SUSTAINABILITY AND RESILIENCE IN SEISMIC AREAS: AN EXCITING CHALLENGE FOR CIVIL ENGINEERS

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1 in collaborazione con: Giornata di Studio Roma, 20 ottobre 2016 ENEA - Via Giulio Romano, 41 SUSTAINABILITY AND RESILIENCE IN SEISMIC AREAS: AN EXCITING CHALLENGE FOR CIVIL ENGINEERS Paolo Clemente, PhD Structural Engineer, Research Director

2 PAOLO CLEMENTE SUSTAINABILITY AND RESILIENCE Search for a satisfactory economic development contrasts with the respect of the environment First question: can sustainability exist without safety? Obviously it cannot! Second question: can safety be acceptable if resilience is low? Obviously it cannot! It is very important to be able to recover in short time the previous situation after a disaster, or even a better one Resilience should be guaranteed first of all by means of: good quality of all the structures a suitable organization of the urban territory:

3 PAOLO CLEMENTE STRUCTURAL ENGINEERING: IMPORTANT ISSUES Definition of seismic actions Freeman saw that it did not make sense to talk about earthquakeresistant design without first knowing more a bout the forces involved in earthquakes (George Housner, EERI Oral History p. 39) Analysis of the structural behaviour Engineering is the art of modelling materials, we do not wholly understand, into shapes, we cannot precisely analyse, so as to withstand forces, we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance (S. Kelsey) New concepts in architectural and structural design Dual use buildings

4 a (cm/s/s) a (cm/s/s) a (cm/s/s) PAOLO CLEMENTE SEISMIC INPUT Correct and complete description of the seismic input acceleration components along three orthogonal axes, two horizontal and one vertical, recorded during a suitable number of real events at the site SGMA.HNNa ns SGMA.HNZa up SGMA.HNEa we t (s) t (s) t (s) Technical codes horizontal and vertical response spectra determine directly the maximum seismic effects on structures (linear analysis) reference spectra for the definition of a suitable set of synthetic accelerograms

5 Se (g) PAOLO CLEMENTE HORIZONTAL ACC. RESPONSE SPECTRUM Horizontal acceleration response spectrum S e (T): rigid soil (type A) with horizontal surface conventional damping ratio =5% horizontal peak ground acceleration PGA A at T= PGA A PGA A F T CA Rigid Soil maximum amplification F = S e,max /PGA A T (sec) T CA = upper limit of the range in which S e =cost All the other parameters, such as T B and T D, can be derived from these How are these hazard parameters defined? Argument about the maximum horizontal acceleration at a site between: followers of the probabilistic approach followers of the deterministic approach But what is the effective difference from the structural engineer s point of view?

6 Se (g) PAOLO CLEMENTE PROB. SEISMIC HAZARD ASS. (PSHA) PSHA is based on: seismic history return period concept knowledge of existing faults, capable or not Soil A =5% 2% 5% 10% 22% 39% 63% PGA A : given for each site as a function of P NCR50 (as well as F and T CA and so the entire spectrum) (P NCR50 = probability of exceedance in 50 years, related to the minimum service life time usually accepted for structures) Minimum P NCR50 = 2% (limit related to our knowledge about the seismic history, with extrapolation that accounts for the uncertainties) T (sec) PGA (g) TCA (sec) F/ P NCR50

7 PAOLO CLEMENTE Question No. 1: PSHA: CRITICS does the map relative to P NCR50 = 2% give the maximum event that one could expect at a site? PSHA doesn't account for high magnitude events, whose occurrence has been assessed in prehistoric age Less frequent events, with a very long return period (very low P NCR50 ), could be unknown to us Some faults could not be identified yet: such that generated the earthquake that on July 16 th, 2007, struck the town of Chuetsu, Niigata prefecture in Japan (Mw = 6.6), where is the Kashiwazaki-Kariwa nuclear power plant, the first in the world with a third generation reactor and the first to suffer a strong earthquake

8 PAOLO CLEMENTE DETERMINISTIC APPROACH (DSHA) DSHA takes into account the historical seismicity, i.e., the observed events, and the characteristics of the sources that could affect the site determine the maximum credible event (MCE), able to produce the reasonably considered highest level of shaking at the site, in terms of magnitude, distance and focal mechanism Neo-deterministic method (Italian territory, Panza et al., 2001): PGA A for P NCR50 = 2% > DGA at almost all the sites in some cases, PGA A >> DGA in a few cases PGA A < DGA Conclusions: PGA A for P NCR50 = 2% generally give values higher than the maximum one could expect at each site but use of both the methods is to be recommended for a safe analysis of the seismic input

