CN103837413B - Concrete tensile creep testing device and concrete shrinkage stress creep testing method - Google PatentsConcrete tensile creep testing device and concrete shrinkage stress creep testing method Download PDF
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- CN103837413B CN103837413B CN201410116179.7A CN201410116179A CN103837413B CN 103837413 B CN103837413 B CN 103837413B CN 201410116179 A CN201410116179 A CN 201410116179A CN 103837413 B CN103837413 B CN 103837413B
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The invention discloses a concrete tensile creep testing device which comprises a bracket, an upper perforated-articulated chuck, a lower perforated-articulated chuck, a perforating test piece, a deformation gauge and a balance weight load, wherein the two perforated-articulated chucks which are connected with the perforating test piece are respectively hung on the bracket and are connected with the balance weight load, so that the testing device can be formed. A concrete shrinkage stress creep testing method adopts a standard creep chamber and natural environmental condition, is restrained by complete or non-complete constraint stiffness, adopts loading ways of 'step loading' and 'follow-up loading', is carried out under the shrinkage threshold value and fixed age period loading control condition, and can be used for testing the concrete shrinkage stress creep. After the testing device and the testing method are adopted, the problems of connection between the concrete test piece and the chucks, physical alignment and load loss can be solved, and the test operability can be improved; furthermore, creep and strain can be tested gradually, so that more creep behaviors and performance problems can be researched; particularly, the concrete shrinkage stress creep test can be realized in the natural environment.
The invention discloses a kind of Analysis of Concrete Tensile creep test device and concrete shrinkage stress creep test method；Special Do not refer to a kind of Analysis of Concrete Tensile creep test device and concrete shrinkage stress creep test method；Belong to civil engineering Middle concrete test technical field, particularly Analysis of Concrete Tensile creep test technology.
In structure, concrete often ftractures because shrinking and constrain.The pass crept as structural concrete resisted shrinkage cracking Key problem, this research in recent years is also gone beyond deeply, to " Analysis of Concrete Tensile Creep Characteristics and pressurized the creeping property studying relative maturity Can be otherwise varied " viewpoint be industry acceptance, the work of correlational study also gets along with, and concrete creep row under shrinkage stress For having load and the mechanical characteristics of time-varying of creeping, and the particularity such as concrete hardening, carry out what concrete shrinkage stress was crept Research and test are significant to xoncrete structure cracking resistance.Under shrinkage stress, Analysis of Concrete Tensile creep test is this research Basis, test method and device also will play a significant role in the Construction control of structural concrete cracking resistance.
Analysis of Concrete Tensile creep test device and the difference of test method, determine the model of gained Creep Characteristics and relevant parameter Enclose and have differences, or the difference of operation difficulty or ease and precision.Carrying out the test method that Analysis of Concrete Tensile creeps at present mainly has:
(1) steelframe-spring force method (see accompanying drawing 1), this Fa Shi China working standard dl/t5150-2001 and sl352- The Analysis of Concrete Tensile creep test method that 2006 " concrete for hydraulic structure testing regulationss " are adopted.Yang Yang [Yang Yang, Xu Sifa, Ye De Gorgeous, etc. Early-age high strength concrete tensile creep characteristic [j]. silicate journal, 2009,37 (7): 1124-1129] etc. adopt Such method carries out the research crept under concrete shrinkage stress, and on the basis of lot of experiments, the Fitting Calculation obtains concrete The characteristic parameter of Creep Characteristics under shrinkage stress, but lack and directly obtain concrete shrinkage stress and creep the result of the test of behavior； Another pulling force is applied by spring because of this test method, this allows for after concrete sample creeps and occur, causing camber of spring value to subtract Little, and change loading stress level；The corresponding deformation (counter-force reduces corresponding steel frame deformation and reduces) producing of steelframe simultaneously also can Impact result.If carrying out creeping (hereinafter referred to as shrinkage stress is crept) of contraction stretching stress under structural constraint, for applying time-varying The shrinkage stress of feature, and reduce the impact to loading stress level for the spring that causes of concrete creep, need constantly to adjust bullet Spring state (readjust assay device and reach setting force value, particularly the latter because need fine setting difficulty bigger), be guarantee test knot Really, work difficulty and amount are all larger.Application publication number cn103149100a " a kind of concrete axle center tensile creep tester and examination Proved recipe method " also belongs to the type, and distinguishing feature is that changing deformation surveys read mode, obtains result.
(2) tstm(temperature-stress testing machine) method, also known as cracking frame test method or axle To leash law (see accompanying drawing 2), German Mo Nihei technology university r.springenschmid proposes test method within 1969, mainly enters The reconstruction the method such as row agent on crack resistance of concrete shrinkage cracking Journal of Sex Research, researcher proposition motor hereafter and sensor obtains mixed Solidifying soil shrinkage stress, domestic have Research Literature [hooton r d. high performance concrete be under constraints for Ma Xinwei, button long core Tension Creep Characteristics [j]. Wuhan University of Technology's journal, 2006,28 (2): 26-29.] adopt the method, this experimental study institute Obtaining concrete creep is concrete creep under shrinkage stress, and this is also development shrinkage stress creep tests few in number at present One of work.Due to this assay device, staff cultivation state is in using step motor control test specimen, load transducer obtains The axial shrinkage stress arriving, by the modulus of elasticity of concrete that separately records and contraction distortion (ilities data), calculates and obtains Shrinkage stress is crept；It is limited to control deformation device, computational methods and the test of ilities number, this research does not propose other constraints Test method in the case of degree；Using constraint steelframe, be not suitable for natural environment (under temperature change) because in assay device, also no phase The method of testing answered；In addition assay device is expensive, limits the method and commonly uses at home；Besides the method device therefor is held high Expensive, and domestic this equipment is once only capable of surveying a test specimen, data volume is limited.Application publication number cn103149094a " early age Measuring method and device that Analysis of Concrete Tensile is crept " also belongs to the type, and its distinguishing feature is to propose deflection≤1 of frame structure μm, self-locking punching jack loads, differential displacement sensor and anti-attrition device etc. require.
(3) lever-counterweight method (see accompanying drawing 3), twentieth century end of the eighties, " the concrete mechanicses that Jiang Futian writes at it Performance and mensure " [Jiang Futian. mechanical performance of concrete and mensure [m]. Beijing: China Railway Press, 1989.] just describe The method, loading counterweight, in addition to available water tank, also can adopt counterweight.The latter relatively, water tank loading is in terms of the fine setting of payload values More advantage, simply metering add water produced load when, the impact being considered as the factors such as temperature and operation can ensure enough Precision.The method can be loaded according to test requirements document, but have no to carry out using the method and creep for shrinkage stress and grind The report studied carefully.In addition, this device considers, because of need, the stability problem that center of gravity causes, the cost of manufacture of lever framework is also higher.Lee Xing Gui [Li Xinggui. under high tensile stress effect, concrete creeps and Creep test [j]. Hohai University's journal, 1996,24(4): 58-64] space that former method reduces test is improved using double lever method, so that the steadily of centre of gravity problem of whole test stand has been changed Kind, its cost of manufacture is still higher.
(4) steelframe-liquid (gas) platen press (see accompanying drawing 4), the method is also a kind of tensile creep test dress envisioned early stage Put, steelframe passes through oil pressure (air pressure-nitrogen) jack and exerts a force, carry out tensile creep test, such as the hydraulic pressure of y.akatsuka Formula tensile creep machine promotes piston come loading by oil pressure.Because of the adjustable feature of hydraulic pressure, the method also can be shunk in theory Stress creep test, but this kind of method affects practical application due to the long-term voltage stabilizing problem of hydraulic pressure (cylinder), then have the method to adopt Steelframe, exists and method (one) identical load shakiness problem.
(5) other, simple bending-pulling method with beams of concrete be subject to pure bending load when, beams of concrete neutral axis lower portion in Tension stress state, carries out tensile creep research, and the method is crept for prestressed concrete beam and studied significant, west Zhang Haobo of peace Polytechnics etc. obtains the significant result of its research field using the method, but whole beams of concrete section Distribution tension and compression stress, there is tension Gradient distribution in advancing side, this result has limitation to understanding concrete pure extension performance； Concrete is made hollow cylinder (cylinder) test specimen by oil pressure-interior plavini, and sealing, connected pipes, by adding pressure fluid The pressure that body (hydraulic pressure, gas-air pressure) produces so that concrete cylinder expands tension, creep by research Analysis of Concrete Tensile, A.d.ross has carried out the method research, and in same concrete, tension has gradient, in addition test specimen sealing and permeability resistance pair The success rate impact of test is very big, and the application of this method is few.
