CN103837413A - Concrete tensile creep testing device and concrete shrinkage stress creep testing method - Google Patents

Abstract

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.

Description

Analysis of Concrete Tensile creep test device and concrete shrinkage stress creep test method

Technical field

The invention discloses a kind of Analysis of Concrete Tensile creep test device and concrete shrinkage stress creep test method; Refer to especially a kind of Analysis of Concrete Tensile creep test device and concrete shrinkage stress creep test method; Belong to concrete test technical field in civil engineering, particularly Analysis of Concrete Tensile creep test technology.

Background technology

In structure, concrete often ftractures because shrinking and retraining.Creep as the key issue of the anti-shrinkage cracking of structural concrete, this research in recent years is also gone beyond deeply, be industry acceptance to the viewpoint of " Analysis of Concrete Tensile Creep Characteristics ripe pressurized Creep Characteristics relative to research distinguished to some extent ", the work of correlative study also gets along with, and the mechanical characteristics that under differential contraction stress, concrete creep behavior has load and becomes while creeping, and the singularity such as concrete hardening, carry out research and test that concrete shrinkage stress creeps significant to xoncrete structure cracking resistance.Under differential contraction stress, Analysis of Concrete Tensile creep test is the basis of this research, and test method and device also will play a significant role in the Construction control of structural concrete cracking resistance.

The difference of Analysis of Concrete Tensile creep test device and test method, determines that the scope of gained Creep Characteristics and correlation parameter there are differences, or the difference of operation difficulty or ease and precision.Carrying out at present the test method that Analysis of Concrete Tensile creeps mainly contains:

(1) steelframe-spring energized method (seeing accompanying drawing 1), the Analysis of Concrete Tensile creep test method that Gai Fashi China act.std DL/T5150-2001 and SL352-2006 " concrete for hydraulic structure testing regulations " adopt.Yang Yang [Yang Yang, Xu Sifa, Ye Deyan, Deng. Early-age high strength concrete stretching Creep Characteristics [J]. silicate journal, 2009,37 (7): 1124-1129] etc. these class methods of employing are carried out the research of creeping under concrete shrinkage stress, on the basis of lot of experiments, the Fitting Calculation obtains the characteristic parameter of Creep Characteristics under concrete shrinkage stress, but lacks the creep test findings of behavior of direct acquisition concrete shrinkage stress; Separately, because this test method applies pulling force by spring, this just makes concrete sample creep after generation, causes that camber of spring value reduces, and changes loading stress level; The distortion (counter-force reduces corresponding steel frame deformation and reduces) of the corresponding generation of steelframe simultaneously also can affect result.If carry out creep (the creeping hereinafter to be referred as differential contraction stress) of contraction stretching stress under structural constraint, for applying the differential contraction stress of time varying characteristic, with reduce the impact of the spring that causes of concrete creep on loading stress level, needing constantly to adjust spring state (readjusts test unit and reaches setting power value, particularly the latter because of need fine settings difficulty larger), for warranty test result, work difficulty and amount are all larger.Application publication number CN103149100A " a kind of concrete axle center stretching creep test instrument and test method " also belongs to the type, and distinguishing feature is to change distortion and surveys read mode, obtains result.

(2) TSTM(Temperature-Stress Testing Machine) method, also claim cracking frame test method or axial constraint method (seeing accompanying drawing 2), within 1969, the German Mo Nihei R.Springenschmid of technology university proposes test method, mainly carry out agent on crack resistance of concrete shrinkage cracking Journal of Sex Research, after this researcher proposes to obtain concrete shrinkage stress by stepper motor and sensor reconstruction the method, domestic have a Research Literature [Ma Xinwei, the long benevolence of button, the tension Creep Characteristics [J] of Hooton R D. high performance concrete under constraint condition. Wuhan University of Technology's journal, 2006, 28 (2): 26-29.] adopt the method, this experimental study gained concrete creep is concrete creep under differential contraction stress, this is also one of work of carrying out differential contraction stress creep test at present few in number.Due to the feature of this test unit, adopt step motor control test specimen in full restrained condition, the axial shrinkage stress that load transducer obtains, by the modulus of elasticity of concrete and the drawdown deformation (ilities data) that separately record, calculates acquisition differential contraction stress and creeps; Be limited to and control deformation device, computing method and the test of ilities number, this research does not propose the test method in other constraint degree situations; Because using constraint steelframe in test unit, be not suitable for physical environment (under temperature variation), also without corresponding method of testing; Test unit costliness in addition, restriction the method is generally used at home; The method device therefor costliness besides, and domestic this equipment once only can survey a test specimen, and data volume is limited.Application publication number CN103149094A " early-age concrete stretch measuring method and the device of creeping " also belongs to the type, and its distinguishing feature is the requirement such as deflection≤1 μ m, the loading of self-locking punching lifting jack, differential displacement sensor and anti-attrition device that proposes frame structure.

(3) lever-counterweight method (seeing accompanying drawing 3), twentieth century end of the eighties, " mechanical performance of concrete and mensuration " that Jiang Futian writes at it [Jiang Futian. mechanical performance of concrete and mensuration [M]. Beijing: China Railway Press, 1989.] just introduced the method, loading counterweight, except available water tank, also can adopt counterweight.The latter relatively, water tank loading is having more advantage aspect the fine setting of payload values, while just measuring the load that adds water produced, should consider that the impact of the factor such as temperature and operation can guarantee enough precision.The method can load according to testing requirements, but have no adopt the method carry out for differential contraction stress creep research report.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.Li Xinggui [Li Xinggui. the concrete destruction [J] of creeping and creep under high tensile stress effect. Hohai University's journal, 1996,24(4): 58-64] adopt double lever method to improve former method and reduce the space of testing, also make the steadily of centre of gravity problem of whole test stand make moderate progress, its cost of manufacture is still higher.

(4) steelframe-liquid (gas) platen press (seeing accompanying drawing 4), the method is also the one stretching creep test device of early stage imagination, in steelframe, pass through oil pressure (air pressure-nitrogen) the lifting jack application of force, the creep test that stretches, as the fluid pressure type of the Y.Akatsuka machine of creeping that stretches promotes piston by oil pressure and carrys out loading.Because of the adjustable feature of hydraulic pressure, the method also can be carried out differential contraction stress creep test in theory, but these class methods are due to the long-term voltage stabilizing problems affect practical application of hydraulic pressure (cylinder), then there is the method to adopt steelframe, has the load shakiness problem identical with method ().

(5) other, when simple bending-pulling method-be subject to pure bending load with beams of concrete, beams of concrete neutral axis bottom is divided in tension stress state, the research of creeping stretches, the method is significant for the research of creeping of prestressed concrete beam, the employing the method such as the Zhang Haobo of Xi'an University of Technology obtain the significant result of its research field, but whole beams of concrete cross-sectional distribution tension and compression stress, tension side exists tension gradient to distribute, and this result has limitation to understanding concrete pure extension performance; Oil pressure-Nei plavini-concrete is made to hollow cylinder (cylinder) test specimen, sealing, connected pipes, by adding pressure fluid (hydraulic pressure, gas-air pressure) produce pressure, make concrete cylinder expansion tension, research Analysis of Concrete Tensile creep, A.D.Ross has carried out the method research, in same concrete there is gradient in tension, and test specimen sealing and permeability resistance are very large on the success ratio impact of test in addition, and this method application is few.

In sum, axial constraint method, lever-counterweight method and steelframe-liquid (gas) platen press can be carried out differential contraction stress creep test, wherein axial constraint method was carried out the lower differential contraction stress creep test research of full constraint, but there is in test condition (research range), detected parameters, device stability and equipment cost the part that complies with one's wishes not to the utmost, be difficult to carry out the test of physical environment.

The test unit that Analysis of Concrete Tensile is crept is except overall architecture, the shape of concrete sample and chuck (joint) affect concrete stress, internal stress distributes, determine creep test testing result (accurate, precision), success of the test and operation difficulty or ease, therefore the shape of concrete sample and chuck are also the keys of test unit.

Stretching creep test need apply tensile load to concrete sample by chuck, first chuck and Specimen Shape should guarantee centering, make the load applying in concrete, produce pure tension, both considered centering how much, while considering concrete formation again because sedimentation causes that the aggregate of test specimen and Density Distribution are along the die trial degree of depth difference of (or claiming specimen thickness), keep physics centering, at least centering as far as possible in the gauge length of reading is surveyed in test, avoids the impact of concrete eccentric tension on test findings; Next is the good usability of chuck, being connected between chuck and test specimen should be well, stable, and chuck is to adverse effects such as test specimen do not damage, chuck should be applicable to the requirement of the wider research contents of creeping in addition, as carry out the early stage creep test of concrete, after form removal, get final product the aspect requirements such as installation test.

