OVERVIEW OF ESSENTIAL DESIGN AND CONSTRUCTION ASPECTS OF PT SPLICED GIRDER BRIDGE Teddy Theryo, P.E....
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Transcript of OVERVIEW OF ESSENTIAL DESIGN AND CONSTRUCTION ASPECTS OF PT SPLICED GIRDER BRIDGE Teddy Theryo, P.E....
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
11
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
Any questions?