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Very limited research studies have been conducted to examine bond of glass fibre reinforced polymer (GFRP) bars with high concrete strength. The current research project aims to compare between bond measured from a pull-out test and a hinged beam test for GFRP bars embedded in high strength concrete. Different parameters influencing bond such as GFRP bar diameter, embedment length and surface configuration were investigated in both test methods, while the bar position, i.e. top or bottom, was only studied in hinged beams. Seventy-two pull-out cubes, eight pull-out prisms and twenty-four hinged beams reinforced with GFRP bars were constructed and tested to failure. Twelve pull-out cubes and four hinged beams reinforced with steel bars were also tested for comparison purposes. The results showed that bond stress – slip curves obtained from various testing methods were similar, consisting of high initial stiffness, followed by nonlinear ascending and softening branches. In addition, it was found that the experimental bond strength obtained from hinged beams was higher than both bond strengths measured by the pull-out cube and pull-out prism. However, when a finite element analysis was conducted for hinged beams, it was shown that the tensile force in the reinforcing bar estimated by equilibrium conditions is overestimated as the large deformation of hinged beams at failure was not considered. Therefore, if the tensile force obtained from the finite element analysis is used to calculate the bond strength, it would be similar to that obtained from pull-out cube and prism. Moreover, it was found that the distribution of tensile and bond stresses was nonlinear along the GFRP embedment length and bond stress at the vicinity of the free end increased with increasing the load due to redistribution of bond stresses along the embedment length. Bond strengths were compared against the prediction methods provided in ACI-440.1R, CSA-S806, CSA-S6 and JSCE 1997. In general, all design codes showed conservative results for all specimens tested and ACI predictions gave a good agreement with experimental data compared to other codes. Artificial neural network models were developed to predict bond strength of GFRP bars in concrete. These models used bar diameter, embedment length, concrete compressive strength and concrete cover as input variables. The developed ANN models showed to be able to predict bond strength of GFRP bars in concrete and, therefore, were used to conduct a parametric study. / Higher Education Institute, Government of Libya

Yes / This paper presents test results of fifteen reinforced engineered cementitious composite (ECC)-concrete beams. The main parameters investigated were the amount and type of reinforcement, and ECC thickness. All reinforced ECC-concrete composite beams tested were classified into four groups according to the amount and type of main longitudinal reinforcement used; three groups were reinforced with FRP, steel and hybrid FRP/steel bars, respectively, having similar tensile capacity, whereas the fourth group had a larger amount of only FRP reinforcement. In each group, four height replacement ratios of ECC to concrete were studied. The test results showed that the moment capacity and stiffness of concrete beams are improved and the crack width can be well controlled when a concrete layer in the tension zone is replaced with an ECC layer of the same thickness. However, the improvement level of ECC-concrete composite beams was controlled by the type and amount of reinforcement used. Based on the simplified constitutive relationships of materials and plane section assumption, three failure modes and their discriminate formulas are developed. Furthermore, simplified formulas for moment capacity calculations are proposed, predicting good agreement with experimental results. / National Natural Science Foundation of China (51678514, 51308490), the Natural Science Foundation of Jiangsu Province, China (BK20130450), Six Talent Peaks Project of Jiangsu Province (JZ-038, 2016), Graduate Practice Innovation Project of Jiangsu Province (SJCX17-0625), the Jiangsu Government Scholarship for Overseas Studies and Top-level Talents Support Project of Yangzhou University.

