Tarbiat Modares University Modares Civil Engineering journal 2476-6763 26 3 2026 08 23 Examination of soil-foundation-structure system response and determination of the optimal target frequency in a substructure method considering soil inhomogeneity with depth Examination of soil-foundation-structure system response and determination of the optimal target frequency in a substructure method considering soil inhomogeneity with depth 7 23 12717 10.48311/mcej.2026.12717 FA Mohammad Shamsi Assistant Professor, Department of Civil Engineering, University of Hormozgan Journal Article 2025 07 13 Despite the particular importance of the subject of soil-structure interaction, unfortunately, this issue has received little attention from engineers, and seismic codes have not given much recommendation to consider its effects. Seismic wave frequencies vary continuously, and the stiffness of springs and damping of dampers connected to structural supports also vary with the loading frequency. To simplify time-domain numerical analysis, a constant target frequency can be used to keep stiffness and damping values constant. In the substructure method proposed in this study, the optimal target frequency is the one that yields results that most closely match those of a more accurate nonlinear 3D model analyzed using a direct method. A common simplification is to ignore the foundation’s non-linear response, justified by design requirements to prevent permanent deformation and the complexity of frequency-dependent soil behavior. Though not fully precise, this approach (considering soil heterogeneity and optimal target frequency) offers a forward-looking analysis and a basis for future nonlinear studies. This study presents a three-dimensional (3D) numerical model for analyzing the seismic response of soil-foundation-structure systems embedded in granular soil (with different relative densities) considering the effects of soil heterogeneity (With varying shear modulus with depth and compatible with the practical HSsmall model). The model is capable of accounting for the effects of loading frequency along with the radiation damping of the soil system and can integrate with the widely-used substructuring method considering an optimal target frequency. After verifying the proposed model, the dynamic equilibrium equations of the substructuring system were solved in the time domain using Matlab software. The target frequency was determined using i) Case 1: the fundamental frequency of the soil (or the dominant frequency of the excitations), ii) Case 2: the fundamental frequency of the structural system, iii) Case 3: the fundamental frequency of the soil-foundation-structure system; iv) Case 4: the fundamental frequency of structure with static stiffness and damping support (Case 4); and v) the fundamental frequency of fixed base structure and modified stiffness, and the results were compared together. A comparison of the impedance (dynamic stiffness and damping) of foundations situated on homogeneous and heterogeneous soil, as well as an investigation of the structural response in both cases, is another objective of this research. The analysis results demonstrated the accuracy of the proposed model and the acceptable calculation speed for estimating the dynamic response of structures located on heterogeneous soils under frequent operational earthquakes. The results also showed that with an increase in soil relative density, the seismic behavior of structures on homogeneous and heterogeneous granular soils converges. For instance, the response of the foundation on homogeneous soil bed with relative densities of 55%, 75%, and 95% is on average 23%, 19%, and 15% lower than that of heterogeneous soil, respectively. Additionally, for determining the target frequency, the use of frequency‐independent Kelvin–Voigt models (i.e., Cases 1-5) provides acceptable responses. According to the data presented in Table 4 and Figs. 9 and 10, the following conclusions can be drawn: 1) The soil's fundamental frequency (Case 1) yielded the least precise results. 2) While Case 3 offered the most favorable response, closely matching the direct method, determining the soil-structure system's fundamental frequency through complex integration in numerical software is often impractical. 3) Employing the target frequency in Case 2 produced more satisfactory results than Case 1. 4) Cases 4 and 5 generated nearly identical frequencies. Compared to Case 2, these cases enhanced response accuracy, bringing them closer to the best response (i.e., Case 3). Therefore, for practical applications, it is recommended to utilize the fundamental frequency from either Case 4 or Case 5 instead of the soil-structure system's fundamental frequency (Case 3) to establish the optimal target frequency. Despite the particular importance of the subject of soil-structure interaction, unfortunately, this issue has received little attention from engineers, and seismic codes have not given much recommendation to consider its effects. Seismic wave frequencies vary continuously, and the stiffness of springs and damping of dampers connected to structural supports also vary with the loading frequency. To simplify time-domain numerical analysis, a constant target frequency can be used to keep stiffness and damping values constant. In the substructure method proposed in this study, the optimal target frequency is the one that yields results that most closely match those of a more accurate nonlinear 3D model analyzed using a direct method. A common simplification is to ignore the foundation’s non-linear response, justified by design requirements to prevent permanent deformation and the complexity of frequency-dependent soil behavior. Though not fully precise, this approach (considering soil heterogeneity and optimal target frequency) offers a forward-looking analysis and a basis for future nonlinear studies. This study presents a three-dimensional (3D) numerical model for analyzing the seismic response of soil-foundation-structure systems embedded in granular soil (with different relative densities) considering the effects of soil heterogeneity (With varying shear modulus with depth and compatible with the practical HSsmall model). The model is capable of accounting for the effects of loading frequency along with the radiation damping of the soil system and can integrate with the widely-used substructuring method considering an optimal target frequency. After verifying the proposed model, the dynamic equilibrium equations of the substructuring system were solved in the time domain using Matlab software. The target frequency was determined using i) Case 1: the fundamental frequency of the soil (or the dominant frequency of the excitations), ii) Case 2: the fundamental frequency of the structural system, iii) Case 3: the fundamental frequency of the soil-foundation-structure system; iv) Case 4: the fundamental frequency of structure with static stiffness and damping support (Case 4); and v) the fundamental frequency of fixed base structure and modified stiffness, and the results were compared together. A comparison of the impedance (dynamic stiffness and damping) of foundations situated on homogeneous and heterogeneous soil, as well as an investigation of the structural response in both cases, is another objective of this research. The analysis results demonstrated the accuracy of the proposed model and the acceptable calculation speed for estimating the dynamic response of structures located on heterogeneous soils under frequent operational earthquakes. The results also showed that with an increase in soil relative density, the seismic behavior of structures on homogeneous and heterogeneous granular soils converges. For instance, the response of the foundation on homogeneous soil bed with relative densities of 55%, 75%, and 95% is on average 23%, 19%, and 15% lower than that of heterogeneous soil, respectively. Additionally, for determining the target frequency, the use of frequency‐independent Kelvin–Voigt models (i.e., Cases 1-5) provides acceptable responses. According to the data presented in Table 4 and Figs. 9 and 10, the following conclusions can be drawn: 1) The soil's fundamental frequency (Case 1) yielded the least precise results. 2) While Case 3 offered the most favorable response, closely matching the direct method, determining the soil-structure system's fundamental frequency through complex integration in numerical software is often impractical. 3) Employing the target frequency in Case 2 produced more satisfactory results than Case 1. 4) Cases 4 and 5 generated nearly identical frequencies. Compared to Case 2, these cases enhanced response accuracy, bringing them closer to the best response (i.e., Case 3). Therefore, for practical applications, it is recommended to utilize the fundamental frequency from either Case 4 or Case 5 instead of the soil-structure system's fundamental frequency (Case 3) to establish the optimal target frequency.

