OVERVIEW OF ESSENTIAL DESIGN AND CONSTRUCTION ASPECTS OF

PT SPLICED GIRDER BRIDGE

OVERVIEW OF ESSENTIAL DESIGN AND CONSTRUCTION ASPECTS OF

PT SPLICED GIRDER BRIDGE

Teddy Theryo, P.E.Bryce Binney, P.E., S.E.Parsons BrinckerhoffSegmental Bridge Group

PCEF COMMITTEE MEETING IN DOVERAUGUST 25, 2009

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22

33

44

55

Definition & HistoryDefinition & History

Construction ProcessConstruction Process

Presentation OutlinePresentation Outline

Design AspectDesign Aspect

Segment DetailingSegment Detailing

Grouting, Anchorage Protection Grouting, Anchorage Protection

OutlineOutline

• Definition

• Reasons for Use

• History (Florida Specific)

• Current Practices

11 Definition & HistoryDefinition & History

Definition of Spliced Girder: Definition of Spliced Girder:

• NCHRP Report 517 “Extending Span Ranges of Precast Prestressed Concrete Girders” Defines as:

Section 1.3.1 “…a precast prestressed concrete member fabricated in several relatively long pieces (i.e., girder segments) that are assembled into a single girder for the final bridge structure. Post-tensioning is generally used to reinforce the connection between girder segments.”

Definition:

Reasons for Use:

• Increasing span lengths• Improving safety by eliminating shoulder piers

or interior supports (beginning applications)• Economic considerations (cost savings over

other materials)

History in Florida: History in Florida:

• 1967 AASHTO Traffic Safety Committee Report“…adoption and use of two-span bridges for overpasses crossing divided highways…to eliminate the bridge piers normally placed adjacent to the shoulders”

Growing concern over highway safety during middle 1960’s

History: History:

• PCI, Prestressed Concrete for Long Span Bridges, 1968.• PCI Bridge Bulletin, “Long Spans with Standard Bridge

Girders”, 1967.

PCI published information to extend spans:

Florida used this approach on bridges in the late 1970’s:

• Chipola Nursery Bridge (Northwest Florida)• I-75 Overpasses (Southwest Florida)• Both used AASHTO Type IV with spans of

approx. 115’

~115' ~115'

Publications addressed splicing using P/T and falsework

Typical UsageTypical Usage

200’ to 300’

150’

65’

• Original concept evolved to bulb-tees with haunches• Intracoastal Waterway Crossings (navigational

clearance)• Spans up to 300’ can be accommodated

Haunch Girder is used for span equal or larger than 250’

Spliced Girder Project Photos Spliced Girder Project Photos

PascagoulaBridge, MS

EscambiaRiver Bridge

Rt.33 Bridge, VA

• Design/Construction Interdependency

• Erection Process

• Design Concept

OutlineOutline

22 Construction ProcessConstruction Process

DESIGN

CONSTRUCTION

Design ApproachDesign Approach

Temporary Support During Construction Temporary Support During Construction

•Robust temporary structures

•Stable structure at all stages

•Avoid using PT bars coupler if possible

•Robust temporary bracing system

•Lock girder Supports against longitudinal

and lateral sliding

Erection ProcessErection Process

1

23 4

Haunch Segment Drop-in SegmentEnd Segment

Install FalseworkInstall Falsework1

Falsework on Pier FootingFalsework on Pier Footing1

Install Haunched SegmentsInstall Haunched Segments2

Transporting Haunched GirdersTransporting Haunched Girders2

Placement of GirderPlacement of Girder2

Erecting Haunched GirdersErecting Haunched Girders2

Install Temporary BracingInstall Temporary Bracing2

Place End SegmentsPlace End Segments3

Strongback

Installing StrongbacksInstalling Strongbacks3

Place End SegmentsPlace End Segments3

Strongback DetailStrongback Detail3

Place Drop-in GirdersPlace Drop-in Girders4

Prepare for Drop-in GirdersPrepare for Drop-in Girders4

Placing Drop-in GirderPlacing Drop-in Girder4

Apply Post TensioningApply Post Tensioning5

Design Concept Design Concept

• Girders erected & supported by falsework or strongbacks

Significant Stages of Construction:

Design Concept Design Concept

• C.I.P. diaphragms or splices poured, Stage 1 P/T applied

Significant Stages of Construction:

Design Concept Design Concept

• Deck poured, Stage 2 P/T applied (deck compression)

Significant Stages of Construction:

• Longitudinally, bridge is fully serviceable. Deck and girders held to an allowable stress (usually 3√f’c).

