Method for evaluating fatigue life of SMA + UHPC pavement layer of separated steel box girder cable-stayed bridge

Abstract

The invention discloses a separate steel box girder cable-stayed bridge SMA + UHPC pavement layer fatigue life evaluation method, which comprises the following steps: carrying out statistical analysis on the traffic volume at the bridge location of a cable-stayed bridge to be evaluated to obtain the bridge crossing traffic volume composition of each characteristic year; classifying according to the axle number of the vehicle type and the composition of the bridge crossing traffic volume of each characteristic year, and selecting a standard fatigue vehicle based on asphalt concrete of a bridge deck pavement layer according to a fatigue equivalent damage principle; establishing a full-bridge model and a local model of the to-be-evaluated cable-stayed bridge, and determining boundary conditions of the local model; the boundary condition acts on the local model, the stress condition of a local beam section under the most unfavorable working condition is simulated, and the stress-strain response of the bridge deck pavement layer considering the whole bridge effect is analyzed; and according to a stress analysis result, evaluating the fatigue performance of the pavement layer by utilizing a linear fatigue cumulative damage theory to obtain the total damage degree of the bridge deck pavement layer. The method has the remarkable effects that the fatigue degree of the SMA + UHPC pavement layer of the steel box girder is accurately evaluated, so that guidance is formed for the design of a steel bridge deck pavement system.

Description

Technical Field

[0001] The present invention relates to the technical field of bridge pavement life evaluation, and particularly relates to a method for evaluating the fatigue life of an SMA+UHPC pavement layer of a separated steel box girder cable-stayed bridge under vehicle loads. Background Art

[0002] Since the 1990s, long-span cable-stayed structures have been increasingly used in infrastructure construction. Generally, orthotropic steel bridge decks are adopted in cable-stayed bridges and suspension bridges, such as the Humen Bridge in Guangdong, the Yangpu Bridge in Shanghai, and the Jiangyin Yangtze River Bridge. The orthotropic steel bridge deck has different stiffnesses in two mutually perpendicular directions, resulting in structural anisotropy. The asphalt pavement layer is laid on the orthotropic steel bridge deck to directly bear vehicle loads and can play a role in protecting the orthotropic steel bridge deck. The orthotropic steel bridge deck has a relatively large flexibility, with a larger deflection than the road surface, and the environment of the steel bridge deck is more complex than that of the road surface and concrete bridges, being affected by many factors such as vehicle loads, vibrations, and high temperatures. Therefore, diseases such as cracking, rutting, and pushing of the steel bridge deck pavement layer are more serious, and the above problems have more or less occurred in the Humen Bridge, the Jiangyin Yangtze River Bridge, etc.

[0003] The diseases of the bridge pavement layer are closely related to the bridge structure, the bridge deck system structure, and the pavement layer materials. However, most of the research focuses on the structure of the single orthotropic plate of the bridge deck system and the modification of asphalt materials, and less consideration is given to the combination of the bridge structure and material modification. Since the wearing course of the pavement usually uses stone mastic asphalt (SMA) with poor flexural performance, and the performance difference between the bottom surface of the asphalt pavement layer and the orthotropic plate is large. When the asphalt material is directly bonded to the orthotropic plate through the bonding layer, large tensile stresses will occur in the asphalt material when the steel box girder bears negative bending moments, resulting in cracking of the pavement layer. Ultra-high performance concrete (UHPC) has strong flexural stiffness and can be connected to the orthotropic plate of the steel bridge deck through studs and bonding layers, effectively improving the stiffness and strength of the steel bridge deck, reducing the vertical deformation of the pavement layer, and extending the service life of the bridge pavement. Therefore, considering the characteristics of the bridge structure and the performance of the pavement layer materials, the mechanical properties of the pavement layer using ultra-high performance concrete as the lower layer are studied, the mechanical response of the pavement layer is explored, and the fatigue performance of the composite pavement structure is analyzed, providing a basis for the design, construction, and operation of the pavement layer.

