University of QomCivil Infrastructure Researches2783-140X11220251222Experimental Investigation of the Effect of Temperature on the Mechanical Properties of Lightweight Concrete Containing Steel FibersExperimental Investigation of the Effect of Temperature on the Mechanical Properties of Lightweight Concrete Containing Steel Fibers116359210.22091/cer.2025.12611.1613FASeyed KomeilHashemiFaculty of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran.0000-0002-1864-2867Seyed RezaMirbozorgiFaculty of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran.0009-0004-4966-3304Journal Article20250327Nowadays, the growth of building construction and the need of lighter but more performance materials are of interest. Adding to, fire incidents highlight the insufficient knowledge of the post fire material properties. Concrete should maintained to resist more and lost less mechanical properties when subjected to high temperatures. Hence, this study investigates the effects of elevated temperatures on the mechanical properties of lightweight concrete containing different volumetric percentage of steel fibers. Specimens were exposed to ambient temperature (25°C), 300°C, and 600°C. Results indicated that increasing the temperature to 300°C led to a relative improvement in compressive and tensile strength. However, at 600°C, a significant degradation in mechanical properties was observed. At 300°C, compressive and tensile strength increased by 12% and 8%, respectively. Conversely, at 600°C, compressive strength decreased by 45%, elastic modulus by 50%, and ultrasonic pulse velocity by 35%. Specimens with 1% steel fibers exhibited optimal performance at 300°C. These findings underscore the necessity of optimizing concrete mixtures with heat-resistant fibers to enhance durability under high-temperature conditions. The achievements of this research not only enhance structural fire safety but are also considered a significant step towards sustainable development by promoting the replacement of conventional dense materials with lightweight concrete.Nowadays, the growth of building construction and the need of lighter but more performance materials are of interest. Adding to, fire incidents highlight the insufficient knowledge of the post fire material properties. Concrete should maintained to resist more and lost less mechanical properties when subjected to high temperatures. Hence, this study investigates the effects of elevated temperatures on the mechanical properties of lightweight concrete containing different volumetric percentage of steel fibers. Specimens were exposed to ambient temperature (25°C), 300°C, and 600°C. Results indicated that increasing the temperature to 300°C led to a relative improvement in compressive and tensile strength. However, at 600°C, a significant degradation in mechanical properties was observed. At 300°C, compressive and tensile strength increased by 12% and 8%, respectively. Conversely, at 600°C, compressive strength decreased by 45%, elastic modulus by 50%, and ultrasonic pulse velocity by 35%. Specimens with 1% steel fibers exhibited optimal performance at 300°C. These findings underscore the necessity of optimizing concrete mixtures with heat-resistant fibers to enhance durability under high-temperature conditions. The achievements of this research not only enhance structural fire safety but are also considered a significant step towards sustainable development by promoting the replacement of conventional dense materials with lightweight concrete.https://cer.qom.ac.ir/article_3592_5a93d11269c1eb8aff5b9c27edf9b254.pdfUniversity of QomCivil Infrastructure Researches2783-140X11220251222Seismic Vibration Control of the Special Truss Moment Frame (STMF) Using Buckling Restrained Braces and Tuned Mass DampersSeismic Vibration Control of the Special Truss Moment Frame (STMF) Using Buckling Restrained Braces and Tuned Mass Dampers1730368610.22091/cer.2025.12392.1603FASasanMostaghimi TehraniSchool of Civil Engineering, Iran University of Science and Technology, Tehran, Iran.0009-0006-9084-9519MortezaRaissi DehkordiSchool of Civil Engineering, Iran University of Science and Technology, Tehran, Iran.0000-0003-2364-1268ElhamRajabiQualitative and Quantitative Analysis of Fluids and Environmental Research Group, Department of Civil Engineer-ing, Tafresh University, Tafresh, Iran.0000-0003-1384-1792Journal Article20250216Vibration control of structures includes passive, semi-active, active and hybrid control. Tuned mass dampers (TMDs) as one of the most effective methods for passive control of structures are in the focus of researches in recent years. In this paper, 10-story special truss moment frame (STMF), in the state without buckling restrained braces (BRBs), with the presence of BRBs, as well as the addition of TMDs on the structure equipped with BRBs, has been investigated under different earthquakes, regardless of the effect of the site. In this regard, TMDs with a mass ratio of 2% of the mass of the structure have been installed at six points on the roof of the structure. The results suggest the appropriate performance of TMDs and BRBs together. The amount of improvement in the results compared to the case without BRBs in structure is 27.95%. The effect of adding TMDs in reducing the vibrations of the structure is