Muhammad Imran, Hassan Amjad, Shayan Khan, Shehroze Ali
The incorporation of carbon nanotubes (CNTs) in concrete can improve the physical, mechanical, and durability properties. However, the interaction of CNTs with concrete and their effect on the mechanical properties remains a challenging issue. Also, the determination of mechanical properties through experimental testing is time‐consuming, laborious, and uneconomical. This study focuses on the development of machine learning (ML) models for the prediction of the mechanical properties of concrete. A comprehensive data set of 758 CNT‐modified concrete specimens was established for the compressive strength (CS), split tensile strength (STS), flexural strength (FS), and modulus of elasticity (MOE) values from the experimental studies in the literature. Afterward, the predictive models were developed using multilinear regression (MLR), support vector machine (SVM), ensemble methods (EN), regression tree (RT), and Gaussian process regression (GPR). It was found that among ML models, the GPR model predicted the CS, STS, and FS at the highest efficiency with the coefficient of determination (R2) of 0.83, 0.78, and 0.93, respectively while the performance of the SVM model was superior for predicting MOE with an R2 value of 0.91. The mean absolute error (MAE) of the GPR model for CS, STS, FS, and MOE were 2.92, 0.26, 0.35, and 1.31, respectively which were also lesser than other models. The training time of different models demonstrated that the GPR model has also a lower training time (~3 s) as compared to other models which indicates it has a high accuracy‐to‐time cost ratio. Further, the most influential parameters on CS were age, cement, water–cement ratio, and carbon nanotubes. The one‐way partial dependence analysis showed a direct correlation for age and cement but an inverse correlation for the water–cement ratio and fine aggregate. The graphical user interface provides the implication of the developed models for practical applications.
{"title":"Machine learning assisted prediction of the mechanical properties of carbon nanotube‐incorporated concrete","authors":"Muhammad Imran, Hassan Amjad, Shayan Khan, Shehroze Ali","doi":"10.1002/suco.202400727","DOIUrl":"https://doi.org/10.1002/suco.202400727","url":null,"abstract":"The incorporation of carbon nanotubes (CNTs) in concrete can improve the physical, mechanical, and durability properties. However, the interaction of CNTs with concrete and their effect on the mechanical properties remains a challenging issue. Also, the determination of mechanical properties through experimental testing is time‐consuming, laborious, and uneconomical. This study focuses on the development of machine learning (ML) models for the prediction of the mechanical properties of concrete. A comprehensive data set of 758 CNT‐modified concrete specimens was established for the compressive strength (CS), split tensile strength (STS), flexural strength (FS), and modulus of elasticity (MOE) values from the experimental studies in the literature. Afterward, the predictive models were developed using multilinear regression (MLR), support vector machine (SVM), ensemble methods (EN), regression tree (RT), and Gaussian process regression (GPR). It was found that among ML models, the GPR model predicted the CS, STS, and FS at the highest efficiency with the coefficient of determination (<jats:italic>R</jats:italic><jats:sup>2</jats:sup>) of 0.83, 0.78, and 0.93, respectively while the performance of the SVM model was superior for predicting MOE with an <jats:italic>R</jats:italic><jats:sup>2</jats:sup> value of 0.91. The mean absolute error (MAE) of the GPR model for CS, STS, FS, and MOE were 2.92, 0.26, 0.35, and 1.31, respectively which were also lesser than other models. The training time of different models demonstrated that the GPR model has also a lower training time (~3 s) as compared to other models which indicates it has a high accuracy‐to‐time cost ratio. Further, the most influential parameters on CS were age, cement, water–cement ratio, and carbon nanotubes. The one‐way partial dependence analysis showed a direct correlation for age and cement but an inverse correlation for the water–cement ratio and fine aggregate. The graphical user interface provides the implication of the developed models for practical applications.","PeriodicalId":21988,"journal":{"name":"Structural Concrete","volume":"4 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2024-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204013","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The capacity of the circumferential joint of the precast concrete segmental tunnel lining (PCTL) structure in terms of shear performance principally includes the dowel action by connector/bolt as well as friction force, and it is a vital parameter to assess the mechanical response of the circumferential joint. Further, as there was no analytical model available for precise estimation of a circumferential joint in terms of the shear‐bearing capacity considering the dowel action of the bolt in the presence of axial/normal force, therefore in this investigation, an analytical model has been proposed to estimate the shear‐bearing capacity of the circumferential joint. Furthermore, the analytical model's precision and accuracy were validated via large‐scale experimental investigation on a circumferential joint of PCTL. Upon comparing analytical model outcomes with experimental results, absolute error varied between +5% and −9%, with an average value of the coefficient of friction at the yield point of the bolt. Moreover, the formation of hinges on the side of the bolt within the segment was considered a failure of the circumferential joint. Additionally, the parametric investigation revealed that with just a 1% change in axial force, the diameter, pre‐tightening, and yield strength of the bolt and concrete strength improved by 2.85%, 1%, 0.27%, 0.26% and 0.17% shear‐bearing capacity of the circumferential joint respectively. Axial force variation greatly influences the shear‐bearing capacity of circumferential joint followed by diameter, pre‐tightening, yield strength of the bolt, and concrete strength. Conclusively, with analysis of axial force distribution around the ring for the tunnel, the proposed model has been applied to a full ring to estimate shear bearing capacity.
