Export 13 results:
Sort by: Author [ Title  (Asc)] Type Year
A B C [D] E F G H I J K L M N O P Q R S T U V W X Y Z   [Show ALL]
Damage Effect on Concrete Columns Confined with Carbon Composites, Faustino, Pedro, and Chastre Carlos , ACI Structural Journal, Volume 113, Number 4, (2016) AbstractWebsite

Five experimental cyclic tests were carried out on reinforced concrete rectangular columns with rounded corners, different condition (new and damaged) and different strengthening systems: that included confinement through carbon fiber (CFRP) jackets, anchor dowels, high strength repair mortar and external longitudinal stainless steel bars. Lateral load - displacement relationship, energy dissipation, ductility and curvature results were analyzed together with two different damage assessment classifications. The overall evaluation concludes that the use of external confinement with CFRP on RC columns is viable and of effective performance enhancement alone and combined with other techniques. Damaged columns that were retrofitted showed an increased load capacity up to 20% along with good ductile behavior within the limits of the US, European, Canadian and Japanese codes, with minor/moderate degree of damage at 1% drift ratio and moderate degree of damage at 2% drift ratio.

Degradação da aderência entre compósitos de GFRP e betão devido a condições ambientais severas, Silva, M. A. G., Biscaia H. C., and Chastre C. , Betão Estrutural 2012, Porto, (2012) Abstractsilva2012bich_-_be2012_-_feup.pdf

A degradação da ligação entre compósitos de matriz polimérica reforçada por fibras (FRP) e o betão é uma das principais causas de possível rotura das vigas e lajes de betão armado reforçadas
externamente por compósitos de FRP. Desde há mais de 10 anos que se estuda, por isso, na UNL o
comportamento dessa ligação, integrado em programa mais alargado de estudo da durabilidade deste tipo de reforço, especialmente quando sujeito a condições ambientais severas que se simulam por processos artificialmente acelerados no laboratório. Em particular a degradação da aderência e o possível descolamento precoce do reforço têm sido modelados física e computacionalmente com principal incidência no uso de fibras de vidro (GFRP) e resina epoxídica. Nesta comunicação mostram-se resultados obtidos em termos de capacidade de carga, força transmitida ao reforço e tensões de aderência após envelhecimentos de pequenas vigas de betão armado (BA) por ciclos de nevoeiro salino, ciclos seco/molhado em solução salina, ciclos de temperatura entre +7,5ºC e +47,5ºC e gelo-degelo de -10ºC a +30ºC. Faz-se recomendação quanto à extensão máxima para diferentes envelhecimentos. Apresenta-se comparação entre resultados de modelação numérica e experimental.

Degradation of EB-GFRP systems due to artificial aging conditions, Biscaia, Hugo, and Chastre Carlos , XVI Portuguese Conference on Fracture (PCF2018), 23-24th April 20, Universidade da Beira Interior, Covilhã, Portugal, (2018) Abstract

The use of adhesively bonded joints between Fiber Reinforced Polymers (FRP) and concrete elements have been spread out in the past decades. However, due to their recent applications, the durability aspects related with these bonded joints requires the use of high safety factors which strongly restricts the mechanical capacity of the FRP composites. The experimental assessment of the degradation of FRP-to-concrete interfaces is an important task because it provides useful data that can be used to calibrate analytical or numerical models with the aim of helping on the correct understanding of the interfacial degradation. In this work, a new and simple interfacial bond-slip model that needs only one parameter to be experimentally defined is proposed. Compared to unaged Glass (G) FRP-to-concrete interfaces, the relative degradation of these bonded interfaces is studied after being subjected to: (i) salt fog cycles; (ii) wet-dry cycles; (iii) temperature cycles between -10ºC and +30ºC; and (iv) between +7.5ºC and +47.5ºC. The subsequent full debonding processes are predicted through an analytical model that takes into account the degradations experimentally determined from the tests.

