W20.1 – Offshore Electrical Substation Planning – Part 1 WBS development

Problem Definition

Within the SPJ project, the offshore / Jetty scope requires construction of an electrical Substation comprising of a 2 storey building using precast concrete frame, masonry external and internal walls, various flooring and ceiling finishes, external handrail and escape ladders as well as usual building services (plumbing, electrical, HVAC, etc).

The current programme and budgets only consider this work package at a higher level (Level 2) and we now need to develop a detailed programme and verify budget adequacy as it is now expected that the work package will become time critical and possibly over budget.

To commence this “re-planning” exercise, we will first develop a suitable WBS. Substation Equipment will be ignored.

Feasible Alternatives

  1. Non Standard WBS
  2. Omniclass table 21
  3. Omniclass table 22

Development of the Alternatives

  1. Non Standard WBS

The  WBS is based on an Activity Breakdown Structure where the project phases are identified at 1st Level including Project Management / Engineering, procurement, Construction and Commissioning. Tasks and work packages are then defined under each Phase. For clarity, the WBS has been reduced to level 3 only.

2. Omniclass Tables 

In developing options 2 and 3, it should be noted that the Omni class tables are not program work breakdown structures however at all levels, the element in the structures are candidates for WBS element descriptors, including work packages.

Table 21 – Elements

An Element fulfils a characteristic predominant function, either by itself, or in combination with other elements; Table 21 is organized by elements’ implied functions. Major elements may be composed of several sub-elements. For example, a shell enclosure might be composed of superstructure, exterior closure, and roofing.

Using table 21, the works would be described as follows

Note that breakdown does not consider the phases of a project such as design, project management, procurement, etc and only considers the work scope based on function. If we used table 21 as a reference for describing the physical works and introduced phases at level 2, the complete WBS look something like this;

Table 22 – Products

Using table 22 on the other hand (Work Results), the breakdown of phycial works would be as follows;


Again, table 22 does not consider the various phases of works but  represents a completed entity that exists after all required raw materials, human or machine effort, and processes have been provided to achieve a completed condition.

As such table 22 cannot be used in isolation and must be incorporated into the overall project structure as follows;

Selection Criteria

The following criteria will be used to assess the preferred WBS structure;

  • Covers all aspects of the works to a suitable level of detail
  • System or Product Orientated and supports a breakdown of work activities into a logical sequence or work flow
  • Includes major procurement, project management and design phases
  • Supports current project Code of Accounts structure which is split into 3 categories; 1. Building Structures 2. Building Archi works 3. Building MEP

Analysis of the Alternatives

Each WBS will be compared using a Non compensatory Lexicography model. Results are as follows

Selection of the preferred Alternative

From the table 3 above, Omniclass Table 21 is considered the most suitable WBS when combined with

This is due to its superior accuracy compared the non standard WBS as well as its superior work flow compared to table 22 (work results)

By decomposing the work scope using table 21, a methodical sequence can be created within the WBS which should allow for more accurate activity relationship and dependencies.

Performance Monitoring

The above WBS will be further detailed to level 4 and 5 to increase accuracy and definition of work scope – using Omniclass table 21. This may include further physical breakdown of the Building by area or level.

Next blog will use the developed WBS within a PDM analysis for estimation of work duration.


  1. Sullivan, G. W., Wicks, M. E., & Koelling, C. P.(2014). Engineering economy 16th Edition. Chapter 14 , pp.603
  2. GAO Cost Estimating and Assessment Guide, March 2009, Appendix IX
  3. Omniclass Edition 1.0, May 2, 2006, Table 21 & Table 22

1 thought on “W20.1 – Offshore Electrical Substation Planning – Part 1 WBS development”

  1. EXCELLENT Tony!!! Very good case study and you did a great job on your analysis.
    As this is an OFFSHORE project, if you have the motivation you may want to do another blog posting using Norsok Z-014 to see if their 3D approach (Component, Resources and Activities) works out better than using the Omniclass Tables?

    Again, great job on a very interesting case study.

    Dr. PDG, Jakarta


Leave a Reply

Your email address will not be published. Required fields are marked *