In sum, axial constraint method, lever-counterweight method and steelframe-liquid (gas) platen press can carry out shrinkage stress and creep examination Test, wherein axial constraint method carried out shrinkage stress creep test research under staff cultivation, but in experimental condition (research range), inspection Survey parameter, device stability and equipment cost and there is the part that complies with one's wishes not to the utmost it is difficult to carry out the test of natural environment.
In addition to overall architecture, the shape of concrete sample and chuck (joint) affect the assay device that Analysis of Concrete Tensile is crept Concrete stress, internal stress distribution, determine creep test testing result (accurately, precision), success of the test and operation difficulty or ease, Therefore the shape of concrete sample and chuck are also the key of assay device.
Tensile creep test need to apply tensile load by chuck to concrete sample, and chuck and Specimen Shape should be protected first Card centering, makes the load of applying produce pure tension in concrete, has both considered geometry centering, it is also contemplated that during concrete formation Because sedimentation causes the aggregate of test specimen and Density Distribution along the difference of die trial depth (or claiming specimen thickness), keep physics centering, extremely Few centering as far as possible in the gauge length that test survey is read, it is to avoid the impact to result of the test for the concrete eccentric tension；Next to that chuck Good usability, the connection between chuck and test specimen should be good, stable, and chuck such as does not damage at the adverse effect to test specimen, separately Outer chuck should be suitable for the requirement of wider research contents of creeping, and such as carry out concrete early stage creep test, can install after form removal The aspects such as test require.
Specimen Shape: conventional tensile test specimen shape has prism, reamed end prism (dog bone-shaped), cylinder and end Head expands cylinder, and because of chuck bad applying pulling force, table and the strain gauge (piece) of test deformation is installed in inconvenience to latter two, seldom adopts With；First two use more, this patent also adopt this two kinds of shape test specimens.
Test chuck (also known as joint): (one) clamp type (see accompanying drawing 5-a), golmerman and shulnan(1928) adopt It is threaded the steel bar shape chuck clamping test piece end of groove, using frictional resistance, test specimen is stretched；Research is had to expand using termination Big test specimen is more conducive to the damage increasing frictional resistance and reducing test specimen termination.This form chuck is to itself machining accuracy and coagulation The dimension precision requirement of native test specimen termination is higher, to avoid the impact to result of the test for the geometric eccentricity of chuck.(2) pre-buried anchor Stationary (see accompanying drawing 5-b), by pre-buried anchor bar, or additional gluing process, by steel plate and concrete binding, transmits stretching lotus Carry, the researcher of Australia-Univ Monash carries out the tension test of fiber concrete using the method, but this kind of chuck is originally Body is limited to eccentric Accommodation, need in addition increase universal joint etc. and improve the eccentric impact of adjustment.(3) adhesive type is (see accompanying drawing 5-c), sheet metal is connected to fetch with test piece end using Strong Adhesive such as epoxy resin etc. and avoids test specimen by w.zheng et al. End affects to keep the effect (title end effect) of pure tensile stress state in the range of specimen equidistance line marking because stress is complicated, gluing measure Employing, also two or more test specimens can be bondd, carry out creep test.But the test that present patent application person is carried out shows, state The adhesive of interior market supply, hardening time is longer, and cohesive force often can not meet tensile creep design load requirement again, makes Become practical operation difficult, especially need to carry out more aobvious prominent during concrete early stage creep test.(4) embedded (see accompanying drawing 5-d), This cartridge form is matched with the shape expanding termination, expands the chuck (embedded chuck) of termination to test specimen using embedded test specimen The transition face of expansion termination and test benchmark intersegmental (deformation gauge length section) (transition face typically adopts arcwall face, also has using tiltedly In face-top view be straight line) squeezing action so that test specimen test benchmark section produce tension, carry out tensile creep test, should Form chuck is higher to the dimension precision requirement of itself machining accuracy and concrete sample termination, nonetheless avoids bias The effect of stress is also limited, and axial constraint method adopts this form chuck, because concrete sample is directly poured into a mould, reduces some processing The requirement of precision.
Above-mentioned each chuck typically should pass through half ball pivot again or universal joint is connected with applying lotus device (pull bar etc.), transmits load.
Content of the invention:
The present invention overcomes the deficiency of prior art, proposes that a kind of apparatus structure is simple, low cost, easy to operate, mechanics close Be simple, clear, tensile load is constant, can carry out relatively wider range the assay device of shrinkage stress Creep Characteristics research and Method.
The Analysis of Concrete Tensile creep test device of the present invention, comprising: support, upper perforation-radial type chuck, lower perforation-hinge Connect formula chuck, perforation test specimen, deformation gauge and counterweight load (see Figure of description 6).The Analysis of Concrete Tensile creep test of the present invention Device is also referred to as " suspension-counter weight type Analysis of Concrete Tensile creep test device ".
Described Analysis of Concrete Tensile creep test device is that described perforation test specimen two ends are pressed from both sides with upper and lower perforation-radial type respectively Head connection, and described deformation gauge, the described two perforation-radial types being coupled with perforation test specimen are set in described perforation test specimen both sides Chuck, hangs on described support respectively, and couples with described counterweight load, forms bulk test device.
Described support is used for hanging perforation-radial type chuck, perforation test specimen and counterweight load, and available steel pipe is built, and also may be used Build by indoor wall, or using existing steelframe etc., setting suspension hook (about 2.5 tons of the load of single test)；
Described perforation-radial type chuck is by steel housing, half ball-joint load connecting rod and hinged use steel pole axle group of boring a hole Become (see Figure of description 7), perforation-radial type chuck that described half ball-joint load connecting rod contains hook deserves to be called perforation-hinged Formula chuck, perforation-radial type chuck that described half ball-joint load connecting rod contains annulus claims lower perforation-radial type chuck, described Hook contained by half ball-joint load connecting rod or annulus in upper and lower perforation-radial type chuck, are only that narration is convenient, non-upper and lower The essential distinction of perforation-radial type chuck, can be configured according to the requirement of convenient test；
Described steel housing is in u-shaped, has segment-shaped hole in crossbeam, and this hole is suitable for forming half with half ball-joint load connecting rod Ball-joint；Be respectively provided with the side rod of both sides one can plug-in mounting bore a hole hinged use steel pole axle circular hole；
Described half ball-joint load connecting rod is steel round bar, and one end is in hemispherical, is suitable for forming hemisphere with steel housing Hinged；Another end head contains hook or annulus, can hang on described support, and couple with described counterweight load；
Described hinged steel pole axle of boring a hole is screw rod standard component containing nut it is desirable to be interspersed in concrete sample middle sleeve Part be light round shape.
Described perforation-radial type chuck technical requirements: each part of perforation-radial type chuck is steel, effectively carries Area must meet test and load requirement, generally higher than 530mm2；The u-shaped inside casing size of steel housing must can place test specimen, for Section shown in Figure of description 7 is the test specimen of 100mm × 100mm, and each side of u-shaped housing is only long to answer >=110mm；
Bore a hole the axis of hinged use steel pole axle and half ball-joint load connecting rod axis in same plane, different surface errors are little In 0.2mm, i.e. the coaxial line of steel housing episphere circular hole and half ball-joint load connecting rod, with two side perforations on steel housing Circular hole and the coaxial line of hinged use steel pole axle of boring a hole, different surface errors are less than 0.2mm；Bore a hole the axis and half of hinged use steel pole axle The holding of ball-joint load connecting rod axis is vertical, and vertical angle error≤± 0.5 ° is it is ensured that test specimen geometry is to neutralization physics pair In.
The principle of the physics centering of described test specimen is, when hinge transmission tensile load, if test specimen geometry is to neutralization physics Centering, then tensile load line overlap with the longitudinal axis face of test specimen, such as Figure of description 8a；If because sedimentation during molding makes test specimen indulge The concrete density of axial plane both sides and rigidity are inconsistent, situation shown in Figure of description 8b after test specimen tension, and because It is made up of low frictional resistance and Materials with High Strength in concrete sample middle punch (pore-forming) sleeve pipe, chuck middle punch steel pole axle surface light Sliding, steel pole axle and perforation sleeve pipe the line of force will be moved, stretch and acted the effect of maintaining the original state, adjustable test specimen by the line of force Recover state shown in Figure of description 8a, play physics centering effect.
