Segmental Concrete Segmental Concrete gg

BoxBox--Girder BridgesGirder Bridgesggดรดร. . สุนิติ สุภาพสุนิติ สุภาพุ ุุ ุDr. Dr. SunitiSuniti SuparpSuparpnisuparp@yahoo.comnisuparp@yahoo.com

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OutlinesOutlines

•• Bridge CharacteristicsBridge Characteristics

•• Advantages and disadvantagesAdvantages and disadvantages

•• Analysis of Segmental BridgeAnalysis of Segmental Bridge

D i f S t l B idD i f S t l B id•• Design of Segmental BridgeDesign of Segmental Bridge

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Segmental Concrete BoxSegmental Concrete Box--Girder BridgeGirder Bridge

External External PrestressingPrestressing SystemSystem3

Structural Element of Segmental BoxStructural Element of Segmental Box--Girder BridgeGirder Bridge

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Structural Element of Segmental BoxStructural Element of Segmental Box--Girder BridgeGirder Bridge

1 2 3 4

1 3

ป ี่

2 4

รูปที 3 Deviator Segment

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Type of Segmental Concrete BoxType of Segmental Concrete Box--Girder BridgeGirder Bridge

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Construction Method of Segmental Concrete BridgeConstruction Method of Segmental Concrete Bridge

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Segmental Concrete BoxSegmental Concrete Box--Girder BridgeGirder Bridge

• safety (e.g. in case of fire)

• extra cost (more prestressing required, single spans, truss)

Disadvantages • high construction loading (overslung truss)

• new construction method – technology (e.g. geometry control of

)segments, design)

• short construction time (segments are prefabricated while the

substructure is being built)

• no interruption of traffic

• precast ‘mass’ production (cost efficient, good controlled quality

shapes)

( )Advantages • weather independent construction (dry joints)

• small light segments

• h ll b ti• hollow box section

• reduced dead load

• cost (reduced reinforcement)• cost (reduced reinforcement)

• Recycling8

External External PrestressingPrestressing

Disadvantages

• additional mild reinforcement required (p)• additional cost for ducts, anchorage, etc.

Disadvantages • only straight tendon layout

• diffusion of post-tensioning forces

• replacement of tendons possible

• inspection of tendons possible

Advantages

• easier Installation of longitudinal tendons

• good corrosion protection of p.t. cables

• less dead load (thin webs)

• less friction (no wobble losses)

( )• prestress forces can be modified after construction (spare ducts)

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Structural ActionStructural Action

•• Simple beam actionSimple beam action in the longitudinal direction causing longitudinal flexural stresses in the longitudinal direction causing longitudinal flexural stresses

and shear stresses across the section.and shear stresses across the section.

•• Shear lag effectShear lag effect in bending.in bending.

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Structural ActionStructural Action

•• Torsion of the crossTorsion of the cross

section due to eccentricity section due to eccentricity

of loading. (St. of loading. (St. Venant’sVenant’s

shear stress and warping shear stress and warping

shear stresses in the shear stresses in the

longitudinal direction)longitudinal direction)

•• Distortion of the sectionDistortion of the section

due to eccentric loading. due to eccentric loading.

(Transverse bending stress, (Transverse bending stress,

shear stress across the shear stress across the

ti l it di l ti l it di l section, longitudinal section, longitudinal

warping stress warping stress

(di t ti l) d (di t ti l) d (distortional), and (distortional), and

corresponding corresponding

(distortional) warping shear (distortional) warping shear (distortional) warping shear (distortional) warping shear

stressesstresses11

Overall Structural Action of Box GirderOverall Structural Action of Box Girder

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Behavior of Segmental Box GirderBehavior of Segmental Box GirderPrecast segmental box girder bridges with external prestressing - design and

construction - Prof. Dr.-Ing. G. Rombach, Technical University, Hamburg-Harburg, Germany

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Behavior of Segmental Box GirderBehavior of Segmental Box Girder (Dry Joint)(Dry Joint)• Whole structure is under compression

at the beginning. (due to PT)

• The structure fails due to crushing of

the concrete in the top

• A ductile behavior of the segmental • A ductile behavior of the segmental

bridge can be seen!!!

• The segments around mid-span are g p

open.

• T. Takebayashi, et.al : A full-scale

destructive test of a precast

segmental box girder bridge with dry

joints an external tendonsjoints an external tendons

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Behavior of Segmental Box GirderBehavior of Segmental Box Girder

Critical sections

• mid-span greatest bending moment

• first joint after support greatest shear force but prestress force not

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2uniformly distributed in cross-section

• diaphragms high concentrated loads due to anchorage 3of tendons

• deviators high concentrated loads due to tendons.4 g

13 3

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224 4 4 2

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Design CodesDesign Codes

- AASHTO (Segment) American Association of State Highway and Transportation

Offi i l G id S ifi ti f D i d C t ti f Officials, Guide Specifications for Design and Construction of

Segmental Concrete Bridges, 1999 (INTERIM 2003)

- AASHTO (STD) American Association of State Highway and Transportation

Officials, Standard Specifications for Highway Bridges, 2002

- AASHTO (LRFD) American Association of State Highway and Transportation

ff l d f Officials, LRFD Bridge Design Specifications, Interim 2005

- BS5400 British Standards Institution, British Standard 5400 (Steel, BS5400 British Standards Institution, British Standard 5400 (Steel,

concrete and composite bridges)

- CEB-FIP Euro-International Committee for Concrete and International

Federation for Prestressing, CEB-FIB Model Code 1990 (Design

Code), 1990

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Loads Loads –– additionaladditional considerationsconsiderations--AA55..1414..22

• According to AASHTO (Segment), all loadings shall be in accordance with AASHO

(STD) including temperature gradient erection loads and creep and shrinkage (STD) including temperature gradient, erection loads, and creep and shrinkage

(ACI, CEB-FIP)

• LRFD-2005 includes some of loadings as specified aboveLRFD 2005 includes some of loadings as specified above.

• For segmentally constructed bridges, the LC shall also be investigated at the

service limit state ;service limit state ;

LRFD2005

AASHTO(Segmemt)

• Additional three types of loading are listed below;

• Construction

• Creep and shrinkage

• Temperature

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Construction LoadsConstruction Loads

ll f bl allows for possible variations in cross section

weight due to construction irregularities

preliminary load from past experience

• formtraveller (2-lane, CIP, 4.5-5m segment :

approx. 710 000 - 800 000 N

• fromtraveller (double cell box section :

approx. 1 250 000 N

• consult contractors for accurate weight!

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