Résumé: This study investigates the performance of sisal fiber-reinforced mortar enhanced with marble filler. To enhance compressive strength, marble waste was introduced as a partial cement replacement in increments of 5.0 % by weight. Additionally, sisal fibers were incorporated at varying proportions of 0.5 %, 1.0 %, and 1.5 % by weight of binder, utilizing two fiber lengths (6 mm and 12 mm). Given their potential to enhance mechanical properties, sisal fibers have gained attention as reinforcement in cementitious materials. Their morphology, physical characteristics, and chemical composition were analyzed in detail. A novel treatment approach was explored to mitigate the hydrophilic nature of sisal fibers. Prior to their integration into the mortar, the fibers underwent chemical modification using chelating agents—ethylenediaminetetraacetic acid (EDTA) and ammonium hydroxide (AM). The impact of these treatments was assessed through Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The study evaluated key physical properties, including workability, water absorption, and density, alongside mechanical properties such as compressive strength, tensile strength, and shrinkage. Experimental findings revealed that chemical treatments, particularly with EDTA, altered the fiber’s morphology by increasing surface roughness and reducing hydrophilicity, as evidenced by FTIR and SEM analyses. These modifications contributed to an approximately 4 % improvement in workability, notably in EDTA F-M (1 %) mortars. Furthermore, flexural tensile strength tests at 28 and 90 days demonstrated an increase of 22–23 % for EDTA-treated mortars. The inclusion of EDTA-treated fibers also led to a 13 % reduction in total shrinkage. Thermogravimetric analysis (TGA) confirmed that the EDTA-treated fibers enhanced cement hydration, leading to the formation of greater amounts of hydration products such as calcium silicate hydrate (C-S-H) and ettringite compared to untreated fibers. Overall, the findings affirm that sisal fibers can effectively reinforce mortar, and chemical treatment with EDTA significantly improves both physical and mechanical properties. This approach presents a viable strategy for developing sustainable and high-performance cementitious composites in construction.

Résumé: 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.

Résumé: 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.

Résumé: In geotechnical engineering, soil stabilization is essential for improving the properties of clayey soils in infrastructure projects. This study explores the use of response surface methodology to optimize the utilization of polyvinyl chloride (PVC) waste as a stabilizing agent in proportions ranging from 2.5 to 30%. The percentages of clay and PVC served as input parameters, while the outputs included the CBR index, compressibility coefficient (Cc), swelling coefficient (Cs), and swelling pressure (Ps). Experimental results showed that replacing up to 30% of clay soil with the PVC improved key properties, such as the methylene blue value which had a relative decrease of 24.9%, consistency limits (LL, LP, and IP) underwent significant reductions of approximately 15.94%, 13.44%, and 17.2%, respectively, compaction parameters OMC and MDD show reductions of 52.38% and 10.32%, and consolidation characteristics Cc, Cs, and Ps show significant reductions of 92.55%, 43.64%, and 77.04%. For mechanical performance, including soaked CBR with a significant increase of 159.69% and penetration pressure, a 10% PVC replacement was identified as optimal. A quadratic predictive model was developed to optimize these responses, achieving a high coefficient of determination (R2 > 0.97) and statistically significant P-values (< 0.0001) for all outputs. These results underscore the model’s reliability and the potential of using PVC waste as a sustainable stabilization material. The approach is cost-effective, scalable, and eco-friendly, utilizing the PVC waste to stabilize soils, reduce environmental impacts, and enable sustainable infrastructure.

