Calculation method of load stress of pavement structure of CRC layer overlaid on old cement pavement

Abstract

The present invention discloses a method for calculating the load stress of a pavement structure of a CRC layer with a separate overlay on an old cement pavement, including obtaining the structure and material parameters of the pavement structure, simplifying the pavement structure into a double-layer plate model, calculating the cross-sectional bending stiffness of the surface plate and the base plate of the double-layer plate model, calculating the bending moment coefficient of the surface plate and the base plate of the double-layer plate model, and respectively calculating the load stress of the surface plate and the old cement road panel under the critical load position based on the calculated cross-sectional bending stiffness and bending moment coefficient. The method solves the problem that the lateral tensile stress on the top surface of the CRC layer and the longitudinal tensile stress on the bottom surface of the old cement road panel cannot be calculated simultaneously, and reduces the difficulty of solving, applying and promoting the load stress of the CRC layer structure of the old cement pavement under the dual modulus theory.

Description

Technical Field

[0001] The invention relates to the technical field of overlaying old cement pavement, and in particular to a load stress calculation method for a pavement structure of a separated overlaying CRC layer of an old cement pavement based on a dual modulus theory. Background Art

[0002] Cement concrete pavement is widely used due to its high bearing capacity, high rigidity and long service life. Cement concrete pavement includes plain joint concrete pavement (JPCP), continuously reinforced concrete pavement (CRCP), reinforced concrete pavement (JRCP), steel fiber concrete pavement (SFCP), prestressed concrete pavement (PCP), prefabricated concrete pavement, etc. During the service life of cement concrete pavement, due to the harsh environment such as heavy load, the cement pavement will produce cracks, broken boards, voids, misalignment and other diseases. In addition, due to the fact that the traffic volume growth rate during the design service life is much higher than expected and affected by other factors, many cement pavements in my country have suffered serious structural damage and functional decline before reaching their service life, which seriously affects the safety and efficiency of highway transportation. Therefore, the durability improvement of cement pavement based on life extension repair has become an important demand for the high-quality development of my country's highway transportation infrastructure.

[0003] The overlaying form of the separated overlay of the continuous reinforced concrete layer (CRC layer or CRC board) on the old cement pavement can combine the characteristics of the old cement pavement and the CRC board. First, the CRC layer can greatly reduce the load and temperature stress of the old cement pavement, thereby extending the life of the old cement pavement. Secondly, the old cement pavement, as the underlying layer of the CRC layer, can greatly reduce the risk of the CRC layer being emptied and reduce the probability of the CRC board being broken. The old cement road slab and the CRC layer are both the main load-bearing structural layers, which greatly improves the bearing capacity of the pavement.

[0004] Although there have been successful application cases of this structure, there is still no systematic and mature design method. In particular, the load stress solution link is important in cement pavement design. Neither the latest draft of the highway cement concrete pavement design specification nor the current highway cement concrete pavement design specification can calculate the load stress of the two structural layers separately at the same time. The draft for comments is because it is impossible to calculate the load stress of the upper base plate in the composite base plate, while the current specification does not distinguish the load stress direction of the CRC layer. The calculation result is still longitudinal tensile stress, which does not meet the failure characteristics of the CRC plate. In addition, the existing load stress calculation formula does not take into account the tensile and compressive anisotropy of cement concrete materials when establishing it, so the established formula lacks accuracy and scientificity.

[0005] In summary, how to establish a load stress calculation method for the pavement structure of the separated overlay CRC layer of the old cement pavement based on the current specification system and combined with the dual modulus theory is a technical problem that needs to be solved urgently. Summary of the invention

[0006] The main purpose of the present invention is to provide a method for calculating the load stress of a pavement structure of a separated CRC layer of an old cement pavement. The present invention is based on the dual modulus theory, draws on the formula form of the current specification, and combines the regression fitting of a large amount of data calculated by finite element calculation to obtain the load stress calculation formula for the life-extending pavement structure.