Delamination process analysis of FRP-to-parent material bonded joints with and without anchorage systems using the Distinct Element Method, Biscaia, Hugo C., Micaelo Rui, Teixeira João, and Chastre Carlos , Composite Structures, Volume 116, Issue September–October, p.104–119, (2014) AbstractWebsite

This study looks at the analysis of the interface between Fiber Reinforced Polymer (FRP)-to-parent material bonded interfaces. The performance of FRP-to-parent material bonded joints for the Externally Bonded Reinforcement (EBR) technique is numerically modelled with the PFC2D software which is based on the Distinct Element Method (DEM). It is believed that this represents the first time the DEM has been used to simulate the delamination process of FRP-to-parent material bonded joints. In order to validate the analysis performed with the DEM, a Pull-out test with no slip constrains was modelled and different linear bond-slip laws were assumed. The numerical results revealed that the DEM is capable of estimating with good accuracy the exact solutions of bond stresses, strains or slippages along the bonded length for linear bond-slip laws. The bi-linear law available in PFC2D was then compared to the numerical results obtained from other another code developed by the author. The delamination process of Pull-out tests with slip constrain at one of the free ends of the FRP plate is also described and analyzed. The results obtained from the DEM revealed that the delamination process ends with stiffness equal to the axial stiffness of the FRP plate. This evidence highlights the need to design mechanical anchor devices capable of preventing premature debonding which is known to occur on EBR systems.

Design method and verification of steel plate anchorages for FRP-to-concrete bonded interfaces, Biscaia, Hugo C., and Chastre Carlos , Composite Structures, 5/15/, Volume 192, p.52-66, (2018) AbstractWebsite

Concrete structures Externally Bonded Reinforced (EBR) with Fibre Reinforced Polymers (FRP) have been studied and used since the end of the last century. However, several issues need to be better studied in order to improve performance. The influence of size of anchorage plates used on Reinforced Concrete (RC) structures strengthened with EBR FRP composites, the external compressive stress to be applied on the anchorage plate and the numerical simulation of this region are some of the topics that need to be more carefully studied in order to clarify the performance of the FRP-to-concrete interface within the anchorage plate region. This study proposes a design methodology to estimate the amount of external compressive stress necessary to be applied on the anchorage plate of EBR systems with FRP composites, in order to avoid premature debonding. The external compressive stress imposed on the FRP composite is intended to simulate the effect produced by a mechanical anchorage system tightened to the EBR system. The results from the design proposal, when compared with the numerical ones, were efficient enough on the prediction of the bond strength improvement of FRP-to-concrete interfaces.

Design model for square RC columns under compression confined with CFRP, Faustino, Pedro, Chastre Carlos, and Paula Raquel , Composites Part B: Engineering, Volume 57, Issue February, p.187-198, (2014) Abstractfaustino_chastre_et_al._2014.pdfWebsite

The enhancement of the mechanical behaviour of reinforced concrete (RC) columns with regard to axial compression is an up-to-date concern, namely if the strengthening of existing structures is to be considered. In view of this, external confinement with FRP systems has been tested in order to become a feasible technique, since it seems to have important advantages over other systems such as its high strength and stiffness in relation to weight and its improvement of strength and ductility while confining RC columns. Square columns confined with FRP show a more complex interpretation of their behaviour, when compared to circular columns. Accordingly, the present work includes the analysis of two experimental programs regarding axial compression on CFRP confined RC columns: one on circular and square specimens with different corner radii; the other on square specimens with side lengths ranging from medium to large. Based on this, modelling equations are proposed to predict maximum axial load, axial strain and lateral strain, as well as the entire behaviour until failure with curves of axial load-axial strain and axial load-lateral strain. The modelling results show that the analytical curves are in general agreement with the presented experimental curves for a wide range of dimensions.

Determination of weathering degree of the Persepolis stone under laboratory and natural conditions using fuzzy inference system, Heidari, Mojtaba, Torabi-Kaveh Mehdi, Chastre Carlos, Ludovico-Marques Marco, Mohseni Hassan, and Akefi Hossein , Construction and Building Materials, Volume 145, p.28-41, (2017) Abstract

Weathering imposes vital effects on stony monuments. Mostly, the degree of weathering is determined by simple test results, ignoring simultaneous effects of various weathering factors. Hence, the main purpose of this study is to develop prediction models with fuzzy inference systems to determine the weathering degree of the Persepolis stone, using various accelerated ageing tests in laboratory condition and to extrapolate the results to the natural condition, considering climatic information. The results suggest reliable conformity between the prediction of the weathering degree of the stone and the weathering degree observed in the Persepolis complex in natural condition.

