Seyed Ali Mahmoudy | University of Isfahan (original) (raw)
Papers by Seyed Ali Mahmoudy
Journal of Rehabilitation in Civil Engineering, 2024
Despite their low stiffness, moment frames (MFs) are considered conventional lateral strength sys... more Despite their low stiffness, moment frames (MFs) are considered conventional lateral strength systems for low- and moderate-rise structures due to their ability to absorb energy and provide suitable ductility, along with architectural considerations. In return, a framed tube system with deep beams and short spans suits the high-rise structures. Due to the differences between the span length-to-depth ratios of the beams in this structural system, the regulations for MFs cannot apply to them. Moreover, a low value for the length-to-height ratio of the beams prevents the proper formation of flexural plastic joints proposed by the regulations. Therefore, a frame with a single story and span has been proposed here consisting of a replaceable shear link made of shape memory alloy (SMA) to study the responses of the structure under the explosive loads (i.e., lateral loading) that can occur due to terrorist attacks, industrialization, or mining actions. Therefore, this study investigates the behavior of different systems under the three types of impact loads, including SMA or steel shear links. The results show that in the frame equipped with a shear link made of an SMA, the base shear is less than that of ordinary steel (the maximum base shear reduction is about 27% for type 2 blast load). This leads to a reduction in the cost of foundation construction. Also, the maximum displacement in the frame equipped with the shear link made of ordinary steel is less than the corresponding value in the frame equipped with a shear link made of an SMA (the maximum displacement reduction is about 43% for type 1 blast load), while the residual displacement of both frames is the same and equal to zero. It was concluded that the free vibration does not significantly affect the maximum responses of the mentioned structures under the impact load.
Journal of building engineering, Jun 1, 2024
Journal of Building Engineering, Mar 31, 2024
This paper studies the influence of two high-performance thermal insulating materials including a... more This paper studies the influence of two high-performance thermal insulating materials including aerogel and phase change materials (PCM) aggregates, on the key characteristics of cementitious composites in experimental and predictive aspects. Thermal conductivity (ThC), rapid chloride migration test (RCMT), permeable pore volume, compressive strength, dry density, and microstructural analysis were performed for the mechanical properties. Moreover, Least Squares Support Vector Regression (LSSVR) as a machine learning method was introduced to evaluate and provide a proper method for non-destructive evaluation of parameters. The results of experiments indicated that both aerogel and PCM aggregates were highly effective although the aerogel showed more efficiency in enhancing the thermal insulation property of cementitious mixtures. In addition, the compressive strength of the mixtures with PCM composites was higher than the aerogel aggregates, where the compressive strength of the mixture containing 20 % paraffin was 50 % higher than the aerogel mixture with similar incorporation levels. Moreover, the mixtures with PCM aggregates had significantly lower water and chloride permeability compared to those of plain mixtures, and mixtures consisted of aerogel aggregates. The scanning electron microscope (SEM) analyses, also, revealed that the use of the aerogel aggregates led to an open and porous structure of the mixtures; however, PCM aggregates had a weak interfacial transition zone (ITZ) in the vicinity of cement paste. Furthermore, LSSVR model provided a close prediction of the effective parameters with an acceptable accuracy in capturing the influences of important parameters.
Structures, Jan 31, 2024
This paper evaluates the application of the endurance time method in the optimum performance desi... more This paper evaluates the application of the endurance time method in the optimum performance design of structures using the uniform deformation theory. The structures used in this study include shear-building systems with 5, 10, and 15 stories, and steel moment-resisting frames with 3, 7, and 12 stories. Initially, shear-building systems are optimized to have uniform story ductility ratios at low, moderate and high seismic hazard levels separately using three sets of ground motion records and a compatible series of endurance time acceleration functions. The effectiveness and accuracy of the endurance time method are assessed by comparing lateral force distribution obtained from this method with its corresponding attained from ground motion records. Moreover, as the number of stories and target ductility increases, the compatibility of these two methods improves. However, it is found that the optimum structure at one seismic hazard level does not necessarily lead to the optimum structure at other seismic hazard levels. Next, by adding dampers with gap to the systems, a procedure is suggested to optimize these structures at different seismic hazard levels simultaneously. These dampers are activated at moderate and high seismic hazard levels. Finally, similar optimization algorithm is used for steel moment-resisting frames to make their story drift ratios or plastic hinge rotations uniform along the height at different seismic hazard levels. Results show that combining endurance time method and uniform deformation theory leads to a promising optimization procedure that can significantly reduce computational costs with reasonable error.