Alternate bars are large-scale bedforms characterised by an ordered sequence of scour zones and depositional diagonal fronts alternating along channel banks, which are typical of straight channelized rivers. Due to their high relief and migration properties, they represent a problem in river management, because they affect navigation, increase the flooding risk and interact with instream structures. For this reason, in the last decades many studies took the challenge of defining suitable criteria able to describe their morphometric properties. Theoretical, experimental and numerical works have clearly demonstrated that bar occurrence is a threshold process governed by the width-to-depth ratio of the channel, β. If this parameter exceeds a critical threshold, βcr, an instability mechanism amplifies the riverbed perturbations occurring due to the effect of the turbulent flow on the cohesionless riverbed, leading to the spontaneous growth of finite amplitude bars. Under steady flow conditions, alternate bars achieve an equilibrium configuration, whose amplitude value is related to the difference β-βcr. Much less information is available to describe bar characteristics under variable flow conditions, when the width-to-depth ratio changes in time and the amplitude of bars evolves depending on the duration and the shape of the hydrograph. The effect of a single idealized flood on bar amplitude evolution was successfully described by the weakly nonlinear model of Tubino (1991), which was able to capture the trajectory of bar amplitude during different stages of the flood. Supported by experimental results, he found that the response of bars crucially depends on the ratio between the flood duration and the bar-growth timescale. Nevertheless, the effect of a complex flow regime, characterised by a sequence of flow events, is to a large extent unexplored. Specifically, (i) the definition of a criterion to predict the average response of alternate bars in a river reach subject to an hydrological flow regime and (ii) the quantification of bar amplitude evolution due to a complex flow regime are still to a large extent unexplored. The goals of this work are: (i) to investigate the dependence of bar properties to variable discharge conditions; (ii) to analyse the effect of flow unsteadiness in terms of duration and sequencing of flood events and derive the main hydrological characteristics that primarily control the average response of bar amplitude; (iii) to determine the long-term bar geometry and define the "bar-forming'' discharge, which is the theoretical discharge that if maintained indefinitely would produce the same long-term bar response as the natural hydrograph; (iv) to analyse the effect that a sequence of flood events composing a complex flow series has on the evolution of bar amplitude. To pursue these purposes, we adopted a methodology primary based on theoretical models, then supported and validated through the analysis of laboratory experiments and field data. The methodology and the key results for the different parts of this thesis can be summarized as follows: 1. First, the response of bar topography to different flow stages has been investigated both theoretically and through the analysis of experimental data, observing the dependence of alternate bars to peculiar threshold conditions. The validity of weakly nonlinear model of Colombini et al. (1987), originally defined in the neighborhood of the critical condition βcr, has been extended taking into account the emersion of bars for low flows. 2. Subsequently, the average response of bars to idealized flow series has been analysed, exploring their dependence on the duration and sequencing of flood events. The probability density function has been found to be the essential hydrological information of the flow series required to determine the long-term response of bar amplitude, while the integral scale of flow sequence is a suitable metric to quantify the unsteadiness of a flow regime. 3. Then, an innovative approach has been introduced to define an occurrence criterion for alternate bars in straightened river reaches that accounts for the hydrological regime, and to determine the average bar state, with the corresponding "bar-forming'' discharge. The key novelty with respect to the classical methods adopted so far to predict the long-term equilibrium channel geometry is that in this case the morphodynamical work acted on river bars by relatively low-flow stages enhancing their formation can be reversed by high-flow stages that suppress them. Therefore, both the occurrence criterion and the average state are found from a balance between the cumulative effects of bar-forming and bar-suppressing events. 4. Finally, the weakly nonlinear model of Colombini et al. (1987), originally defined to predict the evolution of bars under steady flow conditions, has been extended to reproduce a natural flow series by considering the basic flow varying in time. This approach allows us to (i) statistically investigate the effect of flood magnitude and duration on the variations of bar amplitude and (ii) to simulate the morphological response of a river to alterations of the hydrological regime.The long-term analysis of bar amplitude, as such as its evolution subject to the hydrological flow regime, have been applied to four different study cases, each of them characterised by a distinctive average bar response: two reaches of the Alpine Rhine River, upstream and downstream the confluence of the River Ill (Switzerland), respectively, the Adige River near Trento (Italy) and the Isère River near Montmèlian (France). The theoretical model is able to capture both qualitatively and quantitatively the observed bed response. Specifically, it predicts the occurrence of high-relief bars for the upstream reach of the Alpine Rhine River and for the Isère River, while a plane configuration is predicted for the Adige River. Also the intermediate response of the downstream reach of the Alpine Rhine River is reproduced, showing a predominant flat bed morphology with sporadic low-relief bars.

No / Paper accepted for conference.

Energy dissipation in systems with linear viscoelastic damping is examined. It is shown that in such viscoelastically damped systems the use of additional dissipation mechanisms (such as boundary velocity feedback or thermal coupling) may not improve the rate of energy decay. The situation where the viscoelastic stress relaxation modulus decreases to its (positive) equilibrium modulus at a subexponential rate, e.g., like (1 + t)^-x + E, where α > 0, E > 0 is examined. In this case, the nonoscillatory modes (the so-called creep modes) dominate the energy decay rate. The results are in two parts. In the first part, a linear viscoelastic wave equation with infinite memory is examined. It is shown that under appropriate conditions on the kernel and initial history, the total energy is integrable against a particular weight if the kinetic energy component of the total energy is integrable against the same weight. The proof uses energy methods in an induction argument. Precise energy decay rates have recently been obtained using boundary velocity feedback. It is shown that the same decay rates hold for history value problems with conservative boundary conditions provided that an <i>a priori</i> knowledge of the decay rate of the kinetic energy term is assumed. In the second part, a simple linear thermo-viscoelastic system, namely, a viscoelastic wave equation coupled to a heat equation, is examined. Using Laplace transform methods, an integral representation formula for <i>W(x,s</i>), the transform of the displacement <i>w(x, t)</i>, is obtained. After analyzing the location of the zeros of the appropriate characteristic equation, an asymptotic expansion for the displacement <i>w(O,t)</i> is obtained which is valid for large <i>t</i> and the specific kernel <i>g(t) = g</i>(–) + δtη-1 [over]Î (η), 0 < η < 1. With this expansion it is shown that the coupled system tends to its equilibrium at a slower rate than that of the uncoupled system. / Ph. D.

