Investigation of the Influence of Local Low Strength Concrete on the Bearing Capacity of Bending Reinforced Concrete Beams

Reinforced concrete beams can experience local low concrete strength under certain conditions, for example, poor construction practices can cause problems such as concrete voids, surface cavities, block cracking, surface sinks and create areas of low concrete strength. This study presents the response of flexural hinge-supported reinforced concrete beams with different local areas of low concrete strength along the span. Modified models are adopted to describe the concrete properties and an ideal elastic-plastic model is adopted for the steel properties. The beam was divided into three main parts: one sensitive to bending moment, the second sensitive to shear, and the third sensitive to bond. The variables included two types of concrete strength and one reinforcement diameter. The results show that the most critical region with low concrete strength along the span of the beam is the confluence zone near the supports, which is reflected in the ductility of the load-deflection curves. A new generalized empirical model is developed to predict the effect of bearing capacity reduction from local low-strength concrete

On the Stability of Eccentrically Compressed Reinforced Concrete Elements with a Small Eccentricity, Taking into Account the Rheological Properties of Concrete

In the practice of modern construction, flexible centrally and eccentrically compressed reinforced concrete elements are becoming more common. In this regard, the relevance of studying their work and the mechanism of bearing capacity exhaustion increases. There are two directions in determining the bearing capacity of these elements: calculation for stability and calculation for strength. The loss of stability in a number of cases, obviously, can cause the destruction of not only centrally, but also eccentrically compressed rods with small eccentricities, since under certain conditions they can practically turn out to be close in their work. The stability of these eccentrically compressed rods is calculated by multiple integration. Such a calculation is especially laborious for reinforced concrete elements. This article is devoted to the study of the stability of centrally and eccentrically compressed reinforced concrete rods with small eccentricities, taking into account the creep of concrete. An eccentrically compressed rod with a small eccentricity of length l is replaced by a centrally compressed rod of length l0 so that the bending arrow includes the eccentricity. The numerical values of the rheological coefficients are determined from the boundary values of the reduced stiffness, which varies along the length of the rod. Complicated integration is replaced by the solution of the differential equation of the bent axis of the rod in the form of a sinusoid half-wave

Strength and deformability of reinforced concrete beams with indirect reinforcement in the form of welded meshes in compressed zone

One of the ways to improve the strength and deformation characteristics of reinforced concrete structures is the use of indirect reinforcement. Such reinforcement, located perpendicular to the compressive force, by limiting transverse deformations creates a volumetric stress state and increases the efficiency of concrete in compression. The article presents a method for assessing the stress-strain state of structures, which allows to take into account the reserves of bearing capacity and apply more economical design solutions. The calculation of strength is considered and the diagram of concrete deformation reinforced by indirect reinforcement is obtained. It is shown that the relative deformations at the apex of the compression diagram depend mainly on the relative level of lateral reduction and concrete strength. It is shown that the lower the concrete class, the less indirect reinforcement affects its strength characteristics, but the limiting deformations increase more strongly, and therefore an almost horizontal section appears near the top of the diagram, the longer the concrete class and the higher the reinforcement percentage. © 2019 Trans Tech Publications Ltd, Switzerland

The degree of physical depreciation of buildings and structures

The influence of an aggressive environment affects the appearance of physico-mechanical and physico-chemical corrosion processes, which in turn affects the depreciation of concrete properties, the redistribution of internal forces in sections and the depreciation of the working conditions of the reinforcement. The article discusses issues related to the degree of influence of environmental aggressiveness on building structures. It was shown that steel corrosion in concrete occurs due to a change in its passivity, which is associated with a decrease in alkalinity to pH <12 during carbonation of concrete. Data on the average rate of destruction of the material (metal and concrete) are given in case of corrosion. Types of solutions to extend the life of buildings and structures are presented. Methods for calculating physical wear are highlighted. The physical depreciation of the building is shown graphically, considering repair work. The definition of physical depreciation of buildings based on the calculation of the physical depreciations of its individual structural elements is given. An example of calculating the physical depreciation of a building is considered. A formula has been developed for determining the degree of damage to structural elements of a building object. The results of calculations of the degree of damage and the degree of physical depreciation of structural elements of the building are presented. © Published under licence by IOP Publishing Ltd