{"title":"An analytical solution for shear bearing capacity of circumferential joints of precast concrete segmental tunnel linings considering dowel action","authors":"Rizwan Amjad, Yumeng Zhang, Xian Liu","doi":"10.1002/suco.202400250","DOIUrl":"https://doi.org/10.1002/suco.202400250","url":null,"abstract":"The capacity of the circumferential joint of the precast concrete segmental tunnel lining (PCTL) structure in terms of shear performance principally includes the dowel action by connector/bolt as well as friction force, and it is a vital parameter to assess the mechanical response of the circumferential joint. Further, as there was no analytical model available for precise estimation of a circumferential joint in terms of the shear‐bearing capacity considering the dowel action of the bolt in the presence of axial/normal force, therefore in this investigation, an analytical model has been proposed to estimate the shear‐bearing capacity of the circumferential joint. Furthermore, the analytical model's precision and accuracy were validated via large‐scale experimental investigation on a circumferential joint of PCTL. Upon comparing analytical model outcomes with experimental results, absolute error varied between +5% and −9%, with an average value of the coefficient of friction at the yield point of the bolt. Moreover, the formation of hinges on the side of the bolt within the segment was considered a failure of the circumferential joint. Additionally, the parametric investigation revealed that with just a 1% change in axial force, the diameter, pre‐tightening, and yield strength of the bolt and concrete strength improved by 2.85%, 1%, 0.27%, 0.26% and 0.17% shear‐bearing capacity of the circumferential joint respectively. Axial force variation greatly influences the shear‐bearing capacity of circumferential joint followed by diameter, pre‐tightening, yield strength of the bolt, and concrete strength. Conclusively, with analysis of axial force distribution around the ring for the tunnel, the proposed model has been applied to a full ring to estimate shear bearing capacity.","PeriodicalId":21988,"journal":{"name":"Structural Concrete","volume":"40 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204017","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Basalt fiber (BF) is known for its high tensile strength, low elastic modulus, and environmental friendliness. To investigate the influence of basalt fiber reinforced concrete (BFRC) lamination heights on the beams' shear performance, four basalt fiber reinforced concrete and reinforced concrete (BFRC‐RC) beams featuring diverse laminated heights were fabricated and underwent bending tests. To further investigate the impact of stirrup and shear span ratios on the shear performance of BFRC‐RC beams, finite element models (FEMs) were established based on the experiments. The results indicated that four test beams experienced diagonal shear failure. Compared to RC beams, BFRC‐RC beams exhibited heightened ductility and stiffness. Additionally, as the BFRC laminated height rose, both cracking and peak loads increased. Compared to BFRC‐RC beams without stirrups, stirrups in those beams transitioned the diagonal shear failure to flexural failure. Stirrups in BFRC‐RC beams increased both the yield and peak loads, thereby enhancing their ductility. With a reduction in the shear span ratio, BFRC‐RC beams increased in both yield and peak loads, accompanied by a simultaneous decrease in yield and peak displacement. Finally, a model incorporating the influence of laminated height on BFRC‐RC beams' behavior was introduced to predict their bearing capacity. The theoretical values aligned well with the experimental results.