almost the same as the case with BRBs.Vibration control of structures includes passive, semi-active, active and hybrid control. Tuned mass dampers (TMDs) as one of the most effective methods for passive control of structures are in the focus of researches in recent years. In this paper, 10-story special truss moment frame (STMF), in the state without buckling restrained braces (BRBs), with the presence of BRBs, as well as the addition of TMDs on the structure equipped with BRBs, has been investigated under different earthquakes, regardless of the effect of the site. In this regard, TMDs with a mass ratio of 2% of the mass of the structure have been installed at six points on the roof of the structure. The results suggest the appropriate performance of TMDs and BRBs together. The amount of improvement in the results compared to the case without BRBs in structure is 27.95%. The effect of adding TMDs in reducing the vibrations of the structure is almost the same as the case with BRBs.https://cer.qom.ac.ir/article_3686_c929c427ba7faea4d8886500aa206a9c.pdfUniversity of QomCivil Infrastructure Researches2783-140X11220251222Noncoaxial Response of Sands Influenced by Grain Shape and Anisotropy: Insights from Hollow Cylinder TestingNoncoaxial Response of Sands Influenced by Grain Shape and Anisotropy: Insights from Hollow Cylinder Testing3145368710.22091/cer.2025.13107.1628FASalarHafezanPh.D. Student, Department of Civil Engineering, Faculty of Engineering, Urmia University, Urmia, Iran.0000-0001-9932-3907HadiBahadoriProfessor, Department of Civil Engineering, Faculty of Engineering, Urmia University, Urmia, Iran.0000-0002-2735-2626Journal Article20250603A comprehensive understanding of the noncoaxial behavior of sands, particularly under complex loading conditions, is critical for the safe and efficient design of geotechnical structures. Noncoaxiality refers to the deviation between the orientations of the principal stress and the principal plastic strain rate vectors during plastic deformation. This study investigates the influence of particle morphology, specifically shape and sphericity, on the noncoaxial response of granular soils. A series of hollow torsional cylinder tests were conducted on sands with distinct particle characteristics, including Hamedan, Chamkhale, Firoozkooh, Leighton Buzzard, and Ottawa sands. The specimens were subjected to monotonic loading paths under varying principal stress rotation angles of 15°, 30°, and 60° to evaluate the effect of stress directionality on their deformation behavior. The results reveal that both principal stress orientation and particle sphericity significantly affect the degree of noncoaxiality. Furthermore, a comparative analysis was performed to quantify the relative impact of these factors, providing valuable insights into the micromechanical origins of noncoaxial deformation in sands. These findings contribute to enhancing predictive models for soil behavior under multidirectional shear loading conditions.A comprehensive understanding of the noncoaxial behavior of sands, particularly under complex loading conditions, is critical for the safe and efficient design of geotechnical structures. Noncoaxiality refers to the deviation between the orientations of the principal stress and the principal plastic strain rate vectors during plastic deformation. This study investigates the influence of particle morphology, specifically shape and sphericity, on the noncoaxial response of granular soils. A series of hollow torsional cylinder tests were conducted on sands with distinct particle characteristics, including Hamedan, Chamkhale, Firoozkooh, Leighton Buzzard, and Ottawa sands. The specimens were subjected to monotonic loading paths under varying principal stress rotation angles of 15°, 30°, and 60° to evaluate the effect of stress directionality on their deformation behavior. The results reveal that both principal stress orientation and particle sphericity significantly affect the degree of noncoaxiality. Furthermore, a comparative analysis was performed to quantify the relative impact of these factors, providing valuable insights into the micromechanical origins of noncoaxial deformation in sands. These findings contribute to enhancing predictive models for soil behavior under multidirectional shear loading conditions.https://cer.qom.ac.ir/article_3687_aa1157e12209e2a0f19f5310f51c07fc.pdfUniversity of QomCivil Infrastructure Researches2783-140X11220251222Investigating the Cyclic and Post-Cyclic Behavior of Marl Soil Contaminated with Used Motor OilInvestigating the Cyclic and Post-Cyclic Behavior of Marl Soil Contaminated with Used Motor Oil4765370210.22091/cer.2025.11950.1589FAAlirezaDashtiDepartment of Civil Engineering, Faculty of Engineering, University of Qom, Qom, Iran0000-0001-6092-8802MahdiKhodaparastDepartment of Civil Engineering, Faculty of Engineering, University of Qom, Qom, Iran0000-0002-4007-4093MajidYazdandoustDepartment of Civil Engineering, Faculty of Engineering, University of Qom, Qom, Iran0000-0003-4355-118XJournal Article20250106Soil contamination has been on the rise with the increasing demand for oil and its derivatives, leading to both environmental hazards and potential impacts on the geotechnical behavior of soils. Leakage of pollutants such as used motor oil into