Traffic barrier on MSE Wall
Traffic barrier on MSE Wall
(OP)
I have seen previous posts about MSE walls with barriers, but I still need clarification.
Currently, Caltrans requires the use of BDS LFD for MSE wall design in lieu of AASHTO LRFD. Caltrans requires designing the moment slab and top row of MSE reinforcement for traffic impact. However, it is unclear what this impact force should be, or how it should be distributed. The 54 kip load seems way too high, but I can't find anything about the 10 kip load from AASHTO in Caltrans BDS. All I can find is the 1.9 k/ft load for the top reinforcement (BDS 5.9.3.8.2), which still seems too high. I checked the standard XS sheet barrier slab overturning with the 1.9 k/ft load, and it doesn't work.
If anyone has an idea about what loads to use for 1) the moment slab, 2) pull-out, or 3) reinforcement tension, and where these are specified, I would appreciate it.
Thanks!
Currently, Caltrans requires the use of BDS LFD for MSE wall design in lieu of AASHTO LRFD. Caltrans requires designing the moment slab and top row of MSE reinforcement for traffic impact. However, it is unclear what this impact force should be, or how it should be distributed. The 54 kip load seems way too high, but I can't find anything about the 10 kip load from AASHTO in Caltrans BDS. All I can find is the 1.9 k/ft load for the top reinforcement (BDS 5.9.3.8.2), which still seems too high. I checked the standard XS sheet barrier slab overturning with the 1.9 k/ft load, and it doesn't work.
If anyone has an idea about what loads to use for 1) the moment slab, 2) pull-out, or 3) reinforcement tension, and where these are specified, I would appreciate it.
Thanks!





RE: Traffic barrier on MSE Wall
RE: Traffic barrier on MSE Wall
I've read some literature about this, particulary about how the 54 kip load doesn't make sense for designing using pseudo-static method. It ends up requiring a very long and heavy moment slab to resist overturning. Obviously, when you consider stability, the barrier isn't going to fall off the wall if a truck hits it.
Anyway, how did you distribute the 54 kip load? And did you assume some transfer to the wall through friction?
RE: Traffic barrier on MSE Wall
RE: Traffic barrier on MSE Wall
Thanks for your help!
RE: Traffic barrier on MSE Wall
RE: Traffic barrier on MSE Wall
I've checked the reinforcement tables Caltrans released for MSE wall design, and they don't account for traffic barrier impact load. The first level of MSE wall reinforcement in their tables isn't strong enough, and the 1.9 k/ft load the code suggests for top reinforcement due to barrier impact is pretty high. So I'm in limbo now as to how to interpret the loads for a reasonble design. And this project has about 7 MSE walls.
I actually put this question into two forums as well, with no bites except yours!
RE: Traffic barrier on MSE Wall
RE: Traffic barrier on MSE Wall
What constitutes a "correct design" isn't readily apparent to me. Even basic things challenge me like "path of the forces" and "distribution width". Is a proper design published anywhere?
RE: Traffic barrier on MSE Wall
RE: Traffic barrier on MSE Wall
Also, I do recall seeing a recent paper on the internet regarding this specific issue. I don't have it right now, otherwise I'd attach it.
RE: Traffic barrier on MSE Wall
RE: Traffic barrier on MSE Wall
meicz - Yes. I think the idea is that some of the 54 kip load will be transferred to the barrier slab along a length.
In my research, I found the article "Design of roadside barrier systems for MSE retaining walls," which discusses this issue. However, that article assumed transfer over a 6m length (distance between joints in the slab), and Caltrans does not allow joints in the slab.
In the end, I used the barrier slab shown on the standard sheet, which *sort of* works for the load indicated in the article (10 kips over 20 feet). However, I can find no documentation of this in the code, although I believe it was an old AASHTO standard.
RE: Traffic barrier on MSE Wall
Or type this into your search engine: Design of roadside barrier systems for MSE retaining walls. Also get a hold of an old FHWA publiction for MSE Walls. I can't remember the pub No. I believe Reinforced Earth also has some guidelines. There is a guideline book for segmental walls that all proprietary wall systems have to follow. Try that.