[0007] To solve the above problems, the technical solutions proposed by the present invention are as follows:

[0008] A method for calculating load stress of a pavement structure of a separated CRC layer of an old cement pavement, characterized in that it comprises the following steps:

[0009] S1. Obtain the structural and material parameters of the pavement structure;

[0010] S2. Simplify the pavement structure into a double-layer plate model;

[0011] S3. Calculate the cross-sectional bending stiffness of the surface plate and the base plate of the double-layer plate model; the surface plate is the CRC layer and the base plate is the old cement road plate;

[0012] First, calculate the neutral plane height of each layer h 0 , the calculation formula is:

[0013]

[0014] in, E 1 and E 2 is the tensile and compressive elastic modulus, the unit is MPa; μ 1 and μ 2 is the tensile and compressive elastic modulus, the unit is MPa; h is the thickness of the laminate, in m

[0015] Next, based on the neutral plane height obtained in step S301, the neutral plane height cross-sectional bending stiffness D of each layer is calculated, and the calculation formula is:

[0016]

[0017] S4. Based on the maximum transverse tensile stress on the surface of the CRC slab and the maximum longitudinal tensile stress on the bottom of the old cement pavement slab under different load sizes obtained by finite element calculation, the bending moment coefficients of the surface slab and the base slab of the double-layer slab model were fitted;

[0018] Among them, the calculation expression of the bending moment coefficient of the surface layer plate is:

[0019]

[0020] The calculation expression of the base plate bending moment coefficient is:

[0021]

[0022] in, r g It is the equivalent relative stiffness radius of the laminate when calculating the load stress, and its unit is mm; α is the equivalent load radius of double wheel load on one side, in m;

[0023] S5. Based on the calculated cross-section bending stiffness and bending moment coefficient, calculate the load stress of the surface layer plate and the old cement road slab at the critical load position respectively;

[0024] Among them, the calculation formula for solving the surface plate load stress is:

[0025]

[0026] The calculation formula for solving the base plate load stress is:

[0027]

[0028] In the formula, D c is the cross-sectional bending stiffness of the surface layer plate, and its unit is MPa•m 3 ; D b is the cross-sectional bending stiffness of the base plate, and its unit is MPa•m 3 ; Ps The single axle weight is the design axle load, and its unit is MN; φ is the moment distribution coefficient; M c is the bending moment coefficient of the surface plate; M b is the bending moment coefficient of the base plate; h c is the CRC layer thickness; h b1 is the thickness of the old cement concrete panel.

[0029] Specifically, when the base layer of the old cement road slab is a semi-rigid or rigid base layer, the old cement road slab is the upper base layer, the old road base layer is the lower base layer, and the old cement road slab and its road base layer are regarded as a composite base layer.

[0030] Specifically, when the base plate is a composite base plate, the calculation formula for the composite section bending stiffness of the composite base plate is as follows:

[0031]

[0032] in, D b1 is the bending stiffness of the upper base plate section, MPa•m 3 ; D b2 is the bending stiffness of the lower base plate section, MPa•m 3 .

[0033] Specifically, when the base plate is a composite base plate, the load stress of the base plate is solved becomes the nominal load stress of the composite plate , further solve the load stress of the upper base plate, the calculation formula is:

[0034] .

[0035] Specifically, the specific calculation process of the bending moment coefficient of the surface plate and the base plate is as follows:

[0036] A large number of pavement structure finite element models of separated overlay CRC layers of old cement pavements are established. The structural layer thickness and material parameters of the above pavement structure finite element models are different. Among them, the dual modulus constitutive model of the material is set through the UMAT subroutine;

[0037] Calculate and read the maximum transverse tensile stress on the surface of the CRC layer and the maximum longitudinal tensile stress on the bottom surface of the old cement road slab under different load sizes in the finite element model of the pavement structure;

[0038] Calculate the bending stiffness and moment distribution coefficient of the surface plate and base plate sections of the pavement structure finite element model, and substitute the data into the surface plate and base plate load stress calculation formula to obtain the moment coefficient of the surface plate and base plate of the pavement structure finite element model;

[0039] Calculate the equivalent relative stiffness radius and equivalent load radius corresponding to the finite element model of the pavement structure. Combined with the bending moment coefficients of the surface layer and base layer obtained in the previous step, the calculation formulas for the bending moment coefficients of the surface layer and base layer are fitted respectively.

