scholarly journals EXPERIMENTAL INVESTIGATIONS OF THE LOSSES OF PRESTRESSING IN FINE REINFORCED CONCRETE ELEMENTS

2018 ◽  
Vol 22 (1) ◽  
pp. 112-117 ◽  
Author(s):  
S. G. Parfenov ◽  
M. V. Morgunov
Keyword(s):  
Experimental Data ◽  
Reinforced Concrete ◽  
Experimental Studies ◽  
Reinforced Concrete Beams ◽  
Experimental Investigations ◽  
Fine Grained ◽  
Concrete Shrinkage ◽  
Prestressing Force ◽  
Shrinkage And Creep

The article deals with late losses of prestressing of reinforcement due to shrinkage and creep in fine reinforced concrete structures. Creep deformations can several times exceed the elastic straincaused by load. The most common in practice caseof the development of concrete creep is slowly decreased creeping with timewith a rather high initial rate of the development in the first hours after loading. It is typical for stresses that do not exceed the long-term resistance of concrete. Experimental study of deformation of shrinkage and creep of fine-grained concrete allows us to compare the loss of prestressing due to concrete shrinkage and creep. Usually there is an aggregate effect of these factors, which significantly complicates the study of the processes occurring in concrete during long-term exposures. Basically, the results obtained during testing of concrete prisms are used to compare stress-related properties of concrete, but this is not enough to study the loss of prestressing due to concrete shrinkage and creep and testing should be carried out on elements reinforced with prestressed reinforcement to take into account changes in prestresses and redistribution of stresses on the height of the cross section (depth) of the element with a prolonged action of the prestressing force. The results of experimental studies of rectangular reinforced concrete beams at loadcase of different ages of t = 14, 28, 280 and 320 days are analyzed. The losses from rapid creep, shrinkage losses, total losses from shrinkage and creep are considered. The experimental data are presented in the form of graphs and tables. There was performed comparison of the experimental data with the calculated ones determined according to the current standards, and for shrinkage according to the method proposed by I.I. Ulitsky as well.

scholarly journals Structural behaviour of CFRP reinforced concrete members under monotonic and cyclic long-term loading

2021 ◽  
Vol 54 (4) ◽  
Author(s):  
Redouan El Ghadioui ◽  
Dominik Hiesch ◽  
Lukas Bujotzek ◽  
Tilo Proske ◽  
Carl-Alexander Graubner
Keyword(s):  
Experimental Data ◽  
Reinforced Concrete ◽  
Structural Engineering ◽  
Creep Behaviour ◽  
Time Dependent ◽  
Experimental Investigations ◽  
Structural Behaviour ◽  
Displacement Sensors ◽  
Precise Knowledge

AbstractA large percentage of the damages to reinforced concrete structures is caused by corrosion of the reinforcement steel, which often leads to expensive repairs or new construction of existing structures. Due to their high strength and resistance to corrosion, reinforcements made of carbon fibre-reinforced polymers (CFRP) are becoming more and more important in structural engineering. It is expected, that the service life of CFRP reinforced concrete (RC) members can be significantly increased as the strength-reduction due to corrosion is negligible compared to conventional RC members. Therefore, precise knowledge of the long-term behaviour of CFRP RC members is required in order to ensure safe and economic design. This paper presents experimental investigations on the long-term behaviour of CFRP RC members as well as steel-reinforced RC members under monotonic and cyclic long-term loading with varying load levels, different cross-sectional shapes and shear slendernesses. Accompanying experiments on the concrete creep behaviour that were conducted within the investigations are shown. Within the scope of the experiments, the deflections as well as the strains on the top and bottom side of the RC members were measured using displacement sensors and strain gauges. The experimental data is evaluated, especially with regard to the time-dependent deflections. The data is compared to existing mechanical and empirical models, which are usually derived for steel-reinforced RC members. Based on the experimental data, the time-dependent reduction of stiffness and conclusions for the calculation of deflections are shown.

scholarly journals Experimental Investigations of the Stress and Strain State of Continuous Reinforced Concrete Beams Under the Action of Low-Cyclic Repetitive and Alternating Loads

