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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

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Issues in Seismic Zoning and Seismic Building Codes in Ethiopia

Samuel Kinde Kassegne, PhD, PEHenri Samueli School of EngineeringUniversity of California – IrvineIrvine, CA

ICEMGCE-03

International Conference on Earthquake Engineering, Mechanics, Geotechnical and Civil Engineering Addis Ababa, Ethiopia - January 9-10, 2003.


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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.

EACE Int'l Conference - Addis Ababa, Ethiopia


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Earthquake Hazards – Issue for Ethiopian Engineering Community

a) Case for Seismic Design in Ethiopia

Courtesy: Fekadu Kebede EASEE, Feb 1996 Publication and L.M. Asfaw – Sinet 1990.

EACE Int'l Conference - Addis Ababa, Ethiopia


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Earthquake Hazards – Issue for Ethiopian Engineering Community

EACE Int'l Conference - Addis Ababa, Ethiopia

Courtesy: Fekadu Kebede EASEE, Feb 1996 Publication


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Earthquake Hazards – Issue for Ethiopian Engineering Community

b) High population density areas coincidence with areas of high-seismic activity

EACE Int'l Conference - Addis Ababa, Ethiopia


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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.

EACE Int'l Conference - Addis Ababa, Ethiopia


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Seismic Zoning in Ethiopia Community

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 Community

Addis Ababa – Zone 3

PGA = 0.07g

Seismic Hazard Map of Ethiopia – EBCS-8 1995

EACE Int'l Conference - Addis Ababa, Ethiopia


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Seismic Zoning in Ethiopia Community

Maximum PGA in Addis Ababa = 0.50g

EACE Int'l Conference - Addis Ababa, Ethiopia


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Seismic Design Codes in Ethiopia Community

  • 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)?

EACE Int'l Conference - Addis Ababa, Ethiopia


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Seismic Design Codes in Ethiopia Community

  • 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 non-conservative 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.

EACE Int'l Conference - Addis Ababa, Ethiopia


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Seismic Design Codes in Ethiopia Community

  • 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.

EACE Int'l Conference - Addis Ababa, Ethiopia


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Seismic Design Codes in Ethiopia Community

  • 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.

EACE Int'l Conference - Addis Ababa, Ethiopia


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Seismic Design Codes in Ethiopia Community

  • Structural Analysis Provisions [EBCS8-95]

    • 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.

    • 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

    • 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.

EACE Int'l Conference - Addis Ababa, Ethiopia


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Some Thoughts on Seismic Design in Ethiopia Community

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]

  • EACE Int'l Conference - Addis Ababa, Ethiopia


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    Some Thoughts on Seismic Design in Ethiopia Community

    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].

    EACE Int'l Conference - Addis Ababa, Ethiopia


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    Some Thoughts on Seismic Design in Ethiopia Community

    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.

    EACE Int'l Conference - Addis Ababa, Ethiopia


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    Social and Economic Implications Community

    • Putting monetary values

    • Do clients (building/structure owners) accept premium required for aseismic design?

    • how do code implementations fit in current economic environment?

    EACE Int'l Conference - Addis Ababa, Ethiopia


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    Vision for future of Earthquake Engineering in Ethiopia Community

    • (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.

    EACE Int'l Conference - Addis Ababa, Ethiopia


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    Vision for future of Earthquake Engineering in Ethiopia Community

    • (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

    EACE Int'l Conference - Addis Ababa, Ethiopia