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Timber/Concrete Composite Module - Testing and Performance

Timber/Concrete Composite Module - Testing and Performance. Presenters: John McPhail - Manager, Bridge Maint. & Rehabilitation Methods Gordon Chirgwin – Manager, Bridge Policy Standards & Records RTA Bridge Technology Section. Australian Small Bridges Conference 2005.

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Timber/Concrete Composite Module - Testing and Performance

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  1. Timber/Concrete Composite Module - Testing and Performance Presenters: John McPhail - Manager, Bridge Maint. & Rehabilitation Methods Gordon Chirgwin – Manager, Bridge Policy Standards & Records RTA Bridge Technology Section Australian Small Bridges Conference 2005 12 Oct 2005

  2. Timber/Concrete Composite Module bridges Typical timber/concrete composite module bridge

  3. Timber/Concrete Composite Module bridges Side view

  4. Timber/Concrete Composite Module - Background • Deterioration of Timber Beam Bridges • Rot and wear in decking • Rot and termites in girders • Stumpy & Scrubby Creek bridges – 1954 • Trial composite deck • Cast in place deck, plate shear connectors • on Pacific Hwy, one bridge still in service • Overlays in RTA - 1980’s & 1990’s • Limited extension of life of existing spans • Some success, most still in service

  5. T/C Composite Module - Timber beam bridges Typical timber beam bridge

  6. T/C Composite Module -Timber bridge deterioration Advanced rot [old Johnston's Creek truss bridge, Glebe]

  7. T/C Composite Module -1954 trial composite design Scrubby Creek bridge (a.k.a. Maria River N/B), still in service on Pacific Highway – composite construction

  8. T/C Composite Module -1954 trial composite design Scrubby Creek bridge – showing composite construction

  9. T/C Composite Module -1954 trial composite design Scrubby Creek bridge – termite attack at end of timber beam over pier

  10. T/C Composite Module - Concrete overlay Corowa No. 2 Approach bridge on MR86

  11. T/C Composite Module - Concrete overlay Side view

  12. T/C Composite Module -The Terry Doolan Concept • Composite Timber/Concrete design • Eliminates water & termite pathways • Modular – faster, more repair options • Precast – better quality & economy • Standardised units and designs • Use of timber – renewable • Usually for replacement of timber bridges

  13. T/C Composite Module – Doolan Concept 31 Timber/Concrete Module bridges in service with RTA (Aug 2005), including 11 on State Highways

  14. T/C Composite Module -Original Design Concept • Design Parameters • NAASRA 1976 Section 10 (for timber) • Design Loading T44 • Design Life 100 years • Barrier ABDC Level 2 or 3 • Detailing • Timber capped at ends, indirect support • Plate and coach screw shear transfer • Normally 2 beams per module (except edge modules) • Transverse joints at piers – rotation only • Longitudinal joints clear of wheel paths • Braking normally taken to abutments

  15. T/C Composite Module -Design Details – Cross Section Underside of deck showing modular construction Normally 2 beams per module (except edge modules)

  16. T/C Composite Module – Design Details - Elevation Elevation of skewed bridge, note timber beams and end blocks

  17. T/C Composite Module -Design details - Beams Girder size Coach screws Shear plates

  18. T/C Composite Module – Design Details - Shear connectors Fabricated beam prior to pour. Note plates and coach screws for shear transfer, also end anchorage detail.

  19. T/C Composite Module -Design Details - Module End Timber capped at ends, indirect support (suspended from slab), end block rests on rubber bearings

  20. T/C Composite Module -Design Details - Module End Timber capped at ends, indirect support (suspended from slab)

  21. T/C Composite Module – Design Details – Pier Connection End blocks tied together with longitudinal bolts

  22. T/C Composite Module – Design Details – Deck joints Transverse and longitudinal deck joints

  23. T/C Composite Module - Foreseen Performance Issues • Multiplicity of joints • Performance of shear connectors • Performance of module end • Suspended girder arrangement • Torsion and shear in concrete • Effects of timber shrinkage • Differential deflection of units

  24. T/C Composite Module – Testing – UniSyd, Field & UTS • Uni of Sydney - 1996 • Exploratory push-out shear tests • Static test of two full size modules • Fatigue test of full size module (500,000 cycles) • Ultimate static test after fatigue testing • Bending! • Field Testing – Macleay R & Orara R - 1997 • RTA Bridge Test Truck (GVM up to 56 tonnes) • Demonstrated partial composite action • Linear elastic design confirmed • Uni of Technology Sydney (UTS) - 2002 • Extensive push-out shear tests to AS 1649 • Definitive capacity for shear (ultimate)

  25. T/C Composite Module – UniSyd Test Module in testing machine

  26. T/C Composite Module – UniSyd Test Ultimate test –module has excellent tolerance for flexure

  27. T/C Composite Module – UniSyd Test Push out test specimens (before test)

  28. T/C Composite Module – UniSyd Test Ultimate flexural test (Module 2 - 400 mm dia beams). Note torsional failure in end block.

