e e r i technical briefing on september 30, 2009 padang, indonesia earthquake observations and...

E E R I TECHNICAL BRIEFING ON SEPTEMBER 30, 2009 PADANG, INDONESIA EARTHQUAKE

Observations and Lessons on Earthquake and Tsunami Risk

Mitigation in Padang, Indonesia

Nick Alexander, Degenkolb Engineers

Veronica Cedillos, GeoHazards International

Louise Comfort, University of Pittsburgh


Reconnaissance Team Members

• EERI TeamDeierlein, Alexander, Cedillos, Hausler, Henderson, Comfort, Hart, Rudianto, Wijanto, Wood.

• Other US ParticipantsMooney & McGarr, USGSFranco, DiBarnaba, Sandoval Kizzee, Cabrera, Scawthorn

• InternationalAndalas UniversityITB UniversityIndonesian Society Geotech. Engrg.Nanyang Tech. UniversityNew Zealand Engineers


Acknowledgements

NSF: EERI Learning From Earthquakes Program

with additional support from• Blume Earthquake Engineering Center, Stanford• Pacific Earthquake Engineering Research (PEER) Center• USGS• University of Pittsburgh, GSPIA• Team host organizations:

– Degenkolb Engineers– Forell Elsesser– Build Change– GeoHazards International– Risk Management Solutions, Inc.


History of Padang

Batang Arau River

Old City

City Center

Padang City 17th Century Trading Center Population 900,000 (20x growth since 1940) Capital of West Sumatra


Impact – Road Damage

Sengara, I.W. et al., 2009


Impact – Bridge Damage


Impact – Foundation Damage

Provincial Public Works Building• 4 story, built 1976• Soft/Weak first story• Columns experienced 12” drift• Site experienced liquefaction• 100 m from Batang Arau River


Impact – Utility and Lifeline Systems

• Airport– closed 3 hrs, regular ops 1 day

• Electric Power– distributed transformer damage– restored 20% within 5 days– fully restored within 8 days

• Phone/Communication– landlines OK, cell restored within days

• Water– 1 of 2 main supply pipes and 1 of 2

main distillation tanks ruptured– back to 60% within 2 weeks

• Port Facility– little damage, south of town

damaged water treatment


Outline

• Building Types and Occupancies

• Acceleration Response vs Design Base Shear in Building Code

• Typical Building Damage & Collapse Mode

• Building Design & Construction in Padang

• Building Case Studies

• Summary of Buildings Performance

• Improving Buildings Performance


Building Types and Occupancies

• Government Offices

• Schools

• Hospitals

• Commercial Buildings– Offices and Banks– Retail Malls– Hotels– Home-shops (Ruko)

• Residential Homes

Primarily Reinforced Concrete Frames with Brick Infill Walls

URM, Confined Masonry, Wood

Few Steel Moment Frames


Comparison to Building Code

Building Code Requirements1970: Base shear = 0.1g, working stress design

1987: PGA = 0.25 – 0.36g, 2 soil types, inelastic R=4

2002: Similar to 1987, 3 soil types, capacity design

increase in short period spectral demands

Spectral Acceleration - 5% damping - NS component - stiff soil site

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.5 1 1.5 2

Spec

tral

Acc

eler

ation

(g)

Period (sec.)

measured

SNI-2002

SNI-1987


Building Damage and Collapse

Story Collapse Complete Collapse


Brick MasonryInfill Wall & NS Damage

Building Damage and Collapse


Building Design & Construction

• Seismic Design Codes– Established by national committee (Jakarta)– First established 1970, updates in 1987 and 2002– Currently revising to model after U.S. IBC & ASCE 7

• Expertise of Local Professionals– Engineering education at university– Little professional development & continuing education in Padang– Little training/certification of contractors

• Code Compliance & Quality Assurance– Field observations and interviews suggest lack of compliance – Problems most significant with small projects and renovations– Common to other developing countries (lack of well established

process, insufficient resources to implement, lack of education)


