CN102359931A - Concrete fatigue load and environmental coupling experiment apparatus - Google Patents

Abstract

The present invention discloses a concrete fatigue load and environmental coupling experiment apparatus. The apparatus comprises a first fulcrum, a second fulcrum, a third fulcrum and a fourth fulcrum, wherein the first fulcrum and the second fulcrum are arranged on the upper part of a concrete specimen, the third fulcrum and the fourth fulcrum are arranged on the lower part of the concrete specimen. The distance between the first fulcrum and the second fulcrum is more than the distance between the third fulcrum and the fourth fulcrum. The apparatus further comprises a corrosion resistance container, wherein the corrosion resistance container is arranged between the first fulcrum arranged on the upper part of the concrete specimen and the second fulcrum arranged on the upper part of the concrete specimen. With the present invention, the generated fatigue failure of the concrete structure under the comprehensive effect of the environmental factors and the load can be accurately detected.

Description

Concrete fatigue load and environment coupling experiment device

Technical field

The present invention relates to a kind of concrete fatigue load and environment coupling experiment device.

Background technology

Many xoncrete structures; To bear the traffic loading that the cycle repeats in the process under arms like the road surface of airfield runway, street, highway and bridge, crane girder, railroad sleeper etc., and some new structures such as skyscraper, gravity offshore platform, nuclear power plant concrete protective seam etc. also will bear the effect of earthquake load, wind load, wave load etc.Except the effect of these imposed loads; The effect of environmental factor (like villaumite, sulphate attack, variation of temperature, freeze thawing circulation etc.) all can accelerated material or inside configuration damage and (can make reinforcing bar generation corrosion in the middle of infiltrating concrete like villaumite; The bearing capacity of reinforcing bar descends on the one hand; The corrosion of reinforcing bar is expanded on the other hand, and when pulling force that bulging force can bear greater than concrete, concrete will destroy).Under these reloading effects, repeated stress and strain will be born in each position of structure (or structural elements), so that fatigue failure take place being lower than under the static load intensity.Just simple superposition behind environment and the load alternating action is handled in the research formerly, with actual condition relatively large difference is arranged like this, be difficult to accurately detect the situation that fatigue failure takes place xoncrete structure under environmental factor and load coupling.

Summary of the invention

Goal of the invention: the problem and shortage to above-mentioned existing existence the purpose of this invention is to provide a kind of coupling experiment device that can comparatively accurately assess the fatigue failure of xoncrete structure under environmental factor and load coupling.

Technical scheme: for realizing the foregoing invention purpose; The technical scheme that the present invention adopts is a kind of concrete fatigue load and environment coupling experiment device; Comprise first fulcrum and second fulcrum that are located at concrete sample (hereinafter to be referred as " test specimen ") top; Be located at the 3rd fulcrum and the 4th fulcrum of concrete sample bottom; The spacing of said first fulcrum and second fulcrum is greater than the spacing of the 3rd fulcrum and the 4th fulcrum, also comprises first fulcrum that is located at concrete sample top and the corrosion-resistant container between second fulcrum.

Said corrosion-resistant container can be non-covered container.The bottom of said corrosion-resistant container can have a hole.Said corrosion-resistant container and concrete sample can through gluing connect fixing.Said glue can be silica gel.The thickness of said silica gel can be 1mm to 2mm.

The surface of said concrete sample can be provided with the water conservation layer except the part that contacts with said corrosion-resistant container.

Beneficial effect: the present invention is applicable to general fatigue test of materials machine (like American MTS 810 series metal and nonmetallic materials fatigue test system); Way breaks traditions; The spacing between lower fulcrum is gone up in adjustment respectively; Test specimen is bent in the four-point bending test middle and upper part, corrosive liquid is placed advancing side as environmental factor, come simulated environment and load double factor concrete destruction mechanism.

Description of drawings

Fig. 1 is concrete fatigue load and environment coupling experiment apparatus structure synoptic diagram;

Fig. 2 is three stage synoptic diagram of Rust of Rebar in Concrete;

Fig. 3 is fatigue load-displacement relation curve map;

Fig. 4 is that chlorine ion concentration is with stress level and change in depth trend map.

Embodiment

Below in conjunction with accompanying drawing and instantiation; Further illustrate the present invention; Should understand these instances only be used to the present invention is described and be not used in the restriction scope of the present invention; After having read the present invention, those skilled in the art all fall within the application's accompanying claims institute restricted portion to the modification of the various equivalent form of values of the present invention.

As shown in Figure 1, utilizing fatigue tester (like American MTS 810) is platform, at first adjusts test parameters, and (S is defined as: the stress that cyclic load produces and the ratio S=σ/f of static load intensity are divided into S in each cyclic load for major parameter such as stress level S _MaxAnd S _Min) be generally 0.45～0.9 between, cycle stress ratio R (R=S _Min/ S _Max) be 0.1 (the border situation is decided factually), adopt sinusoidal wave the loading, it is general that stress level＞0.75 o'clock frequency is 2～3Hz; And frequency is 10Hz when stress level≤0.75.Next confirm the distance of four fulcrums in the four-point bending experiment according to the size of test specimen, comparatively crucial is that the distance of bottom two fulcrums is turned down, and the distance of top two fulcrums is bigger, and each fulcrum connects the fatigue tester (not shown) respectively.The unit of sample dimensions is " mm " among Fig. 1.

