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CN-122021189-A - Shrinkage effect considered large-volume concrete pouring damage cracking prediction and grading evaluation method

CN122021189ACN 122021189 ACN122021189 ACN 122021189ACN-122021189-A

Abstract

The invention relates to the technical field of concrete structure engineering, and provides a method for predicting and grading and evaluating cracking of a large-volume concrete pouring damage by considering shrinkage effect, which comprises the steps of modeling in layers according to a pouring scheme in ABAQUS and adopting a life-death unit to simulate construction; calculating a temperature field based on a HETVAL subprogram composite index hydration heat release and FILM subprogram time-varying heat exchange boundary, introducing Arrhenius equivalent age coupling ACI 209R-92 shrinkage through USDFLD and UEXPAN subprograms, combining UFIELD subprograms to realize elastic modulus and thermal expansion coefficient age evolution to obtain a temperature-shrinkage stress field, adopting a CDP model to calculate pulling/compression damage and output a damage cloud picture, giving out three-level maintenance and crack control measures according to damage factor partition, and combining on-site temperature/strain monitoring and checking parameters. The scheme realizes the transition from point discrimination to global identification and hierarchical control, gives consideration to the time-varying characteristics of a temperature field, a shrinkage effect and materials, improves the prediction precision and operability, reduces the risks of cracks and leakage, improves the durability and reduces the reworking cost.

Inventors

  • ZHANG HENG
  • XU YIHANG
  • DU CHANGSHENG
  • SUN AOYUN
  • MA YUANBO
  • LIU XIAOYU
  • SUN PEIPEI
  • WU KE
  • SUN YINDONG
  • Yin Enze
  • ZHENG YANG
  • YU YALIN
  • LIU YAJUN

Assignees

  • 山东大学

Dates

Publication Date
20260512
Application Date
20260409

Claims (10)

