14 DAY TRIAL // News about earthquakes and the damage they produce are becoming more frequent as the media now reach almost all "four corners" of the Earth.
An earthquake is the result of the sudden release of stored energy in the Earth's crust that creates seismic waves. At the Earth's surface, earthquakes may manifest themselves by a shaking or displacement of the ground and sometimes cause tsunamis, which may lead to loss of life and destruction of property. An earthquake is caused by tectonic plates getting stuck and putting a strain on the ground. The strain becomes so great that rocks give way by fault planes breaking.
Even a big truck or a train passing by a building causes a miniature earthquake, whose effects are not immediate, but are observed in time, when cracks start appearing in the building structure.
Both natural and manmade earthquake can seriously affect the resistance structure of buildings, and many architectural monuments and sites have been damaged this way.
A civil engineer and earthquake specialist has developed new wireless sensors in the simulated structural control of a model laboratory building, that can help improve constructions security in case of natural earthquakes.
Shirley J. Dyke, Ph.D., the Edward C. Dicke Professor of Civil Engineering and director of the Washington University Structural Control and Earthquake Engineering Laboratory, combined the wireless sensors with special controls called magnetorheological dampers to limit damage from a simulated earthquake load.
Attached to the sides of buildings, the wireless sensors, about a square inch in size, monitor the force of sway when shaking, similar to an earthquake, occurs. Then they transmit to a computer program that translates the random units read by the sensors into units useful for the engineers and computer programmers. The computer sends a message to magnetorheological dampers, or MR dampers, that are within the building's structure to dampen the effect of the swaying on the structure.
MR dampers act like shock absorbers for a building. Filled with a fluid that includes suspended iron particles, the MR dampers lessen the shaking by becoming solid when an electrical current (turned on by the computer, which has been alerted to the swaying by the sensors) is run through the MR dampers, aligning all of the iron particles.
Until now, approximately 50 structures in Japan used wired sensors for structural control, with most of these structures using what is called a variable orifice damper.
But wireless sensors applications seem to be the next step in damage control. "This is where structural control technology is going," said Dyke. "If you put a wired system in a building, the cost can be prohibitive. Soon, wireless sensors will become even cheaper, making this a nice application. It will be much easier putting wireless sensors into a building compared with taking walls out and installing wires and cables."