Durability by Design - a-hagl-ingenieure

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Durability by Design - a-hagl-ingenieure

Durability by DesignNew Results on Load Carrying Silicone BondingStructure of the PresentationApplication of U-type Bonding GeometryMaterial TestsBonding Geometry and DurabilityConclusions of Bonding Geometry AnalysisDenver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives2


Durability by DesignNew Results on Load Carrying Silicone BondingExample: Herz JesuChurch, MunichArchitectural objective:Minimum of visible loadcarrying structures‣ Horizontal and verticalglass beams for supportof the glass façade‣ Load carrying bondingby Silicone adhesivesapplied to glass beamsDenver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives3


Vertical Façade Stringer70/50/4,5Durability by DesignNew Results on Load Carrying Silicone BondingGlass Beam AttachmentDesign Idea:‣ Selection of parallel flangechannel (PFC)‣ Three sided bonding design– one front region– two side regionsBolt d = 10 mmAdhesive DC 993Dow CorningQuestion:Denver, ColoradoJune 26, 2008PFC – 54/30/3Stainless Steel with PrimerVertical Glass Beam(3 x 12 mm)How to assess durability of sucha bonding geometry or similardesigns?Third Symposium on Durability of Building and ConstructionSealants and Adhesives4


Durability by DesignNew Results on Load Carrying Silicone BondingCritical Parameters affecting Joint Durability(Kinloch, A. J. „Durability of Structural Adhesives“)EnvironmentAdhesive typeAdherend, adherendsurface pretreatmentApplied stressJoint designPresence of moisture identified as most hostileenvironment, especially in combination with hightemperatureChemical type of structural adhesives important forjoint durability, depending on physical and chemicalattack mechanismsApplication of primers helpful in producing durablejoints by stabilizing surface layers e.g. oxidesIncreased rate of strength loss by presence ofexternally applied or internal stress by loweringenergy barrier unbroken/brokenEmphasized durabilitiy effects by high stressdistributions on interface between adhesive andadherend (interfacial failure typical afterenvironmental attack)Focus in this presentation: - Adhesive: see material test results- Applied stress: see discussion on bonding geometriesDenver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives5


Durability by DesignNew Results on Load Carrying Silicone BondingContents of the PresentationApplication of U-type Bonding GeometryMaterial TestsBonding Geometry and DurabilityConclusions of Bonding Geometry AnalysisDenver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives6


Durability by DesignNew Results on Load Carrying Silicone BondingTest Procedures for Material TestsAging Creep‣ 3 days 80° C temperature‣ 10 days 45° C temperature de-mineralizedwater with cleaning agent (5%)‣ 3 days 80° C temperature‣ 10 days 45° C temperature de-mineralizedwater, UV radiation 50 +/-5 W/m 2‣ 1 day 23° C temperature - baselinelaboratory conditions‣ 8 days 45° C temperature salted water(50 g salt/l), UV radiation 50 +/- 5 W/m 2‣ 2 days - 30° C temperature‣ 1 day 23° C temperature - baselinelaboratory conditions‣ Creep duration 105 dayscontinuous loading‣ Creep load correspondingto 20% of fracture strain– Tension 16.5 N– Shear 115.0 N‣ Tension test within24 hours after unloadingDenver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives7


Durability by DesignNew Results on Load Carrying Silicone BondingTension Tests Including Aging and Creep5040Load [N]unaged, without creep after creep agedTension test database‣ 10 specimens inbaseline conditions5 aged specimens5 specimens exposedto creep3020‣ Strength of thespecimens is slightlyaffected by aging orcreep (load history)100Displacement [mm]0 20 40 60 80‣ Stiffness of specimensis affected by agingonly increased flexibilityfor aged specimensSource: Fachhochschule München, FB02, Geklebte Verbindungen im Konstruktiven Glasbau, Final Research Report, BMBF Projekt, AIF-Nr.: 1755X04, 2007Denver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives8


5004003002001000Load [N]Durability by DesignNew Results on Load Carrying Silicone BondingShear Tests Including with Aging and Creepunaged, without creep after creep agedDisplacement [mm]0 5 10 15 20 25 30 35Shear test database‣ 5 specimens inbaseline conditions5 aged specimens5 specimens exposedto creep‣ Strength of thespecimens is slightlyaffected by aging orcreep‣ Stiffness of specimensis mainly affected byaging increased flexibilityfor aged specimens‣ Results generallysimilar to tension testsSource: Fachhochschule München, FB02, Geklebte Verbindungen im Konstruktiven Glasbau, Final Research Report, BMBF Projekt, AIF-Nr.: 1755X04, 2007Denver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives9