Described perforation test specimen is concrete prism, or reamed end prism, prism test specimen longitudinal direction two ends, or termination The two ends expansion end expanding prism test specimen is respectively provided with a perforation/through hole, and perforation test specimen stage casing side is arranged with change Shape is surveyed and is read gauge length；On the longitudinal axis face of level in specimen molding for the axis of described perforation test specimen two ends perforation, and hang down with the longitudinal axis Directly；
Two perforation of described perforation test specimen are in specimen molding by rigid, the low frictional resistance on the side form being arranged on die trial Sleeve pipe is formed, and can use commercially available hard plastic tube or metal tube, a diameter of φ 26mm～φ 32mm of described sleeve pipe, the axis of described perforation Away from perforation test specimen, nearest end face distance answers >=50mm, and test specimen middle punch is used for interting the perforation of described perforation-radial type chuck Hinged use steel pole axle, make to be formed between test specimen and chuck hinged, transmit load；Described perforation test specimen outside of sleeve in molding is preset There is spiral reinforcing rod, spiral reinforcing rod is made using the reinforcing bar of φ 4～8mm, the centrage of the helical ring of described spiral reinforcing rod With the dead in line of described through hole or sleeve pipe, and spiral reinforcing rod contains elbow, and described elbow is reinforcement end, parallel to examination The bending segment of part transverse section, the tensile load of transmission between the hinged perforation with steel pole axle and test specimen of boring a hole of chuck is uniformly transferred To test specimen advancing side；
Described deformation survey read gauge length by bore a hole specimen molding when pre-buried two pairs of gauge head built-in fittings formed, described gauge head is pre-buried Part is by detachable installation in specimen molding, is connected on the side form of molding die trial, is embedded in test specimen after form removal Gauge head built-in fitting, gauge head built-in fitting be used for install deformation measure read deformation, calculate strain；Survey shown in 9 in " Figure of description 7 " Head surveys a read apparatus part for test piece deformation, including built-in fitting and fixture, is made up of copper material, during specimen molding, gauge head is pre- Embedded part is screwed onto the inner side of side form, in the concrete of embedded test specimen after concrete formation, mounting fixing parts during creep test, and Deformation gauge etc. forms the whole test piece deformation survey read apparatus that deformation is read in survey, carries out test piece deformation and surveys reading；Described deformation is surveyed and is read gauge length Between two of test specimen perforation of perforation, it is desirable between gauge head and perforated base axle on the coupon level longitudinal axis face in molding Away from l ' >=0.8a+1/2d, wherein: a is the test specimen cross section length of side, d is casing diameter, gauge length l >=120mm, described perforation test specimen Deformation to survey the cross section read at gauge length be square, the length of side is >=the conventional sample dimensions of 100mm.
Described deformation gauge is used for surveying test piece deformation in reading test, calculates strain, using amesdial, displacement transducer and can answer Become other general deformation such as meter to extend device；
Described counterweight load is formed by connecting steel cable, frame disk and counterweight, sees " Figure of description 6 ", also can steel cable, water With the composition such as water tank it is desirable to can accurate load needed for load test.
Concrete shrinkage stress creep test method of the present invention, comprising: creep room and two kinds of rings of natural environment according to standard Border condition, completely with non-fully two kinds of restraint conditions of structural constraint rigidity, two kinds of employing " step loading " and " covariant loading " adds Load mode, and collapse threshold and fixing two kinds of Loading Control conditions of age, the test side that test concrete shrinkage stress is crept Method, the method carrying out concrete shrinkage stress creep test.Test is surveyed and is read each Under Concrete deformation, basic by formula (1) Relation (principle) calculates concrete shrinkage stress and creeps,
In formula: εcThe shrinkage stress of concrete (test specimen) is crept；
εtctIn test, the overall strains loading the generation of duration concrete sample at different levels, abbreviation overall strain, during test Reading can directly be surveyed by deformation gauge from " Analysis of Concrete Tensile creep test device "；
εshThe contraction strain of concrete, by " concrete restriction expansion and the contraction measurement that adopt in auxiliary shrinkage test Instrument " survey read, because contraction strain is negative value, should be changed to during calculating on the occasion of；
εeAdded by corresponding shrinkage stress during load, the elastic strain that test specimen occurs, by " Analysis of Concrete Tensile is crept in test Assay device " or auxiliary Analysis of Concrete Tensile test are surveyed and are read or calculate.
Described fundamental relation (principle) is that in structure, concrete (strains, i.e. labelling of the present invention because shrinkage stress deforms Overall strain) with contraction distortion (strain), elastic deformation (strain), the pass of shrinkage stress time deformation (creeping) under shrinkage stress System.The present invention be reduced to test in duration, the overall strain of concrete sample and the contraction from loading of every grade of load The relation that under strain, shrinkage stress, elastic strain, shrinkage stress are crept.
Described auxiliary shrinkage test, for surveying the cubic deformation (to strain as index) reading to occur when concrete is unfettered Test, using in " cement expansive material " gb23439-2009 annex b " mixes concrete limited expansion rate and the receipts of extender Contracting test method ", or " Standard for test methods of longterm performance and durability of ordinary concrete standard " gb/t50082-2009 test side Method is carried out；Described cubic deformation (strain) includes drying shrinkage, chemical shrinkage, self-constriction etc., for also including flatulence of heat type under natural environment Shrinkage, the present invention is referred to as contraction strain；
Described auxiliary Analysis of Concrete Tensile test includes obtaining the tension test of concrete elastic deformation, and empirically formula is borrowed Help the methods such as pressurized elasticity modulus test, in acquisition and shrinkage stress creep test, load corresponding concrete elastic strain.
Based on formula (1) relation, for standard creep room and natural environment, completely and non-fully in the case of structural constraint rigidity Concrete shrinkage stress is crept, and " present invention " research design is with " step loading " and " covariant loading " two kinds of load modes, contractions Threshold value and fixing two kinds of control conditions of age carry out concrete shrinkage stress creep test.Each concrete test method is as follows:
1. standard is crept room condition step loading-concrete shrinkage stress creep test method
Described standard room condition of creeping meets " Standard for test methods of longterm performance and durability of ordinary concrete standard " gb/ The required temperature and humidity conditions of concrete shrinkage test in t50082-2009, or " concrete for hydraulic structure testing regulationss " dl/t5150- The standards of 2001 regulations are crept room condition, and test selectes during one of which condition it should be noted that the difference of humiture, and its to creeping The impact of result.
Described step loads, i.e. " step load tensile creep test method ", by contraction distortion threshold value and fixing age two Kind of loading environment carries out concrete shrinkage stress creep test, because the creep curve of PRELIMINARY RESULTS of gained concrete shrinkage stress is in Micro- level consecutive variations, therefore claim " step load tensile creep test method ".
Described contraction distortion threshold value, the contraction for test specimen in test and the net strain (ε causing that creepsT, i=-εsh,i-εc,i) Reach threshold value (th) when the condition that loaded, that is, work as εT, i≥thWhen load, calculate loading capacity (p at different levelsi) and load, loading capacity (pi) press column count:
pi=ki·a·et,i·(-εsh,i-1-εc,i-1) i=1,2,3 ... n ... (2)
In formula: piI level loaded value, kn, generally it is scaled kg；
A test specimen lifting surface area, mm2；
et,iThe Analysis of Concrete Tensile elastic modelling quantity of corresponding age when i level loads, gpa, is surveyed during desirable interpolation tensile load Elastic modelling quantity, or auxiliary Analysis of Concrete Tensile the surveyed elastic modelling quantity of test；
kiI level loads correction factor it is recommended that kiFor 1.05～1.60, standard is crept room environmental, preferably takes ki=1.4, natural Environment, preferably takes ki=1.2,；
εc,i-1The creeping of i-1 level load duration, μ ε；
εsh,i-1I-1 level load duration (before i-1 level is loaded onto the loading of i level) contraction strain, μ ε, because of contraction distortion For negative value, therefore add "-".
Described loading correction factor (ki), it is to consider, age, Analysis of Concrete Tensile elastic modelling quantity was relatively just during 1～28d Phase elastic modelling quantity has 50～100% growth, and early stage increases comparatively fast；Secondly, during i level loads to i+1 level, receive with concrete Contracting and the net strain (ε causing that creepsT, i) will continue to increase, shrinkage stress increases；In another aspect natural environment, concrete exists Flatulence of heat type and bulking are possible, therefore choose above-mentioned kiValue；
The contraction strain of described i-1 level load duration (before i-1 level is loaded onto the loading of i level) is by same match ratio mixing simultaneously Test specimen free shrink deformation (strain) of concrete for making, can be surveyed and be read by " concrete limits and expands and contraction measuring instrument ".
