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  • Writer's pictureSi Shen

Conceptual design (2)

For the previous post on this topic follow the link:

Conceptual design stage may come across being not-so-technical as technical designs are done at a high level, without much detailed calculations involved. In my opinion, quite the contrary, the best available people should be utilised at conceptual design stage. It is at this stage that the final, and hopefully the best, option is confirmed, and all parties become fully coordinated. This decision will be locked in as final. There is no going-back. Every party is forced to be bound by the decision. The fate of the project will fundamentally depend on the early development path. Making sound decisions require highly experienced personnel, quite possibly with the support from multiple specialists in various fields of study. These team needs to possess the following capabilities:

· The ability to identify likely governing design conditions by inspection, without conducting detailed analysis

· A sense of whether a design outcome falls in the right ball-park

· An appreciation of design principles and constraints of other disciplines

· A sense of appropriate assumptions to be made in the face of uncertainty

· The ability to make sound judgement of the risk level of the design

· The ability to identify value engineering opportunities

In my opinion, these are high-threshold skills that only comes with years and years of experience. They are fundamentally different from detailed design technical skills, which typically requires skills in modelling or line-by-line calculations.

It is prudent to build in structural redundancy at conceptual design stage. The level of redundancy should depend on the level of risk, complexity and uncertainty of each component. There is no hard and fast rule, but generally for infrastructure projects, I target between 50% to 80% of the maximum . some questions may prompt the designer to assess the risk level:

· What are the assumptions associated with the design? The number and/or criticality of design assumptions should gradually reduce as the maturity of the design advances.

· What information is still outstanding? Say ground investigation results, or designs from an interfacing party

· How critical is the design element? Is it on the primary load path?

· Is there a way back? In case the structure proves to be of insufficient capacity at later design stage, do I get a shot at revising the design without causing a chain reaction of changes?

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