Axial load transfer in non-slender ultra-high-strength concrete columns through normal-strength concrete floor slabs

Three slab-column specimens, which represent interior, edge, and corner connections, and three isolated column specimens were tested to investigate the axial load transfer in non-slender ultra-high-strength concrete (UHSC, f_c^′ ≈ 200 MPa) columns through normal-strength concrete (NSC, f_c^′ ≈ 50 MPa) slabs. The test results showed that the confinement of the slab-column joint from the surrounding slab increased the axial capacity of the column even though the column strength (f_c^′ ≈ 200 MPa) as well as the ratio of the column concrete strength to the slab concrete strength f_cc^′/f_cs^′≈4.0 are very high. This strength enhancement is a function of the degree of joint confinement provided by the surrounding slab, and even corner slab-column connections showed some degree of strength enhancement. The experimental results from this study and from other researchers were also compared with current code approaches in the ACI Code (ACI 318-14) and CSA Standard (CSA A23.3-14). These approaches were found to be conservative and hence represent lower bound predictions for design purposes for corner and edge slab-column connections. It was found that the ACI Code approach can give unconservative predictions for interior slab-column connections for cases with the slab carrying loads. The CSA Standard approach provides reasonable lower bound predictions for interior slab-column connections, even for cases where the slab is loaded.