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This paper aims to experimentally study the compressive and flexural characteristics of cement-based composites developed for fabricating thin, lightweight, and high-performance components of buildings. Expanded hollow glass particles with a 0.25–0.5 mm particle size were used as lightweight fillers. Hybrid fibers made of amorphous metallic (AM) and nylon fibers were used to reinforce the matrix with a total volume fraction of 1.5%. The primary test parameters included the expanded glass-to-binder (EG/B) ratio, the fiber volume content ratio, and the length of the nylon fibers in the hybrid system. The experimental results demonstrate that the EG/B ratio and the volume dosage of the nylon fibers exhibited insignificant effects on the compressive strength of the composites. Additionally, the utilization of nylon fibers with a longer length of 12 mm resulted in a slight compressive strength reduction of approximately 13% compared to that of the 6 mm nylon fibers. Further, the EG/G ratio exhibited an insignificant effect on the flexural behavior of lightweight cement-based composites in terms of their initial stiffness, strength, and ductility. Meanwhile, the increasing AM fiber volume fraction in the hybrid system from 0.25% to 0.5% and 1.0% improved flexural toughness by 42.8% and 57.2%, respectively. In addition, the nylon fiber length significantly affected the deformation capacity at the peak load and the residual strength in the post-peak stage.

A railway bridge over several decades will be degraded due to localized corrosion. As a result, the load capacity of the bridge decreases, especially under the live load caused by trains. This paper examines the residual load capacity of a bridge deteriorated by localized corrosion by using the multibody dynamics approach. This approach allows an accurate description of the interaction between trains and bridges. At the same time, it allows the formation of corrosion marks on each structural member of the bridge in a numerical model precisely based on actual measured data. In order to describe accurately the remaining load of the bridge under the moving load of the train, a dynamic testing and finite element modeling of a steel bridge are conducted and compared. At the same time, the results are also compared with the simulation results of the bridge model before being corroded. In addition, the paper also tests the reliability of the numerical model for assessments of similar bridges without actual measurement results that are costly and time-consuming.

International audience; In civil engineering, a seismic fragility curve is popularly used to predict failure probability of structures under different earthquakes, and hence propose essential rehabilitation strategies through risk assessment for future earthquakes. The curve shows the failure probability as a function of seismic intensity, e.g., spectral acceleration at fundamental frequencies of structures (Sa, T1), and can be obtained using one of three approaches: engineering judgment, empirical studies or numerical simulations. The paper focuses on constructing seismic fragility curves using numerical simulations, where robust approaches of seismic reliability analysis are based on direct Monte Carlo simulation technique. The MCS based method usually requires a relatively large number of simulations to obtain a sufficiently reliable estimate of the fragility. It therefore becomes computationally expensive and time consuming as generating the simulations using the actual model or called full model of the structure. In this regard, this paper suggests using Kriging metamodel as a viable alternative of the actual model to reduce computational costs in seismic fragility computation. The Kriging metamodel is constructed based on the training samples of input and corresponding output responses of the structure. The validation of this method is performed on two numerical examples.

Old reinforced concrete buildings constructed around 1980’s in many developing countries have been designed against mainly gravity load. Beam-column joints in these buildings contain slightly or no shear reinforcement inside the panel zones due to the construction convenience, and are vulnerable to shear failure in beam-column joints under the action of earthquake loads, especially for the exterior beam-column joints. This experimental study aimed to investigate the seismic performance of five half-scale exterior beam-column joints simulating the joints in existing reinforced-concrete buildings with non-shear hoop details. The test results showed that the structural performances of the beam-column joints under earthquake including failure mode, load-drift ratio relationship, shear strain of the joints and energy dissipation are strongly affected by the amount of longitudinal reinforcing bars of beams.

International audience; Seismic fragility curves presenting some probability of failure or of a damage state exceedance versus seismic intensity can be established by engineering judgment, empirical or numerical approaches. This paper focuses on the latter issue. In recent studies, three popular methods based on numerical simulations, comprising scaled seismic intensity, maximum likelihood estimation and probabilistic seismic demand/capacity models, have been studied and compared. The results obtained show that the maximum likelihood estimation (MLE) method is in general better than other ones. However, previous publications also indicated the dependence of the MLE method on the ground excitation input. The objective of this paper is thus to propose a novel method improving the existing MLE one. Improvements are based on probabilistic ground motion information, which is taken into account in the proposed procedure. The validity of this new approach is verified by analytical tests and numerical examples.