Assumed Erection SequenceAssumed Erection SequenceConstruction Sequence to be included in contract documents

• Span to Depth Ratios

• Staged Construction Loading

• Post-Tensioning Layouts

• Deck Replaceability

OutlineOutline

33 Design AspectDesign Aspect

Design PhilosophyDesign Philosophy

• Two Stages of Post-Tensioning

• Stability

• Serviceability

• Time Dependant Analysis

• Ultimate Limit States

Span to Depth Ratios Span to Depth Ratios

• Simple span AASHTO prestressed girders (L/20)

General Guidelines:

** See AASHTO LRFD Article 2.5.2.6.3. Agency may adhere to these requirements.

L/20

L/25 – L/28

L/20 – L/25

• Continuous post-tensioned spliced girder (L/25 to L/28)

• Haunched pier continuous post-tensioned spliced girder (L/20 to L/25)

Staged Dead LoadsStaged Dead Loads

• Erect girders

+

• After P/T, removal of temp. supports**

+• Deck pouring

Example of Dead Load Staging:

** Notice change in static scheme in this stage to a continuous unit

Staged Construction Staged Construction

• Incremental summation of all loads• Changes in static system throughout construction• Time dependant creep & shrinkage, including

beam/slab differential (CEB-FIP Model Code Capability Preferable)

• Temporary loads & supports• Preferably ability to pour deck in stages

*Forces/stresses in structure are sum of all load casesFinal analysis program should account for:

A few available software packages:

• BD2• TANGO• ADAPT• Consplice (LEAP)• MIDAS• RM• LARSA 4D

Post Tensioning Post Tensioning

Typical Tendon Profile

• Parabolic profile

• Inflection points at 0.9 to 0.95 of span length

Parabolic

90% to 95% of Span

Post Tensioning Post Tensioning

• 3 to 5 tendons per girder• 9 to 15 strands per tendon• Normally 50% of the

tendons stressed on non-comp. structure

Typical Tendon Sizes

Double End Stressing

• For tendons with excessive lengths, dual

end stressing may be required to overcome

large friction loss.

Other Considerations Other Considerations

• Non-Linear Temperature Gradient

• Check Principle Web Stress (composite section complicates this procedure, perhaps check at non-composite & composite C.G.) If stresses are high, 3.5√f’c to 4.0√f’c, consider using a thicker web.

Miscellaneous Considerations

Vertical GeometryVertical Geometry

Spliced FBT-78 Navigational UnitFinished Grades vs. Top of Beam Elevations

71.0

71.5

72.0

72.5

73.0

73.5

74.0

74.5

75.0

75.5

0.0 100.0 200.0 300.0 400.0 500.0

Distance From Begin Main Unit

Fin

ish

ed

Gra

de E

levati

on

Finished Grades Top Of Beam

Deck Replaceability Deck Replaceability

Common Practice to include the deck as part of

composite section in supporting SDL and Live

LoadsCan the deck be replaced ?

Answer: Yes

How can the deck be replaced ?

It must be designed for deck replacement

Deck Replaceability Deck Replaceability

Design Strategy for Deck Replacement

•Use light weight Concrete Deck

•Use Precast Deck Panel (ABC)

•Stress all tendons prior to deck placement

•Add temporary / permanent straight top tendon

•Deck and girder is a composite section for SDL

and LL (no prestress in the deck section)

• Web Thickness

• Pier Segment

• End Span Segments

OutlineOutline

44 Segment DetailingSegment Detailing

Beam DesignBeam Design

Web ThicknessWeb Thickness

• PT Ducts

• Concrete Placement

• Vibratory Clearance

• Radial Stresses

Pouring Concrete

Radial StressesRadial Stresses

• Strand Tensioning

• Grout Pressure

Post Tensioning DuctsPost Tensioning Ducts

Oval Ducts Round Ducts

Longitudinalcracking

Spall ofouter concrete

Haunched BeamsHaunched Beams

Pier Segment Considerations Pier Segment Considerations

• Support self-weight during transport and erection• Support weight of “drop-in” girders with prestressing

(other loads: diaphragms, strongbacks, construction loads)

Erection Load Case

Prestressing Configuration• Positive and negative moments during construction• Use eccentricity vs. 1/P diagrams to satisfy both

conditions

Pier Segment Considerations Pier Segment Considerations Pier Segment Cross-Section

Pier Segment – Vertical BurstingPier Segment – Vertical BurstingVertical Bursting

P

P

P

P

@ 0.6H @ 0.4H

3”

1.75”

11.5”

26.5”

End of Beam Elevation

T

Ult. Negative Moment Capacity Ult. Negative Moment Capacity

Over-reinforced(AASHTO Formulas)

Under-reinforced(AASHTO Formulas)

32”

40”

20”

52”

Neg. Moment

Ult. Negative Moment Capacity Ult. Negative Moment Capacity

Local Widening of Compression Flange

End Segment Considerations End Segment Considerations

• Use local thickening of beam to accommodate anchorages

• Consider staging of P/T in bursting models

• If beam reaction is > approx. 10% of P/T force, consider in S & T

Bursting Forces

Anchorage Block

• Use web tapering to transition to typical beam cross-section

PT AnchoragePT Anchorage

DSI old Anchorage

DSI Multi Strand Anchorage DSI Multi Strand Anchorage SystemSystem

Post-Tensioning Anchorage Post-Tensioning Anchorage

Post groutingPost grouting

Inspection Inspection accessaccess

Grout poGrout portrt

COMPLY WITH FDOT SPEC

VSL MULTI STRAND ANCHORAGE SYSTEM

SYSTEM PRESSURE TESTING (COMPLY WITH FDOT SPEC)

