Steel-reinforced Concrete Elements Research Articles

Numerical and experimental studies of the strength of compressed steel-reinforced concrete elements made using high-strength concrete and square steel pipes of class C345

In this article, numerical and experimental studies of the strength of compressed steel-reinforced concrete elements made using high-strength concrete and square steel pipes of class C345 are considered in order to determine the bearing capacity. The main issue in the calculation of pipe-concrete structures is the question of the design strengths of materials working as part of a pipe-concrete section. These strengths differ from the strengths of materials in a uniaxial stressed state and depend on a number of parameters. Concrete with small eccentricities of longitudinal force is in a state of triaxial compression, and its strength increases compared to uniaxial compression. The steel of the pipe is in a flat stressed state. When the eccentricity of the longitudinal force application increases, the strengths of materials approach to the strength under uniaxial compression. The issue of changing the strength of materials with a change in the eccentricity of the longitudinal force has been studied quite well. Therefore, the main issue is the strength of materials in the central compression of the pipe-concrete structure. The work of materials in the composition of a square tube-concrete section is fundamentally different from the work of materials in the composition of a round tube-concrete section. The main difference lies in the uneven lateral compression of concrete in a square pipe.

FRP-Reinforced/Strengthened Concrete: State-of-the-Art Review on Durability and Mechanical Effects

Fiber-reinforced polymer (FRP) composites have gained increasing recognition and application in the field of civil engineering in recent decades due to their notable mechanical properties and chemical resistance. However, FRP composites may also be affected by harsh environmental conditions (e.g., water, alkaline solutions, saline solutions, elevated temperature) and exhibit mechanical phenomena (e.g., creep rupture, fatigue, shrinkage) that could affect the performance of the FRP reinforced/strengthened concrete (FRP-RSC) elements. This paper presents the current state-of-the-art on the key environmental and mechanical conditions affecting the durability and mechanical properties of the main FRP composites used in reinforced concrete (RC) structures (i.e., Glass/vinyl-ester FRP bars and Carbon/epoxy FRP fabrics for internal and external application, respectively). The most likely sources and their effects on the physical/mechanical properties of FRP composites are highlighted herein. In general, no more than 20% tensile strength was reported in the literature for the different exposures without combined effects. Additionally, some provisions for the serviceability design of FRP-RSC elements (e.g., environmental factors, creep reduction factor) are examined and commented upon to understand the implications of the durability and mechanical properties. Furthermore, the differences in serviceability criteria for FRP and steel RC elements are highlighted. Through familiarity with their behavior and effects on enhancing the long-term performance of RSC elements, it is expected that the results of this study will help in the proper use of FRP materials for concrete structures.

Management of degradation processes and strengthening of soils and foundations of transport structures

The method of strengthening the soils and foundations of transport structures used for their preservation, especially buildings of architectural and historical value, as well as during mass renovation in large cities in cramped conditions with high density of existing buildings, is considered. The method of constructing a horizontal distributor by pushing through round-section sleepers in the form of steel-reinforced concrete elements made of pipes filled with concrete is considered. In the article, the dependence of the radius of the compacted zone on the initial characteristics of the soil density and the diameter of the pressed pipe concrete element is analyzed. The method of installing a pipe-concrete horizontal distributor for simultaneous strengthening of the foundation and soils is considered, as well as it is the most environmentally friendly and does not negatively affect the surrounding buildings and structures. An assessment of the change in the height of the surface discharge of the foundation soil is presented, which allows to regulate the process of leveling the deformation of the building as a whole.

