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2015
Punching of high strength concrete flat slabs without shear reinforcement, Inácio, Micael M. G., Almeida André F. O., Faria Duarte M. V., Lúcio Válter J. G., and Ramos António Pinho , Engineering Structures, nov, Volume 103, p.275–284, (2015) AbstractWebsite

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.

Flat Slab Punching Behaviour under Cyclic Horizontal Loading, André Almeida, Micael Inácio, Válter Lúcio, and Ramos António , fib symposium Copenhagen 2015, Concrete – Innovation and Design, Copenhagen, (2015) Abstract

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Reforço de Lajes Fungiformes com Betão Complementar- Ligação Betão-Betão, e Hugo Fernandes, António Ramos Válter Lúcio , SILE 2015 – Seminário Internacional Sobre Ligações Estruturais, Lisbon, (2015) Abstract

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2014
Análise Numérica do Punçoamento em Lajes Fungiformes Pré-Esforçadas, e Nuno Mamede, Duarte Faria António Ramos , 5ªs Jornadas Portuguesas de Engenharia de Estruturas, Encontro Nacional de Betão Estrutural 2014, 9º Congresso Nacional de Sismologia e Engenharia Sísmica, Lisbon, (2014) Abstract

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Análise Numérica Não Linear do Punçoamento em Lajes Fungiformes – Calibração, Mamede, Nuno, Faria Duarte, and Ramos António , Revista Internacional Tech ITT, Volume 12, Issue 35, p.4-13, (2014)
Análise Numérica Não Linear do Punçoamento em Lajes Fungiformes – Estudo Paramétrico, Mamede, Nuno, Faria Duarte, and Ramos António , Revista Internacional Tech ITT, Volume 12, Issue 35, p.14-24, (2014)
Determinação de Relações Tensão-Abertura de Fendas de BRFA através de Análise Inversa, Gouveia, N.D., Custódia Faria Ramos A. L. D. M. , 9º Congresso Nacional de Mecânica Experimental, Aveiro, (2014) Abstract

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The effect of the vertical component of prestress forces on the punching strength of flat slabs, Ramos, Pinho A., Lúcio Válter J. G., and Faria Duarte M. V. , Engineering Structures, Volume 76, p.90–98, (2014) Abstract

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.

Estudo Teórico-Experimental da Resistência ao Punçoamento de Lajes Fungiformes de Betão Aramado com Pilar de Canto Reentrante sem Armadura de Punçoamento, e Elaine Albuquerque, Guilherme Melo, António Ramos Válter Lúcio , 5ªs Jornadas Portuguesas de Engenharia de Estruturas, Encontro Nacional de Betão Estrutural 2014, 9º Congresso Nacional de Sismologia e Engenharia Sísmica, Lisbon, (2014) Abstract

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Influence of prestressing on the punching strength of post-tensioned slabs, Clement, Thibault, Ramos Antonio Pinho, Ruiz Miguel Fernandez, and Muttoni Aurelio , Engineering Structures, Volume 72, p.56–69, (2014) Abstract

Previous researches on punching of post-tensioned slabs have shown a number of phenomena significantly influencing their strength and behaviour. However, no general agreement is yet found on a physical theory (either in codes of practice or in design models) suitably describing the influence of prestressing and how should it be accounted on the punching shear behaviour. In this paper, the authors present the results of tests on 15 slabs (3000. ??. 3000. ??. 250. mm) tested to failure under different loading conditions. The aim of the tests was to investigate in a separate manner the different actions induced by prestressing on the punching shear strength (in-plane forces, bending moments and bonded tendons). These results are finally investigated on the basis of the physical model of the Critical Shear Crack Theory. The fundamentals of this theory are presented and adapted to post-tensioned slabs, providing a rational explanation of the observed phenomena and measured strengths. ?? 2014 Elsevier Ltd.

A Minimization Prodecure for the Determination of SFRC Tensile Behaviour, Nuno Gouveia, Ana Luísa Custódio, Duarte Faria António Ramos , EngOpt 2014, 4th International Conference on Engineering Optimization, Lisbon, (2014) Abstract

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On the efficiency of flat slabs strengthening against punching using externally bonded fibre reinforced polymers, Duarte, Duarte M., Einpaul Jurgen, Ramos António M., {Fernandez Ruiz} Miguel, and Muttoni Aurelio , Construction and Building Materials, Volume 73, p.366–377, (2014) Abstract

One possibility for strengthening existing flat slabs consists on gluing fibre reinforced polymers (FRPs) at the concrete surface. When applied on top of slab-column connections, this technique allows increasing the flexural stiffness and strength of the slab as well as its punching strength. Nevertheless, the higher punching strength is associated to a reduction on the deformation capacity of the slab-column connection, which can be detrimental for the overall behaviour of the structure (leading to a more brittle behaviour of the system). Design approaches for this strengthening technique are usually based on empirical formulas calibrated on the basis of the tests performed on isolated test specimens. However, some significant topics as the reduction on the deformation capacity or the influence of the whole slab (accounting for the reinforcement at mid-span) on the efficiency of the strengthening are neglected. In this paper, a critical review of this technique for strengthening against punching shear is investigated on the basis of the physical model proposed by the Critical Shear Crack Theory (CSCT). This approach allows taking into account the amount, layout and mechanical behaviour of the bonded FRP's in a consistent manner to estimate the punching strength and deformation capacity of strengthened slabs. The approach is first used to predict the punching strength of available test data, showing a good agreement. Then, it is applied in order to investigate strengthened continuous slabs, considering moment redistribution after concrete cracking and reinforcement yielding. This latter study provides valuable information regarding the differences between the behaviour of isolated test specimens and real strengthened flat slabs. The results show that empirical formulas calibrated on isolated specimens may overestimate the actual performance of FRP's strengthening. Finally, taking advantage of the physical model of the CSCT, the effect of the construction sequence on the punching shear strength is also evaluated, revealing the role of this issue which is also neglected in most empirical approaches.

