CN114486723A - Method for verifying binding performance of basalt reinforced alkali-activated concrete - Google Patents
Method for verifying binding performance of basalt reinforced alkali-activated concrete Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N19/00—Investigating materials by mechanical methods
- G01N19/04—Measuring adhesive force between materials, e.g. of sealing tape, of coating
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/38—Concrete; ceramics; glass; bricks
- G01N33/383—Concrete, cement
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
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Abstract
The invention discloses a method for verifying the binding performance of basalt reinforced alkali-activated concrete, which comprises the following steps: s1, obtaining the bonding failure form of the basalt bar alkali-activated concrete test piece through a center drawing test, drawing a bonding slip curve, and researching and analyzing the influence factors of a bonding stress mechanism and bonding performance; s2, obtaining a bonding slip constitutive model suitable for basalt reinforced alkali-activated concrete by using Origin software fitting; s3, calculating to obtain a plastic damage model suitable for alkali-activated concrete; s4, establishing a finite element model of the drawing test piece, setting interaction, inputting boundary conditions, substituting into a plastic damage model suitable for alkali-activated concrete, adopting a nonlinear spring unit to carry out numerical simulation and analysis on a bonding slip test, and verifying the accuracy of test data. The invention utilizes the strengthening and toughening mechanism of the alkali-activated concrete, comprehensively analyzes the bonding performance of the basalt ribs and the alkali-activated concrete, and provides a reference basis for the application of the alkali-activated concrete structure in engineering.
Description
Technical Field
The invention relates to the technical field of alkali-activated concrete, in particular to a method for verifying the binding performance of basalt bar alkali-activated concrete.
Background
Basalt Fiber (BFRP) rib is a Fiber Reinforced polymer rib formed by taking Basalt ore as a basic material, crushing the Basalt ore, adding the Basalt ore into a melting furnace, melting the Basalt ore in a high-temperature state, and then carrying out processes such as stretching and extruding. Compared with the common reinforcing steel bar, the BFRP reinforcing steel bar has the advantages of high strength, light weight, corrosion resistance, fatigue resistance, insulation and the like, and can still keep good basic mechanical properties in an alkaline environment, so that the BFRP reinforcing steel bar has wide application prospect in the fields of building construction and the like. The alkali-activated concrete is a novel cementing material concrete formed by taking fly ash, slag and the like of corresponding components as main materials and acting through an alkali activator, and has the advantages of low energy consumption, high strength, excellent corrosion resistance and excellent freeze-thaw cycle resistance. Compared with common concrete, the alkali-activated concrete has better fire resistance and durability and better protection effect on reinforcing steel bars.
Although basalt bars and alkali-activated concrete have so many excellent characteristics, no relevant research has been conducted on the bonding performance between the two. In order to better realize the application of the basalt reinforcement and the alkali-activated concrete in practical engineering and facilitate subsequent scientific research personnel and engineering technical personnel to better understand the basalt reinforcement alkali-activated concrete, the study on the bonding performance between the basalt reinforcement and the alkali-activated concrete has important significance.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for verifying the binding property of basalt bar alkali-activated concrete, which is used for researching the binding property of the basalt bar and the alkali-activated concrete, verifying the accuracy of test data and providing a reference for the application of the two novel materials in engineering.
In order to achieve the purpose, the invention provides a method for verifying the binding performance of basalt reinforced alkali-activated concrete, which comprises the following steps:
s1, obtaining the bonding failure form of the basalt bar alkali-activated concrete test piece through a center drawing test, drawing a bonding slip curve, and researching and analyzing the influence factors of a bonding stress mechanism and bonding performance;
s2, summarizing the trend law of the binding slip curves of the test pieces, dividing the whole binding slip process into different stress stages, comprehensively considering the influence of different factors on the binding strength, and fitting by using Origin software to obtain a binding slip constitutive model suitable for basalt reinforced alkali-activated concrete;
s3, measuring a cubic compressive strength test, a splitting tensile property test, an axial compressive strength and an elastic modulus of the alkali-activated concrete and a tensile strength of the basalt bar through a basic mechanical property test, and calculating to obtain a plastic damage model suitable for the alkali-activated concrete;
s4, establishing a finite element model of the drawing test piece, setting interaction, inputting boundary conditions, substituting the boundary conditions into the plastic damage model suitable for alkali-activated concrete, adopting a nonlinear spring unit to carry out numerical simulation and analysis on the bonding slip test, and verifying the accuracy of test data.
