Bond Differences at Two Ends of Steel Fiber-Reinforced Concrete Columns

To avoid certain difficulties in concrete-encased composite construction such as interference between the shaped steel and reinforcing bars and poor concrete placement quality, steel fiber-reinforced concrete-encased composite (SFRCEC) section was proposed by replacing the steel reinforcing bars with steel fibers. The bond property between shaped steel and steel fiber-reinforced concrete (SFRC) is crucial to composite members. According to the pushout test of 20 specimens, this paper studies the bond property and interface damage between shaped steel and SFRC. The load-slip curve, bond strength, interface energy dissipation, and other important data are obtained. The differences at the interface from uneven bond force distribution are analyzed. The load and slip are not always the same at different locations along the interface. The influences of embedded length of shaped steel (Le), steel fiber ratio (rho(sf)), and the thickness of concrete cover (C-ss) are also discussed. For every 100 mm increase in Le, the slip difference between two ends increases by 0.257 mm, which shows a linear growth. When the ratio of steel fiber is between 1 and 3%, the thickness of concrete cover is between 20 and 60 mm, with bigger C-ss or higher rho(sf), and the difference within a unit length becomes smaller. Increasing the rho(sf) or the C-ss will enhance the bond and constraint between SFRC and the steel and give higher crack resistance to the concrete cover. This also helps the bond stress distribution along the interface, which means a more balanced loading distribution between two materials at the interface under maximum loading.