Safety Evaluation of Reinforced Concrete Structures Using Multi-Source Fusion Uncertainty Cloud Inference and Experimental Study.

Structural damage detection and safety evaluations have emerged as a core driving force in structural health monitoring (SHM). Focusing on the multi-source monitoring data in sensing systems and the uncertainty caused by initial defects and monitoring errors, in this study, we develop a comprehensive method for evaluating structural safety, named multi-source fusion uncertainty cloud inference (MFUCI), that focuses on characterizing the relationship between condition indexes and structural performance in order to quantify the structural health status. Firstly, based on cloud theory, the cloud numerical characteristics of the condition index cloud drops are used to establish the qualitative rule base. Next, the proposed multi-source fusion generator yields a multi-source joint certainty degree, which is then transformed into cloud drops with certainty degree information. Lastly, a quantitative structural health evaluation is performed through precision processing. This study focuses on the numerical simulation of an RC frame at the structural level and an RC T-beam damage test at the component level, based on the stiffness degradation process. The results show that the proposed method is effective at evaluating the health of components and structures in a quantitative manner. It demonstrates reliability and robustness by incorporating uncertainty information through noise immunity and cross-domain inference, outperforming baseline models such as Bayesian neural network (BNN) in uncertainty estimations and LSTM in point estimations.

Simultaneously distributed temperature and dynamic strain sensing based on a hybrid ultra-weak fiber grating array.

A fiber-optic sensing system based on two types of ultra-weak fiber Bragg gratings (UWFBG) for simultaneous temperature and vibration sensing was proposed. Narrowband and broadband UWFBGs are alternately written into an optical fiber with equal spacing. Distributed temperature sensing is realized by demodulating the wavelength shift of the narrowband UWFBG, while distributed vibration sensing is achieved by detecting phase variation between two adjacent broadband UWFBG interference pulses. The experimental results show that the proposed hybrid UWFBG array can perform temperature and vibration sensing simultaneously. The experimentally conducted temperature measurement ranges from 20°C to 100°C, with the measurement error less than 0.1°C. Vibration signals at different temperatures can be accurately restored, and the signal-to-noise ratio (SNR) is improved by 21.1 dB compared with a normal single-mode fiber (SMF).

Highly sensitive torsion senor based on dual-side-hole fiber Mach-Zehnder interferometer.

We experimentally demonstrate a highly sensitive directional torsion sensor based on a helical dual side-hole fiber (DSHF). The sensor is constructed by splicing a fraction of DSHF in between two short lengths of multi-mode fibers (MMFs), which forms a Mach-Zehnder interferometer (MZI) based on the interference between the core and cladding modes in the DSHF. The middle part of the DSHF is heated and twisted to get a spiral cladding, so that the cladding mode in the DSHF travels along a helical path. The introduction of the helical structure can greatly improve the torsion sensitivity of the senor and enables it to recognize the twist direction. Experimental results show that the torsion sensitivity can reach as high as 1.666 nm/(rad/m) and -1.413 nm/(rad/m) in the range of 0 ± 5.517 rad/m. Besides, strain sensitivity of the sensor is about -4.5 pm/µÉ›.

Ultra-highly sensitive gas pressure sensor based on dual side-hole fiber interferometers with Vernier effect.

We have presented and demonstrated a fiber optic gas pressure sensor with ultra-high sensitivity based on Vernier effect. The sensor is composed of two integrated parallel Mach-Zehnder interferometers (MZIs) which are fabricated by fusion splicing a short section of dual side-hole fiber (DSHF) in between two short pieces of multimode fibers (MMFs). Femtosecond laser is applied for cutting off part of the MMF and drilling openings on one air hole of the DSHF to achieve magnified gas pressure measurement by Vernier effect. Experimental results show that the gas pressure sensitivity can be enhanced to about -60 nm/MPa in the range of 0-0.8 MPa. In addition, the structure possesses a low temperature cross-sensitivity of about 0.55 KPa/°C. This presented sensor has practically value in gas pressure detection, environmental monitoring and other industrial applications.

Ultra-weak FBG and its refractive index distribution in the drawing optical fiber.

For the online writing of ultra-weak fiber Bragg gratings (FBGs) in the drawing optical fibers, the effects of the intensity profile, pulse fluctuation and pulse width of the excimer laser, as well as the transverse and longitudinal vibrations of the optical fiber have been investigated. Firstly, using Lorentz-Loren equation, Gladstone-Dale mixing rule and continuity equation, we have derived the refractive index (RI) fluctuation along the optical fiber and the RI distribution in the FBG, they are linear with the gradient of longitudinal vibration velocity. Then, we have prepared huge amounts of ultra-weak FBGs in the non-moving optical fiber and obtained their reflection spectra, the measured reflection spectra shows that the intensity profile and pulse fluctuation of the excimer laser, as well as the transverse vibration of the optical fiber are little responsible for the inconsistency of ultra-weak FBGs. Finally, the effect of the longitudinal vibration of the optical fiber on the inconsistency of ultra-weak FBGs has been discussed, and the vibration equations of the drawing optical fiber are given in the appendix.