https://mcej.modares.ac.ir/article_12717_646e058fac455de8d1e52c4c49baac06.pdf

Tarbiat Modares University Modares Civil Engineering journal 2476-6763 26 3 2026 08 23 Free Vibration Analysis of Composite Plate Using Higher Order Haar Wavelet Free Vibration Analysis of Composite Plate Using Higher Order Haar Wavelet 25 41 28409 10.48311/mcej.2026.99105.0 FA Ali Mirahmadi Chenaruiyeh Department of Civil Engineering, Faculty of Engineering, Shahid Bahonar University Mohammad Javad Fadaee Fathabadi Department of Civil Engineering, Faculty of Engineering, Shahid Bahonar University Hamed Saffari Department of Civil Engineering, Faculty of Engineering, Shahid Bahonar University Journal Article 2024 09 24 In the last few decades, laminated composite plates, due to their high characteristics resistance and hardness, have been used in a variety of designs as structural components. Considering the structural complexities of laminated composite plates, choosing the appropriate method to solve the equation governing the dynamic equilibrium of these plates in order to analysis their vibration behavior has been attracted the attention of many researchers. In the present research, free vibration of a laminated composite plate, has been investigated using numerical solution. In order to model the behavior of the composite plate, the refined Zigzag theory in which the transverse shear stress distribution is allowed through the thickness of the layers and also satisfies the condition of zero shear stress on the top and bottom surfaces of the composite plate without need to use shear correction factor, have been deployed. In this theory, seven independent displacement variables are considered and according to the continuity condition of displacement between layers, the number of variables will be independent of the number of layers. Principal of virtual work and minimization of the potential energy have been used for deriving the partial differential equations of motion. The higher order Haar wavelet method have been developed to replace displacement variables and numerically solve the partial differential equations and calculating eigenvalues. In most of the similar researches, the use of Haar wavelet numerical solution has mostly been discussed on beams, annular plates and shells, and research in the field of the rectangular composite plate has not been observed. In this paper, the numerical solution is modeled in a simple form and the equations governing the rectangular laminate composite plate have been replaced by linear algebraic series and so, the free vibration of laminate composite plate has been investigated. Finally, the accuracy and convergence of solution method in analysis of laminated composite plates are evaluated and the results of the proposed method, earned from programming in the Matlab software, have been compared with the results of other solutions methods that mentioned in this paper. The comparison of these results shows good accuracy compared to other solution methods. Meanwhile, by converting multivariable equations of motion into linear algebraic expressions, the results of the proposed method have been obtained without any particular complexity and with a small number of collection points. Achieving the results by the proposed method with the same accuracy as the Haar solution results using smaller matrix dimensions and so reducing the computational cost is another advantage of this proposed method. It can be used instead of the Haar solution method in the numerical solutions of various solid mechanics’ problems. Examining the convergence of this proposed method shows that this solution has a good ability to approach the exact solution by increasing the resolution and collection points. It was also observed that the dimensionless frequency index increases with the increase in the ratio of longitudinal to transverse modulus regardless of the number of layers. In the last few decades, laminated composite plates, due to their high characteristics resistance and hardness, have been used in a variety of designs as structural components. Considering the structural complexities of laminated composite plates, choosing the appropriate method to solve the equation governing the dynamic equilibrium of these plates in order to analysis their vibration behavior has been attracted the attention of many researchers. In the present research, free vibration of a laminated composite plate, has been investigated using numerical solution. In order to model the behavior of the composite plate, the refined Zigzag theory in which the transverse shear stress distribution is allowed through the thickness of the layers and also satisfies the condition of zero shear stress on the top and bottom surfaces of the composite plate without need to use shear correction factor, have been deployed. In this theory, seven independent displacement variables are considered and according to the continuity condition of displacement between layers, the number of variables will be independent of the number of layers. Principal of virtual work and minimization of the potential energy have been used for deriving the partial differential equations of motion. The higher order Haar wavelet method have been developed to replace displacement variables and numerically solve the partial differential equations and calculating eigenvalues. In most of the similar researches, the use of Haar wavelet numerical solution has mostly been discussed on beams, annular plates and shells, and research in the field of the rectangular composite plate has not been observed. In this paper, the numerical solution is modeled in a simple form and the equations governing the rectangular laminate composite plate have been replaced by linear algebraic series and so, the free vibration of laminate composite plate has been investigated. Finally, the accuracy and convergence of solution method in analysis of laminated composite plates are evaluated and the results of the proposed method, earned from programming in the Matlab software, have been compared with the results of other solutions methods that mentioned in this paper. The comparison of these results shows good accuracy compared to other solution methods. Meanwhile, by converting multivariable equations of motion into linear algebraic expressions, the results of the proposed method have been obtained without any particular complexity and with a small number of collection points. Achieving the results by the proposed method with the same accuracy as the Haar solution results using smaller matrix dimensions and so reducing the computational cost is another advantage of this proposed method. It can be used instead of the Haar solution method in the numerical solutions of various solid mechanics’ problems. Examining the convergence of this proposed method shows that this solution has a good ability to approach the exact solution by increasing the resolution and collection points. It was also observed that the dimensionless frequency index increases with the increase in the ratio of longitudinal to transverse modulus regardless of the number of layers.

