Structural Analysis
Structural Analysis
(OP)
My company is looking at an existing steel structure to determine if it is capable of handling increased loading due to the heavier equipment being installed on the operating deck.
The steel structure was originally designed and constructed in the 70s using A36 steel, ASD design to the 7th edition steel manual. We have CMTRs for all of the steel used in the building.
We have run into a situation where we need to either reinforce certain beams under the new equipment per the analysis using fy=36ksi or sharpen the pencil in the analysis. When reviewing the CMTRs for the steel, the steel averaged > fy=42ksi. When using the CMTR reported yield strength of the steel we limited the number of modifications to the existing steel.
Any guidance on whether this is a code accepted practice? Do we need to do some form of destructive testing to verify the yield strength of the steel?
Thanks.
The steel structure was originally designed and constructed in the 70s using A36 steel, ASD design to the 7th edition steel manual. We have CMTRs for all of the steel used in the building.
We have run into a situation where we need to either reinforce certain beams under the new equipment per the analysis using fy=36ksi or sharpen the pencil in the analysis. When reviewing the CMTRs for the steel, the steel averaged > fy=42ksi. When using the CMTR reported yield strength of the steel we limited the number of modifications to the existing steel.
Any guidance on whether this is a code accepted practice? Do we need to do some form of destructive testing to verify the yield strength of the steel?
Thanks.






RE: Structural Analysis
RE: Structural Analysis
We want to use the reported minimum values less a small percentage for uncertainty.
Fortunately, budget is not a problem for this project... we could always take samples from the steel to prove the steel yields at a higher value than 36 ksi.
RE: Structural Analysis
RE: Structural Analysis
RE: Structural Analysis
For a nuke plant, I say reinforce.
RE: Structural Analysis
Part of the safety factor is that the steel will be stronger than Fy. For temporary structures I have used the tested Fy, but not for permanent.
RE: Structural Analysis
RE: Structural Analysis
RE: Structural Analysis
Running some new material tests so that you can take advantage of that extra strength seems like the most cost effective way to proceed.
You obviously don't want to cut any corners for nuclear work. But, this shouldn't be viewed as cutting corners. More like reducing the uncertainty from the original design....
RE: Structural Analysis
They do however allow the use of concrete cylinder test results. But you have to be very particual with this and gather all of the cylinder results for the area in question, then use the minimum. Atleast that is how I have seen it done.
RE: Structural Analysis
It may be that there is actually a statistical way to determine an applicable Fy which would be sensitive to the variability of the data.
I don't have a clue where you'd go to look for that statistical treatment of the scatter (i.e. to get a 90% confidence value based on the variability) - so to me - using 36 ksi would be my first choice anyway - or if I absolutely had to - use some value below 36 and the lowest test/coupon value. So if your lowest test/coupon was, say, 41.5 ksi, I'd perhaps use something like 38 or 39 ksi for Fy.
RE: Structural Analysis
and especially JAE's first post might also be of interest here.
RE: Structural Analysis
RE: Structural Analysis
RE: Structural Analysis
Sorry for stepping on your post, I didnt read it before I posted.
RE: Structural Analysis
I'd also tend to think that if you were designing to today's AISC code vs 1970's, there will be some inherent reserve capacity.
RE: Structural Analysis
This is actually the issue I'm running into because the NRC tells us that it is not in compliance with the AISC code if we use the CMTR for yield strength. I disagree with their approach, but then again this is a nuclear world where things are very different. Thank goodness this is just our turbine building that does not serve any safety functions.
We are trying to limit the number of steel modifications because of time. Even though we have a healthy budget, we simply don't have to the time to be doing the reinforcement on the building. Obviously we will if we have to, but that causes serious construction delays.
RE: Structural Analysis
Thanks to everyone for your responses on this post! I appreciate all of your expertise.
RE: Structural Analysis
Is this the proper thing to do?
RE: Structural Analysis
RE: Structural Analysis
RE: Structural Analysis
for this reason (like it or not) most of the 737s flying today are certified to 1960s rules (with some updates, like fuel sys, cabin sys, ...). Boeing might have updated the basis of certification for their latest model, but i'd be abit surprised if they did; not that they're doing anything Wrong.
RE: Structural Analysis
RE: Structural Analysis
And no worries AUCE98.
RE: Structural Analysis
I do not know of the top of my head where it is stated. I just know I had an action that was due today (2/17) to review all pending modifications for the use of CMTRs and create additional actions as req'd.
Have you tried an OPEX search for CMTRs? If I get some time, I will do some digging and see what I can find. Good Luck!!!
RE: Structural Analysis
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Structural Analysis
At least I don't glow in the dark.
RE: Structural Analysis
...Yet.