  29. T/C Composite Module – UniSyd Test Ultimate flexural test (Module 2 - 400 mm dia beams). Note torsional failure in end block.

  30. T/C Composite Module -RTA Rockdale Fatigue Test • Uni of Sydney test • did not explore moving load shear envelope • end connection not sufficiently tested in fatigue • Rockdale fatigue test - 2004 • loaded to shear envelope • end detailing was fully tested • Note – applied loading magnifies bending effects • fatigue failure assessed on relative movement of beam and end block (cf. Uni of Sydney test)

  31. T/C Composite Module -Rockdale Fatigue Test Overall view of test

  32. T/C Composite Module -Rockdale Fatigue Test Loading points to produce shear envelope

  33. T/C Composite Module -Results of Rockdale Fatigue Test • Failure in shear, commencing from end connection • 1st failure at 110,000 cycles – E beam • 2nd failure at 253,000 cycles – W beam • 1st failure – detail deficiencies contributed to early failure • No ultimate test • Failures forensically examined

  34. T/C Composite Module -Rockdale Fatigue Test Deemed fatigue failure of eastern beam (after ~110,000 cycles) NOTE: beam undersize

  35. T/C Composite Module -Rockdale Fatigue Test Close-up of delaminated zone - eastern beam NOTE: Horizontal shear failure in timberobserved near end

  36. T/C Composite Module -Rockdale Fatigue Test Typical cracks radiating from shear plates

  37. T/C Composite Module -Rockdale Fatigue Test Deemed fatigue failure of western beam (after 253,000 cycles)

  38. T/C Composite Module -Rockdale Fatigue Test Spalled zone of western beam

  39. T/C Composite Module -Rockdale Fatigue Test Fractured coach screw shear connector

  40. T/C Composite Module -Rockdale Fatigue Test Beyond spalled zone – western beam

  41. T/C Composite Module -Field Performance Issues • Separation between girders and concrete • Excessive relative movement? - indication of shear failure

  42. T/C Composite Module - Field Performance Issues Separation of girder and possible relative movements at end block

  43. T/C Composite Module - Field Performance Issues Separation of girder at deck slab

  44. T/C Composite Module -Bridge Field Test - 2005 • Camp Creek Bridge on SH12 nr Grafton • Simple load test using loaded rigid truck • Measurement of relative movements • Relative movements within expected working load limits • Found that separation was entirely due to shrinkage • No fatigue failure

  45. T/C Composite Module - Conclusions of all testing • Optimised design layout • Ultimate bending capacity established • Shear capacity for design established • Shear failure is progressive from end • Fatigue failure starts in steel components • Detailing critical • Some improvements to detailing indicated

  46. T/C Composite Module –Conclusions of all testing • No flexural fatigue failure in any test (despite severe load) • Ultimate failure mode from flexural test – torsional failure in end block • Shear fatigue capacity will be higher than test for low traffic applications

  47. T/C Composite Module -Proposed RTA Guidelines • Design Rules • Shear connector design capacity (working load) 15 kN for coach screws (M24 x 300 long, embedded 200 mm) 107 kN for plates(75 x 250 x 16, embedded 37 mm) • Bending capacity • Fatigue capacity – 500,000 cycles at service load • Detailing Ensure plates & coach screws effectively combined End block & end connection of beam • RTA Standard Drawings

  48. T/C Composite Module -Proposed RTA Guidelines • Inspection Criteria • (also refer Timber Bridge Manual - Section 7) • Must include observations under transient loads • Reference points to detect loss of composite action • Relative movements between end block and girder • Crushing /spalling of concrete at shear connectors • Observation of cracks

  49. T/C Composite Module -Proposed RTA Guidelines • Inspection Criteria • (also refer Timber Bridge Manual - Section 7) • Joint seals • Pier connections – tie bolts and gap • Lateral ties • Global horizontal movements of modules • Condition of timber beams • General condition of deck

  50. T/C Composite Module – Overall Conclusions • The timber/concrete composite module is a reliable, engineered bridge design • Main application as low-cost replacement for timber beam bridges • Environmental, cost and quality advantages • Use restricted to low traffic routes (joints) • Tested ultimate and fatigue capacity provides assurance for service loads • Fatigue failures will be progressive and manageable through routine inspection

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