Evoluzione della Normativa Sismica Italiana ed Europea. Le ...

Evoluzione della Normativa Sismica Italiana ed Europea.

Le proposte italiane per l’EC8.

Franco Braga, Giorgio Monti

Structural Eurocodes• EN1990 Eurocode 0: Basis of structural design• EN1991 Eurocode 1: Actions on structures• EN1992 Eurocode 2: Design of concrete structures• EN1993 Eurocode 3: Design of steel structures• EN1994 Eurocode 4: Design of composite steel and

concrete structures• EN1995 Eurocode 5: Design of timber structures• EN1996 Eurocode 6: Design of masonry structures• EN1997 Eurocode 7: Geotechnical design• EN1998 Eurocode 8: Design of structures for

earthquake resistance• EN1999 Eurocode 9: Design of aluminium structures

Eurocode 8 - Design of structures for earthquake resistance

• EN1998-1: General rules, seismic actions and rules for buildings

• EN1998-2: Bridges• EN1998-3: Assessment and retrofitting of

buildings• EN1998-4: Silos, tanks and pipelines• EN1998-5: Foundations, retaining structures

and geotechnical aspects• EN1998-6: Towers, masts and chimneys

EN1998-1

• EN1998-1: General rules seismic actions rules, seismic actions and rules for buildings – EN1998-1 to be

applied in combination with other Eurocodes

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Nationally Determined Parameters

• Parameters which are left open in the Eurocodes for national choice (NDPs - Nationally Determined Parameters):– values and/or classes where alternatives are given in the

Eurocode,– values to be used where a symbol only is given in the

Eurocode,– country specific data (geographical, climatic, etc.), e.g. snow

map,– the procedure to be used where alternative procedures are

given in the Eurocode.• It may also contain

– decisions on the application of informative annexes,– references to non-contradictory complementary information

to assist the user to apply the Eurocode.

Nationally Determined Parameters

Nationally Determined Parameters (NDPs) in EN 1998-1:General aspects and definition of the seismic action: 11Modelling, analysis and design of buildings: 7Concrete buildings: 11Steel buildings: 6Composite buildings: 4Timber buildings: 1Masonry buildings: 15Base isolation: 1

TOTAL 56

L’Italia e l’EC8

• L’Assemblea Generale del Consiglio Superiore dei Lavori Pubblici ha espresso parere favorevole all’adozione degli Annessi Tecnici Nazionali agli Eurocodici, altrimenti detti Appendici Nazionali (voti n. 98 del 24.09.2010 e n. 4 del 25.02.2011)

• L’avvenuta approvazione da parte del Consiglio Superiore costituisce la necessaria tappa tecnica propedeutica alla loro adozione formale.

L’Italia e l’EC8• Attraverso i 59 Annessi (o Appendici) i contenuti

degli Eurocodici hanno piena operatività nel settore della progettazione strutturale e geotecnica, in coerenza con il quadro delle Norme Tecniche per le Costruzioni di cui al D.M. 14.01.2008.

• L’Ufficio Legislativo del Ministero delle Infrastrutture ha indicato che, per il proseguimento dell’iter approvativo, deve essere predisposto un apposito Decreto interministeriale, sentita la conferenza Stato-Regioni, ai sensi degli art. 52, 60 e 83 del DPR 380/01

Criticità nell’EC8

• Alcuni aspetti meritano approfondimento in relazione all’avanzamento delle conoscenze avvenuto dopo l’approvazione

• Alcune impostazioni sono più “datate”rispetto alla NTC-08

• Alcune parti potrebbero essere semplificate

Fundamental requirements

• Damage limitation requirement:– For ordinary structures this requirement

should be met for a seismic action with 10% probability of exceedance in 10 years (recommended value) i.e. with 95 years Return Period

Reliability differentiation

• Target reliability of requirement depending on consequences of failure– Classify the structures into importance

classes– Assign a higher or lower return period to the

design seismic action• In operational terms, multiply the reference

seismic action by the importance factor �I

Valori di riferimento dell’indice di affidabilità β

• Valori di riferimento dell’indice di affidabilità β per gli elementi strutturali di Classe RC3, RC2 e RC1, per gli Stati Limite Ultimi e di Esercizio, e per vita di riferimento VR pari a 1 anno e a 50 anni. I valori in grassetto sono riportati nell’EC0, mentre gli altri sono dedotti