[0004] At present, the highway steel structure bridge design code in China does not have a special fatigue design for the steel bridge deck pavement layer, nor does it have an axle load conversion for the asphalt pavement layer of the steel bridge deck. The fatigue design uses the axle load conversion of the road surface. However, the traffic composition has different degrees of damage to the asphalt pavement layer of the steel bridge deck. Therefore, it is necessary to study the fatigue damage of the pavement layer based on the traffic use conditions and the overall structure of the bridge, combined with the mechanical properties of the pavement layer materials. Summary of the Invention

[0005] The object of the present invention is to provide a fatigue life evaluation method for the SMA+UHPC pavement layer of a separated steel box girder cable-stayed bridge. This method aims at various factors that may cause fatigue of the steel box girder pavement layer and the beam segments where fatigue failure may occur. Based on the damage mechanics theory, it evaluates the stress response and fatigue life of the asphalt concrete pavement layer, and can solve the defects existing in the background technology.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A fatigue life evaluation method for the SMA+UHPC pavement layer of a separated steel box girder cable-stayed bridge, which is characterized by including the following steps:

[0008] Step 1, traffic volume statistical analysis: Statistically analyze the traffic volume at the cable-stayed bridge location to be evaluated, and obtain the composition of the traffic volume crossing the bridge in each characteristic year;

[0009] Step 2, vehicle type classification: Classify according to the number of vehicle axles based on the composition of the traffic volume crossing the bridge in each characteristic year, and select a standard fatigue vehicle based on the asphalt concrete of the bridge deck pavement according to the fatigue equivalent damage principle;

[0010] Step 3, boundary condition determination: Establish a full-bridge model and a local model of the cable-stayed bridge to be evaluated, and determine the boundary conditions of the local model;

[0011] Step 4: Stress analysis: Apply the boundary conditions to the local model, simulate the stress conditions of the local beam segment under the most unfavorable working conditions, and analyze the stress and strain response of the bridge deck pavement considering the integral bridge effect;

[0012] Step 5: Fatigue performance calculation: According to the stress analysis results, use the linear fatigue cumulative damage theory to evaluate the fatigue performance of the pavement layer and obtain the total damage degree of the bridge deck pavement layer.

[0013] Furthermore, the specific steps of the traffic volume statistical analysis in Step 1 are as follows:

[0014] Step 1.1, obtain the traffic data of the cable-stayed bridge to be evaluated;

[0015] Step 1.2, conduct traffic flow analysis on the traffic data, construct a traffic volume prediction model, and predict the trend-type transfer traffic volume according to the "four-stage method";

[0016] Step 1.3, use the elastic analysis method to determine the traffic volume growth rate, and conduct statistical analysis on the traffic volume in the characteristic years to obtain the composition of the traffic volume crossing the bridge in each characteristic year.

[0017] Furthermore, the specific steps of the vehicle type classification in Step 2 are as follows:

[0018] Step 2.1: Classify the vehicle type composition ratio, vehicle type, and vehicle weight according to the cross - bridge traffic volume composition in each characteristic year, merge the statistical information of vehicles with the same number of axles, and obtain representative vehicle types.

[0019] Step 2.2: Statistically analyze the occurrence frequency of each axle weight in the representative vehicle types to obtain the axle load frequency - value spectrum under full - load conditions.

[0020] Step 2.3: Based on the axle load frequency - value spectrum, calculate the equivalent axle weight of each representative vehicle type according to the principle of equivalent fatigue damage.

[0021] Step 2.4: Calculate the load data of each representative vehicle type based on the equivalent axle weight.

[0022] Step 2.5: Perform characteristic fitting on the load data of each representative vehicle type, conduct fatigue contribution analysis of the vehicles, and select the type of representative vehicle with the largest proportion of fatigue damage as the standard fatigue vehicle.

[0023] Furthermore, the specific steps for determining the boundary conditions in Step 3 are as follows:

[0024] Step 3.1: Use Midas finite - element software to establish a full - bridge model of the cable - stayed bridge to be evaluated, and find the most unfavorable beam segment of the bridge deck pavement.

[0025] Step 3.2: According to Saint - Venant's principle, extract the bending moment, axial force, and shear force of the most unfavorable beam segment of the bridge deck pavement as boundary conditions, and use Solidworks software to establish a solid model.

[0026] Step 3.3: Import the solid model into the finite - element analysis software ABAQUS in the form of a component to establish a local model of the most unfavorable beam segment of the bridge deck pavement.

