The Boumerdes, Algeria, The Boumerdes, Algeria, Earthquake of May 21, 2003Earthquake of May 21, 2003

Svetlana Brzev, P.Eng., Ph.D.Instructor, Civil &Structural

Engineering

Algeria: Where Europe meets Africa

A Mediterranean country in North Africa

Current population 30 million (tripled in

the last 30 years)

French colony until 1962

Majority of the population lives in the

northern part

Over 80% of the country covered by the

Sahara desert

The Earthquake

May 21, 2003 at 19:44 local time

A shallow earthquake of Mw = 6.8

The epicentre: the Province of

Boumerdes, 50 km east of the

capital Algiers

The Earthquake

Damaged area 100 km long x 50 km

wide

Hardest hit regions: Boumerdes,

Zemmouri, Thenia, and eastern

districts of the capital Algiers

The Impact2,287 people dead, more than

11,000 injured

About 182,000 housing units

(apartments and private houses)

damaged

Out of these, over 19,000 units

beyond repair (uninhabitable)

The Impact

Economic loss > $6 billion

(10% of Algeria’s total

GDP for 2001)

Over 120,000 homeless

Seismotectonic Setting

Northern Algeria is located at the

margin between the north moving

African plate and the Eurasian plate

A series of thrust and normal faults

mapped in the area of the Boumerdes

eq.

Tectonic Plates

Algeria

Historic Seismicity

1716 Algiers (intensity Io X, 20000 deaths)

1790 Oran (Io X)

1889 Mascara (Io IX)

1980 El Asnam (M 7.3)

6 other damaging earthquakes of magnitude

close to 6.0 in the last 20 years

Historic Seismicity-Algeria

Source: EERI

Zemmouri fault

The earthquake was caused by previously

unknown Zemmouri fault

An offshore south dipping thrust fault

10 km focal depth (shallow)

Over 1,000 aftershocks (largest M=5.8)

Uplift of the seafloor by 0.5 m

Minor landslides

Liquefaction along the coastline

Zemmouri fault

Source: EERI

Strong motion data

Soil

Rock

E-W component predominant

Algiers

Major surface fractures in the epicentral area of the May 21, 2003 earthquake close to the port of Zemmouri-El-Bahri.

Seismic Codes

1955: AS55= French regulations

developed after the 1954 earthq.

1969: AS55 revised by the Algerians

1983: RPA81 – Algerian seismic

regulations (after the 1980 El Asnam

eq.) developed in collaboration with

Stanford University

Seismic Codes

1999: RPA99 – modern seismic code

The country divided into 3 seismic

zones (zone of highest intensity is

III)

Algiers and Boumerdes in Zone II

(corresponding design acceleration

0.15g for residential construction)

Building Construction

The affected area mainly urban

and densely populated

Prevalent modern construction

(over 67% of buildings

constructed in the last 30

years)

Building Construction

Before 1960s – loadbearing masonry

buildings

After 1960- reinforced concrete

frames with hollow clay tile infills

Building height: 5-8 storeys

(apartment buildings) or up to 3

storeys (private construction)

Building Construction

Other types: precast panel

construction, cast-in-situ

concrete walls

RC Frame Construction –Major Features

RC columns and beams, without

structural walls

100 mm hollow clay tile partitions

Façade walls: 2 layers of hollow

tiles with a 50 mm air gap

Open stairs without shaft

RC Frame Construction

Composite masonry and concrete

floor slabs

Spread footings

No basements

Typical RC multi-family residential construction

Ground floor with open stairway

Typical private single-family construction (the damages located at the first storey).

RC Frames “Look Alike”Cast-in-situ concrete columns and

beams

Absence of moment connection (the

structural system called “poteau-

poutre” (post-beam) indicating an

absence of a rigid (moment)

connection

Absence of lateral confinement in

the column hinge zones (ends) =>

inadequate ductility

RC Frames “Look Alike”“Strong beam–weak column” mechanism:

Characterized by extreme damage in the

columns

Plastic deformations usually occur in

the columns in one storey (usually

first storey in the Algerian case)

Strong beam- weak column

Many reinforced concrete buildings experienced damage at the first storey

Major ProblemsInherently deficient structural system

Inadequate seismic design and detailing

Poor quality of concrete - compressive

strength 14-17 MPa, instead of the min. 25MPa

required per the Code

Inadequate steel properties (high carbon

content, very brittle, uncontrolled quality)

– yield strength should be 400 MPa

Major ProblemsIn spite of earthquake history, general

lack of awareness of seismic construction

requirements

Engineers, architects, and contractors not

licensed (licensing not available!)

