Midwest States Pooled Fund Program Consulting Quarterly Summary

Midwest Roadside Safety Facility

04-01-2013 to 07-01-2013


Rigid Barrier Height Transitions

Question
State: IA
Date: 04-02-2013

I am aware of recommendations that changes in the top height of rigid barriers occur at a rate of 8:1 or 10:1. These rates are not always practical, however, and in some cases the use of a more aggressive taper rate may be necessary. Could you please provide a recommendation for the maximum allowable taper rate for height transitions of rigid barriers? Also, would this recommendation vary depending on the degree of change in height? For example, couldn't a more aggressive taper rate be tolerated for minor height differences (say 4 inches or less) compared to the taper rate for major height differences (12 inches or more)?

Response
Date: 05-15-2013

We have used more aggressive slopes for vertical height transitions in the past. Recent testing of the median transition from free-standing TCB to a 42" tall single slope barrier used a sloped, steel cap to transition between the 32" tall PCB segments and the 42" tall single slope barrier.

That steel cap was constructed with a 5:1 flare. It performed well under crash testing. Based on the performance of the this 5:1 flared cap, it would seem reasonable to use slopes as high as 5:1 when transitioning from 32" tall b! arriers up to higher heights. We could not recommend the use of these higher flares for shorter barrier heights below 32" as the potential for the vehicle to climb the flared section may increase if the starting height of the flare is lower.

Response
Date: 05-15-2013
Thanks.  Could you provide a recommendation for maximum vertical flare rate for rigid barriers with heights ranging from 27 to 32 inches?

Response
Date: 05-15-2013

Before addressing the 27"-32" height transition, we should be clear about the guidance for the 5:1 slope. The 5:1 height transition slope that we tested with the PCB transition used a steel cap to create the vertical transition flare. There is some concern that using concrete to create the 5:1 flare may increase friction and or gouging of vehicle components in the flared region. Thus, the 5:1 is an aggressive approach with some co! ncerns for its use. 

 

For your 27" to 32" transition, the recommendation would still be the 8:1 slope. We would recommend this based on the concerns noted above regarding the difference in the slope materials. In addition, as noted in the first response, we would not want to go to steeper slopes for barrier heights below 32" on the low side due to concerns for increased vehicle exposure to the slope and climb.



Yield Line Analysis calculation example

Question
State: MN
Date: 04-06-2013

As we discussed in our meeting last Thursday, attached is a concrete barrier detail for you review. As a reminder, we would like to know what your design methodology is (assumptions and process) and what recommendations you might have for both the interior and end regions of the barrier. The steel reinforcing is 60 ksi, and the minimum concrete strength is 4 ksi

**Deflection joints were a concept that was supposed to allow the rail to rotate and expand more freely as the bridge moves under live load and expands with temperature. It was an attempt to limit cracking in our barriers. They don't work and we no longer use them. I forgot that we haven't changed the standard yet. You can ignore them, we have moved to a tooled joint 10 ft were the rebar runs right through the joint.



Response
Date: 04-18-2013
I conducted a full Yield Line analysis on one of the bridge rails you sent, and I tried to list / show all of the assumptions that I made.  I attempted to be as detailed as possible in order to show every step.  Take a look at the attached file.  Is this what you were looking for in regards to methodology of calculating barrier strength?
Attachment: https://mwrsf-qa.unl.edu/attachments/a2b8e93e1668f089c3ba9e9e09213013.pdf


Response
Date: 04-29-2013

Joe's questions are below, answered in RED

 

Again, thank you for helping us with our barrier design.  We appreciate your time and expertise in this matter. After reviewing the design you provided, I had some questions concerning some of your assumptions.

First, the design assumes that the rebar in the barrier yields both longitudinally and vertically, front and back.  Because the bars are so close to the compression face, shouldn't a yield check be performed to make sure the bars yield as assumed?

I use an Excel spreadsheet program to calculate the bending strength of reinforced concrete cross sections.  It calculates the strain distribution throughout the entire cross section and relates that to the estimated stress in the steel (assumes elastic, perfectly plastic behavior).  Thus, the program should have checked for yielding and calculated all stresses according to strain at each depth.

Second, the hook on the dowel into the deck does not appear to be fully developed, should this be accounted for when calculating Mc for both the interior and exterior regions?

I assumed adequate anchorage to develop the yield strength of each bar.  Yield Line Theory requires that the barrier deflects/bends/yields to absorb energy and balance out the energy of the impact.  If no yielding occurs, the analysis procedure would not be valid.

If a dowel will not develop full yield strength, I would recommend altering the bar / hook details.  Of course, the development lengths found in ACI 318 are conservative in nature and designed for static loading.  Under dynamic loading, failure stresses are typically increased.  Thus, often times we can rely on field proven or crash tested embedment/anchorage designs.

Third, a f of 0.90 was used to modify the barrier resistance, where does this value come from?  As I read AASHTO f is equal to 1.0 for extreme event cases.

The 0.9 factor comes from ACI 318 for bending strength.  We typically use it to give some safety factor to designs, but you may elect not to.

Last, We have always assumed that the longitudinal bars need to be fully developed on both sides of the yield line.  Some of the longitudinal bars in the barrier are underdeveloped for the end region by this assumption, should this be considered when calculating the capacity of the end region?

My answer here will mirror what was said above… yield line requires the full yield strength of the reinforcement.  Thus, it's easier to just extend longitudinal bars to obtain the proper development length.  When designing end section reinforcement, we specify longitudinal bar lengths that span the critical length, an additional foot or two for conservatism, and the required development length (or splice length if being splice to interior section reinforcement).

Thanks again for your help,

 



Barrier height on outside of superelevation

Question
State: WI
Date: 04-08-2013



Wisconsin
superelevates the high side shoulders (first chart).  Is there an issue
with barrier height when a shoulder breaks away from the superelevation (second
chart)?




Attachment: https://mwrsf-qa.unl.edu/attachments/cda346de26b01c013d3dad040e444896.jpg

Attachment: https://mwrsf-qa.unl.edu/attachments/63a3033cec2f0903f05fa8d248e86c93.jpg


Response
Date: 04-08-2013

Yes, there could be containment issues with barriers placed off a shoulder for the second situation you illustrated (roadway has positive superelevation and shoulder has negative superelevation).  If the difference in slopes is severe enough, the vehicle could become an airborne projectile as it exits the roadway – similar to the effects of vehicles rolling over the front slope breakpoint of a median ditch in the cable project.  To my knowledge, there have not been any studies to evaluate vehicle trajectories or  barrier placement and containment for these situations.  There is an NCHRP project that is investigating barriers placed on curved, superelevated roadways, but I am not sure if they will be investigating situations with differing roadway and shoulder superelevations.



Termination of the Texas HT steel bridge railing

Question
State: IA
Date: 07-18-2011

Scott and I like the options which flare back onto the parapet at the same elevation. Option 5 may be easier to deal with considering it may use a smaller anchor plate on the back wall. To mitigate concerns for snag increased snag on the posts, it may be necessary to use a minimum tangent length of the tube prior to bending it back to the parapet. Let me know if you have additional questions regarding this matter. Thanks!


Attachment: https://mwrsf-qa.unl.edu/attachments/21c438bcafa06ef856b8e038d0aecc16.pdf


Response
Date: 07-19-2011

Thanks, Ron.  Just one point of clarification: the termination of the elliptical tube is a free end; it is not attached to the concrete.  Does this have any impact on your recommendation?

Do you know if the end that TXDOT uses was ever crash tested?  (it's a free end as well)



Response
Date: 07-25-2011

I am not aware of any passenger vehicle crash tests being performed on the Texas HT bridge rail. I have contacted my colleagues at TTI to also inquire about any passenger vehicle crash tests on the original system as well as a similar rail on a vertical parapet where a lower rail was added. Based on this inquiry, both TTI and TxDOT have stated that no passenger vehicle crash tests were performed.


Attachment: https://mwrsf-qa.unl.edu/attachments/0f63009ff7a0e10de41554f3fa7aa31f.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/f909276a25c7d6fd1516a51c09fdbdf8.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/c6b07abd72d3265acc8986204a819c82.pdf


Response
Date: 01-29-2013

Could you share your opinion on the preferred treatment at the trailing end of a BR-27C bridge railing?  See both pages of the attachment.  Note that in some cases, the trailing end could lie within the clear zone of opposing traffic.

