Eurocode 8 General rules and seismic actions

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaEurocode 8 - Design of structures forearthquake resistance• EN1998-1: General rules, seismic actions andrules for buildings• EN1998-2: Bridges• EN1998-3: Assesment and retrofitting of buildings• EN1998-4: Silos, tanks and pipelines• EN1998-5: Foundations, retaining structures andgeotechnical aspects• EN1998-6: Towers, masts and chimneysAll parts published by CEN (2004-2006)Workshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaEN1998-1: Generalrules, seismic actionsand rules for buildingsEN1998-1 to be applied incombination with otherEurocodesWorkshop - 27-29 November 2006, Varese, Italy

Building the Future in the Euro-Mediterranean AreaEUROCODESBuilding the FutureEN1998-1: General rules, seismic actions and rulesfor buildings• General• Performance requirements and compliance criteria• Ground conditions and seismic action• Design of buildings• Specific rules for:Concrete buildingsSteel buildingsComposite Steel-Concrete buildingsTimber buildingsMasonry buildings• Base isolationWorkshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaObjectivesIn the event of earthquakes:Human lives are protectedDamage is limitedStructures important for civil protectionremain operationalSpecial structures – Nuclear Power Plants, Offshorestructures, Large Dams – outside the scope of EN 1998Workshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaFundamental requirementsNo-collapse requirement:Withstand the design seismic action withoutlocal or global collapseRetain structural integrity and residual loadbearing capacity after the eventFor ordinary structures this requirement should be met for areference seismic action with 10 % probability ofexceedance in 50 years (recommended value) i.e. with 475years Return PeriodWorkshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaFundamental requirementsDamage limitation requirement:Withstand a more frequent seismic actionwithout damageAvoid limitations of use with high costsFor ordinary structures this requirement should be met for aseismic action with 10 % probability of exceedance in 10years (recommended value) i.e. with 95 years Return PeriodWorkshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaReliability differentiationTarget reliability of requirement depending onconsequences of failureClassify the structures into importanceclassesAssign a higher or lower return period tothe design seismic actionIn operational terms multiply the reference seismic action bythe importance factor γ IWorkshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureImportance classes for buildingsBuilding the Future in the Euro-Mediterranean AreaImportance factors for buildings (recommended values):γ I = 0,8; 1,0; 1,2 and 1,4Workshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaFundamental requirementsCompliance criteria (design verifications):Ultimate limit stateResistance and Energy dissipation capacityDuctility classes and Behaviour factor valuesOverturning and sliding stability checkResistance of foundation elements and soilSecond order effectsNon detrimental effect of non structural elementsSimplified checks for low seismicity cases (ag < 0,08 g)No application of EN 1998 for very low seismicity cases (ag < 0,04 g)Workshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaFundamental requirementsCompliance criteria (design verifications):Damage limitation stateDeformation limits (Maximum interstorey driftdue 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 structureSufficient stiffness of the structure for theoperationality of vital services and equipmentDLS may control the design in many casesWorkshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaFundamental requirementsCompliance criteria (design verifications):Specific measuresSimple and regular forms (plan and elevation)Control the hierarchy of resistances andsequence of failure modes (capacity design)Avoid brittle failuresControl the behaviour of critical regions (detailing)Use adequate structural model (soil deformabilityand non strutural elements if appropriate)In zones of high seismicity formal Quality Plan for Design,Construction and Use is recommendedWorkshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaGround conditionsFive ground types:A -RockB - Very dense sand or gravel or very stiff clayC - Dense sand or gravel or stiff clayD - Loose to medium cohesionless soil or softto firm cohesive soilE - Surface alluvium layer C or D, 5 to 20 mthick, over a much stiffer material2 special ground types S1 and S2 requiring special studiesGround conditions defined by shear wave velocities in the top 30m and also by indicative values for N SPT and c uWorkshop - 27-29 November 2006, Varese, Italy

