Size effect study of the fracture properties of steel fiber reinforced concrete using a novel 3D mesoscale modelling approach

Significance 

While concrete remains the most popular and widely used construction material, significant research efforts have been devoted to improving concrete properties to meet current construction needs. To this end, steel fiber reinforced concrete (SFRC) has been developed. Unlike conventional concrete, SFRC consists of fine, short and high-strength discontinuous steel fibers randomly distributed in its matrix. These fibers contribute to the superior toughness, strength and ductility properties of SFRCs, making them suitable for engineering structures.

Many parametric tests about the characteristics of steel fibers, such as slenderness and shape, have been extensively carried out to enhance the mechanical performances of SFRC under different loading conditions. Likewise, the amount of experimental and theoretical research on the properties of these structures under different loading conditions has increased in the past decades. However, most experimental studies, especially those on large-sized SFRC members, are still limited in terms of technique, high cost and test error.

Numerical simulation is acknowledged as an effective approach for understanding the mechanical properties and responses of SFRC members, but most existing numerical models are unsuitable for studying the size effect law of SFRC members in terms of fracture characteristics. With the growing demand for large-size concrete structural members, the size effect law is considerably significant to understand the fracture and tensile properties of SFRC. Moreover, it requires a high-precision modeling approach, which is currently lacking.

On this account, researchers at the Nanjing University of Aeronautics and Astronautics: Dr. Zhangyu Wu and Prof. Hongfa Yu, in collaboration with Prof. Jinhua Zhang from the Southeast University of China, Prof. Xinguo Liu at the PLA Rocket Force University of Engineering, and Prof. Qin Fang from Army Engineering University of PLA, numerically investigated the size effect on the fracture properties of notched SFRC structural members under quasi-static bending loading. A novel three-dimensional (3D) two-phase mesoscale model considering the effects of random orientation and distribution of steel fibers in the concrete matrix was developed by the research team to realize their numerical investigation. The work has been published in the international journal, Engineering Fracture Mechanics.

In their approach, a generation algorithm for the 3D mesoscale model as well as supporting methods was developed. The interfacial relationship between the concrete matrix and the steel fibers was described using a new coupling method. The proposed 3D mesoscale model was validated against the available test data and then employed to perform various numerical simulations of the flexural behaviors of the SFRC beams with different depths: 30, 60, 90, 120 and 150 mm. The numerical study was performed regarding the fracture process zone evolution, load versus cracking mouth opening displacement curve, fracture failure patterns, and nominal flexural strength.

The authors reported the negligibility of the size effect on the fracture patterns of the SFRC members and a decrease in the nominal flexural strength with an increase in the beam depth from 30 to 150mm. The effectiveness of the newly proposed coupling method in simulating the relationships and interfacial behaviors between the concrete matrix and steel fibers was demonstrated. The load versus cracking mouth opening displacement curve entailed three key segments: the hardening stage, linear elastic and post-softening segments.

The enhancing effects of the steel fibers was more pronounced in the hardening stage before being removed gradually from the matrix of the concrete during post-softening stage. The role of the discontinuous steel fibers in suppressing the cracking propagation was revealed and was attributed to the gradual propagation of the stress along the beam central line. As a result, distributing the steel fibers in the weak zone improved the fractural toughness properties of the structural members.

In summary, the analysis of the size effects provided an efficient approach for evaluating the fractural properties of notched SFRC beams using a 3D mesoscale modeling approach. The size effect on the nominal flexural strength of the beam could also be evaluated using Bazant’s size effect law and the simulation results agreed with the corresponding test data. In a statement to Advances in Engineering, the authors explained that the new proposed mesoscale modeling approach would contribute to advanced studies on the mechanical properties and performance of SFRC to expand their application scope.

Size effect study of the fracture properties of steel fiber reinforced concrete using a novel 3D mesoscale modelling approach - Advances in Engineering

About the author

Dr. Jinhua Zhang is a professor of Civil Engineering at the Southeast University, China. He earned his Ph.D. in civil engineering from PLA University of Science and Technology, China. He is an active member of the International Association of Protective Structure (IAPS).

His main research interests are related to the three-dimensional (3D) mesoscale modelling approach of engineering material, the computation theory and designation method for engineering structure under severe dynamic loads, the protection technology against impact and blast loading. He hosted and participated in several research projects of National Natural Science Foundation.

Through his research he has presented several contributions in several research fields, including the establishment of 3D random mesoscopic model, the analysis method for the macro- and micromechanics of engineering material and structure under intense dynamic loading, and the designation and application of new material and structure in protection engineering. He has published more than 70 journal and conference papers.

About the author

Dr. Xingguo Liu is an Associate Professor in the School of Rocket Force University of Engineering of China. He obtained the PhD degree in Aerospace Propulsion Theory and Engineering in 2019. He is an active member of the Chinese Society of Astronautics.

