Experimental study on demountable CFST K-joints designed with blind bolts

Abstract

Developing demountable structures that enable the replacement of damaged components and the reuse of intact parts in their extended service-life is an effective approach to reducing carbon emissions and prompt sustainable construction. This paper presents an experimental investigation on the behavior of novel demountable K-joints formed by concrete-filled steel tubular (CFST) chords and circular hollow sectional (CHS) braces connecting through blind bolts and curved endplates. A series of tests are conducted on the demountable K-joint specimens, where pined supports are applied at the ends of two braces whilst one end of the chord is under tension and the other is left free. Based on the tests, the failure mode, the ultimate capacity, the joint stiffness and the deformability of the demountable joints are investigated. After the initial loading, the damaged components are disassembled and replaced by new ones to form new joints which are then loaded again for the 2nd and 3rd service periods. It is found that the differences in joint ultimate capacity during multiple service periods are generally within 5%, testifying the effective reuse of the main structural components such as CFST chords and blind bolts. The effects of important parameters related to the demountability design, the joint configuration and the material strengths are evaluated through the tests. Finally, a simplified ultimate capacity prediction method for such demountable CFST K-joints is proposed and validated.