High Strength Concrete (HSC) slab–column connections with relatively low concrete strengths compared to today’s capabilities have been tested under seismic-type loading in the past. Herein, the hybrid use of HSC with compressive strength around 120 MPa and Normal Strength Concrete (NSC) is investigated through three reversed horizontal cyclic loading tests with different geometries of the HSC region and a reference NSC specimen. The results show that HSC applied in the vicinity of the column can significantly enhance the seismic performance of slab–column connections. The best result in terms of drift capacity and economic use of HSC was achieved in the case of full-depth HSC extended from the column’s face up to 2.5 times the effective depth. Drift ratios up to 3.0% were achieved. A comparison with previous tests showed that the hybrid use of HSC and NSC can achieve similar results to the provision of punching shear reinforcement.

Advances in concrete technology during the last decades have resulted in the development of materials with enhanced mechanical properties, such as High Strength Concrete (HSC), Fibre Reinforced Concrete (FRC) and Ultra-High Performance Fibre Reinforced Concrete (UHPFRC). The application of these materials in flat slabs, which are a popular structural solution in Reinforced Concrete (RC) buildings worldwide, has the potential of significantly reducing raw material consumption by enabling the design of slenderer and therefore lighter structures. However, flat slabs are susceptible to punching shear failure, which is a complex phenomenon that remains challenging, even though significant efforts have been made to experimentally study it. For advanced concrete materials (HSC, FRC and UHPFRC), the challenge is further accentuated by the continuous and rapid development of these materials. With the purpose of identifying and highlighting gaps in the published literature, a review of tests with HSC, FRC and UHPFRC slab-column connections in non-seismic and seismic loading applications is presented in this paper. It is shown that future research directions in this field include, among others, testing thicker slabs, HSC slabs with higher concrete compressive strength, HSC combined with FRC and several more cases related to seismic loading conditions.

The behavior of flat slab – column connections under seismic-type loading is complex and not exhaustively studied. Among the many variables involved, this paper focuses on the influence of flexural reinforcement on the seismic performance of such connections. Three specimens were tested and analyzed in conjunction with two previously published specimens tested under similar conditions, under constant vertical loading and cyclic horizontal displacements, resulting in a total of five specimens. Among these specimens, the top flexural reinforcement varied from 0.64% to 1.34% and the approximate value of applied gravity shear ratio (GSR, equal to the ratio between the applied gravity load and the punching shear resistance) was around 55%. Two of the specimens (low and median reinforcement ratio) were also reinforced with headed studs against punching shear to study the unbalanced moment transfer capacity of the slab – column connections. The specimens are described and analyzed in detail. The results show that the performance under cyclic loading is affected by the amount of flexural reinforcement, even though GSR was almost the same for all specimens. It is shown that current code-based approaches for the estimation of unbalanced moment capacity, as well as drift capacity, are generally safe sided for the specimens under investigation but do not fully capture the trends observed in the experimental campaign.

Reinforced concrete flat slabs are used worldwide in multi-story buildings. In these slabs, the design is often governed by punching shear and serviceability. The mitigation of these issues during design usually leads to increased raw material consumption and costs. Previous studies have shown that using Fiber Reinforced Concrete (FRC) or High-Strength Concrete (HSC) only at the vicinity of the column, while casting the rest of the slab with Normal Strength Concrete (NSC), can lead to an improved behavior under gravity loads in terms of both serviceability and ultimate capacity. Motivated by these results and the scarcity of previous tests, the present paper experimentally investigates the applicability of High-Performance Fiber Reinforced Concrete (HPFRC) as an alternative material that can be seen as an improvement over FRC and HSC, allowing a combination of ductility and strength. In addition, the HPFRC used in this paper is self-compacting, thus reducing the labor costs associated with concrete vibration. Five 150 mm thick flat slabs were tested under monotonically increasing punching load. The experimental variables were the flexural reinforcement ratio and the extent of the HPFRC zone. One of the specimens was cast only with NSC and served as a reference slab. Results show that the solution was effective for both flexural reinforcement ratios considered. Cracking load, maximum load, as well as the displacement capacity were increased significantly, even for a small extent of HPFRC (1.5 times the effective depth from the face of the column). Regarding the ultimate load capacity, it was observed an increase of 44% to 58% for the specimens with lower reinforcement ratio (0.64%) and between 15%–21% for the specimens with higher reinforcement ratio (0.96%). The results indicate that the use of HPFRC is a promising solution regarding both serviceability and ultimate limit state design of reinforced concrete flat slabs under gravity loading, with obvious advantages in material savings and labor costs.