roadbeds and subgrade layers is considered a major challenge. Fine-grained cohesive soils, such as marl, are particularly more sensitive to moisture and hydrocarbon pollutants compared to other soil types. Despite numerous studies on the monotonic behavior of marl soils, less attention has been given to their cyclic and post-cyclic behavior. This study has evaluated the effect of used motor oil contamination on the cyclic and post-cyclic behavior of marl soil using a simple shear device. Marl soil samples were mixed with 0, 4, 8, 12, and 16% by weight of used motor oil and subjected to testing. The results indicated that an increase in the percentage of used motor oil up to 16% led to a 27% reduction in shear strength. Moreover, this contaminant reduced soil cohesion and internal friction angle by up to 47 and 6% before cyclic loading, and by 29% and 14% after it, respectively. However, the shear strength and cohesion improved after cyclic loading. Under cyclic loading, an increase in the oil content resulted in higher damping ratios and lower shear modulus values. Additionally, increasing the vertical stress led to an increase in shear modulus and a decrease in damping ratio. An increase in strain amplitude after 20 cycles led to a maximum of 89% increase in damping ratio, observed in the samples containing 16% oil under a vertical stress of 150 kPa. SEM analysis of the contaminated samples revealed reduced porosity and increased sample cohesion after cyclic loading compared to pre-loading conditions.Soil contamination has been on the rise with the increasing demand for oil and its derivatives, leading to both environmental hazards and potential impacts on the geotechnical behavior of soils. Leakage of pollutants such as used motor oil into roadbeds and subgrade layers is considered a major challenge. Fine-grained cohesive soils, such as marl, are particularly more sensitive to moisture and hydrocarbon pollutants compared to other soil types. Despite numerous studies on the monotonic behavior of marl soils, less attention has been given to their cyclic and post-cyclic behavior. This study has evaluated the effect of used motor oil contamination on the cyclic and post-cyclic behavior of marl soil using a simple shear device. Marl soil samples were mixed with 0, 4, 8, 12, and 16% by weight of used motor oil and subjected to testing. The results indicated that an increase in the percentage of used motor oil up to 16% led to a 27% reduction in shear strength. Moreover, this contaminant reduced soil cohesion and internal friction angle by up to 47 and 6% before cyclic loading, and by 29% and 14% after it, respectively. However, the shear strength and cohesion improved after cyclic loading. Under cyclic loading, an increase in the oil content resulted in higher damping ratios and lower shear modulus values. Additionally, increasing the vertical stress led to an increase in shear modulus and a decrease in damping ratio. An increase in strain amplitude after 20 cycles led to a maximum of 89% increase in damping ratio, observed in the samples containing 16% oil under a vertical stress of 150 kPa. SEM analysis of the contaminated samples revealed reduced porosity and increased sample cohesion after cyclic loading compared to pre-loading conditions.https://cer.qom.ac.ir/article_3702_06fbfb98d8cec568b3a9fb121c2c96e9.pdfUniversity of QomCivil Infrastructure Researches2783-140X11220251222Optimal Design of Space Structures Considering Connection Stiffness Using a Machine Learning Based Surrogate ModelOptimal Design of Space Structures Considering Connection Stiffness Using a Machine Learning Based Surrogate Model6782369510.22091/cer.2025.13271.1635FAMajidIlchi GhazaanSchool of Civil Engineering, Iran University of Science and Technology, Tehran, Iran0000-0001-6689-9301MostafaSharifiSchool of Civil Engineering, Iran University of Science and Technology, Tehran, Iran.0009-0003-8992-4321SevimRahimbaksh KhiabaniSchool of Civil Engineering, Iran University of Science and Technology, Tehran, Iran.0009-0000-4252-9234Journal Article20250702In this research, the optimal design of space structures considering the actual stiffness of connections is performed using a surrogate model based on a machine learning algorithm. Space structures, as one of the most important types of lightweight and robust structural systems, often have semi-rigid connections whose behavior is conventionally idealized as either rigid or pinned. This unrealistic assumption can lead to an increase in structural weight or construction costs. Therefore, incorporating the actual stiffness of connections into the optimal design process can result in reduced overall structural weight and improved efficiency. Since accurately calculating the total structural weight including the weight and costs associated with connections, which account for approximately 15 to 45 percent of the total weight is essential, connection weight has also been included in the objective function. To reduce computational costs, a surrogate model based on a machine learning algorithm is employed. Moreover, to enhance the accuracy and efficiency of the surrogate model, an active learning method is used for the intelligent selection of training data. The results indicate that the proposed method is capable of finding