 

My personal preference is the non-flared version.  With this version, would it be further advisable to attach the end of the rail to the concrete with a plated connection?  Or perhaps to use a reduced post spacing near the end
Attachment: https://mwrsf-qa.unl.edu/attachments/200e97b1ace0861a96b95b25297af70c.pdf


Response
Date: 01-30-2013

To begin with, I will assume that both the combination bridge rail and the concrete parapet are crashworthy.  The tapered/flared concrete end (proposed) is more desirable for downstream end impacts as the non-flared end (original) could potentially cause snag issues during vehicle redirection.  However, the flared end (proposed) is drawn such that it leaves the end of the rail open for potential snag issues for reverse direction hits.  As such, we recommend using the flared concrete end, but extending the rail to flared concrete end.  Thus, snag potential will be minimized for both directions of travel. 

 

A few notes on the design:

(1)    The concrete taper/flare should begin on the same plane as the face of the posts (or further back for a more conservative design.)  This flare depth will best minimize snag potential.

(2)    The flare/taper angle should be gradual / shallow enough to minimized snag. (i.e., 3:1 – 4:1)

(3)    There are benefits to bolting the rail to the concrete parapet to ensure stiffness and full lateral capacity.  However, if the concrete end is flared and the rail is extended to the flared and cut to match the slope of the flare, the free end of the rail would be supported laterally by the sloped face of the concrete parapet.  Thus, attaching the rail to the concrete is not necessary and the rail can remain free.



Response
Date: 04-09-2013

I realize I'm reviving an older question, but could you take a minute and review page 2 of the attached drawing?  Specifically, I'm curious if you would consider this design acceptable for both directions of travel (forward- and reverse-direction impacts).  The tube railing is cut to match the flare of the concrete with an approximate 1-inch gap between the two. 

 

Please feel free to suggest any enhancements as well.
Attachment: https://mwrsf-qa.unl.edu/attachments/beb5830cb30a14ff9087f12058235e90.pdf


Response
Date: 04-10-2013

Here's another option for you to consider.


Attachment: https://mwrsf-qa.unl.edu/attachments/9705e5670d307c41dd465f6e162a2bad.pdf


Response
Date: 04-26-2013

Both rail termination details you have included should perform well during impacts from either direction.   Having the free end of the rail cut with a flare to match the taper of the concrete parapet should minimize vehicle snag during impacts.  Also, the flared cut allows the rail to utilize the tapered concrete parapet as a lateral support to insure rail strength at this termination location (after a small lateral deflection the rail would be pressing against the concrete wall).  The short distance between the free end of the rail and the first post also helps insure strength at the end of the rail.

 

If I was to pick one design over the other, I would go with the straight rail section.  Thus, end section rail fabrication would be simple as a standard rail segment would just have to be cut to correct flare.  Also, the straight rail design forms a more continuous barrier face near the top of the bridge rail.  Although the change in barrier profile is rather minimal for the second design you sent me (with the rail bent backward away from traffic), continuity always helps create a smooth, stable redirection.

Response
Date: 04-29-2013

I wanted to get your opinions regarding the termination of the metal tube portion of the Texas HT railing (TXDOT drawing attached). We have a project where we will be using the HT railing on a bridge and using a 44" tall F-shape concrete barrier off both ends of the bridge, and we are developing ideas on how to transition between the two.

Please see the attached PDF. It presents 5 different options for transitioning from the Texas HT barrier (on the bridge) to Iowa's 44-inch concrete barrier (off the bridge). Please provide your comments and/or recommendations regarding the use of each of the 5 options. Note that the top width of our 44-inch barrier is 8-1/2 inches.


Attachment: https://mwrsf-qa.unl.edu/attachments/21c438bcafa06ef856b8e038d0aecc16.pdf


Concrete Barrier Design Guidance with End Sections

Question
State: MN
Date: 03-06-2013



As we discussed in our meeting last Thursday, attached are
two barrier details for you review.  As a reminder, we would like to know
what your design methodology is (assumptions and process) and what
recommendations you might have for both the interior and end regions of the
barrier.


Each half of the split median barrier (Fig 5-397.131) is
treated as TL-4.


I also have a question:



Could I get a PDF copy of the Guidelines for Attachments
to Bridge Rails and Median Barriers (February 26,2003)
?


If you need any more information, please let me know.


Thanks again for the help,



 




Attachment: https://mwrsf-qa.unl.edu/attachments/e1045fde7b54495d76c3fc30b20e4a18.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/46ebd8b599bc95244869b802fc7841ce.pdf


Response
Date: 03-18-2013

I conducted a full Yield Line analysis on one of the bridge rails you sent, and I tried to list / show all of the assumptions that I made.  I attempted to be as detailed as possible in order to show every step.  Take a look at the attached file.  Is this what you were looking for in regards to methodology of calculating barrier strength?

 

Let me know what questions you have.


Attachment: https://mwrsf-qa.unl.edu/attachments/28908854d224057a4714f6b74d30c426.pdf


Response
Date: 04-19-2013

Sorry it has taken so long to get back to you.  We wanted to arrange a phone conference to discuss the barrier design, but because of the schedule of the others involved with the barrier design question, we've decided to try and resolve our questions using e-mail.  If a phone conference become necessary, we can try and arrange one.

 

Again, thank you for helping us with our barrier design.  We appreciate your time and expertise in this matter.

 

After reviewing the design you provided, I had some questions concerning some of your assumptions.

 

First, the design assumes that the rebar in the barrier yields both longitudinally and vertically, front and back.  Because the bars are so close to the compression face, shouldn't a yield check be performed to make sure the bars yield as assumed?

 

Second, the hook on the dowel into the deck does not appear to be fully developed, should this be accounted for when calculating Mc for both the interior and exterior regions?

 

Third, a f of 0.90 was used to modify the barrier resistance, where does this value come from?  As I read AASHTO f is equal to 1.0 for extreme event cases.

 

Last, We have always assumed that the longitudinal bars need to be fully developed on both sides of the yield line.  Some of the longitudinal bars in the barrier are underdeveloped for the end region by this assumption, should this be considered when calculating the capacity of the end region?

 

Attached is the original e-mail and pdf of the calculations you sent me for your reference.

 

Thanks again for your help,



Response
Date: 04-29-2013

I have answered your questions in RED below.

 

______________________________________________________

 

Sorry it has taken so long to get back to you.  We wanted to arrange a phone conference to discuss the barrier design, but because of the schedule of the others involved with the barrier design question, we've decided to try and resolve our questions using e-mail.  If a phone conference become necessary, we can try and arrange one.

 

Again, thank you for helping us with our barrier design.  We appreciate your time and expertise in this matter.

 

After reviewing the design you provided, I had some questions concerning some of your assumptions.

 

First, the design assumes that the rebar in the barrier yields both longitudinally and vertically, front and back.  Because the bars are so close to the compression face, shouldn't a yield check be performed to make sure the bars yield as assumed?

I use an Excel spreadsheet program to calculate the bending strength of reinforced concrete cross sections.  It calculates the strain distribution throughout the entire cross section and relates that to the estimated stress in the steel (assumes elastic, perfectly plastic behavior).  Thus, the program should have checked for yielding and calculated all stresses according to strain at each depth.

 

Second, the hook on the dowel into the deck does not appear to be fully developed, should this be accounted for when calculating Mc for both the interior and exterior regions?

I assumed adequate anchorage to develop the yield strength of each bar.  Yield Line Theory requires that the barrier deflects/bends/yields to absorb energy and balance out the energy of the impact.  If no yielding occurs, the analysis procedure would not be valid.

If a dowel will not develop full yield strength, I would recommend altering the bar / hook details.  Of course, the development lengths found in ACI 318 are conservative in nature and designed for static loading.  Under dynamic loading, failure stresses are typically increased.  Thus, often times we can rely on field proven or crash tested embedment/anchorage designs.

 

 

Third, a f of 0.90 was used to modify the barrier resistance, where does this value come from?  As I read AASHTO f is equal to 1.0 for extreme event cases.

The 0.9 factor comes from ACI 318 for bending strength.  We typically use it to give some safety factor to designs, but you may elect not to.

 

Last, We have always assumed that the longitudinal bars need to be fully developed on both sides of the yield line.  Some of the longitudinal bars in the barrier are underdeveloped for the end region by this assumption, should this be considered when calculating the capacity of the end region?