706050403020100700600500Load [N]Load [N]Tension Tests- 20°C + 23°C + 80°C after aging after average creepShear TestsDurability by DesignNew Results on Load Carrying Silicone BondingaveragemaxminmaxminOverview of Test Results‣ Strength of specimens is slightlyaffected by aging or creep incomparison with 23°C - tests‣ Specimen strength is significantlyaffected by temperature – strengthis much lower for increasingtemperature‣ Results between tension and shearare in general agreement4003002001000- 20°C + 23°C + 80°C after aging after creepDenver, ColoradoJune 26, 2008Conclusions are:In case of strength requirements: critical case is high temperatureIn case of stiffness requirements: critical case is agingThird Symposium on Durability of Building and ConstructionSealants and Adhesives10


Durability by DesignNew Results on Load Carrying Silicone BondingContents of the PresentationApplication of U-type Bonding GeometryMaterial TestsBonding Geometry and DurabilityConclusions of Bonding Geometry AnalysisDenver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives11


Durability by DesignNew Results on Load Carrying Silicone BondingAssumptions for Assessing Durability ofDifferent Bonding Geometries‣ Environmental impact of aggressivemedia and solar radiation is a functionof distance below the free surface ofadhesiveDistanceFreesurface‣ Physical principles are:Absorption– Absorption of radiation– Diffusion of aggressive media‣ Highest impact on damage is expectedfor the free surface and will decreasewith increasing distance inside theadhesive‣ Maximum principal stress level invicinity of free surface is assumed to bea measure of durabilityAggressivemediaDiffusionDistanceFreesurfaceDenver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives12


Durability by DesignNew Results on Load Carrying Silicone BondingStress Investigations by Numerical Models‣ Application of Finite ElementAnalysis (FEA) is useful‣ Hyper-elastic material laws usedfor representation of Siliconeadhesives‣ For the following studies a 2Dplain strain state is considered‣ Critical load case for bonding istension‣ Loading of models adjusted to2.1 N/mm² maximum principalstress (based on experimentalresults)Example of a quarter model of aU-type bonding with finite lengthApproximately plainstrain conditions2.11.9251.751.5751.41.2251.050.8750.70.5250.350.1750.Denver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives13


Durability by DesignNew Results on Load Carrying Silicone BondingExperimental Results: Failure of U-type BondingLoad [N]50004000Representativeload level:max. service loadTotal failure offront region3000Beginning failureof front regionShift of load path(shear) to sideregions2000Total failure10000Denver, ColoradoJune 26, 2008Fully operationalbondingDisplacement [mm]0 5 10 15 20Third Symposium on Durability of Building and ConstructionSealants and Adhesives14


Durability by DesignNew Results on Load Carrying Silicone BondingStress Distribution of U-type Bonding Geometry‣ Half 2D model taking into account symmetry conditionsSteel‣ Plotting of max principal stresses for three different levels‣ Stress level in vicinity of point A relevant for durabilityaspectsBACL f =22 mm2.5Max Princ. Stress [N/mm²]21.510.50Anear glassnear steelmid of adhesiveB2.1 N/mm²0 20 40 60 80 100CLength [%]GlassBAC2.11.9171.7331.551.3671.1831.0.8170.6330.450.2670.0833-0.1-0.5Denver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives15


Durability by DesignNew Results on Load Carrying Silicone BondingStress Distribution at Flanges for Different L f‣ Results presented near glass or steel: values in middle of adhesive less critical‣ Small stress levels at free surfaces (A) observed for L f >12 mm‣ Therefore adequate durability behavior is expected for these designs1,2Max Princ. Stress [N/mm²]10,80,60,40,20-0,20 5 10 15 20 25 30ALf =2 mmLf =12 mmLength [mm]Lf =22 mmglass sidesteel sideB L f =A2 mmBAL f =22 mmDenver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives16


Durability by DesignNew Results on Load Carrying Silicone BondingStress Distribution of T-type Bonding GeometryMax Princ. Stress [N/mm²]‣ Half 2D model taking into account symmetry conditions‣ Plotting of max principal stresses for three different levels‣ Stress level near point A relevant for durability aspects2.521.510.50ADenver, ColoradoJune 26, 2008Bnear glassnear steelmid of adhesive2.1 N/mm²0 20 40 60 80 100Third Symposium on Durability of Building and ConstructionSealants and AdhesivesCDLength [%]ASteelABCGlassBCDDL f =35 mm2.11.9251.751.5751.41.2251.050.8750.70.5250.350.1750.17


