Need advice to design reservoir 3

[fa2070]

Hi,

I have to design a rectangular concrete reservoir for containing sugar cane molasses/syrup (density=1500 Kg/m[sup]3[/sup]).
Dimensions: length=100m, width=35m, depth=6m
Some of the project constraints are:
[ul][li]The walls must be of precast reinforced concrete panels. (no prestressing or post-tensioning, except as a very, very last resort)[/li]
[li]The reservoir can be fully or partially underground (see Pics. #2a-#2b and #3)

[/li]

[li]The floor will be of poured concrete.[/li]
[li]The whole structure will be roofed.[/li]
[li]Walls and floor must be watertight.[/li]
[li]The jobsite is in a moderate seismic zone.[/li]
[li]Several smaller reservoirs instead of a huge one is not an option.[/li]
[li]Unlimited crane availability.[/li][/ul]

If poured concrete for the whole structure were allowed, then the easiest approach would be to implement sloped sides and treat the walls as inclined extensions to the floor. In fact, the reservoir could be thought of as a big slab on grade. See pic. #1 for the concept.

With that option out of consideration I have to fall back to other alternatives that contemplate vertical walls made of precast panels. Basically I'll have to stick with variations of the concepts depicted in Pics. #2a, #2b and #3.

There's also another alternative with a more elaborate panel with heel and toe, like the one manufactured by the Italian company Paver. See this page and the PDF here . Their products, however, are meant for grain storage.

I'd rather think of this structure not as a plain old rectangular tank, but as a long retaining wall whose worst load case is when the reservoir is empty. Prevention of wall overturning, translation and rotation are my biggest concerns (maybe the internal columns/beams for supporting the TT roof panels could serve as struts to prevent OT/trans./rot.?)

To sum up, I'm in the early stages of self brainstorming on this subject and, based on the experience of the members of this forum, would like to know opinions on the most efficient, safe and economic design I should focus on going forward, satisfying the constraints set above.

How would you tackle the desing of a reservoir like this one?.

Thanks.

 

[kslee1000]

"The whole structure will be roofed", what is material proposed for the roof, how it is loaded, and to be supported? What is the transverse length (into/out of paper)of the rectangle? These info may help people to gain better ideas.

 

[cvg]

couldn't sloped pre-cast walls be used instead of vertical? That would eliminate the need for counterforts or tiebacks.
How will you approach waterproofing a pre-cast structure?

 

[graybeach]

How high does the water table get? If it can go above the bottom of the structure, you will need to make sure the think can't float up out of the ground, and you will need to design the bottom slab for hydrostatic pressure.

 

[civilperson]

Check out the effect of sugar cane harvest trailers traveling Portland Cement Concrete roads. The MIC, (microbial induced corrosion), on concrete is a known detriment to concrete.

 

[fa2070]

@kslee1000:

what is material proposed for the roof, how it is loaded, and to be supported?

Roof material:
Prestressed TT's

Roof load: Self weight.
Roof support: internal reinf. concrete columns and beams

@cvg:

couldn't sloped pre-cast walls be used instead of vertical? That would eliminate the need for counterforts or tiebacks.

How do I assemble the panels on the sloping ground?

How will you approach waterproofing a pre-cast structure?

Non-shrinking cement grout plus polyurethane sealant in the joints.

@graybeach

How high does the water table get?

No, the water table is not an issue.

@civilperson

Check out the effect of sugar cane harvest trailers traveling Portland Cement Concrete roads. The MIC, (microbial induced corrosion), on concrete is a known detriment to concrete.

Advice taken!

Thanks.

 

[hokie66]

Your approach of using tied back precast panels seems appropriate. But you should use an internal membrane rather than relying on the concrete and sealants to achieve liquid tightness.

As someone pointed out, you have to consider hydrostatic uplift when the tank is empty.

 

[cuels]

Check out the website of

http://www.imxtechnologies.com

(xypex) for all your waterproofing needs. The xypex admixture and xypex dri-pack is approved for use in culinary water tanks. It is also chemically resilient. They have locations and reps throughout the world. They are more than willing to work with the local pre-cast company to help create a water tight tank that is also resilient to chemicals (if that is a concern). There is also the use of hydrophilic waterstops that can be included in a joint detail for a precast wall panel. The website has lots of joint detail ideas for waterproofing a tank.

For the tank design, I would recommend the PCA Rectangular Concrete Tanks, 5th Ed. book. It is very useful to understand the "behind the scenes" workings of a FEM model and helps in determining the loading. The PCA also has a "Design of Liquid-Containing Concrete Structures for Earthquake Forces" that may help in the seismic design.

I don't know if this is the design helps you were looking for, but fyi.

 

[RWF7437]

"How would you tackle the desing of a reservoir like this one?."

First, I would ask why so many constraints and are they all really necessary ?

good luck

 

[avfc]

hi I know this is very cheeky...but I have a similar problem but on a smaller scale,I have a design for a baptistry,2 skins of 100mm blockwork with a 80mm cavity to be filled with concrete.To be built on a existing floor.The baptistry is approx. 2m *2m*1m deep.The walls will have to retain about 3cubic metres of water..my questions are is the design good enough ?or do they need to think about drilling re bars into the floor within the cavity ??

