https://ajce.aut.ac.ir/ AUT Journal of Civil Engineering en daily 1 Mon, 01 Jun 2026 00:00:00 +0330 Mon, 01 Jun 2026 00:00:00 +0330 https://ajce.aut.ac.ir/article_5982.html Accurate determination of the frequency–amplitude relationship in strongly nonlinear oscillators remains a critical challenge in engineering dynamics, particularly when classical linearization and traditional perturbation methods fail due to the absence of small parameters. This limitation complicates the analysis and design of systems where nonlinear effects dominate, such as mechanical vibrations, structural dynamics, and nonlinear control applications. This study investigates the applicability and effectiveness of the Energy Balance Method (EBM) for analytical modeling of relativistic and Duffing-type oscillators. The method provides reliable and computationally efficient expressions for system frequencies across a wide range of oscillation amplitudes without relying on restrictive perturbation assumptions. The formulation assumes conservative systems undergoing periodic motion, limiting its application to undamped oscillators; within these constraints, EBM offers a simple and robust solution strategy. The approach constructs an energy balance over a single oscillation period using a single-term trial function, requiring only one iteration to obtain the frequency–amplitude relationship. The main novelty lies in demonstrating that such a minimal framework delivers highly accurate results even in strongly nonlinear regimes. Quantitative comparisons with exact solutions and established analytical methods—including the Harmonic Balance Method, Variational Iteration Method, Homotopy Perturbation Method, and the method of multiple scales—show excellent agreement, with negligible relative errors over a broad amplitude range. These results confirm that EBM achieves comparable or superior accuracy with significantly reduced computational effort. Future work may extend the method to damped, forced, and multi-degree-of-freedom systems, further broadening its applicability to complex engineering problems. https://ajce.aut.ac.ir/article_6004.html This study presents a comprehensive experimental investigation into the enhancement of interfacial shear strength at the bond interface between old and new concrete layers using polypropylene (PP) fibers and acrylic resin. Given that weak interface performance is a persistent challenge in multilayer concreting and repair operations, particularly when casting delays are unavoidable, this research addresses the necessity of developing material-based solutions capable of improving bond integrity under practical construction conditions. Three placement configurations were examined: monolithic casting (Type A), cold joint with initial set (Type B), and construction joint with final set (Type C). Unlike previous studies that typically evaluated modifiers independently, this work introduces an integrated fiber–polymer strategy and quantifies its performance across varied execution scenarios, thereby emphasizing its innovative and application-oriented contribution. Key variables included PP fibers (12 mm) at 0–1.2% and acrylic resin at 0–7% by weight of cement. Cubic specimens (150×150×150 mm) were tested in direct shear at 7, 14, and 28 days. Results indicated a strong dependence of modifier efficiency on placement conditions. In Type A specimens, the use of 0.7% fibers increased shear strength by 23%. In Type B, while 3% resin alone had negligible effect, its combination with 1.2% fibers improved strength by 11%. Most notably, in Type C, the synergistic application of 0.4% fibers and 3% resin produced a remarkable 71% improvement in interfacial shear strength. These findings demonstrate that the hybrid fiber–polymer system, through crack bridging and enhanced adhesion, provides a robust enhancement mechanism. https://ajce.aut.ac.ir/article_6012.html The dynamic compaction method for soil improvement was introduced by Louis Menard in 1970. Numerical studies on dynamic compaction have predominantly been conducted on dry granular soils, with less consideration given to its application in municipal solid waste compaction. The present study aims to numerically investigate the effect of tamper weight and drop height on the dynamic compaction of landfills. This was done using the finite element software Abaqus 6.14-2 in two time steps, geostatic and explicit dynamic, using the coupled Eulerian–Lagrangian approach. The study results demonstrate that increasing the drop height of a tamper with a weight of 5t from 5m to 30 m increases the depth of the cavity created in the soil from 12.6cm to 50cm, increases the stress developed in the soil from 747kg/m² to 4111kg/m², and increases the plastic strain from 0.16 to 1.3. Moreover, increasing the drop height for a tamper weight of 30 t from 5m to 30m increases the crater depth in the soil from 50cm to 2.73m, increases the soil stress from 4111kg/m² to 27176.5kg/m², and increases the plastic strain in the soil from 1.3 to 12.27. It can thus be summarized that although both the weight and the drop height of the tamper are effective in the momentum, the applied stresses, the crater depth, and the plastic strain of the landfill, the use of heavy tampers, which require high-capacity cranes, is not recommended for dynamic compaction in landfill improvement due to limitations in their use and increased project implementation costs. https://ajce.aut.ac.ir/article_6015.html Portland cement production is a major source of greenhouse gas emissions, and while the integration of supplementary cementitious materials (SCMs) and alkali‑activated materials (AAMs) offers a sustainable pathway to reduce environmental impacts and enhance durability, the effectiveness of these systems is critically governed by curing