CN103698224B - Fracture Toughness of Concrete Material method of testing without effect of weight - Google Patents

Abstract

The present invention relates to a kind of Fracture Toughness of Concrete Material method of testing without effect of weight, belong to physical measurement techniques field.This assay method comprises the following steps: 1) sets up test beam on two roller supports of existing three-point bending beam assay device, arranges load measuring equipment and strain gauge means on test beam；2) peak load F of applying is measured by load measuring equipment_max, measure initial cracking load F by strain gauge means_Q；3) toughness and initiation angle are calculated.This eliminates the member dead weight impact on test result without the Fracture Toughness of Concrete Material method of testing of effect of weight, thus be better able to accurately measure concrete crack initiation toughness, and concrete material (containing concrete for hydraulic structure) the crack initiation toughness meeting big seam height ratio or large scale test specimen measures demand.

Description

Fracture Toughness of Concrete Material method of testing without effect of weight

Technical field

The present invention relates to a kind of Fracture Toughness of Concrete Material method of testing without effect of weight, belong to In physical measurement techniques field.

Background technology

It is anti-that stability at Crack Propagation In Concrete Structures is evaluated with concrete structure Split, in Crack Control Design, be both needed to provide Fracture Toughness of Concrete parameter.Fracture Toughness of Concrete is joined Number includes initiation angle and toughness.

Measure the fracture toughness of concrete material, can refer to People's Republic of China's power industry mark The regulation of accurate " concrete for hydraulic structure destructive test code ", uses to be inserted into and splits traction therapy and three-point bending Beam method measures, and carries out the test of two kinds of methods simultaneously, when test result is variant, curved with 3 Curved beam method is as the criterion.

At present, the calculating of initiation angle and toughness all be use test gathered load- Dehisce displacement curve, load-strain curve, determine initial cracking load and unstability load.But Applicant finds through repetition test, with reference to the side in " concrete for hydraulic structure destructive test code " Method calculates initiation angle and toughness, and the small-size test piece being suitable for for it, result is also forbidden Really；The non-standard concrete component that its inapplicable big seam height ratio or large scale test specimen are required The mensuration of fracture toughness, result is more inaccurate, even can not obtain, thus can not meet Widely test requirements document.

Summary of the invention

The technical problem to be solved in the present invention is, not enough for prior art, proposes one more Accurately mensuration concrete material crack initiation toughness method of testing, and meet big seam height ratio or big chi The Fracture Toughness of Concrete Material method of testing without effect of weight of very little test specimen demand.

The present invention solves that the technical scheme that above-mentioned technical problem proposes is: a kind of without effect of weight Fracture Toughness of Concrete Material method of testing, comprise the following steps:

1) on two roller supports of existing three-point bending beam assay device, test beam is set up, Described test beam arranges load measuring equipment and strain gauge means；

Making the distance between two roller supports is the 1/2 of described test beam length, makes each rolling Dynamic bearing is the 1/4 of described test beam length to the distance of one end of its adjacent test beam；

2) with described test beam end face midpoint for the point of application to described test beam imposed load F, logical Cross capacity value survey device and measure peak load F of applying_max, measured by strain gauge means Split load F_Q；

3) toughness and initiation angle are calculated according to the following formula:

ToughnessCalculating:

$K_{\mathrm{IC}}^S=\frac{1.5F_{\max }\×{10}^{-3}\·S\·{a_c}^{1/2}}{{\mathrm{th}}^2}f\left(\mathrm{\α}\right)$

Wherein

$f\left(\mathrm{\α}\right)=\frac{1.99-\mathrm{\α}(1-\mathrm{\α})(2.15-3.93\mathrm{\α}+{2.7\mathrm{\α}}^2)}{(1+2\mathrm{\α}){(1-\mathrm{\α})}^{3/2}},\mathrm{\α}=\frac{a_c}{h}$

In formula, S is the span between test specimen two bearing, a_cFor effective crack length, t is that test specimen is thick Degree, h is height of specimen,

Wherein, a_cShould be calculated as follows

$a_c=\frac{2}{\mathrm{\π}}(h+h_0)\arctan {(\frac{{\mathrm{tEV}}_c}{{32.6F}_{\max }}-0.1135)}^{1/2}{-h}_0$

In formula, h₀For device Clip Gauge edge of a knife steel-sheet thickness, V_cFor critical of crack Mouth displacement；E is for calculating elastic modelling quantity.

