M. Sokol, l. konečná, M. čuhák, Milan SOKOL · 2011-10-07 · M. Sokol, l. konečná, M....

M. Sokol, l. konečná, M. čuhák, M. DalleMule

Very Low SeiSmicity AreAS in SLoVAkiA And compAriSon of SeiSmic riSkS in centrAL europeAn countrieS

key wordS

• Very low seismicity,• wind action,• seismic action,• peak ground acceleration,• effective ground acceleration,• seismic hazard.

ABStrAct

A parametric study concerning the importance of very low seismicity for Slovakia is introduced. Analyses were performed for ordinary buildings such as family houses, residential brick buildings, residential panel buildings and high-rise buildings. Both horizontal wind and seismic actions were analysed and compared in detail for all the regions and conditions in Slovakia.

Milan [email protected] field: dynamics of structures, seismic engi-neering,modellingofstructures

Lenka KONEČNÁ [email protected] field: dynamics of structures, seismicengineering,modellingofstructuresAddress:DepartmentofStructuralMechanics

Marek ČUHÁK [email protected]:concretestructuresAddress:DepartmentofConcreteStructuresandBridges

Marián DALLEMULE [email protected]:steelstructuresAddress:DepartmentofSteelandTimberStructures

FacultyofCivilEngineeringRadlinského1181368Bratislava,Slovakia

Vol. XIX, 2011, No. 3, 1 – 9

1. introduction

The effects of all possible actions should be taken into accountduringthedesignofastructure.Becauseananalysisofastructurethatassumesseismiceffectsisaverysophisticatedanddemandingprocess, there are timeswhen aseismic analysis is not necessary.Theselimitsarespecifiedbyaseismicactionlevelwhichiscalledavery low seismicity area. These limits are especially defined in[2].Inotherwords,itisnecessarytospecifyunderwhatconditionsit would not be required to consider seismic effects. The paperprovides an answer to the question of whether it is necessary totake into account seismic effects in cases of the common typesof buildings in Slovakia (family houses, residential buildings,residential multi-storey buildings and high-rise buildings). Theserepresentativebuildingswereexaminedonall typesof soilwhichcouldsignificantlybeaffectedbyaseismicresponse.Ifthereisaconstructionsitewhichcouldnotbedescribedasavery

low seismicity area, there is one more possible simplification ofaseismicanalysis if the seismic effects arenotverygreat. In thiscase the seismic analysis does not have to be done in so muchdetail.Thesesitesarecalled low seismicityareas.Thismeans thatonly afew restrictions in such areas are necessary for an area tobeapproved.Inmanycasesthatmeansthatonlydetailedrulesarenecessaryandthatthereisnoneedtoperformaseismicanalysisatall.

2. SeiSmicALLy VuLnerABLe AreAS

Due to the simplicity of designing aseismic design procedure,there are only afew basic parameters needed to describe theseismicvulnerabilityofalocation. InEurocode8 [2],peakgroundacceleration(PGA)onarockysoil is themainrepresentativevaluedefiningtheseismicvulnerabilityofanarea.Themapofacountry

2011 SLoVAk uniVerSity of tecHnoLoGy 1

2 Very Low SeiSmicity AreAS in SLoVAkiA And compAriSon of SeiSmic riSkS ...

2011/3 PAGES 1 — 9

describing this value provides the answer as to where the mostvulnerable seismic areas are. In some countries such as Slovakia,thecharacteristicvalueof suchamap isdefined inaslightlymoreappropriatemannerandiscalledeffectivepeakacceleration(EPA),whichmorepreciselydescribesthepossibilityofstructuraldamageorcollapseatasite(Fig.7a).EPAisdefinedasaspectralaccelerationduring aperiod ofT1=0.5s divided by afactor of 2.5. PeriodT1 isassumedtobethefirstvibrationperiodofanordinarystructure.

