Seismic strengthening of beam-column joints with multidirectional CFRP laminates

An experimental program was carried out to analyse the potentialities of a technique based on the use of multidirectional CFRP laminates (MDL-CFRP) for the seismic repair and strengthening of reinforced concrete (RC) beam-column joints. This experimental program comprises cyclic tests on three full-scale RC joints, representative of interior beam-column connections in buildings. The joints were initially submitted to a cyclic test inducing a damage pattern representative of a seismic event. Subsequently, they were repaired and strengthened with MDL-CFRP. The strengthened joints were then tested for the same loading history of the original ones up to their failure. The adopted strengthening technique uses the MDL-CFRP that are simultaneously glued and anchored to the concrete surfaces. This technique is called Mechanically Fastened and Externally Bonded Reinforcement (MF-EBR). In the present study, the effectiveness of two different strengthening configurations was investigated. The tests are described and the main results are presented and analyzed

Seismic retrofit of RC beam-column joints using the MF-EBR strengthening technique

The strengthening technique based on the application of multi-directional laminates of CFRP (MDL-CFRP) simultaneously glued and anchored to the surface of the elements to be strengthened has been recently proposed. This technique was designated Mechanically Fastened and Externally Bonded Reinforcement (MF-EBR) and combines the fasteners from the MF-FRP technique with the externally glued properties from the EBR. With the aim of assessing the potentialities of this technique for seismic retrofitting, three interior RC beam-column joints were strengthened according to the MF-EBR technique and tested. This work presents the entire test program executed, including test configuration, results and corresponding analysis

Steel fibre reinforced self-compacting concrete for lightweight and durable pedestrian bridges : creep behaviour

In recent years, pedestrian bridges built from composites materials have notably increased. This growth is related to the durability problems of traditional materials, as well as the need for fastest construction times. In this context, fiber reinforced concrete (FRC) becomes an important material in this type of structures, since the ductility, high post-cracking tensile strength, high compressive stiffness and strength of FRC can be combined with the benefits derived from the use of FRP profiles to obtain high performance structural systems. In addition, FRC exhibits a durable behaviour since, in general, does not have corrosion problems. In this paper a 12 m length single span pedestrian bridge composed by a Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC) deck and two Glass Fiber Reinforced Polymer (GFRP) pultruded I shape profiles was designed. The SFRSCC deck has a constant thickness of 40 mm and 2000 mm wide and a content of hooked ends steel fibers in its mixture, which ensures the necessary strength and ductility for the acting loads. The high post-cracking tensile strength of the SFRSCC allowed the use of pre-stressed solutions in the bridge structural system, which caused an upward deflection and, consequently, tensile stresses in the SFRSCC deck. Two prototypes of this structural system were built and monitored in order to assess their long-term deformational behavior when subjected to a loading configuration correspondent to the load combination for the deflection serviceability limit states. The main results are presented and discussed

Influence of fatigue and aggressive exposure on GFRP girder to SFRSCC deck all-adhesive connection

To assess the influence of fatigue loading and environmental conditions on the bond behavior between glass fiber reinforced polymer (GFRP) systems and steel fiber reinforced self-compacting concrete (SFRSCC) that are adhesively bonded, an experimental program composed of push-out tests was carried out. The following three scenarios were selected for the environmental conditions: natural conditions; wet-dry cycles; and temperature cycles. Half of the specimens were submitted to monotonic loading up to failure, and the other half were submitted to a fatigue load configuration of 1-million cycles and then subjected to a monotonic loading up to failure. The results have shown that for the investigated environmental conditions the GFRP-SFRSCC push-out specimens never failed up to 1 million cycles. However, temperature cycles caused a considerable reduction on the stiffness and load carrying capacity in the specimens submitted to fatigue loading, while wet-dry cycles did not modify significantly the maximum shear stress transfer in the investigated connection. This paper describes in detail the experimental program, presenting and discussing the relevant results.AD

Development of a pedestrian bridge with GFRP profiles and fibre reinforced self-compacting concrete deck

In recent years, the number of pedestrian bridges built from composites materials has notably increased. The combination of fiber reinforced polymers (FRP) profiles with fiber reinforced concrete (FRC) elements is being adopted in this type of structures, since the ductility, high post-cracking tensile strength, compressive stiffness and strength of FRC can be combined with the benefits derived from the use of FRP’s profiles to obtain high performance structural systems. In the context of the present work a 12 m long single span pedestrian bridge with two composite Iprofiles was designed. In terms of deflection requirements imposed by serviceability limit states, the influence of the height and thickness of GFRP (Glass Fiber Reinforced Polymer) profiles, as well as the addition of a thin layer of prestressed carbon fiber sheet in the bottom flange of the GFRP profile was evaluated. Using software based on the finite element method, the structural behavior of the developed structural systems was analyzed. Furthermore, two prototypes of this structural system were built and monitored in order to assess their long-term deformational behavior when subjected to a loading configuration correspondent to the load combination for the deflection serviceability limit states. The main results obtained are presented and discussed.This work is part of the research project QREN number 3456, PONTALUMIS- Development of a prototype of a pedestrian bridge in GFRP-ECC concept, involving the Company ALTO - Perfis Pultrudidos, Lda., the ISISE/University of Minho and the ICIST/Technical University of Lisbon. The first and fourth authors wish to acknowledge the research grants under this project. The authors also wish to acknowledge the Civitest Company for the conception and development of the steel fiber reinforced self-compacting concrete used in this work, and to Secil, S&P Clever Reinforcement Iberica Lda. and Hilti Portugal - Productos e Servicos Lda. for the supplied materials and technical support