Punçoamento em Lajes Fungiformes de Betão de Elevada Resistência – Estudo Experimental, e Micael Inácio, Duarte Faria, Válter Lúcio António Ramos , 5ªs Jornadas Portuguesas de Engenharia de Estruturas, Encontro Nacional de Betão Estrutural 2014, 9º Congresso Nacional de Sismologia e Engenharia Sísmica, Lisbon, (2014) Abstract

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Punçoamento em Lajes Fungiformes Sujeitas a Ações Cíclicas horizontais – Estudo Experimental, e André Almeida, Micael Inácio}, Válter Lúcio António Ramos , 5ªs Jornadas Portuguesas de Engenharia de Estruturas, Encontro Nacional de Betão Estrutural 2014, 9º Congresso Nacional de Sismologia e Engenharia Sísmica, Lisbon, (2014) Abstract

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Reabilitação Estrutural de Edifícios com Pós-Tensão, Lúcio, Válter, Faria Duarte, Ramos António, and Ferreira João , ReHabend 2014, Santader, (2014) Abstract

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Reforço de Lajes Fungiformes com Betão Complementar Armado na Face Tracionada, Lúcio, Válter, Fernandes Hugo, and Ramos António , Construção Magazine, Volume 64, (2014)
SFRC flat slabs punching behaviour - Experimental research, Gouveia, Nuno D., Fernandes Nelson A. G., Faria Duarte M. V., Ramos António M. P., and Lúcio Válter J. G. , Composites Part B: Engineering, Volume 63, p.161–171, (2014) Abstract

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.

2013
Experimental and parametric 3D nonlinear finite element analysis on punching of flat slabs with orthogonal reinforcement, Silva Mamede, Nuno F., Pinho Ramos A., and Faria Duarte M. V. , Engineering Structures, mar, Volume 48, p.442–457, (2013) AbstractWebsite

This work refers to experimental and 3D nonlinear FEA on punching. Numerical results were compared with experimental ones in order to benchmark the FE model and afterwards a parametric study was conducted, changing the reinforcement ratio, slab thickness, concrete strength and column dimensions, running a total of 360 models, where their effect on punching capacity is shown. EC2 and MC2010 provisions agreed approximately with experimental and FEA results. Based in the FEA results it is proposed an equation to predict the punching capacity with the introduction of fracture mechanics parameter, which was compared with several experimental results, giving good approximation.

A physical approach for considering how anchorage head size influences the punching capacity of slabs strengthened with vertical steel bolts, Silva, Ricardo, Faria Duarte Viúla M., Ramos Pinho A., and Inácio Micael , Structural Concrete, dec, Volume 14, Number 4, p.389–400, (2013) AbstractWebsite

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Discussion of “Strengthening Two-Way Reinforced Concrete Floor Slabs Using Polypropylene Fiber Reinforcement” by Matthew J. Radik, Ece Erdogmus, and Travis Schafer, Faria, Duarte M. V., Lúcio Valtér J. G., and Pinho Ramos António M. , Journal of Materials in Civil Engineering, aug, Volume 25, Number 8, p.1142–1142, (2013) AbstractWebsite

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Design for punching of prestressed concrete slabs, Clement, Thibault, Ramos Antonio Pinho, Ruiz Miguel Fernandez, and Muttoni Aurelio , Structural Concrete, Volume 14, Number 2, p.157–167, (2013) Abstract

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Development of a Design Proposal for a Slab Strengthening System using Prestress with Anchorages by Bonding, Duarte Faria, Válter Lúcio, and Ramos António , fib symposium Tel Aviv 2013, Tel Aviv, p.281–284, (2013) Abstract

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Discussion: Pull-out and push-in tests of bonded steel strands, VIULA FARIA, Duarte M., LUCIO Válter J. G., Pinho Ramos A., and MARTI-VARGAS José R. , Magazine of concrete research, Volume 65, Number 17-18, p.1128–1131, (2013) AbstractWebsite

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Punching of High Strength Concrete Flat Slabs - Experimental Investigation, Micael Inácio, António Ramos, Válter Lúcio, and Faria Duarte , fib symposium Tel Aviv 2013, Tel Aviv, p.377–380, (2013) Abstract

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Punching of Steel Fibre Reinforced Concrete Flat Slabs, Gouveia, Nuno, Fernandes Nelson, Faria Duarte, Ramos António, and Lúcio Válter , fib symposium Tel Aviv 2013, Tel Aviv, p.1–4, (2013) Abstract

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