Specimen Shape: conventional have-prism of tensile test specimen shape, reamed end prism (dog bone shape), right cylinder and reamed end right cylinder, latter two applies pulling force because chuck is bad, and table and the strainometer (sheet) of inconvenient installation testing distortion, seldom adopt; First two is used more, and this patent also adopts this two kinds of shape test specimens.

Test chuck (also claiming joint): (one) clamp type (seeing accompanying drawing 5-a), Golmerman and Shulnan(1928) adopt the steel bar shape chuck that is threaded groove to clamp test piece end, utilize friction resistance to stretch to test specimen; The damage that has research to adopt reamed end test specimen to be more conducive to strengthen friction resistance and to reduce test specimen termination.The dimension precision requirement of the machining precision of this form chuck to itself and concrete sample termination is higher, to avoid the geometric eccentricity of chuck on the impact of test findings.(2) pre-buried anchoring type (seeing accompanying drawing 5-b), by pre-buried anchor bar, or additional gluing processing is by steel plate and concrete binding, transmit tensile load, the researcher of Australia-Univ Monash adopts the method to carry out the tension test of fiber concrete, but this kind of chuck itself is limited to eccentric corrective action, needs to increase in addition the improvement such as universal joint and adjust eccentric impact.(3) adhesive type (seeing accompanying drawing 5-c), the people such as W.Zheng adopt Strong Adhesive to fetch the effect (title end effect) of avoiding test piece end to keep pure tensile stress state within the scope of specimen equidistance line marking because stressed complexity affects as epoxy resin etc. is connected sheet steel with test piece end, the employing of gluing measure, also can, by two or more test specimen bondings, carry out creep test.But the test that present patent application person carries out shows, the tackifier of home market supply, set time is longer, and cohesive force often can not meet again the design load requirement of creeping that stretches, cause practical operation difficulty, more aobvious outstanding while especially needing to carry out the early stage creep test of concrete.(4) embedded (seeing accompanying drawing 5-d), this chuck form matches with the shape that expands termination, utilize and embed test specimen and expand the transition face of the chuck (embedded chuck) of the termination expansion termination to test specimen intersegmental with test benchmark (being out of shape gauge length section) (transition face generally adopts arcwall face, also have in employing inclined-plane-vertical view is straight line) squeezing action, make the test benchmark section of test specimen produce tension, creep test stretches, the dimension precision requirement of the machining precision of this form chuck to itself and concrete sample termination is higher, nonetheless avoid the effect of eccentric force also limited, axial constraint method adopts this form chuck, because concrete sample is directly poured into a mould, reduce the requirement of some machining precisioies.

Above-mentioned each chuck generally should be again by half ball pivot or universal joint with execute lotus device (pull bar etc.) and be connected, transmit load.

Summary of the invention:

The present invention overcomes the deficiency of prior art, proposes that a kind of apparatus structure is simple, cost is low, easy to operate, mechanical relationship simple, understand, tensile load is constant, can carry out test unit and the method for the differential contraction stress Creep Characteristics research of relative wider range.

Analysis of Concrete Tensile creep test device of the present invention, comprising: support, upper perforation-radial type chuck, lower perforation-radial type chuck, perforation test specimen, deformation gauge and counterweight load (seeing Figure of description 6).Analysis of Concrete Tensile creep test device of the present invention also claims " 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 connect with upper and lower perforation-radial type chuck respectively, and in described perforation test specimen both sides, described deformation gauge is set, described two perforation-radial type chucks that connect with perforation test specimen, hang on respectively on described support, with connect with described counterweight load, form 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 can build by indoor wall, or utilize existing steelframe etc., and suspension hook (approximately 2.5 tons of the loads of single test) is set;

Described perforation-radial type chuck is by steel housing, half ball-joint load connecting link and perforation are hinged with steel pole axle composition (seeing Figure of description 7), described half ball-joint load connecting link deserves to be called perforation-radial type chuck containing perforation-radial type chuck of hook, described half ball-joint load connecting link claims lower perforation-radial type chuck containing perforation-radial type chuck of annulus, on described, contained hook or the annulus of half ball-joint load connecting link in lower perforation-radial type chuck, only that narration is convenient, on non-, the essential distinction of lower perforation-radial type chuck, can arrange according to the requirement of convenient test,

Described steel housing is U-shaped, has segment-shaped hole in crossbeam, and this hole is applicable to forming half ball-joint with half ball-joint load connecting link; On the side rod of both sides, be respectively provided with one can plug-in mounting the hinged circular hole with steel pole axle of perforation;

Described half ball-joint load connecting link is steel round bar, and it is hemispherical that one end is, and is applicable to forming half ball-joint with steel housing; Another end bar head, containing hook or annulus, can hang on described support, and connect with described counterweight load;

Described perforation is hinged is the screw rod standard component that contains nut with steel pole axle, and requiring the part of interting in concrete sample middle sleeve is light circle shape.

Described perforation-radial type chuck technical requirement: each parts of perforation-radial type chuck are steel, effective bearing area must meet test and load requirement, is generally greater than 530mm ²; The U-shaped inside casing size of steel housing must can be placed test specimen, the test specimen that is 100mm × 100mm for the cross section shown in Figure of description 7, the clean long answer>=110mm in each limit of U-shaped housing;

Bore a hole the hinged axis with steel pole axle and half ball-joint load connecting link axis at same plane, different surface errors are less than 0.2mm, it is the coaxial line of steel housing episphere circular hole and half ball-joint load connecting link, with two side perforation circular holes on steel housing and the hinged coaxial line with steel pole axle of perforation, different surface errors are less than 0.2mm; The hinged axis with steel pole axle of boring a hole is vertical with the maintenance of half ball-joint load connecting link axis, vertical angle error≤± 0.5 °, guarantee how much of test specimens in physics centering.

The principle of the physics centering of described test specimen is, in the time that hinge transmits tensile load, if how much of test specimens in and physics centering, tensile load line overlaps with the longitudinal axis face of test specimen, as Figure of description 8a; If the sedimentation during because of moulding makes concrete density and the rigidity of test specimen longitudinal axis face both sides inconsistent, after test specimen tension, there is situation shown in Figure of description 8b, again because being made by low friction resistance and Materials with High Strength at concrete sample middle punch (pore-forming) sleeve pipe, chuck middle punch steel pole axle smooth surface, steel pole axle with perforation sleeve pipe the line of force will be moved, the stretching effect of maintaining the original state that play by the line of force, capable of regulating test specimen recovers state shown in Figure of description 8a, performance physics centering effect.

Described perforation test specimen is concrete prism, or reamed end prism, longitudinal two ends of prism test specimen, or the expansion end, two ends of reamed end prism test specimen is respectively provided with a perforation/through hole, and perforation side, test specimen stage casing is arranged with distortion and surveys and reads gauge length; On the longitudinal axis face of the level of the axis of described perforation test specimen two ends perforation in the time of specimen molding, and vertical with the longitudinal axis;

Two perforation of described perforation test specimen are formed by the rigidity, the low friction resistance sleeve pipe that are arranged on the side form of die trial in the time of specimen molding, available commercially available hard plastic tube or metal tube, the diameter of described sleeve pipe is φ 26mm～φ 32mm, the axis of described perforation is apart from the nearest answer >=50mm of end face distance of perforation test specimen, test specimen middle punch is for the hinged steel pole axle of using of perforation of interspersed described perforation-radial type chuck, make to form between test specimen and chuck hinged, transmit load; Described perforation test specimen outside of sleeve in the time of moulding is preset with spiral reinforcing rod, spiral reinforcing rod adopts the reinforcing bar of φ 4～8mm to make, the dead in line of the center line of the helical ring of described spiral reinforcing rod and described through hole or sleeve pipe, and spiral reinforcing rod contains elbow, described elbow is reinforcement end, is parallel to the bending segment of test specimen transversal section, the tensile load transmitting between hinged the perforation of the chuck perforation with steel pole axle and test specimen is evenly passed to test specimen tension side;

Described distortion is surveyed and is read gauge length two pairs of pre-buried gauge head built-in fittings when boring a hole specimen molding and form, described gauge head built-in fitting is by detachable installation in the time of specimen molding, be connected on the side form of moulding die trial, after form removal, be embedded in the gauge head built-in fitting in test specimen, gauge head built-in fitting is used for installing distortion instrumentation and reads distortion, calculates strain; In " Figure of description 7 ", gauge head shown in 9 is that test piece deformation is surveyed a read apparatus part, comprise built-in fitting and fixture, made by copper material, when specimen molding, gauge head built-in fitting is screwed onto the inner side of side form, after concrete formation, embed in the concrete of test specimen, mounting fixing parts when creep test, and the formation such as deformation gauge surveys the whole test piece deformation of reading distortion and survey read apparatus, carries out test piece deformation and surveys and read; Described distortion is surveyed and is read gauge length between two perforation of perforation test specimen, on test specimen horizontal longitudinal axis face in the time of moulding, require spacing the l ' >=0.8a+1/2d of gauge head and perforation central shaft, wherein: a is the test specimen xsect length of side, d is casing diameter, gauge length L >=120mm, it is square that the xsect of reading gauge length place is surveyed in the distortion of described perforation test specimen, the length of side is >=the conventional sample dimensions of 100mm.

