Analytical bond model for GFRP bars to steel fiber reinforced self-compacting concrete

The objective of this study is to present a computational algorithm to analytically evaluate the bond behavior between GFRP bar and steel fiber reinforced self-compacting concrete (SFRSCC). The type of information to be derived is appropriate to study the flexural behavior of SFRSCC beams reinforced with GFRP bars in terms of serviceability limit states requirements; in fact the bond between bars and surrounding concrete influences significantly the crack width and crack spacing. The proposed bond model was established by calibrating the parameters of a multilinear bond-slip constitutive law using the experimental results of pullout bending tests carried out by the authors, taking into account the experimental pullout force versus slip at loaded and free ends. According to the comparison between theoretical and experimental pullout force-slip, an acceptable accuracy of the model was observed. Additionally, by considering the proposed bond-slip relationship, a parametric study was carried out to evaluate the influence of the involved bond-slip law’s parameters on the maximum force transferred to the surrounding concrete. Finally, the development length of two GFRP bars utilized in the experiments (deformed and smooth bars) was determined by means of the proposed model, and it was compared with the values recommended by codes.Fundação para a Ciência e a Tecnologia (FCT

Interfacial bond behaviour of GFRP bar in self-compacting fiber reinforced concrete

In an ongoing research project, discrete steel fibers are being used in a self-compacting concrete (SFRSCC) to replace completely steel stirrups for pre-fabricated beams reinforced longitudinally with pre-stressed glass fiber reinforced polymer (GFRP) and steel bars. To take the advantages of the non-corrodible character and high tensile strength of GFRP bars, the minimum SFRSCC cover needs to be determined in order to assure the adequate bond performance between these bars and the surrounding SFRSCC. Since bond of the longitudinal bars has a relevant impact on the cracking behavior of RC elements (crack opening and crack spacing), an extensive experimental program composed of pullout bending tests was carried out where the influence of the following parameters was assessed in terms of bond behavior: GFRP bar diameter, surface characteristics of the GFRP bars, bond length, SFRSCC cover thickness. The local bond law was derived from inverse analysis and it was used to define the slip mode of the constitutive law adopted for interface finite elements. These interface finite elements were used to assess the crack opening and crack spacing on SFRSCC beams flexurally reinforced with GFRP bars. This paper resumes the experimental program, describes the strategy to derive the local bond law and presents and discusses the numerical simulations

Shear capacity of HPFRC beams flexurally reinforced with steel and prestressed GFRP bars

This paper presents the relevant results from an experimental program to assess the shear capacity of high performance fiber reinforced concrete (HPFRC) beams flexurally reinforced with a hybrid system of passive steel and prestressed GFRP longitudinal bars. Three series of two beams with different level of prestressing were tested. The effect of prestressing level on the shear capacity of the beams was the main investigated parameter. The results showed an enhancement of the load carrying capacity, ductility and energy absorption with the increase of the prestress level. Based on the obtained results, the predictive performance of the analytical formulations of CEB-FIP Model Code 2010 and RILEM TC 162-TDF for the shear capacity of FRC beams was assessed. Both formulations seem appropriate for design purposes, but the CEB-FIP formulation predicts more conservative shear capacity. The experimental results demonstrated that the prestressing level has an effect on the shear capacity much higher than the one recommended by the codes

Experimental and theoretical study on bond behavior of GFRP bars in steel fiber reinforced self compacting concrete

To estimate the cracking and the deformational behavior of steel fiber reinforced selfcompacting concrete (SFRSCC) beams reinforced with glass fiber reinforced polymer (GFRP) bars, it is fundamental to understand the interfacial bond behavior of embedded bars. Hence, the evaluation of the bond behavior between GFRP and (SFRSCC) was investigated in this study. A closed-form formulation was derived, adopting a new local bond stress-slip relationship. Furthermore, an experimental program composed of pullout bending tests was carried out in order to assess the influence of the following parameters on the bond behavior: bar diameter, bar surface treatment, embedment length and SFRSCC cover thickness. Finally, a numerical simulation was performed with a FEM-based computer program in order to simulate the bond behavior between GFRP bar and SFRSCC by means of a non-linear bond-slip relationship assigned to the interface finite element. The predictive performance of the theoretical models was appraised by comparing experimental and numerical results

Experimental study on bond performance of GFRP bars in self-compacting steel fiber reinforced concrete

Reinforcing bars made of Glass-Fiber-Reinforced Polymers (GFRP) are more and more common as internal reinforcement of concrete structures and infrastructures. Since the design of GFRP reinforced concrete members is often controlled by serviceability limit state criteria (i.e., deflection or crack width control), an accurate knowledge of the GFRP-concrete bond behavior is needed to formulate sound design equations. Furthermore, bond laws currently available and widely accepted for conventional steel rebars cannot be straightforwardly applied for GFRP ones. Hence, an experimental program consisting of 36 pullout bending tests was carried out to evaluate the bond performance between GFRP bars and steel fiber reinforced self-compacting concrete (SFRSCC) by analyzing the influence of the following parameters: GFRP bar diameter, surface characteristics of the GFRP bars, bond length, and SFRSCC cover thickness. Based on the results obtained in this study, pullout failure was occurred for almost all the specimens. SFRSCC cover thickness and bond length plaid important role on the ultimate value of bond stress of GFRP bars. Moreover, the GFRP bars with ribbed and sand-coated surface treatment showed different interfacial bond behaviors.Fundação para a Ciência e a Tecnologia (FCT

Numerical calibration of bond laws for GFRP bars embedded in steel fiber-reinforced self-compacting concrete

An experimental program was carried out at the Laboratory of Structural Division of the Civil Engineering Department of the University of Minho (LEST-UM) to investigate the bond behaviour of glass fibre reinforced polymer (GFRP) bars embedded in steel fibre reinforced self-compacting concrete (SFRSCC) for the development of an innovative structural system. Thirty-six pull-out-bending tests were executed to assess the influence of the bond length, concrete cover, bar diameter and surface treatment on the bond of GFRP bars embedded in SFRSCC. This paper reports the results of a numerical study aiming to identify an accurate GFRP–SFRSCC bond-slip law. Thus, the above mentioned pullout bending tests were simulated by using a nonlinear finite element (FE) constitutive model available in FEMIX, a FEM based computer program. The bond-slip relationship adopted for modelling the FE interface that simulates the interaction between bar and concrete is the key nonlinear aspect considered in the FE analyses, but the nonlinear behaviour of SFRSCC due to crack initiation and propagation was also simulated. The evaluation of the values of the relevant parameters defining such a bond-slip relationship was executed by fitting the force versus loaded end slip responses recorded in the experimental tests. Finally, correlations are proposed between the parameters identifying the bond-slip relationship and the relevant geometric and mechanical properties of the tested specimens.Fundação para a Ciência e a Tecnologia (FCT

Length-Independent Charge Transport in Chimeric Molecular Wires

Advanced molecular electronic components remain vital for the next generation of miniaturized integrated circuits. Thus, much research effort has been devoted to the discovery of lossless molecular wires, for which the charge transport rate or conductivity is not attenuated with length in the tunneling regime. Herein, we report the synthesis and electrochemical interrogation of DNA-like molecular wires. We determine that the rate of electron transfer through these constructs is independent of their length and propose a plausible mechanism to explain our findings. The reported approach holds relevance for the development of high-performance molecular electronic components and the fundamental study of charge transport phenomena in organic semiconductors