My answer here will mirror what was said above… yield line requires the full yield strength of the reinforcement.  Thus, it's easier to just extend longitudinal bars to obtain the proper development length.  When designing end section reinforcement, we specify longitudinal bar lengths that span the critical length, an additional foot or two for conservatism, and the required development length (or splice length if being splice to interior section reinforcement).

 

Attached is the original e-mail and pdf of the calculations you sent me for your reference.



Taper on end of concrete barrier

Question
State: MN
Date: 04-24-2013

In April of 2011 staff from MnDOT conducted a conference call with you and Dean Sicking to discuss a wide range of barrier design/geometry and crash testing related issues.  One specific issue we discussed was the taper at the end of concrete barrier sections, where the barrier transitions to a guardrail connection (see issue #3 highlighted in yellow in the first attachment).  The concluding statement for issue #3 includes the language (see first attachment), “End tapers for barriers taller than 34" should be modified to 1V:8H."  We have adjusted the taper to 1V:8H for most of our barriers that are taller than 34", but have a question regarding the MnDOT structural tube railing that was crash testing at your facility.  The second attachment is our standard plan sheet for the structural tube barrier, which has a height of 38".  Please note the portion of the drawing in the upper left hand corner with the red border.  Should the taper on this shape also be modified to 1:8?  The current taper is 5:12, the same taper we use on all of barriers with a height of 34" of less.

Please let me know what you think.

Thanks!


Attachment: https://mwrsf-qa.unl.edu/attachments/859d95d588d559d16564b38ed56b2425.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/d95f81df3e556eb74ea2ec68c6f8e114.doc


Response
Date: 04-25-2013

A couple of comments on the detail you sent.

 

1.       We do believe that the concrete end section that you have shown in the detail should use the 8H:1V taper that we discussed previously for other concrete rail height transitions.

2.       A second comment should be made regarding the termination of the tubing adjacent to the increased height concrete end section shown. As the detail is currently shown, the vertical face of the concrete barrier at the end of the tube rail section poses a significant vehicle snag hazard for vehicles impacting from right to left as shown on the detail plan. We have been in discussions with other states that use similar end sections with their combination rails and have recommended flaring the vertical face of the barrier back and extending the tube section to mitigate the potential for vehicle snag at that location. I have attached a schematic showing the idea so you can get a picture of the type of modification we are suggesting.

 

Please contact me with any comments or questions.


Attachment: https://mwrsf-qa.unl.edu/attachments/50beda48178bd1938841918e15d801ca.pdf


Guardrail on Soil Nail Walls

Question
State: WA
Date: 05-01-2013

From: Victoria.Brinkly@dot.gov [mailto:Victoria.Brinkly@dot.gov]
Sent: Tuesday, May 01, 2012 10:39 AM
To: Nick.Artimovich@dot.gov
Cc: will.longstreet@dot.gov; rfaller1@unl.edu
Subject: RE: Guardrail on Soil Nail Walls

Thanks Nick.
I can't remember if MWRSF was working with Central Fed Lands and TTI had some similar “rail on wall" design, or if it was vice versa. I do know the result was guardrail posts not set as close to the wall as our (western) geotechs were hoping for.

I've asked for more info on the sonotube installation and I'll be interested to hear what Ron Faller thinks of this situation.

Tori

From: Artimovich, Nick (FHWA)
Sent: Tuesday, May 01, 2012 8:04 AM
To: Brinkly, Victoria (FHWA)
Cc: Longstreet, Will (FHWA); Ronald K. Faller (rfaller1@unl.edu)
Subject: RE: Guardrail on Soil Nail Walls

Tori,
I know you don't have an extra inch to work with in that situation, but I am concerned that there is not enough embedment for the posts. The sonotubes might be a good way of installing the posts, but it does not appear that there is enough soil behind the tubes to resist the impact forces on the guardrail.

I am copying Ron Faller of the Midwest Roadside Safety Facility on this as they recently completed a project to design the Midwest Guardrail System to be placed at the top of a gabion wall – not too dissimilar to the Agness Road situation in the photos you sent. Western Direct Federal may be able to contract with MWRSF to adapt a guardrail system for these situations.

There is also research recently completed and underway to design barriers for the top of reinforced earth walls. I am not familiar with the details, but I believe they need a concrete barrier with a moment slab to be able to perform effectively.
Nick

Nicholas Artimovich, II
Highway Engineer, Office of Safety Technologies
Federal Highway Administration HSST
1200 New Jersey Avenue SE, Room E71-322
Washington, DC 20590
email: nick.artimovich@dot.gov
phone: 202-366-1331
fax: 202-366-3222
web: http://safety.fhwa.dot.gov

From: Brinkly, Victoria (FHWA)
Sent: Tuesday, May 01, 2012 10:45 AM
To: Artimovich, Nick (FHWA)
Subject: Guardrail on Soil Nail Walls

Hi Nick…have you ever heard of any issues with guardrail on soil nail walls? Or the process the contractor outlined in photos below?
In theory it seems similar to the post in rock detail, but there's not much info below on the size of the sonotubes or the material used for backfill.

Tori

From: Ulrich, Malcolm A (FHWA)
Sent: Tuesday, May 01, 2012 7:33 AM
To: MOEN, Margaret L (FHWA); Dissen, Charles (FHWA)
Cc: Brinkly, Victoria (FHWA)
Subject: FW: DSR sites on the Agness - Powers Road

FYI – would this system be acceptable? Doubt there has been crash testing, but…………

From: Bryan Wavra [mailto:bryan@gsi3.com]
Sent: Monday, April 30, 2012 7:53 PM
To: Ulrich, Malcolm A (FHWA)
Subject: RE: DSR sites on the Agness - Powers Road

Malcom,

Our MP 20.3 stabilization concept will incorporate a soil nail wall/buttress down the slope about 15 to 20 feet. Therefore, guardrail could be installed without penetrating shotcrete or subsurface soil sails. A rather minor addition to the scope of work if so desired.

We regularly install guardrail in circumstances where the wall is in close proximity to the travel surface. In these cases, sonotubes are cast into the shotcrete and backfilled with sand to facilitate guardrail installation. The following photos illustrate this process:









I met Chuck Dissen at the site during my reconnaissance. I mentioned, as indicated in our proposal, that we are willing to drill a few exploratory borings at MP 13.1 and MP 15.1 Pro Bono to aid in the drafting of proposals to better stabilize those locations. FHWA would of course be invited to observe the borings to collect data as well. Sampling won't be possible but we will be able to distinguish relative the relative consistency of the underlying soil….worthwhile information for sure.

The slides at MP 47.8, 48.0, and FS 3348 have all resulted in loss of road width. We can fix these as well and would include a GRS (GCS) wall to regain road width. We will work up proposals for your consideration.

Please feel free to reply or call me with further questions.

Best regards,
Bryan


Bryan Wavra, P.E.

Mobile (503) 999-4187
bryan@soilnaillauncher.com



From: Malcolm.Ulrich@dot.gov [mailto:Malcolm.Ulrich@dot.gov]
Sent: Monday, April 30, 2012 7:21 PM
To: Bryan Wavra
Subject: RE: DSR sites on the Agness - Powers Road

Bryan,

Thanks for making the site visit and proposal for the Agness Road slide.
One question that has come up is the width and other specifics needed for guardrail installation along a nailed wall. What considerations and recommendations for guardrail are included in your design?


Malcolm Ulrich
Geotchnical Team Lead
610 E Fifth Street
Vancouver, WA 98661
malcolm.ulrich@dot.gov
360.619.7816 Office
360.607.4503



From: Bryan Wavra [mailto:bryan@gsi3.com]
Sent: Tuesday, April 24, 2012 9:15 PM
To: Ulrich, Malcolm A (FHWA)
Subject: RE: DSR sites on the Agness - Powers Road

Malcom,

I was able to locate these slides in google earth and have gps coordinates so I think I am in good shape….although more information is certainly a bonus. It appears as though these slides are at least in the vicinity of the Agnes Road slide and should be able to stop by this week while I am down south.

The Hurricane Ridge Road shoring project certainly sounds intriguing. It may be tough to get to your office before the end of the day tomorrow but my flight to Billings doesn't leave until 1 p.m. on Monday (April 30th) and could meet you that morning. It would also give me a chance to go over our proposal and concept for Agnes Road…perhaps in the company of the Contracting Officer. In the meantime, any information you may have readily available to send over by email would give me a chance to review.