Periodo di ritorno del fallimento• Valori di riferimento dei periodi di ritorno del fallimento e

dei relativi tassi di fallimento per gli elementi strutturali diClasse RC3, RC2 e RC1, per gli Stati Limite Ultimi e di Esercizio. Tali valori sono gli stessi per tutte le vite di riferimento VR

Tasso di fallimento• Dalla Tabella precedente si evince che,

indipendentemente dalla vita di riferimento, il tasso di fallimento del relativo stato limite rimane costante all’interno della classe di affidabilità. Ciò implica che la progettazione eseguita in questo inquadramento affidabilistico mira a produrre strutture a tasso di fallimento costante

Probabilità di fallimento• Dalla tabella si evince che, rimanendo costante il tasso

di fallimento, la probabilità di fallimento aumenta all’aumentare del periodo di riferimento

Compliance criteriaDesign verifications•Ultimate limit state (ULS)

– Resistance and Energy dissipation capacity– Ductility classes and Behaviour factor values– Overturning and sliding stability check– Resistance of foundation elements and soil– Second order effects– Non detrimental effect of non structural elements

•Simplified checks for low seismicity cases (ag < 0,08 g)•No application of EN 1998 for very low seismicity cases (ag < 0,04 g)

Compliance criteriaDesign verifications•Damage limitation state (DLS/SLS)•Deformation limits (Maximum interstorey drift due to the “frequent” earthquake):

– 0,5 % for brittle non structural elements attached to the structure

– 0,75 % for ductile non structural elements attached to the structure

– 1,0 % for non structural elements not interfering with the structure

•Sufficient stiffness of the structure for the operationality of vital services and equipment

Compliance criteria (!)Design verifications•Take specific measures intended to reduce the uncertainty and promote a good behaviour of the structure, even under seismic actions more severe than the design seismic action•Implicitly equivalent to the satisfaction of a third performance requirement:

– Prevention of global collapse under a very rare event (1.500 to 2.000 years return period).

– Denoted Near Collapse (NC) Limit State in EN 1998-3, very close to the actual collapse of the structure and corresponds to the full exploitation of the deformation capacity of the structural elements

Compliance criteriaSpecific measures•Simple and regular forms (plan and elevation)•Control the hierarchy of resistances and sequence of failure modes (capacity design)•Avoid brittle failures•Control the behaviour of critical regions (detailing)•Use adequate structural model (soil deformability and non structural elements, if appropriate)

L’Italia e l’EC8

• Come vengono riportate in sede europea queste osservazioni (ed altre…)?

• Che riflessi hanno sulla NTC-08?

Riunione SC8 del 14 gennaio 2011 a Parigi

PRESENTI•Eduardo Carvalho (PT) C•J. Marques (PT)•Jean Charles Rutman (FR)•Alain Pecker (FR)•Philippe Bisch (FR)•Wolfganga Jalil (FR)•Jean-Armand Calgaro (FR)•P. Pillard (FR)•André Plumier (BE)

•Franco Braga (IT)•Claudio Chesi (IT)•Giorgio Monti (IT)•Giandomenico Toniolo (IT)•Enrique Alarcon (SP)•Suikai Lu (AT)•H. Fredmund (UK)•P. Chysostomou (CY)•Peter Fajfar (SL)

Project Proposals

• Evolution of EN 1998-1– General, seismic action and buildings

• Evolution of EN 1998-2– Bridges

• Evolution of EN 1998-3– Assessment and retrofitting of buildings

• Evolution of EN 1998-5– Foundations, retaining structures and

geotechnical

Evolution of EN 1998-1General, seismic action and

buildings• Activity 1 (15 months)

– Preparation of a Technical Report on EN 1998-1 including the main aspects and matters to be developed for its evolution

– A vision of the long term objectives and future contents of EN 1998, having in mind:

• the expected evolution of (for instance) the seismic input models for design,

• the construction types and materials in seismic areas, • the structural modelling and analysis capabilities, and • the force-based vs. displacement-based design approaches.

