On duct work, complexity, evolution and reliable work flow (in under 500 words)
November 7th, 2002 by GregRectangular duct is manufactured and installed in six steps. Sheet metal is cut (1) to length and folded (2) in half. Then the halves are assembled (beat together in the lingo of the trade) (3) into a sections (a box with a hole in both ends). A series of sections are joined (4) and then lifted (5) and secured (6) in place. Steps 1 & 2 are almost always done in the fabshop. And 4,5 & 6 in the field. Step 3 may be done in the shop or in the field. I asked a mechanical contractor what considerations drove the choice between shop and field assembly. He said that it was a matter of determining the most economic solution. Completing step 3 in the shop was less expensive but that raised shipping costs as folded pieces could be nested for transport. So decision was based on the distance from the shop to project — or so he said.
This sounded good but the rule wasn't followed. Sometimes duct was shipped unassembled to nearby projects and assembled clear across town. When pressed the contractor said, "The superintendent make the call." So I went down the block to the nearby project and asked why the duct wasn't shipped to this nearby project in assembled sections. After some weight shifting and attempts to change the subject, the superintendent explained it this way.
"Sure it is cheaper to assemble pieces in the shop, and that works great if the project is well run. But this is a crazy job. Coordination is terrible so work rarely available in a predictable amounts. I can't always join sections and lift them in place. So I keep the crew small and move them between assembling (3) and 4, 5 & 6. It cost me more to assemble but doing it here is cheaper than having those people standing idle. The crazy thing is, the worse coordination gets, the more work contractors bring to site so there is more to do onsite, making coordination harder. As a general rule, I only bring assembled units to well-run projects." (Well I know he didn’t say it just this way but you get the drift.)
Nature builds complex systems the same way. It works from the bottom up by aggregating small units (cells) into larger chunks (organisms). Evolution starts then from "cooperation" as these smaller units learn to work together and continues as they form ever more complex systems. Complex systems do not arise from competition between units. Competition weeds out the units least able to propagate. Evolution of sub-units by cooperation continues as long as the resulting units can evolve fast enough to keep up with changes in the environment. A stable environment helps and a larger population of standard chunks (with a few oddities) is a must if larger units are to form.
Back to construction: Projects can be built better, quicker and less expensively by increasing prefabrication but that will require increased workflow reliability. New forms of commercial contract don't hurt — they open new possibilities for cooperation and aggregation — but they aren't enough. Evolution demands cooperation and reliability. (along with time, and lots of failed experiments.)
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