Advances in Science and Technology Vol. 171

Abstract: The pressure histories resulting from blast wave interactions with structures are highly influenced by the level of confinement. Fully confined blast events are more severe than their unconfined counterparts due to multiple wave reflections and residual quasi-static pressures, which result in prolonged shock-structure interactions and complex pressure profiles. Most experimental studies have primarily focused on spherical or hemispherical blast waves in free-field conditions, supporting simplified models like the CONWEP algorithm commonly integrated into Finite Element (FE) solvers for unconfined explosions. However, this approach is unsuitable for more complicated scenarios, such as explosions in confined scenarios. The current study presents an approach that integrates CFD with a FE framework. This work focuses on extending the capabilities of the FE solver Abaqus/Explicit to handle these complex load histories, which are beyond the scope of its default built-in configurations. User-defined subroutines are developed to enable an Uncoupled Lagrangian-Eulerian (UEL) framework. CFD simulations are performed independently to calculate pressure histories, then they are subsequently mapped onto structural FE models as input loads. The results demonstrate that the proposed framework extends the range of scenarios that can be analysed for blast wave propagation and its effects on structures. By employing this uncoupled approach, diverse structural simulations can be performed using a single FE model. This study provides a numerical tool for simulating confined explosions, with applications in industrial safety and structural design facilitating improved engineering designs for mitigating blast effects.

Abstract: The collapse of buildings during explosions or other extreme events is often linked to the failure of key structural elements such as columns. As vertical load-bearing members, reinforced concrete (RC) columns are essential for maintaining the stability of structures, but are also among the most vulnerable components when exposed to blast loads. This study focuses on the numerical prediction of the dynamic behavior of RC columns subjected to explosive-driven shock tube (EDST) loading. The analysis is based on an experimental campaign using a laboratory-scale RC column specimen with a height of 1500 mm and a circular cross-section of 100 mm, tested under blast loading generated by a 30 g C4 charge. To simulate the structural response and optimize computational performance, three finite element techniques are evaluated and compared: Multi-Material Arbitrary Lagrangian-Eulerian (MM-ALE), Load Blast Enhanced (LBE), and the Idealized Triangular Loading (ITL) method. All three models are validated against experimental data. In terms of mid-span out-of-plane displacement, MM-ALE showed the best accuracy with a 2.1% discrepancy, followed by LBE at 8.8%, and ITL at 10.6%. Regarding computation time, MM-ALE required 12 hours, while LBE was three times faster and ITL was six times faster than MM-ALE. The LBE method presents a balance between speed and accuracy but relies on precise input values for reflected pressure and impulse, which are typically derived from MM-ALE simulations or analytical expressions. The ITL method, while computationally efficient, tends to overestimate peak displacements due to its simplified and uniform pressure application. Among the three approaches, MM-ALE remains the most accurate.

Abstract: This research addresses key challenges in progressive collapse prevention by introducing an advanced method to enhance the complex structural systems monitoring. The study focuses on variation of deformation work patterns with the aim to identify the most critical load paths while a random element within the structure undergoes damage. A comprehensive mathematical model has been developed to analyze changes in load paths due to damage in structural elements. The method utilizes an energy-based metric introduced by De Biagi and Chiaia, allowing for a detailed assessment of damage progression. The damage is simulated through the alteration of the stiffness of structural elements by applying progressive cross section reduction. The predictions of the model were validated through its application to simple systems composed of rods, where changes in load paths were observed as damage advanced in random elements. For more complex structural systems, the method was applied using numerical simulations, providing a detailed evaluation of its performance in more load cases scenarios. The proposed metric effectively captures the effects of localized damage and its propagation through the system, offering valuable insights for the monitoring and prevention of progressive collapse. The method yields two significant outcomes: first, mapping the variation of deformation work with respect to the damage allows for the visualization of the variation in the load path during the damage of a random element within the structure, thus, identifying which elements are loaded and which are unloaded; second, the study of evolution of the variation of deformation work with respect to the damage for different stiffnesses allows identifying the value of critical stiffnesses that determine whether the element remains part of the main load-bearing path. In this work, the method is applied to 2D and 3D truss systems, which are representative of critical infrastructure like bridges and towers, as well as to ad hoc designed structural schemes created to highlight specific aspects and demonstrate the effectiveness of the method. The aim of the method is not only to ensure the safety of vital infrastructure by improving resilience against catastrophic events, but also to offer practical insights by identifying the most critical areas for sensor placement, enabling optimal monitoring and early detection of failure points.

