L.F.A. Bernardo

Torsion in High-Strength Concrete Hollow Beams: Strength and Ductility Analysis

To date, no studies have focused on high strength concrete (HSC) beams under pure torsion, even though HSC beams are more problematic than normal strength concrete beams and hollow beams are more problematic than plain beams as far as torsional ductility is concerned. This paper studies the ultimate behavior of HSC hollow beams with respect to their strength and ductility. Sixteen beams were tested. The hollow beams had a constant square cross section and were symmetrically reinforced. The variable parameters were the concrete?s compressive strength, from 46.2 to 96.7 MPa (from 6699 to 14,022 psi), and the total amount of torsional reinforcement, from 0.30 to 2.68%. The findings show that the torsional ductility is low and that the range of reinforcement ratio where ductility still occurs is very narrow. Different codes of practice were compared in the light of the experimental results, with the ACI Code appearing to be the most appropriate for predicting torsional strength and limiting torsion reinforcement. Some of the other codes were found to be excessively permissive and could lead to the acceptance of brittle beams or unsafe values of the predicted maximum torque.

High-strength Concrete Hollow Beams Strengthened with External Transversal Steel Reinforcement Under Torsion

Abstract Some bridges have to withstand high levels of torsion forces. As a consequence, box type beams are often the obvious solution. It could be possible that the balance of transversal to longitudinal torsion reinforcement is not fully reached. If the transversal reinforcement is somehow underestimated, the box beam needs to be transversally strengthened. From the various solutions, external transversal reinforcement is certainly one possibility. The investigation presented here aimed to study such solution. The authors tested four hollow beams under pure torsion. The level of the non balanced ratio between internal longitudinal and transversal torsion reinforcement was one of the parameters that were considered in this investigation. Other parameter was the existence or the no existence of external transversal strengthening reinforcement. The experimental results of the tests have shown the effectiveness of the use of the external transversal strengthening steel reinforcement to compensate the lack o...

Reinforced and prestressed concrete hollow beams under torsion

AbstractRecently a new rational theoretical model for beams under torsion has been proposed. This model, called Softened Membrane Model for Torsion (SMMT), is able to predict well the global behaviour of reinforced and prestressed concrete solid beams under torsion. This paper presents a study in order to check the SMMT for reinforced and prestressed concrete hollow beams under torsion. Theoretical predictions from SMMT are compared to some experimental results of hollow beams available in the literature and also with the predictions of another theoretical model previously proposed from the authors. It is shown that SMMT, with some corrections, is able to predict satisfactorily the overall behaviour of reinforced and prestressed concrete hollow beams under torsion.

Mechanical Properties of Epoxy Nanocomposites Using Alumina as Reinforcement - A Review

Polymers and their composites find use in many engineering applications as alternative products to metal-based ones and, nowadays, have wide technical applications. One of the most used composite materials is the epoxy resins (EP), which is a thermoset polymer matrix. After cure, this material displays some excellent mechanical, thermal, electrical and chemical properties. For these reasons, it has been widely used for a wide range of automotive and aerospace applications, as well as for shipbuilding or electronic devices. However, EP has poor resistance to crack propagation and is brittle. So, in recent years, a considerable amount of research has been carried out to improve the performance of the toughness of EP. The most common studied technique consist to reinforce the EP matrix with rigid nanoparticle fillers, such as alumina, silica, mica, talc, organoclays, nanoclays, carbon nanotubes, TiO2, among others. Among these nanofillers type, nanosize alumina particles has not been widely studied. However, recent studies have reported that the use of functionalized nanosize alumina particles as nanofiller can significantly improve the properties of the nanocomposite, even with low contents. These results, combined with the low cost of the alumina, show that the reinforcement of EP with alumina nanoparticles is a viable solution. In this paper, an attempt is made to review and highlight some recent findings and also some trends to show future directions and opportunities for the development of polymer nanocomposites reinforced with alumina nanoparticles.