Building Case Studies

• SMK 9• M Djamil Hospital• Provincial Planning

Building• Ambacang Hotel• Hotel Mariani• Dutch Colonial &

Chinatown Buildings• Lasano Kampong Dalam

Village• Padang Ruko Buildings


SMK 9 School

• High School• 3 story, built 1997• Partial floor and stair

collapse• Weak/Captive Columns• 2 casualties (non-students)

• many students at time of EQ• EQ Drills teach duck and

cover• Students ran out of building• No student victims


Sentral Plasa Raya Mall

• 3 story concrete frame/brick infill building built in 2005

• Back end collapsed• Brick infill failures• Non-structural

damageFRONT END

BACK END


Sentral Plasa Raya Mall

• Heavy mass at the back end

• Column detailing:• Small ties with 90 degree

hooks

• Column failure at lap splice


Provincial Planning Building

• 3 story, 1981-83• 1st Floor Collapse

– Configuration– Design and Detailing

• smooth bars

• small ties w/ 90 degree hooks

– Construction quality

• 2 Casualties– 80 occupants in building

during EQ

• Impact on rebuilding effort– Many files still in building


M Djamil Hospital

• Largest hospital in Padang (800+ beds)

• 13 buildings, only 1 building sustained major damage

• Outpatient Building– 3 stories, built in 1982– First floor collapsed– No casualties– Pounding between

segments


M Djamil Hospital

Vaulted roof at the atrium

Damage at the one end of the cross shape


Ambacang Hotel

• Originally a 1900 Dutch 2-story masonry warehouse, later expanded to 5 stories• Both concrete & steel frames

• Irregular, no clear load path

• Partial story collapse at 2nd Floor of main building BEFORE EQ


Ambacang Hotel

• Separate 6 story steel building (built in 2005) fully collapsed

• Poor moment frame connection detail• No continuity plate

• Weak way bending

• Slender columns

• 200 fatalities in the hotel (est.)


Hotel Mariani

• 4-6 story 2006 steel building collapsed, 3-story 1963 concrete building damaged but survived

• One of few steel buildings in Padang• Weak axis column bending led to progressive collapse


Hotel Mariani

Moment frame failed weak way

Building collapsed towards the back


Dutch Colonial & Chinatown Districts

• 100+ year old buildings, adjacent to the river

• Unreinforced masonry buildings w/ wood roofs & floors

• Out-of-plane collapse


Lasano Kampong Dalam Village

• Small village in hills outside of Pariaman

• URM, confined masonry• URM houses sustained

the most damage• Settlement resulted in

damage to several homes• Liquefaction


Lasano Kampong Dalam Village

Confined Masonry Buildings

• Improved version of URM• Promoted in rural areas in

Indonesia• Reinforced concrete

element for confinement• Fairly well performance


Ruko Buildings in Padang

• Ruko – very common in Padang

• 2 to 3-story tall • commercial & residential

• Stiffness irregularity• Various performance

• Some collapse some minor damage

• No comprehensive plan check


Performance of Concrete Buildings

• Soft/weak story• Weak columns• Inadequate steel

reinforcement– not enough steel– nonconforming details

• Poor quality concrete• Insufficient lateral strength

and stiffness• Brittle architectural finishes


Performance of Concrete Buildings

• Damage to older buildings is not unexpected

• Damage to newer buildings was greater than expected


Performance of Steel Buildings

• Poor moment frame detailing– Weak way bending– Poor welding– Nonconforming to code

• Slender column sections for moment frame

• Insufficient strength and stiffness - significant drift

• Non-familiarity with steel design and construction in the area


Performance of Masonry Buildings

• Unreinforced Masonry– Poor quality materials and workmanship– No confinement to prevent out-of-plane wall

failure

• Confined Masonry– Performed fairly well– Guidelines available for single family homes

but no code provision


Improving Buildings Performance

• Proper enforcement & implementation of the Building Code– continuing education– quality assurance– training/certifications of contractors