Abstract: The integrated structure and remarkable thickness values of 3D woven fabrics provide their composites with outstanding properties such as high fracture toughness, advanced damage tolerance, high impact energy absorption capacity, etc. However, the orientation of the yarn groups through the thickness direction of the fabric degrades the in-plane mechanical properties of 3D woven fabrics/composites. This phenomenon led to the development of multi-axial 3D woven fabrics. Due to the advanced weaving methods, the bias warp yarns can be incorporated into the 3D woven structure. Previous studies have shown that the bias warp yarns significantly improve the in-plane shear properties of 3D woven fabrics/composites. On the other hand, the impact properties of multi-axial 3D woven composites have not been extensively studied. In this study, the low velocity impact properties of multiaxial 3D woven composites were investigated. First, the composites were impacted at impact energy levels of 20J, 45J and 55J. The damaged specimens were then tested at the 300J impact energy level to determine the effect of the woven fabric architecture on the impact properties and damage mechanisms of the composites. In addition, the 3D warp interlock woven and conventional laminated composites were fabricated and tested for comparative study. From the research study, it was concluded that the biased warp yarns distribute the impact energy more homogeneously to the other parts of the composite. Therefore, multiaxial 3D woven composites can absorb more impact energy than 3D warp interlock woven and laminated composites. The results obtained make multiaxial 3D woven fabrics and their composites one of the best solutions for impact applications among the current fabric technologies.

Abstract: Dedicated metal armor protection for land transport vehicles is an effective solution against blast threats. However, the added weight of these solutions can reduce the vehicle's maneuverability and, indirectly, its maximum payload capacity. To overcome this weight problem, the use of composite materials as additional armor for the vehicle can be an innovative and lightweight solution. In previous studies, different configurations have been subjected to the blast effect in order to analyze and understand their dynamic behavior. The first fiber reinforcements used for composite materials, based on stacked layers of E-glass fabric, were able to withstand dynamic blast loads. However, these reinforcements tend to have the same performance as the all-steel solution for the same areal weight. Therefore, the objective of this study is to investigate the use of 3D woven fiber reinforcements based on E-glass yarn in composite materials for better dynamic performance under blast loading. The fabricated targets were tested against the same blast threat in a free field configuration. The distance between the charge and the targets was kept constant (except for the full thickness 3D woven composite). During the blast, the dynamic deformation in the thickness direction was recorded and different targets were compared. According to the resulting dynamic deformation under the impact of the blast, a better performance of the full thickness 3D woven composite material matched with the protective steel plate was revealed.

Abstract: Over the past decades, Shape Memory Alloys (SMAs), have revolutionized the field of seismic and structural engineering, offering their unprecedented unique properties such as superelasticity, energy dissipation, and the ability to undergo remarkable deformations and reverting to their original shape. The origins of SMA date back to the 1930s when Swedish scientist Arne Ölander initiated revolutionary research on iron alloys, exploring the distinctive characteristics of Iron-Manganese (Fe-Mn) alloy. Ever since, researchers have extensively investigated the mechanical properties of SMAs, leading to increasingly utilizing them in a wide variety of applications, including self-centering braces, structural elements, and systems frequently exposed to harsh working conditions, such as in regions susceptible to earthquakes and dynamic loading. However, a critical limitation has emerged, particularly those made of Nitinol (Nickel­­­­­­–Titanium), which possesses a smooth surface that makes it hard to implement in most structural elements, therefore anchorage systems are often required. Consequently, this smooth surface increases the possibility for slippage, therefore conventional methods to anchor steel reinforcement bars may not be applicable. A few recent studies have investigated the anchorage of SMA rebars, but there is still a big research gap. To fill this research gap, this paper presents an experimental test to evaluate the possible anchorage systems for smooth-surfaced Nitinol-SMA rebars. A total of 6 specimens were tested under uniaxial tensile loading reaching a maximum strain level up to 6%, utilizing the two different anchorage systems. The tests were conducted at a constant loading rate of 0.5 mm/min to evaluate the effectiveness of these anchorage systems. The findings show that both proposed anchorage systems are appropriate for high-deformation seismic zones since it preserved the nitinol bar to sustain up to 6% strain without showing any signs of slippage. These results provide vital insights for creating structural parts with SMA integration that are more dependable. This paper's key findings include ultimate tensile strength, force/displacement relationship, and stress/strain relationship under different constant strain. This paper highlights the need for a more thorough investigation of innovative anchorage systems suitable with SMA bars to pave the way for researchers to enable their wider application in more structural elements.

