Fire behaviour of non-welded concrete-filled-tube columns with strip connectors

Conventional concrete-filled-tube columns may have welding defects when welders of limited skill have been involved in their production; such defects could cause a rapid degradation of the columns' strength during a fire. In the study reported in this paper, non-welded columns with mechanical strip connections were developed. Their structural performance, plus that of a typical welded column, was evaluated under both ambient and elevated temperatures. Axial loads were applied to all specimens; for fire resistance the axial load ratio was 40% and an ISO 834 standard fire curve was applied without fire protection. The non-welded columns with mechanical strip connections showed 15% higher strength under ambient temperature and resisted 40 min longer under elevated temperature compared to the typical welded column. Also, local buckling by compression was barely observed in the non-welded columns, whereas a large buckling was shown in the typical welded column under both ambient and elevated temperatures. It is concluded that non-welded columns with mechanical strip connections provide a viable way to avoid the welding problems of typical concrete-filled-tube columns, providing good performance under fire without fire protection.