optimal solutions with fewer analyses compared to metaheuristic algorithms. According to the results, 800-member and 1016-member space structures with semi-rigid connections have 4.25% and 14.48% less weight, respectively, compared to structures with pinned and rigid connections.In this research, the optimal design of space structures considering the actual stiffness of connections is performed using a surrogate model based on a machine learning algorithm. Space structures, as one of the most important types of lightweight and robust structural systems, often have semi-rigid connections whose behavior is conventionally idealized as either rigid or pinned. This unrealistic assumption can lead to an increase in structural weight or construction costs. Therefore, incorporating the actual stiffness of connections into the optimal design process can result in reduced overall structural weight and improved efficiency. Since accurately calculating the total structural weight including the weight and costs associated with connections, which account for approximately 15 to 45 percent of the total weight is essential, connection weight has also been included in the objective function. To reduce computational costs, a surrogate model based on a machine learning algorithm is employed. Moreover, to enhance the accuracy and efficiency of the surrogate model, an active learning method is used for the intelligent selection of training data. The results indicate that the proposed method is capable of finding optimal solutions with fewer analyses compared to metaheuristic algorithms. According to the results, 800-member and 1016-member space structures with semi-rigid connections have 4.25% and 14.48% less weight, respectively, compared to structures with pinned and rigid connections.https://cer.qom.ac.ir/article_3695_536cdaf2e07c43f71f27fee68ce0c213.pdfUniversity of QomCivil Infrastructure Researches2783-140X11220251222Investigating the Effect of Different Sediment Thicknesses on the Seismic Behavior of the Javeh Concrete Roller Dam at Different Reservoir Elevation LevelsInvestigating the Effect of Different Sediment Thicknesses on the Seismic Behavior of the Javeh Concrete Roller Dam at Different Reservoir Elevation Levels8396369610.22091/cer.2025.13136.1629FAMajidPasbani KhiaviProfessor, Faculty of Engineering, University of Mohaghegh Ardabili, Ardabil, Iran.0000-0002-8233-0155EhsanTeymouriPh.D. Graduated, Faculty of Engineering, University of Zanajn, Zanjan, Iran.AmirmohammadIrannejadMsc. Student, Faculty of Engineering, University of Mohaghegh Ardabili, Ardabil, Iran.Journal Article20250604Concrete dams are critical infrastructures, and their seismic safety assessment is of great importance. Among various influencing factors, the presence of sediment in dam reservoirs can significantly affect the seismic response of these structures. This study aims to investigate the impact of sediment on the dynamic behavior of concrete roller-compacted dams, using the Javeh Dam as a case study. Finite element analysis was performed using ANSYS software, with sediment layers ranging from 2 to 20 meters and reservoir levels set at 50%, 70%, and 100%. Key parameters evaluated include maximum horizontal displacement and the first and third principal stresses at the heel and toe of the dam. The results indicate that sediment thickness and water level can either increase or decrease stress and displacement depending on the specific conditions. At 50% and 70% reservoir levels, sediment presence had minimal influence on structural response. However, under full reservoir conditions, sediment thicknesses up to 7 meters increased stress and displacement values. Beyond 7 meters, these values began to decrease. Specifically, for sediment thicknesses of 2, 5, and 7 meters under full reservoir conditions, the first principal stress at the dam heel increased by 19.06%, 14.65%, and 5.20%, respectively, compared to the no-sediment case. These findings emphasize the importance of accounting for actual sediment conditions in seismic analysis and design of concrete dams to ensure structural integrity and safety.Concrete dams are critical infrastructures, and their seismic safety assessment is of great importance. Among various influencing factors, the presence of sediment in dam reservoirs can significantly affect the seismic response of these structures. This study aims to investigate the impact of sediment on the dynamic behavior of concrete roller-compacted dams, using the Javeh Dam as a case study. Finite element analysis was performed using ANSYS software, with sediment layers ranging from 2 to 20 meters and reservoir levels set at 50%, 70%, and 100%. Key parameters evaluated include maximum horizontal displacement and the first and third principal stresses at the heel and toe of the dam. The results indicate that sediment thickness and water level can either increase or decrease stress and displacement depending on the specific conditions. At 50% and 70% reservoir levels, sediment presence had minimal influence on structural response. However, under full reservoir conditions, sediment thicknesses up to 7 meters increased stress and displacement values. Beyond 7 meters, these values began to decrease. Specifically, for sediment thicknesses of 2, 5, and 7 meters under full