[0040] Specifically, the material parameters acquired in step S1 include tensile elastic modulus, compressive elastic modulus, tensile Poisson's ratio and compressive Poisson's ratio.

[0041] Compared with the existing similar methods, the advantages of the present invention are:

[0042] 1. The present invention takes into account the tensile and compressive anisotropy of cement concrete, introduces the dual modulus theory when establishing the calculation method, and takes into account the failure characteristics of the CRC layer thrust. The transverse tensile stress on the top surface of the CRC layer and the longitudinal tensile stress on the bottom surface of the old cement road slab are used to fit the surface layer bending moment coefficient and the base layer bending moment coefficient respectively. The load stress solved by the established calculation method is more in line with the structural failure characteristics, and is more scientific, reasonable and accurate.

[0043] 2. The present invention fully combines the current cement pavement design specifications and the calculation method of the latest draft for comments, solves the problem of being unable to simultaneously calculate the transverse tensile stress on the top surface of the CRC layer and the longitudinal tensile stress on the bottom surface of the old cement road slab, and plays a role in improving and supplementing the current specifications.

[0044] 3. Compared with the finite element method, the present invention greatly reduces the difficulty of solving the load stress of the CRC layer structure of the old cement pavement under the dual modulus theory, and reduces the application threshold and promotion difficulty of the dual modulus theory. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the flow of the present invention when solving load stress. DETAILED DESCRIPTION

[0046] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereby.

[0047] See also Figure 1 A method for calculating the load stress of a pavement structure of a separated overlay CRC layer on an old cement pavement comprises the following steps:

[0048] S1. Obtain the structural and material parameters of the pavement structure (life extension overlay structure). CRC refers to the continuous reinforced concrete overlay of the old cement pavement.

[0049] The parameters obtained include: tensile and compressive elastic modulus, tensile and compressive Poisson's ratio and thickness of each structural layer. The tensile and compressive modulus and tensile and compressive Poisson's ratio of the material can be determined through indoor tests, or through any mechanical parameter in Table E.0.3-1 and E.0.2.2 of the "Highway Cement Concrete Pavement Design Code" (JTG_D40-2011), to determine the elastic modulus (compression modulus), and then determine the tensile modulus based on the tensile and compressive modulus ratio of 0.55.

[0050] S2. Simplify the pavement structure into a double-layer slab model.

[0051] When simplifying the pavement structure into a double-layer slab model, the CRC layer is the surface slab and the old cement road slab is the base slab. If the base of the old cement road slab is a semi-rigid or rigid base, the old cement road slab is the upper base slab and the old road base is the lower base slab. The old cement road slab and its base slab are regarded as a composite base slab, and then simplified into a double-layer slab model together with the CRC layer.

[0052] S3. Calculate the cross-sectional bending stiffness of the surface layer and base layer.

