Seismic Design of a water reservoir - percent fill 3

[RiverBeav]

So I am checking a water reservoir (Square 5000 cubic meter capacity) and checking it for seismic loads. I am curious if there is a code reference on what percentage of fill of the water reservoir is appropriate to consider with the full seismic load. Presumably, this reservoir would fill up initially, and then get used throughout the year, so most of the time the reservoir would be at some variable level of water depth. Just seems to be an unlikely scenario for it to be full at the exact time an earthquake hits, but just curious if any reference addresses this issue. Using ACI 350.3, ASCE 7-16, IBC 2018. Also open to opinions.

Thanks for any help or opinions

 

[GC_Hopi]

Check with the agency that owns the reservoir usually they have there own design codes/standard/manual. If not a few good places to start are the Bureau of Reclamation and Army Corps of Engineers, they have design manuals for the reservoirs they operate.

 

[dhengr]

RiverBeav:
Take a good look at Prof. Anil K. Chopra’s work and textbooks on EQ analysis and design. He’s done a fair amount of work in this area of EQ problems. He was at Berkeley, and I think he is retired now. I took my first EQ analysis and design courses from him at the UofMinn. in the 60’s. He’s very knowledgeable in this subject area.

 

[JStephen]

I was just doing a 2-hour ASCE on-demand webinar on seismic design of horizontal tanks on saddles, which touches on the topic briefly.
References used are "The Dynamic Behaviour of Tanks by" G.W. Housner (1963) and “Analysis of Pressurized Horizontal Vessels Under Seismic
Excitation” (Di Carluccio et al, 14th World Conference on Earthquake Engineering, October 2008). I think the Housner work was the basis of the current tank seismic codes.
The more common tank shapes are round, and so all the codified information I've seen has been for round tanks, but the theory is similar, and I think some of the round-tank designs were derived by considering vertical slices as rectangular tanks. However, you'll have to work out the corresponding seismic acceleration factors, which change with every new edition of the codes.

In general, you calculate the sloshing wave height and increase the tank sidewall height to accommodate it, or reduce the operating level. In low seismic areas, the sloshing wave height may be just a few inches. In high-seismic areas, it can be several feet. An alternative is to calculate the pressures on the tank roof and confirm that the roof can handle those pressures. This was covered to some extent in a seminar several years ago by Praveen Malhotra, and it may be in his paper "Simple Procedure for Seismic Analysis of Liquid-Storage Tanks"- I've got a copy of that somewhere, but don't see it free online at the moment, a bit of searching may turn it up. The paper is for round tanks, not rectangular, though.

The sloshing wave idea is pretty simple on paper, but there are some Youtube videos of swimming pools in earthquakes, and the actual sloshing can be pretty random-looking, not always the gentle back-and-forth wave you might expect.

 

[RiverBeav]

Thanks for the responses so far. The question is more of a question about the probabilities of a major seismic event occuring at that point in time when a water reservoir (30m x 30 m x 6 m deep square concrete tank) was 100% full. Sort of like even in a cold location, you don't design for full code seismic combined with full code snow, just because the two occurring at exactly the same time is unlikely. But full code snow is usually more of a once in a century event, so that makes sense. The full reservoir is probably a once in a year event, so it probably should be pretty high. We are repairing a water reservoir in a poorer country so are trying to make it as cost effective as we can make it.

Thanks for your help,

 

[GC_Hopi]

What exactly are you checking... the 30m x 30 m x 6 m deep square concrete tank? I was thinking an earthen reservoir but now it sounds like a concrete tank. How confident are you in the levels of liquid in the tanks? Do you have detailed data sets showing time vs height of liquid?

 

[RiverBeav]

My mistake, definitely a concrete tank . . . the job is described as a reservoir, but it is a contained tank. I am not confident in the levels of liquid in the tank and there are no data sets.

 

[HTURKAK]

Dear RiverBeav (Structural),

I think you look to (ACI 350.3-06) Seismic Design of Liquid-Containing Concrete Structures and Commentary

The liquid ht ( hl) is the design liquid height..( max. height that could be ). i.e. the liquid ht dictated by overflow level etc..


There are solved examples at the following doc.

( IITK-GSDMA GUIDELINES for SEISMIC DESIGN OF LIQUID ...)

https://www.sefindia.org/forum/sear...GN+OF+LIQUID+STORAGE+TANKS&sa=Search&siteurl=

http://www.sefindia.org/forum/viewtopic.php?t=13524&ref=yandex.com.tr/&ss=

 

[GC_Hopi]

Without any data, its not possible to do any sort of probabilistic analysis on the liquid level. I think you are stuck using the overflow liquid level or normal liquid level (given by the hydraulics but it sounds like you don't have this info) since you can not justify/quantify what the liquid level is during operation of the tank.

 

[WARose]

It can be kind of tricky. One reference I'd recommend is 'Design of Liquid-Containing Concrete Structures for Earthquake Forces' by PCA. I don't know if a newer version is out there. But I've used it quite a bit over the years.