Retrofitting of reinforced concrete beams using composite laminates

This paper presents the results of an experimental study to investigate the behaviour of structurally damaged full-scale reinforced concrete beams retrofitted with CFRP laminates in shear or in flexure. The main variables considered were the internal reinforcement ratio, position of retrofitting and the length of CFRP. The experimental results, generally, indicate that beams retrofitted in shear and flexure by using CFRP laminates are structurally efficient and are restored to stiffness and strength values nearly equal to or greater than those of the control beams. It was found that the efficiency of the strengthening technique by CFRP in flexure varied depending on the length. The main failure mode in the experimental work was plate debonding in retrofitted beams.     

Applicability of rheological models to high-performance grouts containing supplementary cementitious materials and viscosity enhancing admixture

The knowledge of yield stress and plastic viscosity of cement-based materials is of special interest in various applications, including consolidation grouting, post-tensioning systems, and for numerical simulations. These rheological parameters are generally estimated from the shear stress-shear rate data using an empirical model. Highly pseudoplastic systems may not be adequately modeled using flow models typically used for conventional grouts. This paper summarizes the results of a study undertaken to evaluate the applicability of a number of analytical models to fit experimental data obtained on cement grout. In total, 44 grouts containing silica fume replacements of 1.5%, 3%, and 5% by mass of cementitious materials, blast furnace slag substitutions of 20% and 40%, and various combinations of high-range water-reducer and viscosity-enhancing admixture were evaluated. All mixtures were prepared with 0.40 water-cementitious material ratio.Test results highlight the difficulties encountered when using conventional models to fit flow data of highly pseudoplastic mixtures of low yield stress. This is true for mixtures incorporating a viscosity-enhancing admixture, especially when combined with low dosage of high-range water-reducer. In general, the Herschel-Bulkley, Robertson, De Kee, and Casson models were found to be adequate for use with highly pseudoplastic grouts. A new model is proposed to provide better fitting of rheological profiles of highly flowable, yet stable, pseudoplastic mixtures that exhibit particularly low yield stress values.     

Evaluation of cement grouts for embedding anchors under water

Approximately 110 pull-out tests were conducted on grouted anchors cast in the laboratory to investigate the effects of the rheological and mechanical properties of cement grouts, the initial free drop distance of grout, as well as the age of testing on the behavior of anchorages cast in dry and submerged conditions. The anchors consisted of 19-mm, conventional steel bars with an embedment length fixed at five times the bar diameter. Two different casting procedures corresponding to initial free drop of the grout in water of 20 and 200 mm were investigated. The cement grouts used in this investigation incorporated either a Type 10 or a blended silica fume cement and a fixed water-binder ratio of 0.40. The grouts incorporated various concentrations of a high-range water reducer, a rheology-modifying admixture, and silica fume. The rheology-modifying admixture and high-range water reducer were jointly incorporated to enhance both fluidity and washout resistance. The test results indicate that properly designed grouts can be easily cast into place, and yet be cohesive enough to resist the washout of cementitious materials. The spread in load-carrying capacity between anchor bars cast in dry versus submerged conditions can decrease when cement grouts having a greater washout resistance level are used which can be secured by incorporating a rheology-modifying admixture and silica fume. The bond strength is shown to increase when incorporating silica fume regardless of the casting condition.     

A Rigorous Global Filtering Algorithm for Quadratic Constraints*

This article introduces a new filtering algorithm for handling systems of quadratic equations and inequations. Such constraints are widely used to model distance relations in numerous application areas ranging from robotics to chemistry. Classical filtering algorithms are based upon local consistencies and thus, are often unable to achieve a significant pruning of the domains of the variables occurring in quadratic constraint systems. The drawback of these approaches comes from the fact that the constraints are handled independently. We introduce here a global filtering algorithm that works on a tight linear relaxation of the quadratic constraints. The Simplex algorithm is then used to narrow the domains. Since most implementations of the Simplex work with floating point numbers and thus, are unsafe, we provide a procedure to generate safe linearizations. We also exploit a procedure provided by Neumaier and Shcherbina to get a safe objective value when calling the Simplex algorithm. With these two procedures, we prevent the Simplex algorithm from removing any solution while filtering linear constraint systems. Experimental results on classical benchmarks show that this new algorithm yields a much more effective pruning of the domains than local consistency filtering algorithms.*This article is an extended version of [23].     

A novel classification approach based on Extreme Learning Machine and Wavelet Neural Networks

Multimedia Tools and Applications - In this paper, we present a novel classification approach based on Extreme Learning Machine (ELM) and Wavelet Neural Networks. We introduce two novel...