Capacity Difference of Circular Hollow Section X-joints Under Brace Axial Compression and Tension
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International Journal of Steel Structures https://doi.org/10.1007/s13296-020-00374-w
Capacity Difference of Circular Hollow Section X‑joints Under Brace Axial Compression and Tension Bida Zhao1,2 · Chengqing Liu2,3 · Zeyang Yao1 · Yangzheng Cai1 Received: 22 October 2019 / Accepted: 5 July 2020 © Korean Society of Steel Construction 2020
Abstract In the current regulations, there are two methods to describe the relationship between the two capacities of circular hollow section (CHS) X-joints under brace compression (Nuc) and brace tension (Nut): Nut = Nuc and Nut = fNuc (f is a coefficient larger than 1.0). In order to study the difference between Nuc and Nut of the X-joints, two experimental tests (monotonic compression load and cyclic axial load) and finite element (FE) analysis are performed to study the difference between Nuc and Nut. Test results show that the ultimate capacity is close to the resistance load corresponding to the connection deformation of 3% of chord diameter (limit deformation criterion). Both two specimens showed good deformability and ductility. The final failure modes are chord wall buckling and chord wall tearing for the specimens under monotonic compression load and cyclic axial load, respectively. Test and FE results indicate that Nut is significantly larger than the corresponding Nuc, and the ratio Nut/Nuc increases as the chord radius-to-thickness ratio γ increases. It is also found that the ratio Nut/Nuc increases as the brace-to-chord diameter ratio β increases, especially β larger than 0.8. Based on test and FE data, a new equation for the ratio Nut/Nuc is proposed to overcome the defect of the current specifications that cannot consider the influence of β. The equation is proved to be reasonable by tests and FE results. Keywords Circular hollow section (CHS) X-joints · Brace compression · Brace tension · Tensile-to-compressive capacity ratio · Experimental test · Finite element (FE) analysis
1 Introduction Unstiffened tubular joint are used extensively in all kinds of offshore and civil engineering structures, but the ultimate strength of these unstiffened tubular joints are usually relative low due to their structural characteristics of the brace welded * Chengqing Liu [email protected] Bida Zhao [email protected] Zeyang Yao [email protected] Yangzheng Cai [email protected] 1
College of Civil Engineering and Architecture, Zhejiang University of Technology, Hangzhou 310014, China
2
School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China
3
Key Laboratory of High-Speed Railway Engineering of Ministry of Education, Chengdu 610031, China
directly to the chord surface. Hence, strength and suitable strengthening techniques are one of the research priorities of tubular joints (Liu et al. 2017, 2018; Liu and Ma 2017). Based on pressure vessel plastic limit analysis concept (Gerdeen 1980), Choo et al.(2003) presents a new method to define the capacity of thick-walled circular hollow section (CHS) unstiffened X-joint under brace axial force. It
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