Concrete‐filled steel tubes (CFTs) have been used widely in the world in structures of varying heights and configurations, both in low to moderate and high-seismic regions. These elements combine the high strength and ductility of steel with the ability of concrete to efficiently carry compressive loads. The concrete infill delays local and global buckling of the steel tube, while the perimeter steel provides longitudinal and transverse reinforcement for the concrete. This experimental study aims to investigate the three-dimensional seismic response of CFT columns from the onset of damage to the state of complete collapse. A series of quasi-static cyclic and hybrid simulation tests are conducted using the multi-axis substructure testing (MAST) system at Swinburne. The experiments provide valuable data on the seismic response of these elements when subjected to complex load transfer and multi-directional loading during seismic events.
Numerous experimental studies have been performed to examine the behaviour of concrete-filled steel tube (CFT) columns under either pure axial or combined axial-lateral loads. Due to testing difficulties, however, limited data are available from the response of CFT columns under complex time-varying six-degrees-of-freedom (6-DOF) boundary forces during seismic events. This project attempts to address this issue by conducting a series of large-scale multi-axis tests on square and circular CFT columns. A state-of-the-art facility, referred to as the multi-axis substructure testing (MAST) system, is used that it is capable of controlling all six-degrees-of-freedom (6-DOF) boundary conditions in mixed load and deformation modes. The specimens are first subjected to bidirectional lateral deformation reversals that follows the hexagonal orbital pattern suggested in FEMA 461. In the next stage, hybrid simulation is used to provide more insight into the three-dimensional response of these elements under realistic scenarios of seismic events. In the hybrid model, the specimens serve as the first-story column of a symmetrical 5×5 bay 5-story framed building that is subjected to sequential biaxial ground motions with increasing intensities to collapse. The ground motions are the two horizontal components of the 1979 Imperial Valley earthquake recorded at El Centro station. The generated experimental data obtained from this project is used as a benchmark to calibrate the state-of-the-art analytical tools employed in collapse assessment and reliability analysis of buildings constructed with CFT columns.
2015 to present
In this study, a comprehensive literature review on the seismic behaviour of concrete-filled steel tube (CFT) is conducted. These studies consist of experimental and numerical works on different shapes and configurations of CFT columns with various material properties of steel and infill concrete. Most of these studies, however, investigated the columns performance under pure axial or a combination of axial and lateral loads. In this project, multi-axis testing is employed to evaluate the three-dimensional response of CFT columns under complex time-varying six-degrees-of-freedom (6-DOF) boundary forces during seismic events. A total of four half-scale columns including two square and two circular concrete-filled steel tubes (CFTs) are constructed. All specimens have similar axial load bearing capacity and for each of the three types (i.e. square and circular) two identical specimens are tested using quasi-static cyclic and hybrid simulation methods. In the quasi static tests, the specimens are subjected to bidirectional lateral deformation reversals that follow the hexagonal orbital pattern suggested in FEMA 461, combined with axial load variation. The variation of the axial load follows the variation of the lateral drifts. The rotational axes (roll, pitch, and yaw) are controlled in zero-angle to form a double-curvature deformation of the columns. In hybrid simulation tests, a column element identical to the one previously tested in the quasi-static cyclic experiment is used. A half-scale symmetrical 5-story (height of first story h1=2.0m, height of other stories htyp=1.75m) 5×5 bay (column spacing b=4.2m) ordinary moment frame building is selected as the hybrid model. The physical specimens serve as the first-story column of the building, considered as the critical element of the structure. The rest of the structural elements, inertial and damping forces, gravity and dynamic loads and second-order effects are modelled numerically in the computer. An advanced three-loop hybrid simulation architecture that uses OpenSees, OpenFresco and the xPC-Target real-time digital signal processor is implemented. The hybrid model is subjected to biaxial excitations using the two horizontal components of the 1979 Imperial Valley earthquake ground motions recorded at El Centro station. The entire sequence of loading, namely, the gravity load followed by sequential ground motions, is performed and automated using OpenSees. Similar to the quasi-static test, the rotational axes (Roll, Pitch and Yaw) are controlled in zero-angle forming a double-curvature deformation of the column. The hysteretic response behaviours obtained from the quasi-static and hybrid simulation tests are then used for calibrating the analytical models employed in a comparative collapse risk assessment.
The project provides valuable scarce large-scale experimental data of the three-dimensional response of CFT elements under seismic excitations. This significantly advance engineering understanding about damage evolution, global hysteretic behaviour, stiffness degradation, load-bearing capacity, and energy dissipation of the CFT columns when subjected to biaxial bending combined with axial load variations. At a broader scale, this provides direct benefit to building construction industry, building owners, the insurance industry, building code committees and policy makers involved in risk reduction strategies and disaster management.