Hardware System – FDOT 462 Hardware System – FDOT 462

Anchorages – Including Inspection Ports

Grout & Inspection Port

Hardware System – FDOT 462 Hardware System – FDOT 462

Pressure Tested Ducts

Anchorages/End BlockAnchorages/End Block

Adjacent Span or backwall placed after bottom strands are jacked

Anchorages/End BlockAnchorages/End Block

Adjacent Span or backwall placed after bottom strands are jacked

Anchorages/End BlockAnchorages/End Block

Top View

Adjacent span or backwall can be placed before tensioning

End Segment Design End Segment Design

1st Stage Post-Tensioning

2nd Stage Post-Tensioning

• Also need to consider case at prestressing

T

T

1st Stage & P/S

T

T

T

2nd Stage P/T

Stage 1 & P/S

End Segment Details End Segment Details

• Recent research has reveled the importance of good grouting practices

• Anchorages shall receive multiple layers or protection to avoid ingress of contaminants

• Florida DOT has implemented a stringent / robust PT and grouting spec. to enhance durability

OutlineOutline

55 Grouting & Anchorage ProtectionGrouting & Anchorage Protection

Duct

Stressing

Anchorage Grout Tube/Drain

VentStrand

Bundle

Grout Dead End

Anchorage

Grout

Flow

Simply Supported BeamSimply Supported Beam

Continuous BeamContinuous Beam

Grout Tube/Drain

Vent Vent

Grout

Flow

Grout FlowGrout Flow

Grout Tube/Drain

Vent Vent

Min.

3 ft.

Grout Tube and Grout Vent LocationsGrout Tube and Grout Vent Locations

Grout from lowest point and one direction grout flowGrout from lowest point and one direction grout flow

Highlights of Florida GroutingHighlights of Florida GroutingGrout Vent

Drain

Highlights of Florida GroutingHighlights of Florida Grouting

• Grout Material– Zero Bleed Water, Pre-Bagged, Pre-Approved

• Duct Material– Plastic Duct, Light Color– Sealed & Pressure Tested

• Grouting Procedure– Injected Solely from Extreme Low Point– High Points & Anchorages Inspected After Grouting– Secondary (Vacuum) Grouting if Needed

Anchorage Protection (FDOT Standard)Anchorage Protection (FDOT Standard)

PermanentGrout Cap

Epoxy GroutPour-back

Diaphragm

Deck Slab PourFull Width

PermanentGrout Cap

Epoxy GroutPour-back

Drain Hole (extendOutside of Beam – fillWith Epoxy Grout)

Diaphragm

Four Levels of Protection:• Grouted Tendon• Permanent Grout Cap• Epoxy Grout Pour-Back• Encapsulating Diaphragm

Summary Summary

• Spliced girder explanation• Construction process• Design philosophy• Segment detailing/design• Addressed durability and grouting

Topics Presented

Final Statement:Concrete spliced girders provide an

economical and durable alternative for medium span ranges. With increasing familiarity to owners and contractors, they will likely become a common solution…..

References References • Anon., “Highway Design and Operational Practices Related to

Highway Safety,” Report of the Special AASHTO Traffic Safety Committee, February 1967.

• Anon., Prestressed Concrete for Long Span Bridges, Prestressed Concrete Institute, Chicago, 1968.

• Anon., “Long Spans with Standard Bridge Girders,” PCI Bridge Bulletin, March-April 1967, Prestressed Concrete Institute, Chicago.

• Castrodale, R. W., and C. D. White. 2004 “Extending Span Ranges of Precast, Prestressed Concrete Girders.” NCHRP Report 517. TRB, National Research Council, Washington, D.C.

• “Detailing for Post-Tensioning”, VSL International, Bern Switzerland, 1991.

• FDOT, New Directions for Florida Post-Tensioned Bridges, Volumes 1 & 4.

• Podolny, Jr., Walter, and Jean Muller, “Construction and Design of Prestressed Concrete Segmental Bridges,” John Wiley & Sons, Inc., New York, 1982.

• PTI. 2000. Post-Tensioning Manual, 6th ed., Post-Tensioning Institute, U.S.A., Ch. VIII, Anchorage Zone Design.

• Ronald, H. D. 2001. “Design and Construction Consideration for Continuous Post-Tensioned Bulb-Tee Girder Bridges.” PCI Journal, Vol. 46, No. 3, Prestressed Concrete Institute, Chicago, IL, May-June 2001, pp. 44-66.

Thank you for your timeThank you for your time

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