A Temperature Driven Method For Structural Health Monitoring

Abstract

Structural Health Monitoring (SHM) is the process of equipping a structure with sensors in order to assess the condition of that system using a combination of structural and analytic techniques. In every application, SHM involves the comparison of an unknown structural state to a baseline of healthy behavior. SHM as a field has come to prominence as a solution to aging infrastructure but still lacks the ability to consistently monitor and assess different types of structures. One obstacle is that the uniqueness of bridges and buildings necessitates individualized monitoring strategies. Another challenge is the influence of environmental effects on structures, especially temperature. In bridges, daily temperature changes can influence the strain on the structure more than daily traffic loads. Many SHM techniques struggle to compare a baseline, healthy structural state to a new unknown state because of differences in the environmental conditions.

Temperature Driven-Structural Health Monitoring (TD-SHM) considers temperature as the driving force in structural behavior and therefore the driving force in monitoring. TD-SHM compares an input temperature to an output strain and displacement to form three- dimensional signatures for the structure. These signatures describe the behavior for the structure across all monitored temperatures. Changes in these signatures indicate unusual behavior or damage in the structure. Two immediate benefits of this method are the universal nature of temperature effects on structures and the ability to measure temperature as an input on a structure for the formulation of a complete input-output model.

This thesis develops TD-SHM using strain, temperature, and displacement data measured on the Streicker Bridge at Princeton University. The main conclusions are the following: 1) thermal gradients on structures can obscure the temperature-strain relationship, but it is possible to filter out time periods where these effects are present; 2) the coefficient of thermal expansion (CTE) of concrete structures varies throughout seasons and throughout structures but are consistent through the years, and 3) three-dimensional temperature signatures can provide insight into the thermal behavior of the structure and highlight unusual behavior based on changes to that signature.