The Influence of Sensor Length on Strain Measurement at Locations of Concentrated Forces

Abstract

Structural Health Monitoring is a non-destructive method to monitor the behavior of structures. Most structural health monitoring systems measure the internal strains of a structure. This thesis addressed the challenge of monitoring strain at locations where concentrated forces are applied. The aim of this research was to identify a method to predict the strains at this type of location because the strain field is perturbed and non-linear and evaluate the accuracy of long-gauge sensors that are installed at the location of concentrated forces. Using theoretical approaches, the strain field perturbation was studied and modeled. A linear relationship was found between the sensor data. Furthermore, a finite element model was made using SAP2000 to validate the model and relationship. Sensor data from two locations of the real structure Streicker Bridge, at the campus of Princeton University, was used to confirm this relationship. Each observed location was equipped with three sensors with different gauge lengths of 30-, 60-, and 120- centimeters. The method to model theoretical strain was found to be effective at predicting the strain values at locations of concentrated force. This research demonstrates that strain perturbation due to a concentrated load affects sensors with shorter gauge lengths the most. In addition, sensors with the shortest length were observed to be most influenced by temperature changes. The objectives of this research were met and provide a basic understanding of the effects sensor length has on strain measurement. Future work analyzing additional data from an existing structure such as Streicker Bridge can be done in order to further prove these findings and gain more information about strain sensor length.