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Roadway is in the process of adapting a Texas SSCB for median applications. I’ve attached the original Texas plans and the adapted plans we’re building.

NDOT widened the barrier by 4 inches (top and bottom) to accommodate Nebraska lighting fixtures without having to interrupt the slipforming process, as I understand it. Do you see any issue with this? My judgement is that it’s increasing capacity if all else is held constant, but I could foresee an issue where the increased stiffness of the barrier makes any impacts play out differently than the originally crash-tested configuration. Essentially, how extreme do modifications need to be before an appurtenance needs to undergo new testing?

Additionally, we were discussing running yield-line calcs on the updated barrier to have a record of capacity. Do you think that’s beneficial or is it superfluous? I’m not sure it’s necessary given that barrier crashworthiness is evaluated by testing and not by calcs.

Any perspective you can offer would be appreciated.

Thanks,

The NDOT proposed barrier will work fine as shown.  There is no need for further testing or evaluation.  The TxDOT barrier was already a MASH crashworthy barrier, and you only increased the strength of a rigid barrier system.

Here is a listing of references for 42” tall Single slope tested to MASH:

Bligh, R.P., Menges, W.L., Kuhn, D.L., MASH Evaluation of TxDOT Roadside Safety Features-Phase I, FHWA/TX-17/0-6946-1, Texas Transportation Institute, College Station, TX, January 2018.

Sheikh, N.M., Griffith, B.L., Kuhn, D.L., MASH Test 4-12 on Keyed-In Single-Slope Barrier with 40-ft Segment Length, 610221-01-1, Texas Transportation Institute, College Station, TX, October 2018.

Williams, W.F., Sheikh, N.M., Menges, W.L., Kuhn, D.L., Bligh, R.P., Crash Test and Evaluation of Restrained Safety Shape Concrete Barriers on Concrete Bridge Deck, FHWA/TX-15/9-1002-15-3, Texas Transportation Institute, College Station, TX, January 2018.

There may be more references for the TxDOT single slope within the following report:

https://mwrsf.unl.edu/researchhub/files/Report495/TRP-03-454-24.pdf

We’re still wrestling with this Texas SSCB anchorage. The #6 rebar at 8’ centers is giving us pause because we don’t know how Texas’ epoxy adhesives compare to what we use and because according to TRP-03-454-24, that anchorage configuration was only tested at TL-3 in a transition barrier to the 42” SSCB. We are looking at adapting Iowa’s SSCB anchorage of 2-#8 post-installed rebar at 2’ centers, but we’re waiting to hear back from them regarding how they came by that configuration. I attempted a yield line calculation but based on the adhesive anchorage calculations from ACI 318-19, I can’t get it to pass on the end segment. I’m also a little leery of using calcs to justify a configuration that hasn’t been crash tested.

Do you have any advice or resources that could help us here? Any crash tested TL-4 post-installed anchorage configurations we might be able to piggyback on? We’re also considering the asphalt key-in configuration but I don’t know how our roadway folks will feel about that.

Additionally, Texas’ calls out continuously reinforced concrete pavement. We don’t use reinforcement in our pavement – do you think that affects the anchorage at all?

Any help you can provide would be deeply appreciated.

Thanks,

First off, MwRSF currently has 2 concrete barrier projects within the Pooled Fund program.  The first is dealing with quantifying the effects of inertia and torsion on the strength of a concrete median barrier.  The second has component testing to compare the anchorage strengths of doweled anchors and shear keys.  These projects are just getting started, so we wont have the answers for a couple of years.  This won’t help you right now, but I figured I would let you know that the questions you are asking have been an issue in barrier design for some time and we are finally getting a chance to address them.  Honestly, I think we finally got the Pooled Fund to go after these projects due to TRP-03-454-24 having a lot of “uncertain” conclusions due to anchorage concerns.

TxDOT has tested their doweled anchorage configuration at TL-4 in a newer crash test – link below.  This is a flared median installation for overhead sign/luminaire supports, so it is not a direct comparison.  However, I do feel that it is relevant.

https://www.roadsidepooledfund.org/wp-content/uploads/2022/02/TRN0611901-06-Final-1.pdf

There is also nothing wrong with increasing the amount of dowels (tightening the spacing between dowels) to increase anchorage strength.  8-ft centers is pretty far apart.  Many DOTs use something more like 18”-24”, at least for interior sections.

As for the strength of the end section, you may consider utilizing an end section design where the vertical bars are extended/embedded into the supporting slab/foundation – similar to a bridge rail.  Doing so over the outer 6-8 ft is pretty common to ensure end section strength.

As for the strength of anchors in unreinforced concrete, there may be a reduction in strength as compared to a reinforced pavement.  Steel bars help to prevent concrete breakout, and I believe there is a strength factor to help account for this in Chapter 17 of ACI 318.  The strength increase is far more prominent when the rebar are running in the same direction as the anchors (vertical in your anchorage case), but even horizontal bars would provide additional strength against concrete failure.