Cement pavement axle load conversion method considering concrete mechanics and fatigue tension-compression anisotropy
By combining the dual-modulus theory and the damage equivalence principle, the problems of tensile-compressive anisotropy of concrete and fatigue tensile-compressive anisotropy in cement pavement design are solved, achieving more accurate axle load conversion and improved structural design safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-14
- Publication Date
- 2026-04-03
AI Technical Summary
Existing cement pavement designs fail to effectively consider the tensile-compressive anisotropy and fatigue tensile-compressive anisotropy of concrete, resulting in inaccurate axle load conversions and affecting the reliability and safety of design life predictions.
The stress and material strength of cement pavement structure are calculated using the bimodulus theory. Combined with the fatigue parameters of alternating tension and compression loads, the axle load is converted using the damage equivalence principle, taking into account the tension-compression anisotropy of concrete and probabilistic fatigue life.
It improves the scientific validity and safety of axle load conversion, more accurately reflects the damage contribution of cement pavement, and appropriately increases the safety redundancy and reliability of structural design.
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Figure CN121789867A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of cement pavement design technology, and in particular to a method for calculating axle loads of cement pavement that takes into account concrete mechanics and fatigue tension-compression anisotropy. Background Technology
[0002] Cement concrete pavements are widely used in heavy-duty traffic roads due to their high load-bearing capacity, high stiffness, and long service life. However, in actual use, many cement pavements often fail to reach their designed service life, exhibiting premature aging. This not only affects the sustainability of road services but also results in a huge waste of economic and social resources. Besides external factors such as traffic overload and environmental erosion, this problem is closely related to the simplified assumptions made in current cement pavement design theory regarding the mechanical behavior and fatigue characteristics of concrete materials.
[0003] Firstly, my country's "Specifications for Design of Cement Concrete Pavement for Highways" (JTG D40-2011) and related design methods typically treat cement concrete as a linear elastic, isotropic material, using a single modulus of elasticity for structural analysis and stress calculation. However, as a typical composite material, cement concrete exhibits significant differences in its modulus of elasticity under tension and compression, demonstrating marked anisotropy. Continuing to use the single modulus theory for load stress calculations on cement pavements may introduce non-negligible errors, particularly in areas such as mid-slab deflection and stress distribution, thus affecting the accuracy of axle load conversion and the reliability of pavement structure design.
[0004] Secondly, the fatigue life of cement pavement is one of the core bases for axle load conversion. Traditional fatigue equations are usually based on stress ratios. S and stress level ratio R ( R The test data for the ≥0) test were mostly derived from indoor beam fatigue tests under a single stress mode (such as continuous tension or compression). In these tests... R The value range is mostly between 0 and 0.5, which has not been systematically considered. R The value <0 indicates fatigue behavior under alternating tensile and compressive loads. In reality, cement concrete pavements are often under complex stress states of alternating tensile and compressive stresses during use due to factors such as temperature gradient changes, poor interlayer contact, and the coupling effect of under-slab support conditions and vehicle loads. While the newly released "Design Specification for Cement Concrete Pavements of Highways (Draft for Comments)" (JTG 3340-202*) attempts to indirectly consider such effects by introducing a voiding coefficient, it has not yet established a systematic model at the material fatigue constitutive level. Therefore, the axle load conversion method based on existing fatigue equations cannot accurately reflect the damage accumulation process of the pavement under alternating tensile and compressive loads, leading to an unsafe prediction of design life. Summary of the Invention
[0005] The main objective of this invention is to provide a method for converting axle loads on cement pavements that considers the mechanics and fatigue anisotropy of cement concrete. This method takes into account the influence of concrete mechanics and fatigue anisotropy, fully considering the impact of the probabilistic fatigue life of concrete, thus improving the scientific accuracy of axle load conversion for cement pavements. To solve the above problems, the technical solution proposed by this invention is as follows: A method for converting axle loads on cement pavements that considers concrete mechanics and fatigue tension-compression anisotropy includes the following steps: S1. Determine basic parameters for traffic load, climate environment, pavement structure, and materials. Obtain the traffic load composition, number of axle loads at each level, and maximum temperature gradient at the highway location; preliminarily design the pavement structure, determine the material mechanical parameters, and obtain the tensile-compressive elastic modulus ratio. r ; S2. Calculate the stress and material strength of the pavement structure under the bimodulus theory. Based on the single-modulus theory, the load stress of each level of axial load and the temperature stress under the maximum temperature gradient are calculated, and then converted into stress and strength under the bimodulus theory using the following formula:
[0006] in: s 单 and s 双 These refer to the strength or stress under single-modulus and dual-modulus theories, respectively. r The ratio of tensile to compressive elastic modulus; S3. Axle load conversion based on the damage equivalence principle. Determine the target reliability and corresponding fatigue parameters based on the highway grade. a , b , c ; Calculate the nominal stress level of each axle load. :
[0007] in: for i The nominal stress level of the grade axle load; s p,i The load stress of the i-th level axial load under the bimodulus theory; s t This is due to temperature stress; f r For flexural strength; If any level of axle load If the value is greater than 1, return to step S2 to redefine the road surface structure; otherwise... Calculate the conversion factors of each axle load to the design axle load. k i:
[0008] Among them, subscript s Indicates the design axle load. This indicates the nominal stress level of the design axle load; Convert each level of axle load into the equivalent design axle load application number. N s,i :
[0009] in: N i for i Number of times the axle load is applied.
