Expected Earthquake damage for IFR

[KiwiTanks]

As some of you may be aware, a very destructive earthquake has hit near Christchurch in NZ. The epicentre was almost in the Port of Lyttelton.

We have recently built a 30m diameter tank, 16m high, which has been fitted with an Internal Floating Roof (IFR). At the time of the quake, the tank was undergoing a float test of the IFR on water and I believe it was at the highest possible position testing the iHHLA (Hi-Hi Level Alarm).
The IFR is a light weight aluminium pontoon type, with restraint chains (not legs).

At this stage I have not been able to get to Christchurch to check out the damage, but our site engineer (who was in the compound at the time of the quake) says that the tank sides vibrated, and the compound walls wobbled like jelly.

Other than initial thoughts of damage that may have happened to the IFR, (words like munched, sunk, and stuffed have been talked of)has anyone encounteered IFR damage related to earthquakes?
Any other foreseeable problems? (Hang up)

Comments / precautions / photos all appreciated

Oh and by the way, the three new tanks are still standing after the initial 7.1 shock in September, and this more destructive 6.3

 

[IFRs]

Frankly, I'd be surprised if there was more than light damage to the IFR. Shaking, especially if it coincided with the tank's resonance frequency would cause the liquid would slosh, forming crests and troughs and elevating towards one side and then the other. The last time I did calculations of this nature we determined that the IFR was flexible enough to not be damaged if it assumed the shape of the liquid yet strong enough to span between crests without yielding. Damage would be limited to where columns or gauge poles contacted the IFR wells or if the seal contacted the tank shell. This type of damage is easily discerned and repaired. Of course, I could be all wet and your IFR could be sunk. Inspections from the roof vents will tell you a lot. Some liquid on the surface might be expected but may not mean that the roof is junk. Of course, it might have been junk when it was installed - some of the low priced roofs are not the best engineered products out there (IMHO). Good luck and please report back your findings. I'd certainly entertain an all expense paid inspection trip to your neck of the woods, if that would help....

 

[KiwiTanks]

HI IFR, (and anyone else interested)

Just an update to the above thread...

The accellerations encountered in the Feb 2011 Christchurch earthquake were in the order of 1:2500 yrs, which is well above the normal design quake of 1:500 yrs.

The IFR has sustained very little damage, as you had suggested. There are two marks where the roof trusses have punctured through the cover. Otherwise there seems to be hardly any other damage. (will try to attach a photo or two of the damage)

I believe that two other IFR's in the vicinity had a variety of minor problems, including sagging of the blanket below the product level, and seal damage.

http://files.engineering.com/getfil...8-afa7-fda38fd43594&file=Blanket_Puncture.jpg

http://files.engineering.com/getfil...bfdeb1231f&file=Blanket_Puncture_close_up.jpg

 

[IFRs]

Those pictures seem to show a very old design floating roof in very good condition. Glad you had only small problems!