Sergio M.R. Lopes

A non-linear 3D FEM model to simulate timber-concrete joints

This paper, presents 3D non-linear FEM models developed to predict the mechanical behaviour of timber-concrete joints made with dowel-type-fasteners. They consider isotropic behaviour for steel and concrete and orthotropic behaviour for timber, all the materials are modelled with non-linear mechanical behaviour. Besides, the interaction between materials is modelled using contact elements associated with friction. The results obtained in the numerical simulations are evaluated and compared with results obtained in laboratory shear tests. The model developed showed the capacity to simulate the behaviour of the joints if the materials used are properly modelled. Nevertheless further research is still necessary to improve the modelling of the materials particularly timber.

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.

Interlayer Influence on Timber-LWAC Composite Structures with Screw Connections

Timber-concrete composite structures are often used as upgrade solutions for existent timber floors. The timber cross section is maintained and a concrete layer is poured over the floorboard surface. Floorboards help with loading distribution on the beams. The study presented is based on laboratory tests that used specimens made with a lightweight aggregate concrete (LWAC). The use of this type of concrete, compared with normal weight concrete (NWC), has the advantage of lower dead weights, and might be very important in many cases, namely, when the supporting structure has limited strength. Many design works of timber-concrete composite connections do not take into account the timber interlayer, which is known to reduce the load-carrying capacity and the stiffness of the connection. Previous investigations of NWC found that the inclusion of the interlayer leads to average reductions of 30% and 50% for the load capacity and slip modulus, respectively. The current investigation with LWAC found that such re...

Available plastic rotation in continuous high-strength concrete beams

An experimental program was formulated to study moment redistribution in continuous high-strength concrete beams. The evaluation of ductility is important for this type of beam as, for high-strength concrete, the ductility decreases as the concrete strength increases. It is therefore necessary to determine whether the critical sections are able to develop appreciable plastic rotations to justify the application of a linear elastic analysis with moment redistribution. This work specifically examined the influence of the tensile reinforcement ratio and the transverse reinforcement ratio on the rotation capacity of plastic hinges. The moment redistribution obtained experimentally is compared with the guidelines recommended in Eurocode 2, CEB-FIP Model Code 1990, and ACI 318. The results show that ACI 318 recommendations for linear analysis with moment redistribution are too conservative and that the predictions, according to Eurocode 2 and CEB-FIP Model Code 1990, agree with experimental evidence.

Flexural Response of Continuous Concrete Beams Prestressed with External Tendons

This article presents the results of a numerical investigation of the flexural behavior of continuous externally prestressed concrete beams. Aspects of behavior studied include the increase in stress in external tendons, moment redistribution in the postelastic range, and secondary moments as a result of prestressing. A finite-element model for the full-range analysis of continuous externally prestressed concrete beams is introduced. The model predictions agree well with the experimental results. The analysis shows that the ultimate stress increase in external tendons of continuous beams is dependent on both the number and rotation of plastic hinges that can be developed at failure load. The degree of moment redistribution is significantly influenced by the nonprestressed tension steel and the pattern of loading. An approach based on the linear transformation concept is designed to examine the secondary moments over the entire loading up to the ultimate. The results indicate that the secondary moments increase linearly with the prestressing force and can be conveniently calculated by an elastic analysis.

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...

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.

Interaction between Time-Dependent and Second-Order Effects of Externally Posttensioned Members

AbstractFor external tendon members subjected to sustained loads, the time-dependent effects resulting from concrete creep, shrinkage, and tendon relaxation would interact with the second-order effects resulting from the change in tendon eccentricities with the development of time-dependent deformations. This interaction should be adequately considered in a time-dependent analysis of this type of member. This paper presents a numerical model developed to predict the long-term behavior of externally prestressed concrete members at service conditions, taking into account the interaction between time-dependent and second-order effects. The proposed method of analysis is verified with the available experimental results. The time-dependent behavior of externally prestressed concrete members is evaluated, focusing on the effect of deviators and nonprestressed steel. The results demonstrate that the second-order effects result in significant changes in long-term responses other than the prestress loss. The effec...

Influence of Span-Depth Ratio on Behavior of Externally Prestressed Concrete Beams

This paper describes a numerical study on the flexural behavior of concrete beams prestressed with external tendons, focusing on the effect of the span-depth ratio on the response characteristics and the ultimate stress in tendons and ductility behavior. A nonlinear model, calibrated by the available experimental results of externally prestressed specimens, is used for the parametric evaluation. The results show that the second-order effects of externally prestressed beams with two deviators at third points become increasingly important with the increase of the span-depth ratio and that, due to these effects, a higher span-depth ratio registers a lower ultimate moment capacity. The effect of the span-depth ratio on the ultimate tendon stress is dependent on the type of loading for internal unbonded tendons and on the configuration of deviators for external tendons. The analysis also indicates that, irrespective of second-order effects, the span-depth ratio has an insignificant effect on the ductility of beams, and center-point loading mobilizes higher deflection ductility than third-point or uniform loading.

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.