Barrier Wall Impact Loading

[SE2B]

I have been told to use a 124 kip impact load perpendicular to the plane of the wall for the design of a barrier wall required to protect the toll booth. My issue is that the lane size is restricted and I don't see how a vehicle could create a 124 kip load. I would believe it if I could use total load of 124 kips and a skew angle of like 15 deg and would have a approx. 30 kip load perpendicular and 120 kip in the plane of the wall. Does anyone have any thoughts or any info? It would be much appreciated. Thanks

 

[JAE]

This seems high to me in any case...have you checked how this compares with the AASHTO barrier design criteria?

 

[40818]

Who has told you to use the 124kip value? Sometimes you wont be aware of all the reasons for carrying out design or analysis for a particular project. You have your instructions, and as such you should continue to carry them out, but raise your query with the person whom instructed you. The value does seem high, but your boss might be aware of rationale that will require the design to be satisfactory above and beyond the immediate requirements, such that future-proofing might be going on, or maybe just a layer of safety factors being applied. In anycase, raise your query, but continue with the instructions, if anything the results will be conservative so i wouldn't loose sleep, if the load where extremely light then you would be more worried.

 

[shin25]

It seems at the toll booth, a collision will involve number of vehicles. If the impact is with the barrier, then the momentum from these vehicles should transfer to the barrier. Does this seem like a valid reason for this high design force?

 

[msquared48]

You are not looking at normal vehicles here. Look at a 10 yard concrete truck, fully loaded, in the order of 70 kips having his brakes fail doing a minimum of 30 mph for starters. I would hate to be in front of it.

Mike McCann
McCann Engineering

 

[SE2B]

I have been told to use that value from the my boss who has a fax from the DOT where it is written. There is no rational, just they just have this value written on a page from a book which says "Section 13: Railings" and someone wrote AASHTO LRFD on it. They did also write to consider this a "TL-5: Test Level Five," whatever that means exactly. I can't locate this book at the office if we even have it. My boss does thinks it is high as well and we have limited space to put this barrier wall. If I had the room, I would just design it and be done. Does anyone know what book I am talking about? Thanks.

 

[MarcbSE]

I have had plenty of dealings with DOT's and have often run into similar situations. The DOT has its own guidelines and design requirements they have developed over the years that you don't have any choice but to follow if it is a DOT funded project.

 

[csd72]

What if a guy in a concrete truck falls asleep travelling 60mph while approaching the toll gates?

A similar thing happened in connecticut, many people died, and it is the reason why there are no tolls on roads in CT.

If I spent 8 hours a day in one of those toll booths, I would expect the barriers to take anything that could happen, not just the likely occurences.

Stick to the 124k, probably wiser people than you have come up with it.

 

[jdonville]

SE2B,

The book is AASHTO LRFD Bridge Design Specifications, Customary U.S. Units, 4th Edition (link follows)

https://bookstore.transportation.org/item_details.aspx?ID=879

If you are doing DOT work and plan on doing more, this is the main design Bible.

Jeff

 

[msquared48]

I just talked to my friend today who is a concrete mixer driver, and, aside from the mixer weight previously mentioned, he referred to a fully loaded semi at 110,000 pounds. The previous value is not unreasonable at all, in fact, maybe a little conservative considering an impact factor of 1.5.

Mike McCann
McCann Engineering

 

[SE2B]

Thanks everyone for the info. Much appreciated.