Matjaž Dolšek

Design of earthquake-resistant structures: past, present and future

International Summer School “Natural Disasters”

Ljubljana, 21st May – 10th June 2017

Lisbon, mid 18th century

http://nisee.berkeley.edu/elibrary/browse/kozak

Lisbon, mid 18th centuryhttp://nisee.berkeley.edu/elibrary/browse/kozak

Ljubljana, 1895Vir: MOL, Ocena ogroženosti Mestne občine Ljubljana, 2001

Ljubljana, 1895

http://zgodbe.siol.net/ljubljanski-potres/

Ljubljana, 1895

http://zgodbe.siol.net/ljubljanski-potres/http://zgodbe.siol.net/ljubljanski-potres/

L’Aquila, 2009

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

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)

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)

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

Prediciton of earthuqakes

Source: Slovenian Environment Agency

Effects of earthquakes on strucutres

Effects of Earthquakes

Objectives

• Eurocode 8:

Example: 8-storey RC frame

• Design earthquake: agR=0.25 g, soil type C

• Behaviour factor q4

• Ductility class medium

Present: Calculations and “actual performance”

Jure ŽižmondRoof displacement (% of height of structure)

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

Future: Risk assessment

• Let us return to the example

• and estimate TR or Pf,50

Future: Equation of seismic risk

• Fragility function in seismic hazard function

• Collapse: TR=8500 years, Pf,50 = 0.6%

Nuša Lazar Sinković

Future: Equation of seismic risk• Loss function

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

Future: New information

• Other measures of seismic risk

• Example: Masonry buildings

Jure

Sn

oj

Future: Risk-based (Resilience-based) seismic design

• Design of responsibility for taking on risk in order to establish resilience

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

Conclusions

• Risk for damage of buildings due to earthquakes is not negligible. It is necessary to design (plan) the responsibility.

Thank you for your attention!

Similar talk is available in Slovenian at VideoLectures.net