Numerical simulation of galvanized rebars pullout

The usage of rebars in construction is the most common method for reinforcing plain concrete and thus bridging the tensile stresses along the concrete crack surfaces. Usually design codes for modelling the bond behaviour of rebars and concrete suggest a local bond stress – slip relationship that comprises distinct reinforcement mechanisms, such as adhesion, friction and mechanical anchorage. In this work, numerical simulations of pullout tests were performed using the finite element method framework. The interaction between rebar and concrete was modelled using cohesive elements. Distinct local bond laws were used and compared with ones proposed by the Model Code 2010. Finally an attempt was made to model the geometry of the rebar ribs in conjunction with a material damaged plasticity model for concrete.

Bond of NSM FRP strengthened concrete: round robin test initiative

Despite the extensive research that has been conducted on the debonding behaviour of FRP strengthening systems, no standard methodology has been yet established on its experimental characterization. In this context, to assess the performance and reliability of small scale testing on NSM (near surface mounted) FRP strengthening systems, an experimental program was carried out on a series of nine NSM FRP strengthening systems, in the framework of an international Round Robin Testing (RRT). Eleven laboratories and seven manufacturers and suppliers participated in this extensive international exercise, which regarded both NSM and EBR FRP strengthening systems. Test results obtained for the NSM systems by the participating laboratories are discussed and compared in this paper to investigate the feasibility of the adopted single/double pulling shear test method, to investigate the mechanism of bond between NSM FRP reinforcement and concrete, and to investigate the level of variability obtained between the participating laboratories testing the same material batches. It is concluded that the tested variants in the adopted single/double shear pulling test have a significant influence, stressing the importance of the level of detail of standardized test protocols for bond verification. On overall, given the variants included in this study, the obtained variation in bond stress-slip behaviour between the laboratories remained fairly limited.

A FEM-based model to study the behaviour of corroded RC beams shear repaired by NSM CFRP rods technique

This paper presents the main features of finite element FE numerical model developed using the computer code FEMIX to predict the near-surface mounted NSM carbon-fiber-reinforced polymer CFRP rods shear repair contribution to corroded reinforced concrete RC beams. In the RC beams shear repaired with NSM technique, the Carbon Fibre Reinforced Polymer (CFRP) rods are placed inside pre-cut grooves onto the concrete cover of the RC beam’s lateral faces and are bonded to the concrete with high epoxy adhesive. Experimental and 3D numerical modelling results are presented in this paper in terms of load-deflection curves, failure modes and slip information of the tensile steel bars for 4 short corroded beams: two corroded beams (A1CL3-B and A1CL3-SB) and two control beams (A1T-B and A1T-SB), the beams noted with B were let repaired in bending only with NSM CFRP rods while the ones noted with SB were repaired in both bending and shear with NSM technique. The corrosion of the tensile steel bars and its effect on the shear capacity of the RC beams was discussed. Results showed that the FE model was able to capture the main aspects of the experimental load-deflection curves of the RC beams, moreover it has presented the experimental failure modes and FE numerical modelling crack patterns and both gave similar results for non-shear repaired beams which failed in diagonal tension mode of failure and for shear-repaired beams which failed due to large flexural crack at the middle of the beams along with the concrete crushing, three dimensional crack patterns were produced for shear-repaired beams in order to investigate the splitting cracks occurred at the middle of the beams and near the support.

A model to simulate the moment-rotation and crack width of FRC members reinforced with longitudinal bars

