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Criterion treshinostojkosti loaded and korrozionno damaged concrete at a flat stress condition

The decision of problems of a long warping of reinforced concrete constructions of the integral sectional view maintained in the conditions of impact of power loading and an excited environment besides check of durability of concrete as means to a honey agaric of a limiting resource for check of rigidness of sectional view by the moment of formation of the first crack (fig.

2.7).

Drawing 2.7 Characteristic stress conditions, types of cracks in ploskonaprjazhennyh reinforced-concrete elements () and schemes egpor the bent moments and shear forces on a considered lot of a girder ()

Advancement in time of front of neutralisation by an excited environment depending on permeability of concrete and varying depending on stress condition level at a tensioning, unlike compression, increases with growth of pressure in connection with density reduction. As according to the accepted hypothesis about developments of rust for the stretched working area of a design the general kinetic model of Century of M of Bondarenko [21,32] remains:

Where

In formulas (2.29) and (2.30) δ - the running depth of corrosion damage; - relative deficiency of the running value of depth of corrosion damage; to, t - the process beginning, running time of supervision; - empirical parametres of a kinetics of damages

Connected with weighting level, an excited environment, prochnostnymi characteristics of concrete and age of concrete to the corrosive attack beginning (and - parametre of speed of corrosion process, m - parametre of the kinetic characteristic of rust, δκ p - critical depth of corrosion damage at t = ∞).

According to the accepted hypothesis about invariancy of processes of rust for the compressed and stretched working area of a design empirical parametres of a kinetics of development of damages as a first approximation can be calculated with use of dependences [21J described for a stress condition compression (fig. 2.8 formulas (2.29) and (2.30) dependences of work [150] for a stress condition a tensioning (fig. 2.8).

For an unaxial tensioning of a trajectory of schedules (fig. 2.8)

It is possible to approximate sort functions:

At values of relative tensile loads in concrete where koeffitsientyvychisljajutsja with the help

Experimental values параметровαtсоответствующих

To fixed values T|t:

Drawing 2.8 - the Scheme of change of parametres δκ p, α, m at, and - an unaxial tensioning and - unaxial compression, depending on level and a sign on stress conditions η and η,

From the schedule (fig.

2.8) follows that excited environment impact on reinforced concrete construction concrete depends on character of a stress condition and accordingly quantitative values of relative efforts i//, in a considered working area. At a biaxial stress condition a tensioning-compression permeability of concrete will increase depending on value of stretching stresses, in comparison with permeability of concrete at unaxial compression. Accordingly, parametres δκ p, t, and characterising process of rust and intensity of distribution of an excited environment in ploskonaprjazhennyh the elements, defined under schedules (fig. 2.8) and to the equations (2.14,2.31), will be will be specified by carrying out of corresponding experimental researches.

As a rule, in the settlement scheme of final elements of the reinforced-concrete girder-wall located in working areas of formation of slope cracks, there is a biaxial stress condition - compression, with value compressing relative usilijv one direction and

Tensionings, with value of stretching relative efforts in other direction. Presence of main stretching stress N2увеличивает permeability of concrete, and accordingly depth on permeability of a concrete and reinforced-concrete element at a difficult stress condition a tensioning-compression as a first approximation can be considered the Account of influence of stretching stresses decrease in values of empirical parametres of a kinetics of development of damages r) ∖7>, t, and, received for a case of unaxial compression, it is proportional to values of stretching relative efforts η.

The decision (2.29) for kolmatatsionnoj rust reinforced-concrete konsgruktsii, being in conditions of gradual attenuation of corrosion process pridlja a case biaxial

Stress condition can be presented as

Also it is led to following special cases:

At пі = 1

Where parametryjavljajutsja empirically opredeljaeymymi

Characteristics korrodirujushchego concrete at a biaxial stress condition a tensioning - compression.