It was a pleasure meeting you today.

Best regards,
Bryan


Bryan Wavra, P.E.

GeoStabilization, Inc.
Phone: 503-999-4187
www.geostabilization.com

a Soil Nail Launcher, Inc. Partner Company
www.soilnaillauncher.com


From: Malcolm.Ulrich@dot.gov [mailto:Malcolm.Ulrich@dot.gov]
Sent: Tuesday, April 24, 2012 7:14 PM
To: Bryan Wavra
Subject: DSR sites on the Agness - Powers Road

Bryan, here are the milepost locations: FSR 33 MP 47.6 and FSR 3348 MP 0.2. These two sites are reportedly within ½ mile of each other. The map that was sent to me is rather crude, just a general area circled in red that I assume encompasses both sites. I will see if I can get more precise locations for you and a better map as well, in the event that you can work site visits into your schedule for your trip south later this week.

I should have thought of this when you were here today: I have another project that I would like to get your opinion about, one where we need temporary shoring at the base of a 160 foot long fill slope. The shoring is needed in order to excavate and replace 25 feet at the outlet end of a long culvert (30 inch diameter) before lining the whole pipe. The site is on the Hurricane Ridge Road in Olympic National Park, a few miles south of Port Angeles. I am thinking that launched nails might be an effective tool for ensuring stability of the excavation. One of our geotechs has visited the site and has done an analysis of the site based on assumed/interpreted soil parameters. I could send you some details via email or perhaps next time you pass through, maybe on your way back from Seattle (?) this week, I could describe the project directly to you. Access is difficult and the work space will be very constricted as the fill pinches down into the gully where the pipe is located. Let me know if you will have time to talk this over, and if it just won't work this week I'll plan to email you a plan sheet of the site and we can discuss by phone.


Thanks.


Malcolm Ulrich
Geotchnical Team Lead
610 E Fifth Street
Vancouver, WA 98661
malcolm.ulrich@dot.gov
360.619.7816 Office
360.607.4503


Attachment: https://mwrsf-qa.unl.edu/attachments/d04e39c18e0a3ac8be81b8ae1c8149eb.jpg

Attachment: https://mwrsf-qa.unl.edu/attachments/4739cd1847a62d20c6484132eb806f9c.jpg

Attachment: https://mwrsf-qa.unl.edu/attachments/508290b41c55e47134870fa59637324d.jpg

Attachment: https://mwrsf-qa.unl.edu/attachments/f654e29d2b3ab1b6321696a20912de28.jpg


Response
Date: 05-01-2013

MwRSF conducted the research on the wire-faced MSE wall and configured a non-blocked, steel-post MGS for use. Our final recommendations included a minimum lateral placement from outer edge of 4 ft 9 in. based on post embedment 1 ft away from 3-ft wide wall facing fill (larger stones).

 

TTI conducted an NCHRP study to develop guidelines for rigid barriers used on MSE walls, including recommendations and details for using configuring moment slabs. The Phase II effort is in progress to extend the guidelines to TL-4 and TL-5.

 



Swapping MGS post locations at obstructions

Question
State: IA
Date: 05-01-2013


I'd like your opinion on swapping MGS post locations
in order to avoid an underground obstruction.  This situation is shown in
the attached drawing.  Note that post spacing would not exceed 6'-3".

 

Thanks,



 





Response
Date: 05-01-2013

Previously, we have recommended that posts not be placed at a splice location when using the standard post spacing. When moving to a reduced post spacing, we have also suggested that one allow 1 to 2 half-post spacing prior to locating a splice at a post. Based on your figure, a splice is located at a post which is adjacent to a 6-ft 3-in. span. To remedy this scenario, the interior two 12-ft 6-in. long panels could be replaced with a 25-ft 0-in. long panel, as shown in the attached figure. Can you accommodate one larger panel? If not, we could use a 6-ft 3-in. panel to make a shift and then add some extra posts to make it work out.



Response
Date: 05-01-2013

I think we could accommodate the one larger panel, but I'm also curious about the 6'-3" panel option.  Could you send me a sketch?



Response
Date: 06-13-2013
See attached.
Attachment: https://mwrsf-qa.unl.edu/attachments/b8262398df9c734f05d0ff67605d729b.pdf


Backup Plates

Question
State: OH
Date: 05-01-2013


One of our guardrail suppliers asked if it would be
acceptable to use a 12" wide backup plate on the S3x5.7 bridge rail post
instead of the 6" wide. We already have the 12" wide ones in the
inventory as a standard part… Any reason to say no (other than the
smaller one should be cheaper)?




Response
Date: 05-01-2013

I don't believe that there is any reason one can't use a larger backup plate. Smaller might be an issue, but larger should be ok.



cable barrier line post footing design

Question
State: WI
Date: 05-02-2013

At our pooled fund meeting, MwRSF indicated that they have done some work on line post anchors designs. The design that you have come up still have some cracking issues but it is an improvement to what we have seen. I was wondering if I could get a CADD design of the drawing. I was wondering how I could write specifications to get manufacturers to design similar line posts.

Response
Date: 05-13-2013
During our evaluation of the socketed foundations for cable posts, we aimed to simulate a worst-case impact to the post/foundation while preventing both damage and displacement.  Testing was conducted with a bogie vehicle equipped with a rigid impact head centered 12" above ground line impacting the post at a target speed of 20 mph.  Note, weight of the bogie was around 1,800 lb, but lighter surrogate vehicles would be applicable as long as they have enough energy to bend and ultimately override the post.  This impact was created to replicate small car bumper or bottom frame impacts.

The foundations were evaluated for both damage and displacement. Displacements less than 1" were considered acceptable, although less than 1/2" were desired.  Foundations with more that 1" of displacement were considered to shallow and/or narrow to prevent excessive movements that would require the foundation to be reset during barrier repair.  Similarly, damage was to be held to a minimum so as to not require repairs. It was determined that cracking and small scale concrete spalling or chipping would be allowable.  Large concrete fractures would be deemed a structural failure.

The foundations have not been finalized at this time.  Once they are finalized, I can get you the CAD drawings.


welded beam guard atttachment to low-fill culverts

Question
State: WI
Date: 05-02-2013

I know that you are working on a report about this. Is it possible to get the CADD in english units, for bolting through the box culvert. If you have an epoxy version with the epoxy information I would like it too.

Response
Date: 05-15-2013
I have atttached the CAD from the recent bogie testing for the guardrail posts mounted to the top slab of concrete box culverts.  Note, the recent study covered component testing of single posts, not the entire system.  Thus, the entire system was not drawn.
Attachment: https://mwrsf-qa.unl.edu/attachments/88169b50b0cd0bb353c7bf1b30a58e1a.DWG

Attachment: https://mwrsf-qa.unl.edu/attachments/840609952d51fc985a3ceccbaa81c27c.DWG

Attachment: https://mwrsf-qa.unl.edu/attachments/d6f982ce17ea3ba502961caabeebdf63.DWG

Attachment: https://mwrsf-qa.unl.edu/attachments/7d4272d4640b0ed61a797e5d0fcfd778.DWG

Attachment: https://mwrsf-qa.unl.edu/attachments/0320dd3e1a9b1e79647b6bee96610186.DWG

Attachment: https://mwrsf-qa.unl.edu/attachments/31e4b775301fac025e45e2f9beff5626.DWG


MGS BLOCK ROTATION

Question
Date: 05-08-2013

When you tested the MGS system, you added a ¼" hole at the top of the post to drive a nail into the block to keep the block from rotating.  From a manufacturing standpoint, this hole is a pain in the behind.  This hole cannot be punched and has to be drilled in a separate operation.

I would like to propose a couple of options to this hole. 

1. We drill two holes in the post for placing the rail bolt.  One on each side of the web.  Could this hole be used?
2. Could a nail be placed into the top of the block and then bent over the top of the post?
3. Could a nail be placed into the side of the block and then bent over the side of the post?
4. If routered blocks are used, is a nail required at all?

We would like to come to a better solution than drilling the ¼" hole.

