FIELD TRIALS

What happens when earthquakes hit

Bridges Article December 28, 2000
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Earthquakes are a fact of life in California, damaging buildings and bridges, and posing serious danger to the general populati

Earthquakes are a fact of life in California, damaging buildings and bridges, and posing serious danger to the general population. Major earthquakes have resulted in millions of dollars in property damage over the years. The losses, however, are often measured in more than just dollars and cents. Thousands of citizens lose their homes, suffer injuries or death, and otherwise have their lives adversely affected by earthquakes.


After the San Fernando earthquake of 1971, the Strong Motion Instrumentation Program (SMIP) was established within the Department of Conservation, Division of Mines and Geology. SMIP has employed numerous resources to measure the affects of earthquake shaking in California buildings, bridges and other structures.


In a joint effort with the California Department of Transportation (Caltrans), SMIP instrumented many bridges with seismic monitoring and event notification equipment throughout California.


In the area surrounding Eureka, Calif., the Sensaphone 2000 from Phonetics Inc. of Aston, Pa., is a component of a monitoring system used by Caltrans on a select number of bridges.


SMIP designed the system for the Eureka bridges so that every time a strong tremor shakes the bridge structure beyond a certain point, traffic control gates close the bridge entrance to temporarily block access.


The SMIP development team, consisting of Carl Peterson, Alan Cramlet and Richard Pane, contacted several vendors to supply integral equipment items required for the project. Among the vendors was the ACEI Co. of Santa Ana, Calif., a group that specializes in communications and information systems and related products.


The SMIP development team requested cost quotes and specification from the ACEI Co. on the Sensaphone 2000 system as a possible component to be integrated into the design of the overall seismic monitoring system to be used for the bridge gate projects.


The development team determined that the Sensaphone 2000 unit suited the needs for a voice notification device primarily because of its cost-effectiveness and voice notification capabilities.


The unit features eight universally configurable units, which in the bridge applications monitor information from a field computer that performs the seismic monitoring activities. It also features built-in power monitoring, battery level monitoring and non-volatile memory with optional battery backup designed forrechargeable


Ni-Cad batteries. It can communicate with up to 32 destinations in order to deliver alarm messages or status reports. Communication is made via fax machines, voicemail, computer modem, numeric or alphanumeric pager, or e-mail address.


Equipped with Windows software, the user-programmable, remote monitoring unit sends alarm messages to any preselected communication destination in addition to being capable of saving up to 32,000 time-stamped records of selected inputs.


In April 1998, installation of the seismically activated gate systems began on two historic bridges 100 miles south of Eureka and on three newer bridges in the Eureka area. Two months later the installations were completed.


The instrumentation mounted on the bridges was connected to a computerized control and measured earthquake activity. In the event of strong seismic shaking, the monitoring computer initiated commands for closure of the seismically activated gates, blocking the bridges’ entrances, while sending alarm signals to the Sensaphone 2000 units which in turn initiated a telephone calling sequence that delivered a pre-recorded message over a satellite telephone link. The message notified SMIP and 24-hour traffic control dispatch personnel of the bridge closure situation. The message from the unit indicated the location of the bridge and reason for the alarm, allowing the dispatchers to send appropriate personnel to the affected site for inspection.


Caltrans selected the two historical bridges to be fitted with the seismically activated gate system because the cost of retrofitting the bridges was high in regards to the small amount of traffic present on those bridges. Concurrently, the other three bridges in the project were fitted with the systems as an interim measure until planned seismic upgrades are completed.


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