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Lourenco L.A.P.,Institute for Sustainability and Innovation in Structural Engineering ISISE | Barros J.A.O.,University of Minho
American Concrete Institute, ACI Special Publication | Year: 2011

Synopsis: In the last decades, technical and scientific efforts have been done to increase the concrete strength, based on the assumption that more economic, lightweight, durable and good looking structures can be built. This strength enhancement, however, has been obtained by increasing the compactness of the concrete internal structure, resulting concretes with voids of smaller size, and lower connectivity than in concretes of current strength classes. Research and fire accidents have shown that the concrete failure of structures exposed to fire is as explosive as high is the concrete strength class, since the restrictions for the escape of water vapor from the interior of concrete increase with the concrete compressive strength. In the present work a fiber reinforced concrete of enhanced fire resistance is developed and its properties are characterized by experimental research. This concrete is intended to have enough strength for concrete precast tunnel segments, while the performance of the fibrous reinforcement system is evaluated in terms of verifying its possibilities for replacing, partially or totally, conventional reinforcement used in these structural elements.

Pereira C.,Institute for Sustainability and Innovation in Structural Engineering ISISE | Correia A.G.,Institute for Sustainability and Innovation in Structural Engineering ISISE | Ferreira C.,Center for Construction Studies | Araujo N.,Institute for Sustainability and Innovation in Structural Engineering ISISE
Geotechnical Engineering for Infrastructure and Development - Proceedings of the XVI European Conference on Soil Mechanics and Geotechnical Engineering, ECSMGE 2015 | Year: 2015

This paper presents a study aiming to improve the quality and repeatability of shear wave velocity measurements by means of the bender element (BE) technique. For this purpose, studies were carried out to improve the contact between the bender elements and the specimen, namely by the use of a BE puncher and/or the use of an interface coupling material between the BE and the specimen. A series of tests was carried out on clay and silty sand specimens, with different geometries and two different time domain methods were used to measure travel time (tt): i) the first direct arrival of the wave (to) and ii) the first peak-to-peak interval (tPk-Pk). The influence of the cantilever length of the BE was also addressed. Furthermore, in order to verify the repeatability of the performed tests, a second group of tests was carried out using BE, as well as shear plates and compression transducers. Finally, recommendations are made regarding the geometry of the samples and the different time domain methods used for travel time interpretation. © The authors and ICE Publishing: All rights reserved, 2015.

Cunha V.,Institute for Sustainability and Innovation in Structural Engineering ISISE | Barros J.,University of Minho | Cruz J.S.,University of Minho
American Concrete Institute, ACI Special Publication | Year: 2010

In the present work the tensile behavior of a self-compacting concrete reinforced with two hooked ends steel fiber contents was assessed performing stable displacement control tension tests. Based on the stress-displacement curves obtained, the stress-crack width relationships were derived, as well as the energy dissipated up to distinct crack width limits and residual strengths. The number of effective fibers bridging the fracture surface was determined and was compared with the theoretical number of fibers, as well as with the stress at crack initiation, residual stresses and energy dissipation parameters. In general, a linear trend between the number of effective fibers and both the stress and energy dissipation parameters was obtained. A numerical model supported on the finite element method was developed. In this model, the fiber reinforced concrete is assumed as a two phase material: plain concrete and fibers randomly distributed. The plain concrete phase was modeled with 3D solid finite elements, while the fiber phase was modeled with discrete embedded elements. The adopted interface behavior for the discrete elements was obtained from single fiber pullout tests. The numerical simulation of the uniaxial tension tests showed a good agreement with the experimental results. Thus, this approach is able of capturing the essential aspects of the fiber reinforced composite's complex behavior.

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