Analysis of damage building in the north region of Portugal

A damaged building in the North Region of Portugal is analysed. Geotechnical characterisation of the soil foundation is presented. This soil has a low bearing capacity and the water level is near the ground surface. The reinforced concrete structural skeleton of this building consists of a mat foundation and slabs joined by walls. The façades of the building are in air brick masonry. Instrumental devices to measure the settlements of the building were installed. To observe the behaviour of the developed cracks, a monitoring system was also applied. The water table was observed with piezometers. A tridimensional numerical linear-elastic analysis using a finite element computer program considering soil-structure interaction is done. The soil is modelled using springs distributed continuously and the values of the modulus of subgrade vertical reaction are estimated from the geotechnical properties. The numerical results reveal the deformations and the damages of the building. These results are compared with the field observations. A rehabilitation structural solution is analysed in order to decrease the differential settlements and the soil pressure, and sustain the crack development.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/ECM/59033/2004 “CUTINSHEAR - Performance assessment of an innovative structural FRP strengthening technique using an integrated system based on optical fiber sensors

Strategy to evaluate the stress-crack opening relationship of the SFRC

No presente trabalho é descrita a metodologia desenvolvida para a determinação dos parâmetros de fractura do betão reforçado com fibras de aço, designadamente, a forma da relação tensão-abertura de fenda e a energia subjacente ao processo de fendilhação deste compósito. Para tal recorreu-se a resultados experimentais obtidos em ensaios de flexão efectuados segundo as recomendações do TC 162-TDF da RILEM e foram desenvolvidos dois modelos numéricos, um com base num modelo de secção e o outro utilizando elementos finitos de interface para modelar a progressão da fenda.The methodology developed to determine the fracture parameters of the steel fibre reinforced concrete is described in the present work. The shape of the stress-crack opening displacement relationship and the fracture energy were assessed. For this purpose, the forcedeflection relationships obtained in experimental tests carried out according to the recommendations of the RILEM TC 162-TDF were taken and two numerical approaches were developed, one based on the cross-section layer model and the other using interface finite elements to model the crack opening propagation

Modelling the SFRC flexural behavior using a stress-strain relationship

No presente trabalho foi desenvolvida uma estratégia numérica de forma a avaliar a possibilidade de ser definida uma lei tensão-extensão capaz de simular o comportamento fendilhado do betão de custo competitivo reforçado com fibras de aço (BRFA) concebido no âmbito de um projecto de investigação. Essa estratégia englobou dois modelos de complexidade distinta. O primeiro, designado por modelo de secção, foi utilizado para, com recurso a análise inversa e utilizando respostas força-flecha registadas em ensaios experimentais, se determinarem os parâmetros que definem uma lei trilinear tensão-extensão capaz de reproduzir as respostas experimentais com o rigor desejado. De seguida, esta lei foi utilizada para definir o modo I de fractura da lei constitutiva da fenda, no âmbito de um código computacional de análise não linear material de estruturas submetidas a estado plano de tensão, suportado no método dos elementos finitos, onde o processo de fendilhação é simulado por um modelo de fendilhação distribuída. Da aplicação dos dois modelos constatou-se que o modelo de secção não permite definir a lei tensão-extensão pós pico (lei de amolecimento) com o rigor necessário. Enquadrado numa análise inversa, o modelo baseado no MEF foi de seguida utilizado para se determinar a lei de amolecimento do BRFA, tendo-se constatado que essa lei não pode ser explicitada unicamente em função do conceito de resistência equivalente, tal como sugere o RILEM TC 162-TDF.To assess the post-cracking stress-strain relationship for a developed cost competitive steel fibre reinforced concrete (SFRC), a numerical strategy involving two numerical models of distinct complexity was carried out. Inserted into an inverse analysis framework, a cross-sectional-layer-model (CSLM) was used to evaluate the post-cracking stress-strain relationship able of reproducing, with the desired accuracy, the force-deflection relationship recorded in three-point bending tests carried out according to the RILEM TC 162-TDF recommendations. This relationship was used as the strain softening law of the fracture mode I crack constitutive law of a smeared crack model based on the strain decomposition concept, under the framework of the finite element method (FEM). Applying this model it was verified that the CSLM couldn't define a strain softening law able of simulating, with the necessary accuracy, the fracture mode I of the SFRC. Using an inverse analysis and the FEM model, the softening law for the SFRC analysed was evaluated. From the values obtained for the definition of this law it was concluded that this law cannot be exclusively dependent on the concept of equivalent flexural tensile strength, as RILEM TC 162-TDF recommends

Comportamento à tracção directa de elementos laminares de betão armado reforçado com fibras de aço