{"title":"Shear performance of basalt fiber composite RC beams with different laminated heights of basalt fiber","authors":"Ting Xia, Wei Zhang, Min Huang, Hua Huang","doi":"10.1002/suco.202400032","DOIUrl":"https://doi.org/10.1002/suco.202400032","url":null,"abstract":"Basalt fiber (BF) is known for its high tensile strength, low elastic modulus, and environmental friendliness. To investigate the influence of basalt fiber reinforced concrete (BFRC) lamination heights on the beams' shear performance, four basalt fiber reinforced concrete and reinforced concrete (BFRC‐RC) beams featuring diverse laminated heights were fabricated and underwent bending tests. To further investigate the impact of stirrup and shear span ratios on the shear performance of BFRC‐RC beams, finite element models (FEMs) were established based on the experiments. The results indicated that four test beams experienced diagonal shear failure. Compared to RC beams, BFRC‐RC beams exhibited heightened ductility and stiffness. Additionally, as the BFRC laminated height rose, both cracking and peak loads increased. Compared to BFRC‐RC beams without stirrups, stirrups in those beams transitioned the diagonal shear failure to flexural failure. Stirrups in BFRC‐RC beams increased both the yield and peak loads, thereby enhancing their ductility. With a reduction in the shear span ratio, BFRC‐RC beams increased in both yield and peak loads, accompanied by a simultaneous decrease in yield and peak displacement. Finally, a model incorporating the influence of laminated height on BFRC‐RC beams' behavior was introduced to predict their bearing capacity. The theoretical values aligned well with the experimental results.","PeriodicalId":21988,"journal":{"name":"Structural Concrete","volume":"66 1 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper aims at assessing the failure time of a 7‐story reinforced concrete (RC) frame in a post‐earthquake fire (PEF) event probabilistically. Cumulative distribution functions (CDF) of the studied frame's failure time in various seismic load intensities have been calculated and presented with the aid of Monte Carlo analysis. Seismic load intensity, failure time, and failure probability are three parameters that are correlated through probabilistic analysis. The effects of cracking, spalling, and residual deformations resulted from the seismic load are considered in the strength of structure against the fire load. Seismic load intensity, materials properties, gravity load, and geometry are considered as random variables and one probabilistic analysis has been carried out for each seismic load intensity. The results have illustrated that in low seismic load intensities, probabilistic values of failure time in a structure subjected to pure fire load are equal to the one exposed to PEF. With the increase of seismic load intensity, the effects of cracking, spalling, and residual deformations would lead to a decline in the strength of structural elements against PEF scenario. The failure time in 50% failure probability for Sa = 0.2 g, Sa = 1 g, and Sa = 2 g intensities has been calculated as 14,300, 12,200, and 5100 s, respectively. The analysis results have shown that in an unspecified seismic load intensity, the failure time of the 7‐story RC frame for the 50% occurrence probability is equal to 9750 s.