Development of an injectable grout for concrete repair and strengthening, Bras, Ana, Gião Rita, Lúcio Válter, and Chastre Carlos , Cement and Concrete Composites, (2013) AbstractWebsite

This paper deals with the coupled effect of temperature and silica fume addition on rheological, mechanical behaviour and porosity of grouts based on CEMI 42.5R, proportioned with a polycarboxylate-based high range water reducer. Preliminary tests were conducted to focus on the grout best able to fill a fibrous network since the goal of this study was to develop an optimized grout able to be injected in a mat of steel fibers for concrete strengthening. The grout composition was developed based on criteria for fresh state and hardened state properties. For a CEMI 42.5R based grout different high range water reducer dosages (0, 0.2%, 0.4%, 0.5%, 0.7%) and silica fume (SF) dosages (0, 2%, 4%) were tested (as replacement of cement by mass). Rheological measurements were used to investigate the effect of polycarboxylates (PCE) and SF dosage on grout properties, particularly its workability loss, as the mix was to be injected in a matrix of steel fibers for concrete jacketing. The workability behaviour was characterized by the rheological parameters yield stress and plastic viscosity (for different grout temperatures and resting times), as well as the procedures of mini slump cone and funnel flow time. Then, further development focused only on the best grout compositions. The cement substitution by 2% of SF exhibited the best overall behaviour and was considered as the most promising compared to the others compositions tested. Concerning the fresh state analysis, a significant workability loss was detected if grout temperature increased above 35°C. Below this temperature the grout presented a self-levelling behaviour and a life time equal to 45 minutes. In the hardened state, silica fumes increased not only the grout’s porosity but also the grout’s compressive strength at later ages, since the pozzolanic contribution to the compressive strength does not occur until 28 days and beyond.

Displacement Estimation of a RC beam test based on TSS algorithm, Almeida, G., Biscaia H., Chastre C., Fonseca J., and Melício F. , CISTI'2010 - 5ª Conferencia Ibérica de Sistemas y Tecnologías de Información, Santiago de Compostela, (2010) Abstract

The traditional methodology used in civil engineering measurements requires a lot of equipment and a very complex procedure especially if the number of target points increase. Since the beginning of the current century, several studies have been conducted in the area of photogrametry using digital image
correlation associated with block motion algorithms to estimate displacements in reinforced concrete (RC) beams during a load test. Using image processing techniques it is possible to measure the whole area of interest and not only a few points of the tests materials. In this paper, block-matching algorithms are used in order to compare the results from photogrametry techniques and the data obtained with linear voltage displacement transducer (LVDT) sensors during the load tests of RC beams, which are very common to find in civil engineering laboratories.

Displacement measurements with ARPS in T-beams load tests, Almeida, G., Melicio F., Chastre C., and Fonseca J. , Volume 349 AICT, p.286-293, (2011) Abstract

The measurement of deformations, displacements, strain fields and surface defects in many material tests in Civil Engineering is a very important issue. However, these measurements require complex and expensive equipment and the calibration process is difficult and time consuming. Image processing could be a major improvement, because a simple camera makes the data acquisition and the analysis of the entire area of the material under study without requiring any other equipment like in the traditional method. Digital image correlation (DIC) is a method that examines consecutive images, taken during the deformation period, and detects the movements based on a mathematical correlation algorithm. In this paper, block-matching algorithms are used in order to compare the results from image processing and the data obtained with linear voltage displacement transducer (LVDT) sensors during laboratorial load tests of T-beams. © 2011 IFIP International Federation for Information Processing.

Double shear tests to evaluate the bond strength between GFRP/concrete elements, Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G. , Composite Structures, Volume 94, Number 2, p.681-694, (2012) AbstractWebsite

Externally bonded reinforced systems have been widely used in civil engineering. However, the problems associated with bond between structural elements are not yet fully solved. As a consequence, many researchers have been proposing tests and techniques to standardize procedures and reach better agreement for design purposes. In the present paper, an experimental program is described that was developed to characterize the glass FRP/concrete interface by double shear tests made on 15 cm side cubes with GFRP bonded on two opposite faces. The GFRP wrap had two layers applied by the wet lay-up technique and three classes of concrete were considered. With the support of the experimental program, cohesion and friction angle for GFRP–concrete interfaces were found leading to different envelope failure laws, based on the Mohr–Coulomb failure criterion for each concrete class, capable of predicting GFRP debonding. Results are discussed.

