To the Analysis of the Reliability of Structures of Beam Systems

The article discusses the issues of reliability for various types of failures of beam systems. A single-span bending beam is analyzed. The limit state functions for moment failure modes in the characteristic sections of the beam are determined. The ways of forming a plastic hinge for a beam are shown. The lower and upper limits of the beam reliability are calculated. Limit state functions corresponding to failure mechanisms are presented

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

Conceptual Approaches to Robustness Assessment of Building Structures, Buildings and Facilities

Some examples of failures of structures, buildings, where the lack of robustness was recognized, are analyzed. Several author’s definitions for robustness are presented and discussed. Special emphasis is given to the fact that define robustness as an intrinsic structural property and the other hand it as a property of the structure and its environment. Some related concepts are presented and discussed.The most important proposed measures for robustness are also present-ed including some illustration examples. Finally, a comparison between them is made and the respective shortcomings are identified. After anal-ysis of the robustness nature, a new structural oriented definition is pro-posed. Based on the highlighted shortcomings of the existing measures, in particular those related with the application to deteriorated structures, a conceptual framework for robustness assessment is proposed

Influence of Formwork Structure on Heat Treatment of Precast Concrete Elements by Solar Energy

The present paper aims to study the influence of the formwork structure on the efficiency of heat treatment (HT) of precast concrete elements (PCE) by solar energy in various climatic conditions. The objects of the study were different types of formworks composed of solar energy equipment for HT of PCE. In total, six types of formworks, made of steel sheet, laminated plywood and timber, with and without insulation were studied. Calculation and experimental study were carried out for humid continental, and subtropical climates. Experimental study was carried out in the laboratory and in the open air. According to the obtained results, the heat insulation material in the formwork structure contributes to increase the strength of concrete. Formwork with heat insulation layer of 40 mm gave the best results. However, the level of the contribution depends on climatic conditions. Heat insulation material in the formwork structure is necessary in humid continental climate. Even the thickness of the insulation layer of 20 mm gives good results and the difference between the concrete strength with thickness of 20 mm and 40 mm is insignificant. On the contrary, in humid subtropical climate, the heat insulation material in the formwork structure is favorable, but not compulsory, since the difference between the concrete strengths is not significant and the strength values, obtained in all six types of formwork, allow it to be removed after 24 hours of curing

Optimization of reinforced concrete structures: importance of design detail level

The study of the influence for design solution detailing on the cost of reinforced concrete structures during their optimization is carried out. A hypothesis is formulated on the final improvement of the target criterion with an increase in the number of variable parameters. Depending on this number, the concepts of three levels of detail are introduced, at which optimization can be carried out, and the degree of risk of failure of the structure is indicated for them. Using the example of finding a constructive solution for a reinforced concrete beam by the cost minimization criterion, the relationship of the cost change is shown when the number of independently variable parameters changes. The normal operation of the beam and the emergency action effects in the form of local damage to a single corner connection are taken into account. Genetic algorithms are used for the optimization

The efficiency of varying parameters when optimizing reinforced concrete structures

The actual issue is considered related to the purpose of the type of variable parameters, their number and grouping of structural elements in the optimization of reinforced concrete structures. The genetic search algorithm is used to solve the problem of minimizing the cost of frame systems. The rate of convergence of the iterative procedure is taken as one of the criteria for the significance of the parameter when varying. The comparison of optimization results for a reinforced concrete beam and a frame is given. A conclusion is made about the expediency of varying parameters of different types and their ranking is performed from the standpoint of the goal function sensitivity to parameter changing

Strength of reinforced concrete columns under special complex influences

A method for evaluating the strength, stiffness and stability of medium-flexible columns with a square cross-sectional shape and symmetrical reinforcement is proposed. Combined impacts from constant longitudinal force, horizontal impact with trapezoidal pulse shape and deterioration in mechanical properties of concrete from natural influences such as corrosion are taken into account. Various combinations of such influences are also considered. The computational model is represented by volumetric concrete elements rigidly connected to rebars. The dynamic transient process is based on an implicit integration scheme using a stepwise procedure. At each step, the nonlinear problem is solved by the Newton-Raphson method. The data characterizing the degree of danger of occurrence of local strength deterioration for column variants have been compared. The dependence of the value of longitudinal force on the value of transverse impact is found, provided that the load-carrying capacity of the column is ensured