Major ProblemsConstruction regulations (codes) control

only government-built projects or private

buildings used by the general public

Since the 1990, over 40% of privately

owned buildings built without building

permit (over 60% construction is privately

built)

Damage Slides

Zemmouri

A small township, around 5 km

away from the epicentre

Mainly private residential

construction – up to 3 storeys

RC concrete frames with infill

Some loadbearing masonry

construction (adobe, brick)

Total collapse of a single-family buildings

Total collapse (Zemmouri)

Total collapse of a concrete house caused by the collapse of the firststorey columns

Column failure – note laps at the floor level and 90 degree tie hooks (Zemmouri)

Column buckling: a real life experiment !!!

Complete collapse of “Cite Cooperative” building at Boumerdes (Photo: M. Farsi)

Total collapse of the first floor (Photo: EERI)

Soft storey effect – commercial ground floor and residential above (Photo: EERI)

Beam failure due to the inadequate development length and lack of ductility (Photo: EERI)

Apartment buildings at Boumerdes: beams in one direction only (Photo: M. Farsi)

A 16-storey tower at Regaia, Algiers survived main shock but completely collapsed in one of the aftershocks (Photo: M. Farsi)

RC Column DamageDamage concentrated at the top of the

first storey columns (marginal damage

to the upper floors)

Buckling of vertical reinforcement

Inadequate size and spacing of

transverse ties in the plastic hinge

zones and crushing of the concrete

Vertical reinforcement fractured, inadequate ties (Photo: M. Farsi)

Buckling of column reinforcement, no ties

Photo: M. Farsi

Buckling of column reinforcement

Shearing of the first storey column (Photo: EERI)

Shearing of the first storey column

Short columns (Photo: M. Farsi)

Short columns (Photo: M. Farsi)

Well tied column, poor quality of concrete

Column buckling – a real life experiment

•Beam and column fell apart (note the beam anchorage)•Column reinforcement lapped at the floor level

Seismic detailing provisions for RC moment frames per RPA99

Column lap length = 40 dia

A Mystery Case Study:Derguana, Algiers

A façade view: ground + floor

Complete Collapse

Repairable Damage

Repairable Damage

Three identical buildings …

The collapsed building (identical to the one standing on the left)

Corner column

Side columns

Corner column

Side columns

Floor-slab

Seismic joint

Seismic joint

Why some buildings collapsed and some remained standing?

Identical, brand new buildings

(supposed to be inhabited in June 2003)

Cause(s) of collapse?

Pounding effect?

Soil effect or slope? (the collapsed

buildings were located uphill)

Concrete Wall Buildings

Substantial damage to some

buildings

Cast-in-place shear walls inside

Precast concrete panels at the

exterior

Extensive shear wall damage in an older

building

Fractured horizontal reinforcement ( 6mm bars)

Buckled vertical rebars

Spandrel beam damage (inadequate shear reinforcement)

Failure of precast façade elements in cast-in-place concrete tunnel buildings (Photo: EERI)

… and much less damage found in a

building with modern seismic shear wall

provisions

Coupled shear walls

Spandrel beam (with diagonal reinforcement)

Shear wall at the ground floor level (with corner element)

X-cracks in a shear wall

Older Masonry Construction (pre-1960s)

A scene from downtown Algiers(Greater Algiers has a population of 3.5 million)

Typical older (pre-independence) masonry buildings

Medium rise buildings (5-6 storeys)

Stone masonry walls

Vaulted brick floors (jack arch)

Not significantly damaged in the May 21

eq.

A 6-storey stone masonry building in Algiers –out-of-plane wall failure (Photo: M. Farsi)

A partial stone wall collapse in a 5-storey building, Algiers (Photo: M. Farsi)

For a detailed description on older masonry buildings in Algeria refer to

www.world-housing.net (click on Africa on the map and then Algeria)

Damage to Infill Masonry(100 mm thick hollow

clay tiles)

Headers

Retrofit Solutions

Retrofit solution for reinforced concrete frame buildings proposed by the CTC

New shear wall

Existing column (jacketed)

Acknowledgements

Industry Canada – Sustainable

Cities Initiative

Neil Griggs & Bogue Babecki,

Builders Without Borders,

Vancouver

Mohammed Farsi, CGS, Algeria

Marjorie Greene, EERI

Canadian team in Algeria

Further information on the May 21, 2003 Eq.

EERI report (to be published)

www.eeri.org Learning from

Earthquakes (click on Algeria)

Thank You !