Ductilidade e resistência no reforço de pilares de betão armado sem aumento de secção, Chastre, Carlos , Construção Magazine, Março/Abril de 2, Volume 84, Number Março/Abril, p.48-49, (2018) AbstractWebsite

O aumento da resistência e/ou da ductilidade é um objetivo primordial quando se procede ao reforço de pilares. Um método bastante eficaz de aumentar a ductilidade, particularmente em regiões sísmicas, é através do encamisamento com coletes de FRP, uma vez que esta técnica permite uma diminuição da deformação transversal do pilar e a limitação da encurvadura das armaduras longitudinais, aumentando consequentemente a ductilidade do mesmo. Diversos ensaios experimentais permitiram detetar que os incrementos são maiores em secções circulares do que em secções quadradas ou retangulares [1, 2]. A atenuação deste efeito é obtida através do arredondamento dos cantos nos pilares de secção retangular. Contudo, o encamisamento com coletes de FRP, por si só, não aumenta significativamente a resistência do pilar à flexão composta. Para que isso aconteça e se mantenha um nível elevado de ductilidade, é necessário adicionar armaduras longitudinais à armadura do pilar e posteriormente proceder ao encamisamento com colete de FRP. Uma forma muito eficiente de o conseguir, mantendo a seção transversal do pilar, é utilizando o sistema CREatE (Continuous Reinforcement Embedded at Ends) desenvolvido na Universidade NOVA e já anteriormente apresentado nesta coluna, na edição de Junho/Agosto de 2017 [3], para o caso do reforço de vigas. O sistema CREatE foi idealizado para ser utilizado com diversos materiais e diferentes elementos estruturais [4-7], em que é necessário aumentar a sua capacidade resistente através de armaduras pós-instaladas, caracterizando-se pela utilização de armaduras contínuas embutidas nas extremidades do elemento estrutural sem o uso de dispositivos mecânicos para as fixar. Antes da ancoragem da armadura de reforço no interior do elemento, é necessário utilizar uma curva de transição suave para alterar a forma da armadura de reforço e evitar a ocorrência de concentrações de tensões na armadura ou na interface [4, 7, 8]. Este conceito foi aplicado no reforço de pilares realizado no âmbito da tese de doutoramento de Faustino Marques [9].Na Figura 1 é possível observar dois pilares de seção retangular (20x40cm2) encamisados com coletes de 3 camadas de CFRP (200gr/m2) em que foi utilizado o sistema CREatE com armaduras pós-instaladas de aço inox (2x20x5mm2) ou de laminados de CFRP (2x(10+20)×1.4 mm2/face) para reforço longitudinal [7, 8]. Na Figura 2 pode observar-se os resultados dos ensaios experimentais de um conjunto de pilares de seção retangulares sujeitos a esforço axial e a ações horizontais cíclicas. O pilar P11 é o de referência pois, não foi reforçado, enquanto os pilares P12, P15 e P16 foram encamisados com coletes de 3 camadas de CFRP e nos pilares P15 e P16 foi utilizado adicionalmente o sistema CREatE com armaduras pós-instaladas de aço inox (P15) ou de laminados de CFRP (P16) para reforço longitudinal [7]. Na Figura 3 mostra-se a envolvente dos diagramas Força-Deslocamento dos ensaios dos diferentes pilares de seção retangular (P11; P12; P15 e P16), sendo possível de constatar um excelente desempenho não só em termos de ductilidade (incremento de 67%) como de resistência (incrementos entre 29% e 43%, para drifts entre 2 e 4%) dos pilares reforçados com o sistema CREatE relativamente ao pilar de referência não reforçado.

Durability Assessment of Consolidation Effect on Sandstone Monuments, Ludovico-Marques, Marco, and Chastre Carlos , 41th IAHS Word Congress of Housing. Sustainability and Innovation for the Future, 13-16 September , Albufeira, Portugal, p.10p, (2016) Abstract41_iahs_2016_-_marco_marques_-_ext-abstract_durability_assessment_of_consolidation_effect_on_sandstone_monuments_ludovico_marques__chastre.pdf

The façades of St. Leonard’s church and the castle in Atouguia da Baleia village in western region of Portugal are monuments built in Middle Ages. Significant stone degradation patterns are visible, being the alveolization an outstanding case study.The more porous type of sandstones similar to the variety found in the vernacular architecture of Atouguia da Baleia was treated with ethyl silicates. In order to allow the study of the durability of these conservation treatments, accelerated artificial ageing salt crystallization tests were carried out and an automatic ageing chamber was developed.Physical and mechanical behaviour was assessed on consolidated specimens before and after accelerated artificial ageing salt crystallization tests. The authors propose a prediction of the durability of these consolidation treatments by means of the salt crystallization ageing results.