EUROPEAN EXPERIENCE: OVERVIEW ON END USER ORIENTED RESEARCH OPERE E SISTEMI GEOTECNICI Roma, 21 aprile 2015

PERFORMANCE BASED DESIGN IN EARTHQUAKE GEOTECHNICAL ENGINEERING

Stefano Aversa Università di Napoli Parthenope

European experience: overview on end user research

SUMMARY

1.  TRADITIONAL APPROACH IN EARTHQUAKE GEOTECHNICAL ENGINEERING 2.  PBD IN EARTHQUAKE GEOTECHNICAL ENGINEERING 3.  APPLICATION TO PILED FOUNDATIONS 4.  TOPPLING IN ROCK CLIFFS

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

TRADITIONAL APPROACH 1.  Pseudostatic approach 2.  Conventional seismic actions (indipendent of the type of structure) 3.  Evaluation of a Safety Factor 4.  Fixed safety margin (not dependant on the effects)

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

TRADITIONAL APPROACH 1.  Pseudostatic approach 2.  Conventional seismic actions (indipendent of the type of structure) 3.  Evaluation of a Safety Factor 4.  Fixed safety margin (not dependant on the effects)

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

Conventional Seismic Actions

What ah is? What av is (if used in the analysis)? When I was a student, I was thinking that ah is the maximum horizontal acceleration expected at the site It is not true! Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

Conventional Seismic Actions

The acceleration ah and av are conventional accelerations Structures (and other situations) verified with these values should have a “good” seismic performance! Should the value of ah be the same for all the types of structures? Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

Soil natural slope vs – rock cliff Ductile mechanism

Brittle mechanism

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

Soil natural slope vs – rock cliff Ductile mechanism

Same design accelerations? Brittle mechanism

Same accelerations of those used for buildings?

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

We analysed with the same acceleration different structures and situations: • buildings • retaining walls • dams • levees • slopes • cliffs •  ………. without considering: •  the importance •  the admissible behaviour •  the consequences of collapse or of damages •  the costs of repair Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

PERFORMANCE BASED DESIGN IN EARTHQUAKE GEOTECHNICAL ENGINEERING 1.  In performance based design appropriate levels of earthquake motions and corresponding acceptable levels of damage must be defined. approach is suggested by AGI 2.  A Twosimilar levels of earthquake are typically used as design reference motion: L1 and L2 The EUROCODE (EN 1998-5, guidelines 2003) consider a dual level approach. The performance requisites under L1 and L2 are respectively: ‘DAMAGE LIMITATION’ and No COLLAPSE REQUIREMENTS.

Example : PIANC (2001) Performance grade Design earthquake L1 Design earthquake L2 S Serviceable (deg. I) Serviceable (deg. I) A Serviceable (deg. I) Repairable (deg. II) B Serviceable (deg. I) Near Collapse (deg. III) Performance based design in earthquake geotechnical engineering C Repairable (deg. II) Collapse (deg. IV)

European experience: overview on end user research

Basic ideas of PBD in Earthquake Geotechnical Engineering •  different earthquake levels •  different importance (Performance grade) •  different required performances •  different levels of investigation •  sometimes, also, of analysis (Pseudostatic; Simple dynamic analyses ; Complete dynamic analyses)

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

Advantages of PBD in Earthquake Geotechnical Engineering •  better understanding of the earthquake behaviour •  increase of reliability of the analyses •  mitigation of risks •  possible reduction of costs •  reduction of interventions in seismic retrofitting of existing structures (historical masonry and recent rc buildings) •  rational use of public (and private) money Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

Researches on PBD in EGE in Italy (ReLUIS project) •  Slopes •  Dams •  Retaining walls •  Flexible Retaining walls •  Shallow and piled foundations •  Tunnels •  Toppling in rock cliffs Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

Researches on PBD in EGE in Italy (ReLUIS project) •  Slopes •  Dams •  Retaining walls •  Flexible Retaining walls •  Shallow and piled

foundations (retrofitting)

•  Tunnels

•  Toppling in rock cliffs Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

PILED FOUNDATIONS Decomposition of Kinematic and Inertial Effects

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research PILE-SOIL KINEMATIC INTERACTION

Foundation Input Motion (FIM) Free-field input signal Soil deflection Pile deflection

Bedrock signal

Foundation Input Motion (FIM) and filtering action exerted by piles

European experience: overview on end user research DECOMPOSITION OF KINEMATICA AND INERTIAL INTERACTION

The above phenomena occurs almost simultaneously. However it is convenient, both conceptually and computationally to separate them into two successive stages referredo to as ‘Kinematic interaction’ and ‘Inertial interaction’;