Described deformation gauge is read test test piece deformation for surveying, and calculates strain, can adopt other general distortion such as clock gauge, displacement transducer and strainometer device of extending;

Described counterweight load forms by connecting steel cable, frame dish and counterweight, sees " Figure of description 6 ", also can steel cable, the composition such as water and water tank, and requirement is the required load of load test accurately.

Concrete shrinkage stress creep test method of the present invention, comprise: according to standard creep chamber and two kinds of environmental baselines of physical environment, two kinds of restraint conditions of complete and non-complete lattice constraint rigidity, adopt " step loading " and " covariant loading " two kinds of load modes, and collapse threshold and the fixing length of time two kinds of Loading Control conditions, test the test method that concrete shrinkage stress is crept, carry out the method for concrete shrinkage stress creep test.Test is surveyed and is read each Under Concrete distortion, and calculate concrete shrinkage stress by the fundamental relation of formula (1) (principle) and creep,

ε _c=ε _TCT-ε _sh-ε _e （1）

In formula: ε _cthe differential contraction stress of-concrete (test specimen) is crept;

ε _tCTin-test, the overall strain that the duration of at different levels loading, concrete sample occurs, is called for short overall strain, when test, can directly survey and read by the deformation gauge from " Analysis of Concrete Tensile creep test device ";

ε _sh-concrete contraction strain, is surveyed and is read by " concrete confined expansion and the contraction measuring instrument " that adopt in auxiliary shrinkage test, because contraction strain is negative value, when calculating, should change on the occasion of;

ε _ewhen-corresponding differential contraction stress adds load, the elastic strain that test specimen occurs, is surveyed and is read or calculate by " Analysis of Concrete Tensile creep test device " or the test of auxiliary Analysis of Concrete Tensile in test.

Described fundamental relation (principle) is for concrete in structure is because of the deform relation of elastic deformation (strain) under (strain, the i.e. overall strain of mark of the present invention) and drawdown deformation (strain), differential contraction stress, differential contraction stress time deformation (creeping) of differential contraction stress.The present invention be reduced in test every grade of load from loading duration, the relation that under the overall strain of concrete sample and contraction strain, differential contraction stress, elastic strain, differential contraction stress are crept.

Described auxiliary shrinkage test, for surveying the test of reading the cubic deformation (using strain as index) that concrete occurs when unfettered, adopt Appendix B in " cement expansive material " GB23439-2009 " mixing concrete limited expansion rate and the shrinkage test method of swelling agent ", or " Standard for test methods of longterm performance and durability of ordinary concrete standard " GB/T50082-2009 test method is carried out; Described cubic deformation (strain) comprises drying shrinkage, chemical shrinkage, self-constriction etc., expands with heat and contract with cold for also comprising under physical environment, and the present invention is referred to as contraction strain;

Described auxiliary Analysis of Concrete Tensile is tested and is comprised the tension test that obtains concrete elastic distortion, and presses experimental formula by methods such as pressurized elasticity modulus tests, in acquisition and differential contraction stress creep test, loads corresponding concrete elastic strain.

Based on formula (1) relation, creep for the standard concrete shrinkage stress in chamber and physical environment, complete and non-complete lattice constraint rigidity situation of creeping, " the present invention " research and design with " step loading " and " covariant loading " two kinds of load modes, collapse threshold and the fixing length of time two kinds of controlled conditions carry out concrete shrinkage stress creep test.Each concrete test method is as follows:

1. the standard chamber condition step loading-concrete shrinkage stress creep test method of creeping

The described standard chamber condition of creeping meets concrete shrinkage in " Standard for test methods of longterm performance and durability of ordinary concrete standard " GB/T50082-2009 and tests desired temperature and humidity conditions, or " concrete for hydraulic structure testing regulations " DL/T5150-2001 specified standard chamber condition of creeping, when the selected wherein a kind of condition of test, should note the difference of humiture, and impact on the result of creeping.

Described step loads, i.e. " step load stretching creep test method ", by drawdown deformation threshold value and the fixing length of time two kinds of loading environments carry out concrete shrinkage stress creep test, because the creep curve of PRELIMINARY RESULTS of gained concrete shrinkage stress is micro-level and changes continuously, therefore claim " step load stretching creep test method ".

Described drawdown deformation threshold value is the clean strain (ε that in test, the shrinkage and creep of test specimen causes _{t, i}=-ε _{sh, i}-ε _c,i) reach threshold value (T _h) time the condition that loads, work as ε _{t, i}>=T _hin time, loads, and calculates heap(ed) capacity (P at different levels _i) and load heap(ed) capacity (P _i) press column count:

P _i=k _i·A·E _t,i·(-ε _sh,i-1-ε _c,i-1) i=1、2、3…n… （2）

In formula: P _i-i level loaded value, kN, is scaled kg conventionally;

A-test specimen lifting surface area, mm ²;

E _t,ithe Analysis of Concrete Tensile elastic modulus in corresponding length of time when-i level loads, GPa, the elastic modulus of surveying when desirable interpolation tensile load, or the auxiliary Analysis of Concrete Tensile test elastic modulus of surveying;

K _i-i level loads correction factor, recommends k _ibe 1.05～1.60, the standard room environmental of creeping, should get k _i=1.4, physical environment, should get k _i=1.2;

ε _{c, i-1}the creeping duration of-i-1 level load, μ ε;

ε _{sh, i-1}(i-1 level is loaded on before the loading of i level) contraction strain duration of-i-1 level load, μ ε, because drawdown deformation is negative value, therefore add "-".

Described loading correction factor (k _i), be to consider, the length of time, the relative initial stage elastic modulus of Analysis of Concrete Tensile elastic modulus had 50～100% growth during 1～28d, and early stage growth comparatively fast; Secondly, i level is to i+1 level loading duration, the clean strain (ε causing with concrete shrinkage and creep _{t, i}) will continue to increase, differential contraction stress increases; In physical environment there is heat expansion and bulking possibility in concrete on the other hand, therefore choose above-mentioned k _ivalue;

The duration of described i-1 level load, (i-1 level is loaded on before the loading of i level) contraction strain, by the test specimen free shrink distortion (strain) of mixing concrete for making simultaneously of same match ratio, can be surveyed and be read by " concrete confined expansion and contraction measuring instrument ".

The sequence number that when i is test in described each symbol, loadings at different levels and survey are read, i=1,2,3 ... n ...

During described i level loads, the first loaded value (P in the time of i=1 ₁), its calculate value be, E _{t, 1}the Analysis of Concrete Tensile elastic modulus in corresponding length of time when-1 grade of loading, the desirable auxiliary Analysis of Concrete Tensile test elastic modulus of surveying, ε _{sh, 0}concrete free shrink distortion (strain) when-1 grade of load age, ε _{c, 0}when-1 grade of load age, concrete shrinkage stress is crept, E _{t, 1}, ε _{sh, 0}and ε _{c, 0}value is taken from existing data or data, obtains P ₁, kN; Concrete calculating value can be referring to " 6.2.1 loading " related content of " 6. embodiment " in " embodiment ";

Described threshold value (T _h), be set as T _h=5 μ ε, it is the accuracy requirement according to meeting deformation gauge (clock gauge etc.) that this value is set, and meets again period of change and the corresponding heap(ed) capacity thereof of volume change of concrete and differential contraction stress time deformation, and tests the factors such as facility and determine;

The described fixing length of time, by being the length of time 1d, 2d, 3d, 5d, 7d, 14d, 21d, 28d ..., calculate heap(ed) capacities at different levels (P ' _i) and load, survey and read distortion (strain), measuring and calculating concrete creep (ε _c,i);

After loadings at different levels, survey and read distortion (strain), comprising: contraction strain (ε _shi), elastic strain (ε _e,i), clean strain (ε _t,i) and overall strain (ε _{tCT, i}), measuring and calculating concrete creep (ε _c,i);

The sequence number that when i is test in above-mentioned each symbol, loadings at different levels and survey are read, i=1,2,3 ... n ...

2. consider the situation of structural constraint stiffness effect

The situation of described consideration structural constraint stiffness effect, is, for structure, the difference constraint rigidity of concrete shrinkage is produced to different differential contraction stresses, and the different differential contraction stress of the corresponding generation problem of creeping, and the test of carrying out.

Calculate loaded value (P according to restraint condition _i' '), and load described P _i' ' press formula (3) calculate:

P _i''=k _i·R·A·E _t,i·(-ε _sh,i-1-ε _c,i-1) （3）

In formula: R-structure is to concrete constraint factor;

All the other symbols are the same.