reservoir conditions, the first principal stress at the dam heel increased by 19.06%, 14.65%, and 5.20%, respectively, compared to the no-sediment case. These findings emphasize the importance of accounting for actual sediment conditions in seismic analysis and design of concrete dams to ensure structural integrity and safety.https://cer.qom.ac.ir/article_3696_c27397fbb58cd518b6e714ad631865bc.pdfUniversity of QomCivil Infrastructure Researches2783-140X11220251222Damage Identification in Moment Frames Using Mode Shape Parameters and IMRFO AlgorithmDamage Identification in Moment Frames Using Mode Shape Parameters and IMRFO Algorithm97116372710.22091/cer.2025.13741.1648FASoheilSabzevariPh.D Candidate of Structural Engineering of Semnan University, Semnan, Iran.0000-0002-8972-0711HoseinNaderpourProfessor, Faculty of Civil Engineering of Semnan University, Semnan, Iran0000-0002-4179-7816MajidGholhakiProfessor, Faculty of Civil Engineering of Semnan University, Semnan, Iran0000-0002-9904-8623Journal Article20250610This study presents a novel finite element model updating approach for accurate damage identification in moment-resisting frames. The proposed objective function, which integrates mode shape parameters with natural frequencies, demonstrates high sensitivity in detecting both the location and severity of structural damage. To solve the associated optimization problem, an Improved Manta Ray Foraging Optimization (IMRFO) algorithm is employed, enhanced with a Tent chaotic map, bidirectional search strategy, and Lévy flight to address the limitations of the standard MRFO, such as low convergence accuracy and susceptibility to local optima. The Tent map ensures a uniform distribution of initial solutions, the bidirectional search broadens the exploration space, and Lévy flight enables escape from local optima. IMRFO achieves high accuracy and robustness in optimizing the objective function across multiple damage scenarios and noise levels, with an average error below 2% over 20 independent runs, outperforming other algorithms. This framework, combining the mode shape-based objective function with IMRFO, offers a precise, robust, and computationally efficient solution for structural health monitoring.This study presents a novel finite element model updating approach for accurate damage identification in moment-resisting frames. The proposed objective function, which integrates mode shape parameters with natural frequencies, demonstrates high sensitivity in detecting both the location and severity of structural damage. To solve the associated optimization problem, an Improved Manta Ray Foraging Optimization (IMRFO) algorithm is employed, enhanced with a Tent chaotic map, bidirectional search strategy, and Lévy flight to address the limitations of the standard MRFO, such as low convergence accuracy and susceptibility to local optima. The Tent map ensures a uniform distribution of initial solutions, the bidirectional search broadens the exploration space, and Lévy flight enables escape from local optima. IMRFO achieves high accuracy and robustness in optimizing the objective function across multiple damage scenarios and noise levels, with an average error below 2% over 20 independent runs, outperforming other algorithms. This framework, combining the mode shape-based objective function with IMRFO, offers a precise, robust, and computationally efficient solution for structural health monitoring.https://cer.qom.ac.ir/article_3727_237d737afb1d52d561ff98914d52df70.pdfUniversity of QomCivil Infrastructure Researches2783-140X11220251222Predicting Compressive Behavior of Inorganic Matrix Composite Confined Columns Using Empirical and Machine Learning MethodsPredicting Compressive Behavior of Inorganic Matrix Composite Confined Columns Using Empirical and Machine Learning Methods117140379210.22091/cer.2025.13648.1646FAAtefehSoleymaniDepartment of Civil Engineering, University of Birjand, Birjand, Iran0000-0003-0277-1055Ali MohammadMohammadiCivil Engineering Department, University of Birjand, Birjand, Iran.0009-0006-7663-9013HashemJahangirDepartment of Civil Engineering, Research Group of Novel Technologies in Civil Engineering, University of Bir-jand, Birjand, Iran0000-0003-3099-4045Journal Article20250815Inorganic matrix composites are considered an advanced method for structural retrofitting due to their low weight, high strength, rapid installation, and environmental compatibility. This study evaluates the confinement behavior of circular concrete columns wrapped with inorganic matrix composites. A database of 92 experimental specimens was compiled, considering key input parameters: column diameter, number of confinement layers, fiber elastic modulus, fiber thickness, ultimate strain, and unconfined compressive strength. Existing empirical models were found inadequate for accurately predicting strength enhancement. Consequently, an artificial neural network (ANN) with nine hidden neurons was developed, achieving high prediction accuracy (R=0.9952 and 0.9990; MSE=0.000187 and 0.0000069; MAPE=1.6871% and 0.6795% for training and testing, respectively). Among previous models, Triantafillou et al.’s formula showed the best performance. Sensitivity analysis quantitatively indicated that unconfined compressive strength (fco) has the greatest influence