Thin-Walled Structures, Oct 31, 2023
Although cold-formed steel (CFS) members have been widely used in structures, their application i... more Although cold-formed steel (CFS) members have been widely used in structures, their application is limited due to the buckling and instability of these members. To enhance their strength and stiffness, they are often combined with other materials like concrete or timber. One of the main challenges in composite structures is ensuring proper connection between different components to facilitate safe shear load transfer. This is achieved through various types of shear connectors. Bolted shear connections are preferred over headed shear studs because they offer greater strength and can be easily dismantled. Headed shear studs welded onto a steel section are unsuitable for CFS members due to their low thickness.
Structures, 2024
This paper evaluates the application of the endurance time method in the optimum performance desi... more This paper evaluates the application of the endurance time method in the optimum performance design of structures using the uniform deformation theory. The structures used in this study include shear-building systems with 5, 10, and 15 stories, and steel moment-resisting frames with 3, 7, and 12 stories. Initially, shear-building systems are optimized to have uniform story ductility ratios at low, moderate and high seismic hazard levels separately using three sets of ground motion records and a compatible series of endurance time acceleration functions. The effectiveness and accuracy of the endurance time method are assessed by comparing lateral force distribution obtained from this method with its corresponding attained from ground motion records. Moreover, as the number of stories and target ductility increases, the compatibility of these two methods improves. However, it is found that the optimum structure at one seismic hazard level does not necessarily lead to the optimum structure at other seismic hazard levels. Next, by adding dampers with gap to the systems, a procedure is suggested to optimize these structures at different seismic hazard levels simultaneously. These dampers are activated at moderate and high seismic hazard levels. Finally, similar optimization algorithm is used for steel moment-resisting frames to make their story drift ratios or plastic hinge rotations uniform along the height at different seismic hazard levels. Results show that combining endurance time method and uniform deformation theory leads to a promising optimization procedure that can significantly reduce computational costs with reasonable error.
Journal of Building Engineering, 2024
This paper studies the influence of two high-performance thermal insulating materials including a... more This paper studies the influence of two high-performance thermal insulating materials including aerogel and phase change materials (PCM) aggregates, on the key characteristics of cementitious composites in experimental and predictive aspects. Thermal conductivity (ThC), rapid chloride migration test (RCMT), permeable pore volume, compressive strength, dry density, and microstructural analysis were performed for the mechanical properties. Moreover, Least Squares Support Vector Regression (LSSVR) as a machine learning method was introduced to evaluate and provide a proper method for non-destructive evaluation of parameters. The results of experiments indicated that both aerogel and PCM aggregates were highly effective although the aerogel showed more efficiency in enhancing the thermal insulation property of cementitious mixtures. In addition, the compressive strength of the mixtures with PCM composites was higher than the aerogel aggregates, where the compressive strength of the mixture containing 20 % paraffin was 50 % higher than the aerogel mixture with similar incorporation levels. Moreover, the mixtures with PCM aggregates had significantly lower water and chloride permeability compared to those of plain mixtures, and mixtures consisted of aerogel aggregates. The scanning electron microscope (SEM) analyses, also, revealed that the use of the aerogel aggregates led to an open and porous structure of the mixtures; however, PCM aggregates had a weak interfacial transition zone (ITZ) in the vicinity of cement paste. Furthermore, LSSVR model provided a close prediction of the effective parameters with an acceptable accuracy in capturing the influences of important parameters.
Although lithium-ion batteries have extensively been used in various applications because of thei... more Although lithium-ion batteries have extensively been used in various applications because of their high energy capacity, fracture and failure, the by-products of large strains and stresses caused by fast charging and discharging need yet to be addressed. The size effects on the mechanical behavior of the nano-sized structures are significant; however, the classical elasticity theory may not consider such effects. On the other hand, surface stress theory, as a robust and potential theory, is suitable in considering size effects in nano-scale structures. Therefore, in this paper, in order to involve the surface stress effects on the fracture behavior of Li-ion batteries, the following steps are taken. Firstly, a phase-field model is used to determine the evolution of the concentration profile. Subsequently, the stress distribution is obtained by using the surface stress theory combined with chemical equations for a planar electrode. Afterward, by using the weight function method for an edge crack in the plate, the stress intensity factor is derived for all time steps and possible crack lengths during the process. It is found that with increasing phase boundary thickness parameter or decreasing phase-separation phenomenon, the surface mechanics parameters become more influential. Furthermore, in the presence of positive surface stress, the diffusion-induced stress distribution decreases, which in turn reduces the stress intensity factor. In addition, in this paper, the two states of surface stress are compared either for elastic or total strain. Concerning stresses and concentrations, the results indicate a big difference at the beginning of the deintercalation process showing, in particular, 2% for stresses, but the differences diminish gradually.