In described each symbol, i is the sequence numbers loading and surveying reading at different levels, i=1,2,3 ... n ... during test.
First loaded value (p during described i level loads, as i=11), it calculates value is, et,11 grade corresponds to when loading The Analysis of Concrete Tensile elastic modelling quantity of age, can use auxiliary Analysis of Concrete Tensile and tests surveyed elastic modelling quantity, εSh, 01 grade of load age When concrete free shrink deformation (strain), εc,0During 1 grade of load age, concrete shrinkage stress is crept, et,1、εSh, 0And εc,0 Value takes from existing data or data, obtains p1, kn；The concrete value that calculates can be found in " specific embodiment " " 6. " 6.2.1 loading " related content of embodiment "；
Described threshold value (th), it is set as th=5 μ ε, the setting of this value is will according to the precision meeting deformation gauge (amesdial etc.) Ask, meet the period of change of volume change of concrete and shrinkage stress time deformation and its corresponding loading capacity again, and test is just The factors such as profit determine；
Described fixing age, is 1d, 2d, 3d, 5d, 7d, 14d, 21d, 28d ... by age, calculates loading capacity (p ' at different levelsi) And load, survey and read deformation (strain), calculate concrete creep (εc,i)；
Survey after loadings at different levels and read deformation (strain), comprising: contraction strain (εshi), elastic strain (εe,i), net strain (εt,i) With overall strain (εtct,i), calculate concrete creep (εc,i)；
In above-mentioned each symbol, i is the sequence numbers loading and surveying reading at different levels, i=1,2,3 ... n ... during test.
2. consider the situation of structural constraint stiffness effect
The described situation considering structural constraint stiffness effect, is for structure, the different constraint rigidity of concrete shrinkage to be produced The different shrinkage stress of life, and its problem that the corresponding different shrinkage stress producing is crept, and the test carrying out.
Calculate loaded value (p according to restraint conditioni' '), and load, described pi' ' press formula (3) calculate:
In formula: r structure is to concrete constraint factor；
Remaining symbol is the same.
After loading, survey and read deformation (strain), calculate Analysis of Concrete Tensile Xu of the loadings at different levels considering constraint factor (r) situation Become (εc-c,i)；Can be by contraction distortion threshold value and fixing age two ways.
3. natural environmental condition concrete shrinkage stress creep test method
Described natural environmental condition concrete shrinkage stress creep test method, is natural environmental condition (natur Entironment under), the problem crept of shrinkage stress that occurs for concrete in structure, and the test carrying out；
Natural environmental condition test method it is characterised in that: by creep test and test specimen, and shrink (cubic deformation) test specimen Be placed in environmental condition and tested, by deformation threshold value (set | εT, i|≥th) and fixing age two ways, and considered Complete and non-fully two kinds of situations of structural constraint rigidity, step by step plus (subtracting) carries, survey and read itself to collapse deformation/strain (εE, sh, i), elasticity Strain (εE, e, i), net strain (εE, t, i) and overall strain (εe,tct,i), test concrete creep (εe,c,i)；
Described setting | εT, i| it is to consider that in natural environment, concrete is because temperature rises and drenches with rain (or air humidity increase), Cause and itself collapse deformation/strain (εE, sh, i) it is swell value；During described plus (subtracting) carries, off-load is because rising for concrete in structure Temperature/and when drenching with rain and expanding, shrinkage stress reduces corresponding off-load；
Described survey reads itself to collapse deformation/strain (εE, sh, i) it is that deformation test specimen is placed in deformation, measuring instrument in natural environment The standard of being placed in is crept room environmental, takes and is placed in natural environment test specimen to standard room environmental of creeping and surveys and read itself to collapse deformation/strain (εe,shi) it is desirable to complete in 3～5min, the survey completing to deform in described 3～5min reads to require, and is according to the research knot such as Jiang Jianhua Really [Jiang Jianhua, Yuan Yingshu, Zhang Ximei. temperature-responsive in the temperature action spectrum of natural climate environment and concrete is expected [j]. in Southern college journal, 2010,41 (5): 1923-1930] with regard to concrete to the corresponding of ambient temperature and its temperature distributing rule in Result of study be designed, this requirement can meet to itself collapsing deformation/strain (εe,shi) survey the required precision reading result. Described deformation test specimen and measuring instrument are swollen using carrying out concrete restriction in gb23439-2009 " cement expansive material " for the present invention The test specimen of swollen test, concrete limit and expand and contraction measuring instrument, and making must be with " longitudinally limiting in gauge head replacement test specimen during test specimen Device ", and the installation of gauge head should meet the range finding of gb23439 and require；Described survey reads elastic strain (εE, e, i), net strain (εE, t, i) With overall strain (εe,tct,i), and calculate concrete creep (εe,c,i) with aforementioned.
4. covariant loading-concrete shrinkage stress creep test method
Described covariant loads, and refers under complete deflection constraint, and it is zero (ε that test keeps the overall strain in specimen equidistance line markingTct, i =0).Work as εTct, iWhen ≠ 0, that is, require to keep ε by adjusting counterweight (tensile load)Tct, i=0, therefore it is referred to as " covariant loading ".
Standard is crept room environmental, when not adjusting load (not adding load), drying shrinkage and to creep be time-varying function, leads to Often εTct, i＜ 0, keeps ε by continuing loadingTct, i=0.
For natural environment, when not adjusting load, volume change of concrete (or itself collapsing deformation-strain) and Xu Change is time-varying function, may ε when drying shrinkage and shrinkageTct, i＜ 0, if occur bulking and intensification to be likely to ε when expandingTct, i＞ 0, then Load (counterweight) is corresponding to be increased, or reduces.
Completely under covariant load condition under deflection constraint, shrinkage stress is crept (εC, c, i) calculate, because of εTct, i=0, record ε,c,sh.iAnd ε 'C, e, iAfterwards, you can calculate ε with reference to formula (1)C, c, i.
The covariant of described other constraint degrees (r ≠ 1, usual r ＜ 1) loads, because of εC, tct, i≠ 0, then when must calculate i level age Strain (the ε ' of section (loading of i level)C, tct, i) it is to creep the controlling value of test piece deformation, work as εTct, i≠ε’C, tct, iWhen, adjust counterweight (tensile load)；Described ε 'C, tct, iIt is calculated as follows:
In formula, ε 'C, tct, i、ε,c,sh.i、ε’c,c,iAnd ε 'C, e, iIt is respectively under other constraint degrees (non-fully deflection constraint), examination The overall strain of part, concrete shrinkage strain, shrinkage stress are crept and are loaded the elastic strain of generation.
Described εc.sh.iFor testing measured value；
Described ε 'c,c,iFor the desired value of test, but in this case again need to be with ε 'c,c,iCalculate controlling test value to be tried Test, the present invention recommends to press ε 'C, c, i-1Calculated by linear epitaxy, or the ε being obtained according to actual measurement during r=1c,i,By ε 'C, c, i=r· εc,iCalculate, then test gained ε ' ' with this levelC, c, iRelatively, if the two relative error is within 15%, creep (ε 'C, c, i) can try Test result；Relative error more than 15%, then, in i+1 level with ε ' 'C, c, iAgain matching ε 'C, tct, i+1, creeping after adjusting for several times (ε ' 'C, c, i) result precision by obtain improve；ε’C, e, iFor testing measured value, but in " covariant loading " mode each loading capacity be relatively Little, directly survey and read more difficulty, this patent is recommended to press loading value (p ' ' 'c,i) and actual measurement bullet mould (ei) calculate elastic strain (ε 'C, e, i).
Loading value (the p ' ' ' that the covariant of other constraint degrees loadsc,i) it is:
In formula, r and a is with aforementioned；ec,t,iAnalysis of Concrete Tensile elastic modelling quantity when i level loads；εc,sh.i-1I-1 level load Duration concrete shrinkage strains；εc,c.i-1I-1 level load duration concrete creep.
ε under the covariant load condition of other constraint degreesC, c, iMeasuring and calculating, with the ε ' of aforementioned estimationC, c, iRecord with test ε’’C, c, iThe meansigma methodss of the two (ε as a resultC, c, i), wherein ε ' 'C, c, iIt is calculated as follows:
In formula, ε ' 'C, tct, iTest actual measurement overall strain；εc,sh.iAnd ε 'C, e, iDitto.
Natural environment situation, notes εC, e, sh.iDifference, if occur bulking and heat up expand when be likely to ε 'C, tct, i＞ εC, tct, i, then load (counterweight) should reduce.