Thanks


Response
Date: 05-28-2013

Several years ago, the Iowa DOT installed 1 run of MGS in the north east corner of the state. After a major snow storm with heavy snow, a plow cleared the traveled lanes and move substantial wet snow off of the road, much of which struck the routed blockouts. A short-term fix was to use four nails in the back corners, which were then bent over the post flange to prevent rotation. Here is what we wrote in 2008:

 

We agree that this blockout rotation would appear to be caused by snow removal operations. To resolve your blockout issue and eliminate the requirement to field drill holes in the steel flanges, we recommend that you place four (4) nails in the top and bottom corners on both sides and bend the nails over the flanges. The four nails should provide adequate resistance to block rotation, even under snow removal operations. For this solution, you could use 16-d nails, but it may be preferred to use 20-d nails with this alternative. Please note that it would not be necessary to have the post webs on the back of the blockout using this option."

 

Comments to your email are contained below in red.

 

_______________________________________________________

 

 

Ron

 

When you tested the MGS system, you added a ¼" hole at the top of the post to drive a nail into the block to keep the block from rotating.  From a manufacturing standpoint, this hole is a pain in the behind.  This hole cannot be punched and has to be drilled in a separate operation.

 

I would like to propose a couple of options to this hole. 

 

1.        We drill two holes in the post for placing the rail bolt.  One on each side of the web. Could this hole be used?

**This option would not provide much rotational resistance due to its location in close proximity to the bolt.

2.       Could a nail be placed into the top of the block and then bent over the top of the post?

**I do not like the top bent nail option very much as block could rotate under it.

3.       Could a nail be placed into the side of the block and then bent over the side of the post?

**A minimum of two bent nails would be my recommendation for this concept when nail location placed at upper sides.

4.       If routered blocks are used, is a nail required at all?

**We do not think that nails are required if block is routed. However, we have seen a special case where significant, wet snow was plowed and caused partial rupture of routed block tabs, as noted above. In those scenarios, we had Iowa use four bent nails.

 

We would like to come to a better solution than drilling the ¼" hole.



blocked MGS in front of a retaining wall

Question
State: WI
Date: 05-10-2013

We have a project where there is a need for a retaining wall behind a beam guard. The beam guard is preventing vehciles from droping off the retaining wall. I was asked how close can the retaining wall be to the blocked MGS without interfearing with the post rotation and providing adequate soil mass to absorb impact.

Response
Date: 05-30-2013

Definitive research into minimum MGS guardrail offsets from MSE or retaining walls has not been conducted at this time. Previous research regarding MGS guardrail placed adjacent to a wire-faced MSE or gabion wall was conducted at MwRSF. Our final recommendations included a minimum lateral placement from outer edge of 4 ft 9 in. based on post embedment 1 ft away from 3-ft wide wall facing fill (larger stones). However,the construction of your MSE may be much different than used in our R&D effort and may allow for steel posts spaced closer to outer vertical wall edge.

The main concerns with respect to MGS guardrail placement adjacent to MSE or retaining walls is that the post placement doesn't interfere with the MSE wall, that the offset from the back of the post to the wall does not affect the post-soil resistive forces, and that the rotation of the post does not damage the MSE or retaining wall. Based on previous testing of guardrail posts at MwRSF, a 2-ft offset from the back of the post to the inside edge of the retaining wall should be sufficient to alleviate the latter two concerns. Two feet of soil behind the post should provide adequate space for developing the proper post-soil resistive forces and prevent the rotating post from impacting the inside of the retaining wall.

The above offset guidance is valid for level terrain only. If the MGS was installed adjacent to slopes and a retaining wall, further consideration would be needed.



crash cushion layouts for various situations

Question
State: WI
Date: 01-23-2013

Dear MwRSF, I know that people are probably cringing when I email a question about crash cushions but here I go. I have been digging around trying to figure out how to properly layout crash cushions for point hazards ( e.g. bridge piers, overhead signs...) So I sat down and started drawing some situation out and would like MwRSF to review them. I believe that I will need to add this guidance into our design manual because we are using more and more crash cushions. I've included a couple of PDFs for layouts. "Hazard layouts without concrete transitions.pdf" is a layout for smaller hazards that do not need a concrete transition. I'm using this to set up a size limit (i.e. After a certain size fixed hazard a designer needs to add a concrete transition). "Hazard layouts with concrete transitions.pdf" is a set of drawings showing how to layout a hazard relative to concrete transition section. This PDF also has layouts for median and side of the road. "Roadside layout steps.pdf" is showing the process of layout driveway curb limits for a roadside barrier installation. I know I asked a similar question about what angles to use. I believe that MwRSF indicated that a flatter approach angle on the nose of the crash cushion should be used. The problem I have with using a flatter angle is that in opens the median up for u turns and could cause drainage issues at the roadside. If MwRSF could give review and provide comments it would be appreciated.
Attachment: https://mwrsf-qa.unl.edu/attachments/a7fa755328ff4eb89511b80637c90b9b.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/84cdfd6260fe596dfdf725a3b562d4f6.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/e5852a149552c9812a8e4ac437be6bbf.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/9d65978b65e8ee4e6fc5721ff22e44c5.pdf


Response
Date: 05-10-2013

There are many separate issues that are raised here involving the proper installation of crash cushions across a wide variety of installations. The scope of this inquiry is likely outside what can be answered in this forum.

 

In order to better address this issue, a problem statement was submitted by WisDOT for the 2013 Midwest Pooled Fund meeting.



MASH bridge rails

Question
State: WI
Date: 05-13-2013

Does MwRSF know of any MASH crash tested bridge rails?

Response
Date: 05-13-2013

MwRSF has not conducted any successful MASH TL-4 testing of bridge rail designs, but has conducted TL-3 tests on a limited number of designs.

1. Test nos. NJ-1 and NJ-2 were conducted as part of the NCHRP 22-14 project. These tests consisted of a successful 1100C test and a failed 10000S test on a 32" tall NJ barrier.

2. MASH TL-3 testing was conducted with the 2270P vehicle on a precast bridge rail system for FRP bridge decks. (TRP-03-220-09)

3. MASH TL-3 testing was conducted with the 2270P and 1100C vehicles on the MGS bridge rail system. (TRP-03-226-10)

 

TTI has also conducted a number of bridge rail tests at TL-3 and a limited number of tests to evaluate minimum barrier heights for the TL-4 10000S impact condition. I have attached those reports for your review

 

The file 'bridge rail reports.zip' (153.8 MB) is available for download at
http://dropbox.unl.edu/uploads/20130527/982dd85a93a62bef/bridge%20rail%20reports.zip 
for the next 14 days.
It will be removed after Monday, May 27, 2013.



MGS Thrie Beam Median Barrier

Question
State: WI
Date: 05-19-2013

WisDOT wants to install a double faced MGS with thrie beam.

I have grabbed the cadd for the MGS double faced drawings from the web.

I know that the blocks need different geometry for thrie beam.

I was wondering how to split the double face into separate into two single faced thrie beams.

I was also trying to figure out how to bolt the rails to the blocks and posts.

Thanks,


Response
Date: 05-19-2013

 

To make this simple, I might suggest that you use the modified thrie beam system, which uses a longer steel post and tapered, deep steel blockout. This system is shown in the 2006 RDG, page C-11. If you do not really like this option, then I would adapt from 32" MGS and use shortened wood blockouts (like for W-beam or used down sides of bullnose) on 78" long steel/wood posts. The later would need to be drawn and likely sent to FHWA for comment.

Which path do you prefer?

 



Response
Date: 05-21-2013

I have a call in to Nick A. of FHWA to further discuss the MGS Thrie Beam Median Barrier concept, especially in terms of minimum height and blockout configuration. While we wait for that discussion, I scanned through our Pooled Fund Consulting website to review our prior guidance on thrie beam related issues that seem very relevant. As you will see, several items may be critical, including rail height, post type, blockout size/type/length, rail-to-post attachment, etc. These items will certainly affect the overall configuration.
Ron
**********************************************************
Thrie Beam Blockouts
View as Admin
Question
State WI
Description Text We would like some guidance on the appropriate blockout to use for a standard thrie beam, both for wood posts and steel posts.


WisDOT is working on developing a thrie beam bullnose terminal based on the MwRSF design(report TRP-03-95-00, 6-1-2000) that was approved by FHWA (11-8-2000 letter, HSA-1/HSA-cc68). The blockout for the standard thrie beam construction from posts 9 to 12 is shown as 360 mm (14.17 in) high.