Preferably, in the step S1, the failure mode of each group of test pieces is obtained through a center pull test, the cause of each type of adhesive failure is analyzed, and the adhesive stress is calculated according to the following formula:
in the formula: τ is the bonding stress (MPa); p is an external load (kN); d is the diameter (mm) of the rib; laBond length (mm); f. ofcu,kStandard compressive strength (MPa) for alkali-activated concrete; f. ofcuMeasured value (MPa) of cubic compressive strength of 28 days of alkali-activated concrete;
and (3) drawing a bonding slip curve by combining test data and a bonding stress formula, and researching the bonding failure mechanism of the basalt bar alkali-activated concrete to obtain the influence of various factors of the diameter, the bonding length and the type of the basalt bar on the bonding strength.
Preferably, the bonding slip curve comprises a micro-slip section, a descending section and a residual section, wherein the micro-slip section is a loading initial stage, and the curve linearly rises; the slip section begins to enter a nonlinear rising stage; the descending section shows a nonlinear descending; the residual section exhibits a form of cyclic decay with increasing slip.
Preferably, the expression of the binding slip constitutive model in step S2 is:
a micro-slide section:
a slippage section:
a descending section:
residual section:
in the formula: tau is1、τ2、τ3Respectively corresponding bonding strengths of the adjacent joints of the micro-slip section, the descending section and the residual section; s1、s2、s3Respectively corresponding bonding slip values at the adjacent positions of the micro-slip section, the descending section and the residual section; alpha, beta, theta, gamma, delta, omega and rho are all parameters determined according to test results.
Preferably, in the step S3, the cubic compressive strength test, the cleavage tensile property test, the axial compressive strength and the elastic modulus of the alkali-activated concrete and the ultimate tensile strength of the basalt bar are determined through the basic mechanical property test, and the uniaxial compressive and tensile stress-strain curves of the alkali-activated concrete are determined according to the data obtained from the basic mechanical property test; and then, obtaining a plastic damage model suitable for alkali-activated concrete by referring to a Sidoroff energy equivalent principle, namely the elastic energy of the damaged material under the stress action is equivalent to the elastic residual energy of the undamaged material under the equivalent stress action.
Preferably, the method for determining the uniaxial compressive stress-strain curve in step S3 is as follows: the compressive stress-strain curve of the concrete is divided into three sections: the linear ascending section, the nonlinear ascending section and the nonlinear descending section are calculated according to the following formula:
σ＝(1-dc)Ecε (10)
in the formula: ε is strainc,rFor peak strain under compression, EcIs modulus of elasticity, αcShowing the smoothness of the curve of the inelastic falling section, x showing the ratio of the strain at any moment to the peak strain, being a known value, empirically chosen, fc,rIs the axial compressive strength of concrete, dcRepresenting the compression damage parameter, n, ρcIs a conversion coefficient;
the calculation method is that firstly, the E obtained by the test datacAnd fc,rSubstituting into (11) and (12) to obtain epsilonc,rAnd alphacThen substituted into (6), (7) and (8) respectively to obtain epsilon, n and rho in sequencecFinally, the stress is substituted into (9) and (10) to obtain the compressive stress sigma and the damage parameter dcAnd the compressive stress sigma and strain epsilon are plotted as curves.
Preferably, the method for determining the uniaxial tensile stress-strain curve in step S3 includes: the method for calculating the tensile stress-strain curve is divided into a linear ascending section and a nonlinear descending section when being pressed, and the calculation formula is as follows:
σ＝(1-dt)Ecε (16)
in the formula: epsilont,rIs the peak strain in tension, αtShowing the degree of flatness of the curve of the nonlinear falling section in tension, ft,rIs the compressive strength of the concrete axis, rhotIs a conversion coefficient;
the calculation method comprises the following steps: test data obtained EcAnd ft,rSubstituting into (17) and (18) to obtain epsilont,rAnd alphatThen substituted into (13), (14), (15) and (16) in sequence to obtain epsilon and rhot、dcAnd σ, drawing the tensile stress σ and the strain ε into a curve.
Preferably, the plastic damage model applied to the alkali-activated concrete in the step S3 includes a lossless model, a compression damage model and a tension damage model;
when the stress does not exceed the peak stress, the concrete is a nondestructive model, namely the concrete is elastically deformed under the action of load;
when the stress exceeds the elastic range, the new stiffness becomes (1-d) after compression damagec)E0The rigidity after the tensile damage becomes (1-d)t)E0In the compression damage model,
in order to be subjected to a plastic strain,
indicating the portion of the new stiffness where the deformation is recoverable,
representing no damage to the elastic strain,
for the inelastic strain input in ABAQUS, the inelastic strain is equal to the total strain minus the intact elastic strain, i.e.
In the tensile damage model, the strain is measured,
in order to be subjected to a plastic strain,
indicating the elastically deformed portion at the new stiffness,
which shows the absence of damage to the elastic strain,
the cracking strain in the tensile behavior is expressed by the formula
Preferably, the damage factor calculation formula of the plastic damage model of the concrete in the ABAQUS in step S3 is as follows:
in the formula: d is a damage factor; e0Alkali-activated concrete elastic modulus; σ is compressive stress and tensile stress; ε is the strain; and inputting the damage factor into the ABAQUS material attribute, wherein the finally simulated deformation result is consistent with the test result, which shows that the model is reliable and effective.