Wherein, E is calculated as follows

$E=\frac{1}{{\mathrm{tc}}_i}[3.70+32.60{\tan }^2\left(\frac{\mathrm{\π}}{2}\frac{a_0+h_0}{h+h_0}\right)]$

In formula, a₀For incipient crack length；c_iFor test specimen initial V/F value, bent by test specimen F-V On the straightway of the ascent stage of line, F, V of any point calculate, c_i=V_i/F_i。

Initiation angleCalculating:

$K_{\mathrm{IC}}^Q=\frac{1.5F_Q\×{10}^{-3}\·S\·{a_0}^{1/2}}{{\mathrm{th}}^2}f\left(\mathrm{\α}\right)$

Wherein $f\left(\mathrm{\α}\right)=\frac{1.99-\mathrm{\α}(1-\mathrm{\α})(2.15-3.93\mathrm{\α}+{2.7\mathrm{\α}}^2)}{(1+2\mathrm{\α}){(1-\mathrm{\α})}^{3/2}},\mathrm{\α}=\frac{a_0}{h}.$

In " concrete for hydraulic structure destructive test code " (DL/T5332-2005), toughness Calculating needs consider that deadweight G(G=mg, m are the quality between test specimen bearing, use test specimen gross mass By S/L than conversion, g is acceleration of gravity).As it is shown in figure 1, whole three point test bent beam In central region (region one) part be in toughness calculating formula the gravity model considered Enclose, and two end regions (region two) outside bearing are not accounted for.According to structural mechanics Computational methods, bending moment diagram under action of gravity can be calculated and only consider a span centre regional extent Bending moment diagram (as shown in Figure 2).It can be seen that actual moment envelope 1 He in Fig. 2 Only the moment envelope 2 of consideration mid span area gravity is differentiated.

As shown in Figure 3 and Figure 4, according to deadweight to the contribution of moment of flexure at span centre, can will conduct oneself with dignity It is converted to load P at span centre_Z, therefore deduce that

$\begin{array}{c}{P}_Z=2({\∫}_0^{\frac{S}{2}}\mathrm{\ρgthdx}-{\∫}_0^W\mathrm{\ρgthdx})\\ =\frac{1}{2}\mathrm{\ρgth}(S-2W)\end{array}$

Calculating deadweight P used in toughness calculating formula is:

$\begin{array}{c}P=\frac{1}{2}\mathrm{mg}\\ =\frac{1}{2}\mathrm{\ρgthS}\end{array}$

Thus, according to two kinds of different deadweight translation methods to various sizes of three-point bending beam Deadweight is converted, as shown in table 1.

The deadweight conversion load of table 1 different size three-point bending beam

The deadweight conversion load of the i.e. different size three-point bending beam of upper table 1 is right with piece lengths change Compare catalog.According to 1 two kinds of methods of table (actual conversion loading method, formula conversion loading method) To the result of calculation of deadweight conversion load it can be seen that the most any method, its folding of conducting oneself with dignity Calculating load all to increase along with the increase of sample dimensions, the difference between both the most gradually increases Greatly, as it is shown in figure 5, when piece lengths increases to 2.2m, the conversion load of two kinds of methods Difference is 0.2347kN.Even if less actual conversion gravity laod also reaches 2.1366kN.This is for the initial cracking load in concrete fracture parameter, deadweight conversion load The max calculation toughness values obtained has reached more than the 30% of total value, causes former method of testing to obtain The toughness values arrived is inaccurate.

Table 2 three-point bending beam test specimen initial cracking load under different size

Table 2 be the seam height ratio that existing result of the test counts be 0.4, the outer distance of bearing be 0.1m Three-point bending beam test specimen initial cracking load under different size, with toughness calculating formula in from Heavily conversion load percentage ratio in total load head.From fig. 6 it can be seen that along with piece lengths, The i.e. increase of sample dimensions, the proportion in total load head is constantly increasing.And this group 3 is curved The seam height ratio only 0.4 of curved beam, if seam height is improved than further, by inference, deadweight Conversion load proportion in total load head also will further improve.Thus reasoning can further obtain Going out: when sample dimensions increases further, deadweight conversion load proportion in total load head will enter One step increases, and concrete material toughness test result error is bigger, causes drawing concrete Toughness so that the three-point bending beam method of testing in " concrete for hydraulic structure destructive test code " is not It is suitable for again.

It is found by the applicant that: carry out three-point bending beam according to " concrete for hydraulic structure destructive test code " During destructive test, test beam, by gravity large effect, will produce certain in an initial condition The crack opening displacement of the order of magnitude, causes result of calculation inaccurate.