Journal of building engineering, Sep 1, 2020
The use of additives and their proportioning in concrete to achieve better performance is one of ... more The use of additives and their proportioning in concrete to achieve better performance is one of the challenging issues in concrete technology. In this study, the influence of different percentages of recycled fine and coarse aggregates on rheological, mechanical, and microstructural properties of self-compacting concrete (SCC) is investigated. For this purpose, fine and coarse natural aggregates (FNA and CNA) were replaced with fine and coarse recycled concrete aggregates (FRCA and CRCA), respectively, at replacement rates of 25%, 50%, 75% and 100% (by weight). The results showed that in order to meet the rheological requirements of SCC, the quantity of FRCA or CRCA should be limited to 25%. Furthermore, the mechanical properties showed a decreasing trend with FRCA and CRCA content, however, all mixes satisfied the strength requirement of structural concrete (28day compressive strength of 21 MPa) even at 100% CRCA or FRCA content. In order to enhance the mechanical properties of mixes, 5%, 7.5%, and 10% (by weight) of micro-silica was used as a partial replacement of cement. The results showed that the mix with 25% recycled aggregates and 5% micro-silica presented comparable performance to that of the plain concrete, while using a higher micro-silica content negatively affected the rheological properties. In addition, the effect of recycled aggregate and micro-silica on the microstructure of mixes were examined.
Thin-Walled Structures, 2023
Although cold-formed steel (CFS) members have been widely used in structures, their application i... more Although cold-formed steel (CFS) members have been widely used in structures, their application is limited due to the buckling and instability of these members. To enhance their strength and stiffness, they are often combined with other materials like concrete or timber. One of the main challenges in composite structures is ensuring proper connection between different components to facilitate safe shear load transfer. This is achieved through various types of shear connectors. Bolted shear connections are preferred over headed shear studs because they offer greater strength and can be easily dismantled. Headed shear studs welded onto a steel section are unsuitable for CFS members due to their low thickness.
Iranian Journal of Science and Technology, Transactions of Civil Engineering , 2022
Despite their low stiffness, moment-resisting frames are trendy among lateral load-resisting syst... more Despite their low stiffness, moment-resisting frames are trendy among lateral load-resisting systems due to their high ductility, energy dissipation, and architectural consideration. The low span-to-depth ratio of the beam in the steel framed-tube structure prevents the proper formation of flexural plastic hinges according to the code provisions. Therefore, a replaceable shear link beam made of shape memory alloy (SMA) is recommended to dissipate more energy through shear deformation in the shear link beams and replace it easily after an earthquake. Therefore, here, the effects of substitution of the SMA on entire or some parts of the shear link in steel moment-resisting frames are investigated, and it concluded that the presence of SMA in the web of the shear link increased ultimate strength by 73%. It should be noted that a lower ultimate strength has been observed when all part of the shear link has been made of SMA material. The initial stiffness and ductility increase by 15% and 9% for the model with SMA material in the stiffeners and bolts. Also, the energy dissipation capacity increased by 16% when the SMA material was used in the stiffeners. In other words, using SMA materials locally (i.e., in some parts of the shear link, especially areas that have not entered the plastic range) led to a better performance than using these materials in all parts of the shear link.