EXPERIENCE OF CREATING PRELIMINARY SELF-STRESSED IN COMPRESSED STEEL-REINFORCED CONCRETE ELEMENTS

Problem statement. Compressed steel-reinforced concrete structures work effectively as individual racks or columns of buildings and structures for various functional purposes, and as compressed elements of spatial steel-reinforced concrete structures (for example, compressed truss members). Usually, such structures consist of a steel shell filled with concrete. The creation of the concrete core preliminary compressive stresses allows increasing the overall bearing capacity and reducing the deformability of the specified compressed elements. Purpose of the article is to analyze the existing practical methods of creating preliminary compressive stresses in the concrete core of compressed steel-reinforced concrete structures and to distinguish from them methods of the concrete core self-stressed without the use of special mechanical and force measures. Conclusion. Based on the analysis of existing scientific publications in the indicated direction, it was found that pre-stressed in the concrete core of compressed steel-reinforced concrete elements can be created due to the preliminary compression of the concrete core with jacks in outer steel pipe-shell (in a through shell), cutting outer steel shell with deformation seams into separate sections, installation of a pre- stressed double shell, etc. Preliminary self-stressed in the concrete core are created due to the following measures: use for concrete solution preparation stressed cement or a concrete mixture compaction by centrifugation during the combined structures manufacture. The specified methods of creating preliminary stresses can also be used when strengthening existing steel structures by concreting or inclusion in the steel shell joint operation reinforced concrete columns reinforcement.

Estimation of chloride diffusion coefficient from water permeability test of cementitious materials

Chloride diffusion coefficient of concrete is a critical parameter indicating a durability property of steel-reinforced concrete elements in chloride-laden environments. However, chloride diffusion tests of concrete could take months or even years to finish in order to obtain the steady state chloride diffusion coefficient (Dss). Most engineers have to take a rapid chloride migration test to get a chloride migration coefficient, which could still take one or a few days to finish. In contrast, a water permeability test could be finished within only a few hours, and a steady state water permeability coefficient (k) can be obtained. This study aims to build a theoretical model between Dss and k, and the model has been validated by experimental work. The obtained model shows that relationship between Dss (in m2/s) and k (in m2) can be simply described using a formula Dss/k = 32Daq/d2pore, where Daq (in m2/s) is the chloride diffusion coefficient in free solution, and dpore (in m) is the equivalent pore diameter. The experimental validation work showed that the model is in good agreement with the measured data, and dpore in the formula can be replaced with the average pore diameter da. Applying this model in engineering projects could aid to predict the difficult-to-get Dss of cementitious materials through the rapid measurements of k and da.

Strength of Normal and Inclined Sections of Bent Reinforced Concrete Elements with Zone Reinforcement Made of Steel Fiber

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.

К РАСЧЕТУ СТАЛЕЖЕЛЕЗОБЕТОННЫХ РЕБРИСТЫХ ПЛИТ ДЛЯ ВОССТАНАВЛИВАЕМЫХ ПЕРЕКРЫТИЙ

Analyzes national experience of restoring the old buildings floors. An assessment of the wood-reinforced concrete using experience, steel-reinforced concrete floor structures and methods for calculating load-bearing elements of a composite section is given. It is noted that the current design standards and existing methods for calculating steel-reinforced concrete structures of civil buildings and bridge structures use simplified calculation methods and do not reflect the actual stress-strain state of a bent element, do not take into account the initial pre-operational deformations and stresses, and do not lead to economical design solutions. Sometimes they lead to incorrect results. Expressions of internal moments and forces of steel-reinforced concrete bending elements are presented from the equilibrium conditions of a composite element, taking into account pre-operational forces. The results of our own experiments are presented, where it is shown that during the hardening of concrete, beams and slabs receive deformations in the form of reverse deflection (bending), and internal stresses arise in the sections of steel-reinforced concrete elements. Formulas are given for calculating the deflections of bending elements taking into account their initial deformations. To compare the calculation results of the proposed method for calculating steel-reinforced concrete elements, taking into account the initial deformations and stresses, the data of our own experiments were used and comparisons were given. Satisfactory convergence of the results is shown.

ПРОЧНОСТЬ ИЗГИБАЕМЫХ ЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ С ЗОННЫМ АРМИРОВАНИЕМ ИЗ СТАЛЬНОЙ ФИБРЫ

On the basis of theoretical and experimental studies, the assumptions and calculation method for flexible and compressed-curved reinforced concrete structures with zone reinforcement made of steel fiber operating 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. To confirm the main results of this method, numerical and full-scale experimental studies of reinforced concrete beam structures reinforced with conventional reinforcement and a zone steel-fiber layer were 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 crack formation of steel-reinforced concrete elements under such types of loading. The efficiency of fiber reinforcement of normal and inclined sections for increasing the strength and deformation characteristics of reinforced concrete structures is revealed.