https://mcej.modares.ac.ir/article_28409_da03a6389035b1470aa3d49b3ba4360c.pdf

Tarbiat Modares University Modares Civil Engineering journal 2476-6763 26 3 2026 08 23 Numerical Investigation of Removing Horizontal Continuity Plate in Beam to Column Connection in the Box Columns in Moment Resisting Frame Systems (MRFs) Numerical Investigation of Removing Horizontal Continuity Plate in Beam to Column Connection in the Box Columns in Moment Resisting Frame Systems (MRFs) 43 57 27819 10.48311/mcej.2025.99116.0 FA Mohammadreza Rajaiee Master's Graduate from University of Science and Culture Ali Razavi Tabatabaei Faculty Member at University of Science and Culture 0000-0002-8061-6213 Journal Article 2024 11 06 Continuity plates in box columns play a crucial role in transferring loads from beams to columns. According to seismic code requirements, these plates are often connected to the column flange using full penetration groove welds. Full penetration groove welding of continuity plates to columns presents challenges such as incomplete penetration at corners, difficulty in repairing defective welds, the necessity of using the fourth face or electroslag welding, potential delamination in the column plate, and more. These issues can lead to reduced structural efficiency and safety. In this paper, to address the challenges of embedding and installing horizontal continuity plates inside box columns, which in some cases, due to difficult access and specific geometry and layout, make it very challenging to properly and adequately satisfy seismic design criteria, new and strategic connections are proposed using numerical analysis. These analyses were performed using advanced finite element software, and their results were compared with conventional connections. To achieve a suitable load transfer path from the beam to the column in the connection region and to facilitate the assembly and execution of the frame elements in the connection region, the use of internal vertical stiffeners instead of conventional horizontal continuity plates and widening the beam flanges as a suitable solution has been proposed and examined. These solutions not only help improve structural performance but also simplify the construction and installation process. Additionally, to complement this connection approach, the use of external vertical stiffeners on the beam flange in the beam-to-column connection region, along with the use of internal vertical stiffeners instead of horizontal continuity plates in the connection region, has been proposed. Furthermore, the simultaneous use of widened beam flanges, the presence of external vertical stiffeners on the beam flange, and replacing internal vertical stiffeners instead of horizontal continuity plates in the connection region has also been investigated. The investigations were carried out using finite element analysis on the proposed samples. The results obtained from the numerical analysis of the proposed connections indicate adequate performance compared to conventional moment connections. Connections made using widened beam flanges exhibited an 18% higher energy absorption capacity than conventional moment connections up to a maximum displacement of 6% radians, without showing significant strength degradation. This percentage was reported to be 14% and 28% higher than the conventional moment connection for connections using external vertical stiffeners on the beam flange and connections made using the simultaneous presence of widened beam flanges and external vertical stiffeners on the beam flanges, respectively. Moreover, the rupture index of weld was evaluated in different scenarios. The final results indicate that the simultaneous use of widened beam flanges and external vertical stiffeners on the beam flange along the beam web leads to the creation of a suitable load transfer path from the beam to the column in the connection region. Additionally, the mechanism of moving the plastic hinge away from the column face in this idea has been well achieved, reducing the possibility of brittle fracture of the penetration weld at the beam-to-column connection. These findings highlight the potential for improved structural integrity and safety in seismic design. Continuity plates in box columns play a crucial role in transferring loads from beams to columns. According to seismic code requirements, these plates are often connected to the column flange using full penetration groove welds. Full penetration groove welding of continuity plates to columns presents challenges such as incomplete penetration at corners, difficulty in repairing defective welds, the necessity of using the fourth face or electroslag welding, potential delamination in the column plate, and more. These issues can lead to reduced structural efficiency and safety. In this paper, to address the challenges of embedding and installing horizontal continuity plates inside box columns, which in some cases, due to difficult access and specific geometry and layout, make it very challenging to properly and adequately satisfy seismic design criteria, new and strategic connections are proposed using numerical analysis. These analyses were performed using advanced finite element software, and their results were compared with conventional connections. To achieve a suitable load transfer path from the beam to the column in the connection region and to facilitate the assembly and execution of the frame elements in the connection region, the use of internal vertical stiffeners instead of conventional horizontal continuity plates and widening the beam flanges as a suitable solution has been proposed and examined. These solutions not only help improve structural performance but also simplify the construction and installation process. Additionally, to complement this connection approach, the use of external vertical stiffeners on the beam flange in the beam-to-column connection region, along with the use of internal vertical stiffeners instead of horizontal continuity plates in the connection region, has been proposed. Furthermore, the simultaneous use of widened beam flanges, the presence of external vertical stiffeners on the beam flange, and replacing internal vertical stiffeners instead of horizontal continuity plates in the connection region has also been investigated. The investigations were carried out using finite element analysis on the proposed samples. The results obtained from the numerical analysis of the proposed connections indicate adequate performance compared to conventional moment connections. Connections made using widened beam flanges exhibited an 18% higher energy absorption capacity than conventional moment connections up to a maximum displacement of 6% radians, without showing significant strength degradation. This percentage was reported to be 14% and 28% higher than the conventional moment connection for connections using external vertical stiffeners on the beam flange and connections made using the simultaneous presence of widened beam flanges and external vertical stiffeners on the beam flanges, respectively. Moreover, the rupture index of weld was evaluated in different scenarios. The final results indicate that the simultaneous use of widened beam flanges and external vertical stiffeners on the beam flange along the beam web leads to the creation of a suitable load transfer path from the beam to the column in the connection region. Additionally, the mechanism of moving the plastic hinge away from the column face in this idea has been well achieved, reducing the possibility of brittle fracture of the penetration weld at the beam-to-column connection. These findings highlight the potential for improved structural integrity and safety in seismic design.