Sheet 2 of Minnesota DOT's Standard No. 5-297.611 "Thrie Beam Bullnose Guardrail for Medians" (dated 8-20-2001), which is based on the approved MwSRF design uses a 22-inch high blockout.
Keywords Guardrail
Other Keywords none
Date May 10, 2006

Response
Response Per your inquiry, I have summarized several of the successful thrie beam transition tests that have been conducted according to the NCHRP Report No.
350 requirements. They are as follows:

No. 1 - Wood Post - Wood Blockout
                550 mm center rail height
                804 mm top rail height
                150 mm by 200 mm by 554 mm blockouts
                150 mm by 200 mm by 1.9 m posts
                0.68 m dynamic deflection
                TL-3 pickup truck test (404211-11)

No. 2 - Steel Post - Modified Steel Blockout
                610 mm center rail height
                864 mm top rail height
                W360x33 tapered blockouts
                W150 x14 posts
                0.71 m dynamic deflection
                TL-4 single-unit truck test (404211-5a)

                610 mm center rail height
                864 mm top rail height
                M14x18 tapered blockouts
                W6 x9 posts
                1.02 m dynamic deflection
                TL-3 pickup truck test (471470-30)

No. 3 - Steel Posts - Routed Wood Blockout
                550 mm center rail height
                804 mm top rail height
                150 mm by 200 mm by 554 mm routed blockouts
                W150 x14 posts
                0.58 m dynamic deflection
                TL-3 pickup truck test (404211-10)

In summary, you can use either the long wood blocks, shortened wood blocks, or even the tapered steel blocks in combination with the standard thrie beam guardrail systems after post no. 9.
Date May 15, 2006


Thrie Beam Height Guidance
View as Admin
Question
State IA
Description Text Are you aware of any minimum and/or maximum allowable height guidance for thrie-beam guardrail?
Keywords Guardrail
Other Keywords none
Date September 21, 2010

Response
Response I am not aware of a documented height tolerance for thrie beam guardrail systems. Initially, one may attempt to argue that the minimum height could be as low at that corresponding to W-beam guardrail systems. However, I would suspect that mounting thrie beam with a top height of 27¾ in. would potentially increase the propensity for vehicle climb, barrier override, and/or rollover upon redirection due to the increase face below normal W-beam rail with same top height.

At this time, the roadside safety community has considered the minimum top height for W-beam rail to be approximately 27¾ in., while the maximum top height for the MGS is 32 in. At the minimum W-beam top height, a thrie beam element would extend downward to 7¾ in., thus potentially creating new safety risks. Selected thrie beam guardrail systems have successfully met crash testing guidelines when installed with a top height of 34 in. As such, it is my opinion that the minimum height tolerance for modified thrie beam guardrail may be somewhere around 31 in. for NCHRP 350, while the top height tolerance may be closer to 39 to 40 in. at the TL-3 impact conditions.

Thrie beam has been successfully crash tested over the years. Below, I have provided a few of the test results but not those for the T-39 thrie beam guardrail system.

Test No.                             System Description                                                                                                                           Top Rail Height                                     Result
404211-5a                                               Modified Thrie Beam w/ 81" Steel Post & Tapered Block                                     34"                                        Passed 8000S TL-4 test
404211-11                                               Strong-Post Thrie Beam w/ 81" Wood Post & Wood Block                                  31.65"                                Passed 2000P TL-3 test
404211-10                                               Thrie Beam w/ 81" Steel Post and Routed Wood Block                                         31.65"                                Passed 2000P TL-3 test
471470-31                                               Thrie Beam (G9) w/ 78" Steel Post and Steel Block                                                   32"                                        Failed 2000P TL-3 test
471470-30                                               Modified Thrie Beam w/ 81" Steel Post and Tapered Block                                33.6"                                   Passed 2000P TL-3 test
Recent Test                                             Thrie Beam (G9) w/ 78" Steel Post and Full-Depth Wood Block                       31.5"                                   Failed 2270P TL-3 test (MASH)

Although I have yet to see the results of the recent failed MASH test, it would seem reasonable that improved safety performance could be obtained by using a shortened wood blockout or the modified steel tapered (collapsible) blockout – both of which reduced climb and allow the lower corrugation to fold back.
Date December 13, 2010

Thrie Beam Bullnose Post Length after Post 9
View as Admin
Question
State KS
Description Text What is the allowable post length for the crash tested options for thrie beam guardrail systems? We wlould like to know what post length is acceptable beyond post 9/10 in bullnose. We would like to use 6 ft.
Keywords Bullnose Median Barrier & Short Radius
Other Keywords none
Date February 10, 2012

Response
Response We reviewed the prior research and found that three different thrie beam configurations have met the 350 safety standards. They are listed below. Upon inspection, it would seem appropriate to maintain the use of 6.5 ft long posts for the standard wood post thrie beam guardrail.

________________________________________________________________

Summary

1. Standard Thrie Beam (G9) system did not pass 350 – 6.5 ft W6x9 posts with 21.5" long W6x9 blockouts w/ 32"rail height
2. Modified Thrie Beam = 6'-9" long W6x9 posts with 49.5"embedment and 18" deep M14x18 blockouts w/ 33.6" rail height
a. Tested to TL-3 and Tl-4
3. Thrie beam with 6'-9" long W6x9 posts with 49.5"embedment and 6"x8"x21.8" long routed wood blocks passed NCHRP 350 w/ 31.65"rail height
4. Thrie beam with 78" long 6"x8" SYP posts and 6"x8"x21.8"long routed wood blocks passed NCHRP 350 w/ 31.65" rail height

Short answer, 81" long posts for steel and 78" long wood have passed.
Date February 11, 2012



Response
Date: 05-22-2013

What is the working width of the double faced thrie beam?



Response
Date: 05-23-2013

Estimate W.W.:

 

System width = (3.25")*2 + 6" + (14")*2 = 40.5"

Dynamic Deflection for single-face system w/ pickup truck impact = 36.7" (1.02 m)

Est. Dyn. Defl. In RDG for double-face system = 20"

 

W.W. = 20" + 40.5" = 60.5" which seems somewhat too high

 



Curbs at bridge rail approach transitions

Question
State: IA
Date: 05-21-2013

Do you think TTI's successful crash tests of the TxDOT T131RC bridge rail transition add any weight to our argument that the 4-inch curb at the bridge end is unnecessary?

Response
Date: 05-21-2013

I was reviewing the noted report today before opening your recent email. I wish that Roger would have shown this report and test video at the AASHTO TF13 meeting last month. He did show TTI's 2270P crash test on the IA transition without curb, which rolled over under MASH TL-3. I do not have this report though. However, this test report demonstrates that vehicle instability may not be a function of the ¼-post spacing configuration without a curb but rather that instability is more correlated to magnitude of wheel interaction with the barrier end. Since the new TxDOT transition uses ¼-post spacing without a lower curb, then I would believe that more significant tapered end section would allow for the IA transition to work without curb. This opinion is also supported by the fact that several other crashworthy thrie beam transitions attached to concrete ends that utilize ½-post spacing without a lower curb have contained pickup truck impacts under NCHRP 350, although they include tapered bridge end with a larger lateral offset at the upstream end.

 



Response
Date: 05-21-2013

So what would you recommend for a lateral offset to use at the bridge end?  And what taper rate to bring it back to full width?



Response
Date: 05-21-2013

A 3:1 taper would seem reasonable and with upstream end at least 6 in. away from front face of rail.

 

The new TTI system utilized a 3:1 flare with a 6 in. lateral offset. A prior NDOR system utilized a 3.2:1 flare with an 8 in. lateral offset. CALTRANS had a system with a 1:1 flare and a 6 in. lateral offset. All of these tests were successful with pickup truck testing under either 350 or MASH and no curb leading up to concrete parapet.



10 Foot NJ Temporary Concrete Barrier on Bridge Deck, 30 mph Speed

Question
State: WY
Date: 05-21-2013

We have a situtation where our Traffic Program set up to use our old portable concrete barrier (details attached)on a bridge deck over Interstate 80 placed 6 inches from the edge. The installation is in a workzone while the bridge deck is reconstructed. The speed will be posted at 30 mph and due to geometry it is unlikely the speeds would be much higher. The barrier would not meet NCHRP 350 for TL-3 as it only uses a single loop on each side of the barrier, top and bottom. However, it is likely to be a TL-2 barrier. The question is, for this situation, does it need to be pinned to the deck? If so, is there another solution such as the New York design with box beam mounted on the back of the barrier?

