Transcript Document

Issues in Seismic Zoning and
Seismic Building Codes in Ethiopia
Samuel Kinde Kassegne, PhD, PE
Henri Samueli School of Engineering
University of California – Irvine
Irvine, CA
ICEMGCE-03
International Conference on Earthquake Engineering, Mechanics,
Geotechnical and Civil Engineering
Addis Ababa, Ethiopia - January 9-10, 2003.
OVERVIEW
• Why earthquake hazard should really be considered as
issue in Ethiopia.
• Seismic Zoning Issues
– Accurate Vs Economical
– UBC Vs EBCS Zonings/PGA
• Seismic Design Codes
– models available – Eurocode, IBC, UBC
– what to take what to modify, etc.
• Social and Economic Implications – Putting monetary
values, how do code implementations fit in current
economic environment
• Vision for future of Earthquake Engineering
EACE Int'l Conference - Addis Ababa, Ethiopia
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Earthquake Hazards – Issue for
Ethiopian Engineering Community
Why earthquake hazard should really be considered as issue in
Ethiopia.
With other pressing and more deadly natural disasters around, it is
hard to find enough awareness and sense of urgency for EQ hazard
and mitigation.
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Earthquake Hazards – Issue for
Ethiopian Engineering Community
a) Case for Seismic Design in Ethiopia
Year
Site of EQ
Damage
1906
Langano Area – 110 Km from Addis. 8 on
Marccalli scale
Felt as far as Addis Ababa
1961
Kara Kore – 150 KM from Addis Ababa
Town of Majete destroyed. Kara Kore
seriously damaged.
1969
Central Afar Area
Town of Serdo destroyed
1983
Wendo Genet
1984 (April)
5.2 near Hayk-Wello – 140 Km from AA
1984 (August)
4.9 – 140 Km from AA
1985
4.8 - Langano
1987
Rift Valley Area
1989
Dobi Graben – Central Afar
Several Bridges destroyed on major road
1999
Langano-Shala Lakes Area [Adamitulu?]
Cracks as wide as 2 meters reported.
High-rise buildings in AA shaken
Panic in high-rise buildings in AA
Courtesy: Fekadu Kebede EASEE, Feb 1996 Publication and L.M. Asfaw – Sinet 1990.
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EACE Int'l Conference - Addis Ababa, Ethiopia
Earthquake Hazards – Issue for
Ethiopian Engineering Community
Courtesy: Fekadu Kebede EASEE, Feb 1996 Publication
EACE Int'l Conference - Addis Ababa, Ethiopia
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Earthquake Hazards – Issue for
Ethiopian Engineering Community
b) High population density areas coincidence with areas of high-seismic activity
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EACE Int'l Conference - Addis Ababa, Ethiopia
Earthquake Hazards – Issue for
Ethiopian Engineering Community
c) Expected increase in human development activity in the MER (Main Ethiopian Rift Valley) area
and Afar Area.
E.g.,
Melka Wakena Dam in Bale Area – 100 kms east of the Wonji Fault Belt.
City of Samara in the Afar area – located in one of the most active seismic areas.
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EACE Int'l Conference - Addis Ababa, Ethiopia
Seismic Zoning in Ethiopia
F.Kebede
& LM
Asfaw*
F.Kebede
& LM
Asfaw
EBCS 95
UBC 97
[Eq. 3]
[Eq. 16]
PGA for
0.01p
0.14g
0.53g
0.07g
0.3g
PGA for
0.005p
0.19g
1.05g (??)
1.05g (??)
RADIUS
Strong
Ground
Motion
Data
Not
available
0.13g –
0.5g
(extrapolated)
Not
available
Predicted PGA in Afar Depression as per different Sources.
* FK and LMA, Sinet 1996.)
EACE Int'l Conference - Addis Ababa, Ethiopia
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Seismic Zoning in Ethiopia
Addis Ababa – Zone 3
PGA = 0.07g
Seismic Hazard Map of Ethiopia – EBCS-8 1995
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EACE Int'l Conference - Addis Ababa, Ethiopia
Seismic Zoning in Ethiopia
Maximum PGA in Addis
Ababa = 0.50g
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EACE Int'l Conference - Addis Ababa, Ethiopia
Seismic Design Codes in Ethiopia
•
Models Available – Eurocode Vs IBC
•
What to take what to modify, etc.
•
How about performance-based codes
(FEMA 273, ATC) for PBE
(performance-based engineering)?
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Seismic Design Codes in Ethiopia
•
Models Available – Eurocode, UBC, IBC, NZ, IS etc.
–
UBC is familiar to many engineers around the globe.
–
Eurocode yet to be used widely in even in EU countries.
–
IBC holds promise for universal acceptance in the US. However, it is
highly influenced by US engineering practice and therefore may not
be directly applicable to other countries.
•
•
–
Assumed good QC in US construction practice may give nonconservative designs in developing countries. E.g., reinforcement
details, accidental torsion.
Detailed data on site specific Sds and Sd1 contours is very expensive
to compile.
NZ codes have interesting local (NZ) flavors.