After loading, survey and read distortion (strain), the Analysis of Concrete Tensile that calculates the loadings at different levels of considering constraint factor (R) situation (ε that creeps _{c-c, i}); Can by drawdown deformation threshold value and the fixing length of time two kinds of modes.

3. natural environmental condition concrete shrinkage stress creep test method

Described natural environmental condition concrete shrinkage stress creep test method, under natural environmental condition (natur entironment), the problem that the differential contraction stress occurring for concrete in structure is crept, and the test of carrying out;

Natural environmental condition test method, is characterized in that: by creep test and test specimen, and shrink (cubic deformation) test specimen be placed in environmental baseline and test, by distortion threshold value (set | ε _{t, i}|>=T _h) and the fixing length of time two kinds of modes, and consider two kinds of situations of complete and non-complete lattice constraint rigidity, add step by step (subtracting) and carry, survey and read self to collapse distortion/strain (ε _{e, sh, i}), elastic strain (ε _{e, e, i}), clean strain (ε _{e, t, i}) and overall strain (ε _{e, TCT, i}), test concrete creep (ε _{e, c, i});

Described setting | ε _{t, i}| be to consider in physical environment concrete because of temperature rise and drench with rain (or air humidity increase), cause and self collapse distortion/strain (ε _{e, sh, i}) be swell value; Described adding (subtracting) carry in an off-load be while expanding because heating up/drenching with rain for concrete in structure, differential contraction stress reduces corresponding off-load;

Described survey reads self to collapse distortion/strain (ε _{e, sh, i}) be distortion test specimen to be placed in to physical environment be out of shape, measuring instrument is placed in the standard room environmental of creeping, and gets to be placed in physical environment test specimen to the standard room environmental of creeping and to survey and read self to collapse distortion/strain (ε _{e, shi}), require to complete in 3～5min, requirement is read in the survey that completes distortion in described 3～5min, according to the results of study such as Jiang Jianhua [Jiang Jianhua, Yuan Yingshu, Zhang Ximei. in the temperature action spectrum of natural climate environment and concrete, [J] estimated in temperature-responsive. Central South University's journal, 2010,41 (5): 1923-1930] in, about concrete, the result of study of the corresponding and temperature distributing rule to environment temperature designs, and this requirement can meet self collapsing distortion/strain (ε _{e, shi}) survey read result accuracy requirement.Described distortion test specimen and measuring instrument are that the present invention adopts the test specimen, concrete confined expansion and the contraction measuring instrument that in GB23439-2009 " cement expansive material ", carry out concrete confined expansion test, while making test specimen, must substitute " longitudinally limiter " in test specimen with gauge head, and the installation of gauge head should meet the range finding requirement of GB23439; Elastic strain (ε is read in described survey _{e, e, i}), clean strain (ε _{e, t, i}) and overall strain (ε _{e, TCT, i}), and calculate concrete creep (ε _{e, c, i}) with aforementioned.

4. covariant loading-concrete shrinkage stress creep test method

Described covariant loads, and refers to that it is zero (ε that test keeps the overall strain in specimen equidistance line marking under complete deflection constraint _{tCT, i}=0).Work as ε _{tCT, i}≠ 0 o'clock, require to keep ε by adjusting counterweight (tensile load) _{tCT, i}=0, be therefore called " covariant loading ".

The standard room environmental of creeping, in the time not adjusting load (not adding load), dry shrinage and slow change is time-varying function, conventionally ε _{tCT, i}< 0, loads to keep ε by continuation _{tCT, i}=0.

For physical environment, in the time not adjusting load, volume change of concrete (or self collapses distortion-strain) and to creep be time-varying function, may ε when dry shrinkage and cold shrinkage _{tCT, i}< 0, also may ε while expansion if bulking occurs and heat up _{tCT, i}> 0, the corresponding increasing of load (counterweight), or reduce.

Completely differential contraction stress (the ε that creeps under covariant load condition under deflection constraint _{c, c, i}) calculate, because of ε _{tCT, i}=0, record ε _{, c, sh.i}and ε ' _{c, e, i}after, can calculate ε with reference to formula (1) _{c, c, i}.

The covariant of described other constraint degrees (R ≠ 1, conventionally R < 1) loads, because of ε _{c, TCT, i}≠ 0, must calculate the i level period in the length of time (loading of i level) strain (ε ' _{c, TCT, i}) for the controlling value of the test piece deformation of creeping, work as ε _{tCT, i}≠ ε ' _{c, TCT, i}time, adjust counterweight (tensile load); Described ε ' _{c, TCT, i}be calculated as follows:

ε' _C,TCT,i=ε _c,sh,i+ε' _C,c,i+ε' _C,e,i （4）

In formula, ε ' _{c, TCT, i}, ε _{, c, sh.i}, ε ' _{c, c, i}and ε ' _{c, e, i}be respectively under other constraint degrees (non-complete deflection constraint), the overall strain of test specimen, concrete shrinkage strain, differential contraction stress are crept and are loaded the elastic strain of generation.

Described ε _c.sh.ifor test measured value;

Described ε ' _{c, c, i}for the desired value of test, but in this case again need be with ε ' _{c, c, i}calculate controlling test value and test, the present invention recommends to press ε ' _{c, c, i-1}calculate by linear epitaxy, or the ε that time actual measurement obtains according to R=1 _{c, i,}press ε ' _{c, c, i}=R ε _c,icalculate, then level is tested gained ε ' ' therewith _{c, c, i}relatively, if the two relative error in 15%, creep (ε ' _{c, c, i}) can make test findings; Relative error exceedes 15%,, in i+1 level with ε ' ' _{c, c,i}again matching ε ' _{c, TCT, i+1}, creeping after adjusting for several times (ε ' ' _{c, c, i}) result precision will obtain raising; ε ' _{c, e, i}for test measured value, but in " covariant loadings " mode, each heap(ed) capacity is less, directly surveys and reads comparatively difficulty, and this patent recommends to press loading value (P ' ' ' _c,i) and actual measurement bullet mould (E _i) calculating elastic strain (ε ' _{c, e, i}).

Loading value that the covariant of other constraint degrees loads (P ' ' ' _c,i) be:

P _c'' _,' _i=k _i·R·A·E _c,t,i·(-ε _c,sh,i-1-ε _C,c,i-1) （5）

In formula, R and A are with aforementioned; E _{c, t, i}analysis of Concrete Tensile elastic modulus when-i level loads; ε _{c, sh.i-1}concrete shrinkage strain duration of-i-1 level load; ε _{c, c.i-1}the concrete creep duration of-i-1 level load.

ε under the covariant load condition of other constraint degrees _{c, c, i}measuring and calculating, with the ε ' of aforementioned estimation _{c, c, i}the ε ' ' recording with test _{c, c, i}as a result of (ε of the mean value of the two _{c, c, i}), wherein ε ' ' _{c, c, i}be calculated as follows:

ε'' _C,c,i=ε'' _C,TCT,i-ε _sh,i-ε' _C,e,i （6）

In formula, ε ' ' _{c, TCT, i}-test actual measurement overall strain; ε _{c, sh.i}and ε ' _{c, e, i}ditto.

Physical environment situation, notes ε _{c, e, sh.i}difference, also may ε ' while expansion if bulking occurs and heat up _{c, TCT, i}> ε _{c, TCT, i}, load (counterweight) should reduce.

In the manner described above, step and (6) formula, also can obtain the differential contraction stress (ε that creeps _{c, e, c, i}).

The present invention adopts " perforation-radial type chuck " and " test specimen perforation " design, carries out differential contraction stress creep test.The entire combination of chuck is different from existing chuck form and power transmission, centering method, has: 1. connect firmly, stable, applicant's the past research and test show, this is linked at when concrete limit stretching destroys and also can not destroys; 2. be applicable to how much in and instrumentality reason centering (the stretching bias of avoiding concrete non-uniform settling to cause), on the one hand, adopt the hinged and hemisphere hinge technologies composite design of boring a hole, solve the centering problem under Analysis of Concrete Tensile load, especially aspect a physics centering difficult problem of avoiding causing because of concrete sedimentation unevenness, there is unique advantage, on the other hand, test specimen middle punch and detect the positioning relation of gauge length, guarantee how much in and the pure tension state of concrete in test benchmark section; 3. be applicable to the differential contraction stress creep test beginning the length of time from early, after test specimen 1d form removal, can carry out; The feature such as 4. test specimen perforated material friction resistance is little.

The feature of concrete shrinkage stress creep test method of the present invention is: relatively traditional stretching creep test method, directly carry out concrete shrinkage stress creep test, and leash law is more suitable for testing under physical environment to axial.Test method of the present invention, reads the strain during loads at different levels and creeps because loading step by step, surveying, and can study how concrete behavior and the performance issue of creeping.Device simply, easily go.

