Structure Parameter Identification Based On Long-Gauge Strain

Structure health monitoring plays a vitally important role in the structure security operation, bearing capacity evaluation and long-term performance prediction. Structure parameter identification based on monitoring data is an important part of structure health monitoring system. This paper mainly studies the structure parameter identification based on long-gauge strain data. Research and innovation are as follows:(1)A new sensor technology based on long-gauge strain and its principal theory is introduced. As an important part of area distribution sensor technology, the operating principle, design and install method of long-gauge FBG sensor is introduced.(2) Various kinds of structure parameter identification based on long-gauge strain are introduced. A method of defelction calculation based on long-gauge strain is introduced, and its principle is based on deformation theory of beam and the conjugate beam method. Series formula of long-gauge strain modal theory is derived based on the traditional displacement modal theory and point strain modal theory. It's found that the modal parameter such as frequency, damp, modal mode and strain flexibility of structure can be identified according to the property of long-gauge strain frequency response function.(3)A damage detection method based on long-gauge strain is proposed. The main process is as follows:By performing the impact tests of the intact and damaged structures respectively, long-gauge dynamic strain responses are measured by long-gauge fiber optic sensors. By calculating the principle components of measured strains and their averaged Euclidean norms, a new damage index, defined as the difference of the averaged Euclidean norms of the principle components calculated from the strain measurements of the intact and damaged structures, is generated for structural damage localization. Examples of a steel stringer bridge have been investigated to illustrate the effectiveness of the proposed method.(4)A cable tension measurement method based on long-gauge strain is proposed. Two kinds of linear vibration theory of cable is introduced, and the calculation formulas for cable tension are derived in both cases. The existing methods of cable tension measurement are reviewed, and the theory of frequency method is studied firstly. The existing methods of cable tension measurement based on FBG sensor are reviewed, and a new method of cable tension measurement based on long-gauge FBG sensors in two under two kinds of train of thought is proposed. Examples of cable vibration test in laboratory have been conducted to illustrate the effectiveness of the proposed method.(5) A method of cable flexibility identification and damage detection based on long-gauge strain is proposed. The existing methods of cable modal parameter identification are reviewed, and the concept of cable flexibility is proposed when cable is simulated as a beam with axial force. The detailed process of cable strain flexibility identification is given based on subspace identification method when the onput is known. Examples of finite element model analysis of a cable of Jiangyin Bridge and vibration test in laboratory have been investigated to illustrate the effectiveness of the proposed method. For the current problems of cable damage detection field, a method of cable damage detection is proposed, and two kinds of damage index is defined based on the identified cable strain flexibility. Examples of cable finite element model analysis of a cable of Jiangyin Bridge have been investigated to illustrate the effectiveness of the proposed method.