design of earthquake-resistant structures: past, present
TRANSCRIPT
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Matjaž Dolšek
Design of earthquake-resistant structures: past, present and future
International Summer School “Natural Disasters”
Ljubljana, 21st May – 10th June 2017
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Lisbon, mid 18th century
http://nisee.berkeley.edu/elibrary/browse/kozak
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Lisbon, mid 18th centuryhttp://nisee.berkeley.edu/elibrary/browse/kozak
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Ljubljana, 1895Vir: MOL, Ocena ogroženosti Mestne občine Ljubljana, 2001
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Ljubljana, 1895
http://zgodbe.siol.net/ljubljanski-potres/
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Ljubljana, 1895
http://zgodbe.siol.net/ljubljanski-potres/http://zgodbe.siol.net/ljubljanski-potres/
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L’Aquila, 2009
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Concepts of earthquake-resistant design
• Past: Minimum requirements (1896, Ljubljana)Equivalent static seismic force (1910, after earthquake in Messina)
• Standards in Slovenia: – 1963/64 first standard for earthquake resistant design of structures (1963
Skopje)– 1981 new standard (1979 earthquake in Monte Negro)– 1995 use of pre-standard Eurocode 8 in parallel
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Concepts of earthquake-resistant design
• Present: – Design on the basis of target seismic hazard and capacity design
approach
• Standard: – Eurocode 8 in use from 2008 (Slovenia was the first EU member)
– 2015 start of a process of preparation of second generation of Eurocode 8 (CEN/TC250/SC8,PTs,WGs,TGs)
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Concepts of earthquake-resistant design
• Future (partly today):
– Design of structure for target seismic risk
Seismic hazard
What kind of earthquakes can
be expected?
How often do they occur?
People have no influence
Maps of seismic hazard, seismic
hazard function
Seismic risk
What is the risk of collapse of the
building or loss of life?
What is the risk for financial loss if
the business activity is carried out in
the old or new building?
Related to decisions of societies
Probability of loss of life, expected
annual loss (insurance)
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Key points for the development of the concept of earthquake-resistant
design?
• Good prediction of earthquakes
• Precise description of the effects of earthquakes on buildings (built environment)
• Very clear definition of objectives
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Prediciton of earthuqakes
Source: Slovenian Environment Agency
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Effects of earthquakes on strucutres
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Effects of Earthquakes
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Objectives
• Eurocode 8:
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Example: 8-storey RC frame
• Design earthquake: agR=0.25 g, soil type C
• Behaviour factor q4
• Ductility class medium
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Present: Calculations and “actual performance”
Jure ŽižmondRoof displacement (% of height of structure)
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Future: How safe is safe enough?• The basic measure of seismic risk:
– TR , return period (years)
– Pf 1/TR, probability of an event for a period of 1 year
– Pf,50 50Pf 50/TR , probability of an event for a period of 50 year
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Future: Risk assessment
• Let us return to the example
• and estimate TR or Pf,50
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Future: Equation of seismic risk
• Fragility function in seismic hazard function
• Collapse: TR=8500 years, Pf,50 = 0.6%
Nuša Lazar Sinković
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Future: Equation of seismic risk• Loss function
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Future: How safe is safe enough?• Example: Footprint of earthquake safety, 8-storey frame
• Paradox:
– Society expect high seismic safety (low probability of collapse)
– Investing in assuring safety is unnecessary expense M. Dolšek
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Future: New information
• Other measures of seismic risk
• Example: Masonry buildings
Jure
Sn
oj
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Future: Risk-based (Resilience-based) seismic design
• Design of responsibility for taking on risk in order to establish resilience
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Conclusions
• A lot has been done, but the process of development of design of structures is not yet complete
• Paradox: Society expect high seismic safety (collapse) –Investing in assuring safety is unnecessary expense
• Engineers have to properly communicate with clients, but we cannot accept responsibility for risk posed by natural phenomena such as earthquakes
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Conclusions
• Risk for damage of buildings due to earthquakes is not negligible. It is necessary to design (plan) the responsibility.
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Thank you for your attention!
Similar talk is available in Slovenian at VideoLectures.net