International Journal of Numerical Methods in Civil Engineering, 2020
The optimum seismic design of structures is one of the biggest issues for engineers to build resi... more The optimum seismic design of structures is one of the biggest issues for engineers to build resistant and economic structures. In this research, the application of the endurance time method in optimum performance design of steel moment-resisting frames using the uniform deformation method is evaluated. First, three steel moment-resisting frames with 3, 7 and 12 stories are considered. After that, the structures are optimized by endurance time method analysis and the uniform deformation theory, under a series of acceleration functions. Also, results are compared with the results of time history analysis based on earthquakes. The results revealed that endurance time method and time history analysis of earthquakes at low and moderate seismic hazard levels are well matched, while this adjustment does not exist for high seismic hazard level. In addition, the optimum structure at one hazard level does not lead to optimum structure in other hazard levels. To have the best performance at different hazard levels, the frames should be optimized at the moderate seismic hazard level. In order to optimize the structure at all seismic hazard levels, the GAP dampers can be used. These dampers should be effective after a specified drift at the lower seismic hazard level. In addition, the best values for convergence power of the uniform deformation method are between 0.05 to 0.15 for this purpose. By using such dampers, it is possible to have uniform drift distribution at different seismic hazard levels.
Journal of Building Engineering, 2020
The use of additives and their proportioning in concrete to achieve better performance is one of ... more The use of additives and their proportioning in concrete to achieve better performance is one of the challenging issues in concrete technology. In this study, the influence of different percentages of recycled fine and coarse aggregates on rheological, mechanical, and microstructural properties of self-compacting concrete (SCC) is investigated. For this purpose, fine and coarse natural aggregates (FNA and CNA) were replaced with fine and coarse recycled concrete aggregates (FRCA and CRCA), respectively, at replacement rates of 25%, 50%, 75% and 100% (by weight). The results showed that in order to meet the rheological requirements of SCC, the quantity of FRCA or CRCA should be limited to 25%. Furthermore, the mechanical properties showed a decreasing trend with FRCA and CRCA content, however, all mixes satisfied the strength requirement of structural concrete (28-day compressive strength of 21 MPa) even at 100% CRCA or FRCA content. In order to enhance the mechanical properties of mixes, 5%, 7.5%, and 10% (by weight) of micro-silica was used as a partial replacement of cement. The results showed that the mix with 25% recycled aggregates and 5% micro-silica presented comparable performance to that of the plain concrete, while using a higher micro-silica content negatively affected the rheological properties. In addition, the effect of recycled aggregate and micro-silica on the microstructure of mixes were examined.
Conference Presentations by Seyed Ali Mahmoudy
9th national congress on civil engineering, Iran, 2016
Flood routing in rivers is one of the most important issues in the design of hydraulic structures... more Flood routing in rivers is one of the most important issues in the design of hydraulic structures. Muskingum methods are typically used for flow routing and determine the hydrograph of flow. Since this method is acts based on varied discharge-storage relationship and continuity equations, so, the trial and error method to estimate the parameters of nonlinear models is required. Therefore, in this study, the optimal values of nonlinear parameters of Muskingum model determine using a non-direct search algorithm that developed in MATLAB software. In order to achieve the least amount of deviation between the real and estimated hydrograph, five error function such as SSQ, MARE, NQ, DPO and SAD were defined. The results of developed structure shows that with SAD function can be achieved best match between real and routing hydrograph. In fact, using the proposed approach can be determined the best values associated with the nonlinear parameters of Muskingum model in shortest possible time and with high precision. This method can be used as a basis for estimating the parameters of linear and nonlinear Muskingum models.
Thesis Chapters by Seyed Ali Mahmoudy
Drafts by Seyed Ali Mahmoudy
www.preprints.org, 2021
Although lithium-ion batteries have extensively been used in various applications because of thei... more Although lithium-ion batteries have extensively been used in various applications because of their high energy capacity, fracture and failure, the by-products of large strains and stresses caused by fast charging and discharging need yet to be addressed. The size effects on the mechanical behavior of the nano-sized structures are significant; however, the classical elasticity theory may not consider such effects. On the other hand, surface stress theory, as a robust and potential theory, is suitable in considering size effects in nano-scale structures. Therefore, in this paper, in order to involve the surface stress effects on the fracture behavior of Li-ion batteries, the following steps are taken. Firstly, a phase-field model is used to determine the evolution of the concentration profile. Subsequently, the stress distribution is obtained by using the surface stress theory combined with chemical equations for a planar electrode. Afterward, by using the weight function method for an edge crack in the plate, the stress intensity factor is derived for all time steps and possible crack lengths during the process. It is found that with increasing phase boundary thickness parameter or decreasing phase-separation phenomenon, the surface mechanics parameters become more influential. Furthermore, in the presence of positive surface stress, the diffusion-induced stress distribution decreases, which in turn reduces the stress intensity factor. In addition, in this paper, the two states of surface stress are compared either for elastic or total strain. Concerning stresses and concentrations, the results indicate a big difference at the beginning of the deintercalation process showing, in particular, 2% for stresses, but the differences diminish gradually.
