Bond tests of partially encased composite columns

This paper deals with bond behaviour at the steel-concrete interface of partially encased composite columns. The topic is especially interesting to determine the stress transfer between the two materials at sections where composite structural elements are connected, such as in a beam-column joint, and to ensure a short transfer length to attain the strength of the composite section. The few experimental tests in the technical literature usually concern other types of composite columns. The Authors therefore designed and carried out experimental bond tests to investigate the transfer mechanism and ascertain the reliability of some code provisions (Eurocode 4 [5]; New Italian Code [8]) concerning the design value of bond strength for partially encased columns. A suitable test set-up was designed to measure the shear stresses transferred to the steel profile and the slip between the two materials, allowing compression or tension to be applied to concrete according to monotonic or cyclic load history. The test results give interesting information about the bond stress-slip relationship and bond strength; the cyclic tests highlight the effect of seismic action and indicate considerable degradation of strength and stiffness.