Dowel design - cticm

Precobeam - Composite dowelsDesign guideRiccardo ZANONOliver HECHLERwww.arcelormittal.com/sectionsSections.tecom@arcelormittal.com19/10/2012 Confidential 0October 2012

Field of applicationDowel in upper flangeDowel in lower flange• Simple or double Precobeam• Steel grades:S235 - S460• Concrete grades: C20/25 – C60/7515/10/2012 Recent developments 3

Typical Precobeam element(1) Steel flange: Absorbs stresses from bendingmoments and provides cross-section stiffness.(2) Steel web: Transmission of longitudinal shear forces,ensures steel flange – concrete web distance whereneeded (e.g. to avoid concrete cracking).(3) Composite dowel: Transmit longitudinal shear forcesbetween concrete and steel.(4) Prefabricated concrete web: designed uponstructural demands and is reinforced with the externalsections.(5) Prefabricated concrete plate: 10-12cm thickconcrete-plate which serves as formwork and scaffoldingfor the in-situ concrete and is designed for loads fromconstructions stages.(6) In situ concrete plate: It completes the prefabricatedconcrete-plate and is designed upon structural needs forthe crucial load combinations in the final stages.(7) In situ Longitudinal reinforcement: It is assembledwithin the in-situ concrete-slab for the final constructionstage.(8) Precast Longitudinal reinforcement: designed uponstructural needs for loads from construction stage(s).(9) Transversal shear reinforcement: designed uponstructural needs from transversal shear under specialconsideration of dowel action.(10) Confinement reinforcement: designed uponapproaches from local dowel action. It is essential toensure a ductile load bearing behaviour.15/10/2012 Recent developments 4

Steel dowel geometry+ =• On the basis of the past experience, which showed a better fatigue behaviour and easy fabrication process,it is advised to use the modified clothoidal shape (MCL) for the design of road and railway bridges.15/10/2012 Recent developments 5

Steel dowel geometry EN• The principle is that the basic shape can be scaled in function of e x .• The dowel axis distance e x is the considered as the basis dimension:150 mm ≤ e x ≤ 500mm, usually e x = 250mm, h D = 115mm, h D / e x = 0.4615/10/2012 Recent developments 6

Steel dowel geometry EN• The principle is that the basic shape can be scaled in function of e x .• The dowel axis distance e x is the considered as the basis dimension:150 mm ≤ e x ≤ 500mm, usually e x = 250mm, h D = 115mm, h D / e x = 0.4615/10/2012 Recent developments 7

Field of application• Longitudinal cross-section:• Transversal cross-section:15/10/2012 Recent developments 9

Field of application• Definition of characteristics of the dowel:1) Steel dowel2) Dowel root3) Dowel top4) Dowel base5) Concrete dowel6) Dowel core7) Dowel reinforcement8) Upper reinforcement15/10/2012 Recent developments 10

Table of content• Content– Introduction to structural concept– Dowel design – Ultimate limit state– Dowel design – Serviceability limit state– Dowel design – Fatigue limit state– Conclusion15/10/2012 Recent developments 11

Load Bearing Behavior– Static loading• Standard Push-out tests for headed-studs (EN1994-1-1, Annex B):15/10/2012 Recent developments 12

Load Bearing Behavior– Static loading• Standard Push-out tests for composite dowels:15/10/2012 Recent developments 13

Load Bearing Behavior– Static loading• Standard Push-out tests for composite dowels:700600Dowel force [kN]5004003002001000Slip [ mm]SA-A-1PZ-A-2CL-A-30 5 10 15 20 25 30 35 40Slilp [mm]15/10/2012 Recent developments 14

Experimental background15/10/2012 Recent developments 15

27 Beam tests• Slabs• Beams• Pos./Neg. Moment• Beam distance15/10/2012 Recent developments 16

65 Push-out / Pull-out tests• Dowel geometry• Web thickness• Reinforcing type• Dowel distance• Dowel height15/10/2012 Recent developments 17

Load Bearing Behavior– Static loading• Contribution of the different load bearing mechanisms:15/10/2012 Recent developments 18

Dowel design – Static loadingVerification of longitudinal shear transmission:Static loadingConcrete failureSteel failureFailure criteria:Concrete shearing Pry-Out Spalling concrete coverage Steel failure15/10/2012 Recent developments 19

Concrete shear failure15/10/2012 Recent developments 20

Dowel design – Concrete shear failureConcrete dowel failure on shear:Design equation:A DWith:15/10/2012 Recent developments 21

Concrete pry-out15/10/2012 Recent developments 22

Dowel design – Concrete pry-outPry-out of concrete cone:Design equation:With:15/10/2012 Recent developments 23

Dowel design – Concrete pry-outReduction factor for overlapping of concrete cones:15/10/2012 Recent developments 24