[0010] Specifically, the tensile-compressive elastic modulus ratio r The value is determined through experiments or based on experience and is 0.35.
[0011] Specifically, the target reliability is determined according to Table 3.0.1 in the "Specifications for Design of Cement Concrete Pavement of Highway" (JTG D40-2011). When the pavement slab uses common C30, C35, and C40 concrete, the fatigue parameters are... a , b , c Determine the target reliability by looking up a table.
[0012] Specifically, the fatigue parameter value table is as follows: Table 1. Fatigue parameter values under different target reliability levels. .
[0013] Specifically, if other types of concrete are used, the fatigue parameters... a、b , c The fatigue equation was obtained by fitting a double logarithmic quadratic fatigue equation through bending fatigue tests of cement concrete beams under alternating tension and compression loads. The fatigue equation is in the form of:
[0014] in, N For fatigue life, S This refers to the stress level.
[0015] Compared with existing similar methods, the advantages of the present invention are: 1. This invention considers the influence of the mechanics and fatigue anisotropy of cement concrete. When calculating the axle load conversion factor, the load stress under the bimodulus theory is used, and the fatigue parameters take into account the influence of alternating tensile and compressive loads. Therefore, the resulting axle load conversion method better highlights the weak tensile properties of concrete, making the conversion method more scientific and appropriately increasing the safety redundancy in structural design.
[0016] 2. This invention fully considers the characteristics of probabilistic fatigue life of cement concrete. When converting axle loads, the target reliability is determined according to the safety level of the highway, thereby selecting the corresponding fatigue parameters for determining the axle load conversion coefficient, which improves the systematic nature of the cement pavement reliability method.
[0017] 3. This invention is fully compatible with the current cement pavement design specifications. It can convert the pavement structure load or temperature stress obtained from the specifications into load or temperature stress under the bimodulus theory without having to redefine the solution method for pavement structure load and temperature stress under the bimodulus theory. This reduces the difficulty of applying the bimodulus theory in the axle load conversion of cement pavement. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of the process of axle load conversion in this invention. Detailed Implementation
[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this does not limit the scope of protection of the present invention.
[0020] See Figure 1 A method for converting axle loads on cement pavements that considers concrete mechanics and fatigue tension-compression anisotropy includes the following steps: S1. Basic parameters such as traffic load, climate environment, pavement structure and materials; First, the traffic load composition and climate environment of the highway location were determined. A traffic load survey was conducted according to the relevant provisions in Appendices A.1 and A2.1 of the "Specifications for Design of Cement Concrete Pavement of Highway" (JTG D40-2011), and the standard value of the maximum temperature gradient was determined according to Table 3.0.10. T g .
[0021] Next, the pavement structure was initially designed based on experience, and the mechanical parameters of the materials were determined. The relevant mechanical parameters of the pavement materials were determined according to Appendix E of the "Specification for Design of Cement Concrete Pavement of Highway" (JTG D40-2011), among which the flexural tensile strength and elastic modulus of cement concrete were determined according to Table E.0.3-1.
[0022] When conditions permit, the ratio of the tensile and compressive elastic moduli of the material should be determined by experiment, and the ratio should be calculated according to the following formula. r :
[0023] in: E T The tensile modulus of elasticity, in MPa. E CThe tensile modulus of elasticity is expressed in MPa. For cement concrete, a value of 0.35 is used if conditions do not permit this.
