Safety of autonomous vehicles: A survey on Model-based vs. AI-based approaches

The growing advancements in Autonomous Vehicles (AVs) have emphasized the critical need to prioritize the absolute safety of AV maneuvers, especially in dynamic and unpredictable environments or situations. This objective becomes even more challenging due to the uniqueness of every traffic situation/condition. To cope with all these very constrained and complex configurations, AVs must have appropriate control architectures with reliable and real-time Risk Assessment and Management Strategies (RAMS). These targeted RAMS must lead to reduce drastically the navigation risks. However, the lack of safety guarantees proves, which is one of the key challenges to be addressed, limit drastically the ambition to introduce more broadly AVs on our roads and restrict the use of AVs to very limited use cases. Therefore, the focus and the ambition of this paper is to survey research on autonomous vehicles while focusing on the important topic of safety guarantee of AVs. For this purpose, it is proposed to review research on relevant methods and concepts defining an overall control architecture for AVs, with an emphasis on the safety assessment and decision-making systems composing these architectures. Moreover, it is intended through this reviewing process to highlight researches that use either model-based methods or AI-based approaches. This is performed while emphasizing the strengths and weaknesses of each methodology and investigating the research that proposes a comprehensive multi-modal design that combines model-based and AI approaches. This paper ends with discussions on the methods used to guarantee the safety of AVs namely: safety verification techniques and the standardization/generalization of safety frameworks

Numerical Modelling of One-Way Reinforced Concrete Slab in FireTaking Into Account of Spalling

This paper presents a study of the behaviour of Reinforced Concrete (RC) slabs subjected to severe hydrocarbon fire exposure. In which the spalling phenomena of concrete is to be considered. The hydrocarbon curve is applicable where small petroleum fires might occur, i.e. car fuel tanks, petrol or oil tankers, certain petro-chemical facilities, tunnels, parking structures, etc. Spalling is included using a simplified approach where elements with temperatures higher than 400 °C are assumed to occur and the corresponding thermo-mechanical response of RC slabs is evaluated. The nonlinear finite element software SAFIR has been used to perform a numerical analysis of the spalling risk, by removing layers of concrete covering when a set of spalling criteria is checked. The numerical results obtained by finite element analysis of the temperature distribution within the slab and mid-span deflection were compared with published experimental data. Predictions from the numerical model show a good agreement with the experimental data throughout the entire fire exposure to the hydrocarbon fire. This shows that this approach (layering procedure) is very useful in predicting the behaviour of concrete spalling cases. Doi: 10.28991/cej-2021-03091667 Full Text: PD

Structural behaviour of concrete filled hollow steel sections exposed to parametric fire

This article analyzes steel-concrete composite columns subjected to natural fire scenarios in order to verify that the possibility of structural collapse during or after the cooling phase is real. The main objectives of this study are: first, to highlight the phenomenon of delayed collapse of this type of columns during or after the cooling phase of a fire, and then analyze the influence of some determinant parameters, such as section size, tube thickness, reinforcement (ratio), concrete cover and column length. The results show that critical conditions with respect to delayed failure arise for massive sections, small values of the steel tube thickness and for columns with massive section

Comportamiento post-incendio de columnas CR reforzadas con tubo de acero de sección hueca cuadrada y camisas de concreto RC

