FIELD TEST RESULTS OF AN ULTRASONIC APPLIED STRESS MEASUREMENT SYSTEM FOR FATIGUE LOAD MONITORING

Fatigue loading in bridges due to traffic is an important factor in assessing the structures condition. Fatigue loading is measured by determining the applied stress seen by a structure. Conventional methods for applied stress measurement use strain gages, which are time consuming to install. A possible alternative for making the applied stress measurements is ultrasonic techniques using non-contact electromagnetic acoustic transducers (EMATs). This method requires no time consuming surface preparation and is easy to install. Some of the main difficulties of measuring applied stress fluctuations in bridge members are the relatively low (usually less than 14 MPa [2 ksi]) stress cycles and the frequency of the measurements, which are in the order of several Hertz. A prototype system that uses EMATs to measure applied stress cycles has been built for measuring fatigue loading in bridge structures. This paper discusses results of field test conducted with this measurement system. This includes effects of an actual bridge environment, such as surface conditions, on the system.