The present work describes a model for the determination of the moment–rotation relationship of a cross section of fiber reinforced concrete (FRC) elements that also include longitudinal bars for the flexural reinforcement (R/FRC). Since a stress–crack width relationship (σ–w)(σ–w) is used to model the post-cracking behavior of a FRC, the σ–w directly obtained from tensile tests, or derived from inverse analysis applied to the results obtained in three-point notched beam bending tests, can be adopted in this approach. For a more realistic assessment of the crack opening, a bond stress versus slip relationship is assumed to simulate the bond between longitudinal bars and surrounding FRC. To simulate the compression behavior of the FRC, a shear friction model is adopted based on the physical interpretation of the post-peak compression softening behavior registered in experimental tests. By allowing the formation of a compressive FRC wedge delimited by shear band zones, the concept of concrete crushing failure mode in beams failing in bending is reinterpreted. By using the moment–rotation relationship, an algorithm was developed to determine the force–deflection response of statically determinate R/FRC elements. The model is described in detail and its good predictive performance is demonstrated by using available experimental data. Parametric studies were executed to evidence the influence of relevant parameters of the model on the serviceability and ultimate design conditions of R/FRC elements failing in bending.

Analytical and numerical study of the electro-osmotic annular flow of viscoelastic fluids

In this work we present semi-analytical solutions for the electro-osmotic annular flow of viscoelastic fluids modeled by the Linear and Exponential PTT models. The viscoelastic fluid flows in the axial direction between two concentric cylinders under the combined influences of electrokinetic and pressure forcings. The analysis invokes the Debye-Hückel approximation and includes the limit case of pure electro-osmotic flow. The solution is valid for both no slip and slip velocity at the walls and the chosen slip boundary condition is the linear Navier slip velocity model. The combined effects of fluid rheology, electro-osmotic and pressure gradient forcings on the fluid velocity distribution are also discussed.

Annular flow of viscoelastic fluids: Analytical and numerical solutions

This work provides analytical and numerical solutions for the linear, quadratic and exponential Phan–Thien–Tanner (PTT) viscoelastic models, for axial and helical annular fully-developed flows under no slip and slip boundary conditions, the latter given by the linear and nonlinear Navier slip laws. The rheology of the three PTT model functions is discussed together with the influence of the slip velocity upon the flow velocity and stress fields. For the linear PTT model, full analytical solutions for the inverse problem (unknown velocity) are devised for the linear Navier slip law and two different slip exponents. For the linear PTT model with other values of the slip exponent and for the quadratic PTT model, the polynomial equation for the radial location (β) of the null shear stress must be solved numerically. For both models, the solution of the direct problem is given by an iterative procedure involving three nonlinear equations, one for β, other for the pressure gradient and another for the torque per unit length. For the exponential PTT model we devise a numerical procedure that can easily compute the numerical solution of the pure axial flow problem

Seismic retrofit of masonry-to-timber connections in historical constructions

Tese de Doutoramento em Engenharia Civil.

t-­stories: improving and expanding t-­words

versão acessível em http://ace2015.info/wp-content/uploads/2015/11/ACE_2015_submission_148.pdf

Morfossintaxe em Fernão de Oliveira (1536)

É objetivo deste ensaio mostrar que Fernão de Oliveira, tendo-se esforçado por não ficar muito preso aos modelos latinos, traçou as linhas mestras da gramática stricto sensu (ou morfossintaxe) do português do séc. XVI, isto é, identificou as categorias gramaticais que funcionam efetivamente nesta língua.

Development of hybrid composite plate (HCP) for strengthening and repair of RC structures

Tese de Doutoramento em Engenharia Civil

Influência do tipo de adesivo no comportamento de elementos de betão reforçados com laminados de CFRP de acordo com a técnica NSM

Dissertação de mestrado integrado em Engenharia Civil

Avaliação experimental da utilização de conectores indentados em elementos mistos de aço e betão leve

Dissertação de mestrado integrado em Engenharia Civil

Convex and toric geometry to analyze complex dynamics in chemical reaction systems

Convex cone, toric variety, graph theory, electrochemical catalysis, oxidation of formic acid, feedback-loopsbifurcations, enzymatic catalysis, Peroxidase reaction, Shil'nikov chaos

Comportamento dos cromossômios na meiose de Euryophthalmus rufipennis Laporte (Hemiptera Pyrrhocoridae)

