What is your opinion about the future of design: should it stay as it is, where everything from the composition of materials through technology to finishing is exactly specified or we should rather focus on the desired output? Or simply speaking what is more important: the way or the effect?
I ask this question in the context of bridge design. Our Polish law and regulations specify in every detail the materials (concrete) and the technology of execution of concrete elements of bridges stating that this will ensure the desired effect (strength, durability). E.g. the composition of concrete mix must be based on cements type I which have always been regarded as of the best quality, however, they are characterised with properties which cause negative effects in concrete such as high hydration temperatures or high shrinkage. Nevertheless, nowadays we are able to produce different cements of high quality and we can control that quality. It is possible to use cements of type III and higher to produce concretes of comparable strength and durability but minimising the negative hydration effects. Hence, if the design was based on assuring only the effect - no matter what the way is - I think it could be only for the better.
How does this situation look in your country and area of expertise? Can you give some examples or recommend some further reading?
Thanks for your challenging question. Authorities, engineers, owners, and all related individuals should recognize that current codes are only basic guidelines that, in many cases, didn't convey the latest technologies. Unfortunately, in many countries these codes are changed to some regulations that must be obeyed. Current prescriptive trend would decrease technological pace in the field of Civil Engineering. For example it is found that in many cases low strength concretes would perform better than high strength ones, especially for seismic applications. But engineers cannot use this achievement just because current codes, such as EC or ACI, imposed some minimum values on the concrete strength.
BTW, the term "performance-based design" is a well-understood term in Earthquake Engineering, which is still kind of Prescriptive design. So to clarify the question you can use "non-prescriptive" instead of "performance-based". Accordingly, I vote for non-prescriptive design not only for bridges but for all structures.
Thank for your answer and some look from a different domain of civil engineering.
When it comes to the names, in general structural engineering I mostly read about "performance-based" as opposed to the "prescriptive" so it's interesting to know that it's not understood as such everywhere. However, I have also come ascross the term "descriptive" (as defining the effect) as opposed to the presriptive (as difining the method); it was not used in engineering sense, though. What do you think about such a formulation?
As far as I know, performance-based design (PBD) is still a prescriptive design philosophy. For example, if you want to design an offshore jacket platform, a pile-supported wharf, or even a building per PBD, you need to follow some pre-defined procedure for loading the structure, for analysis, and for determining acceptance criteria. So I didn't find PBD as a non-prescriptive method.
As an example, Steel Plate Shear Walls (SPSW), have just recently adopted by American codes, in 2005 while its first usage in Japan date backs to 1970s for a skyscraper, called Nippon Steel Building...! The same story exist for other seismic resistant systems. This simple sample reflects the turtle-speed of current codes. Actually there is a large list for drawbacks of current codes. I mentioned some of them through a question that I asked a couple of days ago. Drawbacks about concrete mixtures, design philosophy, seismic resistant systems, etc.
As a result, such weak codes, supposed to be non-prescriptive and should be treated as some basic guidelines, not more.
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