Embedded Distributed Optical Fiber Sensors in Reinforced Concrete Structures-A Case Study

Area of Science:

• Structural Health Monitoring
• Materials Science
• Civil Engineering

Background:

• Accurate strain measurement in reinforced concrete is crucial for structural health monitoring.
• Distributed optical fiber sensors (DOFS) offer potential for robust, embedded sensing.
• Balancing sensor protection with measurement accuracy in cracked concrete is challenging.

Purpose of the Study:

• To evaluate the performance of polyimide-coated DOFS for monitoring reinforced concrete structures.
• To assess the accuracy of DOFS during loading, unloading, and reloading cycles, including cracking.
• To determine the feasibility of direct bonding of DOFS to rebars without complex preparation.

Main Methods:

• Two concrete beams instrumented with polyimide-coated DOFS bonded to rebars and concrete surfaces.
• Three-point bending tests were conducted, including loading, unloading, and reloading phases.
• Rayleigh Optical Frequency Domain Reflectometry (OFDR) was used for sensing.
• Strain gauges were co-located with DOFS for validation.

Main Results:

• Polyimide-coated DOFS can be reliably bonded directly to reinforcing bars without indention.
• Accurate strain measurements were achieved in both uncracked and cracked concrete stages.
• DOFS demonstrated capability in capturing strain variations during cyclic loading processes.

Conclusions:

• Thin-coated polyimide DOFS are feasible for direct bonding to rebars in reinforced concrete.
• The proposed Spectral Shift Quality (SSQ) threshold can aid in data interpretation for polyimide-coated DOFS.
• This method simplifies sensor deployment while maintaining measurement accuracy for structural health monitoring.