Help understanding structural steel strength from existing bridge plans
Help understanding structural steel strength from existing bridge plans
(OP)
I need to analyze an existing girder to determine if it can support an additional load my client wants to be placed on it in the form of a new larger concrete barrier wall. My existing plans are from 1971 and the bridge inventory says the bridge was built in 1973. The design data from the existing plans indicate the following "Structural Steel: ASTM A36, Unit Stress 20,000 psi". I thought that if it was called out as "ASTM A36" this indicated that the yield strength was 36 ksi, is this incorrect? In addition, the "Unit Stress 20,000" has me confused, what does this mean? Any information would be greatly appreciated.






RE: Help understanding structural steel strength from existing bridge plans
Allowable stress values are not the same in AASHTO as they are in AISC, and are always lower. The plans are stating that allowable bending stress used was 20 ksi (vs 24 ksi in AISC for buildings)
RE: Help understanding structural steel strength from existing bridge plans
A bridge designed in 1971 would fall under provisions of the AASHO Standard Specifications -10th edition (1969).
RE: Help understanding structural steel strength from existing bridge plans
RE: Help understanding structural steel strength from existing bridge plans
RE: Help understanding structural steel strength from existing bridge plans
RE: Help understanding structural steel strength from existing bridge plans
RE: Help understanding structural steel strength from existing bridge plans
You could take coupon samples from the girders - carefully located to avoid any fatigue issues going forward - and test them to see what is actually there.
This costs money, and time, and may not end up getting you much - but like I said - if you are desperate to get something to work.
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RE: Help understanding structural steel strength from existing bridge plans
Who does/did the bridge belong to, who was it built for? If it was build for any gov’mt. agency they may have a treasure throve of info. in their bridge files, including mill certs. for the materials for critical components, calcs., design drwgs. and shop drwgs., and the like. Who was the bridge designer, an who fab’ed. the bridge, they may have some files, probably no longer on the front shelf, of course. I agree with JAE that the actual yield strength is very likely greater than 36ksi, which was the guaranteed min. yield strength for that ASTM Spec., but you must test almost every critical mat’l. piece unless you can be assured that all of the mat’l. came from the same melt, and same mill order, which is unlikely. Could you shore the girder while the wall is being built, and design the wall as a deep beam, to do part of its own spanning and DL carrying, thus lessening the added load on the old girder? Maybe even post tension the wall as its own girder.
RE: Help understanding structural steel strength from existing bridge plans