Punching shear resistance of post-tensioned steel fiber reinforced concrete flat plates

The paper presents results of an experimental study on punching shear behavior and resistance of post-tensioned steel fiber reinforced concrete (SFRC) slab–column connections using unbonded tendons. Eight large-scale specimens were tested, in which fiber amount and concrete compressive strength were varying. The results show that an increasing amount of steel fibers results in an increase of punching shear resistances and energy absorption capacity and contributes to the improvement of slab–column connection integrity. The paper presents also a semi-empirical formula for estimation of punching shear resistances of post-tensioned SFRC slab–column connections with unbonded tendons. Along with taking into account effects of concrete strength, prestress, and vertical component of prestressing force on the total punching shear resistance, the proposed design formula considers also such factors as: volume of steel fibers, size effect, effect of span to effective slab depth ratio, and effective depth of tendons. The formula enables an adequate estimation of real resistances of post-tensioned slab–column connections, either with or without steel fibers.