[0053] The following formula is used to calculate the neutral plane height of each rigid and semi-rigid structural layer (laminate):

[0054]

[0055] in, E 1 and E 2 is the tensile and compressive elastic modulus, the unit is MPa; μ 1 and μ 2 is the tensile and compressive elastic modulus, the unit is MPa; h is the thickness of the ply (structural layer), in m

[0056] The following formula is used to calculate the neutral plane height section bending stiffness of each rigid and semi-rigid structural layer (laminate):

[0057]

[0058] If the base plate is a composite base plate, the composite section bending stiffness of the composite base plate is calculated based on the section bending stiffness of the upper base plate and the lower base plate:

[0059]

[0060] in, D b1 is the bending stiffness of the upper base plate section, its unit is MPa•m 3 ; D b2 is the bending stiffness of the lower base plate section, its unit is MPa•m 3 ;

[0061] S4. Based on the maximum transverse tensile stress on the surface of the CRC slab and the maximum longitudinal tensile stress on the bottom surface of the old cement pavement slab under different load sizes obtained by finite element calculation, the bending moment coefficients of the surface slab and the base slab of the double-layer slab model were fitted.

[0062] Specifically, the calculation formula for the moment coefficient of the surface plate and the base plate involves the following steps: ① Establish a large number of pavement structure finite element models of the separated overlay CRC layer of the old cement pavement. The structural layer thickness and material parameters of these models are different. Among them, the dual modulus constitutive model of the material is set by the UMAT subroutine. ② Calculate and read the maximum transverse tensile stress (perpendicular to the driving direction) of the CRC layer surface and the maximum longitudinal tensile stress (along the driving direction) of the bottom surface of the old cement road slab under different load sizes of these pavement structure finite element models. ③ Calculate the cross-sectional bending stiffness and moment distribution coefficient of the surface plate and the base plate of these pavement structure finite element models, and substitute the data into the surface plate and base plate load stress calculation formula to calculate the moment coefficient of the surface plate and the base plate of these pavement structure finite element models respectively. ④ Calculate the equivalent relative stiffness radius and equivalent load radius corresponding to these pavement structure finite element models, and combine the moment coefficient of the surface plate and the base plate obtained in the previous step to fit the calculation formula of the moment coefficient of the surface plate and the base plate respectively.

[0063] Among them, the calculation formula of the bending moment coefficient of the surface layer plate obtained by fitting in this application is:

[0064]

[0065] The calculation formula of the bending moment coefficient of the base plate is:

[0066]

[0067] in, r g To calculate the equivalent relative stiffness radius of the double-layer plate when the load stress is applied, the unit is mm, and the calculation method refers to B.2.3-3 in the "Highway Cement Concrete Pavement Design Code" (Draft for Comments JTG 3340-202*); α It is the equivalent load radius of double wheel load on one side, with the unit of m. The calculation method refers to B.2.3-2 of "Design Specification for Highway Cement Concrete Pavement" (Draft for Comments JTG 3340-202*).

[0068] S5. Calculate the load stress of the surface layer slab and the old cement road slab at the critical load position respectively.

[0069] Based on the cross-sectional bending stiffness obtained in step S3 and the bending moment coefficient obtained in step S4, the load stress of the surface layer plate is solved using the following formula:

[0070]

[0071] The load stress of the base plate is solved using the following formula:

[0072]

[0073] in,D c is the cross-sectional bending stiffness of the surface layer plate, and its unit is MPa•m 3 ; D b is the cross-sectional bending stiffness of the base plate, and its unit is MPa•m 3 ; P s The single axle weight is the design axle load, and its unit is MN; φ is the moment distribution coefficient, and its calculation method refers to B.2.2-2 in the "Highway Cement Concrete Pavement Design Code" (Draft for Comments JTG 3340-202*).

[0074] When the base plate is a composite base plate, the load stress of the base plate obtained needs to be calculated. becomes the nominal load stress of the composite plate , and further solve the load stress of the upper base plate. The calculation formula is:

[0075] .

[0076] The present invention takes into account the tensile and compressive anisotropy of cement concrete, introduces the dual modulus theory when establishing the calculation method, and takes into account the failure characteristics of the CRC layer thrust. The transverse tensile stress on the top surface of the CRC layer and the longitudinal tensile stress on the bottom surface of the old cement road slab are used to fit the surface layer bending moment coefficient and the base layer bending moment coefficient respectively. The load stress solved by the established calculation method is more in line with the structural failure characteristics, and is more scientific, reasonable and accurate.

