New insights into the mechanism of load introduction into concrete-filled steel tubular column through shear connection

• New mechanism of load introduction from shear connection to concrete filled columns.
• Assumed load introduction mechanism in EN 1994-1-1 shown not correct.
• Load introduction through column above connection, full column length can be used.
• Complete load introduction can be achieved in almost all concrete filled columns without mechanical shear connectors.

This paper presents the results of an extensive numerical and analytical study to re-investigate the mechanism of load introduction into concrete-filled tubular column through shear connection. The new mechanism of load introduction revealed from this research indicates that the shear load from the connection is introduced through the column length above and within the connection. This is different from the currently assumed mechanism of load introduction from underneath the connection. In fact, a simple free-body diagram analysis would demonstrate that the currently assumed load introduction mechanism is not possible. The results of the numerical simulations also indicate that the load introduction length above the connection is unlimited and can be as long as the entire column height. Based on the new load introduction mechanism and the numerical simulation results, the maximum amount of load introduced into the concrete core can be calculated as the bond strength multiplying the entire steel tube/concrete core contact surface area for the entire column length above and including the connection. Under the new load introduction mechanism and using representative values of column dimensions and concrete cylinder strength, it has been demonstrated that complete load introduction can be achieved in almost all practical arrangements of concrete filled tubular construction.