Active Fatigue Crack Inspection, Detection, and Analysis on Three Steel Pennsylvania Bridges Using the Electrochemical Fatigue Sensor

摘要

One of the most significant problems facing our infrastructure today is fatigue cracking of critical bridge members. Though this type of damage can have devastating results to the structure and to human life, little has been done in the industry to more accurately assess these cracks. Critical funds are often wasted repairing cracks which are not a threat to the health of the bridge (i.e., those that aren't growing). Additionally, a significant portion of fatigue cracks are missed by visual inspection alone, the primary detection method utilized in the industry, and are therefore never addressed. The Electrochemical Fatigue Sensor (EFS) can detect actively growing cracks as small as a few mils in length. Unlike conventional NDT methods, EFS will only detect cracks which are actively growing; and will do so for very small cracks. Also, because the EFS system depends on electrochemical changes that naturally occur in steel during fatigue cracking highway bridge "noise" is not an issue as it is with some other NDT methods. By detecting growing fatigue cracks under ambient loads, EFS inspection can ultimately minimize unnecessary repairs, bridge closures, and postings as well as detect dangerous fatigue cracks that are visually undetectable. The paper discuses the technical background of the EFS system, several case studies with a specific interest in testing completed in October 2006 on three Pennsylvania Interstate steel bridges with documented cracks at fatigue susceptible details. Using EFS, the engineering team determined that some of the cracks were continuing to actively grow while other retrofitted locations were not exhibiting growth, allowing for deferment of repair funds. Also, the engineering team identified additional active cracking locations not previously documented.