In order to predict the future needs of existing bridges, Bridge Management Systems use models to predict the time when damage will reach a level to cause repair, rehabilitation, or replacement of the structure. One such model is the deterioration model, which has three distinct phases. The second phase of the model, the corrosion phase, is the focus of this study. During the corrosion phase, chloride ion concentration reaches a threshold level at the depth of the reinforcing steel which initiates corrosion. The corrosion continues until sufficient pressure is exerted on the surrounding concrete to cause cracking. This study is a continuation of a study implemented in the Materials Division at Va Tech. The study includes the monitoring of the corrosion rate of steel reinforcing bars placed in simulated bridge decks. The corrosion rates were varied by placing between 0 - 9.6 Ibs/yd³ of chloride ions in the concrete to produce six different series. Also, the depth of concrete cover, bar spacing, bar size, and exposure conditions were varied. The specimens were monitored until the time that the cracking of the concrete was observed. At that time, samples of the steel reinforcing bars were removed and the actual amount of corrosion which had occurred was determined as the weight loss of the steel. The actual weight loss of the steel reinforcing bars was then compared to the predicted weight loss from the corrosion rate measurement devices. The time to cracking and the mode of cracking was compared to Bazant's equations for cracking which are the basis for the corrosion phase of the deterioration model. Although only one series cracked during the study, corrections in the use of Bazant's equations were proposed. / Master of Science

The primary objective of this research was to examine the strength degradation of Glass Fiber Reinforced Polymer (GFRP) bars at high temperature and alkalinity and determine if an Arrhenius type relationship can be used as a means of projecting life. The work done includes a thorough literature review, experiments and development of strength prediction models. The experimental work involves exposure of GFRP bars incased in cement mortar to lime-water solution at 30, 45 and 57°C. Overall 100 specimens were included in the experimental program. The tensile strength and modulus of elasticity retention after 180 days of exposure at 57°C was 57% and 82% respectively. The secondary objective was to determine the moisture absorption properties of GFRP bars. The moisture absorption data available is till 80 days from the immersion of the specimens in the tank. The collected data was used in the development of strength retention models. Two strength prediction models, Time Shift Method and Fickian Model for moisture absorption are formulated. Using the Fickian Model, strength is predicted for GFRP bars, if used in bridge decks in Roanoke, Virginia. The strength loss predicted was 45% after 50 years of exposure in real life environment. A linear relationship was observed when the moisture content and strength retention were plotted. The study estimates a strength loss higher than the ACI-440H recommended environmental degradation factor of 0.7 to calculate the design ultimate tensile strength. / Master of Science

The primary objective of this project was to test a full-scale prototype of an actual bridge deck containing GFRP bars as the top mat of reinforcement. The purpose of the tests was to verify that the design would resist the loads for which it was designed and provide assurance that the deck would not unexpectedly fail due to the use of this new material. Behavior of the bridge and deck, such as failure load, failure mode, cracking load, crack widths, deflections, and internal stresses, were examined. Four tests were performed on the deck, all of which tested the deck in negative moment regions. From the tests, it was concluded that the design of the deck was very conservative and that unexpected failure should be of no concern. The secondary objective of this project was to comment on the construction of a bridge deck reinforced with GFRP bars and to note its advantages and disadvantages along with a critique of the current state-of-the-art of designing bridge decks with FRP reinforcement. It was found that the advantages of construction with GFRP bars far outweighed the disadvantages, and that the placing of the top mat of GFRP bars was much easier than the placing of the bottom mat of steel bars. It was also concluded that the current state-of-the-art of designing bridge decks reinforced with GFRP is, for the most part, inaccurate in its prediction of behavior and that more research is needed to create more accurate design equations and procedures. Although current methods do not result in accurate predictions of behavior, they do, as mentioned above, result in conservative designs. / Master of Science