Kausel et al. 1978 (modified by Mylonakis et al. 2006)

HYP: Linear behaviour of soil and structure

European experience: overview on end user research EFFECT OF DEFORMABILITY AND DAMPING OF THE SOILFOUNDATION SYSTEM

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

Effect of deformability and damping Maravas et al. (2014) Equivalent damping

Equivalent natural frequency

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

PERFORMANCE BASED ANALYSIS OF A REAL STRUCTURE FOUNDED ON PILES

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research CASE STUDY: TALL BUILDING IN THE EASTERN AREA OF NAPOLI LARGE piled rafts: L < B; B > 1 5m, Large diameter bored piles L = 42 m

Conventional seismic analysis, based on subsoil classification and fixed base model, would have lead to severe measures for seismic retrofitting Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

MOBILISED SOIL STIFFNESS AND DAMPING RATIO EVALUATED VIA SSR NON LINEAR ANALYSIS

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research INERTIAL INTERACTION IMPEDANCE FUNCTION OF PILED GROUPS

Maravas et al. (2014)

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research INERTIAL INTERACTION ANALYIS REPLACEMENT OSCILLATOR METHOD, Natural frequencies

filtering effect not relevant in this case

Maravas et al. (2014)

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

MODERN TRENDS IN SEISMIC PERFORMANCE BASED DESIGN OF GEOTECHNICAL STRUCTURES

PILED FOUNDATIONS 1. Importance of Pile-soil Kinematic bending effects 2. Compliance base modelling is very relevant for a successful seismic performance evaluation of structures Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

Rock toppling

It can be induced by earthquakes Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

Dynamic model for a rectangular block

UPLIFT CONDITION:

slenderness (-) size parameter (m) Parameters:

polar moment of inertia (kgm2) frequency parameter (rad/s)

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research EQUATIONS AND HYPOTHESES Equation of motion:

IMPACT CONDITION: RESTITUTION COEFFICIENT (Yim et al., 1980):

Hypotheses: •  Single block; •  Both the block and the base are rigid; •  The base is horizontal;

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research VALIDATION OF THE MODEL WITH SIMPLE PULSES

p=1.70 1/s, a=0.197, r=0.89, b=0.5m, h=2.5m

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

DYNAMIC ANALYSES WITH NATURAL TIME HISTORIES PGA(g): 0.32

Performance based design in earthquake geotechnical engineering

PGA(g): 0.32

European experience: overview on end user research

STABILITY ANALYSES (ASTU270) •  No Rocking: zone for which rocking does not start b=PGA(g)*h; •  Safe: blocks swing without oreturning; •  Overturning: blocks overturn. a

0.05

0.07

0.08

0.10

0.11

b (m)

0.13

0.14

0.17

0.20

0.25

0.33

h (m)

0.05

1.00

0.75

0.63

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.1

2.00

1.50

1.25

1.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.2

4.00

3.00

2.50

2.00

1.80

1.60

1.40

1.20

1.00

0.80

0.61

0.4

8.00

6.00

5.00

4.00

3.60

3.20

2.80

2.40

2.00

1.60

1.21

0.6

12.00

9.00

7.50

6.00

5.40

4.80

4.20

3.60

3.00

2.40

1.82

0.8

16.00

11.99

10.00

8.00

7.20

6.40

5.60

4.80

4.00

3.20

2.42

1

20.00

14.99

12.50

10.00

9.00

8.00

7.00

6.00

5.00

4.00

3.03

1.2

24.00

17.99

15.00

12.00

10.80

9.60

8.40

7.20

6.00

4.80

3.64

1.4

28.00

20.99

17.50

14.00

12.60

11.20

9.80

8.40

7.00

5.60

4.24

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

Acceleration time histories

Performance based design in earthquake geotechnical engineering

European experience: overview on end user research

ROCKING SPECTRA: h-b PLOT AND REDUCTION COEFFICIENT !

•  Blocks can sustain earthquakes with maximum acceleration higher than that inducing collapse in pseudostatic conditions •  ! is the reduction coefficient of maximum acceleration to evaluate the equivalent one in pseudostatic analyses Performance based design in earthquake geotechnical engineering

European experience: overview on end user research Discussed only a few applications of Performance Based Design in Earthquake Geotechnical Engineering Some other applications can be considered to demonstrate the importance of this approach More can be done if the consequences of damages and the resilience of the system are taken into account For example The effects of an earthquake on a segmented tunnel can be significantly different , depending on: • The saturation of the soil • The pore water pressure • The permeability of the soil • The use of the tunnel • The upperground conditions Performance based design in earthquake geotechnical engineering