3. Very Low SeiSmicity AreAS

Thebasicprincipleofdefiningverylowseismicityareasisbasedontheassumptionthatseismiceffects(seismicdesignsituations)aresmallerthantheeffectsofotherdesignsituations,i.e.,effectscausedby adead load, wind load, etc. (basic design situations). So bothseismicandbasicdesignsituationsarecompared,and if thebasicdesign situation is unfavourable, such asite is called avery lowseismicityarea.Butthesetwodesignsituationsarequitedifferent,evenintheirphilosophy.Aseismic design situation is described by alimit state whenastructureafteraseismiceventcanbedamagedtoacertainextentbut has not yet collapsed. Plastic joints can develop in aspecificpart of astructure. They can gradually extend at such locationson the structurewhere the earthquake’senergy has dissipated. Sothis means that the analysis of the potential structural responseshouldbeperformedbyanon-lineardynamicanalysis.Thisisquiteademanding process and cannot be done in ordinary practice, sosimplifiedquasi-linearsolutionsshouldbeperformedasareferencecodeprocedure.Ontheotherhand,theeffectscausedbywindarealsoinfluencedbymanyfactors(terrain,orientationofthebuilding,etc.).An appropriate tool for indicating how aseismic design situationcanbecompared toabasicdesignsituation is todefine the factorexpressingtheratiobetweenthehorizontaldesignforceandverticaldeadload:

(1)

where Sh - total design effect caused by horizontal force (windor seismic) in the corresponding design situation foraspecificactionorientation,

G - totaldeadloadofthestructure.

Thehorizontal forceeffect iscombinedwith thedead loadeffect,takingintoaccountthepartialsafetyfactorγG=1.0,whichisvalidin the case of aseismic design situation. Other variable actionssuch aswind and snow actions are not taken into account during

theseismicdesignsituation.Onlythequasi-permanentvalueofthevariableactionisconsideredusingacombinationfactorofψ=0.3accordingto[2].In the caseof different local conditionsof awind load, thebasicwindvelocity,terraincategory,etc.,shouldbetakenintoaccount.Representative buildings were examined in all the wind-specificregionsinSlovakia(Fig.7b).

4. BuiLdinGS AnALyZed

Common typesofbuildings, such as afamilyhouse, aresidentialbrickbuilding,aresidentialpanelbuildingandahigh-risebuilding,weretakenintoaccount.

family houseThe structure examined (Fig. 1) was aone-story family house.Ceramic ceilings with athickness of about 200mm, along withbearing (350mm) and non-bearing (100mm)masonrywallswereassumed.Atimber roofwithceramic tileswasalsoassumed.Thehouse´stotaldimensionswere:10m×12m×7.5m(width×length× height). The total weight was 216 tons (240 kg/m3). The soil-structureinteractionassumingdiscretespringsinallthreedirectionsactingbetweenthefoundationandsoilwastakenintoaccount.

4-story residential buildingA4-story residential masonry building (Fig. 2) was chosen asasecond commonly used structure in Slovakia. The ceilingswere made of reinforced concrete with athickness up to200 mm; the bearing and non-bearing walls were made ofmasonry bricks. Atimber roof as apart of the fourth storeywas assumed. The building´stotal dimensions were:12.4m×48.9m×12.5m.Thetotalweightwas2,102tons (277kg/m3).

8-story r/c residential buildingThe next structure (Figs. 3 and 4) was an 8-story building. Thestructural system is assumed to be aprecast R/C wall system.

Fig.1Family house.

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3Very Low SeiSmicity AreAS in SLoVAkiA And compAriSon of SeiSmic riSkS ...

The ceilings were made of 200 mm thick reinforced concrete;thebearing andnon-bearingwallswere alsomadeof concrete ofvarious thicknesses.The totaldimensionswere:12.6m×30.0m×24m.Thetotalweightequaled2,800 tons(310kg/m3).

