PPM 20-4 Loading

[OSUCivlEng]

I keep seeing this design loading on bridge plans from the late 60s and early 70s. I've been told it was similar to a tandem axle load, but I can't find any references for it anywhere. Any help would be appreciated.

 

[bridgebuster]

I believe it's the alternate loading two 24K axles at 5'.

 

[bridgebuster]

OSU - I was slightly in error. It is the alternate load but the axles are 4' apart. Take a look at the attached. Section 3.2.0 has what you're looking for; its from an old California DOH manual, circa 1960. This was a loading by the Bureau of Public Roads. This morning I looked in the old AASHO's from the 50's, 60's and early 70's; there's no mention of alternate loading. It appears in the 83 AASHTO. I still have to dig out - literally - the '77 AASHTO to see if it's there.

The attachment is from a book left behind by an older man I worked with in the early 80's. He took a correspondence course on bridge design sponsored by CDOH in the 60's. When he retired he left the book behind. About 8 years ago my office was moving and we had to "lighten up". I scanned part of the book but never finished it.

 

[bridgebuster]

PPM = Policy and Procedure Memorandum. I found these blurbs in google Books:

https://books.google.com/books?id=HsvVAAAAMAAJ

United States. General Accounting Office - 1958 - ‎Snippet view - ‎More editions
PPM 20-4, page 2 August 10, 1956 b. ... Bridges supporting Interstate highways shall be designed in accordance with the current Standard Specifications for Highway Bridges of the American Association of State Highway Officials using the H20-S16(44) loading except that, to overcome known deficiencies in floor systems of bridges designed with such loading, all bridges and floor systems with spans under 40 feet shall be designed using an alternate loading of two axles four feet ...

https://books.google.com/books?id=JnFAF5SfyHQC

1972 - ‎Snippet view - ‎More editions
DEPARTMENT OF COMMERCE, POLICY AND PROCEDURE MEMORANDUM 20—4—AUG. 10, 1956 POLICY ON INTERsTATE sYsTEM PROJECTS Supersedes: PPM 20—4 (Aug. 4, 1954) 1. ... deficiencies in floor systems of bridges designed with such loading, all bridges and floor systems with spans under 40 feet shall be designed using an alternate loading of two axles four feet apart with each axle weighing 75 percent of the rear loading of the H20— 816 loading. (1. Designs ...

The alternate load was adopted by AASHTO in the 1976 Interim Specs.