Vertical Vessel Foundation on Piles 2

[structure_engineer]

Hello Engineers,

I have a tall vertical vessel foundation to design. It is an independent vertical vessel on a octagonal pedestal and an octagonal pile cap. The number of piles is 12 numbers of 18" diameter auger cast-in place piles, 60' deep below grade. The choice of software available for me to use is SAFE or RISA-3D. I was told by my manager SAFE is a better software to use as it has better and accurate results. My question has 2 parts: which is a better program to use and how should I approach this problem, in terms of modeling approach.

So I am used to STAAD v8i and I have done finite element problem on STAAD Pro (not sure which version but it was back around 2005 I believe. So it has been awhile since I modeled FEM and a lot have changed since then, as far as progress in FEM and software capability. How should I approach this design?

Top of grade elev. = 100'-0"
Top of pedestal = 101'-0"
Frost depth = 6', thus bottom of pile cap elev. is at 94'-0". Pile cap thickness is 2'-6", pedestal thickness is 4'-6". The sizes are shown on the sketch attached.

- Do I let the program do the meshing or do I model the elements myself. It would be a tedious task.
- How do I impose the wind load overturning moment to the model? Shear is pretty simple, apply shear value at the top of the pile spring node location. Do I model the vertical vessel as a large diameter pipe or model the base ring only. The model has everything to do with the way the load is applied.

On the sketch there are 2 pages showing STAAD did the meshing on the octagonal pedestal and pile cap. This was extracted from an article. Would SAFE or RISA-3D able to do the same meshing? Your input and comments are most appreciated.

 

[ALK2415]

Try STAAD Advanced foundation
it will solve your design [including piles] in few minutes

 

[structure_engineer]

The choices of available software we have is:

SAFE
RISA-3D

We could not just go to our manager and request a software that is not in the list. That would take an act of congress. Your input is most appreciated. Have a great week guys.

 

[ALK2415]

if you could just send me the general dimensions / assumed loadings (my email @ profile)
i could give you a quick run of the software with design calculations ...(including shop drawings). Note: According to ACI ASCE AISC ...
or use the following link [Link]

 

[JoshPlumSE]

Attached is a SAFE file where I have created a very basic Octagonal mat with a column / pedestal at the center and a series of piles in a radial arrangement.

I threw it together pretty quickly, so it's probably a little sloppy. But, the basics were just:
a) Create a radial / circular drawing grid.
b) Draw in an octagon of the proper dimensions.
c) Revise the grid spacing so that I can draw in a radial pile arrangement. Though I could just have easily changed to a rectangular grid if I wanted a rectangular arrangement of piles.

Note: I could make the piles compression only, tension only or such. Heck I could make them non-linear with a tension stiffness that's different from the compression stiffness as well.

Personally, I did this because I have been more familiar with doing this sort of thing in RISAFoundation and I wanted to see how easy (or difficult) it would be in SAFE. IMO it was certainly not difficult.... though I think there would be ways to improve this behavior in the future.

Disclaimer:
I come from a background where I did a lot of vertical vessel design (i.e. heavy industrial, petrochem, power plants and such) early in my career. Then I worked for RISA for 16 years, hence a lot of the RISA programs are already somewhat catered to my personal preferences for this industry. Now I work for CSI (which writes the SAFE program). So, I'm not exactly a neutral observer.

 

[HTURKAK]

In case of piled foundation, frost depth is not applicable..you may revise the thicknesses accordingly ..

 

[AskTooMuch]

Usually (including StaadFoundation) this is designed assuming rigid foundation should be easy using excel or mathcad.

 

[structure_engineer]

Hello AskTooMuch: I had already done the design using Mathcad, assuming rigid foundation, for the small vertical vessel. On a larger vertical vessel, originally I had to combine with the pipe rack on a structural steel skid like 15' away, with the pile on 3 pile circles and the octagonal pile cap gets too big. However, during layout using AutoCAD, using the rectangular pile layout, I was able to shrink the octagonal pile cap to a manageable footprint and hence avoided the combined pile cap for the vertical vessel and the pipe rack.

I was going to combine the east row of the pipe rack, with 5 columns with the vertical vessel pile cap to form a combined pile cap. The west column line of the pipe rack, also with 5 columns, with each column on its own auger cast pile. This would take care of the issue of differential settlement of pipes as the pipes runs north-south. In other words, there will be no differential settlement for one single run of pipe but there will be differential settlement for different run of pipes but that is a not critical. But since I was able to use rectangular layout of piles, the octagonal pile cap is more manageable and I don't have to combine the vessel foundation with the pipe rack foundation.

Thank you to JoshPlumSE for the SAFE file upload. When I have a chance, I will spend some time to look over the manual and figure out how to use the software. With the project on a fast pace, right now I just don't have the luxury to figure it out.

Hello adn26: Is that Link to Staad Foundation really good. I am going to have to check it out. Even with Staad Pro v8i, the demo is only good for a short period of time.

 

[structure_engineer]

I just completed the design on a horizontal vessels on mat using SAFE. Now I am ready to download the file JoshPlumSE uploaded but unfortunately we have an older version of SAFE. JoshPlumSE, can you please save the version 20 file to version 16? The exact version is 16.0.2 Build 1153. The company elected not to upgrade to the latest version due to budget constraints. Your help is much appreciated.