1900 Bridge Design 8

[TobyT]

I'm working on the reconstruction of an historical bridge that was built in the late 1800's (two lane roadway). I'm curious about the live load that might have been used for design at the time it was built?

Thanks.

 

[Dinosaur]

This is a long time ago. The highway loading model used today (in LRFD) is an adaptation of the previous model named the HS20-44 loading. The 44 stands for 1944, when the load model was adopted. The interstate system is the brainchild of President Eisenhour who upon returning from WWII thought a modern highway system in the US could improve the economy and military preparedness. So among the precursor legislation to the interstate system was the National Defense Highway Act. This established minimum loadings and geometric standards for the Interstate system based in part on the requirements for the military. THe minimum loading of a bridge is based in part on the weight of a tank on a low-boy trailer. The clearance of bridges is based on the size of some weapons.

You'll have to go back before 1944, and it may not be found in a national code. I also recommend you research the grade of steel used and the process used to mix and place the concrete. Many pre WWII projects involved a gang of men carrying the river gravel out of the streambed up on the bank where they mixed concrete on site and just poured it into forms, often unreinforced arches. Now, except for self consolidating concrete, everyone emphasizes "Concrete is Placed, no poured."

Good Luck

 

[TTK]

What type of bridge is it?

If it is a metal truss and you can identify the manufacturer by a plaque on the bridge or other historical documents then you may be able to determine their standard design loading.

For example, almost all of the lenticluar truss bridges were designed and built by the Berlin Iron Bridge Company in Berlin, CT and there is very good historical info available on their design specifications.

If you can, try to provide more info on the bridge and/or the original designer.

 

[TobyT]

It's a steel arch - single span bridge.
Don't know the designer.

 

[TTK]

How do you know the age?

Is it on the local or national historic register?

If so, the application forms may have information on the designer and possibly the design specification used.

 

[crossframe]

AASHTO will be of little help, as it was formed in 1914 and the first edition of bridge design specifications wasn't issued until 1931. That first specification cited H-10, H-15, and H-20 Truck Trains (which were based on Cooper Loading for railroads) and introduced lane loading. This truck train idea may give a hint into the typical design procedure of the time. Maybe this was still in place in the late 1800's.

What about looking at other, better-documented bridges of the same time period? You may be able to see common live load approaches.

You may want to consider doing a (Working Stress) rating. At least in that way you can model the live loads in accordance to its intended or expect use.

 

[Qshake]

A book that I have on Bridge Engineering dating to 1897 by the International Correspondance Schools, Scranton, PA does not list a live load but only details dead load calculations. The examples listed in the book are for truss bridges. They present a formula for caculating the weight of the bridge per panel based on a 100 pounds per square foot loading - I would assume so that the 100 can be factored later on if the weight goes up or down.

Waddell (1925) notes that highway bridge live loads were first assumed to be around 100 pounds per square foot and increased as engineers saw fit. Waddell further explains the nature of such live loads: gathering people, cattle, lorries etc.

Based on my reading of Waddell I believe that live load was treated on a case by case basis and generally measured and then applied without the benefit of statistical increases/decreases.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[oldrunner]

I have a book called "Design of Steel Bridges" by F.C. Kunz, C.E., dated 1915. He suggests loads from 100 psf ("which represents a crowd so closely paced as to be unable to move, a condition which is impossible over the whole width of a bridge,...")and other combinations.

(This did happen a few years ago on the Golden Gate Bridge and took the camber out of the road)

The book discusses varies other loads, starting with wagons drawn by horses and provides a interesting chart.

Other parts of the book discuss live load distribution and Chapter VII-B discusses plank flooring, pavement flooring and then stringers and floor beams.

This was not one of my textbooks in college, although I did get bridge design in an architectural-engineering curriculum.

Google the book name and author and a lot of hits come up.

I've worked on some old bridges and they are always a challenge. Good luck.

 

[eureka]

I have a copy of "Structural Engineers Handbook" by Milo S. Ketchum, 1918 edition. It has an 11 page "Gerenal Specifications for Steel Highway Bridges" If you will post a FAX number, I will copy it and sent it to you.

 

[bridgebuster]

The book by Kunz can be downloaded at

http://library.case.edu/ksl/ecoll/books/kundes00/kundes00.pdf

 

[SlideRuleEra]

"eureka" has kindly provided the referenced information from Milo S. Ketchum's 1918 "Structural Engineers' Handbook". I have posted it (in zipped .pdf format) near the top on my website home page (link below).

Have also posted "bridgebuster's" referenced link to "Design of Steel Bridges" (1915) by F. C. Kunz.

http://www.SlideRuleEra.net