on strength enhancement (92.20%), while the number of confinement layers has the least influence (5.81%). The proposed ANN model provides a reliable tool for accurate prediction and practical design of inorganic matrix composites -confined concrete columns.Inorganic matrix composites are considered an advanced method for structural retrofitting due to their low weight, high strength, rapid installation, and environmental compatibility. This study evaluates the confinement behavior of circular concrete columns wrapped with inorganic matrix composites. A database of 92 experimental specimens was compiled, considering key input parameters: column diameter, number of confinement layers, fiber elastic modulus, fiber thickness, ultimate strain, and unconfined compressive strength. Existing empirical models were found inadequate for accurately predicting strength enhancement. Consequently, an artificial neural network (ANN) with nine hidden neurons was developed, achieving high prediction accuracy (R=0.9952 and 0.9990; MSE=0.000187 and 0.0000069; MAPE=1.6871% and 0.6795% for training and testing, respectively). Among previous models, Triantafillou et al.’s formula showed the best performance. Sensitivity analysis quantitatively indicated that unconfined compressive strength (fco) has the greatest influence on strength enhancement (92.20%), while the number of confinement layers has the least influence (5.81%). The proposed ANN model provides a reliable tool for accurate prediction and practical design of inorganic matrix composites -confined concrete columns.https://cer.qom.ac.ir/article_3792_6b74b6ad910849030320814965ab4e51.pdfUniversity of QomCivil Infrastructure Researches2783-140X11220251222Enhancing the Flexural Characteristics of Stabilized Kaolinite Clay by Reinforcing with Composite FiberEnhancing the Flexural Characteristics of Stabilized Kaolinite Clay by Reinforcing with Composite Fiber141157385210.22091/cer.2025.13895.1652FAMahmood RezaAbdiFaculty of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran.0000-0002-3473-9677ElhamAbbasiFaculty of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran.0009-0007-2549-9679MahdiSafdari Seh GonbadFaculty of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran.0000-0003-0612-535XJournal Article20250916In this research, a new type of fiber known as composite fibers has been utilized to enhance the flexural properties of stabilized clay. The core of the composite fiber consists of elastane, while its shell is composed of numerous polyester fibers. In this regard, kaolinite clay, lime at weight contents of 1, 3, and 5%, and composite fibers at weight contents of 1.5, 2.5, and 3.5%, with lengths of 6 and 12 mm, have been employed for sample preparation, along with curing periods of 7 and 28 days. For quantitative and qualitative investigations, three-point bending tests, as well as optical and scanning electron microscopy, have been employed. The results indicated that the reinforcement of stabilized kaolinite with composite fibers led to improvements of 10 to 78% in flexural strength and a factor 3.1 to 41.5 in the corresponding strain. The findings also demonstrated that the performance of composite fibers in enhancing the strength and ductility of stabilized kaolinite is directly related to the content and length of the fibers, the lime content, and the curing time. Furthermore, quantitative evaluations revealed that the dual structure of the composite fibers, particularly the polyester shell wrapped around the elastane core, created suitable mechanical interaction with the soil due to their high number and perpendicular orientation to the tensile direction, effectively strengthening resistance against pull-out forces.In this research, a new type of fiber known as composite fibers has been utilized to enhance the flexural properties of stabilized clay. The core of the composite fiber consists of elastane, while its shell is composed of numerous polyester fibers. In this regard, kaolinite clay, lime at weight contents of 1, 3, and 5%, and composite fibers at weight contents of 1.5, 2.5, and 3.5%, with lengths of 6 and 12 mm, have been employed for sample preparation, along with curing periods of 7 and 28 days. For quantitative and qualitative investigations, three-point bending tests, as well as optical and scanning electron microscopy, have been employed. The results indicated that the reinforcement of stabilized kaolinite with composite fibers led to improvements of 10 to 78% in flexural strength and a factor 3.1 to 41.5 in the corresponding strain. The findings also demonstrated that the performance of composite fibers in enhancing the strength and ductility of stabilized kaolinite is directly related to the content and length of the fibers, the lime content, and the curing time. Furthermore, quantitative evaluations revealed that the dual structure of the composite fibers, particularly the polyester shell wrapped around the elastane core, created suitable mechanical interaction with the soil due to their high number and perpendicular orientation to the tensile direction, effectively strengthening resistance against pull-out forces.https://cer.qom.ac.ir/article_3852_b5a00ca39ec4757aea29d0b83deb08f3.pdfUniversity of QomCivil Infrastructure Researches2783-140X11220251222Opposition-Switching