 

[RWF7437]

avfc,

please start a new thread.

 

[RWF7437]

http://www.nwcn.com/statenews/idaho/stories/NW_012309IDN-molasses-leak-LJ.22183877.html

 

[kslee1000]

Since this reservoir is to be roofed (using prestressed double-tees), can be "partially" burried in the ground, and water table is not an issue. My thought immediately jumps to design of a typical concrete framing system with the precast wall pannels hangining around (similar to pic #3). For burried in shallow depth, the counterforts shown on pic #3 can be replaced with rectangle columns that are to be fixed on the cast-in-place concrete slab, and pinned/fixed on top by beams, or the tees with proper details.

Maybe someone has already pointed out before, without concerns of water, tongue & groove pannels maybe benefitial in many aspects, though could be little bit expensive to produce.

 

[hokie66]

Don't be tempted by admixture suppliers, Xypex or others, who will tell you that their system solves all your problems. Molasses and all sugar syrups are agressive to concrete. For durability, your tank needs a membrane or continuous coating system to protect the concrete from the molasses.

This is an enormous molasses tank, larger than I have heard of, and deserves consultation with an engineer with experience in the sugar industry.

I would think for a tank of this size you would want to compartmentalize it for maintenance.

 

[csd72]

What about using slurry walls?

i.e. dig a trench, fill up with bentonite clay then drop in reinforcement and fill with concrete.

No health and safety issues with regards to shoring e.t.c.

Make it as deep as it needs to be to cantilever.

 

[Apakrat]

No, the water table is not an issue.

Don’t forget “wind swept rain” from eaves back to retaining wall, then percolating down the retaining wall.

May be surprising the speed of damage to interior sealing from acidity at hydraulic head.


At 74th year working on IR-One PhD from UHK - - -

 

[fa2070]

After a few iterations with the upper management and client I finally convinced them that a below-grade concrete reservoir with sloped sides will be the most economical solution. Basically, I envision the structure as a huge floor of cast concrete, as shown in Pic. #1a:

But before I proceed with the design, I'll appreciate some guidance to clarify a few doubts:
[ol][li]
Is it correct to decompose the at-rest earth pressure [σ][sub]h[/sub] in two triangular in-plane and normal distributed forces? (see the red, pink and green arrows respectively on Pic. #1b) .....Do I have soil pressures at all?

[/li]

[li]
When the reservoir is full (or empty), is it correct to analyze a strip of unit width of the structure as a beam on an elastic foundation as shown on Pic. #1c?

[/li]

[li]
The concrete thickness and reinforcing steel of slabs on grade are chosen mostly from engineering judgement based on loads and suitability of the subbase and deeper strata, and 999 out of 1000 times it just works. For this design to be approved by the client I must attach the calcs. So my question is, what is the most suitable software package for analyzing this huge soil-supported concrete slab with inclined sides, including dynamic analysis from seismic effects? What is the learning curve like? This job is in seismic Zone 3. See next item.[/li]

[li]
How do seismic provisions affect the design? With regard to analysis, what things change besides the addition of statically-equivalent loads from shear at the base and hydrodynamic forces from the stored liquid? What's the aim of seismic design in connection with storage reservoirs? Add ductility or strength? I have ACI's 350.3-06 Seismic Design of Liquid-Containing Concrete Structures and Commentary but it's not an easy read and it doesn't have any step-by-step worked examples.[/li]
[/ol]

Thanks.

 

[kslee1000]

1. Yes.
2. For your model, consult a geotech eng, or senior structural engineer, to define proper spring constants. The grade beams at the base are much stiffer than the slab, this will complicate the issue. I will try a model without beams to start with, that might result in thicker walls and base, but will simplify the analysis/design, and help in uplift case (heavier). If you intend to use computer program, why not model the entire reservoir, or a strip, as is (with tilting walls)?
3. Many commercial programs suit your needs, I will say STAADPRO and RISA3D are two easier programs to handle, the learning time depends on your familiarity with structural analysis programs.
4. The success of your project is pending heavily on understanding of dynamic soil-structure interaction, which, unfortunately, is not well covered by most, if not all, of the codes. As pointed out in (2)- you need talk to competent persons about special features such as effects of soil dynamic as well as fluid-dynamic. Also the potential of liquification (if the site has deep sand layer below) and slope stability needs to be investigated/thought of, for both static and earthquake cases.

The above represent a personal opinion. good luck.

 

[BAretired]

Are you using a granular base under the slab and walls? Make sure you have a drainage system capable of removing water quickly in the event of a sudden downpour. The groundwater table may not be an issue, but if the soil at the site is impermeable, the gravel around the walls and under the slab can fill up very quickly unless the drainage is adequate. When the tank is empty, it doesn't take a very large head of water to fail the slab.

Placing granular fill under the walls would be easier if the slope was a bit shallower, say at the natural angle of repose of the gravel base course below the wall.

If there is no hydrostatic head, at-rest pressure seems to me to be overly conservative for the walls.

What supports the upper grade beam? Are you contemplating piles spaced at intervals under the beam? Will there also be a system of piles or footings under the interior columns to support the concrete roof?

What is the function of the lower grade beam?

Best regards,

BA