Journal of Rehabilitation in Civil Engineering, 2024
Despite their low stiffness, moment frames (MFs) are considered conventional lateral strength sys... more Despite their low stiffness, moment frames (MFs) are considered conventional lateral strength systems for low- and moderate-rise structures due to their ability to absorb energy and provide suitable ductility, along with architectural considerations. In return, a framed tube system with deep beams and short spans suits the high-rise structures. Due to the differences between the span length-to-depth ratios of the beams in this structural system, the regulations for MFs cannot apply to them. Moreover, a low value for the length-to-height ratio of the beams prevents the proper formation of flexural plastic joints proposed by the regulations. Therefore, a frame with a single story and span has been proposed here consisting of a replaceable shear link made of shape memory alloy (SMA) to study the responses of the structure under the explosive loads (i.e., lateral loading) that can occur due to terrorist attacks, industrialization, or mining actions. Therefore, this study investigates the behavior of different systems under the three types of impact loads, including SMA or steel shear links. The results show that in the frame equipped with a shear link made of an SMA, the base shear is less than that of ordinary steel (the maximum base shear reduction is about 27% for type 2 blast load). This leads to a reduction in the cost of foundation construction. Also, the maximum displacement in the frame equipped with the shear link made of ordinary steel is less than the corresponding value in the frame equipped with a shear link made of an SMA (the maximum displacement reduction is about 43% for type 1 blast load), while the residual displacement of both frames is the same and equal to zero. It was concluded that the free vibration does not significantly affect the maximum responses of the mentioned structures under the impact load.
Journal of building engineering, Jun 1, 2024
Journal of Building Engineering, Mar 31, 2024
This paper studies the influence of two high-performance thermal insulating materials including a... more This paper studies the influence of two high-performance thermal insulating materials including aerogel and phase change materials (PCM) aggregates, on the key characteristics of cementitious composites in experimental and predictive aspects. Thermal conductivity (ThC), rapid chloride migration test (RCMT), permeable pore volume, compressive strength, dry density, and microstructural analysis were performed for the mechanical properties. Moreover, Least Squares Support Vector Regression (LSSVR) as a machine learning method was introduced to evaluate and provide a proper method for non-destructive evaluation of parameters. The results of experiments indicated that both aerogel and PCM aggregates were highly effective although the aerogel showed more efficiency in enhancing the thermal insulation property of cementitious mixtures. In addition, the compressive strength of the mixtures with PCM composites was higher than the aerogel aggregates, where the compressive strength of the mixture containing 20 % paraffin was 50 % higher than the aerogel mixture with similar incorporation levels. Moreover, the mixtures with PCM aggregates had significantly lower water and chloride permeability compared to those of plain mixtures, and mixtures consisted of aerogel aggregates. The scanning electron microscope (SEM) analyses, also, revealed that the use of the aerogel aggregates led to an open and porous structure of the mixtures; however, PCM aggregates had a weak interfacial transition zone (ITZ) in the vicinity of cement paste. Furthermore, LSSVR model provided a close prediction of the effective parameters with an acceptable accuracy in capturing the influences of important parameters.
Structures, Jan 31, 2024
This paper evaluates the application of the endurance time method in the optimum performance desi... more This paper evaluates the application of the endurance time method in the optimum performance design of structures using the uniform deformation theory. The structures used in this study include shear-building systems with 5, 10, and 15 stories, and steel moment-resisting frames with 3, 7, and 12 stories. Initially, shear-building systems are optimized to have uniform story ductility ratios at low, moderate and high seismic hazard levels separately using three sets of ground motion records and a compatible series of endurance time acceleration functions. The effectiveness and accuracy of the endurance time method are assessed by comparing lateral force distribution obtained from this method with its corresponding attained from ground motion records. Moreover, as the number of stories and target ductility increases, the compatibility of these two methods improves. However, it is found that the optimum structure at one seismic hazard level does not necessarily lead to the optimum structure at other seismic hazard levels. Next, by adding dampers with gap to the systems, a procedure is suggested to optimize these structures at different seismic hazard levels simultaneously. These dampers are activated at moderate and high seismic hazard levels. Finally, similar optimization algorithm is used for steel moment-resisting frames to make their story drift ratios or plastic hinge rotations uniform along the height at different seismic hazard levels. Results show that combining endurance time method and uniform deformation theory leads to a promising optimization procedure that can significantly reduce computational costs with reasonable error.