  1. 1. A method for predicting and grading the cracking of a large-volume concrete pouring damage by considering the shrinkage effect is characterized by comprising the following steps: Step 1, a large-volume concrete structure geometric model is established, the geometric model is subjected to layered sectioning and grid division according to a preset construction pouring scheme, and a construction process is simulated in a life-death unit mode to construct a numerical model; Step 2, performing thermal analysis on the numerical model, and calculating to obtain a temperature field during construction and maintenance by considering concrete hydration heat release and dynamic thermal boundary conditions; step 3, carrying out stress analysis on the numerical model, introducing the temperature field as a thermal load, and calculating to obtain a stress field by considering the mechanical property of the concrete and the time-varying characteristic of shrinkage deformation; step 4, carrying out damage analysis on the numerical model, introducing the stress field, adopting a concrete plastic damage model, and calculating to obtain a damage cracking result; Step 5, arranging sensors on a construction site, monitoring the temperature and strain change of the concrete in real time, feeding back monitoring data to the numerical model for verification and correction, and predicting crack generation positions; And 6, outputting a damage cloud picture based on the numerical model after verification and correction in the step 5, identifying potential damage units, dividing cracking risk areas, carrying out grading evaluation according to damage factors, and taking corresponding control measures.
  2. 2. The method for predicting and grading the cracking of the large-volume concrete pouring damage taking shrinkage effect into consideration as set forth in claim 1, wherein the thermal analysis in the step 2 comprises the steps of designating the divided grid units as DC3D8 type, endowing the concrete with thermal physical properties, defining thermodynamic boundary conditions at least comprising heat exchange between the concrete and air, templates and rock stratum, adjusting convection heat dissipation coefficients and environment temperature with time by calling a FILM (FILM model) subroutine, simultaneously taking heat conduction inside the concrete in the pouring process into consideration, setting an analysis step and an incremental step, and calling HETVAL a subroutine to simulate the hydration heat release process of the concrete based on a composite index model.
  3. 3. The method for predicting and grading the cracking of the large-volume concrete pouring damage considering the shrinkage effect according to claim 2, wherein the thermodynamic boundary conditions of the heat exchange comprise respectively calculating heat loss caused by heat convection and heat radiation by Newton's law of cooling and Stefan-Boltzman's law, and simultaneously adopting a FILM subroutine to realize the simulation of the change of the convection heat dissipation coefficient and the environmental temperature with time, wherein the heat convection and the heat radiation are as follows: , , In the formula, And Is heat convection loss and heat radiation loss; is a convection heat dissipation coefficient; And The concrete temperature and the environment temperature; Is the heat emissivity; for the Stefan-Boltzman constant, take 5.67×10 -8 W/(m 2 ·K 4 ); the heat conduction control equation in the concrete in the pouring process is as follows: , In the formula, The concrete pouring time is set; Is the thermal diffusivity of the concrete; adiabatic temperature rise of concrete; 、 、 is three directions of heat source.
  4. 4. The method for predicting and grading the cracking of the mass concrete pouring damage taking shrinkage effect into consideration as set forth in claim 2, wherein the concrete hydration heat release model expression is as follows: , In the formula, Is the heat release rate of the heat source; maximum value of hydration heat release of concrete; 、 The model influence coefficient; Wherein the said 、 The method is measured by a semi-adiabatic temperature rise test and specifically comprises the following steps: Step 2.1, establishing a finite element model of a semi-adiabatic temperature rise test device in ABAQUS, setting a concrete test block as a cube with a side length of 20 cm, completely wrapping an insulation box consisting of insulation layers, and calling HETVA subroutine to simulate hydration heat release of concrete based on a composite index model; 2.2, respectively carrying out parameter analysis on the thickness of the heat preservation layer, thermodynamic parameters of the heat preservation material and external environment, and selecting reasonable test conditions; step 2.3, manufacturing a test device based on the analysis result of the step 2.2, embedding a temperature sensor in the concrete, and monitoring the temperature change in real time; step 2.4, based on the temperature-age test data obtained in the step 2.3, calling the finite element model in the step 2.1 to calculate, and performing calculation on 、 Performing sensitivity analysis, fitting test curves, and finally obtaining the applicable 、 。
  5. 5. The method for predicting and grading the cracking of the large-volume concrete pouring damage considering the shrinkage effect according to claim 2 is characterized in that in the step 3, the stress analysis comprises the steps of designating the divided grid units as C3D8R types, giving mechanical properties to concrete and reinforced materials, respectively simulating the change of the elastic modulus and the thermal expansion coefficient of the concrete along with the age by calling UFIELD a subroutine and UEXPAN a subroutine, defining mechanical boundary conditions at least comprising a template fixed end constraint, a poured member constraint and a surrounding rock stratum constraint, setting an analysis step and an increment step synchronous with the step 2, introducing the temperature field obtained in the step 2 into a predefined field, calling USDFLD and UEXPAN a subroutine, and simulating the shrinkage process of the concrete based on a shrinkage prediction model and adopting Arrhenius equivalent age to replace actual time.