In the manner described above, step and (6) formula, also can get shrinkage stress and creeps (εC, e, c, i).
The present invention is designed using " perforation-radial type chuck " and " test specimen perforation ", carries out shrinkage stress creep test.Chuck Entire combination be different from existing cartridge form and power transmission, centering method, have: 1. connect firmly, stable, the past of applicant Research and test show, this is linked at when concrete limit stretching destroys and also will not destroy；2. it is suitable for geometry to neutralization instrumentality Reason centering (avoids the stretching bias that concrete differential settlement causes), on the one hand, using hinged and hemisphere hinge technologies of boring a hole Modular design, solve the problems, such as the centering under Analysis of Concrete Tensile load, especially is avoiding causing because of concrete settlement inhomogeneities Physics centering difficult problem aspect has unique advantage, and on the other hand, the positioning relation of test specimen middle punch and detection gauge length is it is ensured that geometry To the pure tension state of concrete in neutralization test benchmark section；3. it is suitable for the shrinkage stress creep test beginning from early age, test specimen 1d tears open Can carry out after mould；4. the features such as test specimen perforated material frictional resistance is little.
The feature of the concrete shrinkage stress creep test method of the present invention is: relatively conventional tensile creep test side Method, directly carries out concrete shrinkage stress creep test, and leash law is more suitable for testing under natural environment to axial.The present invention Test method, because multistage loadings, survey read loads at different levels during strain and creep, the behavior of creeping of more concrete can be studied And performance issue.Device is simple, easy.
Fig. 1 a adopts for China working standard dl/t5150-2001 and sl352-2006 " concrete for hydraulic structure testing regulationss " Tensile creep assay device；
Concrete creep test apparatus [the poplar that Fig. 1 b is published on silicate journal for Zhejiang Polytechnical University Yang Yang for 2009 Poplar, Xu Sifa, Ye Deyan, etc. Early-age high strength concrete tensile creep characteristic [j] .2009,37 (7): 1124-1129]；
Fig. 2 is tstm method (axial constraint method) assay device
Fig. 3 is existing lever-counterweight method Analysis of Concrete Tensile creep test device
Fig. 4 is existing hydraulic concrete tensile creep assay device
Fig. 5 a is the structural representation of clamp type chuck in prior art；
Fig. 5 b is the structural representation of pre-buried anchoring type chuck in prior art；
Fig. 5 c is the structural representation of adhesive type chuck in prior art；
Fig. 5 d is the structural representation of embedded chuck in prior art；
Fig. 6 is Analysis of Concrete Tensile creep test apparatus structure schematic diagram of the present invention；
Fig. 7 is the overall composition schematic diagram of chuck and test specimen in accompanying drawing 6；
Fig. 8 a, the accompanying drawing 8b physics centering principle schematic to test specimen for present invention perforation-articulation；
Fig. 9 a is surveyed c30 concrete standard by embodiment and is crept room contraction strain curve；
Fig. 9 b is surveyed the c30 concrete standard room of creeping by embodiment and is loaded instantaneous (elastic) strain curve；
Fig. 9 c is surveyed c30 concrete standard room shrinkage stress of creeping by embodiment and is crept curve；
Figure 10 a is surveyed contraction strain curve under c30 Concrete in Natural environment by embodiment；
Figure 10 b is surveyed by embodiment loads instantaneous (elastic) strain curve under c30 Concrete in Natural environment；
Figure 10 c is surveyed shrinkage stress under c30 Concrete in Natural environment by embodiment and is crept curve；
In accompanying drawing:
Accompanying drawing 1a, accompanying drawing 1b are all " steelframe-spring force method " concrete creep test apparatus.
In accompanying drawing 6, " Analysis of Concrete Tensile creep test device " is by upper perforation-radial type chuck, lower perforation-radial type folder Head, perforation test specimen and counterweight load composition.Upper and lower chuck is used for transmitting tensile load it is ensured that the test gauge length of concrete sample Scope is in axial tension state；Test specimen is made by by inspection (test) concrete；Configuration load can with Hanging Basket and counterweight or other Metering weight composition.In figure: perforation-radial type chuck on 1-, perforation-radial type chuck under 2-, 3- perforation test specimen, 12- counterweight Load.
In accompanying drawing 7, show the relative position of hinged use steel pole axle, half ball-joint load connecting rod and steel housing of boring a hole； The position of arrangement of reinforcement strengthened by the composition of diagram " perforation test specimen ", sleeve pipe and spiral.In figure: wear under perforation-radial type chuck on 1-, 2- Hole-radial type chuck, 3- perforation test specimen, contain the hemisphere bar that is articulated and connected of hook in perforation-radial type chuck on 4-, with support even Connect, 5- half ball-joint, 6- perforation is hinged to use steel pole axle, the perforation that 7- test specimen middle sleeve is formed, 8- spiral reinforcing rod, the pre-buried survey of 9- Head, 10- deformation gauge (copper rod and gauge head), contain the hemisphere bar that is articulated and connected of annulus in perforation-radial type chuck under 11-, with counterweight Load connects.
In accompanying drawing 8, perforation-articulation to the physics centering principle of test specimen is, when hinge transmission tensile load, if Test specimen geometry is overlapped with the longitudinal axis face of test specimen to neutralization physics centering, then tensile load line, such as accompanying drawing 8a；If because heavy during molding Fall makes the concrete density of test specimen longitudinal axis face both sides and rigidity inconsistent, it may appear that feelings shown in accompanying drawing 8b after test specimen tension Condition, when situation shown in accompanying drawing 8b occurs, hinged will play physics between the perforation-radial type chuck of the present invention and perforation test specimen Centering acts on, because concrete sample middle punch (pore-forming) sleeve pipe is made up of low frictional resistance and Materials with High Strength, chuck middle punch steel pole Axle smooth surface, steel pole axle can roll in perforation sleeve pipe, and steel pole axle can be moved automatically with the touch line of perforation sleeve pipe, makes Stretching is recovered state shown in accompanying drawing 8a by the line of force, plays physics centering effect.
Carry out the concrete of concrete shrinkage stress creep test method using Analysis of Concrete Tensile creep test device of the present invention Implement, comprising: the purpose according to concrete research and engineering detecting determines concrete research method, sets up test chamber and place, system Standby assay device is simultaneously installed, and is tested by test method and corresponding steps, obtains shrinkage stress creep test result etc. main Step.
The test method of the present invention includes creeping room and natural environment, completely and non-fully structural constraint rigidity for standard In the case of the test method crept of concrete shrinkage stress, can " step loading " and " covariant loading " load mode, shrink threshold Value and fix two kinds of control conditions and carry out shrinkage stress creep test, the described purpose according to concrete research and engineering detecting is true Fixed concrete research method, that is, press experimental study and engineering detecting purpose and content, and test accuracy requires and condition, determines test tool Body method；
Described set up test chamber and place, carrying out concrete shrinkage stress creep test needs standard to creep room, this test In addition to place size need to meet test requirements document, its humiture should meet the mark such as gb/t50082-2009 or dl/t5150-2001 for room The regulation of quasi- code；Test under natural environmental condition is also tackled place size and is made requirement, also answer if necessary binding and Testing goal determines place and the seasonal weather of natural environment；
Described prepare assay device and install, because test the unconventional test tool of main device, must preparation meet the requirements Chuck and test specimen die trial, build and be suitable for hanging " suspensions-counter weight type tensile creep assay device " simple beam, or roof truss with (about 2 tons of the loads of single test) such as existing steel bracket setting suspension hooks；The device of the test such as the contraction strain of auxiliary and elastic modelling quantity Tool also needs accordingly to prepare；
Described test procedure includes: test specimen makes, creep test device and test specimen are installed, tested deformation data and survey and read and try Test result (creeping under concrete shrinkage stress) analytical calculation.
Described test specimen makes: first, by the match ratio of research concrete, makes concrete creep test specimen, volume becomes simultaneously Shape (contraction) test specimen and totally three kinds of elastic modelling quantity test specimen, wherein, test specimen of creeping is used for apparatus of the present invention and surveys the numbers such as reading time deformation According to；Cubic deformation (contraction) test specimen press " cement expansive material " gb23439-2009 in annex b " mix extender concrete limit Expansion rate processed and shrinkage test method " is listed to be required, or " Standard for test methods of longterm performance and durability of ordinary concrete standard " Gb/t50082-2009 test is surveyed and is read the making of volume change of concrete (nonmarine strata) test method；Elastic modelling quantity test specimen is this Inventive method surveys complementary testing test specimen when reading concrete sample difficulty, makes by stretching test method.Various test specimens are placed in examination Test the environment of research contents requirement, maintenance is to specifying age, testing data；The test specimen of various tests is three pieces one group, special feelings Condition need to meet correlation standard.
