Two experimental soil-foundation-structure-in- teraction (SFSI) structures installed side-by-side at the NEES@UCSB Garner Valley field site are fully instrumented to record their response to am- bient earthquakes. The larger frame is identified as the SFSI and the smaller one is affectionately called “MiniMe.”
The SFSI experiments are very significant because they record in situ response of structures to earthquakes. While experimental shake table and laboratory testing research is advancing our
understanding of the response of structures and components to fixed base excitation, the “truth” of structural response is found in these in situ recordings. The Garner Valley project, a joint col- laboration between NEES@UCSB and NEES@ UCLA, is unique in its ability to record field data of structural response.
A mobile shaker is installed on the roof of the SFSI. The shaker is run every night and the response of the SFSI is recorded. Running this experi- ment daily has provided a valuable data set that documents the change in structural behavior with changes in the environment such as temperature and ground water level. The structures have been configured with and without bracing for compari- son of response.
Animations of the response, which will be a great asset in teaching seismology and structural engineering, are found at http://vimeo.com/34233690. To the best of our knowledge, these are the first animations to show the response of structures to earthquakes, using recorded data. Many features of structures that are covered in theory in engineering classes can be seen in these animations. For example, in the unbraced SFSI frame, the roof of the structure resonates in response to the base excitation. In the braced MiniMe structure, it is possible to see the greater deflection in the “soft” direction, which is the longer side of the rectangu- lar structure. Features of earthquakes are also vis- ible in these animations, such as the initial vertical motion from the P-wave followed shortly by the larger horizontal motions of the S-wave.
The SFSI facility was designed to study the pas- sage of waves through the soil column below the structure, up through the foundation and into the structure. Often the observations of ground shak- ing recorded on the foundation of structures are not the same as those recorded on open ground
due to the interaction between the soil and foun- dation. Understanding these interactions at a rela- tively simple site using a simple structure is a pri- mary purpose of this facility. The test structures are instrumented with accelerometers, rotational velocity sensors, strain gauges, pressure cells, and uplift displacement sensors. These field studies of structural frames with and without diagonal brac- ing demonstrate the importance of bracing and the primary effect of horizontal accelerations during earthquakes.