[0077] The present invention will be further described below in conjunction with specific embodiments.

[0078] The structural and material parameters to be determined in this embodiment are shown in Table 1.

[0079] Table 1 Pavement structure and material parameters

[0080]

[0081] According to step S2, the pavement structure in Table 1 is simplified into a separated double-layer slab model, in which the CRC layer is used as the surface slab, the old mud concrete panel is used as the upper base slab, the cement stabilized gravel base is used as the lower base slab, the old mud concrete panel and the cement stabilized gravel base are used as the composite base slab, and the graded gravel layer and the soil base are used as the foundation.

[0082] In this embodiment, according to step S3, the cross-sectional bending stiffness of the surface layer board and the composite base layer board is calculated.

[0083] The neutral plane height of the surface layer, i.e. CRC layer:

[0084]

[0085] The neutral surface height of the upper base plate, i.e. the old cement concrete road slab:

[0086]

[0087] The neutral surface height of the lower base plate, i.e. the cement stabilized gravel base:

[0088]

[0089] According to step S3, the neutral plane height cross-sectional bending stiffness of each rigid and semi-rigid structural layer is calculated respectively.

[0090] Surface plate, i.e. CRC layer section bending stiffness:

[0091]

[0092] The bending stiffness of the cross section of the upper base plate, i.e. the old cement concrete road plate:

[0093]

[0094] Bending stiffness of the lower base plate, i.e. cement stabilized crushed stone base section:

[0095]

[0096] If the base plate is a composite base plate, calculate the bending stiffness of the composite section of the upper base plate and the lower base plate.

[0097]

[0098] According to step S4, the bending moment coefficients of the surface layer plate and the composite base plate are calculated.

[0099] Calculate the bending moment coefficient of the facing plate.

[0100] With reference to B.2.3-2 and B.2.3-3 in the Code for Design of Highway Cement Concrete Pavement (Draft for Comments JTG 3340-202*), the equivalent load radius of double wheel load on one side is obtained to be 0.238m, and the equivalent relative stiffness radius of the double-layer slab is 1.124m.

[0101] The calculation process is:

[0102]

[0103] Calculate the bending moment coefficient of the base plate. The calculation process is:

[0104]

[0105] In this embodiment, according to step S05, the bending moment coefficients of the surface layer board and the composite base layer board are calculated.

[0106] According to step S501, the load stress of the surface layer board is solved.

[0107] Referring to B.2.2-2 of the "Highway Cement Concrete Pavement Design Code" (Draft for Comments JTG 3340-202*), the moment distribution coefficient between the surface layer slab and the base layer slab is obtained to be 0.805.

[0108] The load stress calculation process of the surface layer plate is:

[0109]

[0110] The load stress calculation process of the base plate is:

[0111]

[0112] When the base plate is a composite base plate, the load stress of the base plate is converted into the nominal load stress of the composite base plate, and the load stress of the upper base plate is further calculated.

[0113]

[0114] The above calculation results were compared with the load stress data measured in actual engineering, and it was found that the results were highly consistent, which also verified the accuracy and reliability of the load stress calculation of the present invention.