regimes that determine strength development and long‑term performance. In this study investigates the influence of curing regimes on the performance of alkali-activated concretes incorporating ground granulated blast-furnace slag (GGBS) with silica fume (SF) and limestone powder (LP). Concretes were activated using sodium hydroxide (8M) and sodium silicate (water glass) with a silicate modulus of 2.07, and subjected to five curing conditions. Mechanical and durability properties were assessed through volumetric water absorption, rapid chloride permeability test (RCPT), and rapid chloride migration test (RCMT) at 90 days, and compressive strength at 28 and 90 days. Results showed that the specimen containing 85% GGBS and 15% LP exhibited favorable strength and durability under water curing, indicating its suitability for practical applications. In contrast, steam curing caused a sustained reduction in compressive strength, while permeability performance showed no significant improvement. These findings highlight the importance of curing conditions in developing durable, environmentally sustainable geopolymer concretes for broader construction use. https://ajce.aut.ac.ir/article_6057.html In this article, raw materials were used in different ratios without brick firing to achieve the minimum compressive strength required by the standards. An average compressive strength of 8.36 N/mm2 was obtained on the bricks having the highest levels of resistance. A comparison was also made with brick samples available on the market (Gary), which are manufactured in brick kilns. A comparison of the compressive strength of bricks made of different raw materials revealed that they were lower in compressive strength than Gary bricks. In order to solve this resistance gap, it was necessary to strengthen the bricks, this study refers to the technique known as strengthening bricks with hair fibers (SBHF). Here, human hairs were used as natural tensile fibers to achieve this resistance. Based on the combination of different percentages of hairs with bricks obtained from the best combination of materials, the compressive strength of the samples varied between 9.22 N/mm2 and 15.13 N/mm2. In this study, more than 300 bricks were produced without the use of brick kilns, which consume a significant amount of energy and contribute to environmental pollution. In the experiment campaign, it was found that bricks reinforced with 2% human hairs, which are waste materials and pollute the environment, had a higher compressive strength than bricks currently available on the market. Additionally, the SBHF method also resulted in increasing compressive strength of prisms, satisfactory water absorption, and reduction of 30% in production cost compared to samples found on the market. https://ajce.aut.ac.ir/article_6027.html There is a common simplification in seismic design codes that independently computes the seismic force in the two orthogonal directions. Then, individual frames are designed based on the distributed lateral forces. The 3D effects, including the interaction of adjacent and orthogonal frames, are omitted in this process, while research shows that the design results differ between 2D and 3D methods. Although most seismic assessment procedures and philosophies have been developed for 2D frames, there is no standard prescription for adopting them to assess 3D structures. The progress in the computational capability of computers makes the 2D design philosophy not acceptable anymore, and the engineering community needs to move toward a 3D point of view in assessing and designing structures. Many works have investigated the 3D behavior of structures or proposed 3D design strategies for different issues. There is a need to clarify the importance of the problem as an independent research field and urge the researchers to shed light on other aspects of the 3D structural behavior. This paper reviews the research in which the 3D structural design or behavior is addressed and shows weaknesses and future research paths. The study includes four main parts: modeling, assessment, design, and optimization of 3D structures. Finally, the main results and recommendations are presented. https://ajce.aut.ac.ir/article_6058.html The use of concrete pavement has significantly increased due to its advantages over asphalt pavement. Determining the concrete mix ratio for asphalt is a vital and crucial step in the construction process. Concrete should be strong, durable, and resistant to environmental degrading factors. This means it needs to withstand freezing, thawing, shrinkage, and harsh environmental conditions (such as heat and cold. These characteristics result in concrete having a longer lifespan and creating robust structures). One of the challenges in design is balancing quality and cost, which comes with its own complexities.. Over the past few years, the application of models and algorithms for multi-objective problems has been a focus of research. This study introduces adaptive neuro-fuzzy inference system goal programming (NFGPM) and fuzzy-goal programming model (FGPM) as expanded variants of basic goal programming models, as alternative tools for allocating asphalt concrete pavement mixtures proportions with multiple, varied objectives. The actual data laboratory experiment datasets were generated and used to develop proposed models. The outcomes of the proposed NFGPM’s mixture proportions and its prediction of concrete properties —such as slump, flexural strength, abrasion resistance, shrinkage and freeze–thaw behavior— are compared with experimental data. The study confirms that the adaptive neuro-fuzzy inference system goal programming model proposed herein can deliver the most cost-effective and optimally performing concrete pavement mixture proportions.