NEES Centrifuge Laboratories

A centrifuge (pronounced SEN-trih-fyuj) is a machine that rotates, or spins, rapidly. The spinning action creates centrifugal force, which is used to separate substances of different densities or weights. A common type of centrifuge found in most homes is the family washing machine. In the spin cycle, washing machines use centrifugal force to force water out of the wet clothes.

A geotechnical centrifuge is used for research in geotechnical science, an area of civil engineering concerned how geological materials (dirt and rock) interact with the foundations of built structures such as bridges, roads, and houses. In a research laboratory, engineers use centrifuges to study the affect of gravity on soil samples or small-scale models of structures. The experiments serve to measure properties such as the strength, stiffness and capacity of foundations for bridges and buildings, the stability of hillsides and seawalls, etc. Small models do not weigh the same as a full size structure, of course, but the forces created by the centrifuge can artificially recreate the affects of gravity to provide accurate results.



How do centrifuges help earthquake engineering?

Centrifuge tests are important for understanding - and predicting - the effects of earthquakes on buildings, bridges, roads and the ground upon which they stand. That knowledge will enable us to build earthquake-resistant structures and reinforce existing structures to withstand the force of earthquakes.

The NEES Program has two geotechnical centrifuge facilities. They are located at the University of California, Davis and Rensselaer Polytechnic Institute. Each facility has a shake table mounted on the centrifuge. The shake table can be adjusted to simulate a full range of earthquakes.


Why put a shake table on a centrifuge?

Freeway damage resulting from an urban earthquake with epicenter in the San Fernando Valley (Northridge, CA 1994)
- photo courtesty of USGS

In earthquakes much of the structural damage is not the result of just the shaking of the structure but of the liquefaction of the underlying soil. In the 1989 Loma Prieta earthquake, the most severe damage was in areas where buildings and other structures where located on top of loose soils - especially fill dirt.

The spinning of a centrifuge creates pressure on the sample attached to the centrifuge arm. Researchers can adjust the speed of the arm to create different pressures on a soil sample, recreating conditions for a wide range of natural terrain and depth. Thus, if a model of a building or structure is built on soil and mounted on an integrated shake table, the centrifuge will simulate realistic conditions. Wireless sensors and a robot equipped with high speed video cameras are used to monitor the model while the centrifuge is running. That way, engineers see not just the final effects of their simulated earthquakes, but also how the damage occurred over time. The experiments help us learn how to prevent major structural damage during future earthquakes.


Learn more about centrifuges
- Geotechnical Centrifuge at UC Davis
- Geotechnical Centrifuge Center at Rensselaer Polytechnic Institute