Résumé: Advancing the mechanical properties of naturally weak clayey soils is crucial in geotechnical engineering and is often achieved through targeted stabilization techniques. This research focuses on reinforcing clayey soil by integrating inert material, specifically aeolian sand collected from roadside deposits, in varying proportions from 2.5 to 30%. An experimental approach is adopted to analyze the improvement in geotechnical properties resulting from the addition of aeolian sand to clay through a series of geotechnical tests. These tests include the methylene blue test (MBV), the determination of Atterberg limits (LL, PL, PI), compaction characteristics (MDD and OMC), direct shear testing (C and ϕ), and oedometer tests (Cc and Cs). Furthermore, an optimization approach based on response surface methodology (RSM) and a central composite design (CCD) is implemented to determine the optimal mixture composition and accurately predict the evolution of the geotechnical properties of the soil. The experimental findings demonstrate significant improvements in the mechanical characteristics of the soil following the incorporation of aeolian sand, with the best performance achieved at a 30% sand content. The MBV decreased by 34.98%, the LL decreased by 39.62%, the PL decreased by 37.50%, and the PI decreased by 45.45%. In contrast, the MDD increased by 12.25%, enhancing the compaction and load-bearing capacity of the soil. A reduction of approximately 7.59% in the OMC was observed, lowering the water demand. The internal friction angle (ϕ) increased significantly by up to 233.33%, improving the shear strength, whereas the cohesion decreased by 49.78%. Additionally, the Cc and Cs decreased by 16.15 and 54.45%, respectively, which reduced the sensitivity of the soil to volume changes. Mathematical models are developed and statistically validated using the clay and aeolian sand contents as predictive variables, while key parameters such as the maximum dry density (MDD), cohesion (C), internal friction angle (ϕ), compressibility coefficient (Cc), and swelling coefficient (Cs) serve as response metrics. By applying analysis of variance (ANOVA) and refining the quadratic model via RSM, the study demonstrated significant results, with a coefficient of determination (R2) exceeding 0.97 for all the responses. The alignment between R2 and adjusted R2, along with the observed P values for critical parameters, highlights the robustness of the model. These findings pave the way for practical applications in foundation and road infrastructure projects, particularly in arid regions where water management and soil stability are critical concerns. The integration of 30% sand proves to be an effective and sustainable solution for enhancing the strength and stability of clayey soils in moisture-sensitive environments.

Résumé: In recent years, cold-formed steel (CFS) built-up sections have gained a lot of attention in construction. This is mainly because of their structural efficiency and the design advantages they offer. They provide better load-bearing strength and show greater resistance to elastic instability. This study looks at both experimental and numerical analysis of built-up CFS columns. The columns were formed by joining two C-sections in different ways: back-to-back, face-to-face, and box arrangements. Each type was tested with different slenderness ratios. For the experiments, the back-to-back and box sections were connected using two rows of rivets. The face-to-face sections, on the other hand, were joined by welding. In order to improve axial strength and overall stability, all column samples were filled with ordinary concrete, conforming to class C25/30. The numerical modeling was done in ABAQUS to study the mechanical behavior of the columns. This helped in understanding how different joining methods affect their axial compression performance. Analytical checks were also carried out using Eurocode 3 for hollow sections and Eurocode 4 for concrete-filled sections. The role of concrete confinement was examined as well, following American Concrete Institute (ACI) guidelines, for both face-to-face and box-shaped columns. The numerical results matched closely with the experimental findings, with variations of less than 5%. The study identified key failure modes such as local buckling and distortional buckling. It highlighted how section shape, type of connection, and concrete infill all play a major role in improving the strength of built-up CFS columns.

Résumé: Alfa fiber/unsaturated polyester resin (UPR) bio-composites were enhanced in this study using a dual chemical treatment consisting of sodium hydroxide (NaOH, 10%) and acetic acid (CH₃COOH, 20%). Fourier-transform infrared spectroscopy (FTIR) analysis indicated reduced hemicellulose bands with partial wax persistence, while scanning electron microscopy (SEM) revealed a roughened fiber surface. Composites (10–30 phr) were molded and post-cured at 45 °C. Relative to neat UPR (6.30 MPa), tensile strength peaked at 10.3 MPa at 15–20 phr ( ≈ + 63% vs. matrix), followed by a decline due to fiber agglomeration at higher loadings. Chemical treatment increased ductility, with elongation-at-break rising from 4.85% (10 phr, untreated) to 7.15% (10 phr, treated; ≈+47%). Unnotched Izod impact strength reached 2.5 kJ m⁻² at 20 phr, indicating optimal dispersion at intermediate contents. Treated composites exhibited lower water uptake than untreated ones at equal loading and showed increased Shore hardness with fiber addition. The results demonstrate that a simple alkali–acetylation sequence improves fiber/matrix compatibility and mechanical performance while defining processing windows (15–20 phr) that minimize clustering. This study brings something new by using a very simple dual treatment (NaOH + CH₃COOH) on Alfa fibers, which are still not much studied. The work shows that this approach can clearly improve the bond between fiber and resin, giving better tensile and impact strength. It also defines the best fiber loading range (15–20 phr), which can guide practical use of Alfa fibers in sustainable composites.