• Building code provision for residential homes and ruko/homeshops

• Challenge to implement these in the re-construction effort


Outline

• Tsunami Risk

• Preparedness Efforts

• Tsunami Evacuation during 9/30 Earthquake

• Performance of Tsunami Evacuation Structures

• Observations & Lessons Learned


Tsunami Risk in Padang

One of the highest tsunami risks in the world

National Geographic Indonesia

Risk is a function of the hazard and exposure

Padang


Tsunami Hazard in Padang

Killed more than half the population in Banda Aceh

Padang is exposed to a similar hazard from same fault

Indian Ocean TsunamiDecember 2004

After 2004 Tsunami

Before 2004 Tsunami

Banda Aceh

Banda Aceh


Seismological Background


Tsunami Mechanism


First big rupture on the Sundamegathrust occurred in 2004

The second big rupture occurred in March 2005

The third rupture occurred in a series of events, with an aftershock of M7.9

Northern part of Mentawai patch remains locked

Source: Kerry Sieh


Vulnerable Terrain


• 900,000 people

• Almost 9,000/km2 at city center

• >½ the population lives within a 5 meter elevation– Mostly fishermen

• <30 minutes to evacuate

• Inundation distance ~2 km

Population Density and Distribution


• One of 6 cities designated to undertake earthquake and tsunami risk reduction after 2004

• Early warning systems• Planning evacuation routes• Education and evacuation drills

– “duck, cover, hold” – tsunami evacuation

• Over 50,000 people will still be unable to evacuate within < 30 minute tsunami arrival time

Preparedness Efforts in Padang


Evacuation Structures | Examples

Refuge Structures: Designed to rise above the expected tsunami inundation level, and withstand the expected earthquake and tsunami forces; provides vertical evacuation

Bridges: Designed to be earthquake-resistant and serve as element of horizontal evacuation


Evacuation Structures | Existing Buildings

• Regulation requires all buildings > 2 stories to serve as evacuation site during tsunami

• Existing Building Surveys– 5 different organizations– Based on location and capacity,

suitability not thoroughly considered– Seismic deficiencies not considered

• Buildings used as sites in evacuation simulations


Tsunami Evacuation

• Most people evacuated after shaking

• Problems with evacuation plan – sometimes slow to initiate– traffic jams (1-2 hrs)– lack of information and coordination

• Little evidence of vertical evacuation• Roads and bridges generally intact• Performance of evacuation buildings

– 1/3 collapsed or heavily damaged– 3/4 had sufficient damage to be closed


High Ground

Coastline

Evacuation Structures | Bridges


Evacuation Structures | LBA LIA

• 4 story language school

• First 2 stories collapsed

July 2009 October 2009


Evacuation Structures | STBA Prayoga

• 4 story junior college

• Complete collapse



Evacuation Structures | Plasa Andalas

• 4 story mall

• Partial collapse on 4th floor and fire



Good Candidates for Evacuation

Indonesian Bank Complex• Tsunami evacuation

– large building– elevated site– terrace @ 20 m– on-site security

• Moderate EQ damage • Evacuation lessons

– public awareness – individuals must feel safe

& confident


Good Candidates for Evacuation

• Major mosques in general are good candidates for evacuation– Large prayer area– Redundant structures– Better construction quality– Good accessibility– People tend to go to mosques

after disasters

• ~100 people evacuated to Masjid Taqwa after the earthquake


Observations and Lessons• Overview of Damage

– Buildings– Bridges and Transportation– Utility Lifelines

• Deaths and Injuries• Resiliency of Padang City• Tsunami Evacuation

– Tsunami still a threat– Inadequate evacuation capacity – Evacuation structures are crucial

• Building Code provisions and enforcement• Rebuilding Better / Safer?


Thanks!

Questions?

e e r i technical briefing on september 30, 2009 padang, indonesia earthquake observations and...

Documents