Steel Trusses and Wood Purlins

by Don Friedman on 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 chords to allow the roof to serve as a diaphragm for resistance to wind loads.

Given the technology of the era of construction – no plywood, no welding, relatively low ratio of labor-to-material costs for steel – this is just about perfect. I can’t think of any way it could have been built better. With today’s technology we’d design in differently, but not necessarily any better.

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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Historic Structural Detail: The Edge

August 23, 2016

I’ve mentioned heavy-timber construction before. Here’s an interesting detail from an old warehouse: The planks above are four inches thick and splined to one another, which is typical in heavy-timber construction to prevent hot gas from a fire burning through to the next floor. (The thick wood in this kind of construction will char but […]

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Historic Structural Detail: Tree

August 16, 2016

The cellar of an 1890s tenement: That’s a girder running right to left with its original support (a barely-trimmed tree trunk) and a 1990s supplement (a steel pipe column). I’m not sure that there’s anything else to say. Cheap construction was cheap, maybe. And “they don’t build ’em like they used to.”

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Students and Wood

August 10, 2016

The Seward Park Urban Renewal Area (SPURA) has been sitting empty for almost fifty years since the old buildings were demolished. The latest scheme is the kind of large-scale development that we’ve seen a lot of in the city in recent years. The Timber in the City Competition had students competing to do something more […]

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Historic Structural Detail: Clever Carpentry

August 1, 2016

Notice anything interesting about the header in front of the chimney masonry? There’s no visible connection between the header and the trimmer. (There are also no visible connections between the joists and the header, but this photo doesn’t have the right angle to see, or not see, that.) This is a mid-1800s house, and the standard connection […]

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