https://mcej.modares.ac.ir/article_27819_e10bb16c9fc310f560d696ca955e9e03.pdf

Tarbiat Modares University Modares Civil Engineering journal 2476-6763 26 3 2026 08 23 Using Bayesian theory for leak detection in water network systems Using Bayesian theory for leak detection in water network systems 59 68 28410 10.48311/mcej.2026.99140.0 FA Mohammad Ghanbari Vandi PhD student in Hydraulic Structures, Faculty of Civil Engineering, Noshirvani University of Technology, Babol Ali Rahmani Firoozjaee Associate Professor, Department of Structural Engineering, Faculty of Civil Engineering, Noshirvani University of Technology, Babol Alireza Keramat Researcher, School of Civil and Environmental Engineering, Hong Kong University of Science and Technology Amir Zayeri Baghlani Nejad Assistant Professor, Department of Structural Engineering, Faculty of Civil Engineering, Jundi-shapur University of Technology, Dezful Journal Article 2025 02 17 In recent decades, several methods have been developed for leak detection in water supply networks, one of which is the transient wave-based method. The transient wave-based leak detection method offers a growing and promising approach that comes with several challenges. The most important challenges of these methods are model uncertainty and noisy data. Model-based methods do not have high accuracy due to high uncertainties, and data-based methods also do not have high accuracy due to noisy data. This paper presents a method for detecting the leak location for a reservoir pipeline valve system using Bayesian theory. In detecting the pipeline leak location, the noise in the pressure signal collected from the sensors in the pipeline affects the accuracy of detection. In this research, a probability density function for the leak location is obtained by combining the prior probability density function obtained from the model and the data collected by the sensors. Then, the accuracy of the proposed method is investigated by solving a numerical example. In this regard, a pipe with a length of L=3,000m and a diameter of D=0.5m was considered. The Darcy-Weisbach friction factor was set to f=0.03. To initiate a transient wave, an instantaneous complete closure of the valve located at the downstream end of the pipe (x=L) was performed. This closure generated a transient wave with a speed of a=1,200 m/s, which propagated along the length of the pipe. The inlet of the pipe (x=0) was maintained at a constant pressure head of Hin=25 m. To measure the response of the pressure head, a sensor was strategically positioned at the end of the pipe (x*=L=3,000 m). The objective was to observe the pressure variations caused by the transient wave. The time required for the contact discontinuity, generated by the valve closure, to travel from the valve back to the inlet was calculated as τ=L/a=2.5 s. This represented the round-trip travel time of the wave within the pipe. To ensure that the simulations captured the full behavior of the transient wave, the total simulation time was set to T=2τ, thereby covering two complete cycles of the contact discontinuity passing through the sensor. In this numerical study, the effects of data noise, sensor location, and simulation time on the results were carefully investigated. The data collected from the sensors were subject to noise, which could affect the accuracy of leak detection. To investigate the impact of this noise, different scenarios with varying noise levels were simulated and analyzed. In addition, the location of the sensor also influenced the simulation results. Various sensor placements were tested to identify the optimal location for achieving higher accuracy in leak detection. These studies demonstrated that sensor placement could significantly improve the results and increase detection accuracy. Finally, simulation time was examined as a critical factor in the analyses. Different simulation durations were tested to observe their effects on the results and their impact on the accuracy of leak detection. The analyses revealed that selecting the appropriate simulation time could enhance the accuracy and speed of leak detection. The results of the numerical study demonstrated the ability of the method to identify leak locations in a water pipeline network. Overall, this study showed that data noise, sensor location, and simulation time are all factors that can affect the accuracy and quality of leak detection. By effectively managing these factors, the performance of leak detection systems can be improved. This innovative approach not only enhances the accuracy of leak detection but also provides a robust framework for addressing the inherent uncertainties and noise in the data. In recent decades, several methods have been developed for leak detection in water supply networks, one of which is the transient wave-based method. The transient wave-based leak detection method offers a growing and promising approach that comes with several challenges. The most important challenges of these methods are model uncertainty and noisy data. Model-based methods do not have high accuracy due to high uncertainties, and data-based methods also do not have high accuracy due to noisy data. This paper presents a method for detecting the leak location for a reservoir pipeline valve system using Bayesian theory. In detecting the pipeline leak location, the noise in the pressure signal collected from the sensors in the pipeline affects the accuracy of detection. In this research, a probability density function for the leak location is obtained by combining the prior probability density function obtained from the model and the data collected by the sensors. Then, the accuracy of the proposed method is investigated by solving a numerical example. In this regard, a pipe with a length of L=3,000m and a diameter of D=0.5m was considered. The Darcy-Weisbach friction factor was set to f=0.03. To initiate a transient wave, an instantaneous complete closure of the valve located at the downstream end of the pipe (x=L) was performed. This closure generated a transient wave with a speed of a=1,200 m/s, which propagated along the length of the pipe. The inlet of the pipe (x=0) was maintained at a constant pressure head of Hin=25 m. To measure the response of the pressure head, a sensor was strategically positioned at the end of the pipe (x*=L=3,000 m). The objective was to