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Survival Illustrated

Human nature being what it is, it’s no surprise that photographers were wandering around San Franscisco in 1906, taking pictures and, in the example above, stereoscopic pictures. The picture above shows the ruins of several low-rise brick-bearing-wall buildings with the steel frame of an incomplete building in the near background. That stark contrast – the ruin of the masonry buildings and the seemingly untouched steel building – is a bit exaggerated, as I’ll discuss, but it’s hard to get away from the idea that it shows the future of earthquake engineering.

Thanks to The San Fransisco Earthquake and Fire by Abraham Himmelwright, we can easily identify the frame as the 1907 16-story Whittell Building, two blocks away on Geary Street, which is still there, renamed the Grace Building at some point. Himmelwright was a structural engineer employed by the Roebling company, and his book is a forensic overview of the damage that the earthquake and fire caused in different buildings. (It’s important to refer to the disaster as an “earthquake and fire.” While the fire only took place because of the earthquake, it caused a lot of the damage – by some accounts more than half.) Himmelwright’s first comment on the building is “It is remarkable, for the reason that the entire steel skeleton frame has been erected complete without any walls or fire-proof floors.” This is, frankly, describing bad planning. Completing the entire frame before the exterior walls have been started is an inefficient schedule for constructing a high rise.

The Whittell Building is number 13, incorrectly named as the Whitehall Building.

Next, “The levels on the water table indicate that the foundations have not been displaced and remain practically level. Observations on the columns do not indicate that they are out of plumb.” The building is not near the waterfront and, apparently, not supported on liquefiable soils.

“There was no combustible material to cause any structural damage to this building, except some scaffolding lumber that was piled on the tier at the ground level. The burning of this caused the deflection and warping of some of the beams, which is the only damage that was observed.” Again, the fire was at least as much a danger as the earthquake itself.

And then the conclusion: “This building is particularly interesting to the structural engineer. The steel skeleton frame, without any masonry or floors, had sufficient strength and rigidity to resist the sudden and racking motions of the earthquake.” By 1906, people had been constructing modern steel skeleton-frame buildings for 16 years[efn_note]It’s time to mention The Structure of Skyscrapers again.[/efn_note] and Himmelwright certainly understood the principle that in such a building the frame carries all gravity and lateral loads. Without attempting to mind-read the motives of a man writing 115 years ago, this might be an attempt to draw non-engineers’ attention to the new frame technology and it might be a statement that a harsh real-life test showed that the theory worked as expected.

The lack of diagonal bracing in the photo makes it clear that the building has a moment frame, which is an effective means of dissipating the energy of a an earthquake. Also, and unlike wind load, which is proportional to the physical size of a building (its “sail area”), seismic load is proportional to the building’s weight. Without exterior walls and interior partitions – all masonry in that era – the half-complete Whittell had a lower seismic load than it would when completed. So rather than being weakened by the lack of masonry – as an older-technology building would have been – it was aided by that lack.