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Session 7

Session 7. Guardrail End Treatments (Terminals). Session 7 Outcomes. Describe the Tests Required for Acceptance Explain How the Various Systems Function Describe How a Breakaway Cable Anchorage Functions Identify the Aspects of Proper Site Grading. Purpose of an End Treatment.

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Session 7

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  1. Session 7 Guardrail End Treatments (Terminals)

  2. Session 7 Outcomes • Describe the Tests Required for Acceptance • Explain How the Various Systems Function • Describe How a Breakaway Cable Anchorage Functions • Identify the Aspects of Proper Site Grading

  3. Purpose of an End Treatment If hit, minimize the damage to the vehicle and its occupants Develop the necessary TENSION of the guardrail system

  4. 7-4

  5. Results with a Stand-Up Blunt End

  6. Cable Barrier End Treatment Use 350 accepted end treatment (Large concrete block to develop tension, quick release to allow downstream release)

  7. 350 Approved Generic Cable Terminal (AASHTO RDG)

  8. Weak Post W-Beam Terminals There is no approved approach terminal Solution – use 50’ of standard strong post W-beam next to strong post terminal (with transition if necessary) Downstream, run-off side – can use turndown to develop tension

  9. (AASHTO RDG)

  10. Single Rail Buried-in-Backslope (BIB) Terminal

  11. V

  12. V

  13. Double Rail Buried-in-Backslope (BIB) Terminal

  14. Exposed Three Steel Post Anchor

  15. BIB Looking Across Roadway

  16. What do you see here?

  17. Length of Need (LON) for BIB If backslope is very steep (1:1 or steeper), anchor the barrier in as short a distance as possible; a rock anchor may be appropriate. If backslope is 2 1/2:1 or flatter, calculate using AASHTO procedure or LON = 450 – 15 x OFF, where OFF is the lateral distance from the Edge of Travel Way (EOTW) to the toe of backslope. Min 75’ (excluding #1 above) Suggestion: Do not use BIB when backslope is 2 1/2:1 or flatter if toe of slope is less than 20’(?) from edgeline

  18. Details for BIB Installation(double rail) • Top of rail parallel to roadway • Anchorage: 50’ upstream of Point Of Effectiveness (POE), ONE FOOT under existing ground • 75’ minimum downstream of POE to hazard • Sharpest flare rate 12 ½:1 (high speed)

  19. V

  20. A Stand-Up End Treatment

  21. V

  22. 7-22

  23. 7-23

  24. Slot Guard Position 7-24

  25. 7-25

  26. Available Runout - ???

  27. Recent Installation: Available Runout - ??? 7-27

  28. V

  29. SKT (Sequentially Kinking Terminal) 7-29

  30. SKT Sequential Kinking Terminal FHWA Acceptance Letter CC-61 Date; August 27, 1999 Test Level 3 Tangent Terminal All Plug-Welded Steel Post Option Plug-Welded Post Option

  31. SKT - Plug-Welded Post Option

  32. ET – Steel Post (SYTP) Option 7-33

  33. Steel Post SYTP OptionClose-up

  34. Typical State Standard for Parallel Terminal 7-35

  35. Typical Impact Head

  36. Impact Head and Rail – A Fatal Flaw

  37. Impact Head at Post 1 Improper Installation or Application…

  38. MUST HAVE MANUFACTURER’S SHOP DRAWINGS AND INSTALLATION MANUAL TO INSTALL / INSPECT ANY OF THE PROPRIETARY END TREATMENTS

  39. Characteristics of a Breakaway Cable Anchorage (BCA) Transfer of rail tension to the foundation

  40. For Energy Absorbing Heads, the Cable Anchor Bracket MUST Release SKT 7-41

  41. For Energy Absorbing Heads, the Cable Anchor Bracket MUST Release ET

  42. Characteristics of a Breakaway Cable Anchorage (cont.) Bearing plate Proper orientation – needs to be restrained (nail or strap) Must not be buried

  43. Bearing Plate on Steel Post 7-44

  44. Characteristics of a Breakaway Cable Anchorage (cont.) Develop soil resistance to tension For Wood Posts - Short Wood Post Set in short tubes with soil plates or in long tubes For Steel Posts – per Manufacturer’s Specifications Top of Post 1 MUST Separate from Base

  45. Top of a Steel Post 1

  46. Characteristics of a Breakaway Cable Anchorage (cont.) BUT… Strut distributes tension between first TWO posts - type is inconsequential

  47. Characteristics of a Breakaway Cable Anchorage (cont.) Cable – taut (no more than 1” uplift)

  48. No obstacle less than 75’ downstream from any terminal end (delineator)

  49. “Safety” Treatment for Median Structure

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