Thin-Walled Structures, Oct 31, 2023
Although cold-formed steel (CFS) members have been widely used in structures, their application i... more Although cold-formed steel (CFS) members have been widely used in structures, their application is limited due to the buckling and instability of these members. To enhance their strength and stiffness, they are often combined with other materials like concrete or timber. One of the main challenges in composite structures is ensuring proper connection between different components to facilitate safe shear load transfer. This is achieved through various types of shear connectors. Bolted shear connections are preferred over headed shear studs because they offer greater strength and can be easily dismantled. Headed shear studs welded onto a steel section are unsuitable for CFS members due to their low thickness.
Structures, 2024
This paper evaluates the application of the endurance time method in the optimum performance desi... more This paper evaluates the application of the endurance time method in the optimum performance design of structures using the uniform deformation theory. The structures used in this study include shear-building systems with 5, 10, and 15 stories, and steel moment-resisting frames with 3, 7, and 12 stories. Initially, shear-building systems are optimized to have uniform story ductility ratios at low, moderate and high seismic hazard levels separately using three sets of ground motion records and a compatible series of endurance time acceleration functions. The effectiveness and accuracy of the endurance time method are assessed by comparing lateral force distribution obtained from this method with its corresponding attained from ground motion records. Moreover, as the number of stories and target ductility increases, the compatibility of these two methods improves. However, it is found that the optimum structure at one seismic hazard level does not necessarily lead to the optimum structure at other seismic hazard levels. Next, by adding dampers with gap to the systems, a procedure is suggested to optimize these structures at different seismic hazard levels simultaneously. These dampers are activated at moderate and high seismic hazard levels. Finally, similar optimization algorithm is used for steel moment-resisting frames to make their story drift ratios or plastic hinge rotations uniform along the height at different seismic hazard levels. Results show that combining endurance time method and uniform deformation theory leads to a promising optimization procedure that can significantly reduce computational costs with reasonable error.
Journal of Building Engineering, 2024
This paper studies the influence of two high-performance thermal insulating materials including a... more This paper studies the influence of two high-performance thermal insulating materials including aerogel and phase change materials (PCM) aggregates, on the key characteristics of cementitious composites in experimental and predictive aspects. Thermal conductivity (ThC), rapid chloride migration test (RCMT), permeable pore volume, compressive strength, dry density, and microstructural analysis were performed for the mechanical properties. Moreover, Least Squares Support Vector Regression (LSSVR) as a machine learning method was introduced to evaluate and provide a proper method for non-destructive evaluation of parameters. The results of experiments indicated that both aerogel and PCM aggregates were highly effective although the aerogel showed more efficiency in enhancing the thermal insulation property of cementitious mixtures. In addition, the compressive strength of the mixtures with PCM composites was higher than the aerogel aggregates, where the compressive strength of the mixture containing 20 % paraffin was 50 % higher than the aerogel mixture with similar incorporation levels. Moreover, the mixtures with PCM aggregates had significantly lower water and chloride permeability compared to those of plain mixtures, and mixtures consisted of aerogel aggregates. The scanning electron microscope (SEM) analyses, also, revealed that the use of the aerogel aggregates led to an open and porous structure of the mixtures; however, PCM aggregates had a weak interfacial transition zone (ITZ) in the vicinity of cement paste. Furthermore, LSSVR model provided a close prediction of the effective parameters with an acceptable accuracy in capturing the influences of important parameters.
Although lithium-ion batteries have extensively been used in various applications because of thei... more Although lithium-ion batteries have extensively been used in various applications because of their high energy capacity, fracture and failure, the by-products of large strains and stresses caused by fast charging and discharging need yet to be addressed. The size effects on the mechanical behavior of the nano-sized structures are significant; however, the classical elasticity theory may not consider such effects. On the other hand, surface stress theory, as a robust and potential theory, is suitable in considering size effects in nano-scale structures. Therefore, in this paper, in order to involve the surface stress effects on the fracture behavior of Li-ion batteries, the following steps are taken. Firstly, a phase-field model is used to determine the evolution of the concentration profile. Subsequently, the stress distribution is obtained by using the surface stress theory combined with chemical equations for a planar electrode. Afterward, by using the weight function method for an edge crack in the plate, the stress intensity factor is derived for all time steps and possible crack lengths during the process. It is found that with increasing phase boundary thickness parameter or decreasing phase-separation phenomenon, the surface mechanics parameters become more influential. Furthermore, in the presence of positive surface stress, the diffusion-induced stress distribution decreases, which in turn reduces the stress intensity factor. In addition, in this paper, the two states of surface stress are compared either for elastic or total strain. Concerning stresses and concentrations, the results indicate a big difference at the beginning of the deintercalation process showing, in particular, 2% for stresses, but the differences diminish gradually.