Preferably, the specific step of step S4 includes:
s41, establishing a finite element model: establishing a basalt bar alkali-activated concrete separation type model according to the actual size of the test piece, inputting constitutive relation data of each material, and defining section attributes;
s42 setting a nonlinear spring unit; selecting a Spring2 unit for simulation in ABAQUS, and after submitting a job, modifying an inp file to realize simulation;
s43, simulating each group of drawing tests by using the established Abaqus finite element model to obtain a finite element calculation stress cloud chart, and verifying the accuracy of test data.
The invention utilizes the strengthening and toughening mechanism of the alkali-activated concrete, comprehensively analyzes the bonding performance of the basalt ribs and the alkali-activated concrete, and provides a reference basis for the application of the alkali-activated concrete structure in engineering.
Drawings
FIG. 1 is a schematic flow diagram of a method for verifying the binding performance of basalt bar alkali-activated concrete according to the invention;
FIG. 2 is a basalt reinforcement alkali-activated concrete bonding-slip constitutive relation model;
FIG. 3 is a flow chart of the preparation of alkali-activated concrete;
FIG. 4 is a schematic view of a center-drawn test piece;
FIG. 5 test piece failure mode;
FIG. 6 is a graph of a bond slip test curve versus a fit curve;
FIG. 7 is a graph of uniaxial compressive stress-strain of alkali-activated concrete;
FIG. 8 is a graph of uniaxial tensile stress-strain of alkali-activated concrete;
FIG. 9 is a compressive damage stress-strain relationship;
FIG. 10 is a tensile damage stress strain relationship;
FIG. 11 is a diagram of a test piece assembly model;
FIG. 12 is a grid cell model diagram;
FIG. 13 is a simplified non-linear spring unit arrangement;
FIG. 14 is a stress cloud chart of basalt reinforcement alkali-activated concrete calculation;
FIG. 15 bond slip test curves versus simulation curves; .
Detailed Description
The invention provides a method for verifying the binding performance of basalt bar alkali-activated concrete, and in order to make the purpose and the thought of the invention more clear, the method provided by the invention is further explained and explained below by combining the drawings in the embodiment. It should be understood that the following examples are only illustrative of the present invention and do not limit the scope of the present invention.
In the embodiment, 12 groups of basalt rib alkali-activated concrete center drawing tests are designed, and each group comprises 3 test pieces. According to a bonding slippage curve obtained by a drawing test, a bonding stress mechanism and a bonding failure form are researched, the influence of different factors on the bonding performance is discussed, and a bonding slippage constitutive model suitable for basalt reinforced alkali-activated concrete is constructed. And then carrying out a basic mechanical property test on the basalt bar and the alkali-activated concrete, and obtaining a material constitutive model of the basalt bar and the alkali-activated concrete on the basis of the test. And inputting the constitutive model into finite element software, and verifying the accuracy of test data by comparing the bonding slippage test result with the simulation result.
The following is a detailed description of the examples according to the test, as shown in FIG. 3:
(1) test raw materials:
the coarse aggregate is continuous graded crushed stone with the particle size of 5-20 mm, and the apparent density is 2665kg/m3A bulk density of 1530kg/m3。
The fine aggregate is common river sand, the grain size distribution is shown in table 2-1, the fineness modulus is 2.75, and the grain size distribution of the medium sand is shown in table 1.
TABLE 1 particle size distribution of river sands
Fly ash: class i fly ash, water purification materials ltd, blue.
Mineral powder: flouring powder company. The mineral composition of the fly ash and the mineral fines is shown in table 2.
Table 2 mineral composition of cement (%)
Sodium silicate solution: neiguani chemical Limited, density 1.38g/cm3, sodium oxide content 8.35%, silica content 26.54%, modulus 3.28.
Sodium hydroxide: kaiton Chemicals Co., Ltd., granular solid, NaOH content not less than 96%, highest impurity content is shown in Table 3.
TABLE 3 sodium hydroxide impurity content (%)
Water reducing agent: a polycarboxylic acid type water reducing agent.
The basalt rib is a deep thread basalt rib produced by New Material science and technology development Limited of Green grain in Jiangsu province, and has a diameter of 10mm, 12mm and 16 mm.
(2) Designing the concrete mixing proportion:
the mixing ratio of Alkali Activated Concrete (AAC) and Ordinary Concrete (OPC) is shown in table 4. The preparation process of the alkali-activated concrete is shown in figure 3.