[0027] Furthermore, in the local model, shell elements are used for the top plate, web plate, bottom plate, U - ribs, and diaphragms of the steel box girder of the cable - stayed bridge to be evaluated, and solid elements are used for the UHPC layer and SMA layer of the bridge deck pavement of the cable - stayed bridge to be evaluated.

[0028] Furthermore, the specific steps of the stress analysis in Step 4 are as follows:

[0029] Step 4.1: Apply the boundary conditions to the local model, add the loads borne by the local beam segment itself, and simulate the stress conditions of the local beam segment under the most unfavorable working conditions.

[0030] Step 4.2: Use the vehicle axle load spectrum, according to the axle loads of the standard fatigue vehicles, apply different wheel loads to the beam segment of the most unfavorable pavement in the form of uniformly distributed loads, simulate and analyze the stress - strain response of the pavement of the most unfavorable beam segment, and analyze the influence of different pavement parameters on the maximum transverse tensile stress, maximum longitudinal tensile stress, and interlayer shear stress at the top of the asphalt layer.

[0031] Step 4.3: Analyze the stress-strain response of the steel bridge deck pavement considering the whole-bridge effect, establish the correlation between the axle load and the tensile stress and strain under different pavement parameters, and obtain the stress-strain spectrum of the bridge deck pavement considering the whole-bridge effect.

[0032] Furthermore, the specific steps of fatigue performance calculation in step 5 are as follows:

[0033] Step 5.1. Calculate the fatigue life of different axle loads based on the stress-strain spectrum of the bridge deck pavement under different parameters using the linear fatigue cumulative damage theory.

[0034] Step 5.2: Linearly add the damage caused by each level of axle load to obtain the total damage degree of the bridge deck pavement.

[0035] Furthermore, the total damage degree of the SMA layer in the bridge deck pavement layer is calculated as follows:

[0036]

[0037] Where D is the fatigue damage degree of the SMA layer; n i is the number of times the i-level shaft load acts; S i is the stress ratio; N is the number of lanes.

[0038] Furthermore, the total damage degree of the SMA layer in the bridge deck pavement layer is calculated as follows:

[0039]

[0040] Where D is the fatigue damage degree of the SMA layer; n i is the number of times the i-level shaft load acts; S i is the stress ratio; N is the number of lanes.

[0041] Furthermore, the total damage degree of the UHPC layer in the bridge deck pavement is calculated as follows:

[0042]

[0043] Where D is the fatigue damage degree of the UHPC layer; n i is the number of times the i-level shaft load acts; S i is the stress ratio; N is the number of lanes.

[0044] The remarkable effects of the present invention are:

[0045] (1) The present invention aims at various factors that may cause fatigue of the steel box girder pavement and the beam segments that may undergo fatigue failure. Based on the damage mechanics theory, it evaluates the stress response and fatigue life of the asphalt concrete pavement. This evaluation method is of great significance for its design, construction, and subsequent maintenance, and can better ensure the normal and safe operation of the steel bridge deck pavement.

[0046] (2) Based on the performance of UHPC materials, the present invention improves the axle load conversion coefficient of the SMA+UHPC pavement of the steel box girder and proposes a fatigue evaluation method for the SMA+UHPC pavement of the steel box girder.

[0047] (3) Based on the separated cable-stayed bridge model, through on-site investigation, modeling prediction, and statistical analysis, the present invention establishes the full-bridge model of the pavement of the separated steel box girder cable-stayed bridge, quantifies the influence of the UHPC layer as a protective layer on the stress response of the steel bridge deck pavement, and can provide guidance for the design of the steel bridge deck pavement system. At the same time, based on the miner linear damage mechanics, it studies the fatigue life of the combined beam pavement and evaluates the fatigue performance of the composite structure. [[ID=⑧]]