Journal of building engineering, Sep 1, 2020
The use of additives and their proportioning in concrete to achieve better performance is one of ... more The use of additives and their proportioning in concrete to achieve better performance is one of the challenging issues in concrete technology. In this study, the influence of different percentages of recycled fine and coarse aggregates on rheological, mechanical, and microstructural properties of self-compacting concrete (SCC) is investigated. For this purpose, fine and coarse natural aggregates (FNA and CNA) were replaced with fine and coarse recycled concrete aggregates (FRCA and CRCA), respectively, at replacement rates of 25%, 50%, 75% and 100% (by weight). The results showed that in order to meet the rheological requirements of SCC, the quantity of FRCA or CRCA should be limited to 25%. Furthermore, the mechanical properties showed a decreasing trend with FRCA and CRCA content, however, all mixes satisfied the strength requirement of structural concrete (28day compressive strength of 21 MPa) even at 100% CRCA or FRCA content. In order to enhance the mechanical properties of mixes, 5%, 7.5%, and 10% (by weight) of micro-silica was used as a partial replacement of cement. The results showed that the mix with 25% recycled aggregates and 5% micro-silica presented comparable performance to that of the plain concrete, while using a higher micro-silica content negatively affected the rheological properties. In addition, the effect of recycled aggregate and micro-silica on the microstructure of mixes were examined.
Thin-Walled Structures, 2023
Although cold-formed steel (CFS) members have been widely used in structures, their application i... more Although cold-formed steel (CFS) members have been widely used in structures, their application is limited due to the buckling and instability of these members. To enhance their strength and stiffness, they are often combined with other materials like concrete or timber. One of the main challenges in composite structures is ensuring proper connection between different components to facilitate safe shear load transfer. This is achieved through various types of shear connectors. Bolted shear connections are preferred over headed shear studs because they offer greater strength and can be easily dismantled. Headed shear studs welded onto a steel section are unsuitable for CFS members due to their low thickness.
Iranian Journal of Science and Technology, Transactions of Civil Engineering , 2022
Despite their low stiffness, moment-resisting frames are trendy among lateral load-resisting syst... more Despite their low stiffness, moment-resisting frames are trendy among lateral load-resisting systems due to their high ductility, energy dissipation, and architectural consideration. The low span-to-depth ratio of the beam in the steel framed-tube structure prevents the proper formation of flexural plastic hinges according to the code provisions. Therefore, a replaceable shear link beam made of shape memory alloy (SMA) is recommended to dissipate more energy through shear deformation in the shear link beams and replace it easily after an earthquake. Therefore, here, the effects of substitution of the SMA on entire or some parts of the shear link in steel moment-resisting frames are investigated, and it concluded that the presence of SMA in the web of the shear link increased ultimate strength by 73%. It should be noted that a lower ultimate strength has been observed when all part of the shear link has been made of SMA material. The initial stiffness and ductility increase by 15% and 9% for the model with SMA material in the stiffeners and bolts. Also, the energy dissipation capacity increased by 16% when the SMA material was used in the stiffeners. In other words, using SMA materials locally (i.e., in some parts of the shear link, especially areas that have not entered the plastic range) led to a better performance than using these materials in all parts of the shear link.