Modelling of bond between galvanized steel rebars and concrete

In reinforced concrete structures, it is extremely difficult to ensure that steel bars will be not subject, either in a lower or higher extent, to the corrosion effect. The application of hot dip galvanized rebar is an economic and effective way of protecting reinforced concrete against corrosion. This protective technique has an influence, which should not be disregarded, on the performance of the rebar’s coating, its behaviour and, fundamentally, the bond between concrete and galvanized rebar. With the aim of studying the bond behaviour between galvanized steel rebar and concrete, an experimental program was carried out by means of direct pullout tests. To predict the full pullout response, an analytical cohesive interface model was developed to obtain the bond stressslip relationship. To account for the interfacial bond, a nonlinear bond stress-slip law was used. In the present work the numerical method and mathematical tools are detailed and its performance is assessed. Hence, the parameters that define the local bond stress slip relationship are obtained by a fitting procedure between the simulated pullout curve and the experimental one. Finally, the obtained local bond law relationship is compared to the one proposed by the CEB-FIP Model Code

Influence of fatigue loading and environmental conditions on the bond behavior between GFRP systems and SFRSCC substrate

To assess the influence of fatigue loading and environmental conditions on the bond behavior between glass fiber reinforced polymer (GFRP) systems and steel fiber reinforced self-compacting concrete (SFRSCC) that are adhesively bonded, an experimental program composed of push-out tests was carried out. The following three scenarios were selected for the environmental conditions: natural conditions; wet-dry cycles; and temperature cycles. Half of the specimens were submitted to monotonic loading up to failure, and the other half were submitted to a fatigue load configuration of 1 -million cycles and then subjected to a monotonic loading up to failure. The results have shown that for the investigated environmental conditions the GFRP-SFRSCC push-out specimens never failed up to 1 million cycles. However, temperature cycles caused a considerable reduction on the stiffness and load carrying capacity in the specimens submitted to fatigue loading, while wet-dry cycles did not modify significantly the maximum shear stress transfer in the investigated connection. This paper describes in detail the experimental program, presenting and discussing the relevant results

Numerical simulation of galvanized rebars pullout

The usage of rebars in construction is the most common method for reinforcing plain concrete and thus bridging the tensile stresses along the concrete crack surfaces. Usually design codes for modelling the bond behaviour of rebars and concrete suggest a local bond stress – slip relationship that comprises distinct reinforcement mechanisms, such as adhesion, friction and mechanical anchorage. In this work, numerical simulations of pullout tests were performed using the finite element method framework. The interaction between rebar and concrete was modelled using cohesive elements. Distinct local bond laws were used and compared with ones proposed by the Model Code 2010. Finally an attempt was made to model the geometry of the rebar ribs in conjunction with a material damaged plasticity model for concrete

Evaluation of code formulations for NSM CFRP bond strength of RC elements

This paper presents an analytical analysis which intends to verify the accuracy of existing code formulations for predicting the pullout strength of NSM CFRP systems applied to concrete. A database with a limited set of parameters was gathered and two code formulations were tested on it. Then, a new approach was tested. This uses Data Mining algorithms to develop models to predict the pullout strength based on user chosen parameters. The results reveal that existent code formulations aren’t as accurate as expected and that Data Mining can be a sound alternative or, at least, a good complement since it can also help know and understand the key parameters with relevant influence on the pullout strength of such strengthening systems

Investigação no âmbito da utilização de materiais compósitos no reforço de estruturas de betão

Nos últimos anos tem sido crescente a utilização de materiais compósitos no reforço de estruturas de betão armado. Para tal contribui as melhores propriedades mecânicas destes materiais, a sua maior resistência à acção de agentes agressivos e a sua maior leveza e facilidade de aplicação, quando se tem por base de comparação materiais convencionais tais como o aço e o betão. No Subgrupo de Estruturas do Departamento de Engª Civil da Escola de Engª da Universidade do Minho tem-se efectuado investigação experimental e numérica no âmbito da utilização de laminados em fibra de carbono (CFRP) no reforço de estruturas de betão. Estes materiais compósitos têm sido utilizados no reforço à flexão e ao corte de pilares e vigas. A ligação CFRP-adesivo-betão tem sido caracterizada por forma a ser estabelecida a lei que define a transferência de tensões entre os materiais constituintes desta ligação, lei esta a ser implementada num modelo de interface, no quadro do método dos elementos finitos. Os resultados mais significativos obtidos na investigação efectuada são apresentados no presente trabalho