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Presentation on theme: "OVERVIEW OF ESSENTIAL DESIGN AND CONSTRUCTION ASPECTS OF PT SPLICED GIRDER BRIDGE Teddy Theryo, P.E. Bryce Binney, P.E., S.E. Parsons Brinckerhoff Segmental."— Presentation transcript:


2 Definition & History Construction Process Presentation Outline Design Aspect Segment Detailing Grouting, Anchorage Protection

3 Outline Definition Reasons for Use History (Florida Specific) Current Practices 1 1 Definition & History

4 Definition of Spliced Girder: NCHRP Report 517 “Extending Span Ranges of Precast Prestressed Concrete Girders” Defines as: Section “…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)

5 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

6 History: PCI, Prestressed Concrete for Long Span Bridges, PCI Bridge Bulletin, “Long Spans with Standard Bridge Girders”, 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’ Publications addressed splicing using P/T and falsework

7 Typical 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’

8 Spliced Girder Project Photos Pascagoula Bridge, MS Escambia River Bridge Rt.33 Bridge, VA

9 Design/Construction Interdependency Erection Process Design Concept Outline 2 2 Construction Process


11 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

12 Erection Process Haunch Segment Drop-in Segment End Segment

13 Install Falsework 1

14 Falsework on Pier Footing 1

15 Install Haunched Segments 2

16 Transporting Haunched Girders 2

17 Placement of Girder 2

18 Erecting Haunched Girders 2

19 Install Temporary Bracing 2

20 Place End Segments 3 Strongback

21 Installing Strongbacks 3

22 Place End Segments 3

23 Strongback Detail 3

24 Place Drop-in Girders 4

25 Prepare for Drop-in Girders 4

26 Placing Drop-in Girder 4

27 Apply Post Tensioning 5

28 Design Concept Girders erected & supported by falsework or strongbacks Significant Stages of Construction:

29 Design Concept C.I.P. diaphragms or splices poured, Stage 1 P/T applied Significant Stages of Construction:

30 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).

31 Assumed Erection Sequence Construction Sequence to be included in contract documents

32 Span to Depth Ratios Staged Construction Loading Post-Tensioning Layouts Deck Replaceability Outline 3 3 Design Aspect

33 Design Philosophy Two Stages of Post-Tensioning Stability Serviceability Time Dependant Analysis Ultimate Limit States

34 Span to Depth Ratios Simple span AASHTO prestressed girders (L/20) General Guidelines: ** See AASHTO LRFD Article 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)

35 Staged 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

36 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 cases Final analysis program should account for: A few available software packages: BD2 TANGO ADAPT Consplice (LEAP) MIDAS RM LARSA 4D

37 Post Tensioning Typical Tendon Profile Parabolic profile Inflection points at 0.9 to 0.95 of span length Parabolic 90% to 95% of Span

38 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.

39 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

40 Vertical Geometry Spliced FBT-78 Navigational Unit Finished Grades vs. Top of Beam Elevations Distance From Begin Main Unit Finished Grade Elevation Finished GradesTop Of Beam

41 Deck Replaceability Common Practice to include the deck as part of composite section in supporting SDL and Live Loads Can the deck be replaced ? Answer: Yes How can the deck be replaced ? It must be designed for deck replacement

42 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)

43 Web Thickness Pier Segment End Span Segments Outline 4 4 Segment Detailing

44 Beam Design

45 Web Thickness PT Ducts Concrete Placement Vibratory Clearance Radial Stresses Pouring Concrete

46 Radial Stresses Strand Tensioning Grout Pressure

47 Post Tensioning Ducts Oval DuctsRound Ducts Longitudinal cracking Spall of outer concrete

48 Haunched Beams

49 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

50 Pier Segment Considerations Pier Segment Cross-Section

51 Pier Segment – Vertical Bursting Vertical Bursting P P P 0.4H 3” 1.75” 11.5” 26.5” End of Beam Elevation T

52 Ult. Negative Moment Capacity Over-reinforced (AASHTO Formulas) Under-reinforced (AASHTO Formulas) 32” 40” 20” 52” Neg. Moment

53 Ult. Negative Moment Capacity Local Widening of Compression Flange

54 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

55 PT Anchorage DSI old Anchorage

56 DSI Multi Strand Anchorage System Post-Tensioning Anchorage Post grouting Inspection access Grout port COMPLY WITH FDOT SPEC


58 Hardware System – FDOT 462 Anchorages – Including Inspection Ports Grout & Inspection Port

59 Hardware System – FDOT 462 Pressure Tested Ducts

60 Anchorages/End Block Adjacent Span or backwall placed after bottom strands are jacked

61 Anchorages/End Block Adjacent Span or backwall placed after bottom strands are jacked

62 Anchorages/End Block Top View Adjacent span or backwall can be placed before tensioning

63 End Segment Design 1 st Stage Post-Tensioning 2 nd Stage Post-Tensioning Also need to consider case at prestressing T T 1 st Stage & P/S T T T 2 nd Stage P/T Stage 1 & P/S

64 End Segment Details

65 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 Outline 5 5 Grouting & Anchorage Protection

66 Duct Stressing Anchorage Grout Tube/Drain Vent Strand Bundle Grout Dead End Anchorage Grout Flow Simply Supported Beam Continuous Beam Grout Tube/Drain Vent Grout Flow Grout Flow Grout Tube/Drain Vent Min. 3 ft. Grout Tube and Grout Vent Locations Grout from lowest point and one direction grout flow

67 Highlights of Florida Grouting Grout Vent Drain

68 Highlights 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

69 Anchorage Protection (FDOT Standard) Four Levels of Protection: Grouted Tendon Permanent Grout Cap Epoxy Grout Pour-Back Encapsulating Diaphragm

70 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…..

71 References Anon., “Highway Design and Operational Practices Related to Highway Safety,” Report of the Special AASHTO Traffic Safety Committee, February Anon., Prestressed Concrete for Long Span Bridges, Prestressed Concrete Institute, Chicago, Anon., “Long Spans with Standard Bridge Girders,” PCI Bridge Bulletin, March-April 1967, Prestressed Concrete Institute, Chicago. Castrodale, R. W., and C. D. White “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, 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, PTI Post-Tensioning Manual, 6 th ed., Post-Tensioning Institute, U.S.A., Ch. VIII, Anchorage Zone Design. Ronald, H. D “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

72 Thank you for your time ? ? Any questions?

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