AASHTO Braking Loads in Standard Specs

Question

AASHTO Braking Loads in Standard Specs

OSUCivlEng (Civil/Environmental)

(OP)

31 Oct 23 20:05

I am doing some analysis of a bridge that was designed in 1961 and am trying to understand the braking loads that were used for design at that time. I have the 17th edition of the standard specs and it states to use 5% of the live load for the longitudinal force. I dug up the 5th edition from 1949 and it states the same thing, so it doesn't appear that this load changed much in 50 years.

Does anyone have access to the 7th edition, which was published in 1957? My hunch is that it is exactly the same.

Thanks

bridgebuster (Civil) · Answer 1 · 2023-11-01 11:06:06

I have the ‘57 AASHO. When I get home tonight I’ll check.

BTW - did you find the 49 version on line? I used to have the 44 and 49 but they grew legs.

OSUCivlEng (Civil/Environmental) · Answer 2 · 2023-11-01 13:50:33

Thanks bridgebuster. Yes I did find the 49 version online at Scribd.

bridgebuster (Civil) · Answer 3 · 2023-11-01 14:40:28

You're welcome. I'll take a look at Scribd. I have all the AASHO/AASHTO's from 1953 on in hard copy. I would like to find 44 & 49 to complete the collection. You would think that AASHTO would make these available but they don't. I recall at one time they were selling a PDF of the 35 specs but the price was outrageous.

bridgebuster (Civil) · Answer 4 · 2023-11-02 00:03:20

RE: AASHTO Braking Loads in Standard Specs

bridgebuster (Civil) 2 Nov 23 00:03

BridgeSmith (Structural) · Answer 5 · 2023-11-02 04:05:13

It looks like all that changed is the height above the deck where the load is applied. Although, I've never figured out why it matters; Maybe for integral leg piers?

OSUCivlEng (Civil/Environmental) · Answer 6 · 2023-11-03 20:38:10

Quote (BridgeSmith)
It looks like all that changed is the height above the deck where the load is applied. Although, I've never figured out why it matters; Maybe for integral leg piers?

Some use that distance, 4' then, 6' now, as a moment arm for the braking load, and apply a moment to the top of the pier.

OSUCivlEng (Civil/Environmental) · Answer 7 · 2023-11-03 20:39:22

Thanks Bridgebuster. There was not change to the braking load between the 5th and 7th edition.

BridgeSmith (Structural) · Answer 8 · 2023-11-03 21:43:00

Quote:
Some use that distance, 4' then, 6' now, as a moment arm for the braking load, and apply a moment to the top of the pier.

Yeah, I suppose that would be the proper way for a pier that's integral with the superstructure, and since it would be added to the vertical live load, it could be part of a controlling load case.

bridgebuster (Civil) · Answer 9 · 2023-11-03 22:45:08

RE: AASHTO Braking Loads in Standard Specs

bridgebuster (Civil) 3 Nov 23 22:45

You’re welcome OSU.

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AASHTO Braking Loads in Standard Specs