This paper investigates numerically fire-exposed reinforced concrete (RC) columns. As a first step, the study examined the effects of exposing the columns to fire for 60 minutes according to the ISO 834 fire standard on the column's residual load-bearing capacity by considering some decisive geometrical parameters such as the column height and its cross-sectional area. The second step consisted of investigating the effectiveness of the strengthening technique utilized by incorporating composite jackets, considering different strengths of concrete, in order to improve the post-fire behavior of these columns. The results showed that the longer the column is exposed to fire, the lower its bearing capacity. However, it was also found that increasing the column cross-sectional area can reduce the percentage of load-bearing capacity. Finally, it was revealed that the strengthening method used herein allowed restoring the capacity of the columns exposed to fire for a period of one hour by up to 180%.  Este artículo investiga columnas de hormigón armado (RC) expuestas numéricamente al fuego. Como primer paso, el estudio examinó los efectos de exponer las columnas al fuego durante 60 minutos del estándar ISO 834 sobre la capacidad de carga residual de la columna considerando algunos parámetros geométricos decisivos como la altura de la columna y su área de sección transversal. El segundo paso consistió en investigar la efectividad de la técnica de reforzamiento utilizada mediante la incorporación de jackets compuestas, considerando diferentes resistencias del hormigón, con el fin de mejorar el comportamiento post-incendio de estas columnas. Los resultados mostraron que cuanto más tiempo está expuesta la columna al fuego, menor es su capacidad portante. Sin embargo, también se encontró que aumentar el área de la sección transversal de la columna puede reducir el porcentaje de capacidad de carga. Finalmente, se reveló que el método de refuerzo aquí utilizado permitió restaurar la capacidad de las columnas expuestas al fuego por un período de una hora hasta en un 180%.  Cet article étudie numériquement les poteaux en béton armé (RC) exposés au feu. Dans un premier temps, l'étude a examiné les effets d'une exposition des poteaux au feu pendant 60 minutes selon la norme incendie ISO 834 sur la capacité portante résiduelle du poteau en considérant certains paramètres géométriques décisifs tels que la hauteur du poteau et sa section transversale. zone. La deuxième étape a consisté à étudier l'efficacité de la technique de renforcement utilisée en incorporant des chemises composites, en considérant différentes résistances de béton, afin d'améliorer le comportement après feu de ces colonnes. Les résultats ont montré que plus la colonne est exposée au feu longtemps, plus sa capacité portante est faible. Cependant, il a également été constaté que l'augmentation de la section transversale de la colonne peut réduire le pourcentage de capacité portante. Enfin, il a été révélé que la méthode de renforcement utilisée ici permettait de restaurer jusqu'à 180 % la capacité des colonnes exposées au feu pendant une durée d'une heure. &nbsp

Seismic performance assessment of deficient RC structures retrofitted with different steel bracing systems

This paper discusses the use of concentric steel bracing systems as a global technique for retrofitting RC structures. A case study building with a five-story RC structure was retrofitted and tested using different types of bracing systems with different arrangements namely diagonal, X, and a combination between diagonal and X steel braces with tow arrangements. The main objective of the current study is to find out the most effective bracing system to upgrading the seismic behavior of deficient RC structures. The nonlinear static pushover and dynamic time-history analyses were carried out. The first method was applied by pushing the models until they arriving at a predefined target roof displacement. In the second method, a set of three natural earthquakes was employed to perform a dynamic time history analysis. The results indicate that the combined system of the diagonal and X braces using the second arrangement has the highest base shear and reaches the target roof displacement under pushover analysis. On the other hand, when using the response history analysis, it is the best system to reduce roof displacement compared to other techniques. However, steel braces cannot reduce the acceleration of the structure. The proposed combined system with the second arrangement is an effective retrofitting technique that has a much better seismic behavior and improves the ability to withstand even larger earthquake forces compared to other techniques.&nbsp

Assessing Delayed Collapse Risks in Load-Bearing Reinforced Concrete Walls Exposed to Parametric Fires: A Numerical Investigation