TABLE 4 compounding ratio (kg/m)3)
(3) And (3) experimental design:
referring to the test method standard for concrete physical and mechanical properties GB/T50081 plus 2019, the test measures the elastic modulus, the cubic compressive strength and the splitting tensile strength of the alkali-activated concrete and the common concrete for 28 days, wherein the size of an elastic modulus test block is 150mm multiplied by 300mm, the size of a cubic compressive strength test block and a splitting tensile strength test block is 150mm multiplied by 150mm, and the specific results are shown in tables 5 to 7.
TABLE 5 compressive strength of alkali-activated concrete cube (MPa)
TABLE 6 alkali-activated concrete cleavage tensile Strength (MPa)
TABLE 7 axial compressive strength and modulus of elasticity (MPa/GPa) of alkali-activated concrete
The center pull test was divided into 12 groups of 3 specimens each. The diameters of the basalt ribs adopted in the test are 10mm, 12mm and 16mm, the rib spacing is 1d (d is the diameter of the basalt ribs), and the rib depth is 0.06d of the diameter. The bond lengths were 2.5d, 5d and 10d, respectively. The test piece size was 150mm × 150mm × 150mm, wherein for the test piece of the 16mm basalt bead 10d bonding length in the present test, the size was selected to be 150mm × 150mm × 200 mm. The mixing proportion of the alkali-activated concrete and the common concrete in the test is shown in the table 4. In order to form an unbonded area, PVC pipes are sleeved on the reinforcing materials to avoid local extrusion of concrete so as to eliminate the end effect, and the setting of three different bonding length variables is completed by adjusting the length of the PVC pipes. Because the shearing resistance of the basalt rib is poor, in order to avoid the two ends of the test piece from being damaged due to the action of the clamp, a steel sleeve with the length of 400mm is adopted at the loading end of the basalt rib for anchoring. The center pull test protocol is shown in Table 8, and a schematic of the structure is shown in FIG. 4.
TABLE 8 center pull test protocol
Note: in the table, "BFRP" denotes BFRP ribs; "10, 12, 16" indicates the tendon diameter; "CBFRP" means ordinary concrete and basalt tendon; "2.5 d, 5d, 10 d" indicates different bond lengths, where "d" is the tendon diameter.
The test was carried out on a 1000KN universal tester. The loading is carried out through the automatic control of the computer in the test process, and the spherical hinge is arranged between the steel plate at the lower part of the steel frame for fixing the concrete test piece and the steel base plate, so that the drawing bonding test piece can freely rotate in a small range in the test loading process, and the tearing damage in the concrete test process caused by the inclination of a loading end face or the inclination of a basalt rib or a steel bar in the manufacturing process of the drawing bonding test piece is prevented, so that the rib is ensured to be continuously drawn along the axis direction in the test loading process.
Test loading requirements according to the ACI440 standard: during load control, the loading speed does not exceed 20 kN/min; during displacement control, the loading speed is within 1.3mm/min, the loading mode of the test adopts displacement loading, the loading speed is 1.0mm/min, and the loading is stopped immediately when the following conditions occur, and the test is considered to be finished: (1) breaking or pulling out the rib material; (2) splitting damage; (3) the displacement of the free end is similar to that of the loading end of the testing machine.
In order to obtain the slippage generated by the free end, a displacement meter is arranged at the free end of the basalt rib and connected to a static resistance strain gauge in the test process, and the slippage of the free end of the basalt rib is measured and recorded. And the displacement and the drawing force of the drawing end are automatically recorded by a computer of the testing machine, wherein the displacement of the drawing end refers to the displacement of the testing machine and comprises the elongation of the basalt rib and the slippage of the basalt rib drawing end in the drawing process. When the test is just started, the displacement of the testing machine is larger than the displacement generated by the free end, and in the later stage of test loading, the displacements are basically consistent, so that the bonding failure of the concrete and the reinforcement can be considered, and the test is stopped. Because each group of data in the test is relatively close, in order to improve the accuracy of the test result, the average value of the results of the three groups of test pieces is taken for analysis. The results of the center pull test are shown in Table 9.
TABLE 9 center pull test results
Note: three test pieces of BFRP10-2.5d are small in diameter and insufficient in bonding length, so that the test pieces are not well anchored, and the three test pieces are omitted due to the fact that the drawing force is too small in the test process;
as shown in fig. 1, the method for verifying the binding performance of the basalt reinforced alkali-activated concrete mainly comprises the following steps:
and S1, carrying out adhesion performance test research according to the central drawing test scheme to obtain the failure forms of the test pieces. And drawing a bonding slip curve, and researching the bonding failure mechanism of the basalt bar alkali-activated concrete to obtain the influence of factors such as the diameter of the basalt bar, the bonding length, the type of the concrete and the like on the bonding strength.