Accompanying drawing explanation

Accompanying drawing 1a is the stretching creep test device that China act.std DL/T5150-2001 and SL352-2006 " concrete for hydraulic structure testing regulations " adopt;

Accompanying drawing 1b be the Yang Yang of Zhejiang Polytechnical University within 2009, be published in concrete creep test unit on silicate journal [Yang Yang, Xu Sifa, Ye Deyan, etc. Early-age high strength concrete stretching Creep Characteristics [J] .2009,37 (7): 1124-1129];

Accompanying drawing 2 is TSTM method (axial constraint method) test unit

Accompanying drawing 3 is existing lever-counterweight method Analysis of Concrete Tensile creep test device

Accompanying drawing 4 is existing hydraulic concrete stretching creep test device

Accompanying drawing 5a is the structural representation of clamp type chuck in prior art;

Accompanying drawing 5b is the structural representation of pre-buried anchoring type chuck in prior art;

Accompanying drawing 5c is the structural representation of adhesive type chuck in prior art;

Accompanying drawing 5d is the structural representation of embedded chuck in prior art;

Accompanying drawing 6 is Analysis of Concrete Tensile creep test apparatus structure schematic diagram of the present invention;

Accompanying drawing 7 is the overall formation schematic diagram of chuck and test specimen in accompanying drawing 6;

Accompanying drawing 8a, accompanying drawing 8b are the physics centering principle schematic of bore a hole-articulation of the present invention to test specimen;

Accompanying drawing 9a is surveyed the C30 concrete standard chamber contraction strain curve of creeping by embodiment;

Accompanying drawing 9b is loaded instantaneous (elasticity) strain curve by embodiment surveys the C30 concrete standard chamber of creeping;

Accompanying drawing 9c is surveyed the C30 concrete standard chamber differential contraction stress curve of creeping of creeping by embodiment;

Accompanying drawing 10a is surveyed contraction strain curve under C30 Concrete in Natural environment by embodiment;

Accompanying drawing 10b is loaded instantaneous (elasticity) strain curve under C30 Concrete in Natural environment by embodiment surveys;

Accompanying drawing 10c is surveyed under C30 Concrete in Natural environment the differential contraction stress curve of creeping by embodiment;

In accompanying drawing:

Accompanying drawing 1a, accompanying drawing 1b are all " steelframe-spring energized method " concrete creep test unit.

In accompanying drawing 6, " Analysis of Concrete Tensile creep test device " is made up of upper perforation-radial type chuck, lower perforation-radial type chuck, perforation test specimen and counterweight load.Upper and lower chuck is used for transmitting tensile load, guarantees that the test gauge length scope of concrete sample is in axial tension state; Test specimen is by made by inspection (test) concrete; Configuration load can be used Hanging Basket and counterweight or other metering weight compositions.In figure: the upper perforation-radial type of 1-chuck, perforation-radial type chuck under 2-, the 3-test specimen of boring a hole, 12-counterweight load.

In accompanying drawing 7, the hinged relative position with steel pole axle, half ball-joint load connecting link and steel housing shows to bore a hole; The formation of diagram " perforation test specimen ", sleeve pipe and spiral are strengthened the position of arrangement of reinforcement.In figure: the upper perforation-radial type of 1-chuck, perforation-radial type chuck under 2-, the 3-test specimen of boring a hole, in the upper perforation-radial type of 4-chuck containing the hemisphere bar that is articulated and connected of hook, be connected 5-half ball-joint, the 6-hinged steel pole axle of using of boring a hole with support, the perforation that 7-test specimen middle sleeve forms, 8-spiral reinforcing rod, the pre-buried gauge head of 9-, 10-deformation gauge (copper rod and gauge head), under 11-in perforation-radial type chuck containing the hemisphere of the annulus bar that is articulated and connected, be connected with counterweight load.

In accompanying drawing 8, perforation-articulation to the physics centering principle of test specimen is, in the time that hinge transmits tensile load, if how much of test specimens in and physics centering, tensile load line overlaps with the longitudinal axis face of test specimen, as accompanying drawing 8a, if the sedimentation during because of moulding makes concrete density and the rigidity of test specimen longitudinal axis face both sides inconsistent, after test specimen tension, there will be situation shown in accompanying drawing 8b, when situation shown in accompanying drawing 8b occurs, hinged between test specimen of perforation-radial type chuck of the present invention and perforation will play the effect of physics centering, because concrete sample middle punch (pore-forming) sleeve pipe is made up of low friction resistance and Materials with High Strength, chuck middle punch steel pole axle smooth surface, steel pole axle can roll in perforation sleeve pipe, steel pole axle can be moved automatically with the touch line of perforation sleeve pipe, make to stretch and be subject to the line of force to recover state shown in accompanying drawing 8a, play physics centering effect.

Embodiment

Utilize Analysis of Concrete Tensile creep test device of the present invention to carry out the concrete enforcement of concrete shrinkage stress creep test method, comprise: determine concrete research method, set up testing laboratory and place, prepare test unit and install according to the object of concrete research and engineering detecting, test by test method and corresponding steps, obtain the key steps such as differential contraction stress creep test result.

Test method of the present invention comprises for the standard test method that concrete shrinkage stress is crept in chamber and physical environment, complete and non-complete lattice constraint rigidity situation of creeping, can " step loading " and " covariant loading " load mode, collapse threshold and fix two kinds of controlled conditions and carry out differential contraction stress creep test, the described object according to concrete research and engineering detecting is determined concrete research method, by experimental study and engineering detecting object and content, test accuracy requires and condition, determines test concrete grammar;

Described testing laboratory and the place set up, carrying out concrete shrinkage stress creep test needs the standard chamber of creeping, and this testing laboratory need meet testing requirements except place size, and its humiture should meet the regulation of the standard schedule such as GB/T50082-2009 or DL/T5150-2001; Test under natural environmental condition is also tackled place size and is made requirement, also answer if desired binding and testing goal determine physical environment place and season weather;

The described test unit of preparing is also installed, because of the unconventional test tool of main device of test, must prepare satisfactory chuck and test specimen die trial, build and be applicable to hanging " suspension-counter weight type stretching creep test device " simple beam, or at roof truss and existing steel bracket, (approximately 2 tons of the loads of single test) such as suspension hooks is set; The utensil of the auxiliary test such as contraction strain and elastic modulus also needs corresponding preparation;

Described test procedure comprises: test specimen making, creep test device and test specimen are installed, test deformation data is surveyed and read and test findings (creeping under concrete shrinkage stress) analytical calculation.

Described test specimen is made: first, by the concrete match ratio of research, make totally three kinds of concrete creep test specimen, cubic deformation (contractions) test specimen and elastic modulus test specimens, wherein, the test specimen of creeping is read the data such as time deformation for apparatus of the present invention survey simultaneously; Cubic deformation (contraction) test specimen is by " mixing concrete limited expansion rate and the shrinkage test method of swelling agent " listed requirement of Appendix B in " cement expansive material " GB23439-2009, or the making of volume change of concrete (non-loaded deformation) test method is read in " Standard for test methods of longterm performance and durability of ordinary concrete standard " GB/T50082-2009 test survey; Elastic modulus test specimen is that concrete sample complementary testing test specimen is at need read in the inventive method survey, makes by stretching test method.Various test specimens are placed in the environment that experimental study content requires, and maintenance is to stipulating the length of time, testing data; The test specimen of various tests is three one group, and special circumstances need meet correlation standard.

Attention: 1. note the direction of power transmission crotch in spiral reinforcing rod while preparing the perforation test specimen of creeping, guarantee the transmission of load.If 2. concrete shrinkage deformation (strain) test adopts concrete confined expansion and the contraction measuring instrument of GB23439-2009 " cement expansive material " to carry out, must substitute " longitudinally limiter " in test specimen with gauge head, the installation of gauge head should meet the range finding requirement of GB23439.

Described creep test device and test specimen are installed: test piece maintenance, to stipulating the length of time, is installed by " Figure of description 6 ", start differential contraction stress creep test (because concrete shrinkage stress in structure produces after concrete hardening, starting when General Requirements 1d).

Described test deformation data is surveyed and is read: creep test piece deformation and cubic deformation (drawdown deformation) are generally surveyed and read by clock gauge (or other displacement transducers, or strainometer).

The test piece deformation of creeping is read by the clock gauge survey being installed between " Figure of description 6 " middle gauge head and copper rod, calculates strain by specimen equidistance line marking.Can survey read data comprises: clean strain (ε _t,i), elastic strain (ε _e,i) and overall strain (ε _{tCT, i}), and the ε of creep test under different constraint degree _{c, t, i}, ε _{c, e, i}and ε _{c, TCT, i}, the ε of creep test under physical environment _{e, t, i}, ε _{e, e, i}and ε _{e, TCT, i}deng.