Swinburne University of Technology
Dr Riadh Al-Mahaidi is a Professor of Structural Engineering and Director of the Smart Structures Laboratory at Swinburne University of Technology. He also holds the position Vice President (International Engagement). Prior to joining Swinburne in January 2010, he was the Head of the Structures Group at Monash University. Over the past 20 years, he focused his research and practice on lifetime integrity of bridges, particularly in the area of structural strength assessment and retrofitting using advanced composite materials. He currently leads a number of research projects on strengthening of bridges using fibre reinforced polymers combined cement-based bonding agents, fatigue life improvement of metallic structures using advanced composite systems and shape memory alloys. He recently started some projects on hybrid testing of structures.
He received a BSc (Hon 1) degree in civil engineering from the University of Baghdad and MSc and PhD degrees in structural engineering from Cornell University in the United States. To date, Riadh published over 180 journal and 230 conference papers. He was awarded the 2012 Vice Chancellor’s Internationalization Award, the WH Warren Medal 2017 for best paper published by Engineers Australia in civil engineering in 2016, the RW Chapman Medals in 2005 and 2010 for best journal publication in Engineers Australia Structural Journal, best paper awards at ACUN-4 (2002) and ACUN-6 (2012) Composites conferences. Prof Al-Mahaidi and his research group won the 2016 Engineers Australia Excellence Award for Innovation, Research and Development (High Commendation) for the $2.1mil Multi-Axis Substructure Testing (MAST) System they built at Swinburne.
Dr Hashemi is a Lecturer of Structural Engineering and the Deputy Director of the Smart Structures Laboratory at Swinburne University of Technology. He holds a Bachelor of Science and Masters of Science from Sharif University of Technology, the highest-ranked technological university in Iran, and a PhD from the University at Buffalo, the State University of New York, USA. His field of research involves the development of knowledge and innovative tools for extreme load performance assessment of complex structures. More specifically, it concentrates on hybrid simulation, where the flexibility and cost-effectiveness of computer simulation are combined with the realism of large-scale experimental testing.
Dr Hashemi’s research experience during the past 8 years has enabled him to make considerable contributions to the advancement of large-scale hybrid simulation and the development of hybrid testing facilities in USA and Australia. He had a leading role in the development of Australia’s first and only 6-DOF hybrid testing facility, known as the Multi-Axis Substructure Testing (MAST) system, at Swinburne. Dr Hashemi won the 2016 Engineers Australia Excellence Award for Innovation, Research and Development (High Commendation) and was awarded the WH Warren Medal 2017 by the Board of the College of Civil Engineers of Engineers Australia for the best paper in the discipline of civil engineering.
Mr Hamidreza A. Yazdi, is a PhD student of Structural Engineering at Swinburne University of Technology. He holds a Bachelor of Science from Isfahan University of Technology and Masters of Science from Yazd University in Iran. He commenced his PhD in February 2015 under the supervision of Dr Javad Hashemi, Prof. Riadh Al-Mahaidi and Prof. Emad Gad. His PhD project involves collapse assessment of concrete-filled steel tube columns through multi-axis hybrid simulation.
Professor Emad is the Dean of Engineering, School of Engineering within the Faculty of Science, Engineering and Technology. Prior to this appointment, he was the Chair of the Department of Civil and Construction Engineering at Swinburne University of Technology. Earlier he was an Associate Professor at Melbourne University and Research Scientist at CSIRO.
Emad is a civil engineer with extensive experience in structural dynamics, residential construction, structural connections, experimental techniques and finite element modelling. His applied research has contributed to the development of several standards and codes of practice. In addition to his teaching and research contributions, he has completed numerous consulting contracts for local and multinational clients.
He is Chair of the Board of the Australian Engineered Fasteners and Anchors Council (AEFAC), Co-Editor of the Australian Journal of Structural Engineering, appointment member of the Victorian Government Building Advisory Council (BAC) and Fellow of Engineers Australia.
Dr Amin Heidarpour is a Senior Lecturer and Head of Structures Group at Monash University. His research focus is on structural and computational mechanics, with specific application to construction materials subjected to extreme actions such as fire, impact, blast and earthquake. Hi is also currently the Coordinator of Engineering for Extremes in the Department.
He received His BSc (Civil) degree in 2002 with Hons 1 from Isfahan University of Technology, Iran, and received his MSc in Structural Engineering from Sharif University of Technology, Iran, in 2004. He received his PhD from the University of New South Wales (UNSW), Australia, in 2008. After receiving His PhD in 2008 till January 2011, he worked as a Research Associate at UNSW’s Centre for Infrastructure Engineering and Safety. In 2011 he moved to the preeminent research group at Monash as a lecturer and was promoted to senior lecturer in 2014.
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