S11 As shown in fig. 5, the types of cohesive failure can be classified into a bar pull out failure and a split tensile failure. Wherein, the test pieces with the bonding lengths of 2.5d and 5d generate the pulling-out damage of the reinforcing material, the abrasion of the transverse ribs on the surface of the reinforcing material is serious when the damage occurs, and a small amount of concrete fragments are remained between the ribs. In addition, the root of the free end of the alkali-activated concrete is sheared and leveled by the rib of the pulled-out reinforcement. The test piece with the bonding length of 10d generates alkali-activated concrete splitting damage, the damage is mainly caused by that the hoop stress borne by the alkali-activated concrete is gradually increased due to the continuously increased external load in the loading process until the alkali-activated concrete can not resist the hoop tension, the test piece starts to generate cracks, the bonding gradually disappears, and the bonding state is damaged.
S12 referring to the test method for basic mechanical properties of the fiber reinforced composite bar (GB/T30022-2013), the bonding stress is calculated according to the following formula:
wherein τ is the bonding stress (MPa); p is an external load (kN); d is the diameter (mm) of the rib; laBond length (mm); f. ofcu,kStandard compressive strength (MPa) for concrete; f. ofcuThe measured value (MPa) is the cubic compressive strength of the 28d concrete.
And (3) drawing a bonding slip curve by combining test data and a bonding stress formula, and researching the bonding failure mechanism of the basalt bar alkali-activated concrete to obtain the influence of the factors such as the diameter of the basalt bar, the bonding length, the type of the concrete and the like on the bonding strength.
S2, summarizing the trend law of the binding slip curves of the test pieces, dividing the whole binding slip process into different stress stages, comprehensively considering the influence of different factors on the binding strength, and fitting by using Origin software to obtain the binding slip constitutive model suitable for the basalt reinforced alkali-activated concrete.
S21 building of a bonding slip constitutive model: as shown in FIG. 2, the OA section is a micro-slip section at the initial stage of loading, and is linearly ascending at this time; the AB section is a slippage section and starts to enter a nonlinear rising stage; the BC section is a descending section which shows nonlinear descending and is more in line with the result of the test; the CD segment is a residual segment and exhibits a form of cyclic decay with increasing slip. The expression is as follows:
a micro-slide section:
a slippage section:
a descending section:
residual section:
in the formula, τ1、τ2、τ3Bond strength corresponding to point A, B, C in FIG. 2; s is1、s2、s3-bond slip value corresponding to point A, B, C in figure 2; alpha, beta, theta, gamma, delta, omega, rho are parameters determined according to test results.
S22 substituting the experimental data into the above expression, experimental data of A, B, C points and fitting values of each parameter were obtained, as shown in table 10. The test curve and the fitting curve are shown in FIG. 6, and the goodness of fit between the test curve and the fitting curve is good, which shows that the bonding slip constitutive model provided by the invention can better describe the whole process of the drawing stress of the basalt bar alkali-activated concrete.
TABLE 10 test data and parameter fit values
S3 summarizes data obtained by the basic mechanical property test, and obtains a plastic damage model (CDP model) suitable for alkali-activated concrete on the basis of concrete structure design Specification (GB 50010-2010);
s31 determining the uniaxial compressive stress-strain curve: the concrete compression constitutive relation refers to 'concrete structure design specifications', and the compression stress-strain curve of concrete obtained from the specifications can be roughly divided into three sections: the linear ascending section, the nonlinear ascending section and the nonlinear descending section are calculated according to the following formula:
σ＝(1-dc)Ecε (10)
in the formula: epsilonc,rFor peak strain under compression, EcIs modulus of elasticity, αcRepresents the smoothness of the curve of the inelastic falling section, x represents the ratio of the strain at any time to the peak strain (which is a known value and is empirically selected), fc,rIs the axial compressive strength of concrete, dcRepresenting the compression damage parameter, n, ρcAre conversion coefficients. First, the test data is obtained as EcAnd fc,rSubstituting into (11) and (12) to obtain epsilonc,rAnd alphacThen substituted into (6), (7) and (8) respectively to obtain epsilon, n and rho in sequencecFinally, the stress is substituted into (9) and (10) to obtain the compressive stress sigma and the damage parameter dc. Will press to reactThe force σ and strain ε are plotted as shown in FIG. 7.
S32 determining uniaxial tensile stress-strain curve: the method for calculating the tensile stress-strain curve is the same as that in compression, and the specification shows that the tensile stress-strain curve can be roughly divided into a linear ascending section and a nonlinear descending section, and the calculation formula is as follows:
σ＝(1-dt)Ecε (16)
in the formula: epsilont,rIs the peak strain in tension, alphatShowing the degree of flatness of the curve of the nonlinear falling section in tension, ft,rIs the axial compressive strength, rho, of concretetAre conversion coefficients. The calculation method under tension is similar to that under compression, and the test data is obtained as EcAnd ft,rSubstituting into (17) and (18) to obtain epsilont,rAnd alphatThen substituted into (13), (14), (15) and (16) in sequence to obtain epsilon and rhot、dcAnd σ, the tensile stress σ is plotted against the strain ε, as shown in FIG. 8.