observe the pressure variations caused by the transient wave. The time required for the contact discontinuity, generated by the valve closure, to travel from the valve back to the inlet was calculated as τ=L/a=2.5 s. This represented the round-trip travel time of the wave within the pipe. To ensure that the simulations captured the full behavior of the transient wave, the total simulation time was set to T=2τ, thereby covering two complete cycles of the contact discontinuity passing through the sensor. In this numerical study, the effects of data noise, sensor location, and simulation time on the results were carefully investigated. The data collected from the sensors were subject to noise, which could affect the accuracy of leak detection. To investigate the impact of this noise, different scenarios with varying noise levels were simulated and analyzed. In addition, the location of the sensor also influenced the simulation results. Various sensor placements were tested to identify the optimal location for achieving higher accuracy in leak detection. These studies demonstrated that sensor placement could significantly improve the results and increase detection accuracy. Finally, simulation time was examined as a critical factor in the analyses. Different simulation durations were tested to observe their effects on the results and their impact on the accuracy of leak detection. The analyses revealed that selecting the appropriate simulation time could enhance the accuracy and speed of leak detection. The results of the numerical study demonstrated the ability of the method to identify leak locations in a water pipeline network. Overall, this study showed that data noise, sensor location, and simulation time are all factors that can affect the accuracy and quality of leak detection. By effectively managing these factors, the performance of leak detection systems can be improved. This innovative approach not only enhances the accuracy of leak detection but also provides a robust framework for addressing the inherent uncertainties and noise in the data.

https://mcej.modares.ac.ir/article_28410_3ba2523b7e2781fb751a6a9d79af6ebd.pdf

Tarbiat Modares University Modares Civil Engineering journal 2476-6763 26 3 2026 08 23 Design and Performance Improvement of Metro Feeder Bus Lines Using a Metaheuristic Algorithm: A Case Study of Tehran Metro Line 3 Design and Performance Improvement of Metro Feeder Bus Lines Using a Metaheuristic Algorithm: A Case Study of Tehran Metro Line 3 69 82 28412 10.48311/mcej.2026.99168.0 FA Saeid Sherafatipour Assistant Professor Alireza Taheriyan Master of science 0009-0000-8283-8656 Mahmoud Saffarzadeh Professor Journal Article 2025 05 22 Public transportation plays a critical role in promoting sustainable urban development by offering mobility solutions that are efficient, equitable, and environmentally responsible. It encompasses a wide range of transit modes, which are generally classified into mass transit systems—such as metro and rail services—and non-mass transit systems, including buses, minibuses, and other forms of road-based public transport. As cities expand and mobility demands grow, the complexity of managing and integrating various transport modes also increases. One of the key challenges in the planning and operation of public transport systems lies in ensuring seamless integration between these modes, particularly through the design and optimization of feeder networks that connect local bus services to major mass transit infrastructure. This study focuses on improving the operational efficiency and user attractiveness of Tehran’s public transportation system by enhancing the feeder bus services connected to three specific stations—Abdol Abad, Shahrak-e Shariati, and Zamzam—located on Metro Line 3. The primary objective is to increase metro ridership and improve the overall effectiveness of public transport usage by optimizing the sub-network of feeder lines servicing these metro stations. Improving connectivity and reducing transfer times between feeder and metro systems is considered crucial for encouraging the use of public transit, particularly in densely populated urban areas like Tehran. To achieve this goal, a structured four-step methodology was adopted. Initially, the feeder routes relevant to the three metro stations were identified through data collection and analysis of existing traffic patterns. Subsequently, two improvement strategies were formulated and applied: (1) uniform improvements applied across the entire feeder routes, such as reducing headways and enhancing vehicle availability; and (2) targeted enhancements focused on selected high-demand stops, including limited-stop service and priority routing. These strategies were translated into multiple operational scenarios, which were then simulated using the EMME/2 transportation planning software, a recognized tool for multimodal transport analysis. Each scenario was evaluated based on four key performance metrics: the total number of trips made using public transport, the number of boardings on Metro Line 3, the ratio of public transport trips to the number of vehicles (fleet size), and the ratio of metro boardings to the number of deployed feeder buses. The results reveal that reducing headways on feeder bus routes generally leads to an increase in both public transport trips and metro boardings. However, in some cases, this strategy created unintended competition between feeder buses and the metro, which did not necessarily result in higher metro ridership. Among the various scenarios analyzed, those that implemented limited-stop feeder services showed the highest effectiveness in encouraging multimodal travel behavior and promoting better utilization of both bus and metro systems. Conversely, scenarios that increased the number of feeder buses without allocating dedicated lanes led to greater traffic congestion and reduced overall service quality. From a policy and planning standpoint, this research underscores the importance of clearly defined objectives and appropriately weighted performance indicators in selecting the most effective operational scenarios. The insights provided can support transport planners and decision-makers in enhancing the integration of feeder systems with metro services, ultimately contributing to the overall sustainability and quality of urban public transportation