Résumé: This research present a novel investigation, which focuses on the numerical exploration of steel columns having a double curvature, built with both hollow square and circular cross-sections. A finite element model was initially created using ABAQUS software and was validated through a series of compression experiments conducted on square hollow specimens exhibiting double curvature. close agreement was observed in term of ultimate loads, load–displacement curves and deformed shapes corresponding to the failure modes. Based on validated numerical simulations, parametric analyses are carried out to investigate the effects of major geometric parameters on the axial bearing capacity of double curved steel columns. The study consists in a systematic variation of curvature angle (20°, 25°, 30°, and 35°), curvature radius (500 mm, 700 mm, 900 mm, and 1100 mm), square cross-section size (250 mm, 300 mm, 350 mm, and 400 mm), circular diameter (318 mm, 381 mm, 445 mm, and 509 mm) and end offset distance (400 mm, 600 mm, 800 mm, and 1000 mm). The findings highlighted the sensitivity of axial performance to angle curvature, section width and offset distance at column ends. The outcomes of this study provide valuable insights for the design and optimization of curved steel columns in structural engineering applications, particularly where stability and axial strength are critical.

Résumé: Progressive collapse represents a critical failure scenario in steel moment-resisting frames, especially when beam sections are intentionally weakened through flange cuts or web openings. While previous studies reported that circular openings were the most effective configuration among various shapes, the present study investigates whether semi-circular openings, when combined with reduced beam sections (RBS), can provide superior performance. A finite element model was developed in ABAQUS/Explicit v2016 and validated against experimental results to ensure reliability. Parametric analyses considered both circular and semi-circular openings with diameters of 80 mm and 110 mm, placed at various distances from the RBS centerline (L = 0, 65, 140, and 180 mm). The results show that openings located too close to the RBS zone (L = 0 mm and L = 65 mm) significantly reduced strength and suppressed catenary action. Conversely, larger spacings (L = 140 mm and L = 180 mm) enhanced load capacity and ductility by promoting stress redistribution. Importantly, semi-circular openings consistently outperformed circular ones in the present investigation. In particular, the SC3-140-110 specimen achieved the highest peak load (248.7 kN) and the strongest catenary action contribution (227.6 kN), demonstrating superior robustness against progressive collapse. These findings highlight the technical advantage of semi-circular openings as an effective detailing strategy for improving the collapse resistance of steel moment frames.

Résumé: In this work, it was proposed to replace the conventional reinforcement of the unsaturated polyester resin by a mineral, from a siliceous volcanic rock of volcanic nature, perlite. UPR/perlite composites with different proportions of phase components (from 1% to 5% of powder mass part). We used unsaturated polyester resin (UPR) as well as the hardener cobalt octoate and treated and untreated perlite of different dimensions (greater than 60µm, and less than 60µm). The composites were prepared by the contact molding process. The composite plates are hardened for 24 hours at room temperature then placed in an oven for 15 hours at 50°C to undergo post-curing. The composites obtained were subjected to different characterization techniques, namely rheological tests (dynamic mechanical analysis (DMA)), thermal tests (differential calorimetric analysis (DSC)) and Thermogravimetric analysis (ATG) and structural characterization by Fourier transform infrared (FTIR). The DMA measurements showed that the UPR/perlite composites with untreated filler presented conservation modules higher than that of the resin without perlite for the rates of 3% and 4%, while for the composites with treated filler, that at 3% of perlite shown the highest modulus along the glassy zone. Also, the glass transition temperature of the UPR resin was not affected by the addition of perlite. The decrease in intensity at mid-height of the tan δ peaks allowed deducing the existence of a fairly strong UPR/perlite interface. DSC thermograms showed that the exothermic peak is shifted to higher temperatures, due to a delay in the curing reaction caused by the presence of the perlite particles. This study concluded that the perlite enhances the properties of composites.