Large-capacity multiplexing of near-identical weak fiber Bragg gratings using frequency-shifted interferometry.

We demonstrate interrogation of a large-capacity sensor array with nearly identical weak fiber Bragg gratings (FBGs) based on frequency-shifted interferometry (FSI). In contrast to time-division multiplexing, FSI uses continuous-wave light and therefore requires no pulse modulation or high-speed detection/acquisition. FSI utilizes a frequency shifter in the Sagnac interferometer to encode sensor location information into the relative phase between the clock-wise and counter-clockwise propagating lightwaves. Sixty-five weak FBGs with reflectivities in the range of -31 ~-34 dB and with near identical peak reflection wavelengths around 1555 nm at room temperature were interrogated simultaneously. Temperature sensing was conducted and the average measurement accuracy of the peak wavelengths was ± 3.9 pm, corresponding to a temperature resolution of ± 0.4 °C. Our theoretical analysis taking into account of detector noise, fiber loss, and sensor cross-talk noise shows that there exists an optimal reflectivity that maximizes multiplexing capacity. The multiplexing capacity can reach 3000 with the corresponding sensing range of 30 km, when the peak reflectivity of each grating is -40 dB, the sensor separation 10 m and the source power 14 mW. Experimental results and theoretical analysis reveal that FSI has distinct cost and speed advantages in multiplexing large-scale FBG networks.

A time- and wavelength-division multiplexing sensor network with ultra-weak fiber Bragg gratings.

A time- and wavelength-division multiplexing sensor network based on ultra-weak fiber Bragg gratings (FBGs) was proposed. The low insertion loss and the high multiplexing capability of the proposed sensor network were investigated through both theoretical analysis and experimental study. The demodulation system, which consists of two semiconductor optical amplifiers and one high-speed charge-coupled device module, was constructed to interrogate 2000 serial ultra-weak FBGs with peak reflectivity ranging from -47 dB to -51 dB and a spatial resolution of 2 m along an optical fiber. The distinct advantages of the proposed sensor network make it an excellent candidate for the large-scale sensing network.

The mechanical properties and sustainability of phosphogypsum-slag binder activated by nano-ettringite.

The cementitious material based on phosphogypsum (PG) and ground granulated blast furnace slag (GBFS) demonstrates good economy and sustainability, whereas its drawback of ultra-slow strength development seems unacceptable. In this study, an attempt to drive the hydration of PG-GBFS and further facilitate the strength development by introducing nano-ettringite (NE) was carried out. The impact of 1- 5 % NE on the compressive strength, hydration process, dissolution behavior, and microstructure evolution of PG-GBFS were investigated. The results showed that the incorporation of NE significantly increased the compressive strength of PG-GBFS. At 7 d, the strength grew from 0 MPa to a range of 7.6- 20.2 MPa, and at 28 d, it was enhanced from 22.9 MPa to a range of 45.6- 79.0 MPa. The reason was that the introduction of NE induced the formation of AFt, thereby accelerating the hydration process and promoting the development of the skeletal network, resulting in higher early strength. Besides, NE facilitated the formation of C-S(A)-H gel, which further refined the pore structure and led to continuous growth in later strength. Additionally, PG-GFBS with 5 % NE exhibited significantly lower total costs (35.0 % of NaOH-activated slag and 51.7 % of water glass-activated slag) and lower carbon emissions (30.8 % of NaOH-activated slag and 49.8 % of water glass-activated slag) at the same 28 d compressive strength, indicating its strong competitiveness in both sustainability and economy.

On-line Writing of Fiber Bragg Grating Array on a Two-mode Optical Fiber for Sensing Applications.

On-line fabricated fiber Bragg grating (FBG) array and its sensing potentials have attracted plenty of attention in recent years. In this paper, FBG arrays are written on-line on a two-mode fiber, and this two-mode fiber Bragg grating (TM-FBG) is further experimentally investigated for temperature and curvature sensing. The responses of this sensor were characterized by 11.2 pm/°C and -0.21 dB/m-1 for temperature and curvature, respectively. Based on the measurements, a dual-parameter fiber sensing system was developed, which can realize the quasi-distributed, simultaneous detection of temperature and curvature, making it suitable for structural health monitoring or perimeter security.