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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

Session 7

Guardrail End Treatments (Terminals)


Session 7 outcomes
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

Purpose of an End Treatment

If hit, minimize the damage to the vehicle and its occupants

Develop the necessary TENSION of the guardrail system




Cable barrier end treatment

Cable Barrier End Treatment

Use 350 accepted end treatment

(Large concrete block to develop tension, quick release to allow downstream release)



Weak post w beam terminals

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




Session 7

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Session 7

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Length of need lon for bib

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


Details for bib installation double rail
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)


Session 7

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Session 7

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Session 7

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Session 7

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








Session 7

Impact Head at Post 1

Improper Installation

or Application…


Session 7
MUST HAVE MANUFACTURER’S SHOP DRAWINGS AND INSTALLATION MANUAL TO INSTALL / INSPECT ANY OF THE PROPRIETARY END TREATMENTS


Characteristics of a breakaway cable anchorage bca

Characteristics of a Breakaway Cable Anchorage (BCA) MANUAL TO INSTALL / INSPECT ANY OF THE PROPRIETARY END TREATMENTS

Transfer of rail tension to the foundation


Session 7

For Energy Absorbing Heads, the MANUAL TO INSTALL / INSPECT ANY OF THE PROPRIETARY END TREATMENTSCable Anchor Bracket MUST Release SKT

7-41



Characteristics of a breakaway cable anchorage cont

Characteristics of a Breakaway Cable Anchorage (cont.) Release ET

Bearing plate

Proper orientation – needs to be restrained (nail or strap)

Must not be buried



Characteristics of a breakaway cable anchorage cont1

Characteristics of a Breakaway Cable Anchorage (cont.) Release ET

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



Characteristics of a breakaway cable anchorage cont2

Characteristics of a Breakaway Cable Anchorage (cont.) Release ET

BUT…

Strut distributes tension between first TWO posts - type is inconsequential


Session 7

Characteristics of a Breakaway Cable Anchorage (cont.) Release ET

Cable – taut (no more than 1” uplift)


No obstacle less than 75 downstream from any terminal end delineator
No obstacle less than 75’ Release ET downstream from any terminal end (delineator)



Session 7

V Release ET


Session 7

CAT Release ET(Crash Attenuating Terminal)

7-52


Session 7

Double Side Terminal in Median Release ETon Single Side Barrier



Session 7

Downstream End of Barrier Release ET

LENGTH OF NEED

7-56



Session 7

Grading Release ET


Session 7

AASHTO RDG Release ET


Stub height criteria
Stub Height Criteria Release ET

Stub

4” max.

5 feet

Figure 4.1 (AASHTO RDG)


Telltales of poor terminal grading

Telltales of Poor Terminal Grading Release ET

More than 1-2” of air under strut (ideal on the ground)

Soil plate showing

Tube/post more than 4” above ground


Session 7

Grading at Terminal Release ET

7-62



Gaps in runs of barrier

Gaps in Runs of Barrier Release ET

Generally, if there is less than 200’ between successive runs of guardrail and no obvious reason for the break, the barrier is made continuous. (Check with maintenance)


Session 7 review
Session 7 Review Release ET

Which of the following characteristics describe the BIB end treatment?

  • It will always work whenever and wherever it is hit

  • It is very inexpensive to install

  • It is less likely to get impacted because it is farther away from traffic

  • It can be installed on frontslopes as steep as 4:1


Session 7 review1
Session 7 Review Release ET

All of the energy-absorbing end treatments we have discussed are non-gating systems.

  • True

  • False


Session 7 review2
Session 7 Review Release ET

Desirable grading for all the end treatments include:

  • 6:1 grading in front of and extending at least 3’ behind post #1

  • 10:1 grading in front of and extending at least 6” behind post #1

  • 10:1 grading in front of and extending desirably 5’ behind post #1

  • Grading doesn’t affect the performance of the end treatment


Session 7 outcomes1
Session 7 Outcomes Release ET

  • 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