Résumé: The susceptibility of concrete to elevated temperatures is a paramount concern in civil engineering, especially in fire-related scenarios. This material often suffers mechanical weaknesses such as fracturing and reduced durability under high temperatures. Despite its ubiquitous use, concrete’s vulnerability to thermal stress presents significant challenges for maintaining structural integrity and safety. The novelty of this work lies in its innovative approach to addressing these challenges by proposing the utilization of waste plastic fibers, which are readily available due to the extensive use of various plastic products. This approach not only enhances the mechanical resilience of concrete but also contributes to mitigating environmental and health impacts associated with plastic waste. The research focuses on the effects of high temperatures on the mechanical properties of sand concrete reinforced with fibrous materials. Concrete specimens were prepared with different lengths (1 cm and 2 cm) of packing tape fibers at concentrations of 1% and 2%. These specimens underwent controlled thermal treatments ranging from 100 °C to 700 °C with a heating rate of 1 °C/min, following a 90-day water immersion curing period. The evaluation encompassed various tests including visual inspection, residual weight measurement, residual compressive and tensile strength assessments, and ultrasonic pulse velocity (UPV) testing. The analysis revealed a notable improvement in mechanical strength for concrete reinforced with 1% fibers at 300 °C. However, exposure to higher temperatures (500 °C and 700 °C) led to a significant decline in strength across all samples due to the evaporation of fibers, resulting in the formation of voids and conduits within the concrete’s structure. While previous research has extensively investigated the effectiveness of polypropylene fibers in crack mitigation during fire incidents, limited attention has been given to the potential of plastic waste as a reinforcement material. Thus, this study’s novelty contributes to expanding the scientific understanding of using waste plastic fibers to enhance concrete’s resilience to high temperatures, thereby filling a crucial gap in existing literature.

Résumé: Current design trends indicate a rising preference for mixed steel-concrete structures, which provide exceptional opportunities for material optimization and numerous advantages, including improved strength, ductility, and stiffness. This trend aligns with the growing demand for sustainable and resilient construction solutions in civil and structural engineering. The present article provides an analytical and numerical investigation focused on enhancing the performance of cold-formed steel back-to-back C-columns through the application of various strengthening materials, including concrete and carbon fiber-reinforced polymer (CFRP) layers. The study employs advanced finite element modeling techniques to simulate real-world loading conditions and incorporates rigorous parametric analyses to evaluate structural behavior under varying constraints. Furthermore, it investigates the impact of incorporating different types of web stiffeners—namely, simple, square, and triangular—on the mechanical behavior of built-up columns subjected to axial compression. The research also explores how these configurations influence load distribution and failure mechanisms. To validate the analytical approaches, the numerical findings are compared with predictions based on EN 1994-one to one standards, allowing for an evaluation of the effectiveness of the formulations in estimating the contributions of individual components. The results indicate that the addition of concrete significantly enhances the strength and lateral stability of built-up empty columns, with improvements of approximately 70% and 75%, respectively. Conversely, the application of CFRP strips leads to a reduction in lateral instabilities by about 80%. Additionally, the combined use of concrete and CFRP materials demonstrates synergistic benefits, offering a balanced enhancement of both compressive strength and lateral stability. These findings provide essential insights for optimizing the design and performance of thin-walled structures in engineering practice. The study emphasizes the practical implications of these results for designing lightweight, high-performance structures that meet modern construction demands.

Résumé: Several studies have explored the potential of waste marble powder (WMP) and lime (LM) as solutions for issues associated with clayey soils. While WMP enhances mechanical properties and addresses environmental concerns, LM effectively improves soil characteristics. This research investigates the efficacy of LM and WMP, both individually and in combination, in addressing challenges specific to clayey soils in Bouzaroura El Bouni, Algeria. These soils typically exhibit low load-bearing capacity, poor permeability, and erosion susceptibility. LM demonstrates promise in enhancing soil properties, while WMP not only addresses environmental concerns but also enhances mechanical characteristics, providing a dual benefit. The study utilizes a three-variable experiment employing Response Surface Methodology (RSM) Box-Behnken Design, with variations in clay content (88%–100%), LM treatment (1.5%–9%), and WMP inclusion (1.5%–9%). Statistical analysis, including ANOVA, reveals significant patterns with p-values <5%. Functional relationships between input variables (clay, LM, and WMP) and output variables (cohesion, friction angle, and unconfined compressive strength) are expressed through high determination coefficients (R2 = 99.84%, 77.83%, and 96.78%, respectively). Numerical optimization identifies optimal mixtures with desirability close to one (0.899–0.908), indicating successful achievement of the objective with 88% clay content, 3% LM, and 6% WMP. This study provides valuable insights into optimizing clay soil behavior for environmental sustainability and engineering applications, emphasizing the potential of LM and WMP as strategic additives.

