February 2017

Laced Columns

by Don Friedman on February 28, 2017

The last time I talked at length about laced columns, I was talking about their failure from rusting. That seems unfair, so I want to talk about their remarkable success: engineers were convinced for decades that they were a good idea.

Built-up columns are made by fastening (riveting, bolting, welding) relatively small pieces of steel together to create a big cross-section. This was done in the past and is done today when people need columns bigger than those that are rolled in raw steel. In other words, the big columns at the bottom of tall steel-frame buildings are still usually built up.

In an ordinary built-up column, the overall cross-section is the same everywhere. For example, if a wide-flange column is strengthened by welding plates between the flange tips to make it into a box, that box is the same at any point along the column’s length. Laced columns, on the other hand, are a specific form of built-up column where some of the small pieces vary in position along the column length. The usual layout, as seen in the vertical members above, is to create a series of double-diagonal connectors between two main pieces, usually channels. The overall effect looks a bit like the lacing up a tall boot, and hence the name.

When people involved with steel construction today look at laced columns, we see an enormous amount of labor needed to fabricate and assemble all of those short connector pieces for seemingly little gain: a single large plate could be used tie the two main pieces together. That single plate uses more steel than the lacing plates but requires far less cutting. The amount of hole drilling is about the same, since the single plate would have to be fastened at about the same frequency as the lacing plates.

In purely economic terms, it’s a pretty simple decision. If the cost of cutting the lacing plates exceeds the cost of the additional steel for the single plate, than it makes sense to use a single plate. If the cost of cutting is less than the cost of the material, then it makes sense to use lacing. In the nineteenth century, steel was relatively expensive and skilled labor was relatively cheap. Today the situation has reversed. So lacing was the cheaper option then and the more expensive one now.

There are other factors, of course. Laced columns are weaker than solidly built-up columns, so they could only be used in relatively lightly-loaded areas. We often find buildings that have the same size channels used in built-up columns for the top four floors, with lacing at the top two floors and single plates at the third and fourth floors down. Laced columns expose the interior space of the built-up column box section, which can be good or bad depending on your faith in your ability to paint inside. And the geometry of laced columns is more difficult to figure out – the fastest way to get the dimensions involves trigonometry – and may have been beyond the capability of small iron works.

A final note: the picture above obviously shows laced compression struts in a bridge truss, but the design is nearly identical to laced columns in a building.

Dumb Luck

February 27, 2017

That is not good. It’s an old concrete slab – the age is demonstrated by the board-form marks, meaning it was built before plywood was available – reinforced with wire mesh. The mesh is visible on the left and across the middle because the cover concrete has spalled off; the cover spalled off because the […]

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Southeast In The Fog

February 26, 2017

Looking into the harbor, with Governors Island dead ahead. The pillbox to the left of the island is the mid-span ventilation shaft of the Brooklyn-Battery Tunnel.

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West In The Fog

February 25, 2017

From Manhattan past the Hudson River, to Jersey City.

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Serious Engineering For Recreation

February 24, 2017

I mentioned yesterday that the subway lines of southern Brooklyn trace their origins to excursion railroads. Where there are excursion railroads, there must be a destination, and the Brooklyn, Flatbush, and Coney Island Railway took you to the resort hotels of Brighton Beach. That’s the Brighton Beach Hotel above, circa 1900. Shortly after it was […]

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An Unexpected Growth

February 23, 2017

Why is there a plate girder in the street? The easy answer is that there’s a subway line below – this is the Q train at Beverley Road – but that’s not really an explanation. The building on the right, obscured by the fence, is an ornate little train station, more suited to a small […]

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Learning From Failure

February 22, 2017

I first heard the joke in 1982: How dumb are engineers? We can’t learn from success, rather we only learn by destroying something. Thirty-five years later, it occurs to me that the reason I never thought the joke was clever is that I had played Clue and Mastermind when I was a kid and both games […]

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Window Tracery As Structure

February 21, 2017

When a structural engineer tells a colleague that they are working on a window restoration project, the colleague might say, “But windows are not a structural element in a building, other than keeping wind and weather out.” That statement is correct; if you remove the windows from a building, the structural still stands. However when […]

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February 19, 2017

Another good and long read that I recommend: Why is Sketching (Still) Important (To Design)? A longer version of this argument can be found in one of the best books on engineering epistemology, Engineering and the Mind’s Eye. The shortest possible version of the idea: if you can’t draw it, you don’t really understand it. Finally, the […]

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Hidden Technologies

February 18, 2017

I’m torn about the demise of card catalogs. I loved leafing through them and occasionally finding something I wasn’t looking for, but I get my research done a lot faster with modern index databases and full-text searches. In any case, who knew that there were fonts designed just for card catalog use? Thanks to the […]

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