International Journal of Numerical Methods in Civil Engineering, 2020
The optimum seismic design of structures is one of the biggest issues for engineers to build resi... more The optimum seismic design of structures is one of the biggest issues for engineers to build resistant and economic structures. In this research, the application of the endurance time method in optimum performance design of steel moment-resisting frames using the uniform deformation method is evaluated. First, three steel moment-resisting frames with 3, 7 and 12 stories are considered. After that, the structures are optimized by endurance time method analysis and the uniform deformation theory, under a series of acceleration functions. Also, results are compared with the results of time history analysis based on earthquakes. The results revealed that endurance time method and time history analysis of earthquakes at low and moderate seismic hazard levels are well matched, while this adjustment does not exist for high seismic hazard level. In addition, the optimum structure at one hazard level does not lead to optimum structure in other hazard levels. To have the best performance at different hazard levels, the frames should be optimized at the moderate seismic hazard level. In order to optimize the structure at all seismic hazard levels, the GAP dampers can be used. These dampers should be effective after a specified drift at the lower seismic hazard level. In addition, the best values for convergence power of the uniform deformation method are between 0.05 to 0.15 for this purpose. By using such dampers, it is possible to have uniform drift distribution at different seismic hazard levels.
Journal of Building Engineering, 2020
The use of additives and their proportioning in concrete to achieve better performance is one of ... more The use of additives and their proportioning in concrete to achieve better performance is one of the challenging issues in concrete technology. In this study, the influence of different percentages of recycled fine and coarse aggregates on rheological, mechanical, and microstructural properties of self-compacting concrete (SCC) is investigated. For this purpose, fine and coarse natural aggregates (FNA and CNA) were replaced with fine and coarse recycled concrete aggregates (FRCA and CRCA), respectively, at replacement rates of 25%, 50%, 75% and 100% (by weight). The results showed that in order to meet the rheological requirements of SCC, the quantity of FRCA or CRCA should be limited to 25%. Furthermore, the mechanical properties showed a decreasing trend with FRCA and CRCA content, however, all mixes satisfied the strength requirement of structural concrete (28-day compressive strength of 21 MPa) even at 100% CRCA or FRCA content. In order to enhance the mechanical properties of mixes, 5%, 7.5%, and 10% (by weight) of micro-silica was used as a partial replacement of cement. The results showed that the mix with 25% recycled aggregates and 5% micro-silica presented comparable performance to that of the plain concrete, while using a higher micro-silica content negatively affected the rheological properties. In addition, the effect of recycled aggregate and micro-silica on the microstructure of mixes were examined.
9th national congress on civil engineering, Iran, 2016
Flood routing in rivers is one of the most important issues in the design of hydraulic structures... more Flood routing in rivers is one of the most important issues in the design of hydraulic structures. Muskingum methods are typically used for flow routing and determine the hydrograph of flow. Since this method is acts based on varied discharge-storage relationship and continuity equations, so, the trial and error method to estimate the parameters of nonlinear models is required. Therefore, in this study, the optimal values of nonlinear parameters of Muskingum model determine using a non-direct search algorithm that developed in MATLAB software. In order to achieve the least amount of deviation between the real and estimated hydrograph, five error function such as SSQ, MARE, NQ, DPO and SAD were defined. The results of developed structure shows that with SAD function can be achieved best match between real and routing hydrograph. In fact, using the proposed approach can be determined the best values associated with the nonlinear parameters of Muskingum model in shortest possible time and with high precision. This method can be used as a basis for estimating the parameters of linear and nonlinear Muskingum models.
www.preprints.org, 2021
Although lithium-ion batteries have extensively been used in various applications because of thei... more Although lithium-ion batteries have extensively been used in various applications because of their high energy capacity, fracture and failure, the by-products of large strains and stresses caused by fast charging and discharging need yet to be addressed. The size effects on the mechanical behavior of the nano-sized structures are significant; however, the classical elasticity theory may not consider such effects. On the other hand, surface stress theory, as a robust and potential theory, is suitable in considering size effects in nano-scale structures. Therefore, in this paper, in order to involve the surface stress effects on the fracture behavior of Li-ion batteries, the following steps are taken. Firstly, a phase-field model is used to determine the evolution of the concentration profile. Subsequently, the stress distribution is obtained by using the surface stress theory combined with chemical equations for a planar electrode. Afterward, by using the weight function method for an edge crack in the plate, the stress intensity factor is derived for all time steps and possible crack lengths during the process. It is found that with increasing phase boundary thickness parameter or decreasing phase-separation phenomenon, the surface mechanics parameters become more influential. Furthermore, in the presence of positive surface stress, the diffusion-induced stress distribution decreases, which in turn reduces the stress intensity factor. In addition, in this paper, the two states of surface stress are compared either for elastic or total strain. Concerning stresses and concentrations, the results indicate a big difference at the beginning of the deintercalation process showing, in particular, 2% for stresses, but the differences diminish gradually.