[0048] (4) Fatigue cracking of the pavement is an inevitable disease of the steel bridge deck pavement. The fatigue cracking of the pavement will affect the service performance of the bridge and even the safety of the bridge. However, there is relatively little research on the fatigue of the steel bridge deck pavement at present. The form of using the UHPC layer as a protective layer for the pavement is different from the mechanical properties of other double-layer SMA pavements. Therefore, through the present invention, the stress response of the pavement when the UHPC is used as a protective layer can be obtained, and the influence of the thickness of the UHPC layer on the fatigue life of the pavement can be obtained, which is of great significance for its design and construction and can ensure the normal use of the steel bridge deck pavement. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is the flowchart of the method of the present invention;

[0050] Figure 2 is the schematic diagram of the composite model of the orthotropic plate and the pavement established by the present invention;

[0051] Figure 3 is the specific flowchart of the stress analysis in the present invention;

[0052] Figure 4 is the schematic diagram of the linear change of the pavement stress with the axle load at different thicknesses;

[0053] Figure 5 is the stress nephogram of the SMA pavement obtained by stress analysis;

[0054] Figure 6 is the stress nephogram of the UHPC pavement obtained by stress analysis. DETAILED DESCRIPTION OF THE INVENTION

[0055] The specific implementation manners and working principles of the present invention will be further described in detail below with reference to the accompanying drawings.

[0056] As Figure 1 shown, this embodiment provides a fatigue life evaluation method for the SMA+UHPC pavement layer of a separated steel box girder cable-stayed bridge. The specific steps are as follows:

[0057] Step 1. Traffic volume statistical analysis: Statistically analyze the traffic volume at the cable-stayed bridge location to be evaluated to obtain the composition of the traffic volume crossing the bridge in each characteristic year.

[0058] In the embodiment of the present invention, the specific steps of traffic volume statistical analysis are as follows:

[0059] Step 1.1. Obtain the traffic data of the cable-stayed bridge to be evaluated, mainly based on the existing road traffic volume observation data and traffic origin-destination surveys, and refer to the feasibility study report of the expressway from Mianchi to Xichuan and the operation data of the Henan expressway network in 2020.

[0060] Step 1.2. Conduct traffic flow analysis on the traffic data, construct a traffic volume prediction model, and predict the trend-type transfer traffic volume according to the "four-stage method".

[0061] Step 1.3. Determine the traffic volume growth rate by using the elastic analysis method, use transcad to realize the distribution of the road network traffic volume, and conduct statistical analysis on the traffic volume in each characteristic year to obtain the composition of the traffic volume of the bridge crossing the river in each characteristic year.

[0062] Step 2. Vehicle type classification: Classify according to the number of axles of the vehicle type based on the composition of the traffic volume crossing the bridge in each characteristic year, and select the standard fatigue vehicle based on the asphalt concrete of the bridge deck pavement according to the fatigue equivalent damage principle, and then derive the standard fatigue vehicle for loading.

[0063] In the embodiment of the present invention, the specific steps of vehicle type classification are as follows:

[0064] Step 2.1. According to the composition of the traffic volume crossing the bridge in each characteristic year, classify the vehicle type composition ratio, vehicle type, and vehicle weight, and merge the statistical information of vehicles with the same number of axles to obtain 11 typical representative vehicle types.

[0065] Continue to classify the above typical models and combine the vehicles with the same number of axles into the same category to obtain a representative vehicle model.

[0066] Step 2.2. Statistically analyze the occurrence frequency of each axle weight in the representative vehicle types to obtain the axle load frequency spectrum under full load.

[0067] Step 2.3: Based on the axle load frequency spectrum, calculate the equivalent axle weight of each representative vehicle type according to the principle of equivalent fatigue damage.

[0068] Step 2.4: Obtain the load data of each representative vehicle type according to the calculated equivalent axle weight, that is, accumulate the equivalent axle weights of the representative vehicle types to obtain the equivalent total weight.

[0069] Step 2.5: Weight and average (expect) the classified vehicle types according to the weights of different vehicles in their respective same vehicle types to obtain the various axle distances of the model vehicles in this category. Compare and analyze the fatigue contributions of the simplified fatigue vehicles to grasp the relative magnitudes of the fatigue damage caused by the representative vehicle types in the load frequency spectrum to the bridge structure. Thus, conduct characteristic fitting on the load data of each representative vehicle type, and according to the distribution characteristics of vehicle weight and vehicle distance, use Matlab software to analyze the fatigue contributions of vehicles, and screen out the vehicle type with the largest proportion of fatigue damage, which is the standard fatigue vehicle applicable to the fatigue analysis of the steel bridge deck pavement.

