Resumo em Inglês:

Abstract In structural health monitoring (SHM), uncertainties from environmental noise and modeling errors affect damage detection accuracy. This paper introduces a new concept: the Fast Fourier Transform Coefficient Ratio (FFTCR), which develops a damage indicator (DI) based on a probability model. The method involves calculating the probability density function (PDF) of the ratio and the Jensen-Shannon divergence (JSD) square root distance, which measures similarity between probability distributions. A baseline threshold is proposed using the Markov Chain Monte Carlo (MCMC) method and Monte Carlo discordancy test to handle uncertainties in statistical parameters. The robustness of the method is validated through the DBSCAN algorithm, which distinguishes damage states by applying a 1% exclusive threshold to the clustering results. The method requires no postprocessing of raw data, relying solely on response measurements. It is validated through two experiments, including laboratory ambient vibration tests and a field test on a bridge under forced vibration. Results show superior accuracy and broader applicability compared to the Mahalanobis Squared Distance (MSD) method.

Resumo em Inglês:

Abstract In this study, three types of bolted shear connectors (I, V, and X type) were proposed. Push-out tests were performed to investigate the shear behaviour of the Precast Lightweight Concrete Sandwich Slab (PLCSS), whose layers were connected by the suggested connectors. Nine specimens of PLCSS were fabricated and tested, and they were distributed into three groups. Each group included three identical specimens for each type of shear connector. The primary parameter considered in this work was the type of shear connector and its effect on the failure mode. The structural behaviour considered load vs relative displacement (between the top and bottom layer), stiffness, ductility, and deformation index. The proposed shear connectors showed a variance in terms of strength, ductility, hardness, deformation index, and absorbed energy values. The highest values of shear strength were for specimens with X-connectors. In addition to their advantage of the ease of fastening or re-dismantling, the bolted shear connectors showed good compatibility with the fabrication of such a composite lightweight concrete element that demonstrates high shear resistance.

Resumo em Inglês:

Abstract Ultra-high-performance fiber-reinforced concrete (UHPFRC) has emerged as an advanced concrete technology in the sustainable building industry. It can provide better infrastructural development in terms of strength, ductility, toughness, and stiffness than traditional concrete. This paper aims to analytically determine the time-dependent deflection (i.e., creep) of the UHPFRC beam with varying amounts of steel fiber addition. The age-adjusted effective modulus method was used to anticipate the time-dependent deflection of the UHPFRC beam. Experimental data related to time-dependent properties of UHPFRC were extracted from the literature to develop new formulas for creep coefficient and shrinkage strain through curve fitting and data validation. A new range of aging coefficient was proposed for UHPFRC through trial according to the ACI code. The existing shrinkage-induced curvature formula for cracked sections was modified using data validation. The analytical study incorporated all the proposed formulations and coefficient values to anticipate the UHPFRC beam's time-dependent deflection theoretically. Along with the analytic analysis, Finite Element Method (FEM) was also employed to predict the time-dependent deflection of the UHPFRC beam. It was found that for different percentages of steel fibers, both the FEM and the proposed analytical approaches conservatively estimate the deflection values, with an average deviation of around 20% from the experimental results. The accuracy and validation of the proposed theoretical formulation to predict the time-dependent deflection of UHPFRC beams were also demonstrated through statistical analysis.