constructiegedrag van door asr aangetaste viaducten, … · 2017-10-24 · december 6, 2015 2....
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Vermelding onderdeel organisatie
Oktober 21ste 2015
1
Constructiegedrag van door ASR aangetasteviaducten, CUR-Aanbeveling 102 en Resultaten experimenteel onderzoek
Cor van der Veen
Faculty of Civil Engineering and GeosciencesConcrete Structures Section
Wat is ASR? [1]
• Alkali-Silica Reactie (ASR)• In twee fasen te onderscheiden:
• Alkalien + Silica Gelvormig reactieproduct
• Gelvormig reactieproduct + Water Expansie
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ASR-gel [1]
uitbloeiingen ASR-gel
December 6, 2015 3
Typisch scheurenpatroon ASR [1]
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ASR schadebeelden [1]
• “landkaartenpatroon”• Beton met Portlandcement• Na jaren ouderdom
• 5-30 jaar ouderdom
• Voorkeursrichting• Invloed wapening• Drukspanning
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Gevolgen uitzetting beton door ASR [1]
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Voorkomen verdere uitzetting beton
• Pas waterdicht scherm toe aan een zijde omverdere toetreding water te voorkomen
• Laat aan onderzijde beton open (afvoerwater) zodat betonconstructie kan drogen.
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Classificatie CUR-Aanbeveling 102 [3]
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Klasse 3Materiaaleigenschappen
Klasse 2Een-assige treksterkte
Klasse 1Aanleiding scheuren
ClassificatieKlasse 1
• Craquelé scheurenpatroon• Voorkeursrichting?• Gelijkmatig verdeeld?• Scheurafstand/wijdte
• Cumulatieve scheurwijdte
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ClassificatieKlasse 2
• Schatting
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. gemiddeldASR
n w
lε =
ASRε
ClassificatieKlasse 2 : PFM-onderzoek (boorkeren)
cumulatieve scheurwijdtelage treksterkte
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Praktijk NED
ClassificatieKlasse 3 : kernen boren dwarskrachtgebied
• Kerndiameter 75 mm• 6 kernen éénassige
treksterkte• 3 kernen druksterkte
• Relatie treksterkte: Vertikaal en horizontaal
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ClassificatieKlasse 3: eenassige betontreksterkte
• Uitgangspunt van CA is lage eenassigebetontreksterkte
• Verschil treksterkte in horizontale en vertikale richting
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Classificatie [3]
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Klasse 4Constructieve beoordelingdwarskracht
Klasse 4A: handmatigKlasse 4B: numeriek maatgevende
doorsnedeKlasse 4C: gehele constructie
ClassificatieKlasse 4: Constructief onderzoekinvloed zwellen van beton • Voorbeeld:
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30,5 10
0,01
30000
0,937
0,063 0,95
195
: 200000 100
ASR
b
zv ASR
b ASR b
s b
s ASR
x
E MPa
E MPa drukspanning
MPa zonder relaxatie
benaderend x MPa
εω
ε εσ ε
σ σω
σ ε
−=
==
== =
= = →
= =
ClassificatieKlasse 4: Constructief onderzoek
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Gemiddelde eenassige vertikale treksterkte
1
1,5
0,9
:
m
ld
m
langeduur
gemiddelde waarde
γλτ
==
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Probleem definitie; experimenteelonderzoek [den uijl 2]
• ASR in many bridges• Horizontal cracks in deck• Strong reduction of
uniaxial tensile strength • No shear reinforcement• Residual shear resistance?
Two viaducts with ASR investigatedtype: ZB and HS
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10.014.25
7.5
14.2510.0
beam HS1
south north
SP02 SP03 SP04 SP05SP01 core nr. 1
core nr. 24
measures in m
11.0
beam HS2
beam HS3
beam HS4
Position vertical cores HS-bridge
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Strength from vertical HS-cores
Type of South span Entire bridge
test [MPa] [MPa] [%]
Cube 50.5 53.9 14
Splitting ⊥ 3.19 3.35 17
Splitting // 3.30 3.55 16
Uniaxial1 0.93 1.11 42
1 Vertical uniaxial concrete tensile strengthRatio horizontal to vertical uniaxial tensile strength about 0.5
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Evaluation of shear resistance
• Literature
• small scale tests, accelerated ASR
• both reduced and increased shear strength
• First idea (1999)
• in situ loading of bridge until failure
• limited time and little knowledge about mechanism
• Final plan
• shear tests on beams cut from bridge decks
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Specimens (1)
Beams sawn out of ZB-bridge: 8.5×0.6×0.7 m
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Specimens (2)
Beams sawn out of HS-bridge: 7.5×0.5×0.65 m
10.014.25
7.5
14.2510.0
beam HS1
south north
SP02 SP03 SP04 SP05SP01 core nr. 1
core nr. 24
measures in m
11.0
beam HS2
beam HS3
beam HS4
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Specimens (3)
• Plain rebars fsy=220 MPa
• Reinforcement ratio
