Construction History: Psychedelia

I generally try to only write about real structures. I made an exception for the Buffington patent because it has played a part in the written history of skyscrapers. Today’s structure doesn’t require an exception, as I’ve seen one built example of it, but it was exceedingly rare when built and is rarer today.

In 1916, Edward Smulski patented a concrete flat-slab system that later became known as the Spider Web system, for reasons that the drawing above makes clear. Flat slab systems became popular for industrial buildings after 1900, and there was the same kind of intellectual land-rush that had taken place twenty years earlier for floor systems in steel-frame buildings. A lot of systems were patented, often with minor or meaningless differences. The Spider Web system was different in an important way: it was nonsensical.

The reinforcing within reinforced concrete is meant to carry tension in the combined material. In practice, that means that rebar should be running across cracks at right angles (or as near as is possible) to the crack length. Fortunately, the directions of cracks in concrete are reasonably well understood, so the direction that the rebar should run is also understood. In a flat-slab system, without beams, the most important directions are parallel and perpendicular to the column lines, and secondary and less important directions are the diagonals connecting the opposite corners of each bay. (Floors without the diagonals are usually called two-way systems; floors with the diagonals are four-way systems.) This was already known in 1916.

The drawing above and the one below represent two variations on Smulski’s reinforcing concept.

Some of the bars make sense, as they follow the understood pattern of potential tension, represented by cracks. But the distinctive part of the system, the bars running in circles, don’t make any sense. Parts of them are running in the right direction, but the nature of a circle is that if part is oriented correctly relative to straight line, the rest is not. The circular bars around the columns are mildly useful, although the tension at the top of the slab at right angles to the column lines would be better addressed by straight bars. The circles in the middle of the bay and centered between the columns are simply useless. The plans are beautiful as geometric art, as long as you ignore their intended meaning.

The building I saw with this system was 80 years old at the time, and would be 100 years old today. It was performing just fine, which is not proof that it could sustain its design loads but is evidence of reasonable capacity. So the Spider Web system isn’t a complete failure. But bent bars cost more than straight ones and if that additional cost comes with less capacity rather than more, then there’s no point.

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