Calculation of inelastic strain and plastic damage factor of S33: the ABAQUS plastic damage model needs to be input into concrete to be pressedInelastic strain in time and cracking strain in tension, as shown in fig. 9-10 below, when the stress does not exceed the peak stress, the concrete can be regarded as an undamaged model, i.e., elastic deformation occurs under load; when the stress exceeds the elastic range, the new stiffness becomes (1-d) after compression damagec)E0The rigidity after the tensile damage becomes (1-d)t)E0. In the compression of the damage model,
in order to be subjected to a plastic strain,
indicating the portion of the new stiffness where the deformation is recoverable,
representing no damage to the elastic strain,
for the inelastic strain input in ABAQUS, the inelastic strain is equal to the total strain minus the intact elastic strain, i.e.
In the same way, in the tensile damage model,
in order to be subjected to a plastic strain,
indicating the elastically deformed portion at the new stiffness,
which shows the absence of damage to the elastic strain,
the cracking strain in the tensile behavior is expressed by the formula
The plastic damage of the concrete in ABAQUS refers to the loss and recovery condition of the elastic rigidity of the concrete under the action of reciprocating load, and is expressed by a damage factor d. In the text, by referring to the Sidoroff energy equivalent principle, that is, the elastic energy caused by the damaged material under the action of stress is equivalent to the elastic residual energy of the undamaged material under the action of equivalent stress, a calculation formula of a damage factor is provided:
in the formula: d is a damage factor; e0Alkali-activated concrete elastic modulus; σ is compressive stress and tensile stress; ε represents the compressive strain and the tensile strain. The damage factor calculated by the formula is input into the ABAQUS material attribute, and the finally simulated deformation result is very close to the test result, which shows that the model is reliable and effective.
S4, establishing a finite element model of the drawing test piece, inputting boundary conditions, substituting the boundary conditions into a plastic damage model (CDP model) which is obtained by calculation according to basic mechanical property test data and is suitable for alkali-activated concrete, and performing numerical simulation and analysis on the bonding slip test by using a special nonlinear spring unit in ABAQUS finite element software to verify the accuracy of the test data.
S41, establishing a finite element model: and establishing a basalt rib alkali-activated concrete separation type model according to the actual size of the test piece, inputting constitutive relation data of each material, and defining section attributes. The basalt bars and the alkali-activated concrete are endowed with different unit types in the separate model and then are connected together through a coupling effect, wherein the alkali-activated concrete adopts three-dimensional entity C3D8R units, the grid type adopts regular hexagons, the reinforcing steel bars adopt linear beam units, and the unit type is B31. As the rigidity of the basalt rib is higher than that of the alkali-activated concrete, the meshing of the components with low rigidity required in the ABAQUS is required to be tighter, and the ratio of the basalt rib to the alkali-activated concrete in edge distribution is 1: 2. The material properties of the components are input according to the constitutive relation obtained in the test. The loading direction of the model is the X direction, the loading mode is consistent with the test, the displacement loading of 1.0mm/min is adopted, and the loading speed is controlled by an amplitude tool carried by the ABAQUS. A reference point is defined at the joint of the basalt bar and the alkali-activated concrete surface, the coupling effect of the reference point and the concrete surface is set, and all 6 degrees of freedom (including rotational degrees of freedom) in the direction of X, Y, Z of the alkali-activated concrete surface are restrained, so that the basalt bar is ensured to be continuously drawn along the axial direction in the loading process. The test piece assembly model diagram and the grid unit model diagram are shown in fig. 11-12.