Response
Date: 05-21-2013

In the past, MwRSF estimated deflections for the F-shape PCB at a speed of 36 mph and an angle of 27.1 degrees when impacted with the 2000P vehicle. This analysis produced a estimated deflection of 24 in. Based on this, it would seem reasonable to assume that the NJ barrier in question would have similar deflections if impacted at 30 mph. Thus, there is a potential for the cg of the barrier segments to extend over the edge of the bridge deck. This suggests that the barrier segments would require some form of constraint to retain the barrier sections on the deck edge at a spacing of 6 in.

The box beam system that was tested with the New York NJ TCB section was successful in reducing deflections. MASH testing of the NY NJ TCB showed dynamic deflection of 40.3 in. for the free-standing barrier and dynamic deflection of 30.9 in. for the barrier with box beam across the back side. However, it should be noted that the test NY NJ barrier system used a I-beam connection with little to no gap between barrier segments and a 20-ft segment length. In addition, the test NY system pinned/anchored the ends of the barrier system, which further reduced system deflections. Thus, using the box beam to stiffen your system should reduce deflections, but it is difficult to be confident that the deflection reduction would be similar to the tested system due to the barrier differences.

Determination of more accurate deflections and the ability to retain barriers on the deck would likely require analysis and simulation. Thus, the best recommendation for this situation would be to anchor the barrier segments. If the NJ shape you are using does not have pockets for anchor pins, one could use the steel strap tied-down that was tested with the F-shape barrier. This would likely reduced deflections and would help maintain barriers on the bridge deck during an impact event. It uses drop in or mechanical concrete anchors rather than through bolting and should be installable with the loops on you barrier system at TL-2. One item to note is that this system requires a constraint bolt through the base of the pin to prevent it from pulling through the loops under loading.

We have also developed and tested a preliminary version of an unanchored, reduced deflection retrofit for Wisconsin. This system would likely work as well, but would need to be adapted over to work with a NJ shape rather than an F-shape. It would cost significantly more to install than the steel strap tie-down.

We can provide details for either system.

Please contact me with further questions.



MGS attached to concrete paving or deck

Question
Date: 05-22-2013



Is there a detail for base plating MGS (wood or steel posts) to concrete
pavement or a concrete deck? I recall seeing a detail for bolting MGS to the
edge of a bridge deck, but don't recall seeing one for base plating to top of
concrete.



 



Thanks,



 




Response
Date: 05-22-2013

We did develop a couple of systems that may work for this application. The MGS bridge rail system used S3x5.7 posts attached to the edge of the bridge deck. We have also adapted this design for attachment to culverts. There may be potential to mount this type of system to the top of the bridge deck with base plates, however, that technology has not been developed at this time. I have attached a link to the report below.

 

http://mwrsf.unl.edu/reportresult.php?reportId=53&search-textbox=bridge%20rail

 

The closet design that we have developed to what you are requesting was a system for attachment of strong post W-beam to the top of low-fill culverts. That system was designed and tested with the G4(1S) system, but would likely work for the MGS as well. The system was designed for use with the posts mounted 0-9" below grade and directly to a concrete culvert. It used ½ post spacing. I have attached a link to the report below. For the MGS we would recommend the same base plate and anchorage design with slightly longer posts. We believe that the ½ post spacing would need to be retained as well. Further research could be done to investigate/develop more options with the MGS and this attachment design.

 

http://mwrsf.unl.edu/reportresult.php?reportId=144&search-textbox=culvert

 

We do not have any wood post version of these systems. Take a look at the above systems and see if they meet your needs. We can provide further guidance if you need it.



Tolerances for Timber Posts

Question
State: WY
Date: 05-31-2013

What should the tolerances be for timber posts and block outs? For example, the standard barrier guide shows in the drawings a 6"x8" posts as a 6" x 7 7/8" with a tolerence in the direction parallel to the bolt of 1/4 inch, presumably applied to 7 7/8" dimension. No tolerence is indicated for the width dimension of 6". Does this mean it must be 6 inches exactly? Likewise, what should be the tolerences for an 8" round post?

Response
Date: 06-03-2013

First off, I believe the drawings for a timber post should read 6" x 8".  Back in the older guide (1979) the dimensions were listed as 6"x8".  During the metric conversions into the 1994 Guide, the section was converted to a 150mm x 200 mm post through a soft conversion and rounding.  Now, in going back to US Customary Units, someone has converted the 200 mm to 7.87", or 7 7/8".  Thus, two conversions (and rounding twice) has resulted in the 7 7/8" dimension.  I high doubt that this 1/8" difference is going to cause issues, but I thought that the 7 7/8" dimension was a bit silly when the rest of the dimensions for the post are in whole integers.

 

As far as the tolerance issues, a tolerance of 1/4" was specified for the depth of the post because it has a far greater impact on post bending strength than the width of the post does.  Thus, this tolerance was set to hold the strength of the post and prevent premature fracture.  A larger tolerance window may be acceptable for the post width.  However, you don't want to alter the width too far from 6" as this will result in a change to the post-soil interaction forces.  Some states have adopted the 1/4" tolerance for both the depth and the width of a timber post.  You may choose to do this as well, or loosen the tolerance as you see fit.

Concerning round timber post, the 1/4" tolerance can be used for the post diameter in the same manner as the rectangular post depth.  It should be noted that under sized diameters are far more critical than oversized diameters because of the possibility of fracture.  Thus, timber posts with diameters greater than the upper tolerance window are far less of a concern than posts with smaller diameters.  I believe the MGS round timber post report (TRP-03-179-07) describes this in more detail. 



Guardrail connection to low fill culverts

Question
State: NE
Date: 02-14-2013

TRP-03-114-02

 

 

This research shows the guardrail connection to Low fill
culverts.

The posts connected to the culvert are half-spaced.


The diagram of tested guardrail shows 6 – half-spaced posts
prior to and beyond the culvert.


Is this half-spacing required for this full distance? Or can
we start the half-spacing at the culvert?




 






Response
Date: 06-04-2013

I had a significant amount of discussion on this issue with the Kansas DOT and have been providing feedback on their CAD details. When the KsDOT details are complete, I had planned to send them to the Pooled Fund members for discussion. There is a lot of history on the half-post spacing issue for metric-height rail. The KsDOT details were extended to MGS where half-post spacing is typically used.



I have enclosed some of our prior correspondence between MwRSF and KsDOT on the MGS attached to culvert slabs. I also accessed the KsDOT standard details and attached the two most current plans on this matter. Let me know if you have further questions after reviewing the prior email discussion. Thanks!

Attachment: https://mwrsf-qa.unl.edu/attachments/8642fdd6760804bd3042d79aa7ff2df4.zip


TCB Transitions to Permanent Barriers

Question
State: IA
Date: 06-10-2013

I have the following questions regarding TCB transitions to permanent concrete barriers/bridge rails:

1. In the tested median configuration, the thrie beam rails were attached to the first TCB section such that the front-side end shoe was located 45-1/4" from the end of the TCB section. Regarding the general placement of these thrie beam rails, could you provide a minimum and maximum recommended overlap distance for the rails to be installed onto the TCB section? i.e., how close to each end of the TCB section can the thrie beam rails be attached? Consider that Iowa specifies the use of 6'-3" long thrie beam rails in some cases.

2. When is it necessary to install additional anchor bolts at the midpoint of the nested thrie beam rails? These bolts were present in the median testing but not in the roadside testing. If these bolts are necessary, must they engage the TCB section, or can they engage the permanent barrier instead? Must these bolts be located at the midpoint of the thrie beam rails, or could they be shifted upstream or downstream some distance (to the next set of rail slots)? Would these bolts be necessary when using 6'-3" thrie beam sections?

3. For the median transition, would it be acceptable to use a 2-inch thick asphalt pad that extends 24 inches behind the TCB instead of the as-tested 3-inch pad? Thanks!



Response
Date: 07-01-2013

 

I have the following questions regarding TCB transitions to permanent concrete barriers/bridge rails:

 

1.       In the tested median configuration, the thrie beam rails were attached to the first TCB section such that the front-side end shoe was located 45-1/4" from the end of the TCB section. Regarding the general placement of these thrie beam rails, could you provide a minimum and maximum recommended overlap distance for the rails to be installed onto the TCB section? i.e., how close to each end of the TCB section can the thrie beam rails be attached? Consider that Iowa specifies the use of 6'-3" long thrie beam rails in some cases.

