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

Abstract

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.

Comparison of different excitation‐ and data sampling‐methods in structural health monitoring

“…First eigenfrequency vs temperature T 2. The green “o” are data Δ T ∈[−1.5; 1.5]°C; the blue “‘ x ” are only data within T 2 ∈ [0°C; 15°C] and limited slopes …”

“…Several bridges were monitored by this algorithm, an example is the Z24‐bridge in Switzerland . Another is a new composite steel concrete slab bridge in Useldange (Luxembourg) that have been monitored for more than 10 years, as detailed in Reference . Accelerations and temperatures have been recorded at several locations that an example is given in Figure .…”

“…Such a box can easily be used to determine the plot of any eigenfrequencies vs temperature df i /dT , wherefore the slope stays quite constant . Once this slope is provided, it can be used for temperature compensation .…”