Experimental and analytical assessments of force transfer mechanisms in CFST columns with blind-bolted shear connections

This paper presents an experimental investigation into the load transfer behaviour of concrete-filled steel tubular (CFST) columns with blind-bolted shear connections. Eight large scale load transfer tests are described, including two on welded reference specimens. The influence of the connection type as well as the column length above and below the connection are directly examined through a detailed assessment of the failure modes, load-displacement response, and strain development. The results show that blind-bolted connections, including standard configurations, can achieve full load transfer and activate the complete composite resistance of the CFST column, whereas welded connections were limited by insufficient bond interaction. Extended blind-bolts are found to further enhance the load transfer efficiency by mobilising a larger concrete region and reducing the local deformation in the tubular column. Although increasing the upper column length improves the column strength in welded specimens, the results indicate that it has a limited influence on blind-bolted columns once full composite action is achieved. Finally, based on the results, the suitability of existing design provisions associated with idealised conditions, for predicting the strength of CFST columns with blind-bolted connections, are examined and discussed. • Load transfer in CFST columns with blind-bolted connections studied via large-scale tests. • Effects of connection type and column lengths above and below the connection examined. • Blind-bolted connections provide efficient load transfer and enhance concrete participation. • Effective load transfer length identified for CFST column with bolted connection. • Detailed assessment with provisions from codes of practice made for load transfer capacity.