[0070] Step 3: Determine the boundary conditions: Establish the full-bridge model and local model of the cable-stayed bridge to be evaluated, and determine the boundary conditions of the local model.

[0071] In the embodiment of the present invention, the specific steps for determining the boundary conditions are as follows:

[0072] Step 3.1: For a long-span steel bridge deck cable-stayed bridge, use Midas finite element software to establish the full-bridge model of the cable-stayed bridge to be evaluated, and comprehensively consider factors such as vehicle load action and secondary dead load to find the most unfavorable beam segment of the bridge deck pavement. Since the fatigue of the bridge deck pavement is mainly affected by the tensile stress of the pavement, find the beam segment with the largest negative bending moment of the steel bridge deck, that is, find the most unfavorable beam segment of the bridge deck pavement.

[0073] Step 3.2: According to the specific structural form of the bridge, establish a geometric model with corresponding dimensions in Midas software. Since stress boundary conditions need to be applied according to Saint-Venant's principle, the range of the established geometric model is from section to section. Extract the bending moment, axial force, and shear force of the most unfavorable segment of the Midas steel bridge deck pavement as the boundary conditions of the local model, and use Solidworks software to establish a solid model.

[0074] At the same time, according to Saint-Venant's principle, in order to be able to use the stress boundary in the overall model, the range of the established local model needs to be expanded to several meters near the beam segment with the largest negative bending moment.

[0075] Step 3.3: Import the solid model into the finite element analysis software ABAQUS in the form of a component to establish the local model of the most unfavorable beam segment of the bridge deck pavement, analyze the influence of the overall bridge effect on the stress response of the pavement, and lay the foundation for the orthotropic plate model.

[0076] In the process of establishing the corresponding most unfavorable stage model in ABAQUS in this example, shell elements are used for the top plate, web plate, bottom plate, U-ribs, and diaphragms of the steel box girder, and solid elements are used for the UHPC layer and SMA layer in the paving layer. The bonding and slip effect between the steel box girder and the paving layer is not considered. Bending moments, axial forces, shear forces, etc. extracted from Midas are added to both sides of the most unfavorable segment.

[0077] To analyze the influence of wheel load on the steel bridge deck paving layer and compare the stress distributions of the paving layers of the SMA+UHPC paving layer and the double-layer SMA paving form, a composite model of the paving layer is established using finite element software. The model is as Figure 2 shown. A part of the diaphragm of the steel box girder is intercepted vertically, there are 7 U-shaped ribs longitudinally, the spacing between diaphragms is 3.2 m, the height of the U-rib is 290 mm, and the opening width is 300 mm. Shell elements are used to simulate the steel structure, and C3D8R is used to simulate the SMA and UHPC materials in the paving layer.

[0078] It is assumed that the steel, SMA, and UHPC materials are all continuous, homogeneous, and linear elastic materials. The UHPC layer is bonded to the steel top plate, and the SMA layer is bonded to the UHPC layer. The bonding and slip between layers are not considered. The bottom of the orthotropic plate diaphragm is fixed and constrained, and the paving layer is constrained by longitudinal and lateral hinges. The elastic modulus of SMA is taken as 3000 MPa. The elastic modulus of the UHPC material is 40 GPa - 60 GPa, and 50 GPa is taken in this embodiment.

[0079] Step 4: Stress analysis: Apply the boundary conditions to the local model to simulate the stress conditions of the local beam segment under the most unfavorable working conditions, and analyze the stress and strain responses of the bridge deck paving layer considering the integral bridge effect;

[0080] In the embodiment of the present invention, the stress analysis process is as Figure 3 shown, and the specific steps are as follows:

[0081] Step 4.1: Apply the boundary conditions to the local model and add the loads borne by the local beam segment itself to simulate the stress conditions of the local beam segment under the most unfavorable working conditions;

[0082] Step 4.2: Use the vehicle axle load spectrum, according to the standard fatigue vehicle axle load, analyze whether there is an impact on the stress and strain of the paving layer in the most unfavorable beam segment considering the integral bridge effect, that is, compare the stress and strain responses of the SMA asphalt concrete paving layer and the SMA+UHPC paving layer;