In this paper an account is given of the principal facts observer in the meiosis of Euryophthalmus rufipennis Laporte which afford some evidence in favour of the view held by the present writer in earlier publications regarding the existence of two terminal kinetochores in Hem ip ter an chromosomes as well as the transverse division of the chromosomes. Spermatogonial mitosis - From the beginning of prophase until metaphase nothing worthy of special reference was observed. At anaphase, on the contrary, the behavior of the chromosomes deserves our best attention. Indeed, the chromoso- mes, as soon as they begin to move, they show both ends pronouncedly turned toward the poles to which they are connected by chromosomal fibres. So a premature and remarkable bending of the chromosomes not yet found in any other species of Hemiptera and even of Homoptera points strongly to terminally localized kinetochores. The explanation proposed by HUGHES-SCHRADER and RIS for Nautococcus and by RIS for Tamalia, whose chromosomes first become bent late in anaphase do not apply to chromosomes which initiate anaphase movement already turned toward the corresponding pole. In the other hand, the variety of positions assumed by the anaphase chromosomes of Euryophthalmus with regard to one another speaks conclusively against the idea of diffuse spindle attachments. First meiotic division - Corresponding to the beginning of the story of the primary spermatocytes cells are found with the nucleus entirelly filled with leptonema threads. Nuclei with thin and thick threads have been considered as being in the zygotente phase. At the pachytene stage the bivalents are formed by two parallel strands clearly separated by a narrow space. The preceding phases differ in nothing from the corresponding orthodox ones, pairing being undoubtedly of the parasynaptic type. Formation of tetrads - When the nuclei coming from the diffuse stage can be again understood the chromosomes reappear as thick threads formed by two filaments intimately united except for a short median segment. Becoming progressively shorter and thicker the bivalents sometimes unite their extremities forming ring-shaped figures. Generally, however, this does not happen and the bivalents give origin to more or less condensed characteristic Hemipteran tetrads, bent at the weak median region. The lateral duplicity of the tetrads is evident. At metaphase the tetrads are still bent and are connected with both poles by their ends. The ring-shaped diakinesis tetrads open themselves out before metaphase, showing in this way that were not chiasmata that held their ends together. Anaphase proceeds as expected. If we consider the median region of the tetrads as being terminalized chiasmata, then the chromosomes are provided with a single terminal kinetochore. But this it not the case. A critical analysis of the story of the bivalents before and after the diffuse stage points to the conclusion that they are continuous throughout their whole length. Thence the chromosomes are considered as having a kinetochore at each end. Orientation - There are some evidences that Hemipteran chromosomes are connected by chiasmata. If this is true, the orientation of the tetrads may be understood in the following manner: Chiasmata being hindered to scape by the terminal kinetochores accumulate at the ends of the tetrads, where condensation begins. Repulsion at the centric ends being prevented by chiasmata the tetrads orient themselves as if they were provided with a single kinetochore at each extremity, taking a position parallelly to the spindle axis. Anaphase separation - Anaphase separation is consequently due to a transverse division of the chromosomes. Telophase and secund meiotic division - At telophase the kinetochore repeli one another following the moving apart of the centosomes, the chiasmata slip toward the acentric extremities and the chromosomes rotate in order to arrange themselves parallelly to the axis of the new spindle. Separation is therefore throughout the pairing plane. Origin of the dicentricity of the chromosomes - Dicentricity of the chromosomes is ascribed to the division of the kinetochore of the chromosomes reaching the poles followed by separation and distension of the chromatids which remain fused at the acentric ends giving thus origin to terminally dicentric iso-chromosomes. Thence, the transverse division of the chromosomes, that is, a division through a plane perpendicular to the plane of pairing, actually corresponds to a longitudinal division realized in the preceding generation. Inactive and active kinetochores - Chromosomes carrying inactive kinetochore is not capable of orientation and active anaphasic movements. The heterochromosome of Diactor bilineatus in the division of the secondary spermatocytes is justly in this case, standing without fibrilar connection with the poles anywhere in the cell, while the autosomes are moving regularly. The heterochromosome of Euryophthalmus, on the contrary, having its kinetochores perfectly active ,is correctly oriented in the plane of the equator together with the autosomes and shows terminal chromosomal connection with both poles. Being attracted with equal strength by two opposite poles it cannot decide to the one way or the other remaining motionless in the equator until some secondary causes (as for instances a slight functional difference between the kinetochores) intervene to break the state of equilibrium. When Yiothing interferes to aide the heterochromosome in choosing its way it distends itself between the autosomal plates forming a fusiform bridge which sometimes finishes by being broken. Ordinarily, however, the bulky part of the heterochromosome passes to one pole. Spindle fibers and kinetic activity of chromosomal fragments - The kinetochore is considered as the unique part of the chromosome capable of being influenced by other kinetochore or by the poles. Under such influence the kinetochore would be stimulated or activited and would elaborate a sort of impulse which would run toward the ends. In this respect the chromosome may be compared to a neüròn, the cell being represented by the kinetochore and the axon by the body of the chromosome. Due to the action of the kinetochore the entire chromosome becomes also activated for performing its kinetic function. Nothing is known at present about the nature of this activation. We can however assume that some active chemical substance like those produced by the neuron and transferred to the effector passes from the kinetochore to the body of the chromosome runing down to the ends. And, like an axon which continues to transmit an impulse after the stimulating agent has suspended its action, so may the chromosome show some residual kinetic activity even after having lost its kinetochore. This is another explanation for the kinetic behavior of acentric chromosomal fragmehs. In the orthodox monocentric chromosomes the kinetic activity is greater at the kinetochore, that is, at the place of origin of the active substance than at any other place. In chromosomes provided with a kinetochore at each end the entire body may become active enough to produce chromosomal fibers. This is probably due to a more or less uniform distribution and concentration of the active substance coming simultaneously from both extremities of the chromosome.

