Abstract
The structural safety of a beam structure is assessed by a comparison between the maximum stress measured during monitoring and the allowable stress of the beam. However, the strain directly measured from a fiber Bragg grat- ing (FBG) strain sensor may not be identical with the actual maximum strain induced in the structural member. Unless a FBG strain sensor is installed exactly on where maximum strain occurs, the reliability of the evaluated safety based on the measured strain depends on the number and location of sensors. Therefore, in this paper, analytical models are presented for estimation of the maximum values of strains in a linear elastic beam using the local strains measured from FBG sensors. The model is tested in an experiment by comparing estimated maximum strain from FBG sensors and directly measured strain from electrical gages. For the assessment of safety of typical beam structures in buildings and infrastructures, analytical models for various loading and boundary conditions are provided.
Highlights
Maximum stress in a structural member for buildings and infrastructures can exceed an allowable stress when the structure is subjected to various loads such as earthquake, wind, or unexpected loads
Since the actual stress distribution induced in a beam structure by varying amounts and types of loads is non-uniform, the strain directly measured from a strain sensor is not identical with the actual maximum strain induced in the structural member
To reduce the number of sensors, the average strains from long gauge fiber optic sensors (LGFOS) or vibrating wire strain sensors (VWSGs) have been used in estimating the maximum strain, since LGFOS or VWSGs measure integrated strain over a relatively long gauge length (Park et al 2005, 2007; Lee, Park 2011)
Summary
Maximum stress in a structural member for buildings and infrastructures can exceed an allowable stress when the structure is subjected to various loads such as earthquake, wind, or unexpected loads. If a member is subjected to a higher stress than the allowable stress, the safety and serviceability of the member should be checked to prevent unexpected damages For this reason, strain-based structural health monitoring (SHM), the maximum stress in a structural member has been widely used as clear index to assess the state of the member (AISC 1989; Farrar, Worden 2007). In this paper, analytical models are presented for the determination of the maximum values of strains or stresses in a beam structure based on the local strain measured from FBG sensors. The models define the relation between measured local strains and maximum strains for various types of loading and boundary conditions for linear elastic beam structures in buildings or infrastructures. The model is tested in an experiment by comparing estimated maximum strain from FBG sensors and directly measured strain from electrical gages
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