Seismic tests and nonlinear model of beam-CFDST column joints with blind fasteners

Significance 

Composite materials combine two or more materials to produce improved properties derived from the individual material properties. Over the past decades, a significant amount of research has been devoted to developing new composites and improving the properties of the existing ones. Recently, a novel concrete-filled double skin steel tubular (CFDST) composite has been developed by replacing a section of core concrete in concrete-filled steel tubular (CFST) with an inner steel tube. Thus, CFDST has improved bending stiffness, lower-self weight and improved fire resistance with broader application prospects than conventional CFST. To date, substantial research on CFDST structures has been carried out to deduce their mechanical properties. However, to increase the practical application of CFDST, there is a need for systematic research on both CFDST members and joints.

Generally, welded rigid joints or pinned connections commonly used in engineering practice fail to achieve the desired ductility under seismic actions. It also requires a large number of site welding that further possess construction complexities. Pinned connections fail to fully utilize beam capacity due to their inability to transfer the bending moment. To this end, blind fasteners have been adopted to solve these problems, and their applicability in CFDST has been experimentally investigated. These connections were found to improve mechanical performance under seismic actions. Nevertheless, static loading tests, which are commonly used, fail to reveal the dynamic performance of these connections under earthquakes. This can be addressed by conducting pseudo-dynamic tests and developing analytical models to estimate seismic performance, an area that is yet to be explored due to the lack of pseudo-dynamic tests on blind fastened CFDST column joints/connections.

To address these challenges, Professor Jingfeng Wang, Dr. Wanqian Wang and Dr. Lei Guo from Hefei University of Technology conducted pseudo-dynamic tests to investigate the dynamic response of beam-CFDST column joints with blind fasteners. They commenced their research work by prefabricating a series of joint specimens. The seismic test was performed to establish the effects of different types of end plates, beams and column hollow ratios. Analytical models were also developed to estimate the seismic behaviors of the specimens. The analysis of the shear strength-panel zone angle relationship based on the equivalent method involving modifying the shear strength via yield mechanism. The proposed strategy was finally validated by comparing the test and analytical model results. Their work is currently published in the Journal of Building Engineering.

The researchers reported that the blind bolted beam-CFDST column joints exhibited favorable seismic behaviors. An increase in the column hollow ratio resulted in a moderate increase in the ultimate strength, bearing capacity and initial stiffness of the specimen attributed to the presence of steel bar truss deck (SBTD). As a result, the specimen with extended end plated exhibited higher ultimate strength stiffness and bearing capacity than that with a flush endplate. The main failure modes of the bolted connections were identified: warpage of the end plate, local buckling in the beam flange, local crushing and crack in the SBTD slab. More importantly, the authors were the first to develop the analytical model for predicting the shear feature of CFDST joint panel zone, in which two potential yield mechanism of outer tube were accounted to derive the shear strength of confined compression strut. The component method was also employed to calculate the rotational performance of the joint. Finally, a nonlinear model was finally established, which could accurately predict the hysteresis curves of the connections under dynamic loads.

In summary, the researchers carried out pseudo-dynamic tests to establish the failure mechanism and dynamic response of a series of blind bolted connections to CFDST columns. The analytical models accurately predicted the seismic performance of the test specimens. The good agreement between the analytical and test results provided an effective method for assembling CFDSR column to beam connections whose joint performance under different loadings can be accurately predicted by the analytical model. In a statement to Advances in Engineering, the authors explained that the results would contribute to enhancing the practical applications of novel CFDST composites.

Seismic tests and nonlinear model of beam-CFDST column joints with blind fasteners - Advances in Engineering
FIGURE 1 Shear behavior of joint panel zone
Seismic tests and nonlinear model of beam-CFDST column joints with blind fasteners - Advances in Engineering
FIGURE 2 Yield mechanism of outer tube
Seismic tests and nonlinear model of beam-CFDST column joints with blind fasteners - Advances in Engineering
FIGURE 3 Initial stiffness model for blind bolted composite connection to CFDST column

About the author

Prof. Jingfeng Wang is the dean of college of civil Engineering, Hefei University of Technology. He has a Ph.D. degree from Tongji University and a post-doctor experience from Tsinghua University. From 2008 to 2012, he was invited as a senior visiting professor at University of Illinois, Urbana-Champaign, America and University of Western Sydney, Australia.

Prof. Wang’s main research focus is on steel and composite structures, new material and prefabricated technology, earthquake resistant and disaster prevention. He has published more than 200 international and national articles, 15 invention patents, 12 books and 25 national, industrial and local standards. He acts as editors of four international and national journals. He has hosted more than 60 scientific projects, including National Nature Science Foundation, New Century Excellent Researcher Award Program and Anhui Collaborative Innovation Program, etc.

About the author

Lei Guo is now a Ph.D candidate of structural engineering in Hefei University of Technology. He has published more than 30 international and national papers, and developed a solid foundation in professional knowledge and skills of structural engineering during his Ph.D period. Up to now, he has got many awards such as LIU Huixian Earthquake Engineering Scholarship (2021), National scholarship for Ph.D student (2019, 2020), Outstanding graduate, etc. In 2021, he gained the funding of China Scholarship Council and acted as a visiting student at the University of British Columbia under the supervision of Prof. Tony T.Y. Yang.

Dr. Guo’s research is mainly within the steel and composite structures and energy dissipation technology, especially focusing on the assembled joints and frames using blind bolts, development of novel metallic damper and seismic strengthen of existing buildings. He is dedicated to contributing high-quality and advanced scientific research to the world.

About the author

Wanqian Wang is now a Ph.D candidate of structural engineering in Hefei University of Technology. She has published more than 30 international and national papers during her Ph.D career. In 2021, she gained the funding of China Scholarship Council and acted as a visiting student at the University of British Columbia under the supervision of member of the Canadian Academy of Engineering, Prof. Carlos Ventura.

Dr. Wang currently works on the projects of shear wall, cold-formed steel structures, green rural residence, lightweight building materials and seismic design at Hefei University of Technology. She is devoting herself to scientific research and hopes to contribute more meaningful achievements to the world.

Reference

Wang, J., Wang, W., & Guo, L. (2022). Seismic tests and nonlinear model of beam-CFDST column joints with blind fastenersJournal Of Building Engineering, 45, 103415.

Go To Journal Of Building Engineering

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