SJIF Impact Factor: 7.001| ISI I.F.Value:1.241| Journal DOI: 10.36713/epra2016                ISSN: 2455-7838(Online)

EPRA International Journal of Research and Development (IJRD)

          Volume: 5 | Issue: 5 | May 2020                                                                                   - Peer Reviewed Journal

CONTENTS

PRESTRESSED LOSSES FROM SHRINKAGE AND

NONLINEAR CREEP OF CONCRETE OF REINFORCED CONCRETE ROD SYSTEMS

Mirzaakhmedov Abdukhalim Takhirovich¹ 

¹Candidate of technical sciences, associate professor of the  Department of Construction of Buildings and Structures, Faculty of Construction, Fergana Polytechnic Institute,  Fergana city, Republic of Uzbekistan  

Mirzaakhmedova Ugiloy Abdukhalimjohnovna²

²Senior lecturer of the  Department of Construction of Buildings and Structures, Faculty of Construction, Fergana Polytechnic Institute,  Fergana city, Republic of Uzbekistan  

INTRODUCTION

 Prestressed reinforced concrete structures have a complex stress state, varying in time from the effects of external loads, the manifestation of inelastic deformations of concrete, relaxation of stresses in steel and other conditions. In this connection, at designing of prestressed designs it is necessary to know the basic reasons, influence on character and size of change of pressure in armature and concrete at various stages of their work.

MODELS OF SAMPLES AND RESEARCH METHODS

  Precise account of factors influencing the value of losses, as a rule, is a complex and often difficult to solve [1, 2]. In this connection, for practical calculations it is necessary to accept less exact, but simplified methods of preliminary stress losses accounting.

 Pre-voltage losses considered in calculations can be divided into the following types: shrinkage of concrete; creep of concrete; relaxation of stresses in reinforcement; deformation of anchors, washers and gaskets; deformation of joints between blocks of composite structures; deformation of forms for the manufacture of structures; friction of reinforcement in the wall of the channel or concrete surface of structures; concrete buckling under the loops of ring (spiral) reinforcement; temperature difference between the stretched reinforcement and the temperature of the devices that take the stress; multiple repeated load; difference between the coefficients of linear elongation of reinforcement and concrete during the operation of the structure in conditions of increased temperature.

 The above factors affecting the prestressed losses from shrinkage and creep of concrete, the relaxation of steel stresses are manifested over a long period of time.

 In the operational phase, the main shrinkage and creep of concrete acts on the pre-stressed losses.  Let us determine the pre-stress losses from concrete creep using the formula [3].

                              ^b    ^ 

             _n  1e _t                           (1)

_s

where:                             ^H                                          (2) - initial voltage.

 _b _sk

1n_s

                Taking into account the growth of the elastic deformation modulus of concrete in time, the experimental parameters are determined:

 nнs1 nнts ln 11nнnsнst         (3)

Asp As

                ^_s                                               (4)

A A

             As                                             Asp

^_s  ;                  ^_н                               (5)         

             A                        A

                     Es                                           Eн

         ns  t ;                      nн  t .      (6)

                    EM                                         EM

                        _e _1e^b1t                      (7)

_ ^_^c₁^₂^₃ - creep limit characteristic;

^_^c - creep limit characteristic value for average conditions;

^₁ - correction factor dependent on the humidity of the environment in which the   element (construction) is located;

₂ 1,9260,738^l_gb - correction factor that takes into account scaling factors (element size); ^₃ - correction factor depending on the age of the concrete ^t_o d the moment the element is loaded;

E_M^t E_M^o _1e^t  - the elastic-momentous deformations of concrete;

E_M^o _, - constants that depend on curing conditions and concrete composition [4].

 Pre-stressed losses from concrete shrinkage are determined by a formula:

^y^EM(t)    t  ^_s,y     1e                                 (8) s where:

 ^_y ^_y^c₁^₂^₄ - the ultimate relative deformation of shrinkage;

 ^_y^c - the value of the ultimate relative deformation of shrinkage for average conditions;

^_y^c - the correction factor, depending on the time

from which shrinkage and concrete accounting begins.

                Determining the pre-stressed loss from creep and shrinkage in time, we find the value of "compressive force":

N_sp _sk ^_n _sy^A_sp                       (9)

 The calculated ^N_sp load is treated as an external load and is applied to the end of the prestressed rods with a reverse sign.

THE RESULTS OF THE EXPERIMENTS AND THEIR ANALYSIS

  According to the developed algorithms the program is compiled and examples are considered.

 The program is intended for calculation of prestressed concrete trusses taking into account stiffness of knots, creep and shrinkage of concrete, and also for change of prestressed in time, being under the influence of external loads, using the method of consecutive approximations. The general structure of the program calculation process is shown in Figure (1). 