  6. 6. The method for predicting and grading the cracking of the large-volume concrete pouring damage taking shrinkage effect into consideration as set forth in claim 5, wherein the model expression of the concrete elastic modulus changing along with the age is as follows: , In the formula, For concrete at age of Modulus of elasticity at the time; The elastic modulus of the concrete under standard curing conditions when the age is 28 d; For calculating parameters; Correction coefficients for the mineral admixture; The model expression of the thermal expansion coefficient changing along with the age is as follows: , In the formula, For the age of Coefficient of thermal expansion at that time; coefficient of thermal expansion at age 28 d; is a hydration time parameter associated with the admixture; Wherein, the temperature strain calculation formula is as follows: , In the formula, Is temperature strain; T is the temperature variation of the concrete; The calculation formula of the Arrhenius equivalent age is as follows: , , In the formula, Running time variable in the integration process; And Respectively reference temperature and temperature history; 、 And The equivalent age, the drying starting time and the actual equivalent conversion age are respectively; is apparent activation energy; taking 8.314J/(mol.K) as an ideal gas constant; The shrinkage prediction model calculation formula is as follows: , In the formula, Is that Equivalent age of moment; Is that Time-of-day shrinkage strain; is the final shrinkage strain.
  7. 7. The method for predicting and grading the cracking of the large-volume concrete pouring damage by considering the shrinkage effect according to claim 6, wherein the steps of calling USDFLD and UEXPAN subroutines, based on a shrinkage prediction model and adopting an Arrhenius equivalent age to replace the actual time, and simulating the shrinkage process of the concrete comprise the following steps: Step 3.1, invoking USDFLD a subprogram to calculate and output an equivalent age, namely, updating the equivalent age by integrating Arrhenius acceleration factors in each increment step, and transmitting the equivalent age to UEXPAN the subprogram; Step 3.2, invoking USDFLD a subroutine to record equivalent age of drying calculation, and if pouring partitions or layering are different, determining drying calculation time of each point by using field variables or partition logic; And 3.3, calling UEXPAN a subroutine to calculate the shrinkage strain based on the equivalent age of the step 3.1 and the equivalent age calculated by the drying of the step 3.2, outputting the strain increment of the current increment step, storing the strain value of the last increment step, and then calculating the next increment step.
  8. 8. The method for predicting and grading the cracking of the large-volume concrete pouring damage taking the shrinkage effect into consideration, which is characterized in that in the step 4, the damage analysis comprises the steps of endowing the concrete with plastic damage model parameters on the basis of a stress analysis model in the step 3, realizing the time-varying property of the model parameters along with the early mechanical behavior change of the concrete by introducing field variables or calling UFIELD subprograms, introducing the stress field obtained in the step 3 into a predefined field, and calculating and outputting a damage cracking result; the damage factors in the model are calculated according to the uniaxial stress state of the concrete, the damage factors comprise a stretch-break damage factor and a crushing damage factor, and the stretch-break damage factor has the following calculation formula: , In the formula, Is a stretch-break injury factor; is a dimensionless coefficient; Normalized strain ratio; Is a tension descent section parameter; the crushing damage factor is calculated as follows: , In the formula, Is a crush injury factor; is a dimensionless coefficient; Normalized strain ratio; Is uniaxially compressive strain; Is the pressure drop section parameter; is the shape parameter of the pressed rising section.
  9. 9. The method for predicting and grading the cracking of the large-volume concrete pouring damage taking the shrinkage effect into consideration as set forth in claim 8, wherein the step 5 specifically includes: Step 5.1, burying vibrating wire type concrete embedded strain gauges in a layered and partitioned mode before pouring a site concrete structure, wherein the embedded strain gauges are used for acquiring temperature field and strain field time-course data around embedded points in real time; step 5.2, operating the numerical model according to the step 2, calculating an output temperature field result, and checking and adjusting parameters with field temperature monitoring data fed back by the strain gauge to ensure that the relative error is controlled within a range of 5%; And 5.3, calculating the output temperature strain and the strain caused by the structural self weight according to the step 3 based on the model calibration of the step 5.2, and calculating the shrinkage strain according to the field actual measurement strain, wherein the calculation formula is as follows: , In the formula, Is the actual measurement value of the strain gauge; strain values caused by the dead weight of the concrete structure; And 5.4, calculating and outputting the shrinkage strain according to the step 3 based on the calculation result of the step 5.3, and checking and adjusting parameters with the shrinkage strain obtained in the step 5.3 to ensure that the relative error is controlled within 20%.
  10. 10. The method for predicting and grading the cracking of the mass concrete placement injury taking shrinkage effect into consideration as set forth in claim 1, wherein the grading evaluation and the corresponding control measures in step 6 include: when the damage factor is more than or equal to 0 and less than 0.6, adopting conventional maintenance measures including covering heat preservation, moisture preservation maintenance, removing a mold according to a plan and conventional monitoring; when the damage factor is more than or equal to 0.6 and less than 0.9, the secondary risk area is adopted, and the reinforced maintenance measures are adopted, including thickening the heat preservation layer, prolonging the heat preservation and moisture preservation time, delaying the demolding, preventing wind and sun, and encrypting, monitoring and early warning key parts; When the damage factor is more than or equal to 0.9, the three-level risk area is treated by forced maintenance and emergency treatment measures, including multilayer heat preservation and moisture preservation, obviously delaying the form removal, controlling the temperature drop after the form removal, timely sealing and moisture preservation when cracks appear, and sealing or grouting repair if necessary.