Corrosion-resistant container places test specimen top.According to sample dimensions process mating corrosion-resistant container, that container is characterized as is transparent, a circular hole is arranged at uncovered and bottom; Container is placed test specimen top, and with silica gel NQ-704 together, notice that the thickness of silica gel is wanted appropriateness container and test specimen gluing, desirable 1mm to 2mm, this example is 1mm, avoids the influence of glue-line to the test specimen mechanical property as far as possible; Add selected corrosive liquid, begin the experiment, during experiment with corrosive liquid (like NaCl, Na ₂SO ₄Solution etc., this instance are selected NaCl solution) circular hole of bottom of device seals, and avoids solvent to run off, and influence solution concentration, and certain hour is changed corrosive liquid and is stirred at interval, tests in the process that solution concentration does not change and evenly to keep confirmation.

This device main research fatigue load and environmental factor coupling mechanism are to the corrosive attack of structural concrete.Discover; The principal element that causes structural concrete destruction is except that different loads; The corrosion of reinforcing bar is expanded becomes the another leading factor of inefficacy, is after chlorion arrives rebar surface and cause the main cause that steel bar corrosion expands, and its passivating film is destroyed cause steel bar corrosion; As shown in Figure 2, chlorion is grown (T from the time that concrete surface is diffused into rebar surface ₁), so it is comparatively meaningful to study this section.

The rate of diffusion of chlorion is mainly according to Fick (Fick) second law, and is specific as follows:

$\frac{\&PartialD;c}{\&PartialD;t}=D_d\frac{{\&PartialD;\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="HDA0000092358420000022.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}{{\&PartialD;x}^2}$

In the formula, t, time;

X, according to inside concrete according to its surperficial distance;

D _d, chloride diffusion coefficient;

C, chlorine ion concentration.

Starting condition is:

T=0, x＞0 o'clock, C=C ₀

X=0, t＞0 o'clock, C=C _s

Therefore, can solve chlorion one dimension diffusion theory model in concrete does

$C=C_0+(C_S-C_0)\&CenterDot;(1-\mathrm{erf}\frac{x}{2\sqrt{\mathrm{Dt}}})$

In the formula, C ₀, the initial chlorine ion concentration in the concrete;

Cs, the chlorine ion concentration of concrete exposed surface it is generally acknowledged suitable with the chlorine ion concentration of exposed environments medium.

Erf, error function $\mathrm{Erfu}={\&Integral;}_0^u{e}^{-{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000092358420000022.png"\; state="\{\{state\}\}">t</figure-callout>}}^2}\mathrm{Dt}$

Experiment embodiment: under the different stress levels, fatigue load and chlorion diffusion coupling rule, like Fig. 3 and shown in Figure 4:

As can be seen from Figure 3 in fatigue load and chlorion diffusion couple cooperation time spent; The waveform of load still is sinusoidal wave form; Explanation is drawn concrete sample and is changed top into and drawn by traditional lower, the form of load does not squint, and can mate preferably with the chlorion diffusion process.

Can find that by Fig. 4 under every kind of stress level, chlorine ion concentration reduces with the increase of the degree of depth; Along with the raising of answering level, chlorion at the content of each degree of depth in obvious increase, particularly between 0-15mm.This explanation chlorion is under the coupling of fatigue load, and can diffuse to the 30mm place within a short period of time rapidly, and chlorion diffusion process and fatigue load can be coupled preferably.

By the experiment show of Fig. 3 and Fig. 4 the practicality of this coupling device, for later on better scientific research strong assistant is provided.

This device has been realized truly getting off to study concrete permanance in environment (villaumite, sulfate etc.) and load coupling.On the one hand; Concrete is continuing under the load action, and damage is accumulation constantly, and surrounding medium also corrodes concrete synchronously on the other hand; The concrete damage deterioration of research more meets actual its duty status under such device, and particularly important to durability evaluating and life prediction.The invention of this device has overcome the sort of in the past non-synergistic effect mechanism that loads behind back environmental attack or the first environmental attack that loads earlier.

Claims (7)

1. concrete fatigue load and environment coupling experiment device; Comprise first fulcrum and second fulcrum that are located at concrete sample top; Be located at the 3rd fulcrum and the 4th fulcrum of concrete sample bottom; It is characterized in that: the spacing of said first fulcrum and second fulcrum is greater than the spacing of the 3rd fulcrum and the 4th fulcrum, also comprises first fulcrum that is located at concrete sample top and the corrosion-resistant container between second fulcrum.

2. according to said concrete fatigue load of claim 1 and environment coupling experiment device, it is characterized in that: said corrosion-resistant container is a non-covered container.

3. according to said concrete fatigue load of claim 1 and environment coupling experiment device, it is characterized in that: the bottom of said corrosion-resistant container has a hole.

4. according to said concrete fatigue load of claim 1 and environment coupling experiment device, it is characterized in that: said corrosion-resistant container and concrete sample through gluing connect fixing.

5. according to said concrete fatigue load of claim 4 and environment coupling experiment device, it is characterized in that: said glue is silica gel.

6. according to said concrete fatigue load of claim 5 and environment coupling experiment device, it is characterized in that: the thickness of said silica gel is 1mm to 2mm.

7. according to said concrete fatigue load of claim 1 and environment coupling experiment device, it is characterized in that: the surface of said concrete sample is provided with the water conservation layer except the part that contacts with said corrosion-resistant container.

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