22 storey high-rise buildingThestructureexamined(Figs.5and6)isa22-storybuildingwith2additionalundergroundlevels.Themainverticalstructuralsystemconsistsof twoR/Cwalls at theutmost sidesof thebuildingandone longitudinal wall inside the building. The lift cores are alsointegrated into the internal wall (Fig. 6). The ceilings consist of220mmthickconcrete.Thetotaldimensionsare:14.6m×45.6m×74.2m.Thetotalweightequals19,571tons(396kg/m3).

Fig. 2Residential building.

Fig. 38-story R/C residential building – ground plan view.

Fig. 48-story R/C residential building – structural system.

Fig. 5High-rise building –structural model.

Fig. 6High-rise building – detail of modelling.


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5. ASSumptionS of AnALySeS

total dead load None of the underground levels are included in the calculationof the totalweight because the variety of underground levels canconsiderablyinfluencetheresults.

Basic design situation (including the wind effect)The procedure is precisely defined in [3]. Only the horizontalactionsofthewindweretakenintoaccount.TheNationalAnnextotheEurocode[3]dividestheareaofSlovakiaintotwowindregions(Fig. 7b), where the basic values of the wind speed are definedas v =24m/sand v =26m/s, respectively. Further, there are fourterraincategories.WeonlyconsideredcategoryII. (flatareaswithlow vegetation), III. (villages) andIV. (cities).Wind actionswerecalculatedinbothlongitudinalandtransverseorientations,becausetherewasnopredominantorientationofthewindactions.However,in alater comparison, only thewind directionwas used inwhichhigherdesigneffectsforseismicactionwereexpected.

Seismic design situationFor the seismic analyses and initially for defining the designresponse spectrum, 5 different soil categories (Ato E) and allfourdifferentareasofseismic risk (Fig.7a)wereassumed. In thepreliminarystageofpreparingtheNationalAnnextotheEurocode8[2]forSlovakia,therewasquitealongdiscussionaboutthevalueofaverylowseismicityfromagS=0.03gupto0.05g.ThedesigngroundaccelerationonthetypeAground(rock)is:

ag=agRγl=0.3m/s2 (2)

whereagR - referencepeakgroundaccelerationon typeAground(rock),

γl - importancefactor.

In this paper only locations with the lowest seismic accelerationandwith abuilding importance factor of γl = 1.0 are considered.All the soil categories starting from class Ato class E weretaken into account. The first periods were analysed for all theassumedstructures;due to theneedforgeneralization, theprecisevalues were not considered, but the intervals of these periodswere enlarged, e.g., for the family house, the periods betweenT1 = 0 sto 0.125s, for the 4-story residential brick building theperiods between 0.25 – 0.4 s, for the 8-story residential panelbuilding periods between 0.8 – 1.2 s, and for the 22-story high-risebuildingperiodsbetween1.6–2.1swereassumed.ThemostunfavourablevalueSe/ag(seeFig.8troughFig.12)wastakenintoaccount.Thetotalseismicshearforceis:

(3)

whereag - designgroundaccelerationontypeAground(rock) λ - correctingfactoraccordingto[2]λ=0.85 Se - spectralacceleration m - totalmassofthestructure q - behaviourfactor.

FromTables1,2itcanbeseenthatifthekwfactorisgreaterthanks,thenthelocationconcernedisasiteofverylowseismicity,becausethewindloadactionsaregreaterthantheseismicones.The wind effects are summarized in Tables 1 and 2. The valuesfromTable1arehigherthanthoseinTable2,sotheyweretakenintoaccount.Thevalues inTables3and4arepresentedhere forpurposesofcomparison.Note:TohaveterraincategoryIVsurroundinghigh-risebuildingsisveryrare.Inmostcasesaround95%ofthebuildingswerelocatedintheI,II,andIIIcategories.

Fig. 7 a) Slovak seismic risk zones, b) maximum wind speed locations (26m/s, 24m/s).

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Behavioural factorThe resistance and capacity for energy dissipation depend on towhat extent the non-linear response can be used up. In practice,the balance of the resistance and capacity for dissipated energyis characterized by the behavioural factor q. The seismic actionasdefinedby thedesign responsespectrumcanbeapproximatelydivided by this factor. The determination of this factor is quiteacomplicatedprocess.Theprinciplesforhowtochooseavalueforastructureareprovidedincodes[1,2].