本文旨在从概率角度评估一个 7 层钢筋混凝土（RC）框架在震后火灾（PEF）事件中的破坏时间。借助蒙特卡罗分析法，计算并展示了所研究框架在不同地震荷载烈度下破坏时间的累积分布函数（CDF）。地震荷载强度、破坏时间和破坏概率这三个参数通过概率分析相互关联。在计算结构抗火荷载强度时，考虑了地震荷载产生的开裂、剥落和残余变形的影响。地震荷载强度、材料特性、重力荷载和几何形状被视为随机变量，并对每种地震荷载强度进行了一次概率分析。结果表明，在地震荷载强度较低的情况下，承受纯火灾荷载的结构的破坏时间概率值与承受 PEF 的结构的破坏时间概率值相等。随着地震荷载强度的增加，开裂、剥落和残余变形的影响将导致结构构件在 PEF 情况下的强度下降。经计算，在 Sa = 0.2 g、Sa = 1 g 和 Sa = 2 g 强度下，50%破坏概率下的破坏时间分别为 14 300 秒、12 200 秒和 5100 秒。分析结果表明，在未指定的地震荷载烈度下，发生概率为 50%的 7 层 RC 框架的破坏时间等于 9750 秒。
{"title":"Probabilistic evaluation of failure time of reinforced concrete frame in post‐earthquake fire scenario","authors":"Majid Moradi, HamidReza Tavakoli, GholamReza Abdollahzade","doi":"10.1002/suco.202300353","DOIUrl":"https://doi.org/10.1002/suco.202300353","url":null,"abstract":"This paper aims at assessing the failure time of a 7‐story reinforced concrete (RC) frame in a post‐earthquake fire (PEF) event probabilistically. Cumulative distribution functions (CDF) of the studied frame's failure time in various seismic load intensities have been calculated and presented with the aid of Monte Carlo analysis. Seismic load intensity, failure time, and failure probability are three parameters that are correlated through probabilistic analysis. The effects of cracking, spalling, and residual deformations resulted from the seismic load are considered in the strength of structure against the fire load. Seismic load intensity, materials properties, gravity load, and geometry are considered as random variables and one probabilistic analysis has been carried out for each seismic load intensity. The results have illustrated that in low seismic load intensities, probabilistic values of failure time in a structure subjected to pure fire load are equal to the one exposed to PEF. With the increase of seismic load intensity, the effects of cracking, spalling, and residual deformations would lead to a decline in the strength of structural elements against PEF scenario. The failure time in 50% failure probability for Sa = 0.2 g, Sa = 1 g, and Sa = 2 g intensities has been calculated as 14,300, 12,200, and 5100 s, respectively. The analysis results have shown that in an unspecified seismic load intensity, the failure time of the 7‐story RC frame for the 50% occurrence probability is equal to 9750 s.","PeriodicalId":21988,"journal":{"name":"Structural Concrete","volume":"1 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shengyu Li, Erwin Lim, Zhengqing Chen, Yu Hong, Qianhui Pu
The mechanical behavior of cable pylon anchorage zone in a cable‐stayed bridge is complex due to high localized stresses. A strut‐and‐tie model (STM) has been introduced in this paper, which is recommended as an efficient way to analyze the disturbed region. However, predicting the internal forces in the tie members in the STM by integrating stresses was time‐consuming and inefficient. To address this issue, the principle of minimum strain energy was used to analyze the STM of the cable pylon anchorage zone. A simplified method was presented to assess the internal forces in the cable pylon anchorage zone. Moreover, an actual bridge (Cao'e River Bridge) was employed to be analyzed, and the prestressed steel strands in the bridge were obtained by the simplified method. A full‐scale test model of the bridge was fabricated to validate the accuracy of the simplified method. Furthermore, based on the simplified method, the effect of the thickness of front wall, the length of inner opening straight section, the thickness of side wall, the thickness of inner wall and the width of inner opening straight section on the internal force in the tie members in the STM was studied. The results show that the length of inner opening straight section has negligible effect on the internal forces in all tie members. Compared with the thickness of the side wall, the thickness of inner wall and the width of inner opening straight section have limited effect on the internal force of tie members. This study was expected to promote the design of cable pylon anchorage zone.
