The purest performance-based event in athletics has to be the 100-meter dash. All that matters is being the first person to run from the starting line to the finish line. No complicated rules, no requirements for this type of shoe or that type of clothing. Just run! Ah, but then come the prescriptive parts: the runners cannot have taken any performance-enhancing drugs, as defined by a committee. And the fastest man on earth is not simply the one who reached the finish line first.
We actually do have the equivalent of steroids for concrete—various performance-enhancing admixtures—and their use too is restricted. When the long term impacts aren't entirely clear to the specifier, they begin to add in prescriptive requirements. A specification becomes much more complicated when it includes a mix of performance-based requirements (this level of strength, that level of durability) and prescriptive requirements (this much cement, vibrate for exactly this long).
What about jobsite safety? It would seem that this should be performance-based, and it is as far as the insurance companies are concerned. Your experience modification rating depends on how many injuries you have onsite—not whether the workers have worn their hard hats and safety glasses. The insurance company only cares about performance. But then along comes OSHA to make sure you have all of your Material Safety Data Sheets on hand and that the rail around the scaffold is exactly the right height. It has its prescriptive requirements and often seems not to care about how safely you are actually performing.
At a recent meeting of the Strategic Development Council, there was a great deal of talk about simplifying the ACI 318 Building Code. The purpose of a building code is to protect the public from poorly performing buildings, not to dictate what's in the concrete mix. So the conclusion was that the best way to simplify the code and still have it achieve its life-safety mission would be to make it performance based. The engineer or the owner would require the structure to meet some expected level of performance—it could be in-place strength or some other way to measure performance—and it would be up to the concrete producer and the contractor to achieve that performance. Sounds good, but don't hold your breath.
Prescriptive requirements imply that the specifier doesn't trust others to know what's best. If he or she believed that everyone involved would do what's best for the project, without cutting corners, then we could get to performance specifications. If there is truly a team approach to a project, then much of the prescriptive nature of the specification is unnecessary. We will continue to hear about moving from prescriptive to performance requirements in mixes and designs, but be careful what you wish for—this approach also brings with it a lot of responsibility.
William D. Palmer Jr.
Editor in Chief