Tuesday, February 15, 2011

Seismic Matters

Wunderlich Park near Woodside

These high dry stone walls near Woodside California which were built before the big earthquake are still in great condition.

The lush foliage of moss and various species of fern makes this wall an especially attractive border enclosing a grassy area around an old stable.

That these walls have lasted so long seems to indicate that they were built right, even though they didn't build them out of concrete.

For centuries the mortar-free construction has proven to be apparently more earthquake-resistant than using mortar. The stones of the dry-stone walls in the pictures above which were built by the chinese workers in California in the late 1800's for example, could move slightly and resettle without the walls collapsing, which should be recognized as an ingenious passive structural control technique employing both the principle of energy dissipation and that of suppressing resonant amplifications. When walls are built correctly (meaning, well-bonded, properly battered, and having good foundations and built sufficiently thick enough ) they can resist seismic movement because of a certain cohesive elasticity.