BALANCE CANTILEVER BRIDGEBALANCE CANTILEVER BRIDGE––DESIGNDESIGN

Dr. Amorn PimanmasSirindhorn International Institute of Technology, Thammasat UniversityNorconsult Civil Engineering

Design CriteriaDesign Criteria

•• Dead LoadDead Load•• Live LoadLive Load

–– 1.5 HS 201.5 HS 20--44 according to agreement with DOH to 44 according to agreement with DOH to accommodate 28 tons truck and 56 tons semiaccommodate 28 tons truck and 56 tons semi--trailertrailer

•• EarthquakeEarthquake–– Max horizontal ground acceleration 0.2 gMax horizontal ground acceleration 0.2 g–– Details for hoops reinforcement according to earthquake Details for hoops reinforcement according to earthquake

zonezone

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MATERIALSMATERIALS

•• ConcreteConcrete•• Grade 50 for SuperstructureGrade 50 for Superstructure•• Grade 40 for SubstructureGrade 40 for Substructure•• Grade 30 for pilesGrade 30 for piles•• Steel, minimum yield strength 400 Steel, minimum yield strength 400 MPaMPa•• PrestressingPrestressing steel, breaking stress 1860 steel, breaking stress 1860 MPaMPa

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(LAYOUT)(LAYOUT)

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1) ASSEMBLY OF FIRST TRAVELLER

2) FIRST TRAVELLER READY FOR CONCRETINGASSEMBLY OF SECOND TRAVELLERS

3) SECOND TRAVELLER READY FOR CONCRETING

4) STRESSING OF CABLES

5) ADVANCING OF TRAVELLERS CONCRETING OF THIRD SEGMENT FIRST TRAVELLERS READY FOR CONCRETING OF FOURTH SEGMENT

Structural AnalysisStructural Analysis

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Design StepsDesign Steps

•• Section SelectionSection Selection•• Local AnalysisLocal Analysis

–– Transverse BendingTransverse Bending–– Horizontal Shear transferHorizontal Shear transfer–– Anchor block (blisters)Anchor block (blisters)

•• Global AnalysisGlobal Analysis–– Longitudinal reinforcement for Flexure for ULS and SLSLongitudinal reinforcement for Flexure for ULS and SLS–– Shear and Torsion for ULSShear and Torsion for ULS

•• DetailingDetailing

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Section SelectionSection Selection

•• Depth = span length at piDepth = span length at pier head varies to 2.00er head varies to 2.00--

2.50 m at centerline2.50 m at centerline

•• Top slab thickness depends of transverse moment (length between Top slab thickness depends of transverse moment (length between webs)webs)usually 200 mm usually 200 mm --280 mm 280 mm

•• Web thickness (control by shear requirement) approximately 400 mWeb thickness (control by shear requirement) approximately 400 mm for m for castcast--inin--place concrete highway bridge with normal loadingplace concrete highway bridge with normal loading

•• Bottom Slab Thickness varies with maximum value at pier head dueBottom Slab Thickness varies with maximum value at pier head due totonegative moment.negative moment.

2515ll

Design for Transverse BendingDesign for Transverse Bending

•• Dead Load by hand calculation or computer Dead Load by hand calculation or computer modelmodel

•• Live Load by influence surface chart by Live Load by influence surface chart by PucherPucher (1977) or (1977) or HombergHomberg

•• In general, Influence Chart is good enough for In general, Influence Chart is good enough for designdesign purposepurpose

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Misc.Misc.

•• Horizontal Shear TransferHorizontal Shear Transfer–– may be usedmay be used

•• Blisters, provision in AASHTO 9.21 may be Blisters, provision in AASHTO 9.21 may be adoptedadopted

IbVQ

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Global AnalysisGlobal Analysis

•• For SuperstructuresFor Superstructures–– Group 1 normally controlsGroup 1 normally controls

•• For SubstructureFor Substructure–– Group 6 or 7 normally controls for multiple spans Group 6 or 7 normally controls for multiple spans

space frame structurespace frame structure

Design of SuperstructureDesign of Superstructure

•• Unlike buildings, bridge must be designed Unlike buildings, bridge must be designed according to the construction sequenceaccording to the construction sequence

•• Design Check must be carried out forDesign Check must be carried out for–– During ConstructionDuring Construction–– At bridge openingAt bridge opening–– At long termAt long term

•• Effect of moment redistribution due to creepEffect of moment redistribution due to creep

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Construction Sequence AnalysisConstruction Sequence Analysis

•• Pier HeadPier Head

Complete BridgeComplete Bridge

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Typical Bending Moment DiagramTypical Bending Moment Diagram

•• Dead Load (Construction)Dead Load (Construction)

*** European sign convention*** European sign convention

•• Live LoadLive Load

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Bottom Slab (Secondary Moment) for ULSBottom Slab (Secondary Moment) for ULS

Creep RedistributionCreep Redistribution

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Check for the Capacity of the Cross SectionCheck for the Capacity of the Cross Section

•• From calculated M,V from dead and live From calculated M,V from dead and live load, estimate the number of tendon load, estimate the number of tendon requiredrequired

•• At Serviceability Limit StateAt Serviceability Limit State–– Check for Bending StressCheck for Bending Stress

–– Check for Flexural Strength at ULSCheck for Flexural Strength at ULS–– Check for Shear and TorsionCheck for Shear and Torsion

IMc

AP

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Design of SubstructureDesign of Substructure

•• Calculate the factored load from the global Calculate the factored load from the global analysis. Normally, group 6 or 7 dominate the analysis. Normally, group 6 or 7 dominate the designdesign

•• Estimate the strength of column > force Estimate the strength of column > force demanddemand

•• Iterate if requiredIterate if required

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Balanced CantileverBalanced Cantilever

•• CamberCamber–– Time Dependent Deformation of Concrete due to Time Dependent Deformation of Concrete due to

creep and shrinkagecreep and shrinkage–– Depends of Construction SequenceDepends of Construction Sequence–– Accuracy within tolerable limit to avoid problems Accuracy within tolerable limit to avoid problems

at couplingat coupling

( (Approach Bridge)Approach Bridge)

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Construction ProcedureConstruction Procedure

Construction Sequence (continued.)Construction Sequence (continued.)

•• Use of Use of FalseworkFalsework•• Erection trussErection trussสภ

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Type of Erection TrussType of Erection Truss

-- Under Slung TrussUnder Slung Truss

-- Over Head TrussOver Head Truss

Under Slung TrussUnder Slung Truss

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- Segment Over Head

-

-

-

-

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Over Head TrussOver Head Truss

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-

,

- R >/= 85 .

- Truss

-

-

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Design StepDesign Step

•• Similar to Main Bridge only the construction Similar to Main Bridge only the construction procedure are differentprocedure are different

•• Selection of Construction Joint Location= Selection of Construction Joint Location= point of point of ContraflexureContraflexure

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STAGE 1

STAGE 2

STAGE 3

STAGE 2

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