His main research interests are related to mesoscopic mechanical behavior and damage mechanism analysis of composite materials. He hosted and participated in several research projects at the provincial and ministerial levels. Through his research he has presented several contributions in several research fields, including the composite solid propellant damage model, damage quantitative assessment method. He has published more than 30 papers in academic journals at domestic and foreign, and obtained 6 authorized Chinese invention patents and software copyrights.

About the author

Zhangyu Wu is a Ph.D. candidate in the College of Civil Aviation at the Nanjing University of Aeronautics and Astronautics (NUAA) in China. He obtained his master degree in the College of Aerospace Engineering at NUAA in 2019. He has been awarded the Chinese government scholarship funded by the China Scholarship Council to pursue study in the Department of Civil, Environmental & Geomatic Engineering at the University College London of UK from 2021 to 2022. His main research interests are focused on static- and dynamic behavior and failure mechanism of coral aggregate concrete using mesoscale modelling approach. He hosted and participated in several research projects of National Natural Science Foundation, Jiangsu Innovation Program for Graduate Education, etc. So far he has co-authored more than 30 papers in scientific journals and conference proceedings.

About the author

Dr. Hongfa Yu is a professor in the College of Civil Aviation at the Nanjing University of Aeronautics and Astronautics (NUAA) in China. After he has completed a BEng degree from the Department of architectural Engineering at the Shenyang Jianzhu University (SJU) of China in 1985, he worked as an Associate Research Fellow in the Qinghai Institute of Architecture and Building Materials of China. He joined the School of Materials Science and Engineering at SJU in 1998, and was promoted to Professor in 2000. He did his Ph.D thesis entitled “Study on High Performance Concrete in Salt Lake: Durability, Mechanism and Service Life Prediction” and obtained PhD degree in Structural Engineering from the School of Materials Science and Engineering at the Southeast University of China in 2004. His thesis led him to receive the distinction of receiving the “Excellent Doctoral Dissertation” Award of Jiangsu Province and the “National Excellent Doctoral Dissertation Nomination” Award. After that he got a position as a Professor in the Department of Civil Engineering at NUAA, and served as the Chairman of the department from 2005 to 2010.

As an active researcher and academic, he is the Vice President of China Magnesite & Material Association (CMMA), and the member of many professional associations, including the Architectural Society of China, the RILEM (International Union of Laboratories and Experts in Construction Materials, Systems and Structures) China Chapter, the American Concrete Institute (ACI) China Chapter, etc. He is the Research Fellow at the Qinghai Institute of Salt Lakes, Chinese Academy of Sciences (CAS), and was involved in the Hundred Talent Project of CAS from 2008 to 2013. He was also a Distinguished Professor of “Kunlun Scholar” in Qinghai Province (China) from 2012 to 2015. Currently he is also working in the School of Civil Engineering at the Qinghai University as a Full professor.

His main research interests are focused on new cementitious material, civil engineering material and structure, micromechanics of concrete, durability and service-life prediction of reinforced concrete structure, etc. He hosted and participated in several research projects of National Natural Science Foundation. Through his research he has presented several contributions in several research fields, including the preparation method for Magnesium cementitious material and new concrete material, modified chloride-diffusion theory and concrete durability, and micromechanics of concrete. He developed the Life prediction software “ChaDuraLife V1.0” which is suitable for the reinforced concrete structure in chloride environment, and has employed it in the designation of the Dalian Bay Undersea Tunnel of China. He also developed the micro- and macromechanics calculation software “ChaITZV1.0”, which can provide comprehensive result data and calculation formula for the interfacial transition zone (ITZ) of concrete. He has edited three books and co-authored more than 400 papers in scientific journals and conference proceedings, and obtained more than 30 authorized Chinese invention patents.

About the author

Dr. Qin Fang is a professor of Civil Engineering at the Army Engineering University of PLA, China. He earned his Ph.D. in civil engineering from PLA University of Science and Technology, China.

Dr. Fang has more than 40year’s experience in teaching and researching in the aspect of blast-resistant structures. His main research interests are focused on the protective structures under severe dynamic loads, including considerations of both survivability and fragility aspects of military and civil facilities subjected to projectile penetration, blast and shock impact. He has written more than 400 journal and conference papers and published two books entitled Concrete Structures under Projectile Impact and UHPCC Under Impact and Blast. His work has been widely used in the construction of the facilities and also applied in Chinese codes for blast-resistant structures.

Currently, he is a fellow of the International Association of Protective Structures and served as a member of the executive board of International Association of Protective Structures and vice chairman of the Protective Engineering Division of China Civil Engineering Society.

Reference

Zhang, J., Liu, X., Wu, Z., Yu, H., & Fang, Q. (2022). Fracture properties of steel fiber reinforced concrete: Size effect study via mesoscale modelling approachEngineering Fracture Mechanics, 260, 108193.

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