Oakland’s City Hall was the tallest building west of the
Mississippi in 1914, when it was completed. It’s still an
impressive structure, 324 feet high, covered with intricate
stonework and flooding the plaza with warm reflected light
around midmorning. City Hall weathered the 17 October 1989
earthquake without collapse, although there was serious damage
and it is said we nearly lost the clocktower. After the quake
the city was motivated to retrofit the structure. In evaluating
the possibilities, Charles Rabamad and Donald Wells write, “To
minimize the amount of new construction, the existing structure
was given credit for the strength it exhibited during the Loma
Prieta earthquake. This performance-based approach required less
strengthening than conventional, code-based design, which
ignores the existing capacity of the building.” Today City Hall
rides on a grid of 113 big, fat rubber-and-lead base isolators
19 inches high and either 29 or 39 inches wide. These soften the
shaking and allow the building to be