Description

Shrinkage effect considered large-volume concrete pouring damage cracking prediction and grading evaluation method Technical Field The invention relates to the technical field of concrete structure engineering, in particular to a method for predicting and grading cracking of mass concrete pouring damage by considering shrinkage effect. Background The large-volume concrete is widely applied to the engineering of subway stations, underground structure bottom plates, bearing platforms, bridge foundations, hydraulic structures and the like. The cement has large cross section size and difficult heat dissipation, the internal temperature is rapidly increased due to hydration heat release of cement after pouring, the external surface is influenced by heat exchange conditions such as a template, air, surrounding rock and the like to form a remarkable temperature gradient, and the subsequent cooling process is superposed with volume deformation such as self shrinkage, drying shrinkage and the like, and is converted into tensile stress under the constraint actions of a foundation, the surrounding rock, reinforcing steel bars, a poured structure and the like, so that cracks are easily induced at the stage that the early-age strength and the rigidity are not fully developed, and the impermeability and the durability are further influenced. At present, a 'temperature field-temperature stress' path is adopted for cracking analysis, namely, the temperature stress of a certain point of concrete is firstly obtained, and then the temperature stress is compared with the allowable tensile stress to judge whether the point is cracked. The method essentially belongs to point discrimination, and is difficult to visually and comprehensively evaluate the whole cracking range, the spatial distribution and the risk partition of the main body structure. Meanwhile, the traditional method has the common problems of insufficient calibration of hydration heat release parameters, insufficient consideration of boundary heat exchange along with time change, simplified shrinkage effect and coupling treatment with temperature process, insufficient time-varying embodiment of early-age material parameters, lack of closed-loop check of monitoring data and model results, and the like in engineering application, so that crack prediction accuracy and measure pertinence are limited. Therefore, it is needed to propose a cracking prediction and grading evaluation method for the whole process of pouring mass concrete, which can comprehensively consider hydration heat release, boundary heat exchange, shrinkage effect and material time-varying characteristics to realize damage/cracking space identification and risk partition of structural dimensions and provide basis for temperature control and maintenance and cracking control measures. Disclosure of Invention In order to solve the problems in the background technology, the invention provides a method for predicting and grading and evaluating the cracking of the large-volume concrete pouring damage by considering the shrinkage effect, which realizes the transition from point discrimination to global identification and grading management and control of cracking analysis, and simultaneously considers the time-varying characteristics of a temperature field, the shrinkage effect and materials, thereby improving the prediction precision and operability, reducing the risk of cracking and leakage, improving the durability and reducing the reworking cost. In order to achieve the above purpose, the present invention adopts the following scheme: a method for predicting and grading the cracking of a large-volume concrete pouring damage by considering the shrinkage effect comprises the following steps: Step 1, a large-volume concrete structure geometric model is established, the geometric model is subjected to layered sectioning and grid division according to a preset construction pouring scheme, and a construction process is simulated in a life-death unit mode to construct a numerical model; Step 2, performing thermal analysis on the numerical model, and calculating to obtain a temperature field during construction and maintenance by considering concrete hydration heat release and dynamic thermal boundary conditions; step 3, carrying out stress analysis on the numerical model, introducing the temperature field as a thermal load, and calculating to obtain a stress field by considering the mechanical property of the concrete and the time-varying characteristic of shrinkage deformation; step 4, carrying out damage analysis on the numerical model, introducing the stress field, and calculating to obtain a damage cracking result by adopting a concrete plastic damage model (CDP model); Step 5, arranging sensors on a construction site, monitoring the temperature and strain change of the concrete in real time, feeding back monitoring data to the numerical model for verification and correction, and predicting crack generation