António Manuel Pinho Ramos

This paper studies the influence of different longitudinal top reinforcement detailing on the behaviour and punching capacity of flat slabs. Experimental and numerical studies were carried out. The experimental campaign consisted in testing three reinforced concrete slabs 2.20 m wide with a thickness equal to 0.15 m. The numerical study was conducted using the non-linear finite element software ATENA 3D. Using numerical models, which were calibrated using the experimental tests, a parametric study was carried out to include other design solutions beyond the tested ones. The parameters that were changed in this parametric study were the steel reinforcement ratio, the concrete strength and the detailing of the top steel reinforcement, namely using a solution with uniform distribution and other with a higher concentration of reinforcement near the column. Finally, the results were compared with predictions obtained using some of the existing codes (Eurocode 2 and Model Code 2010). From this study it can be concluded that concentrating the top flexural reinforcement, keeping the same total amount of top longitudinal reinforcement, results in a stiffer response, an increment in the punching resistance, and a decrease in the maximum vertical displacement.

This paper presents a study of the behaviour and load capacity of steel-fibre-reinforced concrete (SFRC) flat slabs under monotonically increased concentrated vertical loads. The SFRC was used only in the local region of the slab–column connection, as the rest of the slab was cast using normal concrete without fibres. The six experimental test specimens had a thickness of 150 mm with different longitudinal reinforcement ratios, using a non-uniform distribution over the slab width. The concretes used were made with different Dramix 4D 65/60 BG steel fibre contents (0, 0·5, 0·75 and 1·0% volume content). The slab tests were complemented by flexural tests on notched beams. This made it possible to determine the tension behaviour of the different concretes used, through a linear post-cracking behaviour and inverse analysis. The inverse analysis made it possible to define the stress–crack opening relationship that characterises the tension behaviour of SFRC and to relate it to the observed behaviour and load capacity of the tested slabs. The tests results show that the tensile behaviour of the SFRC plays an important role in the behavioural and load capacity of the slabs and that it can be considered relevant to physically based models.

This paper presents an experimental study of four flat slab specimens subjected to combined vertical and horizontal cyclic loading. Steel fibre-reinforced concrete (SFRC) was used only in the local region of the slab–column connection, while the rest of the slabs were cast using normal concrete. The specimens measured 4·15 m × 1·85 m × 0·15 m and were connected to two steel half columns by 0·25 m × 0·25 m rigid steel plates, prestressed against the slab using steel bolts, to ensure monolithic behaviour. The specimens were tested using an innovative test setup system that accounted for important factors, such as the ability of bending moment redistribution, line of inflection mobility and assured equal vertical displacements at the opposite slab borders, and symmetrical shear forces. Results show that the presence of SFRC in the slab–column connection region is effective in increasing the deformation capacity of slab–column connections, allowing the increase of horizontal drift ratios.

This paper presents a study of the behaviour and load capacity of Steel Fibre Reinforced Concrete (SFRC) flat slabs under monotonically increased concentrated vertical loads. The SFRC was used only in the local region of the slab-column connection, as the rest of the slab was cast using normal concrete (NC) without fibres. The six experimental test specimens had a thickness of 150 mm with different longitudinal reinforcement ratios, using a non-uniform distribution over the slab width. The concretes used were made with different Dramix® 4D 65/60 BG steel fibre contents (0%, 0.5 %, 0.75% and 1.0% volume content). The slab tests were complemented by flexural tests on notched-beams. This made it possible to determine the tension behaviour of the different concretes used, through a linear post-cracking behavior and inverse analysis. The inverse analysis made it possible to define the stress-crack opening relationship that characterize the tension behaviour of SFRC and to relate it to the observed behaviour and load capacity of the tested slabs. The tests results show that the tensile behaviour of the SFRC plays an important role in the behavioural and load capacity of the slabs and that it can be considered relevant to physically based models.

This paper presents an experimental study of four flat slab specimens subjected to combined vertical and horizontal cyclic loading. Steel fibre-reinforced concrete (SFRC) was used only in the local region of the slab–column connection, while the rest of the slabs were cast using normal concrete. The specimens measured 4·15 m × 1·85 m × 0·15 m and were connected to two steel half columns by 0·25 m × 0·25 m rigid steel plates, prestressed against the slab using steel bolts, to ensure monolithic behaviour. The specimens were tested using an innovative test setup system that accounted for important factors, such as the ability of bending moment redistribution, line of inflection mobility and assured equal vertical displacements at the opposite slab borders, and symmetrical shear forces. Results show that the presence of SFRC in the slab–column connection region is effective in increasing the deformation capacity of slab–column connections, allowing the increase of horizontal drift ratios.