• ZB: ρ0,int=1.0 to 1.3 %
• HS: ρ0,int=0.5 %
• Steel strips glued on HS-beams
→ ρ0,tot=1.1 to 1.6 %
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Test set-up
• 4-point bending test• Both beam ends tested
• Shear span: a/d=2.5 to 4.5
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Measurements
• Load
• Deflection
• Concrete strains
• Crack development
• Prestress due to ASR (afterwards)
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Test results
• Failure mode• ZB: 3 bending/shear, 1 bending• HS: 8 shear
• Shear strength (average)• ZB: 0.96 MPa• HS: 1.03 MPa
• Shear crack inclination• ZB: 25 ± 5°• HS: 30 ± 5°
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Bending shear
• Strength without shear reinforcement:
• Strength ratio Vu,test / Vu,Rafla
• ZB: 0.60 (cov 9.5 %) bending governing• HS: 0.77 (cov 7.5 %)
• Note• reduction less than for uniaxial tensile strength• low scatter compared to core strength values• no prestress considered
bdfdV ccuRaflau3
025.0
, ρα −=
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Type of shear failure
bending shear diagonal tension
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Diagonal tension• Mohr’s circle at neutral axis
• τxy = 1.5×τavg = 1.5 MPa
• Effect of prestress on• Shear strength
xctctxy ff στ −= 2
30
35
40
45
0-1-2σx/fct
1,0
1,3
1,6
1,9τxy/fct ϕ [degree]
• Crack inclination
ctx
ctxy
f
f
στ
ϕ−
=1
arctan
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Effect of ASR-induced prestress
• Without prestress ϕ = 45°
• Crack inclination 45° → 30°
• → σx/fct = −2
• and τxy/fct = 1.73fct = 1.5/1.73 = 0.9 MPaσx = -2×0.9 = -1.8 MPa
• measured σx = -0.3 MPa→ calculated >> measured
30
35
40
45
0-1-2σx/fct
1,0
1,3
1,6
1,9τxy/fct ϕ [degree]
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Effect of orientation dependent tensile strength (1)
• Uniaxial tensile strength
• vertical fct,0 = 0.6 MPa
• horizontal fct,90 = 1.2 MPa
• Tensile strength ratio
• β = fct,0 / fct,90 = 0.5
• Splitting tensile strength
• fct,spl = 2,8 MPa
• fcc = 55 MPa → fct,spl = 3,75 MPa
topside of ZB-deck
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Effect of orientation dependent tensile strength (2)
• Conceive the anisotropic material as an isotropic material that is pre-compressed in one direction
fct,9 0 - fct,0
pre-compressed
+fct, 0
fct,0
isotropic
=fct,90
fct,0
anisotropic
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Effect of tensile strength ratio and prestress ratio (1)
• Substitution of • Yields
)( 0,90,, ctctresxx ff −−= σσ0,ctct ff = ( )res
ct
xy
fγβ
τ−= 1
90,
resγβϕ
−=
1arctan
• With and90,
,
ct
resxres f
σγ =
90,
0,
ct
ct
f
f=β
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0.0
0.5
1.0
1.5
0.0 0.2 0.4 0.6 0.8 1.0
β = fct,0/fct,90
γres =
-1.00-0.67-0.33 0.00
τxy/fct,90
15
25
35
45
0.0 0.2 0.4 0.6 0.8 1.0
β = fct,0/fct,90
γres =0.00
-0.33-0.67-1.00
ϕ [°]
Effect of tensile strength ratio and prestress ratio (2)
ZB: ϕ = 25°β = 0.5
→ γres = -1.2 → τxy = -1.05×fct,90 = 1.26τxy,experiments = 1.34
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Practical application
• Orientation ϕ not known
• Difficult to drill horizontal cores
• Therefore
• estimate ASR-induced prestress
• approximate tensile strength ratio with
105.00,
,
0,
+==
cc
ct
splct
ct
f
f
f
fβ
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γres = -0.33• → τxy = 0.72×1.5 = 1.08 MPa
γres = -0.67• → τxy = 0.81×1.5 = 1.22 MPa
γres = 0• → τxy = 0.6×1.5 = 0.9 MPa
γres = -1.0• → τxy = 0.9×1.5 = 1.35 MPa
Practical application ZB-bridge
• fcc = 55 MPa• fct,0 = 0.6 MPa• → β = 0.4• → fct,90 = 1.5 MPa• estimate prestress ratio to
• τxy,exp = 1.34 MPa0.0
0.5
1.0
1.5
0.0 0.2 0.4 0.6 0.8 1.0
β = fct,0/fct,90
γres =
-1.00-0.67-0.33 0.00
τxy/fct,90
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γres = -0.33• → τxy = 0.82×1.8 = 1.48 MPa
γres = -0.67• → τxy = 0.91×1.8 = 1.64 MPa
γres = -1.0• → τxy = 1.02×1.8 = 1.84 MPa
γres = 0• → τxy = 0.7×1.8 = 1.26 MPa
Practical application HS-bridge
• fcc = 50 MPa• fct,0 = 0.93 MPa• → β = 0.52• → fct,90 = 1.8 MPa• estimate prestress ratio to
• τxy,exp = 1.5 MPa0.0
0.5
1.0
1.5
0.0 0.2 0.4 0.6 0.8 1.0
β = fct,0/fct,90
γres =
-1.00-0.67-0.33 0.00
τxy/fct,90
December 6, 2015 38
• Full-scale beam tests yielded insight in shear behavior of ASR-affected bridges without shear reinforcement
• Failure: 8 shear, 3 bending/shear, 1 bending
• Shear strength 65 to 75 % of theoretical value
• Diagonal tension rather than bending shear
• Crack inclination of 25° to 30° could not be explained from ASR-induced prestress alone
• With also an orientation dependent tensile strength the test results could be explained
•
Conclusions
Conclusie CUR_Aanbeveling 102
• Kalibratie Eurocode• Eénassige betontreksterkte vervangen door…• Kennis opgedaan door proefbelasting inzetten
• Dus Nieuwe CA-102 noodzakelijk
December 6, 2015 39