Evolution of EN 1998-1General, seismic action and

buildings• Activity 2 (9 months)

– Consultation of National Standardization Bodies, CENCENELEC Technical Committees and other relevant scientific and technical bodies.

• Activity 3 (24 months)– Development of a revised version of EN 1998-1

based on the results of activities 1 and 2

Evolution of EN 1998-1Summary

• The project is intended to improve EN 1998-1 both in formal and substantial aspects.

• For the formal aspects, the following shall be considered:– 1. Simplification of the code, elimination of

superfluous information, improvement of clarity, removal of ambiguity and improvement of internal consistency.

– 2. Improvement of consistency of EN 1998-1 with other Parts of EN 1998 and with the other Eurocodes.


• For the substantial aspects, the following shall be considered:– 1. Advancement towards a European seismic zonation– 2. Re-evaluation of the concept of secondary seismic

structural elements– 3. Seismic design rules for flat slab systems– 4. Seismic design rules for prestressed concrete elements

in buildings– 5. Improvement of seismic design rules for timber buildings– 6. Improvement of seismic design rules for masonry

buildings– 7. Infilled frames (including cladding systems and other

types of enclosures)– 8. Seismic design rules for aluminium structures– 9. Displacement-based design

Evolution of EN 1998-2Bridges

• Activity 1 (15 months)– Preparation of a Technical Report on EN 1998-2

including the main aspects and matters to be developed for its evolution. This activity includes the evaluation of the information available at the JRC database regarding the national choices in the National annexes


• Activity 2 (9 months)– Consultation of National Standardization Bodies,

CENCENELEC Technical Committees and other relevant scientific and technical bodies







– 2. Improvement of consistency of EN 1998-2 with EN 1998-1 and with the “Bridge Parts” of the other Eurocodes.


• For the substantial aspects, it is proposed to extend the contents of EN 1998-2 to encompass the Assessment and retrofitting of existing bridges.

• Furthermore, resulting from the analysis of the choices made by Member States in their National Annexes, the reduction of NDPs in EN 1998-2 shall be attempted.– Important Note: The aspects of the project related to

Assessment and Retrofitting are proposed with regard to EN 1998-2 (Bridges) but, if later on such is considered more appropriate, its results may, alternatively, be incorporated into EN 1998-3 (Assessment and retrofitting of buildings), extending its scope, presently restricted to buildings, and changing its title to Assessment and retrofitting of buildings and bridges..

Evolution of EN 1998-3Assessment and retrofitting of buildings• Activity 1 (15 months)

– Preparation of a Technical Report on EN 1998-3 including the main aspects and matters to be developed for its evolution. This activity includes the evaluation of the information available at the JRC database regarding the national choices in the National annexes

Evolution of EN 1998-3Assessment and retrofitting of buildings• Activity 2 (9 months)

– Consultation of National Standardization Bodies, CENCENELEC Technical Committees and other relevant scientific and technical bodies





• For the formal aspects, the following shall be considered:– 1. Simplification of the code, elimination of superfluous

information, improvement of clarity, removal of ambiguity and improvement of internal consistency.

– 2. Improvement of consistency of EN 1998-3 with EN 1998-1 or clear identification of the aspects that, being specific of assessment and retrofitting situations, are treated differently in both parts of EN 1998.


• For the substantial aspects, it is proposed to update the contents of EN 1998-3 to encompass the recent advances in this field.– Confidence Factors and Knowledge Levels– Review of Performance Levels (seismic amelioration)– Shear resistance

• Furthermore, the incorporation of the contents (or part of) of the present Informative Annex into the main text of the EN 1998-3 shall be sought.– Important Note: Besides the specific outcome of the project

proposed for EN 1998-3, the outcome of the project proposed for EN 1998-2 (Bridges) in what concerns Assessment and retrofitting of bridges may be incorporated into EN 1998-3 (Assessment and retrofitting).

Evolution of EN 1998-5Foundations, retaining structures and

geotechnical

• Activity 1 (15 months)– Preparation of a Technical Report on EN 1998-5

including the main aspects and matters to be developed for its evolution. This activity includes the evaluation of the information available at the JRC database regarding the national choices in the National annexes

Evolution of EN 1998-5Foundations, retaining structures and

geotechnical

• Activity 2 (9 months)– Consultation of National Standardization Bodies,

CENCENELEC Technical Committees and other relevant scientific and technical bodies


based on the results of activities 1 and 2.





