In the early 1980s, the construction industry began to ask for a lot more flexibility. They were using new materials, they were using new systems, and codes were restrictive and traditional. Codes had to change, and they did. The codes moved from prescriptive to performance-based, and this provided flexibility, but it also added complexity. It created more demanding criteria on designers and contractors. Now we realize that we need not only codes that are highly flexible and performance-based, but also prescriptive models for those in the field who don't want to take on so much engineering.
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