                           The results of the considered examples

(calculation of prestressed reinforced concrete trusses taking into account the stiffness of the nodes in the inelastic stage) show that the stresses from shrinkage and creep in most of the elements do not change significantly and only in the lower zones significantly decreases.

 On the basis of graphs (Figures 2, 3, 4) the increase of ∆σ at different reinforcement percentages obtained in accordance with Table 1 shows that from the action of constant operating loads the stress in the rods of the truss decreases in time in the upper zone and increases in the lower zone, slant and rack. As the percentage of reinforcement increases, the stress increment - ∆σ changes within the following limits:

a) in the lower zone from 2 to 8%; b) in the upper zone from 0.5 to 3.5%; c) in the struts from 0.2 to 2.4%.

 At the same load level, the process of redistribution of effort increases as the percentage of reinforcement increases. This is due to the fact that in the elements of the farm with a high percentage of reinforcement in compressed concrete and, consequently, the non-linearity of deformation increases. Non-linearity of deformation contributes to the redistribution of stresses between the rods of the farm.

Fig.1  General structure of the program calculation process

Fig.2. Stress increase at the increase from the compressed elements

Fig.3. Stress increase at the increase in tension from the stretched elements

Fig.4. Stress increase at increase and consequently in all elements

Note: c, p, s, ditch means that reinforcement percentages change only in compressed, stretched and consequently in all elements of the farm.

REFERENCES

1.        Bondarenko V.M. (1991) "Some questions of nonlinear theory of concrete creep". Kharkov, Kharkov University. P.p. 56.

2.        Bundanov N.A. (1993) "Determination of stress losses in reinforcements of prestressed reinforced concrete structures from the shrinkage and creep of concrete". Moscow: Scientific Journal No 3. P.p.11.

3.        Mirzaakhmedov A.T., Mirzaakhmedova U.A. (2019) "Algorithm of calculation of ferroconcrete beams of rectangular cross-section with one-sided compressed shelf". Problems of modern science and education. Scientific and methodical journal. № 12 (145). Part 2. Moscow.

                P.p.50                  –                  56.                  URL:

https://cyberleninka.ru/article/n/algoritmrascheta-zhelezobetonnyh-balokpryamougolnogo-secheniya-s-odnostoronneyszhatoy-polkoy

4.        Mirzaakhmedov A.T., Mirzaakhmedova U.A., Maksumova S.M. (2019) "Algorithm for calculation of prestressed reinforced concrete farm with account of nonlinear operation of reinforced concrete". Actual science.  International scientific journal.  № 9 (26).

Moscow. P.p.15-20. URL: https://e64f9e97-223d-

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2ae5b404a8ae4aa16a2cb97e9.pdf

 DOI:

METHODS AND TECHNIQUES OF SPEECH

DEVELOPMENT IN CHILDREN  OF PRESCHOOL AGE 

Yuldasheva Dilafruz¹

1

A teacher of Preschool Education department, Preschool and Primary education faculty, Ferghana State University, Uzbekistan, Ferghana city

Matmusayeva Mukhayyo²

2

A teacher of Preschool Education department, Preschool and Primary education faculty, Ferghana State University, Uzbekistan, Ferghana city

Qipchoqova Yorqinoy³

3

 A teacher of Preschool Education department, Preschool and Primary education faculty, Ferghana State University, Uzbekistan, Ferghana city

Mamurova Mushtari⁴

4

 A teacher of Preschool Education department, Preschool and Primary education faculty, Ferghana State University, Uzbekistan, Ferghana city

ABSTRACT

The article under discussion depicts the methods and techniques of speech development in children  of preschool age. The authors of the article consider that  teaching a child a native language, adults simultaneously contribute to the development of his/her intellect and higher emotions, prepare the basis for successful learning at school, for creative work. Speech features of children are related to the form of communication they have achieved. In addition, verbal communication in preschool age is carried out in different activities: in the game, work, household, educational activities and acts as one of the sides of each type.

KEY WORDS: children, preschool age, methods, techniques, speech, activity, tool, writing, speaking, listening, reading, enrich, expand, development, language.

DISCUSSION

 Speech is an integral part of the social being of people, a necessary condition of human society existence. It is estimated that about 70% of the time when a human being is awake, he dedicates to speaking, listening, reading, writing - four main types of speech activity.

 Speech is, on the one hand, a tool for expressing our ideas, thoughts and knowledge and, on the other hand, a means to enrich and expand them. To be perfect in all kinds and manifestations of speech means to possess the most powerful instrument of human mental development and, therefore, the culture of mankind.    Nothing affects the general development as negatively as language backwardness [1].

Speech in human life performs the following basic functions:

•       is a means of cognition, a necessary condition of human cognitive activity (thanks to speech a person acquires knowledge, assimilates and transmits it);

•       is a means of influencing the consciousness, developing a worldview, norms of behaviour, formation of tastes (i.e. speech is used to influence people's views and beliefs, incline them to actions, etc.);

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