The procedure of fire-resistance calculation for compressed reinforced concrete elements

Fire-resistance calculations adopted in the regulatory system (both in the Russian and in European) are based on calculations of isofields of section heatup of structural elements. Heatup isofields for reinforced concrete elements specified in the regulatory system have been obtained by the concrete section calculation not considering inclusions of reinforcement bars. But it is known that accuracy of the fire-resistance calculation of reinforced concrete elements depends on performance accuracy of a thermotechnical calculation. Having performed this calculation the temperature field distribution by element section and strength characteristics depending on it are determined. Temperature distribution by element section depends on such parameters as heat-absorption capacity and thermal conductivity of section parts, section humidity. Within the work the approach to solving the problem of consideration of the actual temperature field when calculating fire-resistance of reinforced concrete and steel-reinforced concrete elements has been reviewed. Calculations of fire-resistance at temperature fields not considering inclusions of reinforcement bars (concrete section) as well as at temperature fields considering reinforcement bar inclusions have been performed. Additional coefficients introduced in the fire-resistance calculation when using Russian and European methods have been calculated for the reviewed section with 600×600 overall dimensions. According to calculation results the change of section bearing capacity upon the calculation considering thermotechnical characteristics of the reinforcement bars has been observed.

Nonlinear Analysis of Compressed Concrete Elements Reinforced with FRP Bars

Although fiber reinforced polymer (FRP) bars have proved their usefulness in the case of reinforced concrete flexural elements, there are still limited data on their performance in such structures under compression. Despite multiple benefits of using FRP bars as the reinforcement in concrete elements, their potential application as main reinforcement in compressed elements is still very controversial, mainly due to the limited amount of published research results. The presented work partly fulfills this knowledge gap. Two series of theoretical analyses—one based on the stress distribution in the cross-section and the second using the finite elements method (FEM)—with reference to the experimental results are presented. The analyses concern basalt FRP, glass FRP, and steel-reinforced concrete elements under axial compression. There are derived calculations of load–displacement relations and stress values in bars. Damage progression was analyzed as well. Main findings are as follows: (1) a good agreement between calculated failure loads and experimental results has been achieved; (2) potential negative influence of FRP reinforcement on the compressive capacity of the reinforced element should not be neglected; (3) nonlinear FEM analysis is useful in predicting the maximum value of load and damage zones; (4) stress values of only about 100 MPa (much lower than their compressive strength value) were obtained in non-metallic bars. The results might be useful for the further establishment of design rules.

Calculation Of Fire Resistance Of Compressed Reinforced Concrete Elements Taking Into Account The Heat And Technical Characteristics Of Reinforcement

The calculation of fire resistance of reinforced concrete elements depends on the accuracy of the thermal calculation. When performing this calculation, the distribution of the temperature field over the cross section of the element and the strength characteristics that depend on it are determined. The temperature distribution over the section of the structure depends on such parameters as the heat capacity and thermal conductivity of the section parts, and its humidity. The article considers an approach to solving the problem of taking into account the actual temperature field when calculating the fire resistance of reinforced concrete and steel-reinforced concrete elements. Fire resistance calculations were performed for temperature fields that do not take into account the inclusion of reinforcement (concrete section), as well as for temperature fields that take into account temperature inclusions. For the section under consideration, additional coefficients are calculated, which are entered into the calculation of fire resistance when using the method STO 36554501-006-2006 "Rules for ensuring the fire resistance and fire safety of reinforced concrete structures". According to the results of this work, an increase in the bearing capacity of rectangular and square sections was noted when calculating with regard to the thermal characteristics of the reinforcement.

The effect of anisotropy of elastic properties of GFRP reinforcement on strength of compressed concrete structural elements

