Acceptable Performance

The picture abide shows the home of the San Francisco Call newspaper following the 1906 earthquake. The Call Building had a modern steel frame that even included some attempts at seismic bracing and, as can be seen here, suffered little earthquake damage. Its interior was, however, severely damaged by the fires that followed the quake, which is not very surprising, as the fires generally caused more building damage than the quake did. The newspaper moved to a different building but the building was refurbished and returned to use; it was heavily modified in the 1930s, with ordinary floors replacing the extravagant dome.

One of the difficulties in designing for extreme events is defining what we consider to be acceptable performance. For example, the development of US building technology 1870s, 80s, and 90s consisted largely of making buildings as fireproof as possible, limiting fire spread and the effect of heat on building materials. That effort was largely successful, as the Call Building shows: despite having burned out of control, the basic structure of the building was not appreciably damaged. It took several horrendous failures, most notably the Triangle fire, to show that protecting the building from structural damage and protecting the inhabitants are two very different things. So acceptable fire performance was redefined from “the building survives” to “the people survive.” Obviously there’s overlap between those two goals, but they lead in somewhat different directions.

Seismic performance has had similar issues with definition. The Call Building performed, no doubt. What about this metal-frame building nearby, whihc appears to have been in construction at the time? The frame and floors survived, but at least some of the side wall collapsed. It’s difficult to tell how much had been complete.

On the other side we have three masonry-bearing-wall buildings with three different fates:

The building on the far right is gone. We’ve got its ghost on the side of the building on the middle and some small remnants of wall, but that’s it. The building on the left is pretty badly damaged, with large chunks of its front facade and far wall collapsed along with at least some of the roof and interior floors. The building in the middle appears to be mostly intact, with a lot of fire damage. The cornice has collapsed from the front facade and parts of the side and rear walls are missing on the right. So in order we’ve got (1) nothing left to repair, (2) a huge repair job or demolition and replacement, and (3) a salvageable building.

Anything can be repaired or rebuilt if money is not an issue, but of course it almost always is. So the capacity of a building to survive an earthquake or fire is not only a safety issue but an economic calculation. The minimum standards in codes are meant, among other things, to prevent owners from deciding that they’d rather pay the least amount possible during construction and simply replace a building if it fails. The Call Building surviving was not enough, as shown by the Triangle fire death toll, but it’s a good place to start.

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