[0083] Apply different wheel loads in the form of uniform loads to the beam segment of the most unfavorable paving layer, simulate and analyze the stress and strain responses of the paving layer of the most unfavorable beam segment, and analyze the influence of various parameters such as the paving layer and wheel load on the stress and strain responses of the paving layer;

[0084] A standard axle load of 100 kN is applied to the paving layer in the form of a uniformly distributed load to explore the most unfavorable transverse position and the most unfavorable longitudinal position of the orthotropic plate paving layer considering the integral bridge effect;

[0085] According to the standard fatigue vehicle axle load, each different axle load is applied to the most unfavorable transverse position and the most unfavorable longitudinal position of the paving layer in the form of a uniformly distributed load. After considering the integral bridge effect in the orthotropic plate paving layer sub-model, the thicknesses of the UHPC layer are selected as 100 mm, 80 mm, 60 mm, 40 mm, and 20 mm, and the thicknesses of the SMA-13 layer are selected as 60 mm, 50 mm, 40 mm, 30 mm, and 20 mm to analyze the influence of the paving layer thickness on the maximum tensile stress of the paving layer. The elastic modulus of the UHPC layer is selected as 50000 MPa, and the elastic modulus of the SMA layer is 3000 Mpa to determine that the maximum tensile stress of the paving layer varies linearly with the axle load.

[0086] When the thicknesses of the UHPC layer are 20 mm, 40 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, and 80 mm, the maximum longitudinal and transverse tensile stresses and the interlayer shear stress of the SMA and UHPC layers are as shown in Figure 4, where Figure 4 (a) is the stress of the UHPC layer, Figure 6 (b) is the stress of the SMA layer.

[0087] Step 4.3: Analyze the stress and strain response of the steel bridge deck paving layer considering the integral bridge effect, establish the correlation between the axle load and the tensile stress and tensile strain under different paving layer parameters, and obtain the stress and strain spectrum of the bridge deck paving layer considering the integral bridge effect, as shown in Figure 5 and Figure 6 shown, where Figure 5 (a), Figure 6 (a) is the transverse tensile stress, Figure 5 (b), Figure 6 (b) is the longitudinal tensile stress.

[0088] Step 5: Fatigue performance calculation: According to the stress analysis results, use the linear fatigue cumulative damage theory to evaluate the fatigue performance of the paving layer and obtain the total damage degree of the bridge deck paving layer.

[0089] Different from the conventional calculation of the fatigue performance of the steel bridge deck paving layer, the fatigue performance of the paving layer is evaluated through the linear fatigue cumulative damage theory, that is, the fatigue damage degree is calculated through the fatigue stress, the curve of the material, and the number of load applications, and the life is predicted through the fatigue damage degree.

[0090] Among them, the linear fatigue cumulative damage theory, also known as the Miner's rule, is an important concept in material fatigue analysis. The linear fatigue cumulative damage theory assumes that the total damage of the material is the linear superposition of the damage of each cycle. If the damage of each cycle is defined as the ratio of the fatigue life of the material at the stress level of this cycle to the total life, then the total damage can be expressed as the sum of the damage of all cycles. When the total damage reaches 1, the material is considered to have accumulated enough damage and fatigue failure is about to occur.

[0091] Step 5.1: Through the linear fatigue cumulative damage theory, calculate the fatigue life of different axle loads according to the stress-strain spectra of the bridge deck pavement layer under different parameters; that is, according to the asphalt concrete strain-fatigue life prediction formula, introduce the axle load spectrum obtained in the previous chapter and the stress-strain of the pavement layer under parameters such as the UHPC thickness and asphalt thickness (i.e., the stress-strain spectra under different parameters) to obtain the fatigue life of different axle loads.