Tab. 1 Factor for the larger windward structure orientation.

Windspeed

Terraincategory

Building1-storey 4-storeys 8-storeys 22-storeys

24m/sII 0.032 0.04 0.037 0.013III 0.023 0.03 0.029 0.011IV 0.018 0.021 0.023 0.009

26m/sII 0.038 0.047 0.044 0.016III 0.027 0.035 0.035 0.013IV 0.021 0.024 0.027 0.011

Tab. 2 Factor for the orientation of the lower windward side.

Wind speed

Terrain category

Building1-storey 4-storeys 8-storeys 22-storeys

24m/sII 0.025 0.007 0.017 0.009III 0.018 0.005 0.011 0.007IV 0.011 0.003 0.009 0.006

26m/sII 0.03 0.008 0.017 0.011III 0.021 0.006 0.013 0.009IV 0.017 0.004 0.001 0.007

Tab. 3 Behaviour factors and mean periods assumed in the analyses.Number of storeys of building Behavioural factor q T[s]1-storeybuilding 1.50 0.154-storeybuilding 2.00 0.258-storeybuilding 2.50 0.8522-storeybuilding 2.50 0.60

Tab. 4 Soil categories assumed in the analyses.Soil category A B C D E

S 1.00 1.10 1.25 1.50 1.32

Fig. 8Spectrum of flexible response for“A” soil category.

Fig. 10Spectrum of flexible response for “C” soil category.

Fig. 9Spectrum of flexible response for “B” soil category.


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Structures inwhich the dissipation of energy is expected only toaverysmallextent,e.g.,masonrystructures,belongtothecategoryof limited ductile structures with aminimum behaviour factorof q=1.5. On the other hand, the lower limit of the behaviouralfactor q for steel and reinforced concrete structures is roughly 2or higher, and the upper limit is almost 5 ormore.The assumedbehaviouralfactorsforourtypesofstructuresarelistedinTable3.Theminimumpossiblevaluesweretakenintoaccountinordertobeonthesafersideofadesign.TheinputvaluesaccordingtoTable3wereconsideredintheanalyses.

6. reSuLtS

All the values needed for acomparison of the seismic and basicdesignsituationsaresummarizedinTable5.

7. compAriSon of SeiSmic Zone mApS in centrAL europe

Of course, there aremany parameters that influence the problemof assessing very low seismicity. One of the most important isaseismicriskmap.DiscussionsaboutthedifferencesatthebordersofadjacentcountriesintheCentralEuropeanregionhaverecentlystarted. Problems arise because the maps were not compared indetailduringtheirpublicationphase.When comparing, e.g., the maps from the National Annexes ofcountriessuchasAustria,SlovakiaandHungary,onecanseethatthedifferencesatbordersarestillsignificant.ThevalueofthereferencegroundaccelerationonrocksoilagRisnotsimilarconsidering,e.g.,thelocationnearBratislava,thecapitalofSlovakia,wherewecangetthefollowingvalues:• 0.6m/s2fromtheSlovakmap(Fig.7a),

Fig. 11Spectrum of flexible response for “D” soil category. Fig. 12Spectrum of flexible response for “E” soil category.

Fig. 13Austrian seismic zone map [7]. Fig. 14Hungarian seismic zone map [5].

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• 0.6m/s2fromtheAustrianmap(Fig.13),• 1.4m/s2fromtheHungarianmap(Fig.14).Amap from Poland either is not available or has not yet beenpublished, not even in [7] where maps from all the Europeancountriesarelisted.TheSlovakmap(Fig.16)fromthissource[7]isnottheoriginalonepublishedintheNationalAnnexin[4].Thisdiscrepancyshouldalsobeexplained in the future.Possiblysome

countries(e.g.,Hungary)havepublishedpeakgroundaccelerationvalues (PGA) that are contrary to the effective peak groundacceleration values (EPA) used in Slovakia, Austria and CzechRepublic.In[7]itisnotedthatinAustria,EPAvaluesarecalculatedas70%ofthePGAvalue,but thedifferencescannotbeexplainedjustforthisreason.TheEPAvaluesintheliteraturearecalculatedalittlebitdifferently[8].

