The influence of service temperature on bond between FRP reinforcement and concrete

The interest in fibre reinforced polymer (FRP) reinforcement in construction has considerably increased and especially the application of FRP as externally bonded reinforcement (FRP EBR) has become more and more established. The use of FRP EBR has been adopted world-wide as a very attractive technique for structural strengthening and rehabilitation. At Ghent university, the fire behaviour of slabs and beams strengthened with advanced composites, including the use of fire protection systems, has been investigated. In addition, the behaviour of the FRP-concrete interface at increased temperatures has been considered, as elevated temperatures may occur during service conditions, especially for outdoor applications. According to fib Bulletin 14, the glass transition temperature of the adhesive used to bond the FRP should equal 20°C in excess of the maximum ambient temperature at normal service conditions, and should be at least 45°C. When reaching the glass transition temperature, the properties of the adhesive decrease to a large extend and bond interaction between the concrete and the external FRP reinforcement may be completely lost. To study the bond behaviour at elevated temperatures, a joint test program between the Universities of Ghent and Lecce has been executed, comprising a series of 20 bond tests performed at the Magnel Laboratory for Concrete Research. The present paper will discuss the experimental work and the main test results obtained

Finite Element Analysis of FRP Debonding Failure at the Tip of Flexural/Shear Crack in Concrete Beam

One of the most common failure modes of strengthened RC beams with externally bonded FRP is intermediate crack (IC) debonding of FRP initiated at the tip of flexural/shear cracks. This study presents a method, using extended finite element method (XFEM), to model IC debonding in an FRP-strengthened concrete beam. In XFEM, as soon as a damage initiation criterion is reached in an element, additional degrees of element freedom are added to model crack initiation. Crack propagation is then modeled using fracture energy criterion. This method can be used to simulate debonding failure along an arbitrary, solution-dependent path without the requirement of remeshing. The numerical results are validated against experimental data and good agreement is found. A sensitivity analysis is conducted to study the effects of damage band properties and geometry on FRP debonding failure. This verifies that shear strength and critical mode II fracture energy are the parameters most affecting the FRP debonding model when the crack tip is subjected to mode II loading

Synthesizing Functional Reactive Programs

Functional Reactive Programming (FRP) is a paradigm that has simplified the construction of reactive programs. There are many libraries that implement incarnations of FRP, using abstractions such as Applicative, Monads, and Arrows. However, finding a good control flow, that correctly manages state and switches behaviors at the right times, still poses a major challenge to developers. An attractive alternative is specifying the behavior instead of programming it, as made possible by the recently developed logic: Temporal Stream Logic (TSL). However, it has not been explored so far how Control Flow Models (CFMs), as synthesized from TSL specifications, can be turned into executable code that is compatible with libraries building on FRP. We bridge this gap, by showing that CFMs are indeed a suitable formalism to be turned into Applicative, Monadic, and Arrowized FRP. We demonstrate the effectiveness of our translations on a real-world kitchen timer application, which we translate to a desktop application using the Arrowized FRP library Yampa, a web application using the Monadic threepenny-gui library, and to hardware using the Applicative hardware description language ClaSH.Comment: arXiv admin note: text overlap with arXiv:1712.0024

Fixed Tree Games with Repeated Players

This paper introduces fixed tree games with repeated players (FRP games) which are a generalization of standard fixed tree games.This generalization consists in allowing players to be located in more than one vertex.As a consequence, these players can choose among several ways of connection with the root.In this paper we show that FRP games are balanced.Moreover, we prove that the core of an FRP game coincides with the core of a related concave fixed tree game.We show how to find the nucleolus and we characterize the orders which provide marginal vectors in the core of an FRP game.games;cooperative games;core

Literature review on reinforced concrete members strengthened with FRP at room and elevated temperature

In the last 30 years, composite materials have been successfully applied as structural reinforcement to strengthen existing structures. The success of applying FRPs (Fibre Reinforced Polymers) for strengthening is due to their excellent mechanical properties and durability, their ease of application and the versatility of FRP strengthening systems. In particular Near Surface Mounted (NSM) reinforcement offers an interesting technology in terms of protection of the FRP from external influences compared to the Externally Bonded Reinforcement method (EBR). Based on a literature review, this paper discusses the structural performance in terms of FRP to concrete bond behaviour at room and elevated temperature. To understand and characterize the bond interaction, researchers conducted bond shear tests, though the lack of a standard test methodology makes comparison of results not always straight forward. As such, this study looks into bond influencing factors such as concrete type, adhesive type, FRP roughness, groove dimensions, glass transition temperature and coefficient of thermal expansion

Analysis of FRP shear strengthening solutions for reinforced concrete beams considering debonding failure