The distortion (contraction strain) of cubic deformation test specimen, by Appendix B in " cement expansive material " GB23439-2009 " mixing concrete limited expansion rate and the shrinkage test method of swelling agent ", or " Standard for test methods of longterm performance and durability of ordinary concrete standard " GB/T50082-2009 test method survey read calculate, can survey read data and comprise: contraction strain (ε _{sh, i}), the contraction strain ε of creep test under different constraint degrees _{c, sh, i}, the contraction strain ε of creep test under physical environment _{e, sh, i}deng.

The elastic modulus of elastic modulus test specimen is pressed stretching test method test measuring and calculating.

The measuring and calculating step of each condition and the strain of mode gained and the data of creeping is as follows:

Test general steps is to load P from test beginning (i=1) ₁, record clean strain (ε _{t, 1}), elastic strain (ε _{e, 1}), overall strain (ε _{tCT, 1}), and contraction strain (ε _{sh, 1}), calculate ε _{c, 1}; After this successively load P _i, survey and read clean strain (ε respectively _t,i), elastic strain (ε _e,i), overall strain (ε _{tCT, i}), and contraction strain (ε _{sh, i}), calculate ε _{c, i}, i=2,3,4 ... n ...

The testing procedure of the test method that each condition and mode form is as follows:

1. the standard chamber condition step loading-concrete shrinkage stress creep test of creeping

1.1 drawdown deformation threshold methods

When i=1, load P ₁, survey and read contraction strain (ε _{sh, 1}), elastic strain (ε _{e, 1}), clean strain (ε _{t, 1}) and overall strain (ε _{tCT, 1}), work as ε _{t, 1}>=T _h(T _h=5 μ ε), measuring and calculating concrete creep (ε _{c, 1}), and start the test of i=2 level;

Work as ε _{t, i}>=T _h, i.e. i=2,3,4 ... n ... time, calculate and load P by formula (2) _i, survey and read contraction strain (ε _{sh, i}), elastic strain (ε _e,i), clean strain (ε _t,i) and overall strain (ε _{tCT, i}), measuring and calculating concrete creep (ε _c,i), ε _c,ibe calculated as follows:

ε _c,i=ε _TCT,i-ε _sh,i-ε _e,i （7）

In formula: ε _c,ithe duration of-i level load, the stretching of test specimen is crept;

ε _{tCT, i}the duration of-i level load, the overall strain of test specimen of creeping that stretches, surveys and reads from perforation test specimen;

ε _{sh, i}the duration of-i level load, with the simultaneously test specimen free shrink distortion (strain) of mixing concrete for making of match ratio, can survey and read by " concrete confined expansion and contraction measuring instrument ", because contraction strain is negative value, when calculating, should change on the occasion of;

ε _e,ithe elastic strain that-i level loading specimen occurs, can directly be surveyed and read by creep test or assistant spring test.

Or, ε _c,i=ε _t,i-ε _{sh, i}(8)

In formula: ε _t,ithe duration of-i level load, the clean strain of test specimen of creeping that stretches, is directly surveyed and reads by creep test;

ε _c,i, ε _sh.i-the same.

1.2 fix method in the length of time

By being the length of time 1d, 2d, 3d, 5d, 7d, 14d, 21d, 28d ..., calculate heap(ed) capacity (P at different levels by formula (2) _i) and load, survey and read contraction strain (ε _{sh, i}), elastic strain (ε _e,i), clean strain (ε _t,i) and overall strain (ε _{tCT, i}), by formula (7) or formula (8) measuring and calculating concrete creep (ε _c,i).

2. consider the situation of structural constraint stiffness effect

When i=1, by formula (3) calculate heap(ed) capacity (P ' ' ₁) and load, survey and read and calculate each strain and creep.

2.1 drawdown deformation threshold methods

Work as ε _{t, i}>=T _h(T _h=5 μ ε), i.e. i=2,3,4 ... n ... time, load P ' ' _i, P ' ' _ipress formula (3) and calculate, survey and read contraction strain (ε _{c, sh.i}), elastic strain (ε _{c, e, i}), clean strain (ε _{c, t, i}) and overall strain (ε _{c, TCT, i}), measuring and calculating concrete creep (ε _{c, c, i}), creep and be calculated as follows:

ε _C,c,i=ε _C,t,i-ε _C,sh,i （9）

In formula: ε _{c, c, i}-consider the i level loading duration of constraint factor (R) situation, Analysis of Concrete Tensile creep (strain);

ε _{c, t, i}the clean strain of test specimen of creeping that the stretches of-i level loading duration of considering constraint factor (R) situation, can directly be surveyed and read by stretching creep test;

ε _{c, sh.i}-consider that the i level loading duration test specimen of constraint factor (R) situation shrinks strain, can survey and read by " concrete confined expansion and contraction measuring instrument ", because contraction strain is negative value, when calculating, should change on the occasion of.

2.2 fix mode in the length of time

By being the length of time 1d, 2d, 3d, 5d, 7d, 14d, 21d, 28d ..., by formula (3) calculate heap(ed) capacities at different levels (P ' ' _i) and load, survey and read distortion (strain), by formula (7) or formula (8) measuring and calculating concrete creep (ε _{c, c, i}).

3. natural environmental condition step loading-concrete shrinkage stress creep test

3.1 drawdown deformation threshold methods

When i=1, load P _{e, 1}, survey and read and calculate each strain and creep.

When | ε _{e, t, i}|>=T _h(T _h=5 μ ε), i.e. i=2,3,4 ... n ... time, add (subtracting) and carry P _e,i, survey and read contraction strain (ε _{e, shi}), elastic strain (ε _{e, e, i}), clean strain (ε _{e, t, i}) and overall strain (ε _{e, TCT, i}), measuring and calculating concrete creep (ε _c,i).

(subtracting) carrying capacity (P of described at different levels adding _e,i) calculating press formula (2);

Concrete creep (ε _{e, c, i}) calculating with (7) formula and (8) formula.

Note the symbol difference that expands and shrink.

3.2 fix method in the length of time

By being the length of time 1d, 2d, 3d, 5d, 7d, 14d, 21d, 28d ..., calculate at different levels adding (subtracting) carrying capacity (P _e,i) and add (subtracting) year, survey and read distortion (strain), measuring and calculating concrete creep (ε _{e, c, i}).

4. covariant loading-concrete shrinkage stress creep test

4.1 complete deflection constraint methods

Completely under deflection constraint, because keeping ε _{tCT, i}=0, work as ε _{tCT, i}≠ 0 o'clock, adjust load, record ε _{, c, sh.i}and ε ' _{c, e, i}after can calculate ε _{c, c, i},, formula is with (6) formula, and the standard chamber of creeping is identical with physical environment situation, notices that the latter understands off-load.

The method of 4.2 other constraint degrees (R ≠ 1)

When i=1, load P ' ' ' _{c, 1}, survey and read and calculate each strain and creep.Described P ' ' ' _{c, 1}=R × P ₁;

I level load reckoning overall strain (ε ' _{c, TCT, i}) calculate by (4) formula;

ε ' _{c, c, i}, by ε ' _{c, c, i}=R ε _c,iestimation;

Loading value (P ' ' ' _c,i), calculate by (5) formula, record ε ' ' _{c, TCT, i}, ε ' ' _{, c, sh.i}and ε ' ' _{c, e, i}, calculate ε ' ' by (6) formula _{c, c, i};

With ε ' _{c, c, i}and ε ' ' _{c, c, i}mean value as ε _{c, e, i}.

Check ε ' _{c, c, i}and ε ' ' _{c, c, i}between error, the two relative error is in 15%, (ε creeps _{c, c, i}) can make test findings; Relative error exceedes 15%,, in i+1 level with ε ' ' _{c, c, i}again matching ε ' _{c, TCT, i+1}, (the ε that creeps after adjusting for several times _{c, c, i}) result precision will obtain raising.

Physical environment situation, notes ε _{c, e, sh.i}difference, also may ε ' while expansion if bulking occurs and heat up _{c, TCT, i}> ε _{c, TCT, i}, load (counterweight) should reduce.With reference to above-mentioned steps and the formula (ε that also can be crept _{c, e, c, i}).

5. the analytical calculation of concrete shrinkage stress creep test result

Record the differential contraction stress corresponding with studying (detection) object (ε that creeps according to above-mentioned test method _c,i, ε _{e, c,i}and ε _{c, c, i}deng), be calculated as follows the accumulative total differential contraction stress that can the obtain concrete each length of time (ε that creeps _t):

${\mathrm{\&epsiv;}}_T=\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{\mathrm{\&epsiv;}}_{c,i}---\left(10\right)$

In formula: ε _t-for before the loading of i=1 to i=n level, (be T the corresponding length of time _n), n=1,2,3 ..., the accumulative total that test specimen occurs is crept, and can be that standard is crept under the condition of chamber and crept, and also under physical environment, creeps; Can be to creep under complete rigidity, also under other constraint degrees, creep; Can be creeping of threshold value loading method, also fix creeping of loading method in the length of time etc.;

ε _c,i-the same, also ε _{e, c, i}and ε _{c, c, i}deng.

