Monitoring the Integrity of a superstructure under heat loads
Detection of imminent structural failure during emergency high heat load conditions is critical to potentially saving the structure or the lives of firefighters. Metallic structural members installed in new building construction are protected by insulation. If this insulation is physically damaged then the structural member could be exposed to high heat loads during a fire or explosion. Excessive heat will cause the integrity of metal structural members to loose their ability to support the loads intended. An inexpensive system to monitor every foot of metal structural members is just as valuable as a fire detection system.
Researchers at the Johns Hopkins University Applied Physics Laboratory have recently invented a system to monitor the several different temperature levels of structural members. This system is continuous therefore covering all structural members. Depending on the type of metal used the system can be adapted to give an early warning that a hot spot has developed. This early warning would provide time for corrective action to be taken at the point of incipient failure. As the temperature increases a second part of the system will indicate that corrective action is not effective. This could prompt more action or evacuation. As the temperature continues to increase a third part of the system will indicate that the structural member is loosing its integrity and that personnel should evacuate. Collapse is imminent. Making this system practical and cost effective was a major challenge. Additionally the system had to be easy to install, cover all the members, have a lifetime of greater than 100 years, be no corroding and nonflammable. The solution is a metal tape consisting of pre-selected materials that is attached to every foot of the metal structure. Continuously throughout the length of the tape there are 3 sensing elements, which will melt and cause an open circuit between the lead wires. This open circuit and the associated location using time domain reflectometry will give the appropriate personnel exact location and temperature conditions. The lead wires will connect to a communication system, which can be multiplex to a safe location for readout and diagnostics. The hardware cost for a system to protect a 400,000 square foot, 10-story building would be $16,000. Installation would be done prior to the insulation of the members.
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