1,721,432 research outputs found
On the influence of uplift pressure in concrete gravity dams
No full textCracks are often present in concrete dams, and may have relevant dimensions. The evaluation of the safety factor of old dams under higher flood levels has been investigated through fracture mechanics in previous years. Crack stability in concrete dams can correctly be predicted when uplift pressures are accurately modelled. Current models consider a uniform uplift pressure distribution, but recent experimental results show that it varies along the crack faces. In the present paper, uplift pressure effects in cracked concrete gravity dams are studied. A parametric study on the influence of uplift pressure on stress intensity factors and crack-propagation angle is performed. Furthermore, uplift pressure effects on the LEFM scale law for the maximum water level carried by cracked gravity dams are examined
Construction methodologies and structural performance of tunnel linings. Optimisation of the structural, technological and functional performance, of construction methodologies and materials, in tunnel linings
No full textThis book aims to give a general survey on the main results obtained in the National Research Project (PRIN 2006) on tunnel linings “Optimization of the Structural, Technological and Functional Performance of Construction Methodologies and Materials in Tunnel Linings” (PRIN 2006), financed by the Italian Ministry of University and Research (MIUR).
The research was carried out within five different Universities spread all over the Country, namely: Brescia, Lecce, Politecnico di Milano, Parma and Politecnico di Torino, for a total budget of about 250.000 euros. Five Research Units (RU) were involved because their specific experience in the fields of tunnel linings. In particular: (RU1) the Department DICATA of the University of Brescia and the Department of Innovation Engineering of the University of Salento (Lecce) have experience in the field of Fiber Reinforced Concrete (FRC) and in the optimization of structural behaviour of segmental lining; (RU2) Department DITAG of Politecnico di Torino has been working on conventional and mechanized tunnels and on the soil-structure in-teraction; (RU3) Department DISTR of Politecnico di Torino did research on the soil-structure interaction and on the structural optimization of final lining in conventional tunnels; (RU4) Department DIS of Politecnico di Milano has been active in the field of mechanical properties of concrete under high temperatures and on the fire resistance of high performance concrete while (RU5) Department of Civil Engineering of the University of Parma did several research studies on nonlinear analyses of reinforced concrete and developed a specific model for FRC based on fracture mechanics.
The book summarizes the main aspects arose during the development of the research project. General issues concerning tunnel linings, both conventional and segmental, were investigated within the main objective of the research that was the improving of the knowledge on the structural behavior and the construction methodologies of these structures. Furthermore, general aspects concerning newer materials for use in tunnel linings are presented with particular reference to Fiber Reinforced Concrete (FRC) and Self Compacting Concrete (SCC)
Shear strength of FRC members with little or no shear reinforcement: a new analytical model
No full textLEFM applications to concrete gravity dams
No full textThe evaluation of the safety factor of old dams under higher flood levels in the last few years has been investigated under the assumptions of fracture mechanics. The extensive need for research in this field was recognized by the U.S. Army Crops of Engineers that now requires a fracture mechanics investigation prior to the rehabilitation of cracked massive concrete structures. In large structures, such as dams, because of the smaller size of the fracture process zone with respect to the structure size, limited errors should occur under the assumptions of linear elastic fracture mechanics (LEFM). In this paper, theoretical considerations and approximate expressions for the evaluation of stress intensity factors and crack propagation in concrete dams are presented. Furthermore, a parametric study of gravity dams under the assumptions of LEFM is performed. Finally, a scale law for the evaluation of the maximum water level carried by cracked dams is propose
La progettazione di strutture in cemento armato mediante l’impiego di barre di grande diametro
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Steel Fibers as Shear Reinforcement for Beams
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Derivation of a simplified stress–crack width law for Fiber Reinforced Concrete through a revised round panel test
No full textThe round determinate panel (RDP), according to ASTM, was found to be a reliable, consistent and repeatable test method for the measurement of the energy absorption in Fiber Reinforced Concrete (FRC) composites. A smaller panel was proposed and experimentally investigated by the authors in previous scientific contributions.
An analytical approach is herein reported toward the definition of a simplified stress-crack width law for FRC, determined from tests on small panels according to the requirements of Model Code 2010 for tension softening materials. To this aim, the measurement of the three crack widths was implemented in the test procedure and, in addition, a kinematic approach was proposed to predict the crack width of panels
On the effectiveness of steel fibers as shear reinforcement
No full textAn experimental study on steel fiber-reinforced concrete (SFRC) beams subjected to shear loading tested at the University of Brescia in recent years is presented and discussed. A total of 18 full-scale experiments were carried out, aimed at investigating the effect of randomly distributed steel fibers within the concrete matrix on shear behavior. The focus was on the parameters influencing the shear response of members, including concrete class, fiber content, and mixture of different fibers. All tested members contained no conventional shear reinforcement. All SFRCs used were characterized in tension according to the provision included in the fib Model Code 2010. A useful database-with other tests published elsewhere-was developed, linking the shear strength of members to the codified residual strengths of the corresponding fiber-reinforced concrete (FRC) materials. Results show that a relatively low amount of fibers (Vf < 0.7%) can significantly increase the shear strength and ductility of concrete beams without transverse reinforcement. Moreover, visible cracking and noticeable deflections offer ample warning of impending collapse in FRC members. A critical discussion of two recent analytical models for calculating the shear strength of FRC materials is also provided.Copyright © 2013, American Concrete Institute. All rights reserved
Fiber Reinforced Concrete Characterization through Round Panel Test - Part I: Experimental Study
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