António Manuel Pinho Ramos

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 approximately 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.

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The present work reports experimental research carried out on repair and strengthening methods of flat slabs for punching. The repair and strengthening methods studied are: strengthening using transversal prestress, repair by substitution of the damaged concrete; and strengthening using steel beams as a column head, connected to the column and to the slab with epoxy resin and mechanical expansion anchors. Four experimental test slabs (AR1 to AR4) were produced and tested: two with transversal prestress, one only repaired and one strengthened with a steel column head. The execution process, its efficiency and design, are discussed.

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The results of a series of experiments on four reinforced concrete flat slab specimens with shear studs and a control specimen without any shear reinforcement are presented. The specimens were tested under constant gravity loads and reversed horizontal cyclic displacements. The main test variables were the applied gravity load and the number of perimeters of studs. One of the specimens was tested in two phases to study the postearthquake behavior. Results showed a considerable improvement of the deformation capacity of specimens with studs compared to the reference specimen. In agreement with previous research, increasing the applied gravity shear ratio resulted in a lower experimental drift capacity. It is shown that a better explanation of the observed ultimate drifts can be made by considering also the flexural capacity and the extent of shear reinforcement. The specimen tested in two phases exhibited considerable residual capacity, even after severe horizontal loading.

The results of a series of experiments on four reinforced concrete flat slab specimens with shear studs and a control specimen without any shear reinforcement are presented. The specimens were tested under constant gravity loads and reversed horizontal cyclic displacements. The main test variables were the applied gravity load and the number of perimeters of studs. One of the specimens was tested in two phases to study the postearthquake behavior. Results showed a considerable improvement of the deformation capacity of specimens with studs compared to the reference specimen. In agreement with previous research, increasing the applied gravity shear ratio resulted in a lower experimental drift capacity. It is shown that a better explanation of the observed ultimate drifts can be made by considering also the flexural capacity and the extent of shear reinforcement. The specimen tested in two phases exhibited considerable residual capacity, even after severe horizontal loading.

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.