Several retrofitting methods for reinforced concrete (RC) beam-column joints in old buildings without seismic details were developed. Four half-scale RC exterior beam-column joints were fabricated and tested under cyclic loading simulating earthquake excitation. The control specimen was designed to fail in joint shear. Two practical retrofitting strategies were applied to the control specimen which consider the architectural characteristic in real buildings, including steel jacketing and haunch retrofit solution. The structural performance of the test specimens was investigated in terms of various factors including damage and failure, load-drift relationship, ductility, dissipated energy, and strain profiles of longitudinal reinforcement. Experimental results confirmed that the proposed retrofit methods were shown to enhance the seismic capacity of the joints in terms of the strength, deformation capacity, and energy dissipation capacity while the shear deformation in the panel zone significantly reduced in comparison with the control specimen.

Colloque avec actes et comité de lecture. Internationale.; International audience; Une courbe de fragilité sismique qui présente la probabilité de défaillance d'une structure en fonction d'une intensité sismique, par exemple, le pic d'accélération du sol (Peak Ground Acceleration - PGA), est un outil très performant pour l'évaluation de la vulnérabilité sismique des structures en génie nucléaire (B. Ellingwood, 1990) ou dans le domaine du génie civil (Karim and Yamazaki, 2003). Il existe dans la littérature trois approches : soit par l'avis d'expert, soit empirique grâce aux données d'observation réelles ou par simulation numérique. L'hypothèse la plus commune de ces approches est que la courbe de fragilité est une fonction cumulative de la loi log-normale (Kafali and Grigoriu, 2007 ; Shinozuka et al., 2000). Dans cet article, nous proposons une nouvelle technique de construction des courbes de fragilité sismique par simulation numérique en utilisant la méthode de calcul de l'évolution des fonctions de densité de probabilité (Probability Density Evolution Method – PDEM). Proposée par Li et Chen (Li and Chen, 2004 ; Chen and Li, 2005), la méthode PDEM permet d'évaluer la probabilité conjointe entre la réponse structurale et les variables aléatoires du système et de l'excitation. A partir le la probabilité conjointe, la courbe de fragilité sismique peut être déduite sans utiliser l'hypothèse de la loi log-normale. La validation de la technique proposée est réalisée sur des exemples numériques. Les résultats obtenus sont présentés et discutés.

A seismic fragility curve of a structure or a mechanical system, presenting its failure probability versus seismic intensity, can be established by an engineering judgment approach, an empirical approach or a numerical approach. In the numerical approach, there exist three popular methods: the scaled seismic intensity method, the maximum likelihood estimation method, and the probabilistic seismic demand/capacity models. This paper is focused on a comparison of these numerical methods. Linear/non-linear oscillators and an eight-storey frame structure were used to derive fragility curves for different tests. The results obtained show a discrepancy of fragility curves between the methods, and their quality is commented in comparison with results of the Monte-Carlo method with a high number of simulations. The maximum likelihood estimation method is in general the recommended method, due to its good accuracy in both numerical examples.

A seismic fragility curve that shows the failure probability of a structure in function of a seismic intensity is a powerful tool for the evaluation of the seismic vulnerability of structures in nuclear engineering and civil engineering.We focus in this thesis on the numerical simulations-based approach for the construction of seismic fragility curves. A comparative work between existent parametric methods with the lognormal assumption of the fragility curves is first performed. It then allows proposing improvements to the maximum likelihood method in order to mitigate the influence of seismic excitation during its construction process. Another improvement is the application of the subsets simulation method for the evaluation of the low probability of failure. Finally, using the Probability Density Evolution Method (PDEM) for evaluating the joint probability between a structural response and random variables of a system and/or excitations, a new technique for construction of seismic fragility curves was proposed. The seismic fragility curve can be derived without the assumption of lognormal law. The improvements and the new technique are all validated by numerical examples.; Une courbe de fragilité sismique qui présente la probabilité de défaillance d’une structure en fonction d’une intensité sismique, est un outil performant pour l’évaluation de la vulnérabilité sismique des structures en génie nucléaire et génie civil. On se concentre dans cette thèse sur l’approche par simulations numériques pour la construction des courbes de fragilité sismique. Une étude comparative des méthodes paramétriques existantes avec l’hypothèse log-normale est d’abord réalisée. Elle permet ensuite de proposer des améliorations de la méthode du maximum de vraisemblance dans le but d’atténuer l’influence de l’excitation sismique lors de son processus de construction. Une autre amélioration est l’application de la méthode de simulations par subsets pour l’évaluation de la probabilité de défaillance faible. Enfin, en utilisant la méthode de calcul de l’évolution des fonctions de densité de probabilité qui permet d’évaluer la probabilité conjointe entre la réponse structurale et les variables aléatoires du système et de l’excitation, nous proposons également une nouvelle technique non-paramétrique de construction des courbes de fragilité sismique sans utiliser l’hypothèse de la loi log-normale. La validation des améliorations et de la nouvelle technique est réalisée sur des exemples numériques.