Behaviour and design of bolt-coupler connections under compression in prefabricated CFST columns

The paper presents the investigated results of bolt-coupler connections under compression experimentally. Bolt-coupler connections have been developed recently for prefabricated column-to-column (PCC) connections to simplify the construction process of prefabricated concrete-filled steel tubular (CFST) columns and to transfer the upper column load to the bottom column through bolt-coupler connections. However, the behaviour of bolt-coupler connections under compression has not been investigated in the past although there are some experimental and numerical studies conducted on bolt-coupler connections under tension. To address these research gaps, the behaviour of bolt-coupler connections under compression has been investigated. The main parameters considered in this study are bolt diameters (M16, M20, M24), bolt grades (8.8, 10.9 grade), gap inside the coupler between two bolts of bolt-coupler connection (0, 10, 20 mm), and coupler grade (5.6, 8.8 grade). It is observed that the ultimate capacity of bolt-coupler connections is reduced significantly with an increase in the bolt gap inside the coupler of the bolt-coupler connection. Based on the test data, a design equation is developed to determine the design capacity of bolt-coupler connections under compression, which will be very useful in designing the PCC connections of sustainable prefabricated CFST columns