Tab. 5 Comparison of kw and ks factors. agR= 1 γI = 1 ag = 0.3 λ = 0.85

Sub-soil ASe/ agR Fb/m [ms-2] ks = Fb/G kw = Fv/G kw = Fv/G agS/g

26m/s 24m/s 1-storey 2.20 0.35 0.035 0.041 0.035 0.0304-storey 2.40 0.29 0.029 0.035 0.030 0.0308-storey 0.90 0.09 0.009 0.035 0.029 0.03022-storey 0.35 0.03 0.003 0.013 0.011 0.030

Sub-soil BSe/ agR Fb/m [ms-2] ks = Fb/G kw = Fv/G kw = Fv/G agS/g


Sub-soil CSe/ agR Fb/m [ms-2] ks = Fb/G kw = Fv/G kw = Fv/G agS/g


Sub-soil DSe/ agR Fb/m [ms-2] ks = Fb/G kw = Fv/G kw = Fv/G agS/g


Sub-soil ESe/ agR Fb/m [ms-2] ks = Fb/G kw = Fv/G kw = Fv/G agS/g



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For agiven return period, the effective peak ground acceleration(EPA) is determined by dividing the corresponding 5% dampingshortperiodspectralaccelerationvalueby2.5asfollows:

, (4)

whereTR is between0.1and0.5s,whicharethefirstperiodsofthemostcommonlyoccurringstructures.

Countries such as the Czech Republic, Hungary,Austria, PolandandSlovakiashouldthereforeharmonizetheirmapsattheborders.

8. concLuSion

FromtheresultsinTable5itcanbeseenthatthevalueofverylowseismicity(agS/g)fortheterritoryofSlovakiacanbesetas:

(5)

becauseinthiscasetheseismiceffectsarealwayssmallerthanthewind effects ks<kw. This statement is valid even if themaximumwindvelocityisonly24m/s.ThisresultisimportantforassessingthevalueoftheverylowseismicityareasinSlovakiaaccordingtoclause3.2.1(5)in[4].The Central European countries should harmonize their seismiczonemapsnotonlybecausetheyusedifferentvaluessuchas,e.g.,PGA or EPA, but also because the reference acceleration of thebordersatsomelocationsdiffersgreatly.

AcknowLedGementWe acknowledge the research program VEGA No. 1/1119/11grantedbytheScientificGrantAgencyofSlovakRepublic.

Fig. 16Seismic zone map of Slovakia published in [7] but not in [4].Fig. 15Seismic zone map of the Czech Republic [7].

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REFERENCES

[1] STN730036.Seismicactionofstructures.SÚTN.1998[2] EN 1998-1. Design of structures for earthquake resistance

– General rules, seismic actions and rules for buildings.Brussels.2005

[3] EN1991-1-4–Actionsonstructures.Part1-4:Generalactions–windactions.Brussels.2004

[4] STN EN 1998-1/NA. Design of structures for earthquakeresistance – General rules, seismic actions andrulesforbuildings. Slovak National Annex. SÚTN. 2009Bratislava

[5]MSZEN1998-1:2008NAnemzetimelleklet.Budapest.2009[6] CSNPENV1998-1-1,NationalApplicationDocument.[7] Areview of the seismic hazard zonation in national building

codes in the context of Eurocode 8. JRC Scientific andTechnicalReports.2008

[8]MATHEU, E.E.; YULE, D.E.; KALA, R.V. Determinationof Standard Response Spectra and Effective Peak GroundAccelerations for SeismicDesign and Evaluation.US Army Corps of Engineers. December 2005, ERDC/CHLCHETN-VI-41,pp.1-16.

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