Quando comparado com o betão simples, o betão reforçado com fibras de aço, BRFA, apresenta melhor comportamento à fendilhação e maior capacidade de absorção de energia. Em consequência, a utilização de BRFA, em determinadas aplicações, pode ser uma mais valia em termos técnicos e económicos. O presente trabalho tem como principal objectivo avaliar a influência das fibras de aço no comportamento à tracção de elementos laminares de betão armado. Os principais resultados experimentais e numéricos são apresentados e discutidos

Betão auto-compactável reforçado com fibras de aço para o reforço à flexâo de estruturas laminares

Com o objectivo de avaliar a influência da adição de fibras discretas de aço no reforço à flexão de estruturas laminares de betão auto-compactável, foi realizado um programa experimental que consistiu no ensaio de faixas de laje armadas com distinta percentagem de armadura longitudinal, mantendo-se constante uma percentagem de fibras de aço julgada adequada para estruturas com elevado grau de hiperestaticidade.Os autores agradecem o apoio da FCT por intermédio do Projecto FICOFIRE - POCTI/ECM/57518/2004 e da empresa Maprel – Empresa de Pavimentos e materiais Pré-Esforçados, Lda. O 1º Autor agradece o apoio financeiro obtido por intermédio da bolsa, ao abrigo do projecto acima referido. À Empresa Bekaert S.A. um reconhecimento pelas fibras gentilmente oferecidas

High strength and ductile fibrous concrete of enhanced fire resistance

In the present work a Fiber Reinforced Concrete of Enhanced Fire Resistance (FRCEFR) was developed and its properties are characterized by experimental research. This concrete is intended to have enough resistance for the most structural engineering applications and is reinforced with a fibrous system to assure the necessary ductility and to improve its fire resistance. Two types of fibers are used to accomplish the aforementioned requisites for the concrete. The research performed for the selection of a nonmetallic fiber type for inclusion on the FRCEFR is resumed. The experimental programs carried out to evaluate the residual compressive and flexural behavior of the developed FRCEFR are presented and the main obtained results are analyzed. The tests were executed at 28 days after FRCEFR have been exposed to the following distinct levels of temperature: 250ºC, 500ºC, 750ºC and 1000ºC

Fibrous reinforcing system to increase the shear resistance of high strength concrete

The available research has evidenced that discrete steel fibers can increase significantly the shear resistance of High Strength Concrete (HSC) structural elements when High Strength Fiber Reinforced Concrete (HSFRC) is designed in such way that fiber reinforcing mechanisms are optimized. In general, the increase of the concrete compressive strength is associated to an increase of its compactness, resulting benefits in terms of durability, but a strong concern emerges related to the integrity of this material, since it fails in a too brittle mode when submitted to high temperatures. To contribute for the knowledge about the benefits provided by discrete steel fibers when added to HSC applied to laminar structures, an experimental program composed of slab strips submitted to shear loading configuration was carried out. Uniaxial compression tests with cylinders of 150 mm diameter and 300 mm height, and bending tests with 600×150×150 mm3 beams were executed to assess the compression and bending behavior of the developed HSFRC. To evaluate the influence of the percentage of fibers in the shear resistance of laminar structures, three point loading tests with slab strips of 800×170×150 mm3 dimensions were performed. Taking the obtained experimental results, the applicability of the formulation proposed by RILEM TC 162-TDF was evaluated. Test results showed that, even with relative low dosages of steel fibers, the increment in shear resistance was significantly increased. The main obtained results in the research program are presented and discussed in this paper.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/ECM/57518/200

Steel fibres for the shear resistance of high strength concrete beams

Available research on the use of steel fibres to increase the shear resistance of concrete structures shows that the effectiveness of this type of reinforcement increases with the increase of the concrete compressive strength, as long as the fibre rupture is avoided. Experimental research has also indicated that the effectiveness of the fibre reinforcement for the shear resistance is more pronounced in shallow beams than in deep beams. In terms of analytical research, some models have been proposed and, recently, RILEM TC 162 TDF recommended an analytical approach for the prediction of the fibre reinforcement contribution in terms of shear resistance of concrete beams. The present work has the purpose to contribute for this topic, discussing the performance of RILEM TC 162 TDF approach, by using the results obtained in an experimental program composed of three point bending tests with shallow beams of high strength concrete (HSC). Six different HSC compositions were developed, varying the dosage of steel fibres (0, 60 and 75 kg/m3) and concrete strength class. The experimental program also included tests to characterize the flexural behaviour of the developed high strength steel fibre reinforced concrete (HSSFRC). Using the force-deflection relationships obtained in the three point-notched beam bending tests, and performing an inverse analysis, the values of the fracture mode I parameters of the HSSFRC were determined. These values were used on the numerical simulation of the tests carried out with HSSFRC beams failing in shear, under the framework of the material nonlinear finite element analysis, in order to evince the influence of using a softening constitutive law for modeling the crack shear sliding. In the present work, the experimental program and the numerical research are described, and the main results are presented and discussed.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/ECM/57518/2004 “FICOFIRE : High performance fiber reinforced concrete of enhanced fire resistance