NSF Award Abstract - #0000027

Development of a Wireless Sensor to Detect Cracks in Welded Steel Connections

Abstract

0000027 The objective of this research project is to develop a wireless sensor to detect cracks in welded steel connections. The 1994 Northridge earthquake caused extensive damage to the connections of structural steel, special moment-resisting frames. Critical welds fractured in more than 200 buildings throughout the epicentral area; however, the damage was difficult and expensive to detect because the steel members are covered with fireproofing. Removal of the architectural cladding and fireproofing for inspection is expensive, time consuming, and disrupted the normal activities of the building occupants.

The proposed sensor relies on RF technology. The sensor is a resonant circuit, similar in design to adhesive Electronic Article Surveillance stickers that are used to control inventory in retail stores around the country. The sensors will be attached to the structural steel frame during construction, and are passive. The frequency characteristics of the sensor will change when a crack in the weld material or base metal beneath the sensor reaches a given size. A wireless transmitter/receiver will be used to interrogate the sensor and obtain information about the presence of cracks without removing any of the architectural finishes or fireproofing. The proposed crack detection sensor is attractive because it is inexpensive, robust, easy to install, and maintenance free.

The research has been divided into eleven tasks need to transfer this technology into structural evaluation. Critical issues that must be addressed include selection of appropriate components for manufacturing of the sensor (polymer film, wire coil, and adhesive layer) determination of required surface treatment for the steel, evaluation of optimal sensor placement based on the configuration of the welded connection, determination of optimal coil geometry, and development of a wireless transmitter/receiver to generate a frequency sweep to interrogate multiple sensors.

This project is supported under the 3rd -Year Competition under NSF 98-36 "US - Japan Cooperative Research in Urban Earthquake Disaster Mitigation"