Spalling of concrete coverage15/10/2012 Recent developments 25

Dowel design – Spalling concrete coverageSpalling of concrete coverage:Design equation:Pcov, k1=ex⋅4⋅lhcr2⋅e2x0,3⋅f0,15+h ⋅bpo3ckc2⎛⎜ 1−⎝hD2⋅hpo⎞⎟⎠15/10/2012 Recent developments 26

Dowel design – Confinement reinforcementFor girders it is recommended to provide confinement reinforcement:Design equation for sufficient confinement reinforcement:If sufficient confinement reinforcement is provided, pry-out of concrete cone andspalling of concrete coverage are prevented and may be disregarded.15/10/2012 Recent developments 27

Dowel design – Concrete pry-out for girdersMinimal confinement reinforcement:In general for girders, confinement reinforcement should be foreseen.15/10/2012 Recent developments 28

Dowel design – Steel failure15/10/2012 Recent developments 29

Dowel design – Steel failureSteel failure – interaction of local bending and longitudinal shear inthe critical section:Design equation:15/10/2012 Recent developments 30

Table of content• Content– Introduction to structural concept– Dowel design – Ultimate limit state– Dowel design – Serviceability limit state– Dowel design – Fatigue limit state– Conclusion15/10/2012 Recent developments 31

Dowel design – Cyclic loadingVerification of longitudinal shear transmission:Cyclic loadingSteelstressesFailure criteria:Steel failureShearconnectionCyclic pry-outConcretestressesConcrete loosening15/10/2012 Recent developments 32

Dowel design – Stress verificationStress pattern in the composite dowel:• Local Forces• σ x• Surface of increased stresses :o Consideration of stress concentration factors forboth local dowel action andglobal bending• σ x• σ x • σ x• Influence from local dowel-action• Influence from global bending15/10/2012 Recent developments 33

Dowel design – Stress verification34Stress concentration for local and global action:Local dowel-actionGlobal bendingHot-spot steel stress:σ s=fLV⋅tLw⋅S⋅ Iyy+fG⎛⋅ ⎜⎝MIyy⋅ z+NA⎞⎟⎠15/10/2012 Recent developments 34

Dowel design – Stress verificationSafe sided assumption:f local.max = 7,3f global.max = 1,515/10/2012 Recent developments 35

Concrete loosening under cyclic loading15/10/2012 Recent developments 36

Dowel design – Concrete looseningAvoiding of concrete loosening under cyclic loading to avoid the softening of theshear connection:Stiff shear connectionPartial shear connectionCyclic load which may cause concrete loosening:15/10/2012 Recent developments 37

Dowel design SLS – verifications:Characteristic combination - Limitation of steel stresses:σsV x Sy⎛ N M ⎞= kf Lk ⎜f Gz ⎟,⋅ +,⋅ + ⋅D≤ 1. 3⋅Iy× twA I⎝ y ⎠f global = 1,5 f Local = 7,95fyCharacteristic combination – Limitation of force in the concrete dowel:( P ; P P )PLD, ser≤ 0.7 minsh.k po.k;co.kCharacteristic combination – Limitation of force in the concrete dowel:PLD,ser≤Pcyc15/10/2012 Recent developments 38

Table of content• Content– Introduction to structural concept– Dowel design – Ultimate limit state– Dowel design – Serviceability limit state– Dowel design – Fatigue limit state– Conclusion15/10/2012 Recent developments 39

Steel failure by fatigue15/10/2012 Recent developments 41

Dowel design – Fatigue verificationStress concentration for local and global action:Test• Geometrical KerfDesign according the structural stress concept – EN1993-1-9:∆Vx Sy∆ σ = kf , L⋅ + kf , GIy× tw⎛⎜∆N⋅⎝ A+∆MIy⋅ zD⎞⎟ ≤⎠∆σSγMf-f local = 6,45-f global = 1,5−∆σ s= 125 for machine gas-cut edges with shallow or regular drag-lines−∆σ s= 140 for machine gas cut or sheared material with grinded edges− In general re-entrant corners have to be improved by grinding (slope < 1 / 4)15/10/2012 Recent developments 42

Table of content• Content– Introduction to structural concept– Dowel design – Ultimate limit state– Dowel design – Serviceability limit state– Dowel design – Fatigue limit state– Conclusion15/10/2012 Recent developments 43

Conclusion15/10/2012 Recent developments 44

Conclusion15/10/2012 Recent developments Vigaun bridge (2008, ÖBB, 45 AT)

Conclusion?15/10/2012 Recent developments Vigaun bridge (2008, ÖBB, 46 AT)

ConclusionVigaun bridge1m dowel10 … 30 shear connectors15/10/2012 Recent developments Vigaun bridge (2008, ÖBB, 47 AT)

AcknowledgementsPreco+: Partners: Support:15/10/2012 Recent developments 48

Many thanks for your kind attention!4915/10/2012 Recent developments 49