2018 ◽  
Vol 7 (3.2) ◽  
pp. 236
Author(s):  
Grigoriy Masiuk ◽  
Oleksandr Yushchuk ◽  
Andrii Paschenko
Keyword(s):  
Mechanical Properties ◽  
Reinforced Concrete ◽  
Strain State ◽  
Concrete Beams ◽  
Experimental Studies ◽  
Physical And Mechanical Properties ◽  
Reinforced Concrete Beams ◽  
Experimental Investigations ◽  
Stress And Strain ◽  
Static Loads

The article is devoted to the experimental studies of the stress and strain state of the two-pass reinforced concrete beams under the influence of low-cyclic repeated and alternating loads. Based on the results of experimental studies, the effect of low-cyclic repeated and alternating loads on the change of the stress and strain state of continuous reinforced concrete beams has been established. In the course of testing the sample, it was found that the stress and strain state of the beams under the action of the above mentioned loads is significantly different from the stress and strain state of the beams under the action of nonalternating static loads, namely, the decrease of the bearing capacity, the increase of the deflections and the width of the cracking. All this is due to the change in the physical and mechanical properties of concrete in response to the above-mentioned loads on experimental.  

scholarly journals Pilot Studies of Concrete Beams Deformability Reinforced with Composite Reinforcement

2020 ◽  
Vol 24 (1) ◽  
pp. 103-114
Author(s):  
O. A. Vetrova
Keyword(s):  
Experimental Data ◽  
Concrete Beams ◽  
Experimental Studies ◽  
Steel Reinforcement ◽  
Reinforced Concrete Beams ◽  
Pilot Studies ◽  
Loading Level ◽  
Design Load ◽  
Composite Reinforcement

Purpose of research. Analysis is done on the basis of experimental data of loading level impact on deformability of beams with steel and composite fiberglass reinforcement at prolonged loads.Methods. Experimental studies of concrete bending elements of two series were carried out: the first is reinforced with composite fiberglass reinforcement of ASK class, the second is reinforced with steel reinforcement of А400 class. Studies of experimental samples were carried out under long-term loads. The structures were under different loads during the experiment: at design load, at 1.2 level from design load and at 1.5 from the design load. Concrete deformations and deflections of experimental beams of two series were fixed.Results. Dependence on time of concrete deformations of experimental samples of two series at different loading levels, dependence of deflection growth on load application level, influence dependence of loading level of elements on speed and intensity of creep deformation growth of beams with fiberglass and steel reinforcement are stated on the basis of experimental data. In particular, the bends of all samples with fiberglass reinforcement exceeded the maximum permissible value, while the maximum deflection of reinforced concrete beams in the middle of the section did not exceed maximum permissible value.Conclusion. On the basis of the obtained data, conclusions are drawn on the nature and magnitude of long-term deformations of beams with fiberglass and steel reinforcement at different levels of long-term loads. This conclusion is significant in practical sense when using concrete structures with composite reinforcement taking into account a small number of research data.

Improvement Of Curvilinear Diagrams Of Concrete Deformation

2019 ◽  
pp. 99-104
Keyword(s):  
Reinforced Concrete ◽  
Peak Load ◽  
Experimental Studies ◽  
Concrete Structures ◽  
Deformation Model ◽  
Reinforced Concrete Structures ◽  
Significant Difference ◽  
Deformation Diagrams

Problems when calculating reinforced concrete structures based on the concrete deformation under compression diagram, which is presented both in Russian and foreign regulatory documents on the design of concrete and reinforced concrete structures are considered. The correctness of their compliance for all classes of concrete remains very approximate, especially a significant difference occurs when using Euronorm due to the different shape and sizes of the samples. At present, there are no methodical recommendations for determining the ultimate relative deformations of concrete under axial compression and the construction of curvilinear deformation diagrams, which leads to limited experimental data and, as a result, does not make it possible to enter more detailed ultimate strain values into domestic standards. The results of experimental studies to determine the ultimate relative deformations of concrete under compression for different classes of concrete, which allowed to make analytical dependences for the evaluation of the ultimate relative deformations and description of curvilinear deformation diagrams, are presented. The article discusses various options for using the deformation model to assess the stress-strain state of the structure, it is concluded that it is necessary to use not only the finite values of the ultimate deformations, but also their intermediate values. This requires reliable diagrams "s–e” for all classes of concrete. The difficulties of measuring deformations in concrete subjected to peak load, corresponding to the prismatic strength, as well as main cracks that appeared under conditions of long-term step loading are highlighted. Variants of more accurate measurements are proposed. Development and implementation of the new standard GOST "Concretes. Methods for determination of complete diagrams" on the basis of the developed method for obtaining complete diagrams of concrete deformation under compression for the evaluation of ultimate deformability of concrete under compression are necessary.