Efficient Analysis of Beam Sections Using Softened Truss Model

In this paper, an efficient solution procedure is proposed to compute the pre-peak behavior of reinforced concrete (RC) beam cross sections under torsion and shear. This calculation procedure is based on the combined-action softened truss model (CA-STM), which idealizes rectangular RC cross sections as the association of four cracked panels. The proposed solution procedure formulates the problem as a system of nonlinear equations with constraints to be solved using optimization algorithms. The previsions obtained from this technique are compared with some experimental results of RC cross sections under pure torsion and torsion combined with shear, where good agreement was observed. Moreover, this procedure showed good computational efficiency, depicted by its ability to compute the load-deformation curves in few seconds. An analysis of a statically indeterminate structure incorporating beams under torsion and shear is also presented, for which a considerable decrease of the beam’s torsional stiffness is observed under the combined actions.

Flexural ductility of lightweight-aggregate concrete beams

AbstractThis paper describes an experimental study on the flexural ductility of lightweight-aggregate concrete beams including concretes with compressive strengths between 22.0 and 60.4 MPa and dry densities between 1651 and 1953kg/m3. Nineteen simply supported beams were tested until failure. Two symmetrical concentrated loads were applied at approximately one third of the span. Ductility was studied by defining ductility indexes. The main variables are the concrete compressive strength and the longitudinal tensile reinforcement ratio. It is shown that the parameter with higher influence on ductility is the longitudinal tensile reinforcement ratio. The test results are also compared with the requirements from some codes of practice. It is shown that ACI Code requirements give more guaranties as far as ductility is concerned, when compared with European codes.

Theoretical model for the mechanical behavior of prestressed beams under torsion

Abstract In this article, a global theoretical model previously developed and validated by the authors for reinforced concrete beams under torsion is reviewed and corrected in order to predict the global behavior of beams under torsion with uniform longitudinal prestress. These corrections are based on the introduction of prestress factors and on the modification of the equilibrium equations in order to incorporate the contribution of the prestressing reinforcement. The theoretical results obtained with the new model are compared with some available results of prestressed concrete (PC) beams under torsion found in the literature. The results obtained in this study validate the proposed computing procedure to predict the overall behavior of PC beams under torsion.

Use of refurbished shipping containers for the construction of housing buildings: details for the structural project

AbstractConstruction using refurbished shipping containers is a recent building system, with already many successful examples around the world. This system presents a huge potential in the field of sustainable construction provided by the recycling of used containers. This paper aims to contribute to a better knowledge of this construction system in what concerns to the structural project. The general constitution of two maritime shipping containers is presented as well as some aspects of their structural behavior. For this purpose, numerical analyses were performed using a finite elements analysis program. Normative aspects for the structural project are also presented. This paper also presents the analysis of a case study with the use of refurbished shipping containers to build a single-family house. The evaluation of the strength of the refurbished shipping containers to building actions is carried out. It is shown that such evaluation is not easy because some mechanical parameters of noncommercial ste...

Reinforced concrete membranes under shear: Ultimate behaviour and influence of thickness

The main purpose of this article is to study the behaviour of thin RC membranes under compression in one direction and tension in the perpendicular direction. The influence of the thickness on the behaviour of the concrete panel is investigated. To study the behaviour of the panels, an experimental programme was carried out. Six RC panels under pure shear were tested up to failure. As a result, new experimental stress–strain relationships of thin plates under pure shear are presented. Such relationships take into account the reduction of the compressive strength due to perpendicular tensile stresses and the influence of the thickness of the RC panels. The good experimental values obtained from this investigation validate the effectiveness of the low cost testing equipment developed for this study. This was a good achievement, because previous tests on this topic were performed using expensive equipment, which very few laboratories could afford. In general, the values obtained for the stress–strain relationships are approximately within the range proposed by other investigators. It is also shown that the strength capacity predicted by European codes is higher than that obtained from the experimental tests. The values predicted by ACI code are very conservative.

Reinforced concrete membranes under shear: Global behaviour

The main purpose of this article is to study compressed reinforced concrete membranes under perpendicular tensile stress. The state-of-the-art is presented and it shows that not much research has been done on this topic, probably because it needed very expensive laboratory equipment. In the current investigation, the authors have tried a new type of equipment, less expensive than that of previous investigations, and it proved to be adequate for the type of tests needed for studying this topic. The authors tested six reinforced concrete panels under pure shear up to failure. A parameter that was studied in these tests was the thickness of the membranes. This is of particular importance in webs or walls of beams under shear or torsion forces. From the experimental measurements, the authors have computed the principal directions and the values of the stresses and strains for the tested beams. In this article, these values are presented and the principal strains and stresses are compared with those at 45° and the two fairly agree with each other, particularly for the case of the stresses.