networks. Public transportation plays a critical role in promoting sustainable urban development by offering mobility solutions that are efficient, equitable, and environmentally responsible. It encompasses a wide range of transit modes, which are generally classified into mass transit systems—such as metro and rail services—and non-mass transit systems, including buses, minibuses, and other forms of road-based public transport. As cities expand and mobility demands grow, the complexity of managing and integrating various transport modes also increases. One of the key challenges in the planning and operation of public transport systems lies in ensuring seamless integration between these modes, particularly through the design and optimization of feeder networks that connect local bus services to major mass transit infrastructure. This study focuses on improving the operational efficiency and user attractiveness of Tehran’s public transportation system by enhancing the feeder bus services connected to three specific stations—Abdol Abad, Shahrak-e Shariati, and Zamzam—located on Metro Line 3. The primary objective is to increase metro ridership and improve the overall effectiveness of public transport usage by optimizing the sub-network of feeder lines servicing these metro stations. Improving connectivity and reducing transfer times between feeder and metro systems is considered crucial for encouraging the use of public transit, particularly in densely populated urban areas like Tehran. To achieve this goal, a structured four-step methodology was adopted. Initially, the feeder routes relevant to the three metro stations were identified through data collection and analysis of existing traffic patterns. Subsequently, two improvement strategies were formulated and applied: (1) uniform improvements applied across the entire feeder routes, such as reducing headways and enhancing vehicle availability; and (2) targeted enhancements focused on selected high-demand stops, including limited-stop service and priority routing. These strategies were translated into multiple operational scenarios, which were then simulated using the EMME/2 transportation planning software, a recognized tool for multimodal transport analysis. Each scenario was evaluated based on four key performance metrics: the total number of trips made using public transport, the number of boardings on Metro Line 3, the ratio of public transport trips to the number of vehicles (fleet size), and the ratio of metro boardings to the number of deployed feeder buses. The results reveal that reducing headways on feeder bus routes generally leads to an increase in both public transport trips and metro boardings. However, in some cases, this strategy created unintended competition between feeder buses and the metro, which did not necessarily result in higher metro ridership. Among the various scenarios analyzed, those that implemented limited-stop feeder services showed the highest effectiveness in encouraging multimodal travel behavior and promoting better utilization of both bus and metro systems. Conversely, scenarios that increased the number of feeder buses without allocating dedicated lanes led to greater traffic congestion and reduced overall service quality. From a policy and planning standpoint, this research underscores the importance of clearly defined objectives and appropriately weighted performance indicators in selecting the most effective operational scenarios. The insights provided can support transport planners and decision-makers in enhancing the integration of feeder systems with metro services, ultimately contributing to the overall sustainability and quality of urban public transportation networks.

https://mcej.modares.ac.ir/article_28412_41caf35ddce1e1f80415f7e5a1dc815f.pdf

Tarbiat Modares University Modares Civil Engineering journal 2476-6763 26 3 2026 08 23 Evaluation of the Effect of Aggregate Gradation on the Mechanical Properties and Moisture Susceptibility of Cold Recycled Asphalt Mixtures Evaluation of the Effect of Aggregate Gradation on the Mechanical Properties and Moisture Susceptibility of Cold Recycled Asphalt Mixtures 83 96 28413 10.48311/mcej.2025.117824.82876 FA Abdul Hamid Bezhan Department of Civil and Environmental Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran Pouria Hajikarimi Department of Civil and Environmental Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran Fereidoon Moghadas Nejad Department of Civil and Environmental Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran 0000-0003-3830-4555 Ali Sarabandi Department of Civil and Environmental Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran 0009-0006-3294-0533 Journal Article 2025 11 20 Asphalt pavements deteriorate over time due to heavy traffic and environmental factors, necessitating frequent maintenance or rehabilitation. Cold recycled asphalt mixtures (CRAM) provide a sustainable approach for reusing reclaimed asphalt pavement (RAP), reducing construction costs, conserving natural resources, and mitigating environmental impacts. However, the mechanical performance and durability of CRAM are highly dependent on aggregate gradation. This study investigates the effect of variations in aggregate gradation, particularly deviations from permissible limits caused by plant production errors or construction-related issues, on the mechanical properties of CRAM. In this research, RAP was used as the coarse aggregate (95% by weight), while virgin aggregate served as filler (5% by weight). Five gradation curves were evaluated, including four outside the permissible range and one base mix within the permissible range, based on the gradation type specified in Code 339. These five mix designs were as follows: (1) Mix A: with the reduction of filler below the permissible range specified in Code 339. (2) Mix B: with the increase of filler beyond the permissible range specified in Code 339. (3) Mix C: with the reduction of coarse aggregates below the permissible range specified in Code 339. Mix (4) D: with the increase of coarse aggregates beyond the permissible range specified in Code 339. (5) Base Mix: with an aggregate gradation within the permissible range of Code 339. Marshall specimens were prepared under ambient conditions and cured for 7 days before testing, while indirect tensile strength (ITS) specimens were tested after 