A Study of Temperature and Aging Effects on Eigenfrequencies of Concrete Bridges for Health Monitoring

This paper discusses the influence of environmental factors and of normal
material aging on the eigenfrequencies of concrete bridges based on monitoring
data registered during 4 years of a specific bridge. It is a new composite
steel-concrete bridge built in 2006 in Luxembourg. The measurements are
analyzed and compared to literature data. The final objective is the use of real
monitored eigenfrequencies for structural health monitoring and damage detection
based on identification of stiffness losses in practical applications.
Therefore, it is very important to identify and compensate for outdoor influences
namely temperature, excitation force level and normal aging effects, like
creep and shrinkage of concrete and their impact on material properties. The
present paper aims at describing these effects in order to separate them from
damage effects. It is shown that temperature change rates and temperature
gradients within the bridge have an influence on the eigenfrequencies. Hence
the key idea for assessment from the full database is to select only measurements
with small temperature differences and slow temperature change rates.