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54 Inch Concrete Barrier

Question
State WY
Description Text

Does anyone
have any details for a 54 inch single slope barrier they would care to share
with me?

Keywords
Other Keywords none
Date December 10, 2014


Response
Response

We have a single slope barrier from Caltrans that is 56” tall.  But I don’t believe that it has the vertical reinforcement required for pier protection.

 

In most cases, we have convinced our structures department and FHWA to hardened new structures for the large truck impact loads.  It is cheaper to do and less of a hazard to the driving public.

Date December 10, 2014


Response
Response

It’s not quite a single slope barrier, but here are details for the (almost) vertical shape with head ejection criteria that we’ve used.

Date December 10, 2014
Attachment 54inchVerticalShape.pdf


Response
Response

I would like this information as well, as we are looking to create a 54” (TL-5) single slope bridge pier protection design for Ohio...   

Florida has a 54” safety shape design. http://www.dot.state.fl.us/rddesign/DS/10/IDx/411.pdf

 

Date December 10, 2014


Response
Response

I have attached a link to a previous question on this topic from the Q&A website (ID #360).  The drawings are of a 54” F-shaped concrete barrier with a footing for both interior and exterior sections.  It was designed specifically for pier protection appilications (hence the footer).  This could easily be converted to a single sloped shaped as long as the reinforcement remained the same (bar size, number of bars, and stirrup spacing) and the top with remained the same.  I will caution against using this design as a vertical-faced barrier as the base would be narrow and may not provide enough over-turning moment strength. 

 

 

http://mwrsf-qa.unl.edu/view.php?id=360

 

Date December 10, 2014


Response
Response

Our median barrier meets the criteria, but we were looking for a roadside version.  Our structures folks also plan to reinforce new structures to avoid the need for such a barrier, but we do still have bridges that don’t have redundant piers, so those will require the protection.

Date December 10, 2014


Response
Response

What is the intended purposed for the 54" barrier?   Is it for pier protection or glare screen/barrier combination?

 

We are currently working on new standards for single slope barriers and bridge rails.  We are using the Texas (10.8 - 11 degree) sloped barrier.  The heights will be 36", 42" and either a 54" or a 56".

 

The purpose of the 54" or 56" height is for a permanent glare screen on top of a barrier, not pier protection.  Our current f-shaped concrete median barrier is 56" and our bridge version is 54", so we are currently trying to reconcile the two.   

 

Bottom line,  we will have (54" or 56") single slope, bridge rail and median barrier designs to share soon, but they will not be designed for pier protection.  We will likely be considering them all MASH TL-4 barriers.

 

Date December 10, 2014


Response
Response

Thank you all for your valuable input.  I may have a few questions as the day goes on, but want to answer Mike's question first.  This barrier is intended for bridge pier protection.  In general, our bridge designers are designing to the LRFD loading (600 Kips I think), but as Maria said, we have many existing structures which are not and some are in vulnerable locations.  We have used 42 inch single slope barrier in the past with the Texas slope design, but we are curious if we should switch to either the steeper Caltrans design (9% ??) or Iowa's more vertical face with head ejection criteria.  I am not aware of head ejection being an issue with the Texas Design, at least for a 42 inch high barrier, but am curious if the Caltrans design is more at risk for head contact. Maybe Scott could weigh in on this.  I am a little concerned about the Iowa design being more difficult to construct, and also if the second, flatter face may allow tankers to slide up over the barrier? Also, it may be harder to transition down to 31 or 32 inches to connect to a crash cushion or MGS barrier.  Maybe Scott and Chris could weigh in on these issues.

Date December 10, 2014


Response
Response

I would agree that Iowa’s vertical-faced barrier is probably more difficult to construct than a single-slope shape due to the multiple angles.  For this same reason, it may be slightly more difficult to transition down to a shorter height barrier.  Having said that, however, the contractor on our first installation was able to construct the barrier and the transitions in accordance with our plans, and the end result looks good.  I can’t really comment on the barrier’s ability to redirect a tanker truck, as it’s my understanding that 90 inches is the minimum height needed to redirect such a vehicle.

 

Date December 10, 2014


Response
Response

Head ejection with the Texas version of the single slope barrier is tough to estimate.  Some tests have the vehicle ride a bit up the slope and cause the vehicle to roll away from the barrier.  Other tests show the vehicle tires staying down and the vehicle rolling slightly toward the barrier.  The risk of head slap is definitely less with the Texas single slope than it would be for more vertical shapes.  The magnitude of this reduction…  I don’t have a good answer for.

Date December 10, 2014


Response
Response

Was vehicle stability good in all of the tests you saw as the vehicle comes off the barrier (Texas design)?

Date December 10, 2014


Response
Response

I don’t recall any vehicle rollovers, only a couple of pickup tests that had >25 degree roll angles.  Textured single slope barriers have caused vehicle instabilities for the CA single slope.  I would assume the same results would occur for textured TX single slopes.

Date December 10, 2014


Response
Response

I am a little late on the response but we do not have the single slope barrier.  Below is what our bridge staff uses.  

Date March 5, 2015
Attachment 54in-King.png


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