[0024] First, calculate the load stress of each axle load level and the temperature stress under the maximum temperature gradient under the single modulus theory. The calculations are performed according to the relevant provisions in Appendix B of the "Specifications for Design of Cement Concrete Pavement of Highway" (JTG D40-2011).
[0025] Next, the stress calculation results and flexural strength are converted to the pavement structure stress and strength under the bimodulus theory. The load stresses of each axle load, the temperature stress under the maximum temperature gradient, and the flexural strength all need to be converted. The calculation formula is:
[0026] in: s 单 and s 双 These represent the strength or stress under single-modulus and dual-modulus theories, respectively, in MPa; r This represents the ratio of tensile to compressive elastic moduli. The stress conversion formula under the dual-modulus theory is derived from the formulas for calculating the maximum flexural tensile stress of a beam under two constitutive theories when the beam is bent at four points.
[0027] First, determine the fatigue parameter values based on the highway grade. When the cement pavement slab uses common ordinary cement concrete (such as C30, C35, or C40), first determine the values according to Table 3.0.1 in the "Specifications for Design of Cement Concrete Pavement of Highway" (JTG D40-2011), and then further determine the fatigue parameter values according to Table 1. If other types of concrete are used, the fatigue parameters should be obtained by conducting bending tests on cement concrete beams considering alternating tension and compression loads, and fitting the fatigue life to a double logarithmic quadratic fatigue equation, as shown in the following form.
[0028]
[0029] Table 1. Fatigue parameter values under different target reliability levels.
[0030] Next, calculate the nominal stress level of each axle load. The calculation formula is: in: The nominal stress level for Class i axle load. s p The load stress under the bimodulus theory is expressed in MPa. s t The temperature stress under the bimodulus theory is expressed in MPa. f ris the flexural tensile strength under the bimodulus theory, in MPa.
[0031] If any level of axle load If the value is greater than 1, it indicates that the load-temperature coupled stress of this axle load level has exceeded the flexural tensile strength of the concrete. The structural design is considered unreasonable, and the pavement structure should be redesigned. In this case, return to step S2 to redesign the pavement structure. Otherwise, calculate the conversion factor of each axle load level to the design axle load. k i ， Based on the Palmgen-Miner damage accumulation theory and the damage equivalence principle, the following is derived: k i The calculation formula is as follows: Finally, the axle loads at each level are converted into the equivalent design axle load application times. N s,i The calculation formula is: in: N i for i Number of axle load applications, s Represents the design axle load.
[0032] The present invention will be further described below with reference to specific embodiments.
[0033] S1. Basic parameters such as traffic load, climate environment, structure and materials; First, the traffic load composition and climate environment of the highway location were determined. The investigation determined that the design axle load for the highway location would be 100 kN, with other axle load levels including 150 kN, 200 kN, 250 kN, and 300 kN, and daily application frequencies for each axle load level being 150, 100, 50, and 5 times, respectively. The highway is classified as Zone III, with the maximum temperature gradient... T g It is 90℃ / m.
[0034] Next, based on experience, a preliminary pavement structure was drafted, and the material mechanical parameters were determined. The proposed pavement structure is a 0.3m ordinary concrete surface layer + a 0.18m roller-compacted concrete base layer + a 0.04m asphalt concrete interlayer + a 0.2m graded crushed stone subbase. The subgrade soil is loess, and the pavement slab dimensions are 5m × 4m. C40 cement concrete is proposed to be used for the concrete surface layer. The mechanical parameters of each structural layer are shown in Table 2, where the tensile-compressive modulus of elasticity ratio of C40 cement concrete was determined to be 0.334 through testing.
[0035] Table 2 Mechanical parameters of road surface materials
[0036] S2. Calculate the load stress, temperature stress, and material strength of cement pavement structure under the dual-modulus theory; First, calculate the load stress of each level of axle load and the temperature stress under the maximum temperature gradient under the single modulus theory.
[0037] The calculation results are shown in Table 3.
[0038] Table 3 Load stress of each axle load and temperature stress under maximum temperature gradient
[0039] Next, the stresses of various pavement structures are converted to the bimodulus theory. Taking the stress conversion under a 100kN axle load as an example, the calculation process is as follows:
[0040] The conversion results are shown in Table 4.
[0041] Table 4. Conversion results of structural stress and strength under dual modulus.
[0042] S3. Perform axle load conversion.