Résumé: At ambient temperature, concrete exhibits excellent mechanical properties. However, understanding the behavior of concrete under high-temperature conditions is crucial, especially for civil engineering applications during fire incidents. The growing use of plastic-based products has led to a significant increase in polymer waste, posing environmental challenges. The valorization of this plastic waste in the form of fibers presents both economic and environmental advantages. This study focuses on the study of the behavior of sand concrete incorporating polyethylene terephthalate (PET) fibers with percentages of 1% and 2% at high temperatures (100, 300, 500 and 700 °C). Specimens are tested for residual mass loss, residual compressive and tensile strength. A complementary analysis of SEM makes it possible to confirm and better clarify the morphology of the concretes of sand before and after the rise in temperature. The results obtained from this study indicate that the residual resistance is reduced with the rise in temperature for all the concretes studied, except in the temperature range of 300 °C, in which a slight improvement in resistance is noticed. The incorporation of PET fibers in the test concretes does not enhance their residual behavior significantly. However, it does serve as an effective solution by reducing the susceptibility to spalling, by preventing cracking and by fulfilling a similar role to that of polypropylene fibers.

Résumé: This article presents the results of a comparative experimental study on the influence of date palm fibers to replace polypropylene fibers used as reinforcement in self-compacting concrete (SCC). Indeed, the use of polypropylene fibers makes it possible to reduce the plastic shrinkage of concrete. Date palm fibers have mechanical characteristics (tensile strength and elasticity modulus) largely sufficient to replace polypropylene fibers. The use of natural fibers has several advantages, they are natural, renewable, have no effect on the environment and require little energy for their transformation unlike synthetic fibers. In this comparative study, polypropylene fiber is used as a control material and date palm fiber as a study material. The results obtained show that the two types of fibers decrease the fluidity and the compressive strength, increase the flexural strength and decrease the shrinkage. Date palm fibers delay the appearance of cracks more than polypropylene fibers. Date palm fibers guarantee the best results of SCC in fresh and hardened state.

Résumé: The use of finite element calculations to deal with geotechnical problems is therefore limited by poor knowledge of the mechanical parameters of soils. The identification of these parameters characterizing the soil behavior model involves solving the inverse analysis problem. This form of inverse analysis consists in calibrating a numerical soil model on experimental data by iterative modifications of the values of the input parameters of the model until the difference between the result of the numerical calculation and the experimental data is minimal. In this article, we study the use of the principle of inverse analysis for the identification of the parameters of the constitutive soil model Mohr–Coulomb: the shear modulus (G) and the friction angle (φ). The inverse analysis problem posed by the determination of the parameters of the model is solved using an optimization technique based on two stochastic optimization algorithms, the genetic algorithm and the hybrid genetic algorithm with the tabu search method. These two optimization methods have been validated on a pressuremeter test. The results obtained by applying the genetic algorithm method and the hybrid genetic algorithm method for the identification of the two Mohr–Coulomb parameters (G and φ) show that the hybridization process of the genetic algorithm with the tabu search method accelerated the convergence of the algorithm towards the exact solution of the problem whereas the genetic algorithm alone takes a much longer computation time to reach an optimum close to the exact solution of the problem.

Résumé: Volume change of expansive soils is a challenging issue, which affects various engineering structures all over the world. Consequently, we need environmentally-friendly and cost-effective soil stabilizers to address the challenges related to expansive soils. The utilization of natural fibers allows for the reduction in environmental impact since they are renewable and biodegradable raw materials. Moreover, the current article presents an experimental approach to study the effect of natural fibers on the mechanical behavior of expansive soils. Various experimental tests—such as Atterberg limits, standard compaction, direct shear, swelling potential, and swelling pressure—were conducted on control and treated soil samples using different percentages of fibers. The results of measurements of the physico-mechanical properties after reinforcement of the soil with 1%, 5%, and 10% of natural fibers indicate that the mechanical behavior of expansive soils is greatly influenced by the addition of natural fibers. To conclude, 86% reduction was observed in the swelling coefficient of treated soil. Future research can be done to check the durability of the current practice in detail.

Résumé: This research focuses on the optimization of formulation, characterization, and damage analysis of plant fiber-reinforced polyester resin composites (jute and date palm). To better understand the characteristics and mechanical behavior of these materials, this study investigates the influence of resin content and plant fibers on the physico-mechanical behavior of the resin composites. Resinous composites consisting of polyester resin and raw earth were studied using a novel formulation based on an empirical method that follows the principle of earth saturation with polyester resin. Saturation was achieved with a 28% content of polyester resin, which appeared to be an optimal blend for the earth–resin composite. Plant fibers were randomly incorporated as reinforcement in the composites at various percentages (1%, 2%, and 3%) and lengths (0.5 cm, 1 cm, and 1.5 cm). Mechanical tests including bending, compression, and indentation were conducted to evaluate the mechanical properties of the composites. Analysis of fracture morphology revealed that the deformation and rupture mechanisms in bending, compression, and indentation of these composites differ from those of traditional concrete and cement mortar. The obtained results indicate that the composites exhibit acceptable performance and could be favorably employed in the rehabilitation of historic buildings.