According to ε _tand T _nas a result, can draw ε _t-T curve (concrete shrinkage stress relation curve in the creep-length of time).

According to ε _t, ε _c,i, ε _{e, c, i}and ε _{c, c, i}deng also can calculating other parameters that concrete shrinkage stress is crept, or research concrete shrinkage stress creep mechanism and behavior.

6. embodiment

Adopt suspension-counter weight type Analysis of Concrete Tensile creep test device and concrete shrinkage stress creep test method, in conjunction with the C30 concrete of high-speed railway construction section road bed board construction, carry out concrete shrinkage stress creep test, be respectively 0.9,0.8,0.7,0.3 differential contraction stress and creep with creep chamber condition, constraint factor of drawdown deformation threshold method testing standard; Test concrete shrinkage stress under physical environment and creep to fix length of time mode.

Concrete main raw material(s) has PO42.5R cement, river sand, rubble, polycarboxylate high performance water-reducing agent, II level flyash, S95 slag powders and tap water etc., and concrete match ratio is such as table 1,

Table 1 concrete mix kg/m ³

Numbering	Water	Cement	Flyash	Breeze	Coarse aggregate	Fine aggregate	Water reducer
								WG	121	291	75	52	1181	734	2.89

6.1 prepare test specimen

By match ratio mixing concrete, the test specimen of 2 number of columns of preparation table.

The various test specimen production quantities of table 2

6.2 test

After test specimen standard curing 1d, at standard creep chamber and natural environmental condition installation test device, start test, survey read data and load after survey read data.

6.2.1 load

(1) primary load: primary load is pressed formula (2) and calculated, A, E in formula _{t, 0}, ε _{sh, 0}and ε _{c, 0}by sample dimensions and the existing data value of C30 concrete, the cross sectional dimensions 100mm × 100mm of specimen equidistance line marking place of the present embodiment, A=100mm × 100mm, E _{t, 0}, ε _{sh, 0}and ε _{c, 0}existing data and data in data be respectively, concrete 1d values of shrinkage strain 70～400 μ ε, the differential contraction stress value of creeping 40～350 μ ε [be equivalent to the stress coefficient of relaxation 57%～86%(that creeps and get 72%)], the early stage elastic modulus 12.0～25.0GPa of concrete, after value, approximate treatment obtains P ₁=1.4 × 100mm × 100mm × 20.0GPa × (1-0.72) × 100 μ ε=7840N, rounds and is scaled kg unit, P ₁≈ 800kg, drawing stress that this load is executed, also lower than early-age concrete 1～2MPa tensile strength, is 45～90% intervals of pulling strengrth, test shows: for C25～C45 concrete, this value is substantially applicable, determines P ₁=800kg.

While considering constraint factor, pressing formula (3) calculates.

(2) subsequent load: formula (2) is pressed in after this loadings at different levels and formula (3) calculates, and deformation data is taken from 6.2.2.

Standard creeps that the differential contraction stress of chamber condition (drawdown deformation threshold mode, R=0.9,0.8,0.7,0.3) is crept and the 56d of natural environmental condition (fixing the length of time mode) in loaded value at different levels, in table 3.

Table 3 loaded value kg at different levels

Load condition explanation: collapse threshold method is not exclusively applicable to constraint factor low (R=0.3), should adopt and fix method in the length of time, or covariant loading method, creeps as fixing method test in the length of time concrete shrinkage stress adopting under physical environment.

Read deformation data 6.2.2 survey

Distortion at different levels are read in survey, calculate contraction strain (ε by gauge length _{sh, i}), elastic strain (ε _e,i), clean strain (ε _t,i) and overall strain (ε _{tCT, i}), by ε _{sh, i}, ε _e,i, ε _t,iand ε _{tCT, i}with T _ncurve plotting, standard creep chamber condition contraction strain curve and load instantaneous (elasticity) strain curve as Figure of description 9a and Fig. 9 b; The contraction strain curve of natural environmental condition and loading instantaneous (elasticity) strain curve are as Figure 10 a and Figure 10 b.

6.3 differential contraction stress creep test results

Standard is crept chamber condition by formula (9), and natural environmental condition presses formula (7) or formula (8) calculates ε _c,i, then press formula (10) and calculate ε _t, draw ε _t-T curve.

Standard creep chamber condition (R=0.9,0.8,0.7,0.3) the concrete differential contraction stress of the C30 that surveys creep curve as Figure of description 9c.

Physical environment (fixing the length of time mode) the concrete differential contraction stress of the C30 that surveys creep curve as Figure of description 10c.

The present invention can record concrete shrinkage stress and creep, and has especially realized concrete shrinkage stress under physical environment and has crept, and can carry out and concrete shrinkage stress creep relevant research and engineering detecting.

Claims (9)

1. Analysis of Concrete Tensile creep test device, described Analysis of Concrete Tensile creep test device comprises: support, upper perforation-radial type chuck, lower perforation-radial type chuck, perforation test specimen, deformation gauge and counterweight load, it is characterized in that, described perforation test specimen two ends connect with upper and lower perforation-radial type chuck respectively, and in described perforation test specimen both sides, described deformation gauge is set, described two perforation-radial type chucks that connect with perforation test specimen, hang on respectively on described support, with connect with described counterweight load, form bulk test device.

2. Analysis of Concrete Tensile creep test device according to claim 1, is characterized in that: described perforation-radial type chuck comprises: steel housing, hemisphere be articulated and connected bar and the hinged steel pole axle of using of boring a hole; Described steel housing is U-shaped, has segment-shaped hole in crossbeam, and this hole is applicable to forming half ball-joint with the hemisphere bar that is articulated and connected, and on the U-shaped both sides side rod of described steel housing, being respectively provided with one can the hinged circular hole with steel pole axle of plug-in mounting perforation; The described hemisphere bar that is articulated and connected is steel round bar, and it is hemispherical that one end is, and is applicable to forming half ball-joint with described steel housing, and another end bar head, containing hook or annulus, can hang on described support, and connect with described counterweight load; Described perforation is hinged is the screw rod standard component that contains nut with steel pole axle; Described perforation-radial type chuck technical requirement: the bore a hole hinged axis with steel pole axle and hemisphere are articulated and connected rod axis at same plane, and different surface errors are less than 0.2mm; The be articulated and connected maintenance of rod axis of the hinged axis with steel pole axle and hemisphere of boring a hole is vertical, vertical angle error≤± 0.5 °, guarantee how much of test specimens in and physics centering.

3. Analysis of Concrete Tensile creep test device according to claim 1, it is characterized in that: described perforation test specimen is concrete prism, or reamed end prism, the expansion end, two ends of the longitudinal two ends of prism test specimen or reamed end prism test specimen is respectively provided with a perforation, and perforation side, test specimen stage casing is arranged with distortion survey and reads gauge length, on the longitudinal axis face of the level of the axis of described perforation test specimen two ends perforation in the time of specimen molding, and vertical with the longitudinal axis, two perforation of described perforation test specimen are formed by the rigidity, the low friction resistance sleeve pipe that are arranged on the side form of die trial in the time of specimen molding, the axis of described perforation apart from the nearest end face distance of perforation test specimen should >=50mm, described perforation test specimen outside of sleeve in the time of moulding is preset with spiral reinforcing rod, the dead in line of the center line of the helical ring of described spiral reinforcing rod and described through hole or sleeve pipe, and spiral reinforcing rod contains elbow, described elbow is reinforcement end, be parallel to the bending segment of test specimen transversal section, the middle punch of described perforation test specimen is for interting the hinged steel pole axle of using of perforation of described perforation-radial type chuck, makes to form hinge formula between test specimen and chuck and connects, described distortion is surveyed and is read gauge length two pairs of pre-buried gauge head built-in fittings when boring a hole specimen molding and form, described gauge head built-in fitting is by dismountable side form that is connected in moulding die trial in the time of specimen molding, after form removal, be embedded in the gauge head built-in fitting in test specimen, gauge head built-in fitting is used for installing distortion instrumentation and reads distortion, calculate strain, described distortion is surveyed and is read gauge length between two perforation of perforation test specimen, on test specimen horizontal longitudinal axis face in the time of moulding, require spacing the l ' >=0.8a+1/2d of gauge head and perforation central shaft, wherein: a is the test specimen xsect length of side, d is casing diameter, gauge length L >=120mm, the distortion of described perforation test specimen is surveyed the xsect of reading gauge length place for square, the length of side is >=the conventional sample dimensions of 100mm.

