research needs in support to eurocode 8 - ipsc -...
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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)
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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
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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
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SESAME Project Map of Seismic Hazard in S. Europe & the Mediterranean : PGA w/ 10% exceedance probability in 50 yrs
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• 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
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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”?
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Seismic Design Rules for Flat Slab SystemsSeismic Design Rules for Flat Slab Systems
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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
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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?
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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.
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•• 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
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Seismic assessment & retrofitting Seismic assessment & retrofitting of masonryof masonry--infilledinfilled frame frame buildings buildings (cont(cont’’d)d)
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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.
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etc., etc..etc., etc..