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As you may be aware, as part of a new AASHTO requirement (attached) we will be required to assign codes to bridge rails and transitions during the upcoming 2024 inspection cycle. While we’ve been able to document many of the common and many of the more obscure bridge rails in use on State bridges in Iowa, we know there are quite a few other types in use on local systems structures throughout the state.

We may receive some training from FHWA later this year to further inform the coding process, but there will still be some decision-making that will fall on the States as far as what meets our own “approved agency standards”. Guidance from UNL/MwRSF is key for us in determining what our comfort level is with some of the more obscure devices we may encounter.

One of the most troubling rail types to code in accordance with the new AASHTO requirement is timber rails. See the 2^nd attachment for some examples I’ve found used in Iowa on bridges the State maintains. These rails are typically found on very low volume, low posted speed roads, often in state parks or similar remote contexts. I am looking for any resources I can find that might help us code these rails.

I found TRP-03-31-93 which gives some indication of timber curb heights (14 inches and taller) that may have acceptable performance, but don’t know if I can extend any of that to any of the rails we have. The timber rails I’ve identified as Types 1, 2 and 3 in the attachment bear some resemblance to the tested curbs in that report, but I’m not sure if we can draw any conclusions from that. Any advice you could extend to us would be helpful. Also, if you know of any other timber rail research or resources against which we might compare rails in Iowa, please point me to them.

No rush on this. Thanks for any help you can provide, but absolutely no worries if there’s nothing available.

We can assist in the future as we have had a fair amount of experience developing railings for timber deck bridges. To help give some background, I will share a few links to relevant reports. Note that I did not receive any attachments so cannot see what systems that you have found in rural county roads.

https://mwrsf.unl.edu/researchhub/files/Report477/TRP-03-467-23-R1.pdf

https://mwrsf.unl.edu/researchhub/files/Report383/TRP-03-429-20-R1.pdf

https://mwrsf.unl.edu/researchhub/files/Report473/TRP-03-465-23.pdf

https://mwrsf.unl.edu/reportResult.php?reportId=70&search-textbox=timber

https://mwrsf.unl.edu/researchhub/files/Report116/TRP-03-31-93.pdf

https://mwrsf.unl.edu/researchhub/files/Report181/TRP-03-54-96.pdf

Would it help to have a Zoom call to review and discuss what you have observed?

Thanks!

Thanks for the info. I will look more closely into these resources next week. In the meantime, the documents I originally sent are attached. A few of the timber rail types we know are in service on our system are illustrated therein.

Here are a few quick thoughts and assuming that robust connections exist between rail elements.

Type 1 – Pickup truck will likely override at TL-1 and TL-2. Uncertain if sufficient rail strength.

Type 2 – Need at least 19.75” for TL-1 at contact point of rail (midpoint) to vehicle and 20” to 24” for TL-2. Override likely as show.

Type 3 – Same comments as Type 1.

Type 4 – Seems to be a nice aesthetic handrail but will not meet geometric criteria to prevent people from falling through or over.

Type 5 – Aesthetic handrail with large openings for pedestrians.

Type 6 – A more robust aesthetic handrail as shown without details but could be configured to be TL-1 and TL-2 with changes. Suggest viewing AASHTO PL-1 and PL-2 systems, NCHRP 350 TL-2 and TL-4 systems, and other systems documented in the reports sent previously.

Thanks!

Thanks again for all the great reference information for timber rails, and for making brief evaluations of the 6 timber rail types we’ve already identified in Iowa.

As far as we know, FHWA won’t be requiring us to update or amend any rails based on the new AASHTO Subsection 2.3 code that is assigned, at least not in the near term. We also don’t know what additional guidance will be provided by FHWA on how to code rails, especially those that haven’t been crash tested.

I’m again looking at TRP-03-31-93 and wondering how the timber rails we’ve found in Iowa might fare if impacted by a pickup truck at 15 MPH at 15 degrees as performed on the timber curbs in that study. As I mentioned to Bob, these rails probably see that kind of very low-speed traffic in many cases. In fact, some bridges with these timber rails are so narrow it would likely be impossible to strike the rail at as much as a 15-degree angle, except at the entrances. If we could assume robust connections, both to the bridge and between the various rail components, do you think any of these would perform satisfactorily under those circumstances?

Types 2 and 3 would have potential for the sub-TL-1 condition. I do not have much confidence with the other 4 systems.