Owing to the three-point bending beam in " concrete for hydraulic structure destructive test code " is affected by gravity, Crack opening displacement (CMOD, the crack mouth of some levels will be produced under preliminary examination state Opening displacement), this partial fracture dehisces displacement (CMOD) the most also Do not count, as shown in Figure 7: the initial CMOD 3 under the conditions of zero gravity and deadweight factor impact Under initial CMOD 4.

According to double K fracture theories, in concrete initiation angle the position of initial cracking load be load- Dehisce that displacement curve (F-V curve) has straight line to transfer the separation of curve to.At gravity load Under effect, compare condition according to mensuration to initial cracking load in table 2, existing size and seam height Under, concrete under the conditions of only gravity load and not up to initial cracking load.Due to crack initiation lotus Before load, the load of concrete-displacement slope of a curve of dehiscing is definite value, thus can release The displacement of dehiscing caused under gravity load effect, as shown in the table 3 of following table:

The displacement presumed value statistical table of dehiscing that table 3 deadweight causes

The displacement presumed value of dehiscing that deadweight listed in table 3 causes is in tradition three-point bending Fail under the conditions of beam to count V_c(CMOD) in, and V_cFor a_cIn an Important Parameters, V_cStandard Really property directly determines a_cAccuracy, therefore tradition three-point bending beam to V_cCollection be exist lack Fall into, V_cUnexpectedly it is affected by gravity and the V caused that ftractures that conducts oneself with dignity_cNot measuring, this is the most indirectly Result in a in concrete fracture parameter_cError.

Further, the fracture of the concrete for hydraulic structure required at big seam height ratio or large scale test specimen is tough During degree measures, deadweight usually produces destructive destruction to the prefabricated crack of three-point bending beam, adopts With method, a in " concrete for hydraulic structure destructive test code "_cMeasure inaccurate, even can not measure.

To sum up, the present invention uses technique scheme to provide the benefit that: 1) present invention is existing There is erection test beam on two roller supports of three-point bending beam assay device, make two to roll and prop up Distance between Zuo is the 1/2 of test beam length, makes each roller support to its adjacent test beam The distance of one end be the 1/4 of test beam length so that at the prefabricated crack of test beam Gravity bending moment is zero thus offsets effect of weight, in initiation angle and the computing formula of toughness In eliminate test beam self gravitation to initiation angle and the impact of toughness, compensate for " water Work concrete fracture test norm " in deadweight cause determining that crack initiation toughness value is inaccurate scarce Fall into；2) three-point bending beam in " concrete for hydraulic structure destructive test code ", is only applicable to little chi Very little, test result is inaccurate, and sample dimensions is severely restricted, because " concrete for hydraulic structure Destructive test code " in three-point bending beam affected by self gravitation, under original state produce Crack opening displacement, if sample dimensions is excessive, can cause test specimen because crack opening displacement is excessive Premature degradation before fracture test.And the gravity bending moment at the prefabricated crack of test beam of the present invention is Zero, displacement of dehiscing will not be produced under original state so that the chi tested of the test beam of the present invention Very little can be greatly improved, meet big seam height than or the requirement of large scale test specimen, meet widely The demand of engineering tough test；3) with 3 points in " concrete for hydraulic structure destructive test code " Bent beam is compared, the test beam fracture of the present invention dehisce the metering method of displacement the most accurate and Close to practical situation；4) present invention is in test loading procedure, truly achieves lotus Load is started from scratch loading.

The improvement of technique scheme is: described existing three-point bending beam assay device is " water conservancy project Concrete fracture test norm " in three-point bending beam assay device.

The improvement of technique scheme is: the described 1st) be additionally provided with following steps before step:

4) base plate, front side board, back side panel, left plate and right plate are assembled into test beam form Tool；

5) first prefabricated crack Interal fixation is hit exactly inside the front side board of described test beam mould Place, then releasing agent is coated in steel plate two sides, prefabricated crack, last casting concrete, and mixed In 3h, prefabricated crack steel plate is extracted after the initial set of solidifying soil, thus form one in test beam bottom surface Prefabricated crack.

The improvement of technique scheme is: described load measuring equipment is load transducer, described Strain gauge means is the resistance strain gage being pasted onto prefabricated crack tip both sides.

The present invention uses technique scheme to provide the benefit that: use load transducer to determine Splitting load, the test beam of the present invention can improve its accuracy judged and success rate.

