Is IBC's 5% & 10% allowable increase rule applicable to existing water tank AWWA D100?

[flyingcow1999a]

We need to check the adequacy of an existing water tank for installing some proposed antennas and supporting mounts on top of it.
Is IBC's rule, 5% and a 10% allowable increase in gravity and lateral loads, applicable to existing water tank? Or it has to be checked rigorously with AWWA D100?

We checked the water tank by following the IBC's rule but received feedback from reviewer. It says
IBC does not refer to AWWA;
AWWA D100 does not specifically menion that the IBC loading provisions prevail;
AWWA D100 presents lower allowable stresses than AISC;
AWWA D100 must be utilized for both loading methodology and allowable stresses (member capacities) for a full rigorous analysis.

Thanks...

 

[JStephen]

AWWA D100 just covers new tanks, so the "rigorous" part is lost right there.
I think different approaches could reasonably be used with different results. In particular, looking at ASCE 7 wind loading in lieu of AWWA wind loading may be very helpful.
If it's an elevated tank, or if you don't have drawings for it, or if it's very old, you may be in for greater challenges.
If it's in a seismic area, that may help.
What configuration is it? Where located?

 

[flyingcow1999a]

Thanks. It is more like a standpipe type tank located at MA.

 

[TLHS]

I haven't touched AWWA D100 in a long time, but in general tank standards tend to be pretty quiet on anything more local than full area loads and pressures any way, so there's a reasonable chance there's not guidance in AWWA D100 for this at all. You'd need to review to see if that's the case, but I'd be surprised if there were detailed local loading requirements.

You'll likely be able to lean on the allowables, but the analysis will go back to first principles. In which case, it's going to be heavily on your own judgement regardless. So whether or not the IBC rule governs is likely not the question, it's whether you own judgement that a small increase is acceptable is reasonable. To me it would depend on the load condition. I probably wouldn't be worried about a five percent increase in vertical load in the tank walls, but I might be looking at local bending stresses in detail.

 

[JStephen]

On a tank of that size and configuration, I would guess that wind overturn was probably not a consideration, so it will likely be feasible to work through the calcs and just show that it meets AWWA allowables and all. Providing you have some good information on how it's actually built. If they happened to hit 100% of allowable soil bearing, that 5% might come up then.