Note: 1. note the direction of power transmission crotch in spiral reinforcing rod during the perforation test specimen that preparation is crept it is ensured that load Transmission.If 2. concrete shrinkage deformation (strain) test is swollen using the concrete restriction of gb23439-2009 " cement expansive material " Swollen and contraction measuring instrument is carried out, and must substitute in test specimen " longitudinal limiter " with gauge head, the installation of gauge head should meet the survey of gb23439 Away from requiring.
Described creep test device and test specimen are installed: test piece maintenance, to specifying age, is installed by " Figure of description 6 ", opened Beginning shrinkage stress creep test (because in structure, concrete shrinkage stress produces after the concrete is cured, typically requires to open during 1d Begin).
Described test deformation data is surveyed and is read: creep test piece deformation and cubic deformation (contraction distortion) general by amesdial (or Other displacement transducers, or strain gauge) survey and read.
Test piece deformation of creeping surveys reading by being installed on the amesdial between gauge head and copper rod in " Figure of description 6 ", by test specimen mark Strain away from calculating.Reading data can be surveyed include: net strain (εt,i), elastic strain (εe,i) and overall strain (εtct,i), and difference is about The ε of creep test under Shu DuC, t, i、εC, e, iAnd εc,tct,i, the ε of creep test under natural environmentE, t, i、εE, e, iAnd εe,tct,iDeng.
The deformation (contraction strain) of cubic deformation test specimen, by " the mixing of annex b in " cement expansive material " gb23439-2009 The concrete limited expansion rate of extender and shrinkage test method ", or " normal concrete long-term behaviour and endurance quality test side Method standard " the survey reading calculating of gb/t50082-2009 test method, reading data can be surveyed and include: contraction strain (εsh,i), different constraints The contraction strain ε of the lower creep test of degreeC, sh, i, the contraction strain ε of creep test under natural environmentE, sh, iDeng.
The elastic modelling quantity of elastic modelling quantity test specimen presses stretching test method test measuring and calculating.
The measuring and calculating step of each condition and the strain of mode gained and data of creeping is as follows:
Test general steps are to load p from test beginning (i=1)1, record net strain (εt,1), elastic strain (εe,1), total Strain (εtct,1), and contraction strain (εsh,1), calculate εC, 1；Hereafter gradually load pi, survey respectively and read net strain (εt,i), elasticity should Become (εe,i), overall strain (εtct,i), and contraction strain (εsh,i), calculate εC, i, i=2,3,4 ... n ....
The testing procedure of the test method that each condition and mode are formed is as follows:
1. standard is crept room condition step loading-concrete shrinkage stress creep test
1.1 contraction distortion threshold methods
During i=1, load p1, survey and read contraction strain (εSh, 1), elastic strain (εe,1), net strain (εt,1) and overall strain (εtct,1), work as εT, 1≥th(th=5 μ ε), calculate concrete creep (εc,1), and start the test of i=2 level；
Work as εT, i≥th, i.e. i=2, during 3,4 ... n ..., calculated and loaded p by formula (2)i, survey and read contraction strain (εSh, i), Elastic strain (εe,i), net strain (εt,i) and overall strain (εtct,i), calculate concrete creep (εc,i), εc,iIt is calculated as follows:
In formula: εc,iI level load duration, the tensile creep of test specimen；
εtct,iI level load duration, the overall strain of tensile creep test specimen, survey from perforation test specimen and read；
εsh,iI level load duration, with match ratio simultaneously mixing concrete for making test specimen free shrink deformation (should Become), can be surveyed by " concrete limit expand and contraction measuring instrument " and read, because contraction strain is negative value, should be changed to during calculating on the occasion of；
εe,iThe elastic strain that i level loading specimen occurs, can directly be surveyed and be read by creep test or assistant spring test.
In formula: εt,iI level load duration, the net strain of tensile creep test specimen, reading is directly surveyed by creep test；
1.2 fixing age methods
It is 1d, 2d, 3d, 5d, 7d, 14d, 21d, 28d ... by age, calculate loading capacity (p at different levels by formula (2)i) and plus Carry, survey and read contraction strain (εSh, i), elastic strain (εe,i), net strain (εt,i) and overall strain (εtct,i), by formula (7) or formula (8) calculate concrete creep (εc,i).
2. consider the situation of structural constraint stiffness effect
During i=1, calculate loading capacity (p ' ' by formula (3)1) and load, survey is read and calculating is each strains and creeps.
2.1 contraction distortion threshold methods
Work as εT, i≥th(th=5 μ ε), i.e. i=2, during 3,4 ... n ..., load p ' 'i, p ' 'iCalculate by formula (3), survey and read to receive Shrinkage strain (εC, sh.i), elastic strain (εC, e, i), net strain (εC, t, i) and overall strain (εC, tct, i), calculate concrete creep (εC, c, i), creep and be calculated as follows:
In formula: εC, c, iDuring considering that the i level of constraint factor (r) situation loads, Analysis of Concrete Tensile creeps (strain)；
εC, t, iDuring considering the i level loading of constraint factor (r) situation, tensile creep test specimen strains only, can be by tensile creep Test is directly surveyed and is read；
εC, sh.iDuring considering the i level loading of constraint factor (r) situation, test specimen shrinks strain, can be by " concrete limits System expand and contraction measuring instrument " survey read, because contraction strain is negative value, should be changed to during calculating on the occasion of.
2.2 fixing age modes
It is 1d, 2d, 3d, 5d, 7d, 14d, 21d, 28d ... by age, calculate loading capacity (p ' ' at different levels by formula (3)i) and Load, survey and read deformation (strain), calculate concrete creep (ε by formula (7) or formula (8)C, c, i).
3. natural environmental condition step loading-concrete shrinkage stress creep test
3.1 contraction distortion threshold methods
During i=1, load pe,1, survey is read and calculating is each strains and creeps.
When | εE, t, i|≥th(th=5 μ ε), i.e. i=2, during 3,4 ... n ..., plus (subtracting) carries pe,i, survey and read contraction strain (εe,shi), elastic strain (εe,e,i), net strain (εe,t,i) and overall strain (εe,tct,i), calculate concrete creep (εc,i).
Described at different levels plus (subtracting) carrying capacity (pe,i) calculating press formula (2)；
Concrete creep (εe,c,i) calculating with (7) formula and (8) formula.
Note the symbol difference expanding and shrinking.
3.2 fixing age methods
It is 1d, 2d, 3d, 5d, 7d, 14d, 21d, 28d ... by age, calculate at different levels plus (subtracting) carrying capacity (pe,i) and plus (subtracting) Carry, survey and read deformation (strain), calculate concrete creep (εe,c,i).
4. covariant loading-concrete shrinkage stress creep test
4.1 complete deflection constraint methods
Completely under deflection constraint, because keeping εTct, i=0, work as εTct, iWhen ≠ 0, that is, adjust load, record ε,c,sh.iAnd ε 'C, e, i After can calculate εC, c, i, with (6) formula, standard room of creeping is identical with natural environment situation, notices that the latter understands off-load for formula.
The method of 4.2 other constraint degrees (r ≠ 1)
During i=1, load p ' ' 'c,1, survey is read and calculating is each strains and creeps.Described p ' ' 'c,1=r×p1；
Reckoning overall strain (the ε ' that i level loadsC, tct, i) calculate by (4) formula；
ε’C, c, i, by ε 'C, c, i=r·εc,iEstimation；
Loading value (p ' ' 'c,i), calculate by (5) formula, record ε ' 'C, tct, i、ε’’,c,sh.iAnd ε ' 'C, e, i, calculate by (6) formula ε’’C, c, i；
With ε 'C, c, iAnd ε ' 'C, c, iMeansigma methodss as εC, e, i.
Inspection ε 'C, c, iAnd ε ' 'C, c, iBetween error, within 15%, creep the two relative error (εC, c, i) knot can be tested Really；Relative error more than 15%, then, in i+1 level with ε ' 'C, c, iAgain matching ε 'C, tct, i+1, (the ε that creeps after adjustment for several timesC, c, i) Result precision will obtain raising.
Natural environment situation, notes εC, e, sh.iDifference, if occur bulking and heat up expand when be likely to ε 'C, tct, i＞ εC, tct, i, then load (counterweight) should reduce.Also can be crept (ε with reference to above-mentioned steps and formulaC, e, c, i).
