the Toe Crushing of the Masonry Wall Panel Toe Crushing of the Masonry Wall Panel

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Tie-Column Failure

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Shear Failure of RC Tie Shear Failure of RC Tie-

  • Columns

Columns

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Causes of Damage Causes of Damage 1.

  • 1. Inadequate

Inadequate wall density wall density 2.

  • 2. Poor quality of masonry materials

Poor quality of masonry materials and construction and construction 3.

  • 3. Inadequate detailing of

Inadequate detailing of reinforcement in confining elements reinforcement in confining elements 4.

  • 4. Absence of confining elements at

Absence of confining elements at

  • penings
  • penings

5.

  • 5. Building layout issues

Building layout issues 6.

  • 6. Geotechnical issues

Geotechnical issues

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  • 1. Inadequate Wall Density Index
  • 1. Inadequate Wall Density Index

d= Aw/nAp

Low d values (0.7 to 0.8 %) observed in severely damaged/collapsed buildings (n denotes number of floors)

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  • 2. Poor Quality of Masonry Materials
  • 2. Poor Quality of Masonry Materials

and Construction and Construction

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  • 3. Inadequate Anchorage of Tie
  • 3. Inadequate Anchorage of Tie-
  • Beam

Beam Reinforcement Reinforcement

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  • 3. Inadequate Anchorage of Tie-Beam Reinforcement

(another example)

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  • 3. Tie-Beam Connection: Drawing Detail

Tie Tie-

  • Beam Intersection: Plan View

Beam Intersection: Plan View

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  • 3. Tie-Column-to-Tie-Beam

Connection: Drawing Detail (prefabricated reinforcement) Tie Tie-

  • column

column Tie Tie-

  • beam

beam

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)

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  • 3. Tie-Column-to-Tie-Beam

Reinforcement: Anchorage 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

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  • 3. Deficiencies in Tie
  • 3. Deficiencies in Tie-
  • Beam

Beam-

  • to

to-

  • Tie

Tie-

  • Column Joint Reinforcement Detailing

Column Joint Reinforcement Detailing

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  • 3. RC Tie-Columns: Absence of Ties in the

Joint Area

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  • 3. Tie-Column

Reinforcement: Drawing Detail

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

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  • 4. Absence of Confining Elements at the Openings
  • 4. Absence of Confining Elements at the Openings
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  • 4. Absence of Confining Elements at the Openings
  • 4. Absence of Confining Elements at the Openings

(another example) (another example)

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  • 5. Effect of Building Layout: Four
  • 5. Effect of Building Layout: Four

Buildings in Buildings in Cauquenes Cauquenes

Severely Severely damaged damaged building building

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  • 5. Effect of Building Layout : Four
  • 5. Effect of Building Layout : Four

Buildings in Buildings in Cauquenes Cauquenes (cont (cont’ ’d) d)

Moderately Moderately damaged damaged buildings buildings

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Multi Multi-

  • storey Confined Masonry Buildings:

storey Confined Masonry Buildings: Soft Storey Collapse Mechanism Soft Storey Collapse Mechanism

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Engineered Confined Masonry Buildings Engineered Confined Masonry Buildings – – Evidence of Collapse 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

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A B C N Building Complex in Constitución: Three-Storey Confined Masonry Buildings

Steep slope on the west side

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collapsed collapsed

Three Building Blocks: A, B and C Three Building Blocks: A, B and C

A B C damaged damaged

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Building Plan – Collapsed Building

RC Tie-Columns: P1= 15x14 cm P2 = 20x14 cm P4 = 15x15 cm P5 = 70x15 cm P6 = 90x14 cm

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Building C Collapse Building C Collapse

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

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Building C Collapse (cont Building C Collapse (cont’ ’d) d)

C

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Probable Causes of Collapse Probable Causes of Collapse

1.

  • 1. Geotechnical issues: a localized influence of

Geotechnical issues: a localized influence of the unrestrained slope boundary and the unrestrained slope boundary and localized variations in sub localized variations in sub-

  • surface strata

surface strata might have generated localized variations of might have generated localized variations of horizontal (and possibly vertical) ground horizontal (and possibly vertical) ground accelerations accelerations 2.

  • 2. Inadequate wall density (less than 1% per

Inadequate wall density (less than 1% per floor) floor)

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Collapse of a Three Collapse of a Three-

  • Storey Building in

Storey Building in Santa Cruz Santa Cruz

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Collapsed Three Collapsed Three-

  • Storey Building

Storey Building

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Soft Storey Collapse Soft Storey Collapse (ground floor missing) (ground floor missing)

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Probable Causes of Collapse 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 32) buildings in the same complex collapsed !

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Acknowledgments

Earthquake Engineering Research Institute

(SPI Projects Fund)

Félix Cáceres, Jorge Jiménez and Rodrigo

González, Serviu Regional Maule, Talca

Patricio Lara, Universidad de Talca Universidad de Chile students Felipe

Cordero, Manuel Nuñez, and Felipe Castro

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