What performance can be expected from a conventional structure?
Traditional structural design is only intended to prevent major failures and loss of life. This design approach does not consider
immediate occupation, the maintenance of operation nor does it provide for easy repair. Isolation ensures that the structure suffers minimal or no damage and is functional immediately following an earthquake.
How have isolation systems performed in earthquakes?
The USC Hospital using DIS isolators remained operational throughout the 1994 Northridge Earthquake with no damage. In contrast the Los Angeles County Medical Center located less than a mile away suffered $400 million of damage and was not
operational after the earthquake.
Isolated Structures have Demonstrated a Record
of Excellent Performance During an Earthquake.
The three million-pound Stanford Linear Accelerator (left) in California, protected by DIS isolators, was unscathed by the 1989 Loma Prieta Earthquake. Elsewhere on campus damage was reported to be approximately $160 million.
The California Eel River Bridge was isolated using DIS isolators in 1988. It experienced accelerations of 0.55g in the 1992 Cape
Mendocino Earthquake. The bridge displaced
nine inches laterally and sustained no damage.
It returned to rest in its original position.
How does isolation provide cost savings?
In bridges, isolation reduces the foundation forces by up to 75%. The smaller
foundation
translates into direct cost savings. A study of the Patria Aqueducto Bridge
in Mexico
showed a reduction in foundation concrete and steel by a factor of 3.5.
In buildings, isolation provides cost savings over the life of the structure. An isolated
building will be essentially undamaged in an earthquake. By comparison a conventional
building’s structure and contents will be significantly damaged resulting in business interruption
for weeks, sometimes even months.
Conventional Structure:
The deformation pattern of a conventional structure
during an earthquake. Accelerations of the ground
are amplified on the higher floors and the contents are damaged.
Seismically Isolated Structure: The deformation pattern of an isolated
structure during an
earthquake. Movement takes place at the level of the isolators. Floor accelerations are low. The building, its occupants and contents are safe.