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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

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)
slide30

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

slide38

Impact Head at Post 1

Improper Installation

or Application…

slide39
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)

Transfer of rail tension to the foundation

characteristics of a breakaway cable anchorage cont

Characteristics of a Breakaway Cable Anchorage (cont.)

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.)

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.)

BUT…

Strut distributes tension between first TWO posts - type is inconsequential

slide48

Characteristics of a Breakaway Cable Anchorage (cont.)

Cable – taut (no more than 1” uplift)

slide56

Downstream End of Barrier

LENGTH OF NEED

7-56

stub height criteria
Stub Height Criteria

Stub

4” max.

5 feet

Figure 4.1 (AASHTO RDG)

telltales of poor terminal grading

Telltales of Poor Terminal Grading

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

Soil plate showing

Tube/post more than 4” above ground

gaps in runs of barrier

Gaps in Runs of Barrier

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

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

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

  • True
  • False
session 7 review2
Session 7 Review

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
  • 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
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