Papers by Keyword: Deformability

Abstract: The article is devoted to the determination of the main physical and mechanical characteristics of compressed concrete at different strain rates of its. A method for predicting the main strength and deformation characteristics of compressed concrete in the widest range of its loading rates is proposed: from instantaneous dynamic to long-term with the maximum possible development of creep deformations. This method is based on the well-known law of conservation of potential energy of material deformation (up to its destruction) and the general patterns of change of the known integral characteristic of concrete - the factor of elasticity-plasticity. The functional interdependence of the levels of strength and deformability of compressed concrete for its different strain rates was established.

Abstract: On the example of shape memory alloys in coarse-grained and ultrafine-grained states there is demonstrated an influence of pulse current on deformation behavior, microstructure and mechanical properties during cold rolling. The combination of cold rolling with the introduction of a pulsed current stimulates an increase in the deformation ability and strong structural refinement into the region of nanograins in a hard-deformed shape memory TiNi alloy. For both coarse-grained and ultrafine-grained structural states, the maximum achievable one-time and the total degree of deformation are higher in the case of using a pulsed current. Subsequent annealing improves the strength and functional properties. It has been shown that effect of pulsed current on deformability during cold rolling is higher in an alloy with a high content of impurities.

Abstract: On the basis of theoretical and experimental studies, the prerequisites and the method of calculation of bent and compressed-curved reinforced concrete structures with zone reinforcement made of steel fiber, working under static and short-term dynamic loads, are formulated. In the developed method for calculating the strength of normal and inclined sections, a nonlinear deformation model is implemented, which is based on the actual deformation diagrams of materials. The developed calculation method is brought to the program of calculation of reinforced concrete structures with zone reinforcement of steel fiber under short-term dynamic loading, taking into account the inelastic properties of materials. The numerical studies made it possible to determine the influence of various parameters of steel-fiber reinforcement on the strength of reinforced concrete elements. To confirm the main results of the developed calculation method, experimental studies of reinforced concrete beam structures reinforced with conventional reinforcement and a zone steel-fiber layer are planned and carried out. Experimental studies were carried out under static and short-term dynamic loads. As a result of the conducted experiments, data were obtained that characterize the process of destruction, deformation and cracking of steel-reinforced concrete elements under such types of loading. The dependences of changes in the energy intensity of reinforced concrete structures with zone reinforcement made of steel fiber in the compressed and stretched cross-section zones under dynamic loading are obtained. The effectiveness of the use of fiber reinforcement of normal and inclined sections of bent and compressed-curved elements to improve the strength and deformative.

Abstract: Two models of hollow core slabs were tested: reinforced concrete and steel fiber concrete. When designing slab models, the proportions of full-sized structures were preserved for the further possibility of correct data comparison. As a result of testing models of hollow core slabs, it was found that the bearing capacity of a slab with combined reinforcement is 24% higher than that of reinforced concrete, the deflection is 36% less, and the crack resistance is 18% higher. The use of steel fiber made it possible to avoid the brittle fracture of a steel fiber reinforced concrete slab, which was observed in the model of a conventional reinforced concrete slab.

Abstract: From the compression test of steel fiber recycled mortar porous brick masonry, it was researched the effects of different amounts of steel fiber and recycled fine aggregate on compressive strength, failure morphology, elastic modulus, stress-strain law and Poisson's ratio performance. The test value is compared with the calculation formula of ordinary mortar porous brick given in GB 50003-2011.The test showed that the steel fiber recycled mortar porous brick masonry had better compressive strength and deformability.

Abstract: In modern construction, a large variety of small architectural forms are used, for the production of which cement concrete is traditionally used, which should have improved physical and mechanical properties and decorative properties, while having a low cost. Improvement of these properties is achieved through the use of carbonate additives - highly dispersed chalk. Experimental results show that the addition of highly dispersed chalk affects the structure of cement stone, which is represented by low-base hydrosilicates, calcium hydrocarbonate and complex compounds that create a dense structure, which reduces the permeability of the material for corrosive media. It is assumed that the addition of highly dispersed chalk improves the elastic-plastic properties, increases the crack resistance, which provides high performance properties of concrete.

Abstract: The main task of construction is providing buildings with the property to remain operable throughout the entire life cycle. The level of bearing capacity, both of individual structures and buildings as a whole, depends on many factors.

Abstract: The results of experimental and theoretical studies of the process of destruction of concrete by the methods of fracture mechanics are considered. Results of studies of long-term strength, durability and deformability of concrete subjected to a preliminary short-term temperature action up to 300° C and 400° C under load and without load are presented. It is shown that after short-term heating up to 300о С the long-term strength of concrete decreases insignificantly. It is established that heating up to 400° C can be considered the boundary of the structural integrity of concrete. The conditions for using the results of these studies in determining the values of a function that characterizes the change in the long-term strength of a material in the mechanics of heterogeneous structures are formulated. The function of the material destruction measure is introduced to describe the nature of the structural changes in the material at a given constant continuous load, and its change for different levels of a continuous load is considered.

Abstract: Numeral experiments to study influence on design strength of conical poles, limitations of crack width and breaking strain have been conducted. The analysis of influence on conical poles crack strength and deformability and relation between areas of prestressing steel and total area of steel (A_sp/A_s,tot) has been performed. Research has revealed that dependence of crack width on relation between A_sp/A_s,tot for all types of conical poles is close to linear. Percentage of reinforcement μ_{s, tot} % does not influence this dependence. A moment of force increase caused by vertical load M_v/M leads to a significant increase of crack width. Presence of prestressing steel (A_sp/A_s,tot) has the greatest influence on the deflection of conical poles. Still total percentage of reinforcement has little influence on a type of function f_пр=f (A_sp/A_s,tot). Calculations of poles made according to a strain pattern showed that regulations understate approximate value of deflection. For that reason, it is advisable to make calculations of poles CONS22, CONS26 according to a strain patter.

Abstract: The article deals with the change in the deflection of partially prestressed elements under repeated loading. Depending on the classes and the ratio of stressed and non-tensioned reinforcement, the effect of different levels of the repeated load application on the deformability index of the bent ferro-concrete elements is analyzed. Analysis of the experimental and calculated values ​​of deflections of rectangular profile beams after application of static repeated loads showed that regulatory documents underestimate the effect of the operational level repeated loads on the change in deflections at both average and high loading levels by more than 30%. Comparison of deflection values ​​was made immediately after application of repeated loads at the level of 60% from the destructive ones and after lifting the load to the level of 80%. To correct the values ​​of deflections within the limits of the calculated dependences of the norms, when subjected to the operational level repeated loads, it is proposed to take the value of the coefficient characterizing the elastoplastic properties of concrete equal to 0.3 for practical calculations. The results of the study increase the convergence of the experimental and theoretical values ​​of deflections in the range considered.