Résumé: The wide use of cold-formed sections (CFS) in the field of steel constructions, favored by the multiple advantages they offer (lightness, ease of installation, etc.), has led us to reflect on a new process for manufacture of metal beams allowing the design of very large span hangars and a reduction in instability problems. This paper presents a study of the theoretical and numerical behavior of a large span CFS beam with different webs, a solid web, a triangular corrugated web, and a trapezoidal corrugated web. These beams are stressed by a concentrated bending load at mid-span. Numerical modeling was done using the finite element software ABAQUS. The results were validated with those theoretically found, based on the effective width method adopted in standard EN1993-1-3. The load capacity and failure modes of the beams were discussed. According to numerical and analytical analysis, corrugated web beams perform better than all other sections.

Résumé: High performance concrete (HPC) is an innovative concrete used widely in modern construction. New techniques of formulating and designing HPC have made it possible to obtain remarkable mechanical performance and durability compared to the conventional concrete. The main advantages of HPC are related to its low porosity, very high mechanical resistance, and excellent durability. The ease of HPC application is obtained by the combined use of superplasticizer and mineral addition, which results in a significant increase in the compressive strength while improving workability and durability. The Algerian steel industry in North Africa generates very large quantities of slag which are currently little or not used for the formulation of hydraulic binders in the field of construction materials. In the current economic climate, research on high-performance concretes in Algeria is mainly focused on their formulations with a view to producing cement-based concretes composed of better strengths and more durable. The objective of this work is to optimize a formulation of HPC based on a ternary binder integrating granulated Algerian blast furnace slag as a cement substitute. This can partially solve an environmental problem by recycling waste and by-products from the steel industry. The manufacture of a HPC with less cement could lead to both environmental benefits thanks to a reduction in CO2 emissions and financial benefits through a lower construction cost and build more sustainable structures.

Résumé: Cold-formed steel (CFS) structural members retain their preferred position in the lightweight construction industry, which is due to their significant advantages. The optimization of these CSF elements will make it possible to construct buildings at very competitive prices, having in addition an increased load capacity, and thus obtaining a stable and economical construction. The main objective of this research being the evaluation of the effectiveness of these new sections in (CSF) and the estimation of the remarkable instabilities as well as the failure modes. This article deals with an experimental study on the behavior of CSF beams of delta and bi-delta shape, solicited by four-point bending loads. These cross section shapes are often used in floors as main and secondary beams. The properties of this type of sections are most often based on the method involving the effective width designated by the Eurocode 3 standard. A nonlinear analysis by finite elements (FE) using the ABAQUS calculation program is carried out, thus making it possible to compare the experimental results with the numerical ones as well as those which are given by the theory proposed by Eurocode 3. Finally, the results obtained essentially showed that the failure modes of the delta and bi-delta beams corresponded to the buckling modes local.

Résumé: This paper is concerned with investigating of the plastic behaviour on gap K-joints of truss girders, made from thin-walled rectangular hollow section members. An experimental study was carried out on a full-scale girder under a concentrated load on two central nodes. A numerical analysis was carried out using ABAQUS in order to clearly see the behaviour of this type of joint and to make a comparison with the experimentation. This study will make it possible to examine attentively and to define the analytical model for this type of joint. The results obtained in this paper have shown that the sections with very thin-walled present different behaviours compared to the thin or more or less thick sections. As a result, the tested truss made it possible to observe the failure mode of this type of section, follow-up of a comparative study on the determination of the joint capacity by Eurocode 3 and CIDECT.