7 and 28 days of curing in both dry and moisture-conditioned states. The results indicate that increasing the coarse aggregate proportion or reducing filler content led to a decrease in Marshall stability by 18% and 7%, respectively, compared to the base mix. Conversely, increasing fine aggregate content and reducing coarse aggregates enhanced Marshall stability by 30% and 22%, respectively. In terms of tensile behavior, reducing fine aggregates decreased Dry ITS by 20%, whereas increasing fine aggregates or adjusting coarse aggregate proportions resulted in Dry ITS increases of 11%, 16%, and 1.5% relative to the base mix. Although some mixtures achieved the minimum Dry ITS requirement after 28 days, certain designs exhibited poor visual quality and insufficient cohesion, emphasizing the importance of precise gradation control during plant production. The base mix failed to meet moisture durability requirements in terms of Dry ITS and tensile strength ratio (TSR), highlighting the need for gradation optimization or the use of suitable additives. Additionally, increasing the emulsified bitumen content in mix B* to 5.5% improved Dry ITS by 21% relative to the base mix, demonstrating the synergistic effect of proper gradation and emulsified bitumen content on moisture resistance. However, the base mix failed to meet moisture durability requirements in terms of Dry ITS and TSR, emphasizing the need for gradation optimization or the use of suitable additives. Additionally, increasing the emulsified bitumen content in mix design B* to 5.5% improved Dry ITS by 21% relative to the base mix, demonstrating the synergistic effect of proper gradation and emulsified bitumen content on moisture resistance. Overall, these findings confirm that aggregate gradation has a significant influence on both the mechanical performance and moisture durability of CRAM. Maintaining optimal proportions of fine aggregate and filler is particularly crucial, as deviations from their ideal levels can substantially compromise the mixture’s strength, cohesion, and durability. Therefore, careful monitoring and control of aggregate gradation and emulsified bitumen content during production are essential to ensure acceptable Marshall stability, ITS, and TSR, providing practical guidance for the sustainable rehabilitation of asphalt pavements using cold recycled mixtures. Asphalt pavements deteriorate over time due to heavy traffic and environmental factors, necessitating frequent maintenance or rehabilitation. Cold recycled asphalt mixtures (CRAM) provide a sustainable approach for reusing reclaimed asphalt pavement (RAP), reducing construction costs, conserving natural resources, and mitigating environmental impacts. However, the mechanical performance and durability of CRAM are highly dependent on aggregate gradation. This study investigates the effect of variations in aggregate gradation, particularly deviations from permissible limits caused by plant production errors or construction-related issues, on the mechanical properties of CRAM. In this research, RAP was used as the coarse aggregate (95% by weight), while virgin aggregate served as filler (5% by weight). Five gradation curves were evaluated, including four outside the permissible range and one base mix within the permissible range, based on the gradation type specified in Code 339. These five mix designs were as follows: (1) Mix A: with the reduction of filler below the permissible range specified in Code 339. (2) Mix B: with the increase of filler beyond the permissible range specified in Code 339. (3) Mix C: with the reduction of coarse aggregates below the permissible range specified in Code 339. Mix (4) D: with the increase of coarse aggregates beyond the permissible range specified in Code 339. (5) Base Mix: with an aggregate gradation within the permissible range of Code 339. Marshall specimens were prepared under ambient conditions and cured for 7 days before testing, while indirect tensile strength (ITS) specimens were tested after 7 and 28 days of curing in both dry and moisture-conditioned states. The results indicate that increasing the coarse aggregate proportion or reducing filler content led to a decrease in Marshall stability by 18% and 7%, respectively, compared to the base mix. Conversely, increasing fine aggregate content and reducing coarse aggregates enhanced Marshall stability by 30% and 22%, respectively. In terms of tensile behavior, reducing fine aggregates decreased Dry ITS by 20%, whereas increasing fine aggregates or adjusting coarse aggregate proportions resulted in Dry ITS increases of 11%, 16%, and 1.5% relative to the base mix. Although some mixtures achieved the minimum Dry ITS requirement after 28 days, certain designs exhibited poor visual quality and insufficient cohesion, emphasizing the importance of precise gradation control during plant production. The base mix failed to meet moisture durability requirements in terms of Dry ITS and tensile strength ratio (TSR), highlighting the need for gradation optimization or the use of suitable additives. Additionally, increasing the emulsified bitumen content in mix B* to 5.5% improved Dry ITS by 21% relative to the base mix, demonstrating the synergistic effect of proper gradation and emulsified bitumen content on moisture resistance. However, the base mix failed to meet moisture durability requirements in terms of Dry ITS and TSR, emphasizing the need for gradation optimization or the use of suitable additives. Additionally, increasing the emulsified bitumen content in mix design B* to 5.5% improved Dry ITS by 21% relative to the base mix, demonstrating the synergistic effect of proper gradation and emulsified bitumen content on moisture resistance. Overall, these findings confirm that aggregate gradation has a significant influence on both the mechanical performance and moisture durability of CRAM. Maintaining optimal proportions of fine aggregate and filler is particularly crucial, as deviations from their ideal levels can substantially compromise the mixture’s strength, cohesion, and durability. Therefore, careful monitoring and control of aggregate gradation and emulsified bitumen content during production are essential to ensure acceptable Marshall stability, ITS, and TSR, providing practical guidance for the sustainable rehabilitation of asphalt pavements using cold recycled mixtures.