Methodology of studying the mechanical properties of composite materials (reinforced concrete)

2018 ◽  
Vol 84 (12) ◽  
pp. 61-67
Author(s):  
V. A. Eryshev
Keyword(s):  
Mechanical Properties ◽  
Reinforced Concrete ◽  
Experimental Studies ◽  
Analytical Relationship ◽  
Hardened Concrete ◽  
Deformation Model ◽  
Joint Work ◽  
Concrete Shrinkage ◽  
Axial Tension ◽  
Tension And Compression

The mechanical properties of a complex composite material formed by steel and hardened concrete, are studied. A technique of operative quality control of new credible concrete and reinforcement, both in laboratory and field conditions is developed for determination of the strength and strain characteristics of materials, as well as cohesion forces determining their joint operation under load. The design of the mobile unit is presented. The unit provides a possibility of changing the direction of loading and testing the reinforced element of the given shape both for tension and compression. Moreover, the nomenclature of testing equipment and the number of molds for manufacturing concrete samples substantially decrease. Using the values of forcing resulting in concrete cracking when the joint work of concrete and reinforcement is disrupted the values of the inherent stresses and strains attributed to the concrete shrinkage are determined. An analytical relationship between the forces and deformations of the reinforced concrete sample with central reinforcement is derived for axial tension and compression, with allowance for strains and stresses in the reinforcement and concrete resulted from concrete shrinkage. The results of experimental studies are presented, including tension diagrams and diagrams of developing axial deformations with an increase in the load under the central loading of the reinforced elements. A methodology of accounting for stresses and deformations resulted from concrete shrinkage is developed. The applicability of the derived analytical relationships between stresses and deformations on the material diagrams to calculations of the reinforced concrete structures in the framework of the deformation model is estimated.

scholarly journals Long-Term Concrete Shrinkage Influence on the Performance of Reinforced Concrete Structures

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 254
Author(s):  
Alinda Dey ◽  
Akshay Vijay Vastrad ◽  
Mattia Francesco Bado ◽  
Aleksandr Sokolov ◽  
Gintaris Kaklauskas
Keyword(s):  
Reinforced Concrete ◽  
Reinforced Concrete Structures ◽  
Tension Stiffening ◽  
Model Code ◽  
Concrete Shrinkage ◽  
Time Period ◽  
Governing Factor ◽  
Model Code 2010 ◽  
Mathematical Process

The contribution of concrete to the tensile stiffness (tension stiffening) of a reinforced concrete (RC) member is a key governing factor for structural serviceability analyses. However, among the current tension stiffening models, few consider the effect brought forth by concrete shrinkage, and none studies take account of the effect for very long-term shrinkage. The present work intends to tackle this exact issue by testing multiple RC tensile elements (with different bar diameters and reinforcement ratios) after a five-year shrinking time period. The experimental deformative and tension stiffening responses were subjected to a mathematical process of shrinkage removal aimed at assessing its effect on the former. The results showed shrinkage distinctly lowered the cracking load of the RC members and caused an apparent tension stiffening reduction. Furthermore, both of these effects were exacerbated in the members with higher reinforcement ratios. The experimental and shrinkage-free behaviors of the RC elements were finally compared to the values predicted by the CEB-fib Model Code 2010 and the Euro Code 2. Interestingly, as a consequence of the long-term shrinkage, the codes expressed a smaller relative error when compared to the shrinkage-free curves versus the experimental ones.

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