In this paper, a fiber beam model previously developed by the authors for the nonlinear analysis of strengthened elements, including the effects of shear, is used to predict the response of reinforced concrete (RC) beams strengthened in shear with fiber reinforced polymers (FRP) sheets. In the previous version of the model, debonding failure of FRP was not included; hence, its application was limited to the simulation of wrapped configurations. The model is now extended to account for debonding failure in order to allow for its application to beams strengthened with U-shaped and side-bonded configurations. Existing experimental tests on RC beams strengthened in shear by FRP sheets in both wrapped and U-shaped configurations were numerically simulated. The model reproduces, with reasonable accuracy, the experimental failure loads, the load-deflection behavior, and the strains in FRP and stirrups with increasing load. The advantages of this proposal are related with the simplicity and straightforwardness of the beam models to be applied in practical engineering problems.Peer ReviewedPostprint (author's final draft

Use of FBG sensors for SHM in aerospace structures

This paper details some significant findings on the use of the fiber Bragg grating (FBG) sensors for structural health monitoring (SHM) in aerospace fiber reinforced polymer (FRP) structures. A diminutive sensor provides a capability of imbedding inside FRP structures to monitor vital locations of damage. Some practical problems associated with the implementation of FBG based SHM systems in the aerospace FRP structures such as the difficulty of embedding FBG sensors during the manufacturing process and interrelation of distortion to FBG spectra due to internal damage, and other independent effects will be thoroughly studied. An innovative method to interpret FBG signals for identifying damage inside the structures will also be discussed

Design philosophy issues of fiber reinforced polymer reinforced concrete structures

The conventional design philosophy for reinforced concrete (RC) relies heavily on the ductile properties of steel. These ductile properties are used as a "fuse" and conceal the large uncertainty in the determination of modes of failure caused directly by concrete. Current design guidelines for fiber reinforced polymer (FRP) RC structures have inappropriately adopted the same design philosophy used for steel RC, leading either to the adoption of conservative safety factors or reduced structural reliability. A reliability-based analysis of FRP RC beams shows that the current, very conservative partial safety factors for FRP reinforcement on their own do not influence the structural safety of overreinforced concrete elements. Proposals are made for the modification of the material partial safety factors to achieve target safety levels

Bond–slip Behavior of Fiber-reinforced Polymer/concrete Interface in Single Shear Pull-out and Beam Tests

It has been assumed that the fiber-reinforced polymer/concrete interface is subjected to in-plane shear condition when intermediate crack debonding failure occurs. Therefore, the single shear pull-out test results are often used to predict the intermediate crack debonding failure in beams. In this study, the behavior of fiber-reinforced polymer-strengthened concrete beams and single shear pull-out specimens were studied experimentally and numerically. The bond–slip behavior of the fiber-reinforced polymer/concrete interface was obtained by single shear pull-out and beam tests. In all beam specimens, a concrete wedge located at the edge of the notch detached with the fiber-reinforced polymer debonding failure. This phenomenon shows that the initiation of debonding is due to a diagonal crack formation close to the major flexural/shear crack inside the concrete. The diagonal crack formation is due to a local moment at the tip of the notch. This causes the different stress state and slip of the fiber-reinforced polymer/concrete interface of beam specimens from that of the pull-out specimens. It is found that the bond–slip relation obtained from the pull-out test does not represent the bond–slip relation of the fiber-reinforced polymer/concrete interface in the fiber-reinforced polymer-strengthened concrete beams, and it cannot be directly used for predicting the load capacity of the fiber-reinforced polymer-strengthened concrete beams

Bond shear stress-slip relationships for FRP-NSM systems at elevated temperature

In the last years Near Surface Mounted (NSM) reinforcement has mainly been applied at ambient temperature, to strengthen reinforced concrete (RC) beams with FRP (fibre reinforced polymer) materials. Thereby, FRP bars/strips are embedded inside the concrete section by means of grooves filled with adhesive. The behaviour of FRP-NSM strengthening systems at elevated temperature is signicantly influenced by the type of adhesive (e.g. cementitious grout is usually more stable than epoxy resin at high temperature). To characterize the FRP-NSM behaviour two steps are needed: 1) shear tests performed in order to determine the FRP-concrete interaction via bond stress-slip curves and 2) constitutive bond stress-slip relationships for use in structural design (analytical and numerical). Hereby, the bond behaviour is to be considered temperature dependent. During two experimental campaigns, double bond shear tests were performed in order to study the behaviour of FRP-NSM systems at elevated temperature using different types of adhesive, epoxy resin and cementitious grout respectively. The bond shear stress-slip curves are discussed including the effect of different types of adhesive. Simplified bond stress-slip relationships are proposed to model the FRP-concrete interaction at high temperature