{"title":"Simplified method for predicting the internal forces in strut‐and‐tie model of cable pylon anchorage zone in a cable‐stayed bridge","authors":"Shengyu Li, Erwin Lim, Zhengqing Chen, Yu Hong, Qianhui Pu","doi":"10.1002/suco.202300926","DOIUrl":"https://doi.org/10.1002/suco.202300926","url":null,"abstract":"The mechanical behavior of cable pylon anchorage zone in a cable‐stayed bridge is complex due to high localized stresses. A strut‐and‐tie model (STM) has been introduced in this paper, which is recommended as an efficient way to analyze the disturbed region. However, predicting the internal forces in the tie members in the STM by integrating stresses was time‐consuming and inefficient. To address this issue, the principle of minimum strain energy was used to analyze the STM of the cable pylon anchorage zone. A simplified method was presented to assess the internal forces in the cable pylon anchorage zone. Moreover, an actual bridge (Cao'e River Bridge) was employed to be analyzed, and the prestressed steel strands in the bridge were obtained by the simplified method. A full‐scale test model of the bridge was fabricated to validate the accuracy of the simplified method. Furthermore, based on the simplified method, the effect of the thickness of front wall, the length of inner opening straight section, the thickness of side wall, the thickness of inner wall and the width of inner opening straight section on the internal force in the tie members in the STM was studied. The results show that the length of inner opening straight section has negligible effect on the internal forces in all tie members. Compared with the thickness of the side wall, the thickness of inner wall and the width of inner opening straight section have limited effect on the internal force of tie members. This study was expected to promote the design of cable pylon anchorage zone.","PeriodicalId":21988,"journal":{"name":"Structural Concrete","volume":"1 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204014","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ultrahigh performance concrete (UHPC) has recently become a major focus garnering substantial attention due to its remarkable mechanical properties. UHPC has been increasingly employed across diverse projects in the construction industry. However, the structural ductility of UHPC members has yet to be fully established and is often compromised by the manifestation of the crack localization phenomenon. This paper presents the flexural test results of five T‐beams and introduces a model for predicting the flexural capacity and failure modes of UHPC T‐beams. The model employs the curvature ductility index as a measurement for evaluating and ensuring the member's ductility. The results show that the flexural behavior of UHPC T‐beams can be characterized by four key points representing cracking, reinforcement yielding, crack localization, and post‐localization capacity. The validity of the model is substantiated by experimental data from this study and complemented by test data collected from the literature. The proposed model is then employed to derive ductility‐oriented design limits, including minimum and maximum reinforcement ratios and minimum localization strain capacity. Finally, the paper summarizes the design recommendations and provides a classification of section conditions, reinforcement limits, localization strain limits, adequate ductility range, and the feasible ductile design range.
超高性能混凝土（UHPC）因其卓越的机械性能而成为近期备受关注的焦点。在建筑行业的各种项目中，越来越多地采用了超高性能混凝土。然而，超高性能混凝土构件的结构延展性尚未完全确定，而且经常因裂缝局部化现象的出现而受到影响。本文展示了五根 T 型梁的抗弯试验结果，并介绍了一种用于预测 UHPC T 型梁抗弯能力和破坏模式的模型。该模型采用曲率延性指数作为评估和确保构件延性的测量方法。结果表明，UHPC T 型梁的抗弯行为可通过代表开裂、钢筋屈服、裂缝定位和定位后承载力的四个关键点来表征。本研究的实验数据证实了该模型的有效性，文献中收集的测试数据也对其进行了补充。然后，利用所提出的模型推导出以延性为导向的设计限制，包括最小和最大配筋率以及最小局部应变能力。最后，本文总结了设计建议，并对截面条件、配筋限制、局部应变限制、足够延性范围和可行延性设计范围进行了分类。
{"title":"Ductility‐oriented design of UHPC T‐beams: Mechanical model and design recommendations","authors":"Mujahed Alsomiri, Zhao Liu, Tao Wang, Jie Meng","doi":"10.1002/suco.202400214","DOIUrl":"https://doi.org/10.1002/suco.202400214","url":null,"abstract":"Ultrahigh performance concrete (UHPC) has recently become a major focus garnering substantial attention due to its remarkable mechanical properties. UHPC has been increasingly employed across diverse projects in the construction industry. However, the structural ductility of UHPC members has yet to be fully established and is often compromised by the manifestation of the crack localization phenomenon. This paper presents the flexural test results of five T‐beams and introduces a model for predicting the flexural capacity and failure modes of UHPC T‐beams. The model employs the curvature ductility index as a measurement for evaluating and ensuring the member's ductility. The results show that the flexural behavior of UHPC T‐beams can be characterized by four key points representing cracking, reinforcement yielding, crack localization, and post‐localization capacity. The validity of the model is substantiated by experimental data from this study and complemented by test data collected from the literature. The proposed model is then employed to derive ductility‐oriented design limits, including minimum and maximum reinforcement ratios and minimum localization strain capacity. Finally, the paper summarizes the design recommendations and provides a classification of section conditions, reinforcement limits, localization strain limits, adequate ductility range, and the feasible ductile design range.","PeriodicalId":21988,"journal":{"name":"Structural Concrete","volume":"33 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204020","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Umang Pulkit, Satadru Das Adhikary, Venkatesh Kodur
Since the world is transitioning toward performance based design, the study of thermo‐hygral behavior of concrete when subjected to real fire becomes crucial. Fire accidents have revealed that nominal fire curves cannot be applied because of varying severity of real fire. In 2008, traveling fire concept was developed in which severity is dependent on heat release rate and fire size. This study explores the effect of fire severity and other concrete properties like strength, aggregate type, and relative humidity. The proposed model has been developed by combining the principles of mechanics and thermodynamics and upon validation with the experimental results, a reasonable agreement has been observed. It can be concluded that severity of fire is directly related to thermo‐hygral behavior of concrete. On the other hand, this study also highlights the influence of type of aggregate and moisture content in addition to the traditional variables like volume fraction of solid and permeability. On studying the influence of type of aggregate, it can be concluded that recycled aggregate concrete performed better than conventional concrete. The integration of proposed model in the performance based design is a leap toward development of resilient structure subjected to dynamic fire conditions.
