research needs in support to eurocode 8 - ipsc -...

LOSS Final WorkshopLOSS Final WorkshopRisk Mitigation for Earthquakes and LandslidesRisk Mitigation for Earthquakes and Landslides

19-20 July 2007Hotel Villa Carlotta, Belgirate (VB) - Italy

Research needs in support to Research needs in support to EurocodeEurocode 8 8

M.N. FardisDepartment of Civil Engineering, Univ. of Patras (GR)

NORMATIVE RESEARCH NEEDS FOR EC 8NORMATIVE RESEARCH NEEDS FOR EC 8Harmonized European Seismic Hazard MapSeismic Design of Buildings for Torsional Effects“Primary” v “Secondary” Elements: Elaboration of the Implications & Re-Evaluation of ConceptSeismic Design Rules for Flat Slab SystemsSeismic Design Rules for Prestressed (Post-Tensioned) Concrete Elements & SystemsSeismic Design Rules for Masonry BuildingsSeismic Protection of Sensitive or Valuable Equipment & Artefacts Seismic Assessment & Retrofitting of Masonry-InfilledFrame BuildingsSeismic Design of the Structure-Foundation-Soil System

Harmonized European seismic hazard Harmonized European seismic hazard map(smap(s))Currently: Discrepancies across EU Member State borders of National seismic zonation maps

• Goal: Include Seismic Map(s) in EN1991-Actions (like the European Snow map) or assist National Authorities for the National Annexes (target ∼2010)

• Scope: Uniform-hazard, 5%-damped spectra for 5 standard ground types) at several hazard levels (f.i. ∼100, ∼500, ∼2500 yrs), hopefully w/ disaggregation of hazard (M & R, intraplate vs interplate events, etc)

• Tool: European attenuation laws for spectral values over 5 standard ground types.

• Precedent: GSHAP & GSHAP & SESAME Seismic Hazard MapsSeismic Hazard Maps

SESAME Project Map of Seismic Hazard in S. Europe & the Mediterranean : PGA w/ 10% exceedance probability in 50 yrs

• Examples:• For large population centres, identify potential faults &

produce by simulation realistic ground motions, taking into account local geology & soil deposits (including, if relevant/feasible, near-fault effects and basin-generated surface waves).

• For sites near known faults, develop realistic near-fault motions & study their structural effects.

• Emphasize features of the motion that are important for performance-based design, but are poorly described by elastic response spectra (e.g., residual displacement, especially for base-isolated structures).

Medium-term objective: More detailed description of seismic action

Seismic Design of Buildings for Seismic Design of Buildings for TorsionalTorsional EffectsEffectsEC8 rules may need revisiting, especially regarding deformation demands on the flexible side of asymmetric buildings.

→ Amplification of “natural eccentricity”? → Definition of “Stiffness center” & “natural eccentricity”?

Seismic Design Rules for Flat Slab SystemsSeismic Design Rules for Flat Slab Systems

Seismic design rules for flat slab systemsSeismic design rules for flat slab systems (cont(cont’’d)d)

PsD test at ELSA

No rules in EC8 for modeling, analysis, design & detailing of flat-slab frames for seismic actions

Seismic Design Rules for PostSeismic Design Rules for Post--Tensioned Tensioned Concrete Elements & Systems (esp. in buildings)Concrete Elements & Systems (esp. in buildings)

• EU: world leader in post-tensioning technology & materials. • Post-tensioning used cost-effectively against gravity loads. • But: No rules in EC8 for design & detailing of Post-

tensioned members as primary elements.• Currently post-tensioned concrete members can only be

considered as secondary elements:– they are relied upon only for gravity loads;– their contribution to lateral force resistance neglected in the model

for the analysis.• However:

– prestressing is not, in principle, detrimental for ductility;– the recentering effect of (con-centric) prestressing may be used to

advantage, to minimize residual seismic deformations.• Question:

– How to reconcile need for eccentric prestress over beam supports with plastic hinging there in beam-sway frames?

Seismic design rules for masonry buildingsSeismic design rules for masonry buildingsMagenes – 1st ECEES-2006:• EC8 doesn’t account for redistribution between walls. Too conservative?• Behaviour factors may need re-visiting.

•• Major gap:Major gap: Although effect of infills on seismic performance is largest, if the structural frame has little engineered earthquake resistance (as in existing buildings):– There are no specific rules in

EC8 for modelling, verification & retrofitting masonry infills.

Residual resistance

δ

Ultimate deformation

Infill resistance

F

Seismic Assessment & Retrofitting of MasonrySeismic Assessment & Retrofitting of Masonry--InfilledInfilled Frame BuildingsFrame Buildings

Seismic assessment & retrofitting Seismic assessment & retrofitting of masonryof masonry--infilledinfilled frame frame buildings buildings (cont(cont’’d)d)

Seismic design considering the StructureSeismic design considering the Structure--FoundationFoundation--Soil as an integrated & interactive systemSoil as an integrated & interactive system

• Important for structures developing large interaction w/ the surrounding ground, e.g., partially or fully embedded structures, underground facilities, such as tunnels, buried storage systems, oil wells, etc., currently outside scope of EC8.

• In general: – Consideration of effects on superstructure of (important)

phenomena in the soil or at its interface w/ structure (e.g. sliding and/or uplift/rocking);

– Alternative cost-effective seismic design concepts, allowing -under certain conditions - concentration of nonlinearity and energy dissipation in the soil or in the foundation;

– May also change ductility demand in superstructure, leading to modification of the values of the behaviour factor, q.

etc., etc..etc., etc..