Building the Future in the Euro-Mediterranean AreaEUROCODESBuilding the FutureGroundconditionsGroundtypeABCDES 1S 2Table 3.1: Ground typesDescription of stratigraphic profileRock or other rock-like geologicalformation, including at most 5 m ofweaker material at the surface.Deposits of very dense sand, gravel, orvery stiff clay, at least several tens ofmetres in thickness, characterised by agradual increase of mechanicalproperties with depth.Deep deposits of dense or mediumdensesand, gravel or stiff clay withthickness from several tens to manyhundreds of metres.Deposits of loose-to-mediumcohesionless soil (with or without somesoft cohesive layers), or ofpredominantly soft-to-firm cohesivesoil.A soil profile consisting of a surfacealluvium layer with v s values of type Cor D and thickness varying betweenabout 5 m and 20 m, underlain bystiffer material with v s > 800 m/s.Deposits consisting, or containing alayer at least 10 m thick, of softclays/silts with a high plasticity index(PI > 40) and high water contentDeposits of liquefiable soils, ofsensitive clays, or any other soil profilenot included in types A – E or S 1Parametersv s,30 (m/s)N SPT(blows/30cm)> 800 _ _c u (kPa)360 – 800 > 50 > 250180 – 360 15 - 50 70 - 250< 180 < 15 < 70< 100(indicative)_ 10 - 20Workshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaSeismic zonationCompetence of National AuthoritiesDescribed by a gR (reference peak groundacceleration on type A ground)Corresponds to the reference return period T NCRModified by the Importance Factor γ I tobecome the design ground acceleration (ontype A ground) a g = a gR .γ IObjective for the future updating of EN1998-1:European zonation map with spectral values for differenthazard levels (e.g. 100, 500 and 2.500 years)Workshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaBasic representation of the seismic actionElastic response spectrumCommon shape for the ULS and DLS verifications2 orthogonal independent horizontal componentsVertical spectrum shape different from thehorizontal spectrum (common for all ground types)Possible use of more than one spectral shape (tomodel different seismo-genetic mechanisms)Account of topographical effects (EN 1998-5) and spatialvariation of motion (EN1998-2) required in some special casesWorkshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaDefinition of the horizontal elastic response spectrum(four branches)0 ≤ T ≤ T B S e (T) = a g . S . (1+T/T B . (η . 2,5 -1))T B ≤ T ≤ T C S e (T) = a g . S . η . 2,5T C ≤ T ≤ T DS e (T) = a g . S . η . 2,5 (T C /T)T D ≤ T ≤ 4 s S e (T) = a g . S . η . 2,5 (T C . T D /T 2 )Se (T)agTB TC TDSηelastic response spectrumdesign ground acceleration on type A groundcorner periods in the spectrum (NDPs)soil factor (NDP)damping correction factor (η = 1 for 5% damping)Additional information for T > 4 s in Informative AnnexWorkshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaNormalised elastic response spectrum (standard shape)Control variables• S, TB, TC, TD (NDPs)•η (≥ 0,55) dampingcorrection for ξ≠5 %Fixed variables• Constant acceleration,velocity & displacementspectral branches• acceleration spectralamplification: 2,5Different spectral shape for vertical spectrum (spectralamplification: 3,0)Workshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaElastic response spectrumTwo types of (recommended) spectral shapesDepending on the characteristics of the mostsignificant earthquake contributing to the localhazard:• Type 1 - High and moderate seismicity regions(Ms > 5,5 )• Type 2 - Low seismicity regions (Ms ≤ 5,5 );near field earthquakesOptional account of deep geology effects (NDP) for the definitionof the seismic actionWorkshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaRecommended elastic response spectraS e/a g.S43210EDCBA0 1 2 3 4T(s)Type 1 - M s > 5,5S e/a g.S543210DECBA0 1 2 3 4T(s)Type 2 - M s ≤ 5,5Workshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaDesign spectrum for elastic response analysis(derived from the elastic spectrum)0 ≤ T ≤ T B S d (T) = a g . S . (2/3+T/T B . (2,5/q -2/3))T B ≤ T ≤ T CT C ≤ T ≤ T DS d (T) = a g . S . 2,5/qS d (T) = a g . S . 2,5/q . (T C /T)≥ β . a gT D ≤ T ≤ 4 s S d (T) = a g . S . 2,5/q . (T C . T D /T 2 )≥ β . a gSd (T) design spectrumq behaviour factorβ lower bound factor (NDP recommended value: 0,2)Specific rules for vertical action:a vg = 0,9 . a g or a vg = 0,45 . a g ; S = 1,0; q ≤ 1,5Workshop - 27-29 November 2006, Varese, Italy

EUROCODESBuilding the FutureBuilding the Future in the Euro-Mediterranean AreaAlternative representations of the seismic actionTime history representation (essentially for NL analysispurposes)Three simultaneously acting accelerograms• Artificial accelerogramsMatch the elastic response spectrum for 5% dampingDuration compatible with Magnitude (Ts ≥ 10 s)Minimum number of accelerograms: 3• Recorded or simulated accelerogramsScaled to ag . SMatch the elastic response spectrum for 5% dampingWorkshop - 27-29 November 2006, Varese, Italy