[0092] For the fatigue design of the asphalt layer of the road surface, the maximum tensile stress (variation) at the bottom of the layer is generally used as the design index to predict its cracking life. For the steel bridge deck pavement layer, the fatigue design is mainly carried out through the maximum transverse and longitudinal tensile stresses at the top of the pavement layer under the action of the wheel static load. Therefore, for the fatigue damage and life prediction of the steel bridge deck pavement layer, the maximum transverse tensile stress and the maximum longitudinal tensile stress of the pavement layer are generally used as the fatigue stresses. The fatigue analysis of the pavement layer does not consider the integral bridge effect, and only considers the tensile stress of the pavement layer under the action of the axle load as the fatigue stress. The number of load applications is calculated according to the axle load spectrum. According to Figure 5 and Figure 6 In the stress nephogram shown, the wheel group coefficient of the SMA+UHPC pavement layer is different from that of the double-layer SMA pavement form, and the SMA+UHPC pavement layer needs to consider the superposition effect of the two side wheels.

[0093] Step 5.2: Divide the actual number of times of action of each level of axle load in a year by the corresponding theoretical service life to obtain the damage degree of the asphalt concrete under the action of this level of axle load in a year. Linearly add the damages caused by each level of axle load to obtain the total damage degree (D) of the asphalt concrete in the steel bridge deck pavement under the action of each level of wheel load in 1 year.

[0094] The specific calculation process is as follows:

[0095] The fatigue life calculation formula of the UHPC layer in the pavement layer is shown in Equation (1).

[0096] S = 1.6065 - 0.1805lgN f (1)

[0097] Due to the large S-N dispersion of SMA materials, two different S-N curves are used for the fatigue analysis of SMA, which are divided into Formula 1 and Formula 2. After the fatigue analysis, a relatively conservative curve is adopted to determine the life.

[0098] Formula 1: The fatigue life calculation formula of SMA mixture is shown in Equation (2):

[0099] lgN f =3.9586 - 2.596lgS i (2)

[0100] Formula 2: The fatigue life calculation formula of SMA mixture is shown in Equation (3):

[0101] lgN f =3.9550 - 2.156lgS i (3)

[0102] Where: N f is the fatigue life; S i is the stress ratio, that is, the ratio of the maximum tensile stress to the flexural tensile strength of the material.

[0103] By referring to relevant literature, the flexural tensile strength of the UHPC layer in this example is 44 MPa; the flexural tensile strength of the SMA layer in Formula 1 is 3.671 MPa; the flexural tensile strength of the SMA layer in Formula 2 is 6.241 MPa.

[0104] According to the principle of linear fatigue cumulative damage, the relationship between the fatigue damage degree of the UHPC layer and stress and load application times can be established, as shown in Equation (4).

[0105]

[0106] According to Formula 1 of the fatigue life of the SMA layer, the relationship between the fatigue damage degree of the SMA layer and stress and load application times is established, as shown in Equation (5).

[0107]

[0108] According to Formula 2 of the fatigue life of the SMA layer, the relationship between the fatigue damage degree of the SMA layer and stress and load application times is established, as shown in Equation (6).

[0109]

[0110] In Equations (4), (5), and (6): D is the fatigue damage degree of the pavement layer; D i is the fatigue damage caused by the i-th axle load acting n i times on the pavement layer; n i is the number of times the i-th axle load acts; N fi is the number of times the i-th axle load acts Nfi After several times, the material is damaged, and 6 is the number of lanes on the bridge deck.

[0111] Engineering example:

[0112] According to the traffic volume of the bridge to be evaluated, within the lane, the vehicle has the highest action frequency on the 50 cm width of the wheel path. Since the specification only stipulates the lane coefficient and does not stipulate the lateral distribution coefficient of the wheel path, considering the obvious channelized traffic on the bridge deck and the obvious local bearing characteristics of the asphalt pavement on the steel bridge deck, it is recommended to take 0.6, that is, about 60% of the vehicles driving in this lane form the action of the critical load position. Since there are 4 lanes during operation, the lane coefficient is taken as 0.7 according to the specification, and 0.5 is taken for two-way lanes. The vehicle traffic volume within the 20-year design life of the bridge is 121.23 million vehicles. After considering channelized traffic, lane coefficient, and two-way lanes, the vehicle traffic volume is 121.23×0.6×0.7×0.5 = 25.45 million vehicles. Based on the distribution of various vehicle types and axle types, the number of single-axle axle times forming the critical load position within 20 years is 65.95 million axle times.

