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2020
Influence of the top reinforcement detailing in the behaviour of flat slabs, Faria, Ricardo, Marreiros Rui, Ramos António Pinho, and Jesus Catarina , Structures, Volume 23, p.718 - 730, (2020) AbstractWebsite

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.

Post-earthquake Performance of a Slab-Column Connection with Punching Shear Reinforcement, Isufi, Brisid, Ramos António Pinho, and Lúcio Válter , Journal of Earthquake Engineering, p.1-23, (2020) AbstractWebsite
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Punching of reinforced concrete flat slabs – Rational use of high strength concrete, Inácio, Micael M. G., Lapi Massimo, and Ramos Antonio Pinho , Engineering Structures, Volume 206, p.110194, (2020) AbstractWebsite

This paper deals with punching of reinforced high strength concrete (HSC) flat slabs. Despite the use of HSC increased significantly in the last years, the experimental research on punching behavior of HSC slabs is still limited. Furthermore, most of this past research adopted concrete compressive strength lower than 90 MPa. In a previous work by this research group three specimens with concrete compressive strength around 120 MPa and one with normal strength concrete (NSC) were tested. The present work represents the continuation of the previous activity and it is focused on the rational use of HSC. Four specimens with HSC and one of NSC were tested under monotonic vertical loading. The HSC was placed only in the slab-column connection region and it was limited to a thin layer in the compressive zone, in order to have a more economical and sustainable solution. This rational use of the HSC showed excellent results in terms of punching strength. Limiting the HSC to a thin layer in the compressive zone resulted in an almost equal punching strength to that obtained with the slab entirely casted in HSC.

Role of punching shear reinforcement in the seismic performance of flat slab frames, Isufi, B., Cismasiu I., Marreiros R., Pinho Ramos A., and Lúcio V. , Engineering Structures, Volume 207, (2020) AbstractWebsite
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2019
Behavior of RC flat slabs with shear bolts under reversed horizontal cyclic loading, Almeida, André F. O., Ramos António P., Lúcio Válter, and Marreiros Rui , Structural Concrete, (2019) AbstractWebsite

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.

Behavior of RC flat slabs with shear bolts under reversed horizontal cyclic loading, Almeida, André F. O., Ramos António P., Lúcio Válter, and Marreiros Rui , Structural Concrete, Volume n/a, Number n/a, (2019) AbstractWebsite

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.

Flat slab strenghtening techniques against punching-shear, Lapi, M., Ramos A. P., and Orlando M. , Engineering Structures, Volume 180, p.160-180, (2019) AbstractWebsite

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Resposta da ligação pilar-laje fungiforme sujeitas a ações horizontais cíclicas reforçadas com estribos, Almeida, André, Ramos António, Marreiros Rui, Lúcio Válter, and Faria Ricardo , Revista Portuguesa de Engenharia de Estruturas, Volume Série III, Issue 9, p.67-74, (2019)
Assessment of SFRC flat slab punching behaviour – part I: monotonic vertical loading, Gouveia, Nuno D., Faria Duarte M. V., and Ramos António Pinho , Magazine of Concrete Research, Volume 71, Number 11, p.587-598, (2019) AbstractWebsite

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.

Assessment of SFRC flat slab punching behaviour – part II: reversed horizontal cyclic loading, Gouveia, Nuno D., Faria Duarte M. V., and Ramos António Pinho , Magazine of Concrete Research, Volume 71, Number 1, p.26-42, (2019) AbstractWebsite

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.

Behavior of thin lightly reinforced flat slabs under concentric loading, Torabian, Ala, Isufi Brisid, Mostofinejad Davood, and Ramos António Pinho , Engineering Structures, Volume 196, p.109327, (2019) AbstractWebsite

The current research aims to study the behavior of thin reinforced concrete (RC) slabs under concentrated loads as well as to investigate the application of Critical Shear Crack Theory (CSCT) to such slabs. For this purpose, four square 100-mm-thick slabs were cast and subjected to concentrated punching monotonic loading. The experimental parameters were the flexural reinforcement ratio, 0.38% and 1.00%, and the presence or absence of shear headed stud reinforcement. It is shown that the failure criteria of CSCT describe reasonably well the observed failure modes and the ultimate loads of the specimens. However, attention is brought to some peculiarities in the analytical derivation of the load-rotation curve for thin lightly reinforced flat slabs, in which large deformations are experienced. Results showed that in such slabs, the behavior can be highly influenced by the post-yield stress-strain curve of the flexural steel reinforcement. As a result, the constitutive law of steel reinforcement should be explicitly taken into account in such cases. The versatility of CSCT to adapt to these conditions is demonstrated.

