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SSCB Thrie Beam Transition

Question
State WI
Description Text

Attached is a draft copy of our thrie beam anchorage.  If MwRSF has any comments, please let me know.

Keywords
  • Approach Guardrail Transitions
Other Keywords none
Date February 9, 2009
Attachment Thrie beam anchor v1.pdf


Response
Response

For your new detail, I briefly glanced through the pages but did not see anything glaringly out of order. However, please note that I did not check dimensions, bar sizes, bar locations, or bar quantities. It appears that you have adapted transition details from a wood post variation of the Iowa Pooled Fund design from the mid- to late 90s. It is also recognized that you utilized the steel adaptor plate from a prior Missouri Pooled Fund design from the mid 90s. Various cross sectional views are also provided. However, I do not see where they are shown on the plans. In addition, it may be worth considering the use of some vertical bars over the first 4-5 ft to the left of the cold joint since a significant change in geometry occurs here when considering the loss of the foundation system.

 

At the present time, Bob is looking into alternatives for attaching the thrie beam end shoe and adaptor plate to the single slope barrier face. It should be noted that the embedded anchors utilized in the research study may no longer be available. For roadside applications, through bolts may be used as an option. We should wait to see what Bob comes up with for other anchorage options.

 

On another point, will the WsDOT be implementing the MGS guardrail in the future. If you anticipate this, you may consider the fact that modifications to the transition will be forthcoming after the project reports are completed.

Date February 10, 2009


Response
Response

I have been looking into your question on the anchorage of the approach transition and I have some comments.


First, the original transition that was tested anchored the thrie beam to the single slope barrier using 7/8" diameter A325 bolts with "self-drilling" Redhead anchors. These anchors had a listed capacity of 20.5 kips in pullout/tension and 24.32 kips in shear. The higher grade bolt was required to address bending of the bolt. The issue that arises is that this anchorage is no longer made. Thus, we looked through the available alternatives.


  1. There are not currently available drop-ins or wedge bolt type anchors that are 7/8" diameter nor are any made in high grade steel. It is possible to get 3/4" diameter anchors the meet the 20.5 and 24.32 kip anchor loads, but the bolts will not handle the same bending loads as those in the original design.
  2. There are 7/8" diameter mechanical stud anchors available, but neither is available in high grade steel. Thus, they may not be strong enough for the bending loads.
    Also, studs are not as easy to use as the original anchors and there is some snag potential on the heads.
  3. Bolting through is a potential option and is likely the best option for a roadside installation. For median installations, the ends of the bolt present a snag potentials similar to the stud anchors mentioned above.
  4. Another option for attachment would be epoxied threaded rod. 7/8" diameter, B7 threaded rod would be stronger than the bolts in the original design and could be epoxied into the concrete. Based on a review of the available epoxies from Powers Fasteners and RedHead, it appears that they would require approximately 7 7/8" of embedment. This may be difficult to embed based on the width of the barrier. Also, there would be potential for snag on the threaded rod similar to the stud option.
  5. Dayton Richmond and Williams Form engineering produce and design cast-in-place anchors. It is likely that they could help you develop a template to cast anchors with similar shear and tensile capacities to the originally tested anchors and that would work with 7/8" A325 bolts.
  6. An alternative to all of these options would be to cast a vertical face on the end of the single-slope that matches the mounting plate used in the testing. This would eliminate the bolt bending and allow for the use of drop-ins with 3/4" diameter A325 bolts. These anchors exist and we have good experience with them. You could also use a wedge-bolt mechanical anchor in this type of option.
Date February 11, 2009


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