Change prochnostnyh and deformativnyh characteristics korrodirujushchego concrete at the accepted law of the description of nonequilibrium processes power and sredovogo and the accepted working hypotheses can be estimated resistance of concrete by means of chemical durability factors materialadlja the stretched working area of concrete:

Where R*b∣предел durabilities of concrete on a tensioning after impact of an excited environment during time t; R ∣, lпредел durabilities of concrete on a tensioning not exposed to excited environment impact.

According to V.M.Bondarenko's theory of a chemical durability of material Kxcявляется of [30] factor an indicator of a share of preservation of initial characteristics of a material and distribution of corrosion damages on height of sectional view of concrete designs.

As well as at construction of a strength condition loaded and korrozionno povrezhdennoju concrete at a stress condition «compression - compression» for a considered stress condition «a tensioning - compression» a total height of the stretched concrete a hook we will divide into following working areas:

- Working area of the greatest damages (or full destruction) located on a surface of an element (design),

- Transitive working area, where in process of removal from a contact surface

The effect of corrosion damage of concrete decreases, on depth

δκ pповреждения are zeroed,

- Working area of the intact concrete.

Forecasting of size of factor of a chemical durability is made with use of dependences resulted in GOST 25881-83 on test results. Thus required function Kxc (τ) preservations

52 initial mechanical properties of concrete at a tensioning from time it is described by logarithmic dependence:

Where factors and and b the equations (2.37 - 2.38) pay off on test results under following formulas

Chemical durability and time of trials in і th series of samples; p - number of series of samples.

Epjura ultimate strength distributions in concrete of the stretched working area of difficult intense element at impact of an excited environment and a stress condition "tensioning-compression" by results of the numerical analysis it is presented in the form of the schedule of change of durability on height of sectional view of an element (design) at single-sided and all-round impact of an excited environment (fig. 2.9).

Using the received values of durability for considered korrozionno the intense final elements damaged plainly on sectional view height it is possible to define criterion crack NOSTOJ bones of elements of the stretched working area.

So for a general case trehosnogo a stress condition the criterion treshchinostojkosti korrozionno damaged concrete in system of the main forces (N1, N2) enclosed at level of a median surface of a characteristic small element of the individual sizes can be presented similarly to a strength condition (2.4).

Drawing 2.9. - the Scheme of change of limiting durability loaded and korrozionno the damaged concrete on height considered ploskonaprjazhennoj structural section working areas: I schedule of change of durability at single-sided (from the stretched working area of sectional view) contact to an excited environment, 2 - the schedule of change of durability at all-round contact to an excited environment

At a flat stress condition (N3=0) greshchinostojkeost korrozionno damaged concrete can be defined a curved line of an elliptic type (fig. 2.10):

At unaxial compression and an unaxial tensioning accordingly, b - width of a considered girder.

Drawing 2. Criterion schedules crack a bone post korrozionno damaged concrete at a flat stress condition: I for the intact concrete (t=0); 2 - for korrozionno the damaged concrete without change of structure of concrete at a weighting; 3 - for korrozionno the damaged concrete taking into account change of structure of concrete at a weighting

In that specific case, for ploskonaprjazhennoj a reinforced-concrete girder - of a wall of integral sectional view criteria treshchinostojkosti for a working area of formation of normal cracks (fig. 2.11а) and working areas of formation of slope cracks (fig. 2.116) can be written down. Thus, in drawings 2.11 change schedules treshchinostojkosti loaded and korrozionno not damaged element (a curved line 1) and schedules treshchinostojkosti for the element loaded and damaged by rust (a curved line 2) are resulted.

Drawing 2.11 Criterion crack nostojkosti ploskonaprjazhyonnogo a concrete element at a stress condition a tensioning - compression before formation of characteristic cracks without 1 and taking into account 2 corrosion damages

2.2.4

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A source: Gubanova Maria Sergeevna. LONG WARPING PLOSKONAPRJAZHENNYH KORROZIONNO of the DAMAGED INTEGRAL REINFORCED CONCRETE CONSTRUCTIONS. The dissertation on competition of a scientific degree of a Cand.Tech.Sci. Kursk - 2018. 2018

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