https://mcej.modares.ac.ir/article_28413_20f3d99862a33c859c8363e50fe09a3f.pdf

Tarbiat Modares University Modares Civil Engineering journal 2476-6763 26 3 2026 08 23 The presence of a block downstream of a type B triangular piano key weir and its effect on increasing flow energy loss The presence of a block downstream of a type B triangular piano key weir and its effect on increasing flow energy loss 97 106 28411 10.48311/mcej.2026.99152.0 FA Hamidreza Ahmadi M.Sc. Student, Department of Civil Engineering, Isf.C., Islamic Azad University, Isfahan, Iran Ali Khoshfetrat Assistant Professor, Department of Civil Engineering, Isf.C., Islamic Azad University, Isfahan, Iran 0000-0002-0113-5287 Journal Article 2025 04 25 Piano key weirs (PKWs) have rectangular, triangular, and trapezoidal shapes in terms of plan. They are available in four types: A, B, C, and D. Type A weir has an overhang upstream and downstream, type B weir has an overhang upstream, type C weir has an overhang downstream, and type D weir has no overhang. Piano key weirs are non-linear, long-crowned spillways that allow a greater flow capacity (3 to 4 times more) over a given width. The first piano key weir was built on the side channel of the Goulours dam in France. Piano key weirs are used in agricultural canals, drainage canals, and irrigation canals in addition to dams due to their lightweight foundation. Piano key weirs are the evolution of nonlinear weirs with high efficiency; therefore, it is important to investigate the flow energy loss and the solution to increase it. In the present study, for the first time, a block with a different geometry was used downstream of the triangular piano key weir type B. Also, two weirs with a height of 0.20 and 0.18 m were used. The blocks are rectangular and a combination of trapezoidal and circular blocks. Four discharges from 0.02 to 0.05 m3/s were also used. The experiments were conducted in a channel 10 m long, 0.8 m wide, and 1 m high. The slope of the channel is zero. The water temperature also varies between 8 and 13 °C. The flow was fed into the tank by a pump and an underground tank with a volume of 10,000 m3 and a monitor. Two triangular piano key weirs type B with constant geometry but different heights of 0.20 and 0.18 m were used. The width of the weir inlet keys (Wi) is 0.613 m, the width of the weir outlet keys (Wo) is 0 m, the length of the weir side walls (B*) is 0.425 m, the length of the upstream overhanging edges of the weirs (Bi) is 0.14 m, the length of the weir crest (L) is 3.04 m, and the thickness of the weirs (Ts) is 0.01 m. Blocks with rectangular and trapezoidal cross-sections with a height of 0.06 m (0.3P) were used downstream of the 0.20 m high weir. The cross-sectional area of ââthe blocks is 0.025 x 0.025 m. The height of the blocks was chosen so that they are submerged at the lowest flow rate (0.02 m3/s). The blocks are made of compressed plastic and were installed downstream of the weir with waterproof adhesive. The blocks were installed in three rows downstream of the weir. The distance between the blocks is 10.25 cm. As mentioned, the study of flow energy loss in piano key weirs is important due to their high efficiency in flow passage. Dimensional analysis was also used to extend the results to other weirs and other types of piano key weirs in channels. As the height of the weir increases, the discharge coefficient decreases, and the flow energy loss increases. The blocks downstream of the weir act as a barrier and the flow energy loss increases. The flow around the blocks has weak eddies and hydraulic jumps, which reduces the specific energy downstream. With increasing Hu/P, the flow energy loss decreases. The flow energy loss in the weir with a combination of trapezoidal and circular blocks is higher than that of rectangular blocks. Next, a relationship with a correlation coefficient of 99.92% was presented to calculate the flow energy loss. Piano key weirs (PKWs) have rectangular, triangular, and trapezoidal shapes in terms of plan. They are available in four types: A, B, C, and D. Type A weir has an overhang upstream and downstream, type B weir has an overhang upstream, type C weir has an overhang downstream, and type D weir has no overhang. Piano key weirs are non-linear, long-crowned spillways that allow a greater flow capacity (3 to 4 times more) over a given width. The first piano key weir was built on the side channel of the Goulours dam in France. Piano key weirs are used in agricultural canals, drainage canals, and irrigation canals in addition to dams due to their lightweight foundation. Piano key weirs are the evolution of nonlinear weirs with high efficiency; therefore, it is important to investigate the flow energy loss and the solution to increase it. In the present study, for the first time, a block with a different geometry was used downstream of the triangular piano key weir type B. Also, two weirs with a height of 0.20 and 0.18 m were used. The blocks are rectangular and a combination of trapezoidal and circular blocks. Four discharges from 0.02 to 0.05 m3/s were also used. The experiments were conducted in a channel 10 m long, 0.8 m wide, and 1 m high. The slope of the channel is zero. The water temperature also varies between 8 and 13 °C. The flow was fed into the tank by a pump and an underground tank with a volume of 10,000 m3 and a monitor. Two triangular piano key weirs type B with constant geometry but different heights of 0.20 and 0.18 m were used. The width of the weir inlet keys (Wi) is 0.613 m, the width of the weir outlet keys (Wo) is 0 m, the length of the weir side walls (B*) is 0.425 m, the length of the upstream overhanging edges of the weirs (Bi) is 0.14 m, the length of the weir crest (L) is 3.04 m, and the thickness of the weirs (Ts) is 0.01 m. Blocks with rectangular and trapezoidal cross-sections with a height of 0.06 m (0.3P) were used downstream of the 0.20 m high weir. The cross-sectional area of ââthe blocks is 0.025 x 0.025 m. The height of the blocks was chosen so that they are submerged at the lowest flow rate (0.02 m3/s). The blocks are made of compressed plastic and were installed downstream of the weir with waterproof adhesive. The blocks were installed in three rows downstream of the weir. The distance between the blocks is 10.25 cm. As mentioned, the study of flow energy loss in piano key weirs is important due to their high efficiency in flow passage. Dimensional analysis was also used to extend the results to other weirs and other types of piano key weirs in channels. As the height of the weir increases, the discharge coefficient decreases, and the flow energy loss increases. The blocks downstream of the weir act as a barrier and the flow energy loss increases. The flow around the blocks has weak eddies and hydraulic jumps, which reduces the specific energy downstream. With increasing Hu/P, the flow energy loss decreases. The flow energy loss in the weir with a combination of trapezoidal and circular blocks is higher than that of rectangular blocks. Next, a relationship with a correlation coefficient of 99.92% was presented to calculate the flow energy loss.

https://mcej.modares.ac.ir/article_28411_f512288bb4d64bba2c024bc73646808d.pdf