Search for Optimal Seismic Control by Tuned Mass Damper Considering Soil-Structure InteractionOpposition-Switching Search for Optimal Seismic Control by Tuned Mass Damper Considering Soil-Structure Interaction159170396710.22091/cer.2025.13052.1630FAMohsenShahrouziCivil Engineering Department, Faculty of Engineering, Kharazmi University, Karaj, Iran0000-0003-3531-1979Seyed HosseinHosseini LavasaniCivil Engineering Department, Faculty of Engineering, Kharazmi University, Karaj, Iran0000-0002-9524-9399JavadGholizadehMSc Student, Faculty of Engineering, Kharazmi University, Karaj, Iran0009-0007-5469-3075Journal Article20250608In this study, the optimal design of a tuned mass damper (TMD) considering soil–structure interaction (SSI) is investigated. To this end, the objective function is formulated based on minimizing the H∞ norm of the roof-displacement transfer function in the frequency domain. The TMD parameters are optimized utilizing Opposition-Switching Search (OSS). It is a powerful metaheuristic algorithm that applies opposition-based learning in its particular steps to effectively seek the design space for global optimum. After obtaining the optimal parameters, seismic performance of the controlled structure is evaluated both in the frequency domain and under a set of far-field and near-field earthquake records in the time domain. Consequently, significant reduction in the seismic responses of structure was observed in each case due to the proposed control by the optimized TMD. Furthermore, the controlled system exhibits better performance under far-field ground motions. In addition, comparison between the rigid, stiff, and soft soil conditions shows that soil flexibility has a remarkable influence on both the optimal parameters and the performance of the TMD. These findings highlight the importance of simultaneous consideration of SSI effects and optimal TMD design in achieving efficient seismic control. In this study, the optimal design of a tuned mass damper (TMD) considering soil–structure interaction (SSI) is investigated. To this end, the objective function is formulated based on minimizing the H∞ norm of the roof-displacement transfer function in the frequency domain. The TMD parameters are optimized utilizing Opposition-Switching Search (OSS). It is a powerful metaheuristic algorithm that applies opposition-based learning in its particular steps to effectively seek the design space for global optimum. After obtaining the optimal parameters, seismic performance of the controlled structure is evaluated both in the frequency domain and under a set of far-field and near-field earthquake records in the time domain. Consequently, significant reduction in the seismic responses of structure was observed in each case due to the proposed control by the optimized TMD. Furthermore, the controlled system exhibits better performance under far-field ground motions. In addition, comparison between the rigid, stiff, and soft soil conditions shows that soil flexibility has a remarkable influence on both the optimal parameters and the performance of the TMD. These findings highlight the importance of simultaneous consideration of SSI effects and optimal TMD design in achieving efficient seismic control. https://cer.qom.ac.ir/article_3967_80d0d7bd958b1a9d32148626c46f170c.pdfUniversity of QomCivil Infrastructure Researches2783-140X11220251222Numerical Evaluation of the Seismic Performance of a Concrete Staircase Isolated with Compression StrutsNumerical Evaluation of the Seismic Performance of a Concrete Staircase Isolated with Compression Struts171183396910.22091/cer.2025.13975.1655FAMohammadChavoshiDepartment of Civil Engineering, Faculty of Engineering, University of Qom, Qom, Iran0009-0002-7204-2763EhsanDehghaniDepartment of Civil Engineering, Faculty of Engineering, University of Qom, Qom, Iran0000-0002-7030-5948ShakibaKamaliDepartment of Civil Engineering, Faculty of Engineering, University of Qom, Qom, Iran0009-0000-9905-2414Journal Article20250928The reinforced concrete stair system, as a critical component of a safe egress path in buildings, has shown considerable vulnerability during past earthquakes. Despite the widespread use of seismic separation techniques, their effectiveness requires careful evaluation. The objective of this study is to numerically assess the performance and failure mechanisms of a commonly used separation method—namely, the use of compression struts in reinforced concrete moment-resisting frames. To this end, four finite element models were developed: a bare frame (baseline), a fully connected stair–frame system, and two separated configurations using compression struts (one with a continuous flight and another with the flights separated at the mid-landing). These models were subjected to nonlinear static analysis in ABAQUS. The results indicate that the commonly used configuration with continuous flights is ineffective in reducing stiffness and seismic interaction with the main structure. This model exhibits similar behavior to the fully connected stair system, with plastic hinges forming in the stair flights. In contrast, separating the flights at the mid-landing eliminates damage in the flights but concentrates it within the compression struts, which may still compromise the safety of the