{"title":"Influence of fire severity and concrete properties on the thermo‐hygral behavior of concrete during fire exposure","authors":"Umang Pulkit, Satadru Das Adhikary, Venkatesh Kodur","doi":"10.1002/suco.202400067","DOIUrl":"https://doi.org/10.1002/suco.202400067","url":null,"abstract":"Since the world is transitioning toward performance based design, the study of thermo‐hygral behavior of concrete when subjected to real fire becomes crucial. Fire accidents have revealed that nominal fire curves cannot be applied because of varying severity of real fire. In 2008, traveling fire concept was developed in which severity is dependent on heat release rate and fire size. This study explores the effect of fire severity and other concrete properties like strength, aggregate type, and relative humidity. The proposed model has been developed by combining the principles of mechanics and thermodynamics and upon validation with the experimental results, a reasonable agreement has been observed. It can be concluded that severity of fire is directly related to thermo‐hygral behavior of concrete. On the other hand, this study also highlights the influence of type of aggregate and moisture content in addition to the traditional variables like volume fraction of solid and permeability. On studying the influence of type of aggregate, it can be concluded that recycled aggregate concrete performed better than conventional concrete. The integration of proposed model in the performance based design is a leap toward development of resilient structure subjected to dynamic fire conditions.","PeriodicalId":21988,"journal":{"name":"Structural Concrete","volume":"6 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204018","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fa‐xing Ding, Xin‐yu Huang, Chen‐jie Gong, Zheng‐bo Pi
Under the influence of wind and horizontal seismic forces, structures such as piers in curved beam bridges, main arches of steel tube concrete arch bridges, and frame columns may experience combined bending‐torsion stress states, affecting the safe usage of the structure. To investigate the mechanical performance of circular concrete‐filled steel tube(CFST) columns under bending‐torsional coupling, a three‐dimensional solid‐shell finite element model of circular concrete‐filled steel tube columns under various bending and torsion ratios (k) was established using ABAQUS software, and validated with existing experiments on such columns under bending‐torsional loading. Parametric analysis was conducted to explore the trends of interface slip and the restraining effect in circular concrete‐filled steel tube columns under different bending and torsion ratios, analyzing the impact of parameters such as the yield strength of steel, concrete strength, steel content in the cross‐section, and shear–span ratio on the combined bearing capacity. The results of the parametric analysis show that: (1) with the increase of k, the relative slip at the interface between the core concrete and the outer steel tube first increases and then decreases, with interface slip leading to a reduction in the load‐bearing capacity; (2) the relative slip at the interface between the core concrete and the outer steel tube first increases and then decreases, with interface slip leading to a reduction in the load‐bearing capacity; (3) with the increase of k, the circumferential and axial stresses in the steel tube surface of the circular concrete‐filled steel tube columns increase, while the shear stress decreases, leading to a transition in the failure mode of the columns from combined bending‐torsional failure to bending‐shear failure. Based on these findings, a practical calculation formula for the bending‐torsional combined bearing capacity of circular concrete‐filled steel tube columns is proposed, offering high calculation accuracy and serving as a reference for the design of such components.
