Protecting life and reducing economic losses
Structural monitoring represents an important part of earthquake engineering science. While seismology provides seismic and seismo-tectonic activity information, engineering seismology converts this information into useful data for earthquake engineering science. The latter takes the information and provides both general and specific codes used by structural engineers in the design process. Due to the relative randomness of earthquake phenomena, each earthquake provides additional information for a known region or brings to light new seismic faults.
A primary goal of earthquake engineering is to define, recommend and implement effective measures against the possible negative effects of earthquakes. To protect life and limb and assist in reducing economic losses is what gives impetus to engineers to fully master structural analysis methods and models so that the actual behavior of the structures coincide as nearly as possible with the behavior they anticipate. Specifically, structural monitoring as part of the experimental process seeks to accomplish the following:
- Prove the dynamic model used in the design process
- Validate or improve seismic design codes
- Monitor structural response during an earthquake
- Provide information used in post-earthquake actions
- Interact with automatic shutdown controls to minimize damage
- Protect the environment against high-risk spillage
- Provide data useful to the retrofit process
- Reduce the monitored structure’s post-earthquake non-operational downtime
The recommended instrumentation for achieving the above structural monitoring goals include the following characteristics:
- Minimum of 12 recording channels
- High dynamic range of at least 108dB
- High sampling rate, adjustable between 10sps and 250sps
- Storage capacity of 20MB or more
- Remote operation
- Precise timing (GPS)
- Interconnection between two or more systems (common timing and triggering)
- Minimum of 36 hours full functional autonomy without AC
- User settable pre-event and post-event memory to provide the beginning of the
- shaking and the free motion of the structure after the event ends
Setting the standards
Kinemetrics began developing this type of instrumentation starting in the late 70s with the CR-1 Central Recording accelerograph for commercial structures and the SMA-3/SMP-1 for the nuclear industry. Recently, as part of the Altus family of instruments, Kinemetrics introduced the Mt. Whitney and K2 for residential structures, the Etna to meet building codes, and the CONDOR for high-risk environmental impact and nuclear applications.
In the world today, thousands of residential and industrial buildings, special structures such as dams, bridges, antenna towers, and high-risk facilities such as chemical or nuclear power plants are instrumented with seismic equipment manufactured by Kinemetrics. The new generation of Altus instruments, the K2 12 channels, Mt. Whitney 18 channels, Etna, and the CONDOR 24 channels, are either installed in new structures or used to replace the old instrumentation. These multi-channel accelerographs provide accuracy in meeting structural monitoring requirements.
Mt. Whitney used as instrument of choice
One of the most "studied" buildings in California is the 10-story Millikan Library at Caltech in Pasadena. The reinforced concrete frame/shear wall structure is instrumented with two Kinemetrics' Mt. Whitney Multi-Channel Central Recording Systems that include 36 accelerometers. Three verticals are placed in the basement and three horizontals are located on each of the floors.
The objective of the system is to provide data for the study of the transmission and propagation of seismic waves in multi-story buildings. From these studies, researchers will be able to develop and test their field testing techniques.
Instrumentation of Caltech's Millikan Library