egress path. This study highlights the inherent limitations of the compression-strut separation method and emphasizes the necessity of complete flight separation at the mid-landing as a design requirement.The reinforced concrete stair system, as a critical component of a safe egress path in buildings, has shown considerable vulnerability during past earthquakes. Despite the widespread use of seismic separation techniques, their effectiveness requires careful evaluation. The objective of this study is to numerically assess the performance and failure mechanisms of a commonly used separation method—namely, the use of compression struts in reinforced concrete moment-resisting frames. To this end, four finite element models were developed: a bare frame (baseline), a fully connected stair–frame system, and two separated configurations using compression struts (one with a continuous flight and another with the flights separated at the mid-landing). These models were subjected to nonlinear static analysis in ABAQUS. The results indicate that the commonly used configuration with continuous flights is ineffective in reducing stiffness and seismic interaction with the main structure. This model exhibits similar behavior to the fully connected stair system, with plastic hinges forming in the stair flights. In contrast, separating the flights at the mid-landing eliminates damage in the flights but concentrates it within the compression struts, which may still compromise the safety of the egress path. This study highlights the inherent limitations of the compression-strut separation method and emphasizes the necessity of complete flight separation at the mid-landing as a design requirement.https://cer.qom.ac.ir/article_3969_941141ffcdb9ca1b2662f6b1d839271a.pdfUniversity of QomCivil Infrastructure Researches2783-140X11220251222Mechanical Behavior of a Cylindrical Chlorobutyl-Based Viscoelastic Damper: An Experimental StudyMechanical Behavior of a Cylindrical Chlorobutyl-Based Viscoelastic Damper: An Experimental Study185200397010.22091/cer.2025.13211.1632FASanamAnsarighadimDepartment of Civil Engineering, Faculty of Engineering, University of Urmia, Urmia, Iran0009-0000-8119-4975AlirezaManafpourAssistant Professor, Department of Civil Engineering, Faculty of Engineering, University of Urmia, Urmia, Iran.0000-0002-9274-5813Journal Article20250618In recent decades, viscoelastic dampers have attracted the attention of many researchers due to their reasonable cost, ease of construction, and high energy dissipation capacity. The mechanical characteristics of these dampers are directly influenced by the properties of the polymeric materials used in their fabrication. Such materials are sensitive to displacement amplitude, loading frequency, temperature, and geometry, making the process of finding a suitable viscoelastic composition for damper design both complex and time-consuming. In this study, small-scale planar dampers were first constructed to compare two polymeric compositions: one based on natural rubber and the other on chlorobutyl rubber. The results of cyclic loading tests showed that the viscoelastic damper made with chlorobutyl polymer exhibited significantly better damping performance than the one made with natural rubber. Based on these findings, full scale cylindrical dampers were fabricated using the chlorobutyl based composition and tested under cyclic loading with a hydraulic jack. The goal was to investigate the effects of loading rate, thickness of the viscoelastic layer, and applied strain. The results indicated that increasing the loading rate and strain led to greater energy dissipation and load bearing capacity. Additionally, while reducing the viscoelastic layer thickness had little impact on damping, it did enhance the load bearing capacity.In recent decades, viscoelastic dampers have attracted the attention of many researchers due to their reasonable cost, ease of construction, and high energy dissipation capacity. The mechanical characteristics of these dampers are directly influenced by the properties of the polymeric materials used in their fabrication. Such materials are sensitive to displacement amplitude, loading frequency, temperature, and geometry, making the process of finding a suitable viscoelastic composition for damper design both complex and time-consuming. In this study, small-scale planar dampers were first constructed to compare two polymeric compositions: one based on natural rubber and the other on chlorobutyl rubber. The results of cyclic loading tests showed that the viscoelastic damper made with chlorobutyl polymer exhibited significantly better damping performance than the one made with natural rubber. Based on these findings, full scale cylindrical dampers were fabricated using the chlorobutyl based composition and tested under cyclic loading with a hydraulic jack. The goal was to investigate the effects of loading rate, thickness of the viscoelastic layer, and applied strain. The results indicated that increasing the loading rate and strain led to greater energy dissipation and load bearing capacity. Additionally, while reducing the viscoelastic layer thickness had little impact on damping, it did enhance the load bearing capacity.https://cer.qom.ac.ir/article_3970_9bdac3ae9ef215bad6ada240c924ef31.pdf