This study delves into the thermo-mechanical analysis of structures exposed to fire, focusing on the evolution of gas temperatures, thermal distribution in structural members, and mechanical behavior during fire scenarios. Traditional prescriptive approaches assume a monotonically increasing temperature, while contemporary performance-based designs incorporate both heating and cooling phases for a more realistic fire resistance assessment. The critical aspect of this research is the modeling of the fire's cooling phase, which, though not commonly practiced in design offices, is essential for evaluating the risk of delayed structural collapse. Utilizing the finite element program SAFIR, numerical simulations were conducted on reinforced concrete walls to investigate their behavior during and post-cooling phase. The findings indicate potential failure not only during the cooling phase but also after the fire has subsided and temperatures have returned to ambient levels. This highlights delayed temperature increases in the core of the element and the consequent loss of concrete strength during cooling as key mechanisms of failure. A parametric study was undertaken, examining various fire scenarios, wall geometries, load levels, wall heights, adjacency, and boundary conditions. The results underscore that short-duration fires pose the most significant risk for delayed failure, particularly for simply supported walls. Additionally, the study scrutinizes the mechanical properties of materials across the heating and cooling phases. This investigation underscores the necessity of incorporating cooling phase analyses in fire resistance evaluations to mitigate the risk of delayed collapses. The insights gained aim to inform safer structural designs and enhance fire safety protocols, emphasizing the importance of realistic fire modeling in performance-based design methodologies

Effectiveness of composite jacket strengthening of reinforced concrete columns under eccentric load after fire exposure

This research presents a numerical study of the behavior of reinforced columns with a square cross section subjected to eccentric stress under the influence of fire. As a first step, the study examined the effects of exposing columns to fire with an increasing temperature up to 600°C for 60 minutes under eccentric loading conditions (e/b = 0, 0.1, 0.15, 0.20). As a second step, the columns were strengthened with a 100-mm concrete jacket and shirts supported by a steel structure consisting of vertical angles and horizontal spreaders to determine the effectiveness of the strengthening in increasing the resistance of these damaged columns. After the fire, this type of reinforcement is considered better than reinforcement with concrete shirts, reinforcement with carbon fiber-reinforced polymers, and others because of its advantages. There are many advantages to the ease and speed of implementation. The results showed that the columns that were repaired and strengthened after the fire with the steel structure casing led to a significant increase in resistance. It was found that the greater the thickness of the steel structure, the greater the resistance, and that the greater the eccentricity ratio, the lower the resistance as well as the collapse load

Collapse of concrete columns during and after the cooling phase of a fire

This paper presents a study performed on the collapse of reinforced concrete columns subjected to natural fire conditions during and after the cooling phase of the fire. The aim is, first, to highlight the phenomenon of collapse of concrete columns during and after the cooling phase of a fire and then, to analyze the influence of some determinant parameters. The main mechanisms that lead to this type of failure are found to be the delayed increase of the temperature in the central zones of the element and the additional loss of concrete strength during the cooling phase of the fire. A parametric study is performed considering different fires and geometric properties of the column. This shows that the most critical situations with respect to delayed failure arise for short fires and for columns with low slenderness or massive sections

Structural Behaviour of Concrete Columns under Natural Fires

Purpose - The paper aims to give an insight into the behavior of reinforced concrete columns during and after the cooling phase of a fire. The study is based on numerical simulations as these tools are frequently used in structural engineering. As the reliability of numerical analysis largely depends on the validity of the constitutive models, the development of a concrete model suitable for natural fire analysis is addressed in the study. Design/methodology/approach - The paper proposes theoretical considerations supported by numerical examples to discuss the capabilities and limitations of different classes of concrete models and eventually to develop a new concrete model that meets the requirements in case of natural fire analysis. Then, the study performs numerical simulations of concrete columns subjected to natural fire using the new concrete model. A parametric analysis allows for determining the main factors that affect the structural behavior in cooling. Findings – Failure of concrete columns during and after the cooling phase of a fire is a possible event. The most critical situations with respect to delayed failure arise for short fires and for columns with low slenderness or massive sections. The concrete model used in the simulations is of prime importance and the use of the Eurocode model would lead to unsafe results. Practical implications – The paper includes implications for the assessment of the fire resistance of concrete elements in a performance-based environment. Originality/value – The paper provides original information about the risk of structural collapse during cooling