Résumé: The reuse of concrete waste as a secondary aggregate could be an efficient solution for sustainable development and long-term environmental protection. However, the variable quality of waste concrete, especially with various compressive strengths, can have a negative effect on the final compressive strength of recycled concrete. In this approach, the major goal of this research is to study the effect of parent concrete qualities on the performance of recycled concrete. To accomplish this task, three grades of different compressive strengths (10 to 15) MPa, (20 to 25) MPa, and (30 to 40) MPa have been analyzed in an experimental test program, in which an unknown compressive strength is introduced as well. The experimental mix use 40% of secondary aggregates (both course and fine) and 60% of natural aggregates. This led to the decreasing of the compressive strength of the test concrete between 14% and 23.7% compared to the normal concrete. This loss was improved by adding an amount of cement equivalent to 4% of the weight of the recycled aggregate used. The achieved results prove that the strength properties of the parent concrete have a limited effect on the compressive strength of the recycled concrete. Additionally, low compressive strength parent concrete, when crushed, generates a high amount of fine aggregate and large percentage of recycled coarse aggregates with less attached mortar, and presents the same compressive strength as an excellent parent concrete.

Résumé: The valorization of local by-products in the manufacture of a new range of sand concrete and the improvement of their properties, will lead to seek an arrangement between performance and cost in order to achieve a resistant material. Waste recycling affects two very important affect namely the environmental impact and the economic impact. The main objective of our work is to contribute to optimize the formulation of sand concrete as part of the recovery of waste, which is harmful to the environment given its bulky and unattractive nature, it is waste plastic. Most PET bottles become waste after use, causing environmental problems. To solve this problem, a method for recycling PET bottles as fibers to strengthen concrete is proposed. Two types of plastic waste are added to sand concrete; the first concerns the recycling of post-consumer bottles in PET, in the form of polyester fiber supplied by the company RET-PLAST and the second type concerns the packaging belts made of polyethylene terephthalate (PET). The properties in the fresh state (workability and density) and in the hardened state (compressive strength, tensile strength and water absorption) of the various produced concretes are analyzed and compared against their respective controls. From the experimental results, it can be concluded that the reinforcement of the cement matrix with PET fibers with a rate of 1% improves the mechanical properties of sand concrete as well as a remarkable decrease in its water absorption capacity.

Résumé: This paper deals with the development of sustainable building earth-based materials. More precisely, it addresses the study of the reinforcement of raw earth with natural fibres originated from Algeria (diss and date palm tree fibres) and their stabilisation with xanthan gum. The aim of this study is the design of extruded earth-based building blocks with improved mechanical properties such as compressive strength and ductility. The effects of separate and simultaneous addition of date palm trees or diss fibres (with length varying between 5 and 15 mm at dosages of 1.5 and 3% in volume) and stabiliser (xanthan gum and HMP at 1 and 2% of the dry earth mass) on the flexural and compressive strength of the stabilised and unstabilised extruded materials are compared. Results show that adding only fibers decreases the compressive strength of the earth in comparison with the unreinforced sample. It is also shown that diss fibres provides better reinforcing efficiency than date palm tree fibres and that a combined addition of xanthan gum and natural fibres create a synergic effect that greatly improved the material mechanical behaviour: higher compressive and tensile strengths and better ductile properties. These results are fully supported by microscopic observations and pull-out tests carried out on single fibres.

Résumé: Explosions, regardless of their origin, have a significant impact on building structures, with the severity and spread of blast pressures being influenced by several factors. Among these, the orientation of the explosive, in addition to its mass, geometry, and direct or indirect interaction with the target, plays a critical role in determining the extent of the damage. Existing literature has primarily focused on blast tests involving explosives placed horizontally, leaving the effects of vertical alignment, particularly with brick-shaped charges, largely unexplored. The increasing frequency of hostile attacks, advanced warfare techniques, and explosive incidents accentuate the need for a comprehensive analysis that accounts for varying explosive orientations to better predict structural responses and enhance resilience. The present study aims to numerically investigate the impact of vertical tilting (from 0° to 75°) of Trinitrotoluene (TNT) explosives on the blast behavior of one-way slabs. To ensure accuracy of employed Abaqus software, the study’s findings are validated through comparison with experimental data found in existing literature. The findings revealed that when the TNT charge was laid flat, the resulting pressure wave moved outward in a mainly tangential or slanted manner, causing a broader yet shallower impact across the slab surface. However, as the orientation of the explosive shifted upward from horizontal to nearly vertical (0° to 75°, at 15° intervals), the pressure front began striking the surface more directly. This led to significantly amplified reflected pressure, overshadowing the initial compression effects. These findings have significant implications for improving safety protocols and structural design strategies in regions vulnerable to explosive threats.