在风力和水平地震力的作用下，曲线梁桥的桥墩、钢管混凝土拱桥的主拱以及框架柱等结构会出现弯扭组合应力状态，影响结构的安全使用。为研究弯扭耦合作用下圆形混凝土填充钢管（CFST）柱的力学性能，利用 ABAQUS 软件建立了不同弯扭比（k）下圆形混凝土填充钢管柱的三维实体-壳体有限元模型，并与现有弯扭荷载下此类柱的实验进行了验证。通过参数分析，探讨了不同弯扭比下圆形混凝土填充钢管柱的界面滑移趋势和约束效应，分析了钢材屈服强度、混凝土强度、截面含钢量和剪跨比等参数对综合承载力的影响。参数分析结果表明(1) 随着 k 的增大，核心混凝土与外层钢管之间界面的相对滑移先增大后减小，界面滑移导致承载能力降低；(2) 核心混凝土与外层钢管之间界面的相对滑移先增大后减小，界面滑移导致承载能力降低；(3) 随着 k 的增大，圆形混凝土填充钢管柱钢管表面的圆周应力和轴向应力增大，而剪应力减小，导致钢管柱的破坏模式从弯曲-扭转联合破坏过渡到弯曲-剪切破坏。基于这些发现，提出了一种实用的圆形混凝土填充钢管柱弯曲扭转组合承载力计算公式，具有较高的计算精度，可作为此类构件设计的参考。
{"title":"Research on the mechanical performance of circular concrete‐filled steel tube columns under bending‐torsional coupling","authors":"Fa‐xing Ding, Xin‐yu Huang, Chen‐jie Gong, Zheng‐bo Pi","doi":"10.1002/suco.202400128","DOIUrl":"https://doi.org/10.1002/suco.202400128","url":null,"abstract":"Under the influence of wind and horizontal seismic forces, structures such as piers in curved beam bridges, main arches of steel tube concrete arch bridges, and frame columns may experience combined bending‐torsion stress states, affecting the safe usage of the structure. To investigate the mechanical performance of circular concrete‐filled steel tube(CFST) columns under bending‐torsional coupling, a three‐dimensional solid‐shell finite element model of circular concrete‐filled steel tube columns under various bending and torsion ratios (<jats:italic>k</jats:italic>) was established using ABAQUS software, and validated with existing experiments on such columns under bending‐torsional loading. Parametric analysis was conducted to explore the trends of interface slip and the restraining effect in circular concrete‐filled steel tube columns under different bending and torsion ratios, analyzing the impact of parameters such as the yield strength of steel, concrete strength, steel content in the cross‐section, and shear–span ratio on the combined bearing capacity. The results of the parametric analysis show that: (1) with the increase of <jats:italic>k</jats:italic>, the relative slip at the interface between the core concrete and the outer steel tube first increases and then decreases, with interface slip leading to a reduction in the load‐bearing capacity; (2) the relative slip at the interface between the core concrete and the outer steel tube first increases and then decreases, with interface slip leading to a reduction in the load‐bearing capacity; (3) with the increase of <jats:italic>k</jats:italic>, the circumferential and axial stresses in the steel tube surface of the circular concrete‐filled steel tube columns increase, while the shear stress decreases, leading to a transition in the failure mode of the columns from combined bending‐torsional failure to bending‐shear failure. Based on these findings, a practical calculation formula for the bending‐torsional combined bearing capacity of circular concrete‐filled steel tube columns is proposed, offering high calculation accuracy and serving as a reference for the design of such components.","PeriodicalId":21988,"journal":{"name":"Structural Concrete","volume":"36 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204019","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The main focus of this study is to assess the slump characteristics of high‐performance concrete (HPC) using decision tree (DT) and support vector regression (SVR) models. In the first step, the models were solely fed via HPC samples to reproduce the slump rates. By coupling phasor particle swarm optimization (PPSO) to main models, hybrid DT‐PPSO and SVR‐PPSO frameworks, simulate the slump rates accurately. Using the correlation of determination and root mean square error (MAE) metrics for the DT, 96.04 and 5.097 were computed, respectively. SVR was obtained at 92.62 and 6.965, alternatively. In the hybrid approach, DT‐PPSO could improve by 3% and 55% in terms of correlation of determination and root MAE, respectively. DT‐PPSO appeared high‐accuracy model compared to others; however, a single DT had more desirable results than SVR. Overall, the advantages of this study encompass its methodological approach, comparative insights, and practical relevance, offering valuable contributions to the understanding and prediction of mechanical slump in HPC.