5. the analytical calculation of concrete shrinkage stress creep test result
Record the shrinkage stress corresponding with studying (detection) purpose according to above-mentioned test method to creep (εc,i、εE, c, iWith εC, c, iDeng), it is calculated as follows and can obtain the accumulative shrinkage stress of concrete each age and creep (εt):
In formula: εtBefore loading for i=1 to i=n level, (corresponding age is tn), n=1,2,3 ..., accumulative Xu that test specimen occurs Become, can be that standard is crept and crept under the conditions of room, but also creep under natural environment；Can be to creep under complete rigidity, also may be used It is to creep under other constraint degrees；Can be creeping of threshold value loading method, but also fix creeping of age loading method；
εc,iDitto, but also εE, c, iAnd εC, c, iDeng.
According to εtAnd tnAs a result, ε can be drawntT curve (concrete shrinkage stress creep-age relation curve).
According to εt、εc,i、εE, c, iAnd εC, c, iCan calculate, Deng also, the other specification that concrete shrinkage stress is crept, or research is mixed Solidifying soil shrinkage stress reversible creep and behavior.
Using suspension-counter weight type Analysis of Concrete Tensile creep test device and concrete shrinkage stress creep test method, tie Close the c30 concrete of high-speed railway construction section road bed board construction, carry out concrete shrinkage stress creep test, with contraction distortion Threshold method testing standard creep room condition, constraint factor be respectively 0.9,0.8,0.7,0.3 shrinkage stress creep；With fixation Age mode is tested concrete shrinkage stress under natural environment and is crept.
Concrete main raw material(s) has p o42.5r cement, fluvial sand, rubble, polycarboxylate high performance water-reducing agent, ii level powder Coal ash, s95 slag powders and tap water etc., concrete match ratio such as table 1,
Table 1 concrete mix kg/m3
|Numbering||Water||Cement||Flyash||Breeze||Coarse aggregate||Fine aggregate||Water reducer|
6.1 prepare test specimen
By match ratio mixing concrete, prepare the test specimen of 2 number of columns of table.
The various test specimen production quantity of table 2
After test specimen standard curing 1d, creep room and natural environmental condition installation test device in standard, start to test, survey and read Survey after data and loading and read data.
(1) primary load: primary load is pressed formula (2) and calculated, a, e in formulat,0、εsh,0And εc,0By sample dimensions and c30 Concrete existing data value, cross sectional dimensions 100mm × 100mm at the specimen equidistance line marking of the present embodiment, a=100mm × 100mm, et,0、εsh,0And εc,0Existing data and data in data be respectively, concrete 1d values of shrinkage strain 70～400 μ ε, shrinkage stress is crept value 40～350 μ ε [be equivalent to the stress coefficient of relaxation 57%～86%(that creeps and take 72%)], concrete early stage Elastic modelling quantity 12.0～25.0gpa, approximate calculation after value obtains p1=1.4×100mm×100mm×20.0gpa×(1-0.72) × 100 μ ε=7840n, round and are scaled kg unit, p1≈ 800kg, the applied tensile stress of this load is also below early age coagulation Native 1～2mpa tensile strength, is that the 45～90% of tensile strength are interval, test shows: for c25～c45 concrete, this value Substantially applicable, determine p1=800kg.
Consider that pressing formula (3) during constraint factor calculates.
(2) subsequent load: hereafter at different levels loading presses formula (2) and formula (3) calculating, and deformation data takes from 6.2.2.
Standard creep room condition (contraction distortion threshold mode, r=0.9,0.8,0.7,0.3) shrinkage stress creep and from So loaded value at different levels in the 56d of environmental condition (fixing age mode), are shown in Table 3.
Table 3 loaded value kg at different levels
Load condition illustrates: collapse threshold method low to constraint factor (r=0.3) is not exclusively applicable, preferably adopts fixing age Method, or covariant loading method, the fixing age method test concrete shrinkage stress as adopted under natural environment is crept.
6.2.2 survey reading deformation data
Survey and read deformation at different levels, calculate contraction strain (ε by gauge lengthSh, i), elastic strain (εe,i), net strain (εt,i) and always should Become (εtct,i), by εSh, i、εe,i、εt,iAnd εtct,iWith tnDraw curve, standard is crept the contraction strain curve of room condition and loading Instantaneously (elastic) strain curve such as Figure of description 9a and Fig. 9 b；The contraction strain curve of natural environmental condition and loading are instantaneous (elastic) strain curve such as Figure 10 a and Figure 10 b.
6.3 shrinkage stress creep test result
Standard creeps room condition by formula (9), and natural environmental condition presses formula (7) or formula (8) calculates εc,i, then by public affairs Formula (10) calculates εt, draw εtT curve.
The creep shrinkage stress of surveyed c30 concrete of room condition (r=0.9,0.8,0.7,0.3) of standard creeps curve such as Figure of description 9c.
The shrinkage stress of natural environment (fixing age mode) surveyed c30 concrete is crept curve such as Figure of description 10c.
The present invention can record concrete shrinkage stress and creep, and especially achieve concrete shrinkage stress under natural environment Creep, can carry out creeping related research and engineering detecting to concrete shrinkage stress.
1. a kind of concrete shrinkage stress creep test method, it adopts Analysis of Concrete Tensile creep test device, described concrete Tensile creep assay device includes: support, upper perforation-radial type chuck, lower perforation-radial type chuck, perforation test specimen, deformation gauge With counterweight load it is characterised in that described perforation test specimen two ends are coupled with upper and lower perforation-radial type chuck respectively, and described Perforation test specimen both sides arrange described deformation gauge, the described two perforation-radial type chucks coupling with perforation test specimen, hang on respectively Couple on described support and with described counterweight load, form bulk test device；Test is surveyed and is read each Under Concrete deformation, presses The fundamental relation of formula (1) calculates concrete shrinkage stress and creeps:
In formula: εcShrinkage stress for concrete is crept；εtctFor, in test, loading duration concrete samples at different levels occur Overall strain, abbreviation overall strain, can directly survey reading by the deformation gauge from " Analysis of Concrete Tensile creep test device " during test；εshIt is mixed The contraction strain of solidifying soil, is surveyed and is read by " concrete limits and expands and contraction measuring instrument " adopting in auxiliary shrinkage test, because shrinking Strain as negative value, should be changed to during calculating on the occasion of；εeAdded by corresponding shrinkage stress during load, the elastic strain that test specimen occurs, examination Surveyed by " Analysis of Concrete Tensile creep test device " or auxiliary Analysis of Concrete Tensile test in testing and read and calculate；
Described concrete shrinkage stress creep test method include standard creep room condition creep test and natural environmental condition Xu Become test；
Described standard shrinkage stress creep test method under the conditions of room of creeping includes: the creep deformation threshold value of room condition of standard loads Method；Standard is crept the fixing age method of room condition step load test method；Standard is crept room condition step load test The loading method of the consideration structural constraint rigidity of method；
Standard is crept the deformation threshold value loading method of room condition, and actual measurement i-1 level loads duration test specimen and shrinks and creep and causes Net strain stresst,i-1, work as εt,i-1≥thWhen, to survey the contraction strain ε of readingsh,i-1, elastic strain εe,i-1With overall strain εtct,i-1, survey Calculate i-1 level duration concrete shrinkage stress to creep εc,i-1；Calculate the loading capacity p of i leveliAnd load；thFor deforming threshold value；
Described i level loading capacity piFor:
pi=ki·a·et,i·(-εsh,i-1-εc,i-1) i=1,2,3 ... n ... (2)
In formula (2): piFor i level loaded value；kiLoad correction factor for i level；A is test specimen lifting surface area；et,iWhen loading for i level Analysis of Concrete Tensile elastic modelling quantity；εsh,i-1For the strain of i-1 level load duration concrete shrinkage；εc,i-1For mixing during i-1 level load The shrinkage stress of solidifying soil is crept；I is the sequence numbers loading and surveying reading data at different levels, i=1,2,3 ... n ... during test；As i=1, et,1Analysis of Concrete Tensile elastic modelling quantity when loading for 1 grade, εsh,0For the contraction strain of concrete during 0 grade of load, εc,0For 0 grade of load When concrete shrinkage stress creep, et,1、εsh,0And εc,0Determined by ancillary test or existing data；
Concrete creep εc,iPress formula (7) by the test survey each parameter of reading to calculate:
In formula (7), each symbol is with aforementioned；
Standard is crept the fixing age method of room condition step load test method, is to load test by fixing age, calculates each Level loading capacity pi' and load, survey and read deformation, be converted to strain, calculate concrete creep ε by formula (7)c,i；Described fixing age Can be 1d, 2d, 3d, 5d, 7d, 14d, 21d, 28d；Described loading capacity pi' calculated and value using formula (2)；
