Experimental investigation of flexural buckling behaviour of self-compacting lightweight concrete-filled cold-formed built-up box section (CFBBS) columns

This paper presents an experimental investigation of the flexural buckling behaviour and resistance of innovative self-compacting lightweight concrete (LWSCC)-filled cold-formed built-up box section (CFBBS) columns. A series of sixteen LWSCC-filled CFBBS columns and four reference hollow columns formed by two nested asymmetric lipped channel sections using breakstem rivets at flanges with various member relative slendernesses ratios, concrete strengths and section sizes were tested under pin-ended boundary conditions. Material tests and initial global geometry imperfection measurements were carried out and reported in present study. The failure modes and deformation developments, lateral deflection distribution along the column specimens, flexural buckling resistance and load-end shortening relationship of the specimens were scrutinised and discussed concerning the effect of parameters and the associated coupling effects. Furthermore, a comprehensive strain analysis was conducted and reported based on the longitudinal and lateral strain developments at both compression and tension zones under flexure; it was found that the composite action abated as the member length increased. Finally, as there is no existing design codes for LWSCC-filled CFBBS columns, the experimental results were used to evaluate the applicability of relevant international codified provisions, including Eurocode (EC4), Australia/New Zealand Standard (AS/NZS 2327) and America Specification (AISC 360-16). It was found that AS/NZS 2327 yielded the most accurate and moderately scattered predictions while the predictions from EC4 were found to be the most scattered but with reasonable accuracy and those from AISC 360-16 were overly conservative, albeit the least scattered among these design codes.