4. concrete shrinkage stress creep test method, it is characterized in that, according to standard creep chamber and two kinds of environmental baselines of physical environment, two kinds of restraint conditions of complete and non-complete lattice constraint rigidity, adopt " step loading " and " covariant loading " two kinds of load modes, and collapse threshold and the fixing length of time two kinds of Loading Control conditions, the test concrete shrinkage stress test method of creeping;

The described standard chamber of creeping refers to that meeting concrete shrinkage in " Standard for test methods of longterm performance and durability of ordinary concrete standard " GB/T50082-2009 tests desired temperature and humidity conditions, or " concrete for hydraulic structure testing regulations " DL/T5150-2001 specified standard chamber condition of creeping;

Described physical environment is the selected outdoor environment of test;

Described complete and non-complete lattice constraint rigidity is the degree of restraint of structure to concrete shrinkage, and degree of restraint characterizes with constraint factor R, complete lattice constraint rigidity R=1, non-complete lattice constraint rigidity R < 1;

Described step load mode is the test method by drawdown deformation threshold value and the fixing length of time, two kinds of loading environments test concrete shrinkage stresses were crept;

Described covariant load mode comprises 2 kinds of modes;

One refers at complete deflection constraint,, under R=1, tests the overall strain ε keeping in specimen equidistance line marking _{tCT, i}=0, work as ε _{tCT, i}, keep ε by adjusting counterweight at ≠ 0 o'clock _{tCT, i}=0;

Another kind refers at non-complete deflection constraint, i.e. R < 1 time, and covariant loads must calculate the overall strain ε ' when i level loads _{c, TCT, i}as the controlling value of the test piece deformation of creeping, when the overall strain of actual measurement is not equal to ε ' _{c, TCT, i}time, adjust counterweight, make the overall strain of actual measurement equal ε ' _{c, TCT, i};

Described collapse threshold Loading Control condition is the clean strain stress that in test, the shrinkage and creep of test specimen causes _{t, i}reach threshold value T _hthe condition that Shi Jinhang loads; Described clean strain stress _{t, i}=ε _{sh, i}-ε _c,i, ε _{sh, i}concrete Free shrinkage strain duration of being i level load, ε _c,iconcrete the creeping duration of being i level load, this value is read by testing direct survey, and described Threshold is T _h=5 μ ε;

Described fixing length of time, Loading Control condition was the condition that loads test the length of time by fixing;

Described concrete shrinkage stress creep test method, be Analysis of Concrete Tensile creep test method under differential contraction stress, form standard creep chamber condition step load test method, natural environmental condition test method and covariant load test method by above-mentioned test condition and mode; Described step load test method refers to drawdown deformation threshold value loading method, fixes loading method in the length of time, retrains the one in loading method in rigidity situation.

5. concrete shrinkage stress creep test method according to claim 4, is characterized in that: the creep drawdown deformation threshold value loading method of chamber condition of standard, the clean strain stress that actual measurement i-1 level loading duration test specimen shrinkage and creep causes _{t, i-1}, work as ε _{t, i-1}>=T _htime, the heap(ed) capacity P of calculating i level _iand load, read contraction strain ε to survey _{sh, i-1}, elastic strain ε _{e, i-1}, clean strain stress _{t, i-1}with overall strain ε _{tCT, i-1}, measuring and calculating concrete creep ε _{c, i-1}; Described i level heap(ed) capacity (P _i) be:

P _i=k _i·A·E _t，i·(-ε _sh，i-1-ε _c，i-1) i=1、2、3…n… （2）

In formula (2), P _ifor i level loaded value, k _ifor i level loads correction factor, A is test specimen lifting surface area, E _t,ianalysis of Concrete Tensile elastic modulus while loading for i level, ε _{sh, i-1}concrete Free shrinkage strain duration of for i-1 level load, ε _{c, i-1}during for i-1 level load, concrete differential contraction stress is crept, the sequence number that when i is test, loadings at different levels and survey are read, i=1,2,3 ... n ..., in the time of i=1, E _{t, 1}analysis of Concrete Tensile elastic modulus while being 1 grade of loading, ε _{sh, 0}concrete Free shrinkage strain while being 1 grade of load, ε _{c, 0}while being 1 grade of load, concrete differential contraction stress is crept, E _{t, 1}, ε _{sh, 0}, ε _{c, 0}determining by ancillary test or existing data, is that the recommendation that 100 × 100mm, 1d load the length of time is P for C25～C45 concrete, specimen equidistance line marking place cross sectional dimensions ₁=800kg;

Concrete creep ε _c,ireading each parameter by test survey calculates by formula (7):

ε _c,i=ε _TCT,i-ε _sh,i-ε _e,i （7）

In formula (7), each symbol is with aforementioned.

6. concrete shrinkage stress creep test method according to claim 4, is characterized in that: the creep method in fixing length of time of chamber condition step load test method of standard is to load test by the fixing length of time, calculates heap(ed) capacity P ' at different levels _iand load, survey and read distortion, be converted to strain, calculate concrete creep ε by formula (7) _c,i, be the common length of time of concrete the described length of time, can be 1d, 2d, 3d, 5d, 7d, 14d, 21d, 28d the fixing length of time Described heap(ed) capacity P ' _iadopt formula (2) to calculate and value.

7. concrete shrinkage stress creep test method according to claim 4, it is characterized in that: the creep loading method of consideration structural constraint rigidity of chamber condition step load test method of standard, according to restraint condition R, by drawdown deformation threshold value and the fixing length of time two kinds of modes, calculate loaded value P _i' ', and load, survey and read distortion, be converted to strain, adopt formula (7) to calculate concrete creep ε _{c-c, i}; Described loaded value P _i' ' press formula (3) calculate,

P _i''=k _i·R·A·E _t,i·(-ε _sh,i-1-ε _c,i-1) （3）

In formula (3), R be structure to concrete constraint factor, all the other symbols are the same; Described test concrete creep ε _{c-c, i}each parameter and calculate the same.

8. concrete shrinkage stress creep test method according to claim 4, it is characterized in that: natural environmental condition test method, by creep test device, and be placed in environmental baseline for the test specimen of measurement volumes distortion and test, by distortion threshold value and the fixing length of time two kinds of methods, and consider two kinds of situations of complete and non-complete lattice constraint rigidity, and load step by step or off-load, survey and read freely to collapse strain stress _{e, sh, i}, elastic strain ε _{e, e, i}, clean strain stress _{e, t, i}with overall strain ε _{e, TCT, i}, calculate concrete creep ε by formula (11) _{e, c, i};

ε _e,c,i=ε _e,TCT,i-ε _e,sh,i-ε _e,e,i （11）

The distortion threshold method of described natural environmental condition test method is to work as ε _{t, i}>=T _h, load, work as ε _{t, i}≤-T _h,it is off-load;

Described survey reads freely to collapse strain stress _{e, sh, i}be that distortion test specimen is placed in to physical environment distortion, measuring instrument is placed in the standard room environmental of creeping, and gets to be placed in physical environment test specimen to the standard room environmental of creeping and to survey and read self to collapse distortion-strain (ε _{e, shi}), require to complete in 3～5min; Described cubic deformation test specimen and measuring instrument adopt the test specimen, concrete confined expansion and the contraction measuring instrument that in GB23439-2009 " cement expansive material ", carry out concrete confined expansion test, while making test specimen, must substitute " longitudinally limiter " in test specimen with gauge head, and the installation of gauge head should meet the range finding requirement of GB23439; Described elastic strain ε _{e, e, i}, clean strain stress _{e, t, i}with overall strain ε _{e, TCT, i}with aforementioned.

9. concrete shrinkage stress creep test method according to claim 4, is characterized in that: covariant load test method is to consider concrete strain under structural constraint degree R=1, keeps concrete sample overall strain ε _{tCT, i}=0, and add, off-loading carries, and tests each strain, calculate by formula (7) and creep;

Other constraint factors R < 1, calculates overall strain ε ' by formula (6) _{c, TCT, i},

ε' _C,TCT,i=ε _sh,i+ε' _C,c,i+ε' _C,e,i （6）

In formula, ε _{sh, i}for concrete freely collapses strain; ε ' _{c, c, i}creep for calculating, by ε ' _{c, c, i}=R ε _c,icalculate; ε ' _{c, e,i}the concrete elastic strain of actual measurement during for loading, or press ε ' _{c, e, i}=R ε _{c, e, i}calculate;

Work as ε _{tCT, i}≠ ε ' _{c, TCT, i}time, plus-minus load, calculates each strain, calculates ε ' ' by (6) formula _{c, c, i}; Check ε ' _{c, c, i}and ε ' ' _{c, c, i}between error, the two relative error is in 15%, with ε ' _{c, c, i}and ε ' ' _{c, c, i}mean value as ε _{c, e, i}; Relative error exceedes 15%,, in i+1 level with ε ' ' _{c, c, i}again matching ε ' _{c, TCT, i+1,}the ε that creeps after adjusting for several times _{c, c, i}result precision will obtain raising.

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