Longitudinal-transverse bending of multilayer concrete rods reinforced with steel reinforcement under the influence of mass forces

В работе рассматриваются многослойные бетонные стержни постоянного поперечного сечения армированные стальной арматурой. Предполагается, что в стержне имеет место одноосное напряженное состояние. На примере армирования сталями марок А240, А400, А800 показано влияние степени армирования на несущую способность стержня. Рассматриваются случаи армирования как только одного из слоев стержня, так и армирование всех слоев одновременно. The paper deals with multilayer concrete rods of constant cross-section reinforced with steel reinforcement. It is assumed that there is a uniaxial stress state in the bar. Using the example of reinforcement with steels of grades A240, A400, A800, the influence of the degree of reinforcement on the bearing capacity of the bar is shown. Cases of reinforcement of both only one of the layers of the bar and reinforcement of all layers at the same time are considered

The structure of carbon nanotubes in a polymer matrix

We carried out an analytical structural analysis of interfacial effects and differences in the reinforcing ability of carbon nanotubes for polydicyclopentadiene/carbon nanotube nanocomposites with elastomeric and glassy matrices. In general, it showed that the reinforcing (strengthening) element of the structure of polymer nanocomposites is a combination of the nanofiller and interfacial regions. In the polymer matrix of the nanocomposite, carbon nanotubes form ring-like structures. Their radius depends heavily on the volume content of the nanofiller. Therefore, the structural reinforcing element of polymer/carbon nanotube nanocomposites can be considered as ring-like formations of carbon nanotubes coated with an interfacial layer. Their structure and properties differ from the characteristics of the bulk polymer matrix.According to this definition, the effective radius of the ring-like formations increases by the thickness of the interfacial layer. In turn, the level of interfacial adhesion between the polymer matrix and the nanofiller is uniquely determined by the radius of the specified carbon nanotube formations. For the considered nanocomposites, the elastomeric matrix has a higher degree of reinforcement compared to the glassy matrix, due to the thicker interfacial layer. It was shown that the ring-like nanotube formations could be successfully modelled as a structural analogue of macromolecular coils of branched polymers. This makes it possible to assess the effective (true) level of anisotropy of this nanofiller in the polymer matrixof the nanocomposite. When the nanofiller content is constant, this level, characterised by the aspect ratio of the nanotubes, uniquely determines the degree of reinforcement of the nanocomposites

The mechanism of reinforcement of nanocomposites polyurethane/graphene

The percolation model of reinforcement was used for the theoretical analysis of reinforcement mechanism for nanocomposites polyurethane/graphene. This model allows to elucidate influence of main factors (level of interfacial adhesion, nanofiller content, interfacial regions) on the degree of reinforcement or modulus of elasticity of the considered nanocomposites. It has been shown that for these nanocomposites actually nanofiller (graphene) serves as main reinforcing element. The sharp increasing of modulus of elasticity of nanocomposite occurs at achievement of critical content of nanofiller (∼9 % mas.). The same effect of increasing the level of interfacial adhesion is obtained by a polymer matrix-nanofiller, characterized by a transition from perfect adhesion to nanoadhesion. The structure type of nanofiller in polymer matrix (exfoliated or intercalated one) in one more factor. The proposed model is universal one for all nanocomposites polymer/2D-nanofiller.

A NEW METHOD FPR ASSESSING THE RESISTANCE OF A REINFORCED CONCRETE COLUMN WITH A CIRCULAR CROSS SECTION

The developed method for assessing fi re resistance relates to the fi eld of fi re safety of buildings and structures and can be used to classify a reinforced concrete column of circular cross-section according to fi re resistance indicators. The essence of the proposed solution is to assess the design limit of fi re resistance of a reinforced concrete column of circular cross-section for the loss of bearing capacity under fi re conditions according to a set of single quality indicators without direct testing. The description of the process of resistance of a reinforced concrete column to fi re impact is presented by a mathematical relationship that takes into account the dimensions of the cross-section of the column, the degree of reinforcement, the intensity of force stresses, the normative strength of concrete to the resistance to axial compression and the rate of thermal diff usion of concrete. To determine the fi re resistance limit of a reinforced concrete column with a circular cross-section, an analytical expression that combines all the described indicators is proposed. The proposed method for determining fi re resistance refers to a thermal strength problem, which makes it possible to determine the fi re resistance of a reinforced concrete column of circular cross-section without full-scale fi re exposure, and reduces economic costs.

THE MECHANISMS OF REINFORCEMENT OF NANOCOMPOSITES POLYURETHANE/CARBON NANOTUBE

The aim of present work is theoretical analysis of high values of reinforcement degree of nanocomposites polyurethane/carbon nanotube. For this two micromechanical models were used, showing identical results. The indicated models demonstrated, that densely-packed high-modulus interfacial regions, which serve the same reinforcing element of nanocomposite structure, as and nanofiller (carbon nanotubes) actually. The formation of interfacial regions defines by strong interactions polymer matrix – nanofiller. This means that nanofiller efficiency is controlled by its ability to generate densely-packed interfacial regions. It is important also to point out, that any micromechanical model, including mixtures rule, describes correctly modulus of elasticity of polymer nanocomposites, if in it real, but not nominal, characteristics of nanofiller were used. The content of interfacial regions in nanocomposite is controlled by structure of nanofiller. This allows to obtain important practical conclusion – for realization maximum degree of reinforcement it is necessary to cause structure of nanofiller, allowing to generate greatest content of interfacial regions. Absence of interfacial regions results to reduction of modulus of elasticity of nanocomposite in comparison with matrix polymer.