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Slab-column connections were tested under combinations of gravity and lateral loads to investigate the effect of using high-strength concrete slab on the structural behavior of the slab-column connections. The variables selected for this study are the strength of concrete slab, the flexural steel reinforcement ratio, and the moment to shear ratio. As the concrete slab strength increases from 35 MPa to 75 MPa, the shear strength increases by 7% and 15% for loading cases of zero and high moment-shear ratio, respectively. However, the current design codes provisions for interior connections have greatly reduced the factor of safety regarding the punching shear strength of high-strength concrete slabs. The use of high-strength slab has a significant effect on the load-deflection characteristics for specimens subjected to high-moment. The ultimate deflection increases and the failure mode becomes less sudden and more gradual, if high-strength concrete slab is used. The first yielding for specimens constructed with high-strength concrete slab occurs at loads considerably lower than those for specimens constructed with normal-strength concrete. The radius of yielding significantly increases for specimens constructed with high-strength concrete slab; therefore, the steel reinforcement is utilized better and a much more desirable steel stress distribution is produced in the area around the column by the use of high-strength slab. In the meantime, connection displacement and rotation ductility increases by 75% for specimens with high-strength concrete slabs under high moment. Therefore, the use of high-strength concrete slabs can be justified economically when good ductility and higher levels of absorbed energy of slab-column connections are required under high moment-shear ratios. On the other hand, the use of high-strength concrete slabs for slab-column connection subjected to gravity loads only is not recommended because of the small increase of the punching shear capacity of the connection compared with the high cost of using high-strength concrete.

Structures located in low seismic zones require only nominal ductility, whereas for structures located in seismic zones significant ductility is required. Ductility of concrete increases as strength increases; the use of high-strength concrete in structures located in moderate to high seismic zones may be advantageous for increasing resistance and energy dissipation, which can be used to enhance ductility and seismic energy. Four interior slab-column connections were tested under simulated earthquake-type loads to investigate the effect of using high-strength concrete in connections. Two slabs were made with high-strenght concrete of 75 MPa and two were made with normal strenght concrete of 35 MPa. The four specimens were made with high-strength concrete columns. Two slabs were reinforced with a steel reinforcement ratio of 0.5 percent and the other two with 1 percent. As concrete slab strength increases from 35 to 75 MPa, the ductility by displacement and rotation increases by 100 and 125 percent, respectively. Also, shear strength, moment capacity, drift percent, and rotation capacity increase by 20, 31, 37, and 50 percent, respectively, when high-strength concrete slabs of 75 MPa are used instead of 35 MPa a normal strength concrete.