[0043] First, the fatigue parameter values are determined based on the highway grade. The highway is a highway with a target reliability of 95%, using C40 cement concrete. The fatigue parameters can be obtained from Table 1. a , b and c The values were 0.920174, 0.009690, and 0.004410, respectively.
[0044] Next, calculate the nominal stress level of each axle load. Taking a 100kN axle load as an example, the calculation process is as follows:
[0045] Nominal stress levels under various axle loads As shown in Table 5.
[0047] Table 5 Nominal stress levels of axle loads at various levels calculate
[0048] Next, the conversion factors for each axle load to the design axle load are calculated. k i When using the direct conversion method, a conversion factor of 150kN axle load is used. k 150kN Taking calculation as an example, the calculation process is as follows: Conversion factors for axle loads at all levels k i The calculation results are shown in Table 6.
[0049] Table 6 Conversion Factors for Axle Loads at Various Levels k i Calculation results
[0050] Finally, the axle loads at each level are converted into the equivalent design axle load application times. N s,i Taking 150kN as an example, the calculation process is as follows:
[0051] Number of times of equivalent design axle load at each level N s,i The calculation results are shown in Table 7.
[0052] Table 7 Number of applications of equivalent design axle loads at each level N s,i Calculation results
[0053] The results show that after considering the anisotropy of tension and compression and the alternating fatigue of tension and compression, the conversion factor of heavy axle load is significantly improved, which more accurately reflects its contribution to pavement damage.
[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.
Claims
1. A method for converting axle loads on cement pavements considering concrete mechanics and fatigue anisotropy, characterized in that, Includes the following steps: S1. Determine the basic parameters of traffic load, climate environment, pavement structure, and materials. Obtain the traffic load composition, number of axle loads at each level, and maximum temperature gradient at the highway location; preliminarily design the pavement structure; determine the material mechanical parameters; and obtain the tensile-compressive elastic modulus ratio. r ; S2. Calculate the stress and material strength of the pavement structure under the bimodulus theory. Based on the single-modulus theory, the load stress of each level of axial load and the temperature stress under the maximum temperature gradient are calculated, and then converted into stress and strength under the bimodulus theory using the following formula: ； in: σ 单 and σ 双 These refer to the strength or stress under single-modulus and dual-modulus theories, respectively. r The ratio of tensile to compressive elastic modulus; S3. Axle load conversion based on the damage equivalence principle. Determine the target reliability and corresponding fatigue parameters based on the highway grade. a , b , c， Calculate the nominal stress level of each axle load. : ； in, The nominal stress level for Class i axle load; σ p,i The load stress of the i-th level axial load under the bimodulus theory; σ t This is due to temperature stress; f r For flexural strength; If any level of axle load If the value is greater than 1, return to step S2 to redefine the pavement structure; otherwise, calculate the conversion factor of each axle load to the design axle load. k i： ； Among them, subscript s Indicates the design axle load; This indicates the nominal stress level of the design axle load; Convert each level of axle load into the equivalent design axle load application number. N s,i； ； in, N i for i Number of times the axle load is applied.
2. The method for converting axle loads on cement pavement according to claim 1, characterized in that: The tensile and compressive elastic modulus ratio r The value is determined through experiments or based on experience and is 0.
35.
3. The method for converting axle loads on cement pavement according to claim 1, characterized in that: When the road slab is made of materials other than C30, C35, and C40 concrete, the fatigue parameters are... a , b , c The fatigue equation was obtained by fitting a double logarithmic quadratic fatigue equation through bending fatigue tests of cement concrete beams under alternating tension and compression loads. The fatigue equation is in the form of: ； in, N For fatigue life, S This refers to the stress level.
4. The method for converting axle loads on cement pavement according to claim 1, characterized in that: When the road slab is made of C30, C35, or C40 concrete, the target reliability is determined according to the "Specifications for Design of Cement Concrete Pavement of Highway" (JTG D40-2011).
5. The method for converting axle loads on cement pavement according to claim 4, characterized in that: The fatigue parameter values are: When the target reliability is 95%, a= 0.920174, b= 0.009690, c= 0.004410; When the target reliability is 90%, a= 0.927150, b= 0.006580, c= 0.004890; When the target reliability is 85%, a= 0.930658, b= 0.004820, c= 0.005100; When the target reliability is 80%, a= 0.933297, b= 0.003740, c= 0.005200; When the target reliability is 75%, a= 0.935793, b= 0.003090, c= 0.005240; When the target reliability is 70%, a= 0.938318, b= 0.002730, c= 0.005230.