Mohammed Benzerara

Following our earlier work on reduced beam section (RBS) connections, this study examines a new set of corrugated-web cell configurations for steel moment-resisting connections. A finite element model, validated against four experimental investigations reported in the literature, was used herein to assess the effects of cell geometry, transverse depth, and position relative to the column face on load-carrying capacity, deformation capacity, and damage evolution. The results show that the proposed configurations alter the stress distribution and shift the plastic hinge away from the beam–column joint, thereby decreasing the stress concentration in critical areas. Structural performance was highly sensitive to the interaction between cell geometry and its position along the beam. The curved cell configuration performed best when located near the column face, whereas the angle-shaped and trapezoidal configurations performed better farther from the column face, with the angle cell configuration giving the best overall response among all four. Comparatively lower efficiency was observed with the double curved configuration. To gain further insight into the viability of the proposed approach, the optimal designs derived from simplified beam analyses were then incorporated into a validated two-story steel sub-frame model. These results confirm that the selected geometric properties remain effective at a larger structural scale, preserving the beneficial effects observed in the beam-level analysis. These results demonstrate the potential of the proposed system to improve steel moment-resisting connections and provide a basis for further research on optimizing more advanced connection design techniques.

In many densely populated towns and semi-urban areas, masonry buildings often stand close to busy roads, exposing them to blasts from improvised explosives or other localized sources. Such structures are rarely designed to resist sudden explosive forces, making severe damage or even progressive collapse likely. Even moderate-intensity blasts can weaken walls, endanger occupants, and cause significant property loss. Unlike reinforced concrete, masonry is highly susceptible to explosive impact. Therefore, understanding how these buildings behave under blast loads and developing affordable protection methods is crucial. Low-rise unreinforced masonry (URM) structures, usually up to about 13 m in height (roughly 2–4 stories), common in villages, semi-urban regions, and conflict-prone zones, are particularly at risk. In many areas, these poorly constructed buildings lack proper engineering design and are therefore highly vulnerable to blast damage. Non-load-bearing internal dividers and perimeter enclosures are especially prone to lateral displacement, which can initiate instability and, in severe cases, lead to overall structural failure. This research focuses on reducing catastrophic damage in URM walls when exposed to close-proximity blast forces using concrete-based protective coatings, both with and without embedded steel-welded wire mesh. The study references a previously tested laterally supported clay brick wall built with cement–sand mortar as the baseline model, with its behavior validated against experimental findings from existing literature. Two blast cases were considered corresponding to scaled stand-off distances of 2.19 m/kg^1/3 and 1.83 m/kg^1/3, representing moderate flexural-shear cracking and full structural failure, respectively. To replicate the observed behavior, a comprehensive 3D numerical simulation was developed using the ABAQUS/Explicit 2020 solver. The model’s predictions were benchmarked and verified through comparison with reported test data. While both blast intensities were used to confirm computational accuracy, the effectiveness of UHPC and UHPFRC protective coatings with and without embedded wire mesh was specifically evaluated under the more severe collapse scenario (Z = 1.83 m/kg^1/3). Results indicated that at a scaled distance of 1.83 m/kg^1/3, the uncoated URM wall could not withstand the blast because of poor tensile and bending capacity. In contrast, the UHPC- and UHPFRC-coatings provided improved confinement and better stress distribution. When welded wire mesh was embedded, crack control improved further, the interface bond strengthened, and a larger portion of blast energy was absorbed and dissipated.

Concrete-filled cold-formed steel (CFS) columns combine a high load-carrying capacity with a low self-weight, which makes them an efficient solution for steel construction. This study presents a numerical and experimental investigation of the axial compression behavior of innovative concrete-filled CFS columns. Two cross-sectional configurations, Omega and Super Omega, were investigated. The proposed system consists of two identical profiles placed back-to-back and connected by resistance spot welds to form a built-up box section, in accordance with the principles of Eurocode 3, Part 1–3. The experimental program included tensile tests on steel coupons, compression tests on concrete cubes, and axial compression tests on eight column specimens with different configurations and slenderness levels. These tests were conducted to characterize the material properties and evaluate the column behavior in terms of load-carrying capacity, deformation, and failure modes. In parallel, a nonlinear finite element model was developed using ABAQUS to reproduce the behavior of the tested columns. The model accounts for material nonlinearities, buckling behavior, and steel–concrete interaction. The numerical results were compared with the experimental results in terms of ultimate load, displacement, strain, and failure mode. The comparison showed good agreement between the numerical and experimental results, highlighting the beneficial effect of concrete filling on the load-carrying capacity and overall stability of the investigated Omega and Super Omega columns under axial compression. Compared with the corresponding unfilled columns, concrete filling increased the load-carrying capacity by 107.24% to 115.98% in the tests (110.26% to 111.76% in the finite element models) and significantly reduced the maximum lateral displacement, demonstrating its beneficial effect on the deformation control and overall stability of the investigated columns.