Introduction. Despite the growing interest to the use of GFRP reinforcement in various concrete structures, its use in the concrete compressed zone is not investigated sufficiently. The use of GFRP reinforcement in compressed concrete elements is limited by a combination of low value of its modulus of elasticity and small ultimate deformation of concrete during compression. A number of researchers suggest solving this problem by means of increase the ultimate concrete deformation due to lateral reinforcement. However, unlike steel reinforcement, the elastic properties of composite reinforcement depend on the stress direction, which is due to the significant difference between the moduli of elasticity of the fibre glass and the binder. Consequently, the stress-deformation state of compressed concrete elements with longitudinal GFRP reinforcement and close-set lateral reinforcement will differ from the stress-deformation state of steel-reinforced concrete elements. Materials and methods. To clarify the effect of the anisotropy of fibre-glass reinforcement elastic properties on its work in the concrete compressed zone, a physical experiment and numerical simulation using the LIRA-SAPR software were carried out. Physical nonlinearity of materials was not taken into account in the model. Results. An assessment of the effect of anisotropy of elastic properties of fibre-glass reinforced plastic (GFRP) reinforcement on the strength of compressed concrete elements was accomplished for longitudinal reinforcement. The experiment showed that the location of the longitudinal GFRP reinforcement in the concrete compressed zone in the absence of lateral reinforcement led to a decrease in the average strength of the tested samples by 9.2 %, while the fracture nature of GFRP-reinforced samples differed from the fracture nature of control samples. As a result of the numerical simulation, it was revealed that the cause of the strength reduction is the anisotropy of the elastic properties of GFRP reinforcement, which affects the stress-deformation state of compressed concrete. Conclusions. The analysis of the results of experiment and numerical simulation showed that the reason for the decrease in strength is the low modulus of elasticity of GFRP when compressed in the lateral direction as compared with the similar characteristic of concrete. The degree of strength reduction will also depend on the relation between the moduli of elasticity of concrete and GFRP when compressed in the longitudinal direction.

Compressed Flexible Steel Reinforced Concrete Elements Investigation

Stress-strain state and compressed flexible steel-reinforced concrete elements resistance capacity are investigated in the work. The experiment program is complied and steel reinforced concrete elements calculations methods are analyzed. Experimental sample design drawings are shown. Raw materials physical and mechanical properties are determined. Steel reinforced-concrete elements experimental and research studies have been carried out. Coboundary dependences N-M for steel reinforced concrete elements construction method is proposed. Resistance capacity diagrams for steel reinforced concrete elements are constructed depending on the element height and the applied eccentricity.

Analyzing of Coatings on Steel - Reinforced Concrete Elements by Mobile NMR

Abstract A large number of infrastructural concrete buildings are protected against aggressive environments by coating systems. The functionality of these coating systems is mainly affected by the composition and thickness of the individual polymeric layers. For the first time ever, a mobile nuclear magnetic resonance (NMR) sensor allows a non-destructive determination of these important parameters on the building site. However, before this technique can be used on steel-reinforced concrete elements, the potential effect of the reinforcement on the measurement, i.e. the NMR signal, needs to be studied. The results show a shift of the NMR profile as well as an increase of the signals amplitude in the case of the reinforced samples, while calculating the thickness of concrete coating leading to identical results.

LIMIT STATE EVALUATION OF STEEL-REINFORCED CONCRETE ELEMENTS BY VON MISES AND MENÉTREY–WILLAM-TYPE YIELD CRITERIA

An advanced version of a recently developed numerical limit analysis procedure for the prediction of peak loads and failure modes of steel-reinforced concrete elements is proposed. The modified procedure allows to take into account possible yielding of reinforcement thus capturing the actual behavior at the collapse of both steel and concrete. This implies a finite element (FE) modeling of the reinforced concrete (RC) elements in which concrete is governed by a Menétrey–Willam-type yield criterion, with cap in compression, while steel bars are governed by a von Mises yield criterion. The peak load of a wide range of RC structures whose behavior at ultimate state is dominated either by the concrete crushing or by the steel bars yielding is then predicted with a very good accuracy.

Measuring the layer thicknesses of concrete coatings by mobile NMR – A study on the influence of steel reinforcements

A large number of infrastructural concrete buildings are protected against aggressive environments by coating systems. The functionality of these coating systems is mainly affected by the composition and thickness of the individual polymeric layers. For the first time ever, a mobile nuclear magnetic resonance (NMR) sensor allows a non-destructive determination of these important parameters on the building site. However, before this technique can be used on steel-reinforced concrete elements, the potential effect of the reinforcement on the measurement, i.e. the NMR signal, needs to be studied. The results show a shift of the NMR profile as well as an increase of the signals amplitude in the case of the reinforced samples, while calculating the thickness of concrete coating lead to identical results.