Mechanical behaviour of self-compacting concrete with hybrid fibre reinforcement

In this study, fibre-reinforced self-compacting concretes were developed for precast building components, incorporating either adherent metal fibres or polymeric synthetic slipping fibres or a combination of both. To achieve the warranted workability, compressive and splitting tensile strengths, compositions were determined by preliminary tests on self-compacting materials with various proportions of metal fibres. Bending tests in controlled deflection confirmed the positive contribution of fibres in the mechanical behaviour of self-compacting concrete. The comparison between vibrated and self-compacting concretes of similar mechanical characteristics indicated a possible better fibre-matrix bond in the case of self-compacting types. The results also showed that the properties of the hybrid fibre-reinforced self-compacting concrete could be inferred from the properties of the individual single-fibre reinforcements and their respective proportions through simple mix-rules.

A Non-Destructive Testing Based on Electromagnetic Measurements and Neural Networks for the Inspection of Concrete Structures

This paper presents a new non-destructive testing (NDT) for reinforced concrete structures, in order to identify the components of their reinforcement. A time varying electromagnetic field is generated close to the structure by electromagnetic devices specially designed for this purpose. The presence of ferromagnetic materials (the steel bars of the reinforcement) immersed in the concrete disturbs the magnetic field at the surface of the structure. These field alterations are detected by sensors coils placed on the concrete surface. Variations in position and cross section (the size) of steel bars immersed in concrete originate slightly different values for the induced voltages at the coils.. The values for the induced voltages were obtained in laboratory tests, and multi-layer perceptron artificial neural networks with Levemberg-Marquardt training algorithm were used to identify the location and size of the bar. Preliminary results can be considered very good.

A cost optimization-based design of precast concrete floors using genetic algorithms

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Numeric evaluation of the stiffness of log-concrete composite beams submitted the cyclical load

In this paper was evaluated, using the software ANSYS, the stiffness (El) of the log-concrete composite beams, of section T, with connectors formed by bonded-in steel rods, type CA-50, disposed in X, with application of cyclical load. The stiffness of the system was evaluated through the simulation of bending tests, considered 1/2 beam, with cyclical shipment varying among 40 % and 5 % of the strength of the connection with the load relationship R=0,125, for a total of 10 load cycles applied. The numeric results show a good agreement with experimental tests.

Non-linear analysis of reinforced concrete plates by the boundary element method and continuum damage mechanics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Bibliographical review of the used tyre in concrete

Due to the progressive increase of vehicles, the number of used tires is globally one of the serious environmental problems faced now. Therefore, several researches have being developed for its reuse. The use of tires' rubber in the concrete is a possible form of its a pplication, aiming a the recycling of this material and the improvement of certain properties, as tenacity, impact resistance, thermal and acoustic isolation. This article presents conclusions that several researchers obtained using the rubberized concrete. Thus there were researched several works enclosing the period of 1993 to 2003, presenting then the results of some characteristics of this concrete such as: physical properties in fresh and hardened state, mechanical properties and properties that remit the durability. The bibliographical revision has as objective to subsidize future researches that can contribute to improve the use of this concrete in civil construction.

Structural analyzes of the use of residues of tires in reinforced concrete

The search for an adequate destination to the tires without use is a problem for many countries. The use of tire rubber in concrete through the partial substitution of the small aggregate has for objective the withdrawal of this material of the environment besides serving as alternative material in places that present sand scarcity. However, to use this type of concrete in civil construction it's necessary to verify its structural behavior. The behavior of the adherence enters the bar of armor and the concrete surrounding it has decisive importance with relation to the load capacity of the structures of reinforced concrete. In this context, this work presents, argues and evaluates the results of the experimental studies for determination of the adherence tension according to pulling up assays pull-out normalized for CEB RC6 and also related in the ASTM C-234 in concrete with and without rubber residues. Armors of nominal diameter of 10,0; 12,5 and 16 mm had been used and concrete contend 10% of rubber fibres in substitution to the sand in volume.

Steel bars identification in reinforced concrete structures by using ANN and magnetic fields

This work proposes a methodology for non destructive testing (NDT) of reinforced concrete structures, using superficial magnetic fields and artificial neural networks, in order to identify the size and position of steel bars, embedded into the concrete. For the purposes of this paper, magnetic induction curves were obtained by using a finite element program. Perceptron Multilayered (PML) ANNs, with Levemberg-Marquardt training algorithm were used. The results presented very good agreement with the expect ones, encouraging the development of real systems based upon the proposed methodology.

Brazilian results on structural masonry concrete blocks

The purpose of this paper is to study the mechanical behavior of concrete blocks and prisms when performing axial compression tests within the Brazilian base of knowledge, intending to foment data of this kind for a world-based network. The blocks were built using five different mixtures in which the quantity of cement and the compacting ratio (density) were varied (during the fabrication process). The three-course-high prisms were assembled using 1 cm (0.39 in.) thick full-bedded joints, always trying to leave the mortar's characteristics constant. The axial compression tests were conducted according to Brazilian practice code recommendations, because most of these standards are very similar to international practice codes. The compressive strength, strains, and rupture form of each mixture studied were recorded. Attempts were made to correlate the strength, efficiency ratio (block strength/prism strength) of the prisms, strains, and rupture form; with the quantity of cement and compacting ratio. The data are presented in tables and figures, and the obtained results are discussed throughout the text. Copyright © 2007, American Concrete Institute. All rights reserved.