SUMMARYThis paper presents a numerical procedure for bond between indented wires and concrete, and the coupled splitting process of the surrounding concrete. The bond model is an interface, non-associative, plasticity model. It is coupled with a cohesive fracture model for concrete to take into account the splitting of such concrete. Bond between steel and concrete is fundamental for the transmission of stresses between both materials in precast prestressed concrete. Indented wires are used to improve the bond in these structural elements. The radial component of the prestressing force, increased by Poisson's effect, may split the surrounding concrete, decreasing the wire confinement and diminishing the bonding. The combined action of the bond and the splitting is studied with the proposed model. The results of the numerical model are compared with the results of a series of tests, such as those which showed splitting induced by the bond between wire and concrete. Tests with different steel indentation depths were performed. The numerical procedure accurately reproduces the experimental records and improves knowledge of this complex process.
This paper presents an analytical model for simulating the bond between steel and concrete, in precast prestressed concrete elements, during the prestressing force release. The model establishes a relationship between bond stress, steel and concrete stress and slip in such concrete structures. This relationship allows us to evaluate the bond stress in the transmission zone, where bond stress is not constant, along the whole prestressing force release process. The model is validated with the results of a series of tests and is extended to evaluate the transmission length. This capability has been checked by comparing the transmission length predicted by the model and one measured experimentally in a series of tests. Keywords:Bond, prestressed concrete, transmission length, modelling, bond strength IntroductionPrecast prestressed concrete elements are widely used for construction in Europe. A frequent problem of the precast industry is to evaluate the real transmission length in precast prestressed concrete structural elements. The semi-empirical formulae proposed by codes are usually thought for conventional concrete and usual cast conditions, but high performance concrete (high-strength, self-compacting, etc.) and non-usual cast conditions (v.gr. accelerated curing processes) are becoming more and more frequent. In these cases experimental measurement is needed, though the standardised methods are expensive and so difficult to apply by industry. Analytical and numerical models, based on parameters measured experimentally with tests being simpler than complete transmission length tests, would be welcomed. This paper presents an analytical model for steel-concrete bond when the prestressing force is transmitted by releasing the steel (wire or strand). The model is applied to evaluate the transmission length. Theoretical backgroundThe prestressing process of the precast prestressed concrete includes: a) steel wire prestressing, and b) prestressing force transmission after an accelerated curing process of concrete. Let be a prism of concrete with a single prestressed wire placed in the prism longitudinal axis (Fig. 1). Be P 0 the initial prestressing force in the wire and, for a given instant, the force at the end of the wire P 0 -∆P,
Classification of time series is a growing problem in different disciplines due to the progressive digitalization of the world. Currently, the state of the art in time series classification is dominated by Collective of Transformation-Based Ensembles. This algorithm is composed of several classifiers of diverse nature that are combined according to their results in an internal cross validation procedure. Its high complexity prevents it from being applied to large datasets. One Nearest Neighbours with Dynamic Time Warping remains the base classifier in any time series classification problem, for its simplicity and good results. Despite their good performance, they share a weakness, which is that they are not interpretable. In the field of time series classification, there is a tradeoff between accuracy and interpretability. In this work, we propose a set of characteristics capable of extracting information of the structure of the time series in order to face time series classification problems. The use of these characteristics allows the use of traditional classification algorithms in time series problems. The experimental results demonstrate a statistically significant improvement in the accuracy of the results obtained by our proposal with respect to the original time series. Apart from the improvement in accuracy, our proposal is able to offer interpretable results based on the set of characteristics proposed.
This paper presents two test procedures for evaluating the bond stress-slip and the slip-radial dilation relationships when the prestressing force is transmitted by releasing the steel (wire or strand) in precast prestressed elements. The bond stress-slip relationship is obtained with short length specimens, to guarantee uniform bond stress, for three depths of the wire indentation (shallow, medium and deep). An analytical model for bond stress-slip relationship is proposed and compared with the experimental results. The model is also compared with the experimental results of other researchers. Since numerical models for studying bond-splitting problems in prestressed concrete require experimental data about dilatancy angle (radial dilation), a test procedure is proposed to evaluate these parameters. The obtained values of the radial dilation are compared with the prior estimated by numerical modelling and good agreement is reached.
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