Durability by DesignNew Results on Load Carrying Silicone BondingT-Type Bonding Stress Distributions for Different L f‣ High stress levels near point A compared to U-type bonding‣ T-type bonding ranked lower concerning durability‣ Variation of L f without major impact on stress levels near point A2Max Princ. Stress [N/mm²]1.510.5ALf 5 near steelLf 5 near glassLf 35 near steelLf 35 near glassABCABDL f =5 mmL f =35 mm00 5 10 15 20Denver, ColoradoJune 26, 2008Length [mm]Third Symposium on Durability of Building and ConstructionSealants and AdhesivesCD18


Max Princ. Stress [N/mm²]Denver, ColoradoJune 26, 2008Durability by DesignNew Results on Load Carrying Silicone BondingStress Distribution of L-type Bonding Geometry‣ Full 2D model due to missing symmetry‣ Stress levels near points A and C relevant for durability aspects‣ Stress behavior near point A corresponding to U-type bonding geometry‣ Stress behavior near point C corresponding to T-type bonding geometry2.5Steelnear glass2.1 N/mm²21.510.50-0.5Anear steelmid of adhesiveB0 20 40 60 80 100Third Symposium on Durability of Building and ConstructionSealants and AdhesivesCLength [%]BAGlassBACCL f2.11.9331.7671.61.4331.2671.10.9330.7670.60.4330.2670.119


Durability by DesignNew Results on Load Carrying Silicone BondingStress Distribution of E-type Bonding Geometry‣ Half 2D model taking into account symmetry conditions‣ Stress levels near point A relevant for durability aspects‣ Stress behavior corresponding to combination of U-type andT-type bonding geometryBCSteelMax Princ. Stress [N/mm²]2.521.510.50-0.5ADenver, ColoradoJune 26, 2008near glassnear steelmid of adhesiveBC2.1 N/mm²0 20 40 60 80 100Third Symposium on Durability of Building and ConstructionSealants and AdhesivesDLength [%]EBAADDECEGlass2.11.9171.7331.551.3671.1831.0.8170.6330.450.2670.0833-0.1L f20


Durability by DesignNew Results on Load Carrying Silicone BondingContents of the PresentationApplication of U-type Bonding GeometryMaterial TestsBonding Geometry and DurabilityConclusions of Bonding Geometry AnalysisDenver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives21


Durability by DesignNew Results on Load Carrying Silicone BondingConclusions of Bonding Geometry Analysis‣ Different bonding geometries investigated for tension load case:U-type, T-type, L-type and E-typeSteelSteelSteelSteelL f =22 mmL f =35 mmL fL fGlassGlassGlassGlass‣ U-type and E-type bonding geometries favorable with respect todurability aspects‣ T-type and L-type bonding geometries less favorable with respect todurability aspectsDenver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives22


Durability by DesignNew Results on Load Carrying Silicone BondingComparison of Stress DistributionsSimilar bonding geometries show similar stress distributionson comparable parts of their geometries– Side region with a free edge: U, L, E– Front region with free edges: T, L– Front region with an encapsulated flange: T, E– Encapsulated front region: U, LMax Princ. Stress [N/mm²]2.52near glassnear steel2.1 N/mm²Cmid of adhesive1.51B0.5ALength [%]00 20 40 60 80 100Max Princ. Stress [N/mm²]2.5near glass2.1 N/mm²near steel2mid of adhesiveD1.5AC1B0.5Length [%]00 20 40 60 80 100Max Princ. Stress [N/mm²]2.5near glass2.1 N/mm²2 near steelmid of adhesive1.51BC0.5ALength [%]00 20 40 60 80 100Max Princ. Stress [N/mm²]2.5near glass2.1 N/mm²2 near steelmid of adhesiveCE1.5DB10.5ALength [%]00 20 40 60 80 100-0.5-0.5-0.5Denver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives23


Durability by DesignNew Results on Load Carrying Silicone BondingGeneralization of Results‣ Results can be applied for a class of bonding geometries with planes paralleland perpendicular to tension loading. Example:Combinedgeometry‣ Durability assessment depending on freesurface configuration‣ For bonding geometries with free surfaceslocated at end of the side region:good durability property expectedSideregionFrontregion‣ For bonding geometries with free surfaceslocated at end of front region:lower durability expectedDenver, ColoradoJune 26, 2008FreesurfaceThird Symposium on Durability of Building and ConstructionSealants and AdhesivesFreesurface24


Durability by DesignNew Results on Load Carrying Silicone BondingDenver, ColoradoJune 26, 2008Third Symposium on Durability of Building and ConstructionSealants and Adhesives25

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