Accompanying drawing explanation

The invention will be further described below in conjunction with the accompanying drawings:

Fig. 1 is that in " concrete for hydraulic structure destructive test code ", the gravity region of three-point bending beam is drawn Component

Fig. 2 is the bending moment envelope diagram of Fig. 1

Fig. 3 is the three-point bending beam schematic diagram in " concrete for hydraulic structure destructive test code "

Fig. 4 is the integration schematic diagram of Fig. 3

Fig. 5 is the conversion load pair under the different size of " concrete for hydraulic structure destructive test code " Than figure

Fig. 6 is gravity folding under the different sample dimensions in " concrete for hydraulic structure destructive test code " Calculate load percentage ratio in total load head

Fig. 7 is the initial CMOD under different conditions

Fig. 8 is the Fracture Toughness of Concrete Material test side without effect of weight of the embodiment of the present invention The test beam schematic diagram of method

Fig. 9 is the left view of Fig. 8

Figure 10 is the test beam gravity bending moment figure of Fig. 8

Figure 11 is the strain gauge means layout drawing in Fig. 8

Figure 12 is the strain-load curve figure of Figure 11

Detailed description of the invention

Embodiment

The Fracture Toughness of Concrete Material method of testing without effect of weight of the present embodiment, as Fig. 8, Shown in Fig. 9 and Figure 10, comprise the following steps:

1) on two roller supports of existing three-point bending beam assay device, test beam is set up, Test beam arranges load measuring equipment and strain gauge means；

Making the distance between two roller supports is the 1/2 of test beam length, makes each rolling prop up Seat is the 1/4 of described test beam length to the distance of one end of its adjacent test beam；

Existing three-point bending beam assay device sees in " concrete for hydraulic structure destructive test code " Assay device in 6.2.Load measuring equipment is located on the end face of test beam, uses load to pass Sensor, precision is not less than 1.The strain gauge means of the present embodiment is to be pasted onto prefabricated crack The resistance strain gage of most advanced and sophisticated both sides.

2) with test beam end face midpoint for the point of application to test beam imposed load F, capacity value is passed through Survey device and measure peak load F of applying_max, measure initial cracking load F by strain gauge means_Q, Initial cracking load F_Q, i.e. the ascent stage of test specimen F-V curve is changed into turning of curved section from straightway Load corresponding to break；

Initial cracking load F_QDetermination use recent years " concrete for hydraulic structure destructive test advised carrying out Journey " strain gauge means that uses in concrete component crack initiation toughness test determination, passes through Following methods determines: as shown in figure 11, initial cracking load F_QDetermination be prefabricated by being pasted onto The resistance strain gage 5 of crack tip both sides change curve in loading procedure determines. Its load-strain curve as shown in figure 12, along with the increase of load, prefabricated crack tip both sides The strain value of resistance strain gage 5 be gradually increased, and be substantially in the form of linear change, belong to that draw should Become；At crack tip, concrete ftractures owing to tension produces stress concentration, concrete release energy Amount, is reflected as stretching strain on curve and is not further added by；Load continues to increase, due to seam end coagulation The cracking of soil, the tension unloading of both sides, tip, incipient crack, stretching strain reduces, even occurs Compressive strain, therefore load-strain curve starts to transfer, corresponding to this turning point 6 Payload values be the initial cracking load F of test specimen_Q。

3) toughness and initiation angle are calculated according to the following formula:

ToughnessCalculating:

$K_{\mathrm{IC}}^S=\frac{1.5F_{\max }\×{10}^{-3}\·S\·{a_c}^{1/2}}{{\mathrm{th}}^2}f\left(\mathrm{\α}\right)$

Wherein

$f\left(\mathrm{\α}\right)=\frac{1.99-\mathrm{\α}(1-\mathrm{\α})(2.15-3.93\mathrm{\α}+{2.7\mathrm{\α}}^2)}{(1+2\mathrm{\α}){(1-\mathrm{\α})}^{3/2}},\mathrm{\α}=\frac{a_c}{h}$

In formula,For toughness, unit is MPa m^1/2；

F_maxFor peak load, unit is kN；

S is the span between test specimen two bearing, and unit is m；

a_cFor effective crack length, unit is m；

T is specimen thickness, and unit is m；

H is height of specimen, and unit is m.

Wherein, a_cShould be calculated as follows

$a_c=\frac{2}{\mathrm{\π}}(h+h_0)\arctan {(\frac{{\mathrm{tEV}}_c}{{32.6F}_{\max }}-0.1135)}^{1/2}{-h}_0$

In formula, h₀For device Clip Gauge edge of a knife steel-sheet thickness, unit is m；V_cFor The critical displacement of dehiscing in crack；E is for calculating elastic modelling quantity.

