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Storage tank anchorage

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Anchorage design of a steel spherical storage tank

by
John Krpan
M.S.C.E., P.Eng
President of ODAN-DETECH Group Inc.

The Odan/Detech Group Inc. based in Ontario-Canada has been using IDEA StatiCa since the beginning of 2016, as one of our first clients in North America who recognized this exciting new technology that the software offers to structural engineers.
Since then, they have been using IDEA StatiCa extensively, and in this case study, they present a project that they have been involved: A Stress analysis and Design of a generic Propane/Butane Storage Sphere in a high seismic area. This analysis and design would determine if the structural support system contemplated will be adequate for the generic design loads, and this would allow for better budgeting of projects.

This 3D model of the main structure was made with a 3rd-party general FEA software

About the project

Some background

  1. Design info was given to Odan/Detech on the Storage Sphere.
  2. A General Design procedure was outlined by Odan/Detech.
  3. Odan/Detech used general FEA programs to analyse and design the general structure and IDEA StatiCa Connection to design the anchor.

Finite Element Analysis of sphere structure

  1. Calculation the fundamental frequency of the dome/support structure empty. This was done using a finite element model. Two independent finite element codes were used.
  2. Calculation of the fundamental frequency of the dome/support structure filled with liquid. This was done using a finite element model. Two independent finite element codes were used.
  3. A short report showing the structural model, mode of vibration and summary of findings based on the two independent finite element codes.
  4. Design of a generic anchor system.

Code check of dome support system

  1. Analysis using dead load, live load, wind load and seismic loading. Load combinations as per AISC ASD. Seismic loading as per UBC (Uniform Building Code)
  2. Code check using AISC ASD. Euler buckling evaluation for the structure as a whole.
  3. Design of shear key at column bottom.
  4. Short report showing the design results.

Anchorage design

Using IDEA Connection which utilizes the CBFEM (Component Based Finite Element Model) we were able to model many different components and geometries knowing that efficient use of material is assured. The anchor joint could have been modeled in the traditional FEA programs, however even with the best of modelers the chore is enormous. IDEA StatiCa is specifically designed for steel joints. Changing stiffeners, member components, welds and bolts are routine in IDEA.

CBFEM method tries to create the model precisely. The analysis plate/walls are not interconnected, no intersections are generated between them, unlike the methods used when modeling structures and buildings. Mesh of finite elements is generated on each individual plate independently of the mesh of other plates. Welds are modeled as special massless force interpolation constraints, which ensure the connection between the edge of one plate and the surface/edge of the other plate. The unique model of bolts provides excellent results – both from the point of view of precision and of the analysis speed. The method is protected by patent. The steel base plate is placed loosely on the concrete foundation. It is a contact element in the analysis model – the connection resists fully compression, but does not resist tension.

3D geometry

Strain check

Deformed mesh

Using IDEA StatiCa:

We asked John Krpan a few questions about his experience on using IDEA StatiCa, and here are the answers:
How did you deal with similar connections in the past?

In the past, we created FEA models with Nastran and did the stress analysis. With simpler connections, we used spread sheets or a program called LIMCON.

Could you estimate the amount of time that it has saved you?

Using IDEA StatiCa we saved at least ¼ the time assuming you got it right the first time. LIMCON was limited to simple connections and couldn’t solve a complicated connection like this anchor.

Do you think that the use of IDEA StatiCa provides you more economical design? If yes, how is that?

For sure we get a more economical design. Based on our FEA experience you see the stresses visually. The effects of a stiffener are prominent. IDEA StatiCa makes the workflow process more efficient and adds the caveat of CODE checks!!

If you could choose only one, what would be the biggest advantage of IDEA StatiCa?

Simple, visual and the power of FEA. The biggest advantage is easy to use. There are other similar programs, but not one like IDEA. This is why we chose IDEA StatiCa.

About ODAN-DETECH Group Inc.:

The ODAN-DETECH Group Inc. is a multi-discipline consulting engineering firm with a staff that has extensive experience in Civil & Structural engineering, Building sciences, and the Construction fields. It was formed in 1992 by the amalgamation of the Odan corporation (formed in 1985) and Detech Engineering (formed in 1988).

Website: www.odandetech.com