Strain flexibility identification of bridges from long-gauge strain measurements

• It is the first time to study strain flexibility identification by processing impact test data.
• A novel long-gauge fiber optic sensor is proposed for macro strain measurement, which provides an excellent opportunity for strain modal identification.
• Numerical and experimental examples verified the effectiveness of the proposed method, and the identified strain flexibility is useful for structural safety evaluation and strain prediction in engineering practices.

Strain flexibility, defined as the strain response of a structure׳s element to a unit input force, is import for structural safety evaluation, but its identification is seldom investigated. A novel long-gauge fiber optic sensor has been developed to measure the averaged strain within a long gauge length. Its advantage of measuring both local and global information of the structure offers an excellent opportunity of developing the strain flexibility identification theory. In this article, the method to identify structural strain flexibility from long-gauge dynamic strain measurements is proposed. It includes the following main steps: (a) macro strain frequency response function (FRF) estimation from macro strain measurements and its feature characterization; (b) general strain modal parameter identification; (c) scaling factor calculation, and (d) strain flexibility identification. Numerical and experimental examples successfully verify the effectiveness of the proposed method.