– 2. Improvement of consistency of EN 1998-5 with EN 1998-1 and with EN 1997.

• For the substantial aspects, one main aspect shall be considered:– 1. Soil structure interaction (including pile interaction

with the soil).


• Also, in view of the proposed advances in EN 1998-1 regarding seismic zonation and methodologies to define the seismic action at different performance levels, the present provisions in EN 1998-5 regarding the evaluation of liquefaction susceptibility shall be reviewed, namely providing more guidance on the appropriate choice of Magnitudes for that effect.

• Furthermore, resulting from the analysis of the choices made by Member States in their National Annexes, the reduction of NDPs shall be attempted.

Ulteriori proposte italiane… con riflessi sulla NTC-08 (GdL1 23.06.11)

• Terminologia– Progettazione della capacità vs. Gerarchia delle resistenze– Zona dissipativa vs. Zona critica

• Requisiti strutturali degli elementi di fondazione• Non linearità geometriche (fattore θ)• Omogeneizzazione fra tipologie costruttive

– Definizione del raggiungimento dello SLV• Verifica SL per elementi strutturali, non strutturali ed

impianti– Verifiche espresse in termini di rigidezza, resistenza,

duttilità• Identificazione degli elementi “secondari”• Utilizzo della redistribuzione nell’analisi lineare• Ruolo delle tamponature• Eccentricità accidentale

Requisiti strutturali degli elementi di fondazione

• Per le strutture progettate sia per CD “A” sia per CD “B”, il dimensionamento delle strutture di fondazione e la verifica di sicurezza del complesso fondazione-terreno devono essere eseguiti assumendo come azione in fondazione trasmessa da ciascun elemento soprastante la minore tra:– la resistenza dell’elemento stesso, amplificata con un γRd pari a

1,3 in CD “A” e 1,1 in CD “B”, determinata in corrispondenza della forza assiale derivante dalla combinazione delle azioni dicui al § 3.2.4;

– la sollecitazione derivante dall’analisi strutturale eseguita in campo lineare con fattore di struttura q, amplificata dello stesso fattore q, oppure la sollecitazione derivante dall’analisi strutturale eseguita in campo non lineare.

• Le travi di fondazione in cemento armato devono avere armature longitudinali per l’intera lunghezza, sia inferiormente sia superiormente, in percentuale non inferiore allo 0,4% dell’area di calcestruzzo. (Si veda EC8-1 par. 5.8.2)

Utilizzo della redistribuzione nell’analisi lineare (4.1.1.1)

• Per le sole verifiche agli stati limite ultimi, i risultati dell’analisi elastica possono essere modificati con una ridistribuzione dei momenti, nel rispetto dell’equilibrio e delle capacità di rotazione plastica delle sezioni dove si localizza la ridistribuzione.

• In particolare la ridistribuzione non è ammessa per i pilastri e per i nodi dei telai, è consentita per le travi continue e le solette, a condizione che le sollecitazioni di flessione siano prevalenti ed i rapporti tra le luci di campate contigue siano compresi nell’intervallo 0,5-2,0.

• Per le travi e le solette che soddisfano le condizioni dette, laridistribuzione dei momenti flettenti può effettuarsi senza esplicite verifiche in merito alla duttilità delle membrature, purché il rapporto δ tra il momento dopo la ridistribuzione ed il momento prima della ridistribuzione risulti 1≥δ≥ 0,70.

Definizione di SL per elementi strutturali, non strutturali ed

impianti• Le verifiche nei confronti degli stati limite di:

– elementi strutturali (ST), – elementi non strutturali (NS),– impianti (IM),

• si effettuano, in dipendenza della CU, in termini di:– resistenza (R), – rigidezza (S),– duttilità (D).

GRAZIE PER L’ATTENZIONE

La prima parte di questa presentazione è stata ispirata dalla presentazione del Dr. Eduardo Carvalho nel workshop “Eurocode 8 – Background and Application – Dissemination of information for training” Lisbona, 10-11 Febbraio 2011

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