António Manuel Pinho Ramos

Abstract Fiber reinforced polymer (FRP) composites can be efficient for flexural strengthening of flat slabs if debonding of the FRP is postponed. However, with the increase of the flexural capacity, the flat slab becomes more susceptible to punching shear failure. In this context, four flexural or simultaneous flexural and punching shear retrofitting systems are investigated in this study to strengthen a flexure-deficient flat slab. Externally Bonded Reinforcement on Grooves (EBROG) and externally bonded reinforcement (EBR) methods are used for flexural strengthening in two cases: slabs without punching shear reinforcement and with post-installed shear bolts as shear reinforcement. According to the results, flexural strengthening of the slab using the EBR and EBROG techniques increased its load capacity by 12% and 21%, respectively. Simultaneous flexural and shear strengthening of the slab using the EBROG technique was the most effective, leading to a 57% enhancement of the load capacity. For specimens whose failure was governed by punching, comparing the results with code predictions showed that Eurocode and ACI (and the respective guide documents fib bulletin 90 and ACI 440.2R) overestimated the capacity of these specimens. In cases where failure was governed by flexure, a simple application of the yield line theory predicted reasonably well the load capacity of the specimens.

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.

Abstract Fiber reinforced polymer (FRP) composites can be efficient for flexural strengthening of flat slabs if debonding of the FRP is postponed. However, with the increase of the flexural capacity, the flat slab becomes more susceptible to punching shear failure. In this context, four flexural or simultaneous flexural and punching shear retrofitting systems are investigated in this study to strengthen a flexure-deficient flat slab. Externally Bonded Reinforcement on Grooves (EBROG) and externally bonded reinforcement (EBR) methods are used for flexural strengthening in two cases: slabs without punching shear reinforcement and with post-installed shear bolts as shear reinforcement. According to the results, flexural strengthening of the slab using the EBR and EBROG techniques increased its load capacity by 12% and 21%, respectively. Simultaneous flexural and shear strengthening of the slab using the EBROG technique was the most effective, leading to a 57% enhancement of the load capacity. For specimens whose failure was governed by punching, comparing the results with code predictions showed that Eurocode and ACI (and the respective guide documents fib bulletin 90 and ACI 440.2R) overestimated the capacity of these specimens. In cases where failure was governed by flexure, a simple application of the yield line theory predicted reasonably well the load capacity of the specimens.

Abstract This paper presents a critical review of the state of the art of experimental research concerning the seismic response of reinforced concrete flat slab frames. After a summary of tests on connections, the paper examines tests carried out on frames with gravity and cyclic lateral loading, and shake table tests; scaled specimens and one real scale study are included. A discussion of the results reached so far is provided focusing on the global response, the different load types and effects; the ultimate rotations at failure in relation to the gravity shear and a classification of different failure modes for different types of connections. Based on this analysis, the research needs are highlighted. An experimental program launched to address these open questions is described. Further open topics are highlighted.

Abstract An experimental work on reinforced concrete flat slab specimens to test the efficiency of postinstalled bolts, as punching shear reinforcement in resisting vertical and cyclic horizontal loads, was conducted and is presented in this paper. The test protocol consisted in increasing horizontal drifts combined with constant vertical load until failure. Two different detailing solutions for the shear reinforcement were considered, one using a radial distribution around the column and another using a cross distribution, being the results compared with a previously tested reference specimen. The dimensions of the specimens were 4.25 x 1.85 x 0.15 m3. The test setup used for these tests was developed by the research team and simulates the boundary conditions with already recognized good results. Postinstalled steel bolts were proven to be an efficient solution for strengthening of existing structures, improving the structural behavior, and the punching resistance.

This paper describes the experimental campaign to study the behaviour of reinforced-concrete flat slab structures with steel stirrups as punching shear reinforcement, under combined vertical and horizontal cyclic loading. The vertical load was first applied and kept constant during the test, while, regarding the cyclic horizontal loading, imposed cyclic drifts were increased until failure. Four slab specimens with shear reinforcement were tested and the results compared to a control slab specimen without shear reinforcement. The studied variables were different shear reinforcement ratios and the number of stirrup layers. The slabs were 4·15 × 1·85 m2 and 0·15 m thick, connected to two steel half-columns. The test setup used was developed by the research team and aimed to simulate the boundary conditions of a flat slab, representing the slab between middle spans in one direction and between zero bending moment points in the other direction. Results show that the use of steel stirrups as shear reinforcement is very effective, increasing shear, drift and energy dissipation capacities. The obtained results were also compared to the provisions given by European and American codes.