San Francisco Considers More Aggressive Measures to Earthquake-Proof High Rises

Seismic activity has spooked San Francisco officials, who are now calling for stricter retrofitting measures, Rong-Gong Lin II writes. "First, a centerpiece of San Francisco's new downtown, the 58-story Millennium Tower, started sinking and tilting. Then last week, the city's new $2.26 billion transbay bus station was abruptly shut after cracks were found in two steel beams."

The city has released a list of over 150 tall buildings, including many constructed prior to modern seismic codes, as a prelude to assessing their need for retrofits. "The inventory comes with a sweeping proposal to more closely examine the city's skyline with an eye of making costly fixes to towers that could collapse amid major shaking. Officials are also calling for rules for new construction, aimed at preventing sinking of buildings as well as making tall buildings even stronger to resist wobbling in an earthquake."

These calls, Lin says, represent heightened rhetoric from several months ago, "when officials emphasized the difficulty in identifying the city's largest vulnerable buildings, such as those made of brittle concrete." Extant city laws, Lin continues, have not been particularly effective in requiring or spurring retrofits. "Current city law does require a seismic retrofit when two-thirds of a building's floors are renovated. But that almost never happens to tall buildings, when only a small fraction of the building undergoes construction at any given time."