Standard creep room condition consideration structural constraint rigidity test method, be according to restraint condition r, by deformation threshold value and solid Determine age two ways, calculate loaded value pi", and load, survey and read deformation, be converted to strain, concrete is calculated using formula (7) Shrinkage stress is crept εc-c,i；Described loaded value pi" press formula (3) calculating,
In formula (3), for structure to concrete constraint factor, remaining symbol is the same for r；Described test concrete shrinkage stress is crept εc-c,iEach parameter and calculate the same；
Creep room condition of standard considers the covariant load test method of structural constraint rigidity:
Standard is crept room condition complete deflection constraint covariant load test method, is to consider complete deflection constraint, constraint factor r= Under 1, keep concrete sample overall strain εtct,i=0, and loading carries, and tests each strain, calculates by formula (7) and creeps；
Standard is crept room condition non-fully deflection constraint covariant load test method, is to consider non-fully deflection constraint, constraint system Number r ＜ 1, calculates overall strain ε ' by formula (4)c,tct,i,
In formula: εc,sh,iFor concrete shrinkage strain；ε'c,c,iCreep for calculating, by ε 'c,c,i=r εc,iCalculate；ε’C, e, iFor adding The concrete elastic strain surveyed during load；Wherein, εc,iObtain for actual measurement during r=1；
Work as εtct,i≠ε'c,tct,iWhen, add and subtract load, calculate ε "c,tct,i, calculate ε by (6) formula "c,c,i,
In formula (6), ε "c,tct,iFor test actual measurement overall strain, εc,sh,iWith ε 'c,e,iThe same formula of parameter (4)；
Inspection ε 'c,c,iWith ε "c,c,iBetween error, the two relative error within 15%, with ε 'c,c,iWith ε "c,c,iMeansigma methodss conduct εc,c,i；Relative error more than 15%, then, in i+1 level with ε "c,c,iAgain matching ε 'c,tct,i+1, the ε that creeps after adjustment for several timesc,c,i Result precision will obtain raising；
The described standard room of creeping refers to meet " Standard for test methods of longterm performance and durability of ordinary concrete standard " gb/t The required temperature and humidity conditions of concrete shrinkage test in 50082-2009, or " concrete for hydraulic structure testing regulationss " dl/t 5150- The standards of 2001 regulations are crept room condition；
Described natural environmental condition shrinkage stress creep test method, is by creep test device, and is used for measuring volume change The test specimen of shape is placed in environmental condition to be tested, and by two methods of deformation threshold value and fixing age, and considers completely and non- Complete lattice constrains two kinds of situations of rigidity, multistage loadings or off-load, surveys and reads freely to collapse strain stresse,sh,i, elastic strain εe,e,i, net Strain stresse,t,iWith overall strain εe,tct,i, calculate concrete creep ε by formula (11)e,c,i；
The deformation threshold method of described natural environmental condition test method is to work as εe,t,i≥th, that is, load, work as εe,t,i≤-tH,I.e. Off-load；
Described survey reads freely to collapse strain stresse,sh,i, it is that deformation test specimen is placed in deformation in natural environment, measuring instrument is placed in standard Xu Become room environmental；Survey and read freely to collapse strain stresse,sh,iWhen, take to be placed in natural environment test specimen and move to standard and creep to survey in room environmental and read, Require in 3～5min, to complete the movement of test specimen and survey read procedure；Described cubic deformation test specimen and measuring instrument, are to adopt gb Carry out in 23439-2009 " cement expansive material " concrete limit expansion test test specimen, and " concrete limit expand and Contraction measuring instrument "；Make and must be substituted in test specimen " longitudinal limiter " with gauge head during cubic deformation test specimen, and the installation of gauge head should accord with The range finding closing gb 23439-2009 requires；
The fixing age method of described natural environmental condition test method is, by age be 1d, 2d, 3d, 5d, 7d, 14d, 21d, 28d, by formula (2) calculate at different levels plus, off-load amount pe,i, and plus, off-load, survey read deformation, by formula (7) calculate concrete shrinkage Stress is crept εe,c,i；
The complete deflection constraint of described natural environmental condition test method, constraint factor r=1 test method is to keep εe,tct,i= 0, work as εe,tct,iWhen ≠ 0, that is, adjust load, record εe,sh,iWith ε 'c,e,i, calculate εc,c,i, formula is with (6) formula；
The non-fully deflection constraint of described natural environmental condition test method, constraint factor r ≠ 1 test method is, reference standard Room condition of creeping non-fully deflection constraint covariant load test method, calculates, by (4) formula, the overall strain ε ' that i level loadsc,tct,i, press (6) formula calculates ε "c,c,i, check ε 'c,c,iWith ε "c,c,i, the two relative error within 15%, with ε 'c,c,iWith ε "c,c,iAverage Value is as εc,c,i；Relative error more than 15%, then, in i+1 level with ε "c,c,iAgain matching ε 'c,tct,i+1, Xu after adjustment for several times Become εc,c,iResult precision will obtain raising；
Described natural environment is outdoor environment selected by test.
2. a kind of concrete shrinkage stress creep test method according to claim 1 it is characterised in that: described perforation- Radial type chuck includes: steel housing, hemisphere bar that is articulated and connected and perforation hinged use steel pole axle；
Described steel housing is in u-shaped, has segment-shaped hole in crossbeam, and this hole is suitable for forming half ball-joint with hemisphere bar that is articulated and connected； Be respectively provided with the u-shaped both sides side rod of described steel housing one can plug-in mounting bore a hole hinged use steel pole axle circular hole；
Described hemisphere bar that is articulated and connected is steel round bar, and one end is in hemispherical, is suitable for forming half ball-joint with described steel housing, Other end head contains hook or annulus, can hang on described support and couple with described counterweight load；
Described hinged steel pole axle of boring a hole is the screw rod standard component containing nut；
Described perforation-radial type chuck technical requirements: the bore a hole hinged axis with the steel pole axle and hemisphere rod axis that are articulated and connected exist Same plane, different surface errors are less than 0.2mm；The bore a hole hinged axis with steel pole axle and hemisphere is articulated and connected the holding of rod axis Vertically, vertical angle error≤± 0.5 ° is it is ensured that test specimen geometry is to neutralization physics centering.
3. a kind of concrete shrinkage stress creep test method according to claim 1 it is characterised in that: described perforation examination Part is concrete prism, or reamed end prism；Prism test specimen longitudinal direction two ends, or the two of reamed end prism test specimen End expands end and is respectively provided with a perforation；Perforation test specimen stage casing side is arranged with deformation and surveys reads gauge length；
On the longitudinal axis face of level in specimen molding for the axis of described perforation test specimen two ends perforation, and and axis oriented normal；Described Perforation two perforation of test specimen are formed by rigid, the low frictional resistance sleeve pipe on the side form being arranged on die trial in specimen molding；Described The axis of the perforation end face distance nearest away from perforation test specimen answers >=50mm；Described perforation test specimen outside of sleeve in molding is preset with Spiral reinforcing rod, the centrage of the helical ring of described spiral reinforcing rod and perforation or the dead in line of sleeve pipe, and spiral reinforcing rod Containing elbow；Described elbow is reinforcement end, the bending segment parallel to test specimen transverse section；Described perforation test specimen middle punch is used for The perforation of interspersed described perforation-radial type chuck is hinged to use steel pole axle, so that formation hinge formula between test specimen and chuck is coupled；
Described deformation survey read gauge length by bore a hole specimen molding when pre-buried two pairs of gauge head built-in fittings formed；Described gauge head built-in fitting is In specimen molding by dismountable connection, it is connected on the side form of molding die trial, is embedded in test specimen during form removal after molding Gauge head built-in fitting；Gauge head built-in fitting is used for installing deformation and measuring reading deformation, calculates strain；Described deformation is surveyed and is read gauge length in perforation Between two of test specimen perforation, on the coupon level longitudinal axis face in molding it is desirable to spacing l' of gauge head and perforated base axle >= 0.8a+1/2d, wherein: a is the test specimen cross section length of side, d is casing diameter, gauge length l >=120mm；The deformation of described perforation test specimen Surveying the cross section read at gauge length is square, and the length of side of perforation test specimen is the >=conventional sample dimensions of 100mm.
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