{"title":"Predicting slump for high‐performance concrete using decision tree and support vector regression approaches coupled with phasor particle swarm optimization algorithm","authors":"Qingmei Sun, Yu Gongping","doi":"10.1002/suco.202300450","DOIUrl":"https://doi.org/10.1002/suco.202300450","url":null,"abstract":"The main focus of this study is to assess the slump characteristics of high‐performance concrete (HPC) using decision tree (DT) and support vector regression (SVR) models. In the first step, the models were solely fed via HPC samples to reproduce the slump rates. By coupling phasor particle swarm optimization (PPSO) to main models, hybrid DT‐PPSO and SVR‐PPSO frameworks, simulate the slump rates accurately. Using the correlation of determination and root mean square error (MAE) metrics for the DT, 96.04 and 5.097 were computed, respectively. SVR was obtained at 92.62 and 6.965, alternatively. In the hybrid approach, DT‐PPSO could improve by 3% and 55% in terms of correlation of determination and root MAE, respectively. DT‐PPSO appeared high‐accuracy model compared to others; however, a single DT had more desirable results than SVR. Overall, the advantages of this study encompass its methodological approach, comparative insights, and practical relevance, offering valuable contributions to the understanding and prediction of mechanical slump in HPC.","PeriodicalId":21988,"journal":{"name":"Structural Concrete","volume":"43 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2024-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204021","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Matthias Hillebrand, Annkathrin Sinning, Josef Hegger
More and more often, semi‐precast reinforced concrete slabs with lattice girders are employed for industrial buildings or bridges, where they are exposed to high cycle fatigue loading. Despite research in recent years that has led to the formulation of an S–N curve for lattice girders, the effects of cyclic loading on semi‐precast slabs have not yet been sufficiently clarified. Moreover, research has so far been limited to single‐span slabs. The effects of continuous slab systems, which are mainly realized in buildings and bridges, cannot be considered in the calculation of fatigue resistance yet. To improve the fatigue design concept for shear and interface shear, theoretical and experimental investigations were conducted at the Institute of Structural Concrete, RWTH Aachen University. In addition to the fatigue behavior of 16 tests under cyclic loading, particular attention is paid to the increase in shear and interface shear resistance at the inner support of continuous slabs. Furthermore, the influences of the support detailing were investigated. The findings illustrate further potential for optimization of the design under cyclic loading.
{"title":"Shear and interface shear fatigue of semi‐precast slabs with lattice girders under cyclic loading","authors":"Matthias Hillebrand, Annkathrin Sinning, Josef Hegger","doi":"10.1002/suco.202400219","DOIUrl":"https://doi.org/10.1002/suco.202400219","url":null,"abstract":"More and more often, semi‐precast reinforced concrete slabs with lattice girders are employed for industrial buildings or bridges, where they are exposed to high cycle fatigue loading. Despite research in recent years that has led to the formulation of an <jats:italic>S</jats:italic>–<jats:italic>N</jats:italic> curve for lattice girders, the effects of cyclic loading on semi‐precast slabs have not yet been sufficiently clarified. Moreover, research has so far been limited to single‐span slabs. The effects of continuous slab systems, which are mainly realized in buildings and bridges, cannot be considered in the calculation of fatigue resistance yet. To improve the fatigue design concept for shear and interface shear, theoretical and experimental investigations were conducted at the Institute of Structural Concrete, RWTH Aachen University. In addition to the fatigue behavior of 16 tests under cyclic loading, particular attention is paid to the increase in shear and interface shear resistance at the inner support of continuous slabs. Furthermore, the influences of the support detailing were investigated. The findings illustrate further potential for optimization of the design under cyclic loading.","PeriodicalId":21988,"journal":{"name":"Structural Concrete","volume":"11 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141930959","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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