S42 sets a nonlinear spring unit: the spring unit is a special arrangement in ABAQUS for connecting force versus displacement at specified two points, and comprises three types: spring1 (ground Spring), Spring2 (two-point Spring), and Spring a (axial Spring). In this test, the bonding relationship caused by the drawing force is substantially the relationship between the force and the displacement between the basalt bar node and the alkali-activated concrete node, and therefore, the Spring2 unit is selected to be most suitable for simulation. The setting of the non-linear spring unit in the ABAQUS needs to be realized by modifying an inp file after the job is submitted. The modified inp file is roughly divided into two parts, one part is a mechanism for adding the node force and displacement of each spring, and the other part needs to modify the BFRP ribs corresponding to the spring units and the node numbers of the alkali-activated concrete. The constitutive relation of force and displacement is determined by a formula F ═ τ d π dx (where τ is the average bonding stress and is determined by basalt reinforcement alkali-activated concrete bonding slip constitutive model, d is the BFRP reinforcement diameter, and dx is the bonding slip length of each spring unit connection). The principle is shown in fig. 13, taking the bonding length 5d (d is the diameter of the reinforcing material) as an example, the alkali-activated concrete test block is divided into 10 units according to rows and columns, and each unit is 15mm long, namely, the alkali-activated concrete test block spans 4 concrete units. The small circles filled with black in the figure are spring units and are virtually arranged, and the small circles are used for connecting the BFRP rib units and the alkali-activated concrete units and transferring bonding stress. The length dx of the bonding area in charge of the spring units at the two ends is half of the length of the alkali-activated concrete unit, and the length dx of the bonding area in charge of the spring unit in the middle is equal to the length of the alkali-activated concrete unit. And finally, substituting the calculated force F into an inp file, and outputting an extracted reaction force (stress) displacement curve on the spring unit by using the ODB field variable, wherein the reaction force (stress) displacement curve is a load (bonding) slip curve.
S43 simulates each drawing test set by using the established Abaqus finite element model, and obtains a finite element calculated stress cloud, as shown in fig. 14. Comparing the test curve with the simulation curve, as shown in fig. 15, the goodness of fit was found to be good, verifying the accuracy of the test data.
Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are merely illustrative and not restrictive, and those skilled in the art can make various changes and modifications within the spirit and scope of the present invention without departing from the spirit and scope of the appended claims.
Claims (10)
1. A method for verifying the binding performance of basalt reinforcement alkali-activated concrete comprises the following steps:
s1, obtaining the bonding failure form of the basalt bar alkali-activated concrete test piece through a center drawing test, drawing a bonding slip curve, and researching and analyzing the influence factors of a bonding stress mechanism and bonding performance;
s2, summarizing the trend law of the binding slip curves of the test pieces, dividing the whole binding slip process into different stress stages, comprehensively considering the influence of different factors on the binding strength, and fitting by using Origin software to obtain a binding slip constitutive model suitable for basalt reinforced alkali-activated concrete;
s3, measuring a cubic compressive strength test, a splitting tensile property test, an axial compressive strength and an elastic modulus of the alkali-activated concrete and a tensile strength of the basalt bar through a basic mechanical property test, and calculating to obtain a plastic damage model suitable for the alkali-activated concrete;
s4, establishing a finite element model of the drawing test piece, setting interaction, inputting boundary conditions, substituting the boundary conditions into the plastic damage model suitable for alkali-activated concrete, adopting a nonlinear spring unit to carry out numerical simulation and analysis on the bonding slip test, and verifying the accuracy of test data.
2. The method for verifying the binding property of the basalt reinforcement alkali-activated concrete according to claim 1, wherein the method comprises the following steps: in the step S1, the failure mode of each group of test pieces is obtained through a center pull test, the cause of each type of adhesive failure is analyzed, and the adhesive stress is calculated according to the following formula:
in the formula: τ is the bonding stress; p is an external load; d is the diameter of the rib material; laIs the bonding length; f. ofcu,kThe standard compressive strength of alkali-activated concrete; f. ofcuThe cube compressive strength measured value of the alkali-activated concrete for 28 days is obtained;
and (3) drawing a bonding slip curve by combining test data and a bonding stress formula, and researching the bonding failure mechanism of the basalt bar alkali-activated concrete to obtain the influence of various factors of the diameter, the bonding length and the type of the basalt bar on the bonding strength.
3. The method for verifying the binding property of the basalt reinforcement alkali-activated concrete according to claim 2, wherein the method comprises the following steps: the bonding slippage curve comprises a micro slippage section, a descending section and a residual section, wherein the micro slippage section is a loading initial stage, and the curve linearly rises at the moment; the slip section begins to enter a nonlinear rising stage; the descending section shows a nonlinear descending; the residual section exhibits a form of cyclic decay with increasing slip.
4. The method for verifying the binding property of the basalt reinforcement alkali-activated concrete according to claim 1, wherein the method comprises the following steps: the expression of the binding slip constitutive model in step S2 is:
a micro-slide section:
a slippage section:
a descending section:
residual section:
in the formula: tau is1、τ2、τ3Respectively corresponding bonding strengths of the adjacent joints of the micro-slip section, the descending section and the residual section; s is1、s2、s3Respectively corresponding bonding slip values at the adjacent positions of the micro-slip section, the descending section and the residual section; alpha, beta, theta, gamma, delta, omega and rho are all parameters determined according to test results.