Finite element analysis of punching shear of R/C slabs: A hybrid approach for model calibration, Secci, L., Teoni E., Lapi M., Orlando M., and a Ramos , Proceedings of the fib Symposium 2019: Concrete - Innovations in Materials, Design and Structures, p.643-650, (2019) Abstract
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Post-earthquake strength and deformation capacity of a flat slab specimen with shear studs, Isufi, B., Lúcio V., and Ramos A. P. , Proceedings of the fib Symposium 2019: Concrete - Innovations in Materials, Design and Structures, p.1684-1691, (2019) Abstract
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Reversed horizontal cyclic loading tests of flat slab specimens with studs as shear reinforcement, Isufi, Brisid, Ramos António Pinho, and Lúcio Válter , Structural Concrete, Volume 20, Number 1, p.330-347, (2019) AbstractWebsite

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.

Static and seismic behaviour of R/C slabs with openings adjacent to columns, Lapi, M., Orlando M., Spinelli P., and a Ramos , Proceedings of the fib Symposium 2019: Concrete - Innovations in Materials, Design and Structures, p.1795-1802, (2019) Abstract
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2018
Efeito do confinamento e da redistribuição de momentos no comportamento de lajes fungiformes, Faria, Ricardo, Marreiros Rui, Ramos António, and Antunes Gonçalo , Encontro Nacional Betão Estrutural 2018, 7-9 Nov., LNEC, Lisboa, (2018)
Influência da distribuição transversal de armaduras longitudinais junto ao pilar na resistência ao punçoamento, Faria, Ricardo, Jesus Catarina, Marreiros Rui, and Ramos António , Encontro Nacional Betão Estrutural 2018, 7-9 Nov., LNEC, Lisboa, (2018)
Resposta da ligação pilar-laje fungiforme sujeitas a ações horizontais cíclicas reforçadas com estribos, Almeida, André, Ramos António, Marreiros Rui, Lúcio Válter, and Faria Ricardo , Encontro Nacional Betão Estrutural 2018, 7-9 Nov., LNEC, Lisboa, (2018)
Assessment of SFRC flat slab punching behaviour – Part I: monotonic vertical loading, Gouveia, Nuno D., Faria Duarte M. V., and Ramos António Pinho , Magazine of Concrete Research, p.1-46, (2018) AbstractWebsite

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.

Assessment of SFRC flat slab punching behaviour – part II: reversed horizontal cyclic loading, Gouveia, Nuno D., Faria Duarte M. V., and Ramos António Pinho , Magazine of Concrete Research, p.1-17, (2018) AbstractWebsite

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.

Experimental and theoretical evaluation of punching strength of steel fiber reinforced concrete slabs, Gouveia, Nuno D., Lapi Massimo, Orlando Maurizio, Faria Duarte M. V., and Ramos António M. P. , Structural Concrete, Volume 19, Issue 1, Number 1, p.217-229, (2018) AbstractWebsite

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.

Reversed horizontal cyclic loading tests of flat slab specimens with studs as shear reinforcement, Isufi, Brisid, Ramos António Pinho, and Lúcio Válter , Structural Concrete, (2018) AbstractWebsite

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.

Performance assessment of flat slabs strengthened with a bonded reinforced-concrete overlay, Lapi, M., Fernandes H., Orlando M., a Ramos, and Lúcio V. , Magazine of Concrete Research, Volume 70, Number 9, p.433-451, (2018) AbstractWebsite
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2017
Accelerated action of external sulfate and chloride to study corrosion of tensile steel in reinforced concrete, Silva, M. A. G., Cunha M. P., Pinho Ramos A., Sena da Fonseca B., and Pinho F. F. S. , Materiales de Construcción, Volume 67, Issue 328, (2017)
Applied element method simulation of experimental failure modes in RC shear walls, Cismasiu, Corneliu, Ramos António Pinho, Moldovan Ionut D., Ferreira Diogo F., and Filho Jorge B. , Computers and Concrete, Volume 19, Issue 4, p.365–374, (2017) Abstract

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