This study focuses on the reinforcement of thermosetting matrices with lignocellulosic fibers and the limited interfacial compatibility that remains a major obstacle to the structural use of bio-based composites. The effect of chemical surface treatment on the interfacial behavior and macroscopic performance of unsaturated polyester resin (UPR) reinforced with Luffa fibers (LF) is studied in depth. LF was treated with two different chemical treatments: (i) alkaline treatment with sodium hydroxide (NaOH) and (ii) a combined NaOH/acetic acid (CH3COOH) treatment. The structural and morphological characteristics of the LF treated were examined using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Composite specimens were fabricated through a contact molding technique. Mechanical performance was assessed via density, tensile strength, impact resistance, hardness test, and water absorption. Results demonstrate that composites containing 10 wt.% LF exhibits improvements in mechanical properties, with tensile strength, impact strength, and hardness increasing by 74%, 192%, and 16.2%, respectively. The chemical treatments further enhance performance by reducing water absorption and improving fiber–matrix interfacial densification. SEM observations indicate uniform fiber dispersion at low fiber contents, while higher loadings lead to fiber agglomeration. The results demonstrate that luffa fibers can serve as an eco-friendly strengthening material in unsaturated polyester resin composites.

A touch-off explosion on concrete slabs is considered one of the simplest yet most destructive forms of adversarial loading on building elements. It causes far greater damage than explosions occurring at a distance. The impact is usually concentrated in a small area, leading to surface cratering, scabbing of concrete, and even tearing or rupture of the reinforcement. Studies available on the behavior of reinforced concrete (RC) slabs under touch-off (contact) and standoff explosions commonly indicate that the maximum damage occurs when the blast is applied to the center of the slab. This observation raises an important question about how the position of an explosive charge, especially relative to the free edge of the slab, affects the overall damage pattern in slabs supported on only two sides with clamped supports. This study uses a modeling strategy combining Eulerian and Lagrangian domains using the finite element tools of Abaqus Explicit v2020 to examine the behavior of a square slab supported on two sides with clamped ends subjected to blast loads at different positions, ranging from the center to the free edge and beyond, under touch-off explosion conditions. The behavior of concrete was captured using the Concrete Damage Plasticity model, while the reinforcement was represented with the Johnson–Cook model. Effects of strain rate were included by applying calibrated dynamic increase factors. The developed numerical model is validated first with experimental data available in the published literature for the case where the explosive charge is positioned at the slab’s center, showing a very close agreement with the reported results. Along with the central blast position, five additional cases were considered for further investigation as they have not been investigated in the existing literature and were found to be worthy of study. The selected locations of the explosive charge included an intermediate zone (between the slab center and free edge), an in-slab region (partly embedded at the free edge), a partial edge (partially outside the slab), an external edge (fully outside the free edge), and an offset position (250 mm beyond the free edge along the central axis). Results indicated a noticeable transition in damage patterns as the detonation point shifted from the slab’s center toward and beyond the free edge. The failure mode changed from a balanced perforation under confined conditions to an asymmetric response near the free edge, dominated by weaker surface coupling but more pronounced tensile cracking and bottom-face perforation. The reinforcement experienced significantly varying tensile and compressive stresses depending on blast position, with the highest tensile demand occurring near free-edge detonations due to intensified local bending and uneven shock reflection.

Blast damage to structural members poses serious risks to both buildings and people, making it important to understand how these elements behave under extreme loads. Columns in reinforced concrete (RC) structures are especially critical, as their sudden failure can trigger progressive collapse, unlike beams or slabs that have more redundancy. This state-of-the-art review brings together the current knowledge of the blast response of RC columns, focusing on their failure patterns, dynamic behavior, and key loading mechanisms. The studies covered include experiments, high-fidelity numerical simulations, emerging machine learning approaches, and analytical models for columns of different shapes (square, rectangular, circular) and strengthening methods, such as fiber reinforcement, steel-concrete composite confinement, and advanced retrofitting. Composite columns are also reviewed to compare their hybrid confinement and energy-absorption advantages over conventional RC members. Over forty specific studies on RC columns were analyzed, comparing the results based on geometry, reinforcement detailing, materials, and blast conditions. Both near-field and contact detonations were examined, along with factors like axial load, standoff distance, and confinement. This review shows that RC columns respond very differently to blasts depending on their shape and reinforcement. Square, rectangular, and circular sections fail in distinct ways. Use of ultra-high-performance concrete, steel fibers, steel-concrete composite, and fiber-reinforced polymer retrofits greatly improves peak and residual load capacity. Ultra-high-performance concrete can retain a significantly higher fraction of axial load (often >70%) after strong blasts, compared to ~40% in conventional high-strength RC under similar conditions. Larger sections, closer stirrups, higher transverse reinforcement, and good confinement reduce spalling, shear failure, and mid-height displacement. Fiber-reinforced polymer and steel-fiber wraps typically improve residual strength by 10–15%, while composite columns with steel cores remain stiff and absorb more energy post-blast. Advanced finite element simulations and machine learning models now predict displacements, damage, and residual capacity more accurately than older methods. However, gaps remain. Current design codes of practice simplify blast loads and often do not account for localized damage, near-field effects, complex boundary conditions, or pre-existing structural weaknesses. Further research is needed on cost-effective, durable, and practical retrofitting strategies using advanced materials. This review stands apart from conventional literature reviews by combining experimental results, numerical analysis, and data-driven insights. It offers a clear, quantitative, and comparative view of RC column behavior under blast loading, identifies key knowledge gaps, and points the way for future design improvements.