This paper deals with the experimental and theoretical evaluation of punching shear capacity of steel fiber reinforced concrete (SFRC) slab–column connections. Five experimental specimens with a thickness of 160 mm, different fiber volume contents (0, 1.0, and 1.5%) and different flexural reinforcement ratios (0.75 and 1.5%) have been tested. The experimental results were evaluated using a physical–mechanical model based on the critical shear crack theory (CSCT). The model has given a good approximation of experimental punching shear strengths. In general, tests have highlighted a significant increase in load and deformation capacity of fiber reinforced concrete slab–column connections in comparison with reinforced concrete connections.

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Abstract Strengthening of concrete structures with a new concrete layer has been commonly used for columns, beams and slabs. This technique is economic and efficient for structural strengthening since it uses the same base materials, steel and concrete. It is usually applied on the compressed face of the concrete element due to concrete’s recognized behaviour under compression, posing several challenges to control cracking and resistance when applied on the tensile face. For assessing the performance of the strengthening method, twelve slab specimens were designed and tested monotonically. The main parameters to assess in this work were the debonding behaviour and load, and the relationship between the latter and the relative displacements at the interface of the two concrete layers. The performance of the strengthened structures strongly relies on the interaction of the two concrete layers, with this being the main subject of the research about overlaid concrete. The load transfer capacity of the interface depends on the interface shear strength, which in turn is highly dependable on substrate roughness, cleanliness and curing conditions of the newly added layer. Interface performance may be improved by using steel connectors crossing the interface, properly anchored on both layers. The importance for these elements grows as the existing concrete is more deteriorated, since adhesion strength will decrease with lower quality concrete. This paper presents the experimental research for the application of bonded concrete overlays on the tensile face of reinforced concrete slabs, mainly aimed at office buildings and parking facilities, where spatial clearances or inaccessibility to the lower side of the slabs are recurrent. A ductile behaviour upon debonding was achieved for the specimens with reinforcement crossing the interface, and a debonding load up to three times that of the reference specimens without reinforcement crossing the interface.

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The experimental research carried out to study the punching behavior of high strength concrete (HSC) flat slabs is reported in the present work. Three flat slab specimens were cast using HSC and another one with normal strength concrete (NSC), to be used as a reference slab. The HSC mix presented a compressive strength of about 130MPa, with a basalt coarse aggregate. The tested specimens were square with 1650mm side and 125mm thickness. The longitudinal reinforcement ratio varied between 0.94{%} and 1.48{%}. The experimental results show that the use of HSC led to a significant load capacity increase when compared with the reference model made with NSC. Furthermore, the experimental results also indicated that as the longitudinal reinforcement ratio increased, the punching capacity also increased. The results obtained in this set of experimental tests and others collected from the literature were compared with the code provisions by EC2, MC2010 and ACI 318-11.

The use of prestress in flat slabs is a common solution, mainly because it allows larger spans and thinner slabs. Nevertheless, smaller thicknesses near the slab-column connections, along with the superposition of high shear and flexural stresses, arise the question of the slab capacity to resist punching. The punching failure results from the superposition of shear and flexural stresses near the column, and is associated to the formation of a pyramidal plug of concrete which punches through the slab. It is a local and brittle failure. The use of prestress can increase the punching capacity of flat slabs-column connections.This work presents the experimental analysis of flat slab specimens with tendons under punching. Nine slabs were tested using unbonded prestress with high strength steel tendons. The influences on the punching capacity of the vertical component of the prestress forces resulting from inclined tendons near the column and their distance to the column are analysed. The in-plane compression force due to prestress was not applied to the slabs, in order to evaluate only the deviation force influence. This work aims to improve the understanding of the behaviour of prestressed flat slabs under punching load in order to properly evaluate the punching resistance of this kind of structures. The experimental punching loads are compared with the provisions of EC2, ACI 318-11 and MC2010. © 2014 Elsevier Ltd.

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The use of randomly distributed steel fibres in the concrete mix improves its mechanical properties. In the particular case of a flat slab-column connection, this solution can provide slabs with an increased load capacity and deformation capacity, allowing a potential reduction of reinforcement. This work presents the experimental study of the behaviour of SFRC flat slabs up to failure under a concentrated loading, accompanied by the study of the mechanical properties of the SFRC, which consisted in three-point loading notched beams, compression and splitting tests. In this study, the hooked end steel fibre dosages varied between 0{%} and 1.25{%} by volume. Test results showed that the inclusion of steel fibres influences both slab stiffness and its load capacity. Increments of load capacity up to 64{%} were obtained in slabs with SFRC compared with the reference slab without fibres. The experimental results were compared with the predictions provided by several existing models. © 2014 Elsevier Ltd. All rights reserved.