Upgrading Surge Tank Anchorage for Seismic

[ahardy89]

Hey All -

I have a project where we have been asked to upgrade the anchorage for an existing steel surge tank at a hydroelectic plant. The existing steel anchors of the steel tank are inadequate to resist the uplift for the design event for seismic. The existing surge tank is more slender (close to 2:1 height to diameter ratio). The tank is built on a mass concrete foundation that extends about 2-feet from the outside radius of the tank. The concrete is founded on competent rock.

I wanted to get thoughts on our proposed approach. First we analyzed the tank following AWWA D100 to determine the overturning moment and then calculated the number of anchors and the required load resistance. I was thinking of extending the radius existing concrete founding and install DYWIDAG Thread bar anchors (number and diameter sized to resist load). The anchors would be drilled/grouted into the rock with adequate embedment to engage the rock mass needed to resist the load.

The tricky part is detailing the new anchor chairs. I am using AISI T-192 to design the anchor chairs. Due to the high load and eccentricity, the anchors chairs need to be pretty tall or the top plate needs to be wide to adequately reduce the stress concentrations in the shell. Right now we are trying to optimize this but I was thinking of just having the top plate as a continuous ring.

There are other details that we need to think through but just wanted to get thoughts on the overall approach or if anyone has had experience with upgrading tank anchors.

Thanks!

 

[JStephen]

You may be able to install reinforcing pads under the new chairs. Generally, use the AIST T-192 approach to check the shell stress using the repad dimensions as the "chair", then check the combined shell+repad using the actual chair dimensions. I've only done this once or twice, but it can be especially helpful for thin shells. There are different ideas on how the composite shell+repad should be handled. Where the stress is due to bending, the thicknesses would not necessarily just be added.

I think the recommendations for side plate thickness in AISI T-192 are unduly conservative for tall chairs, and just checking the side plates as columns per current structural codes or AWWA D100 will let you use thinner and lighter chairs than the reference indicates.

 

[HTURKAK]

Ahardy89 ;

Pls provide more information to get more valuable comments.. The size of the surge tank, age, existing anchorage, foundation size, design criteria etc. I would like to learn the reason why upgrade is necessary .. what about design criterias ?
Did you calculate the seismic loads with maximum water level instead of steady state level ? is this a client requirement?

You were thinking to extend the size of existing foundation ..what was your plan to increase the diameter of the footing ? the above statement implies the size of the footing is also not satisfactory.. Still this is a valid option drilling the existing footing and bedrock and using DYWIDAG Thread bar anchors..


The use of continuous rings instead of individual anchors chairs seems viable.. and you may combine with the DYWIDAG anchors..what is your plan for the existing anchors ?

 

[MJCronin]

aHardy89...

In the late 1980s, condensate Storage tanks on older USA Nuclear power plants were retrofited as they had been re-designated as safety related equipment. The USNRC required a retrofit involving seismic re-evaluation

As I recall, these tanks were typically, thin walled SS, with a height/diameter ratio always > 1.0 .... similar to your situation

Fixes included detailed ANSYS dynamic seismic analysis and redesigned anchorage to the seismic results.

Japan then had their Fukushima Nuclear Accident in 2011

The ASME people then developed an important publication, after work on the Japanese nuclear plants that seems to me would be very useful to you ....

https://asmedigitalcollection.asme.org/ICONE/proceedings-abstract/ICONE24/50046/V004T13A016/251822

Note that the very robust anchorage repairs were required while the plant was operating.

This information may also be useful:

https://www.researchgate.net/public...Storage_Tanks_with_Energy-Dissipating_Anchors

https://www.google.com/url?sa=i&url=https://

http://www.pnws-awwa.org/uploads/PD...ved=0CAIQjRxqFwoTCLij74vSvu0CFQAAAAAdAAAAABAV

I suggest that you use "nuclear"... "condensate storage tank"... "design" and "seismic" .... to see what google will come up with

Please respect us and enrich this valuable website .... tell us details of your final solution and why you chose it

Best Regards and Good Luck



MJCronin
Sr. Process Engineer

 

[MJCronin]

aHardy89....

Thanks so much for keeping us involved in your final decision on these important tank anchors...

Thank God, you are not one of those people who abandons an important thread once they get what they want

You sir, are a true professional and a credit to the engineering community !!

Best of luck in the future !!!!

MJCronin
Sr. Process Engineer