5. The method for verifying the binding property of the basalt reinforcement alkali-activated concrete according to claim 1, wherein the method comprises the following steps: step S3, determining cubic compressive strength test, splitting tensile property test, axial compressive strength and elastic modulus of the alkali-activated concrete and ultimate tensile strength of the basalt bar through a basic mechanical property test, and determining uniaxial compression and tensile stress-strain curves of the alkali-activated concrete according to data obtained by the basic mechanical property test; and then, obtaining a plastic damage model suitable for alkali-activated concrete by referring to a Sidoroff energy equivalent principle, namely the elastic energy of the damaged material under the stress action is equivalent to the elastic residual energy of the undamaged material under the equivalent stress action.
6. The method for verifying the binding property of the basalt reinforcement alkali-activated concrete according to claim 5, wherein the method comprises the following steps: the method for determining the uniaxial compressive stress-strain curve in the step S3 includes: the compressive stress-strain curve of the concrete is divided into three sections: the linear ascending section, the nonlinear ascending section and the nonlinear descending section are calculated according to the following formula:
σ＝(1-dc)Ecε (10)
in the formula: ε is strainc,rFor peak strain under compression, EcIs modulus of elasticity, αcShowing the smoothness of the curve of the inelastic falling section, x showing the ratio of the strain at any moment to the peak strain, being a known value, empirically chosen, fc,rIs the axial compressive strength of concrete, dcRepresenting a compression damage parameter; n, rhocIs a conversion coefficient;
the calculation method is that firstly, the E obtained by the test datacAnd fc,rSubstituting into (11) and (12) to obtain epsilonc,rAnd alphacThen substituted into (6), (7) and (8) respectively to obtain epsilon, n andρcfinally, the stress is substituted into (9) and (10) to obtain the compressive stress sigma and the damage parameter dcAnd the compressive stress sigma and strain epsilon are plotted as curves.
7. The method for verifying the binding property of the basalt reinforcement alkali-activated concrete according to claim 5, wherein the method comprises the following steps: the method for determining the uniaxial tensile stress-strain curve in the step S3 includes: the method for calculating the tensile stress-strain curve is divided into a linear ascending section and a nonlinear descending section when being pressed, and the calculation formula is as follows:
σ＝(1-dt)Ecε (16)
in the formula: epsilont,rIs the peak strain in tension, alphatShowing the gentleness of the curve of the nonlinear descending section in tension, ft,rIs the axial compressive strength, rho, of concretetIs a conversion coefficient;
the calculation method comprises the following steps: test data obtained EcAnd ft,rSubstituting into (17) and (18) to obtain epsilont,rAnd alphatThen substituted into (13), (14), (15) and (16) in sequence to obtain epsilon and rhot、dcAnd σ, drawing the tensile stress σ and the strain ε into a curve.
8. The method for verifying the binding property of the basalt reinforcement alkali-activated concrete according to claim 5, wherein the method comprises the following steps: the plastic damage model applicable to the alkali-activated concrete in the step S3 includes a lossless model, a compressive damage model and a tensile damage model;
when the stress does not exceed the peak stress, the concrete is a nondestructive model, namely the concrete is elastically deformed under the action of load;
when the stress exceeds the elastic range, the new stiffness becomes (1-d) after compression damagec)E0The rigidity after the tensile damage becomes (1-d)t)E0In the compression damage model, dcAs a damage parameter, E0In order to excite the elastic modulus of the concrete by alkali,
in order to be subjected to a plastic strain,
indicating the portion of the new stiffness where the deformation is recoverable,
representing no damage to the elastic strain,
for the inelastic strain input in ABAQUS, the inelastic strain is equal to the total strain minus the intact elastic strain, i.e.
In the tensile damage model, the strain is measured,
to be plasticIn the process of changing the shape of the pipe,
indicating the elastically deformed portion at the new stiffness,
which shows the absence of damage to the elastic strain,
the cracking strain in the tensile behavior is expressed by the formula
9. The method for verifying the binding property of the basalt reinforcement alkali-activated concrete according to claim 5, wherein the method comprises the following steps: the damage factor calculation formula of the concrete plastic damage model in the ABAQUS in the step S3 is as follows:
in the formula: d is a damage factor; e0Alkali-activated concrete elastic modulus; sigma is stress; ε is the strain; and inputting the damage factor into the ABAQUS material attribute, wherein the finally simulated deformation result is consistent with the test result, which shows that the model is reliable and effective.
10. The method for verifying the binding property of the basalt reinforcement alkali-activated concrete according to claim 1, wherein the method comprises the following steps: the specific steps of step S4 include:
s41, establishing a finite element model: establishing a basalt bar alkali-activated concrete separation type model according to the actual size of the test piece, inputting constitutive relation data of each material, and defining section attributes;
s42 setting a nonlinear spring unit; selecting a Spring2 unit for simulation in ABAQUS, and after submitting a job, modifying an inp file to realize simulation;
s43, simulating each group of drawing tests by using the established Abaqus finite element model to obtain a finite element calculation stress cloud chart, and verifying the accuracy of test data.
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