9 Se (g) PAOLO CLEMENTE Seismic waves can be amplified due to site effects Technical codes: Amplifying PGA A PGA= PGA A S S = Soil coefficient, decreases when PGA A F gets higher according to a function that depends also on the soil type PGA = PGA A S SITE EFFECTS PGA A PGA A F T CA PGA F Amplification of motion: higher for lower values of PGA A F An accurate seismic local response analysis is recommended especially for strategic and relevant structures T (sec) T C Amplifying T CA T C Soft Soil Rigid Soil Local effects due to slope accounted for by means of an amplification coefficient, which ranges up to 1.4.

10 PGA A (g) (P NRC50 =10%) PGA A (g) PAOLO CLEMENTE EARTHQUAKE DESIGN Question No. 2: once the seismic hazard has been described, by mean of the probabilistic or the deterministic approach, who chooses the level of safety? It is a political issue In the Italian territory: typical variations of PGA A versus P NCR50 for different sites P NRC Usually P =10% NRC50 In the Italian territory: PGA A PGA A 10% % 0.2 y = 0.55x PGA A (g) (P NRC50 =2%)

11 PGA A / PGA A (2%) PAOLO CLEMENTE DESIGNING WITH P NRC50 = 10% 10%: we design buildings able of withstanding without collapsing an event with probability 10% of being exceeded in 50 years SLU: we design buildings that can stand only one such event; if this happens, the structure could be damaged so much to have to be demolished we cannot guarantee anything for stronger events, for which partial or total collapse may occur, with loss of many lives P NRC50 we safeguard the lives up to a seismic action much lower than that could affect the structure

12 PGA A F PAOLO CLEMENTE ELASTIC RANGE Suitable prevention policy assumption of the most severe seismic actions for the structural design Ultimate Limit State checks (no-collapse): P NCR50 = 2% or MCE Damage Limit State checks: lower earthquake intensity credible and suitable ductility low level of damage P NRC50

13 S e (g) PAOLO CLEMENTE DESIGN IN ELASTIC RANGE Assumptions: Designing traditional structures in the elastic range is not convenient, both for economic and architectural considerations Technical codes: structure must not be able to support seismic actions in the elastic range Design spectrum: amplitudes are reduced by means of the behaviour factor q HSA: Certainly true S d = f (S e, q) MSA and LSA: designing without any reduction of the elastic acceleration values is possible S d = S e Se(HSA) Sd(HSA) Se(LSA) Sd(LSA) T (s)

14 Se (g) PAOLO CLEMENTE DESIGN IN ELASTIC RANGE S d,max = maximum spectral value for which the linear elastic design is requested based on economic and architectural considerations function of the materials and the structural type individualized as the value of S d beyond which the cost increases significantly If S e (T) S d,max S d = S e (T) 1.2 HSA LSA S e (T) > S d,max S d = S d,max and q = S e (T)/S d,max Behaviour factor q: not defined a priori variable also for a given response spectrum Sd max T (sec) The suggested procedure is usual when designing base isolated buildings, for which the period is chosen in order to reach a spectral amplitude low enough in order to design the superstructure in the elastic range

15 PGA A F PAOLO CLEMENTE DESIGN IN ELASTIC RANGE % of Italian territory where would be possible designing with q = 1 N.B.: q min = P NRC50 S d,max P NCR50 = 2% P NCR50 = 10% 0.5g 24% 62% 0.75g 47% 91%

16 PGA A S F S PGA A S F PGA A S F PAOLO CLEMENTE SOIL AMPLIFICATION HSA D C B A D C B A MSA P NRC D C B 1.0 A PGA F (g) LSA P NRC D C B 1.0 A P NRC50

17 PAOLO CLEMENTE DESIGN IN ELASTIC RANGE In order to guarantee the elastic design also in high seismicity areas: limitation of the building height, with respect to the size in plan use of new anti-seismic technologies. As well-known a high ductility is obtained by means of suitable structural details, which are usually prescribed for buildings in seismic areas.