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EACE Int'l Conference - Addis Ababa, Ethiopia
Seismic Design Codes in Ethiopia
• What to take, what to modify from leading Int’l seismic codes
and also add provisions based on unique local issues (design,
construction, topography, seismicity, etc) ?
Adopt requirements based on sound analysis/design concepts.
Strike a balance between conservative design and economical
design. [E.g., reinforcement for boundary element in shear
walls].
Possibly continue on PGA-based ESF procedures unlike the
demanding IBC 2000/2003.
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EACE Int'l Conference - Addis Ababa, Ethiopia
Seismic Design Codes in Ethiopia
•
How about performance-based codes (FEMA
273, ATC) for PBE (performance-based
engineering)?
PBE,by itself, is probably too expensive and hard
to sell in Ethiopia. However, PBE concepts that
may find their way into some codes (like future
versions of UBC(?), NEHRP etc.,) like
‘prescribed displacement-based’ design instead
of ‘force-based’ design methods.
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Seismic Design Codes in Ethiopia
•
Structural Analysis Provisions [EBCS8-95]
1. Requirements on Types of Analysis
•
•
•
3D Dynamic required for plan and elevation irregularity.
3D Equivalent Static Force Procedure required for plan irregularity
only
Otherwise do 2D analysis.
2. Base Shear Calculations [ESF Procedure]
•
•
Fb = Sd(T1) W
Fb = Ft +  Fi, i =1 to n Where Ft = 0.07*T*Fb
Fi = (Fb – Ft) * Wihi / Wjhj
3. Dynamic Response Spectra Analysis
•
•
•
•
At least 90% modal mass participation is required
all modes with effective modal masses greater than 5% are
considered
the minimum number of modes, k, to be considered should satisfy the
following conditions:
k >= 3*Sqrt(n); Tk <= 0.2sec [Note: This is for bldgs with
significant torsional modes]
SRSS scheme of modal combinations if Tj <= 0.9Ti.
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Some Thoughts on Seismic Design in
Ethiopia
Structural Design Provisions [EBCS8-95] – Basic Premises
– Provide adequate resistance of the structural elements to the
seismic combination of actions
– Provide adequate energy dissipation capacity to the structural
elements
– Ensure an overall ductile behavior such that ductile mode of failure
should precede brittle failure.
•Key Design Concepts/Philosophies
– Weak beam-strong column concept
– Ductility of structural elements and systems
[Confinement/Detailing in RC]
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EACE Int'l Conference - Addis Ababa, Ethiopia
Some Thoughts on Seismic Design in
Ethiopia
Proposed Reconsiderations
1) General Torsional Requirements and Accidental Torsion
2) Requirements on Types of Analysis
Why is 2D allowable for elevation irregularity? Mass irregularity.
3) Dynamic Response Spectra Analysis
Dump SRSS. Just use CQC.
4) structural behavioral factor ‘g'
Highly penalizes irregular buildings.
4) Seismic zonings as per EBCS-95 are un-conservative for Addis Ababa and
environs. Site effects and Soil need to be addressed well [A. Worku, Zede 12/01].
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Some Thoughts on Seismic Design in
Ethiopia
5) Proposed Reconsiderations
Myth that EQ design is required only for high-rise. Low to medium
rise buildings which form the vast majority of ‘multi-story’ buildings
in 3rd world cities like Addis Ababa are very susceptible (bad
detailing, no confinement, soft-stories, . Reinforcement detailing
provisions in EBCS, therefore, should be conservative for such
buildings.
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Social and Economic Implications
•Putting monetary values
•Do clients (building/structure owners) accept premium
required for aseismic design?
•how do code implementations fit in current economic
environment?
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Vision for future of Earthquake
Engineering in Ethiopia
(I) Bold Initiatives - National Earthquake Research Center [much like what
Algerians have done].
•Previous and Current emphasis has always been on seismology at a level of
almost a “national lab” – Geophysical Observatory. Seismic analysis and
design practices need to grow. The “Eagle” project (UK, Stanford, AAU) is a
good example.
•AAU [Civil Engineering Dept., Building College], EACE and Ethiopian
academics/engineers outside the country can play big roles here.
•Research and Teaching need to be main focuses. Implementation of Seismic
building codes and awareness of the need for the same begins at the training
level.
•Clearing house for collaborative work with academics and engineers outside
the country. E.g., Possibility of looking at for contour maps of Sds and Sd1.
•Exchange programs with the world’s leading earthquake engineering
research and teaching programs such as UC Berkeley, UCSD, Buffalo, etc.
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EACE Int'l Conference - Addis Ababa, Ethiopia
Vision for future of Earthquake
Engineering in Ethiopia
(II) More work on Code Development and Implementation
•Time to review EBCS-95. Review should include looking at current
trends in EQ codes, e.g., IBC2000/2003.
•Clear guidance on requirements on when to use seismic provisions and
enforcement.
(III) More data collection on seismic hazard and seismology
•Inexpensive accelerograms at prominent mid and high-rise buildings.
Funding – CIDA, UNDP, NSF
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EACE Int'l Conference - Addis Ababa, Ethiopia