Résumé: Slabs, as integral structural components, play a vital role in load transfer within buildings but remain highly susceptible to touch-off explosions, where explosives are in direct contact with their surfaces. Such high-intensity impulsive loads, characterized by extreme strain rates (103–106 s−1), induce complex phenomena like shock wave propagation, dynamic amplification, localized plasticity, and material fragmentation. Despite the escalating use of explosives in global conflicts, such as in Ukraine, Syria, and Israel, and accidental industrial detonations in rapidly urbanizing regions, limited studies address how varying blast durations influence structural response. This research bridges a critical gap by investigating the effects of touch-off explosions on slabs supported only along two opposite edges, emphasizing the practical need for enhanced blast-resistant design methodologies. The study employs a validated numerical model, benchmarked against experimental results from Zhao and colleagues in 2019 for a 2 ms blast duration, and extends it to explore blast durations of 1 ms, 3 ms, 4 ms, 5 ms, and 6 ms. Using an Eulerian-Lagrangian coupled Finite Element framework in Abaqus, the research captures transient blast-wave interactions, pressure-impulse effects, and localized material degradation. The results show that blast duration strongly affects structural damage. Shorter durations cause localized flexural cracking, while longer durations lead to global deformation and flexural-shear failure. Deformation increases nearly sixfold, and plastic damage energy rises 2.5 times as blast duration extends from 1 ms to 6 ms. Perforation size and crushing also increase significantly with longer durations. These findings provide key insights for designing resilient infrastructure to withstand extreme blast loads.

Résumé: Direct surface explosions on structural slabs represent a relatively straightforward mechanism of causing damage when compared to other structural elements. Such explosions tend to produce highly localized and severe damage, often leading the slab to reach its ultimate failure stage and even experience catastrophic collapse, a level of damage that is typically more severe than that caused by non-contact blasts. Recently, the field of blast engineering has seen growing research interest, with several experimental and computational studies focusing on the response and enhancement of thin structural components like slabs under blast loads using both conventional and advanced materials. A critical research gap has been noted by the authors through a thorough review of existing literature, revealing that the incorporation of shear reinforcement to improve slab resistance against contact blasts has received limited attention. This study aims to bridge that gap by investigating the influence of shear reinforcements, specifically vertical stirrups, on the behavior of slabs subjected to contact blast loading. Numerical analyses are conducted utilizing the ABAQUS/Explicit finite element platform, with the model validated against results available in open literature. All materials involved in the slab construction are simulated using appropriate nonlinear constitutive models. The simulation outcomes indicate that the slab with closely spaced shear stirrups and additional compression bars performed exceptionally well. This configuration boosted shear resistance, limited cracking, and helped distribute stresses more evenly, which reduced deformation and prevented perforation under blast.

Résumé: Thin-walled cold-formed steel structural elements with open sections are prone to local, distortional, and global instability modes, which often interact under axial or flexural loads. Current design codes primarily rely on elastic critical load calculations for sizing, but further research is needed to enhance their stability and load-bearing capacity. While previous studies have examined instability modes in conventional cold-formed sections, limited research has focused on composite cold-formed steel sections with concrete infill. This study investigates the compressive strength and instability behavior of cold-formed steel columns with a welded double-sigma configuration. Square and round tubes, combined with concrete infill, were incorporated into the middle section of 5-m-tall columns. A nonlinear finite element analysis was conducted in Abaqus to evaluate their compression behavior and failure modes. The results demonstrated a significant increase in the critical load for all composite models, with deformation reductions of up to 30% compared to empty columns. These findings highlight the effectiveness of integrating concrete infill and steel tubes in improving structural performance. The study provides insights for optimizing cold-formed steel composite columns, making them a viable option for enhancing structural resilience and safety in modern construction.

Résumé: Enhancing existing steel structures becomes imperative upon alterations in usage or geometric configurations, such as introducing web openings in floor beams to accommodate various services. The utilization of welded steel plate and conventional strengthening methods often presents challenges, which may be mitigated through the adoption of composite materials like Fiber Reinforced Polymers (FRP). However, research on the application of FRP to steel beams with web openings remains limited, predominantly focusing on beams with rectangular openings of modest dimensions. This study delves into the application of Glass Fiber Reinforced Polymers (GFRP) to strengthen reinforced steel floor beams featuring trapezoidal openings. Leveraging a rigorously validated numerical model derived from previously published findings by a contributing researcher, the investigation showcases that the proposed GFRP reinforcement scheme exhibits performance comparable to conventional steel plate welding techniques, while preserving the inherent strength of the original solid beams.