18 S e (g) PAOLO CLEMENTE 0.1 Se - fond. S e (T) Se - bedrock VERY LOW SEISMICITY AREAS High ductility: obtained by means of suitable structural details, which are usually prescribed for buildings in seismic areas. 0.2 Effects on the structures : a a g S F 0 g S F 0 = S e, max = max acc. amplitude a g S T (s) If a g S 75 g: F 0 = a g (average) New proposal: a g S 75 g = PGA at the foundation base (local amplification and foundation level) Present definition (Zone 4): a g 5 g = PGA at the bedrock (base seismic hazard) (max) a g S F g 0.20 g F T R = a g (g) Structures low sensitive to the seismic input at the site S e (T) 0.20 g (depends also on the structure and could include base isolated buildings) 18

19 PAOLO CLEMENTE EXISTING BUILDINGS Structural concept, born for new buildings, cannot be used for the seismic retrofit of the existing ones, which were: Old buildings were designed with reference to seismic standards less severe than the current ones or even without taking into account the seismic actions Their complete seismic retrofit is very difficult, or even impossible, for technological and economic reasons Demolition and reconstruction should be always considered also as sustainable economic solution (not for historic buildings)

20 PAOLO CLEMENTE NEW ANTI-SEISMIC TECHNOLOGIES

21 PAOLO CLEMENTE HISTORIC BUILDINGS Different concept of safety should be considered Demolition and reconstruction cannot be considered for historic structures These attract lots of tourists and are often very crowded, so requiring a high level of safety Heavy interventions could guarantee a suitable safety but could be inappropriate from the architectural point of view and cause the final loss of the historic and artistic values It would be suitable first choosing a retrofit intervention, which respects the original structural design and the artistic and historic values, and then verify if the degree of improvement achieved is not lower than a minimum acceptable one The real issue is the definition of this acceptable minimum value

22 PAOLO CLEMENTE B.I. STRUCTURE FOR EXISTING BUILDINGS isolated platform under the foundations of the building, without touching the building itself Gap Earth Rigid connection External wall Internal wall Isolators Inserted after removal of the special elements of the pipes Upper cilindrical sector Lower cilindrical sector Pipes inserted by means of auger boring or micro-tunnelling technique; D 2 m

historic buildings: no schools no hospitals no strategic

23 PAOLO CLEMENTE PREVENTION = INFORMATION BUILDINGS OPEN TO THE PUBLIC, SUCH AS SCHOOLS NON ANTI-SEISMIC BUILDING In historic buildings: no schools no hospitals no strategic structures For just old buildings: demolition and reconstruction

24 PAOLO CLEMENTE EMERGENCY AND POST-EMERGENCY After any natural disaster the next phases follow each other: 1) Emergency phase: the civil protection system intervenes immediately after the event and organizes the housing in tents or hotels in nearby areas 2) Post-emergency: containers or temporary houses are used for the homeless, often single-storey wooden houses but sometimes multi-storeys wooden, concrete or steel buildings 3) Reconstruction phase: at the end of which people are transferred in buildings repaired or rebuilt The recent experiences demonstrated that, in developed countries: 1) Emergency phase can be organized in few hours 2) Construction of temporary houses or buildings requires few weeks or months 3) Reconstruction phase could require several years Costs: quite high in emergency and post-emergency phases Temporary housing and containers, never reusable after reconstruction, or Permanent buildings, whose reuse requires additional costs for the adaptation Effective accommodation and rapid reconstruction reduce time and costs

25 PAOLO CLEMENTE DUAL USE BUILDINGS Earthquakes strike suddenly and organization of emergency and postemergency is always difficult It appears useful the choice and predisposition, in peacetime, of areas to accommodate temporary housing, equipped with the necessary infrastructure The production and the assembly of these housing should be possible in the shortest time after the event public constructions, such as schools, sports halls and public buildings in general, designed with adequate safety factors or equipped with modern seismic protection systems, to be used in the emergency phase. These should be designed flexible or able to contain tents.

26 PAOLO CLEMENTE END THANK YOU

Key Words: Seismic Risk, Hazard analysis, Fragility analysis, Radiation dose, evaluation response spectrum

Key Words: Seismic Risk, Hazard analysis, Fragility analysis, Radiation dose, evaluation response spectrum Development of a Seismic Risk Assessment System for Low and Intermediate Level Radioactive Waste Repository - Current Status of Year 1 Research - 11393 Kim, Min Kyu *, Choi, In-Kil *, Jeong, Jongtae *