[0115] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. The load stress calculation method of the pavement structure of the separated overlay CRC layer of the old cement pavement is characterized by: The steps include: S1. Obtain the structural and material parameters of the pavement structure; S2. Simplify the pavement structure into a double-layer plate model; S3. Calculate the cross-sectional bending stiffness of the surface plate and the base plate of the double-layer plate model; the surface plate is the CRC layer and the base plate is the old cement road plate; First, calculate the neutral plane height of each layer h 0 , the calculation formula is: ； in, E 1 and E 2 is the tensile and compressive elastic modulus, the unit is MPa; μ 1 and μ 2 is the tensile and compressive elastic modulus, the unit is MPa; h is the thickness of the layer, in m; Next, based on the obtained neutral plane height, the neutral plane height section bending stiffness D of each layer is calculated using the following formula: ； S4. Based on the maximum transverse tensile stress on the surface of the CRC plate and the maximum longitudinal tensile stress on the bottom of the old cement road plate under different load sizes obtained by finite element calculation, the bending moment coefficients of the surface plate and the base plate of the double-layer plate model are fitted; where, The calculation expression of the bending moment coefficient of the surface plate is: ； The calculation expression of the base plate bending moment coefficient is: ； in, r g The equivalent relative stiffness radius of the double-layer plate when calculating the load stress, in mm; α is the equivalent load radius of double wheel load on one side, in m; S5. Based on the calculated cross-sectional bending stiffness and bending moment coefficient, calculate the load stress of the surface layer plate and the old cement road slab at the critical load position; where: The calculation formula for solving the surface plate load stress is: ； The calculation formula for solving the base plate load stress is: ； In the formula, D c is the cross-sectional bending stiffness of the surface layer plate, and its unit is MPa•m 3 ; D b is the cross-sectional bending stiffness of the base plate, and its unit is MPa•m 3 ; Ps The single axle weight is the design axle load, and its unit is MN; φ is the moment distribution coefficient; M c is the bending moment coefficient of the surface plate; M b is the bending moment coefficient of the base plate; h c is the CRC layer thickness; h b1 is the thickness of the old cement concrete panel.

2. The method for calculating load stress of pavement structure of separated CRC layer of old cement pavement according to claim 1 is characterized in that: When the base layer of the old cement road slab is a semi-rigid or rigid base layer, the old cement road slab is the upper base layer, the old road base layer is the lower base layer, and the old cement road slab and its road base layer are regarded as a composite base layer.

3. The method for calculating load stress of pavement structure of separated CRC layer overlay of old cement pavement according to claim 2 is characterized in that: When the base plate is a composite base plate, the calculation formula for the composite section bending stiffness of the composite base plate is as follows: ； in, D b1 is the bending stiffness of the upper base plate section, its unit is MPa•m 3 ; D b2 is the bending stiffness of the lower base plate section, its unit is MPa•m 3 .

4. The method for calculating load stress of pavement structure of separated CRC layer overlay on old cement pavement according to claim 3 is characterized in that: When the base plate is a composite base plate, the load stress of the base plate will be solved becomes the nominal load stress of the composite plate , further solve the load stress of the upper base plate, the calculation formula is: 。 5. The method for calculating load stress of pavement structure of separated overlay CRC layer of old cement pavement according to any one of claims 1 to 4, characterized in that: The specific calculation process of the bending moment coefficient of the surface layer plate and the base layer plate is as follows: A large number of pavement structure finite element models of separated overlay CRC layers of old cement pavements are established. The structural layer thickness and material parameters of the above pavement structure finite element models are different. Among them, the dual modulus constitutive model of the material is set through the UMAT subroutine; Calculate and read the maximum transverse tensile stress on the surface of the CRC layer and the maximum longitudinal tensile stress on the bottom surface of the old cement road slab under different load sizes in the finite element model of the pavement structure; Calculate the bending stiffness and moment distribution coefficient of the surface plate and base plate sections of the pavement structure finite element model, and substitute the data into the surface plate and base plate load stress calculation formula to obtain the moment coefficient of the surface plate and base plate of the pavement structure finite element model; Calculate the equivalent relative stiffness radius and equivalent load radius corresponding to the finite element model of the pavement structure. Combined with the bending moment coefficients of the surface layer and base layer obtained in the previous step, the calculation formulas for the bending moment coefficients of the surface layer and base layer are fitted respectively.

6. The method for calculating load stress of pavement structure of separated CRC layer of old cement pavement according to claim 5 is characterized in that: The material parameters acquired in step S1 include tensile elastic modulus, compressive elastic modulus, tensile Poisson's ratio and compressive Poisson's ratio.

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