Abstract: This study investigates the capability of additive manufacturing (AM) technology to produce sandwich composite structures through focusing on the 3D Printing process, experimental testing, and anticipated impact as energy-absorbent elements. The growing cost of manufacturing prototypes that use conventional methods has resulted in exploring the exploration of 3D printing as a viable alternative. The research problem addresses the challenges of manufacturing sandwich composites and the need for automation in the civil, mechanical, aerospace, and aviation industries. The study aims to investigate 3D-printed hybrid sandwich composite structures made of multilayer materials, conduct finite element analysis, produce specimens, conduct flexural and impact tests, and analyze the data. The proposed methodology includes preparation of the 3D printer, 3D printing of the specimen, inspection, finite element analysis, preparing the specimen for testing, conducting different impact tests, and data collection and analysis. The expected mechanical properties of the study lie in the potential for additive manufacturing to reorganize the adoption of sandwich composite structures for energy absorption purposes, reducing costs and automating the process.

Abstract: Glass façades have become a prominent feature in modern architecture, offering aesthetic appeal and abundant natural light. However, in regions exposed to severe weather conditions, particularly during storms, glass façades are vulnerable to damage from wind-borne debris. The impact of such debris can compromise the structural integrity of the façade, leading to potential safety hazards. Despite the significant threat posed by wind-borne debris to the safety and performance of glass façades, the behavior of these materials under impact is not extensively studied. This study presents a comprehensive numerical analysis of the impact behavior of laminated glass panels subjected to debris typically propelled by strong wind forces, using LS-DYNA^®. The simulation models the interaction between wind-borne debris and glass panels of varying debris masses. Mechanical behavior of the glass is incorporated using fracture mechanics to simulate cracking and failure under impact. A range of impact scenarios is considered, including variations in debris mass, impact velocity, and impact locations, to replicate real-world conditions as accurately as possible. The numerical model integrates material properties, layer configurations, and impact conditions to closely reflect actual scenarios. In this study, wooden blocks of different masses are impacted on the laminated glass panels at varying locations and impact velocities. The results reveal the critical factors influencing the glass façade's response, such as the velocity of the incoming debris and the material strength of the glass. This study offers valuable insights for improving the safety and durability of glass façades. Thus, by understanding the complex dynamics of glass response to wind-borne debris, the study contributes to the development of more resilient architectural and structural systems, leading to better risk management strategies for buildings in areas prone to extreme weather events.

Abstract: Sabo soil-cement has the advantages of reducing the amount of sediment transported, reducing costs by using local sediment, and a zero-emission construction method. In addition, the strength development of Sabo soil-cement is based on the interaction between soil compaction and cement hydration. The strength can be determined based on the compressive strength obtained from uniaxial compression tests. However, dynamic loads, such as debris flows, are not evaluated. In this study, an impact loading experiment is conducted on a Sabo soil-cement specimen to examine the impact resistance. In addition, the relationship between the dropping weight accumulation energy and the collapsed volume and the relationship between the dropping weight energy and compressive strength are evaluated to determine the impact resistance of Sabo soil-cement. The results show that the greater the compressive strength, the greater the accumulated weight energy. In addition, there is a proportional relationship between the collapsed volume and dropping weight accumulation energy, and the relationship between the maximum impact load and weight energy increases linearly until cracks occur in the specimen. The impact spectrum of the specimen with a low compressive strength reduces the impact load on the collision surface. Therefore, if the compressive strength of the Sabo soil-cement is high, it has a high impact resistance against the impact load on the collision surface. On the other hand, if the compressive strength is low, Sabo soil-cement absorbs the impact force.

Abstract: Anti-submarine (ASM) ring nets are fundamental components for various passive solutions to mitigate rockfall hazard. While numerical models could accurately assess their performance for all the applications, the modelling of a whole system comprising the net is time-consuming. An analytical model of wire ring nets currently on the market, applicable to the different configurations, can thus represent a profitable tool to investigate the performance of nets used in retaining systems. Currently, for flexible rockfall barriers the whole system structural behaviour is evaluated with real tests impact tests performed in the centre of the system, only, possibly overestimating the system capacity and consequently underestimating the residual risk at installation sites. An analytical model is proposed in this paper with the aim to evaluate the mechanical behaviour of wire ring nets for eccentric impacts too. The model validation is performed using quasi-static experimental punching tests results related to both rigid and flexible boundaries conditions for the centred impact case, while numerical models, realized applying well-established approaches, strengthen the model validation for eccentric impacts. Analyses performed during the barrier design phase and its service life enable to assess the real efficiency of retaining systems.