The Transition From Craft To Industry

by Don Friedman on March 1, 2018

That’s a late 1800s industrial building, looking up at the underside of an upper floor. The first thing that needs to be said has nothing to do with the point of this post: the joists are about twice as deep as they look like here. If you look closely, you can see the ledger strips that are nailed to the sides of the joists to support the flooring between the joists. Usually you see this detail when the floor has been deafened either to (as the name implies) rescue sound transmission or to make the floor better able to carry tile finish.

On to the real point: this floor represents the transition of construction technology to the modern age. Specifically, the joists are attached to the header running left-right with bridle irons rather than the traditional mortise and tenon joint. Mortise and tenon joints, even crude ones that are not meant to be seen, require some skill from the carpenter making them; bridles replace that with a piece of prefabricated metal.

You can argue that the bridle replaced skill in carpentry with skill in ironwork, but that was only true for as long as the bridle were made by blacksmiths bending iron strap. By the last decade of the 1800s, and maybe earlier, bridles were being made in factories by semi-automated machines, twisting and cutting the strap to standardized sizes. You could argue that those machines replaced skill in carpentry and blacksmithing with skill in making machine tools, but there were far fewer people employed making those machines than there and been as joiners.

When we talk about technology advancing, what we’re talking about at the early stages of the process is machinery replacing artisans, often with a loss of quality, at a lower price. Since I enjoy many of the results of that process, I’m not going to say it’s always a mistake, but we should see it for what it is.

The Details of a Technological System

February 20, 2018

This is an underside view of the heel connection of a heavy timber truss. The piece of wood at the top of the picture is the bottom chord, roughly 12 inches by 12 inches in section, and you can’t see the top chord above it. The bolt ties the two chords together, but the real […]

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Point and Counterpoint

December 3, 2017

In the recent discussion of wood skyscrapers (full disclosure: I think they’re a terrible idea) I have noticed any discussion of the extent of exterior maintenance necessary to prevent wood from acting like the biological material it is. A masonry curtain wall can go thirty years with no maintenance and not fail: a lot of […]

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This Is Ungood

October 18, 2017

From a few years ago, some rotting wood beams and a failing brick pier. In 1989, I performed a long and difficult site visit to check on a structure I won’t name (confidentiality is still in place, even after all these years) that had to be reviewed once per year. The fellow who had been […]

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Steel Trusses and Wood Purlins

May 19, 2017

No deep thoughts today, just appreciation for a well-designed roof. It’s an industrial building so finishes were kept to a minimum, and there was no requirement for fire-rating. The trusses are steel because they span about 50 feet; the purlins span 18. The end bays have diagonal rod bracing in the plane of the truss upper […]

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Worse Than Termites

January 26, 2017

That’s a nice early-twentieth-century partition: plaster on expanded metal lath (on the far side of the studs) full 2×4 studs, diagonal fire-blocking between the studs. And, yeah, a big chunk is missing from a stud where an electrician or plumber needed some room to work. We see more damage from guys with saws than we […]

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A Subtle Hint

January 24, 2017

That picture was taken in a mid-to-late-nineteenth-century industrial building, on the top floor with only the attic above. The exposed wood beam is about 8 inches wide and 12 inches deep but appears to span some fifty feet, which is obviously ridiculous. The building has a gable roof so the most likely bet is that […]

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Failure Portrait: Dramatic

October 6, 2016

No, that photo isn’t rotated 90 degrees. The floor above has failed and the bathtub has fallen through. You can’t see it from this angle, but the only thing holding the tub in place is the drain pipe. One of the difficult judgement calls that we face during field investigation is when a building is […]

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September 28, 2016

The white stripes show the gaps between the now-removed lath: Structural engineering is about structure, right? A while ago, while looking at a historic house upstate, we ran into a problem. The building had wood-stud bearing walls sheathed with clapboard and we ran into an obvious problem: the bearing walls were not performing properly. The studs were buckling, […]

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Failure Portrait: A Little Off The Top

September 21, 2016

There’s a lot going on in this picture, and much of it is not good. The center of the picture is a girder* with joists on both sides framing in. (The joists on the left are mostly hidden below the plywood.) The fact that we see the tops of the joists inset past the edge […]

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