Fiber-reinforced plastic (FRP) rebar has drawbacks that can limit its scope, such as poor heat resistance, decrease its strength over time, and under the influence of substances with an alkaline medium, as well as the drawback of a low modulus of elasticity and deformation. Thus, the aim of the article is the nano- and micro-modification of building reinforcing bars using FRP rebars made of basalt fibers, which were impregnated with a thermosetting polymer binder with micro- or nanoparticles. The research discusses the major results of the developed composite reinforcement with the addition of micro- and nanosized particles. The microstructure of FRP has been studied using scanning electron microscopy. It was revealed that dispersion-strengthened polymer composites with the inclusion of microsilica (SiO2) and nanosized aluminum oxide (Al2O3) particles have a much higher modulus of elasticity and strength when compared with the original polymer materials. In the course of the experiment, we also studied the retained plastic properties that are characterized by the absence of fragility. However, it was found that the high strength of materials was attained with a particle size of 10–500 nm, evenly distributed in the matrix, with an average distance between particles of 100–500 nm. It was also exhibited that composite reinforcement had improved the adhesion characteristics in comparison with both steel reinforcement (1.5–2 times, depending on the diameter), and with traditional unmodified FRP rebar (about 1.5 times). Thus, the use of micro-/nanosized powders increased the limit of the possible temperature range for the use and application of polymeric materials by almost two times, up to 286–320 °С, which will undoubtedly expand the range of the technological applications of products made of these materials.
When using friction gripping device with a screw drive to move designs from wood there is relaxation of tightening force of the screw with time due to rheological characteristics of wood. Weakening of tightening leads to a reduction of friction forces, holding the floating structure, which can lead to failure and drop of structure. To ensure reliable holding of wooden construction by gripping device within the specified time, prior increase in torque taking into account dynamics subsequent weakening is required. The article presents description of experimental setup to study the rate of weakening of the torque of the screw clamp and development of elastic deformation of samples of wood and plywood of different thickness with clamps of different hardness. Dependence of elastic strain and associated weakening of tightening force from time which samples stay under load, is revealed. The dependence has general nature for all the samples of wood and derivative materials. Regression analysis of the data and graphs of weakening the tightness of the clamps and development of elastic deformations is performed for each experiment. It is established that approximation to exponential function reflects the dependence of attenuation of torque settings on time in the interval up to 24 hours more accurately, than exponential function. To identify factors influencing the rate of weakening of the torque, regression analysis is made. The dependence of the rate of weakening of the torque by on stiffness of the clamp, thickness of wooden construction in the place of installation of gripping device and of the modulus of elasticity of wood is revealed. With the increase in rigidity of clamp and size of cross section of structure, weakening speed increases. Method of determining the rate of increase in force of pre-tightening of friction gripping device with screw drive to move wooden structures is suggested.
The article gives the description of the experimental facility to define the friction coeffi-cient between the contact elements and the samples of wood and plywood. Steel, rubber were used as materials for the contact elements. The minimum friction coefficients that can be used for engineering calculations are defined for each out of 16 contact pairs. The most preferable material to manufacture the contact elements of the load gripping tools for transferring the glued wood construction is rubber. It has the friction coefficient 1.3-2 times as high as other materials.
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