 

In the design and testing of the TCB to median barrier transition, MwRSF selected a 12'-6" long thrie beam to connect across the joint to provide increased stiffness and reduced the potential for vehicle snag on the edge of the concrete barriers. The 12'-6" section was chosen because it was more common and would fit across a wide variety of barrier sections.

 

With regards to placement of the thrie beam rail, we would prefer that it be centered over the joint when using the 12'-6" thrie beam section. This provides for more even load distribution over the joint between barrier types. 

 

We do believe that a 6'-3" thrie beam section can be used in lieu of the 12'-6" section. The shorter thrie beam should not adversely affect the joint stiffness and may improve it slightly due to placement of the end shoe anchorage closer to the edges of the barriers. The 6'3" section may prove more difficult to flex to meet the TCB on the backside of the transition, but it should still be achievable. Because of the reduced length of the 6'-3" thrie beam, MwRSF believes that the section could be mounted with the end shoe closer to the edge of the permanent barrier and extending onto the TCB.  The end shoe anchorage would need to be placed inside the outermost stirrup on the permanent barrier. This would help reduce issues with flexing the beam to attach to the back of the TCB. We don't believe that we would want to offset the thrie beam closer to the end of the TCB section.

 

2.       When is it necessary to install additional anchor bolts at the midpoint of the nested thrie beam rails? These bolts were present in the median testing but not in the roadside testing. If these bolts are necessary, must they engage the TCB section, or can they engage the permanent barrier instead? Must these bolts be located at the midpoint of the thrie beam rails, or could they be shifted upstream or downstream some distance (to the next set of rail slots)? Would these bolts be necessary when using 6'-3" thrie beam sections?

 

We believe that the anchor bolts are needed at the midpoint of the thrie beam rails to increase the stiffness of the joint across the barrier types. Recall in the roadside testing, we evaluated a system that had similar shapes and a TCB connection pin in place. Thus, the stiffness of the joint was not as critical. For the median transition, we have differing barrier shapes between the TCB and permanent barrier and no connection between them other than the thrie beam.

 

We would recommend that the anchorages engage the TCB section as it is the more flexible part of the system.

 

We would not recommend shifting these bolts away from the tested location a significant distance. Changing the location from the joint between the barrier systems would change the stiffness of the joint. We would recommend that they be used with the 6'-3" section. Thus, this may require an additional hole to be fabricated in the shorter thrie beam section.

 

3.       For the median transition, would it be acceptable to use a 2-inch thick asphalt pad that extends 24 inches behind the TCB instead of the as-tested 3-inch pad?

 

Two inches of asphalt should be sufficient rather than the three inch pad. Previous component testing of the asphalt pins found little difference between the forces developed in 2 or 3 inches of asphalt.



MGS median barrier

Question
State: OH
Date: 06-10-2013


With our previous strong post guardrail system, we had a median barrier version for depressed medians  with a rub rail on the median ditch side for use on slopes up to 6:1:

http://www.dot.state.oh.us/Divisions/Engineering/Roadway/DesignStandards/roadway/Roadway%20Plan%20Insert%20Sheet/GR_5MR.PDF

Any red flags as to why we couldn't shouldn't do a version of this with MGS?


Response
Date: 06-11-2013

There are a couple of concerns related to applying this median guardrail design to the MGS.

1.       The MGS was approved for use with a median barrier configuration. However, that approval did not consider the use of rub rail. No research has been done regarding 31-in. tall guardrail and rub rail combinations to the best of my knowledge. Therefore the effect of the rub rail on the performance of the MGS is unknown. In addition, rub rails, used in combination with thrie beam transitions, have not been met with a high degree of success when evaluated by large pickup truck impacts. Thus, we would be hesitant to recommend rub rails with the MGS without further study.

2.       The MGS median barrier is currently only approved for 10:1 slopes or flatter. Use of the barrier on steeper sloped medians would likely require further study.

3.       In the past several years, we have done a considerable amount of work looking at the placement of cable median barriers in sloped medians. The lessons learned from this work would also apply directly to other barriers used in sloped medians, such as guardrail or the MGS median barrier. Thus, placement of the barriers in these situations is critical and would need to consider ditch width and the resulting vehicle trajectories as well. We know that placement of an MGS median barrier is limited down the slope based on previous work done on the MGS with 8:1 approach slopes. Thus, the barrier would likely need to be placed adjacent to one side of the median. Next, one would need to consider potential vehicle trajectories relative to the barrier for various ditch widths and vehicle types. This could lead to concerns for vehicle underride or override depending on the scenario. Application of the rub rail might help mitigate the underride issue, but would not address the override issue. Thus, further consideration of barrier placement, slopes, and median width are likely needed before recommending the use of the MGS adjacent to steep v-ditches.

 

Let me know if you have further comments or concerns.

 


Attachment: https://mwrsf-qa.unl.edu/attachments/ada2aab3a3d3f939b9dc064d6c2077e6.pdf


Guardrail Placement in a Cut Area

Question
State: IL
Date: 10-04-2010

Here is a question that has been posed to me by a designer in one of our Districts. They want to minimize cut of the existing back slope (virtually not touch it), while squeezing in a curb and guardrail along the roadway. This results in the earth slope rising steeply behind the curb and within the deflection space of the guardrail system.

I am suggesting to them to use a concrete barrier, if a barrier is needed here.

However, can you see any way the guardrail might work? I think this probably is not possible because the increased embedment of the posts would lead us to a shorter post in order to compensate for the increased fill. However, there is not room for deflection before encountering the back slope and the deflecting system will be interfered with by that slope. Also, the vehicle itself will encroach into the back slope area, contributing lifting and/or snagging potential.

Attachment: https://mwrsf-qa.unl.edu/attachments/fa18d95533e003dd793697416c139003.jpg


Response
Date: 10-05-2010
Both the 1:1 and 1.5:1 cut or back-slopes on the upper side of the road would be potentially hazardous and provide an increased propensity for impacting vehicles to climb the unprotected slope and result in vehicle rollover. As such, your group has accurately identified the need to shield the hazard if it cannot be removed, flattened, etc. assuming traffic volumes, speeds, other factors, etc. warrant shielding it.

Placing a standard MGS directly in front of the steep slope would result in the impacted vehicles contacting the slope under the rail as the barrier deformed backward. The guardrail system would likely be more stiff as the built-up soil would provide increased soil resistance for the steel posts in addition to that already provided by the increased fill height located behind the curb section. The back side of the guardrail system would also likely make contact with the back-slope as it deformed during the high-energy impact event.

Although there would exist the possibility for this system to perform in an acceptable manner, full-scale testing would likely be needed to demonstrate satisfactory performance for the MGS with a back-slope starting under the rail and at the post locations. If 12 in. of clear and level terrain (33 in. from rail face) were provided behind the posts, I think the system would likely perform in an acceptable manner with the adjacent 1:1 back-slope shown in the plans.

Unfortunately, it does not appear as though the clear and level terrain can be provided behind the guardrail system. For such situations, it may be necessary to utilize a more rigid barrier system at the base of the back-slope.


Response
Date: 06-11-2013
Could you provide guidance for flatter backslopes?  Would the same 12-inch offset behind the posts be recommended for 3:1, 4:1, 6:1, 8:1 backslopes?  Or at some degree of slope, could the toe of the slope be located closer to the post or face of rail?

Response
Date: 09-12-2014


Extra splice bolt

Question
State: OH
Date: 06-24-2013



Do you think it's OK to leave in this added bolt on the
splice for MGS? The installers put this bolt in first to help line up the
panels.




Attachment: https://mwrsf-qa.unl.edu/attachments/5ee2ac4a489bf0085cfc1dc0d7245b57.jpg

Attachment: https://mwrsf-qa.unl.edu/attachments/346cee68b0a842cfe2c985aae52b3191.png


Response
Date: 06-24-2013

There should be no issue with leaving that bolt in place.



Steel Post, Downstream Anchorage for MGS

Question
State: MN
Date: 06-27-2013



We are looking for an all steel post downstream anchorage
for the MGS system.  We've looked for an all steel anchorage in other
States Standards (including Ohio, Iowa, Wisconsin, Washington, and Texas)
 but found that their anchorages contain at least one wood post.  Is
there a tested MGS anchorage that contains all steel posts?



 



Thanks for your help.





Response
Date: 06-27-2013

To the best on my knowledge there are no steel post downstream anchor systems outside of proprietary end terminal designs. We have not developed such an anchorage for the MGS due to concerns for infringing on existing steel breakaway post patents.