Wherein, E is calculated as follows

$E=\frac{1}{{\mathrm{tc}}_i}[3.70+32.60{\tan }^2\left(\frac{\mathrm{\π}}{2}\frac{a_0+h_0}{h+h_0}\right)]$

In formula, a₀For incipient crack length；c_iFor test specimen initial V/F value, bent by test specimen F-V On the straightway of the ascent stage of line, F, V of any point calculate, c_i=V_i/F_i。

Initiation angleCalculating:

$K_{\mathrm{IC}}^Q=\frac{1.5F_Q\×{10}^{-3}\·S\·{a_0}^{1/2}}{{\mathrm{th}}^2}f\left(\mathrm{\α}\right)$

Wherein $f\left(\mathrm{\α}\right)=\frac{1.99-\mathrm{\α}(1-\mathrm{\α})(2.15-3.93\mathrm{\α}+{2.7\mathrm{\α}}^2)}{(1+2\mathrm{\α}){(1-\mathrm{\α})}^{3/2}},\mathrm{\α}=\frac{a_0}{h}.$

F_QFor initial cracking load, unit is kN, i.e. from straight line in the ascent stage of test specimen F-V curve Section is changed into the load (as shown in figure 12) corresponding to turning point of curved section.

The existing three-point bending beam assay device of the present embodiment is that " concrete for hydraulic structure destructive test is advised Journey " in three-point bending beam assay device.

The 1st of the present embodiment) it is additionally provided with following steps before step:

4) base plate, front side board, back side panel, left plate and right plate are assembled into test beam form Tool, the test beam mould after assembling must not have deformation and spillage phenomenon；The requirement of test beam mould See annex E in " concrete for hydraulic structure destructive test code "；

5) first prefabricated crack Interal fixation is hit exactly inside the front side board of described test beam mould Place, then releasing agent is coated in steel plate two sides, prefabricated crack, last casting concrete, and mixed In 3h, prefabricated crack steel plate is extracted after the initial set of solidifying soil, thus form one in test beam bottom surface Prefabricated crack.Prefabricated crack steel plate requires and placement location sees " concrete for hydraulic structure destructive test Code " in Appendix B.

The present invention is not limited to above-described embodiment.The technical side that all employing equivalents are formed Case, all falls within the protection domain of application claims.

Claims (4)

1. the Fracture Toughness of Concrete Material method of testing without effect of weight, it is characterised in that comprise the following steps:

1) on two roller supports of existing three-point bending beam assay device, set up test beam, described test beam arranges load measuring equipment and strain gauge means；

Making the distance between two roller supports is the 1/2 of described test beam length, and making each roller support is the 1/4 of described test beam length to the distance of one end of its adjacent test beam；

2) with described test beam end face midpoint for the point of application to described test beam imposed load F, peak load F of applying is measured by load measuring equipment_max, measure initial cracking load F by strain gauge means_Q；

3) toughness and initiation angle are calculated according to the following formula:

ToughnessCalculating:

Wherein

In formula, S is the span between test beam two bearing, a_cFor effective crack length, t is test beam thickness, and h is test beam height, and α is the high ratio of seam,

Wherein, a_cShould be calculated as follows

In formula, h₀For device Clip Gauge edge of a knife steel-sheet thickness, V_cFor crack mouth critical crack opening displacement；E is calculating elastic modelling quantity,

Wherein, E is calculated as follows

In formula, a₀For incipient crack length；c_iFor test beam initial V/F value, V is crack mouth opening displacement, F, V of any point on the straightway of the ascent stage of test beam F-V curve calculate, c_i=V_i/F_i,

Initiation angleCalculating:

Wherein

2. as claimed in claim 1 without the Fracture Toughness of Concrete Material method of testing of effect of weight, it is characterised in that: described existing three-point bending beam assay device is the three-point bending beam assay device in " concrete for hydraulic structure destructive test code ".

3. as claimed in claim 1 without the Fracture Toughness of Concrete Material method of testing of effect of weight, it is characterised in that the described 1st) it is additionally provided with following steps before step:

4) base plate, front side board, back side panel, left plate and right plate are assembled into test beam mould；

5) first by prefabricated crack Interal fixation inside the front side board of described test beam mould at center, releasing agent is coated again in steel plate two sides, prefabricated crack, last casting concrete, and extracted by prefabricated crack steel plate in 3 hours after concrete initial set, thus form a prefabricated crack in test beam bottom surface.

4. as claimed in claim 3 without the Fracture Toughness of Concrete Material method of testing of effect of weight, it is characterised in that: described load measuring equipment is load transducer, and described strain gauge means is the resistance strain gage being pasted onto prefabricated crack tip both sides.