Comportamento dos cromossômios no gênero Hypselonotus (Hemiptera -Coreidae)

The three species studied have 19 chromosomes, being one heterochromosome, one pair of microchromosomes and 8 pairs of autosomes. The microchromosomes of Hypselonotus fulvus are amongst the largest we know. During the synizesis, in Hypselonotus fulvus, we can see in several strands that scape from the chromatic knot a place in which they are widley open. As, in that phase the chromosomes have both ends converging to the same place, the openings suggest a side-to-side pairing of the chromosomal threads. The tetrads are like that studied by Piza (1945-1946). The bivalents are united side by side at their entire length. The unpaired part at the midle of the bivalents gives origin to the arms of the cross-shapede tetrads. The chromosomes have a kinetochore at each end. The bivalents sometimes unite their extremities to form ring-shaped figures, which open themselves out before metaphase. The tetrads are oriented parallelly to the spindle axis. At telophase the kinetochores repeli one another, the chiasmata, if present, slip toward the acentric extremities and the chromosomes rotate in order to arrange themselves parallelly to the axis of the new spindle. Separation is therefore through the pairing plane. In the spermatogonial anaphase of Hypselonotus subterpunctatus the chromosomes are curved to the poles, like those described by PIZA (1946) and PIZA and ZAMITH (1946). The sex chromosomes in Hypselonotus interruptus and Hypselonotus fulvus appears longitudinally divided. It is oriented with the ends in the plane of the equator and its chomatids separate by the plane of division. In the second division the sex chromosome, provided as it is with an actve klnetochore at each end, orients itself with its length parallelly to the spindle axis and passes undivided to one pole. Sometimes it is distended between the poles. This corresponds to case (a) established by PIZA (1946) for the sex chromosomes of Hemiptera In Hypselonotus subterpunctatus the sex chromosome, in the first division of the spermatocytes, orients like the tetrads and divides transversaly. In the second division, as its kinetochore becomes inactive, it remans monocentric, does not orient in the spindle, and is finally enclosed in the nearer nucleus. In the secondary telophase it recuperates its dicentricity like the autosomal chromatids. This behavior corresponds to case (c) of PIZA (1946).