[0113] There are two processes for fatigue damage analysis. The first is to use the load stress under the standard axle load as the basic parameter for axle load conversion, and obtain the cumulative standard equivalent axle times according to the axle load conversion coefficient. The second is to find the maximum transverse and longitudinal tensile stresses of the pavement under each level of axle load, calculate the fatigue damage degree under the action of each level of axle load respectively, and then calculate the total fatigue damage degree under the action of all axle loads through the principle of linear superposition. However, the current axle load conversion theory for steel bridge decks is not yet perfect, and both method one and method two are based on the principle of linear fatigue cumulative damage. Therefore, method two is used to calculate the fatigue life of the pavement to avoid complex axle load conversion of the bridge deck pavement. According to the S-N curve, combined with the axle load spectrum and stress, the fatigue performance of the SMA+UHPC layer under different influencing factors is evaluated. The calculation results of the fatigue stress of the pavement under each parameter are shown in Tables 1 and 2, and the calculation results of the fatigue damage degree are shown in Tables 3 and 4.

[0114] Table 1 Maximum tensile stress and number of axle load actions of the SMA layer under each level of axle load

[0115]

[0116] Table 2 Maximum tensile stress and number of axle load actions of the UHPC layer under each level of axle load

[0117]

[0118] Table 3 Fatigue damage degree D of the SMA layer under different UHPC layer thicknesses

[0119]

[0120] Table 4 Fatigue damage degree D of the UHPC layer under different UHPC layer thicknesses

[0121]

[0122] In summary, the present invention aims at various factors that may cause fatigue of the paving layer of steel box girders and the beam segments that may undergo fatigue failure. Based on the damage mechanics theory, through on-site investigation, modeling prediction, and statistical analysis, a bridge axle load spectrum is established, and a full-bridge model of the paving layer of a cable-stayed bridge with a separated steel box girder is established. In addition, the axle load conversion coefficient of the SMA+UHPC paving layer of the steel box girder is improved, and a fatigue assessment method for the SMA+UHPC paving layer of the steel box girder is proposed. The influence of the UHPC layer as a protective layer on the stress response of the steel bridge deck paving layer is quantified, and the fatigue degree of the SMA+UHPC paving layer of the steel box girder can be accurately evaluated. Therefore, it can guide the design of the steel bridge deck paving system, and is of great significance for the design, construction, and subsequent maintenance of long-span cable-stayed bridges with separated steel box girders, and can better ensure the normal and safe operation of the steel bridge deck paving layer.

[0123] The technical solution provided by the present invention has been introduced in detail above. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A fatigue life evaluation method for the SMA+UHPC paving layer of a separated steel box girder cable-stayed bridge, characterized in that It includes the following steps: Step 1, traffic volume statistical analysis: Conduct statistical analysis on the traffic volume at the cable-stayed bridge location to be evaluated, and obtain the composition of the traffic volume crossing the bridge in each characteristic year; Step 2, vehicle type classification: Classify according to the number of axles of vehicle types based on the composition of the traffic volume crossing the bridge in each characteristic year, and select the standard fatigue vehicle based on the asphalt concrete of the bridge deck pavement according to the principle of fatigue equivalent damage; Step 3, boundary condition determination: Establish the full-bridge model and local model of the cable-stayed bridge to be evaluated, and determine the boundary conditions of the local model; Step 4: Stress analysis: Apply the boundary conditions to the local model, simulate the stress conditions of the local beam segment under the most unfavorable working conditions, and analyze the stress and strain response of the bridge deck pavement considering the whole-bridge effect; Step 5: Fatigue performance calculation: According to the stress analysis results, use the linear fatigue cumulative damage theory to evaluate the fatigue performance of the pavement layer and obtain the total damage degree of the bridge deck pavement.

2. The fatigue life evaluation method of the SMA+UHPC pavement layer of the separated steel box girder cable-stayed bridge according to claim 1, characterized in that: The specific steps of the traffic volume statistical analysis in Step 1 are as follows: Step 1.1, Obtain the traffic data of the cable-stayed bridge to be evaluated; Step 1.2, Conduct traffic flow analysis on the traffic data, construct a traffic volume prediction model, and predict the trend-type transfer traffic volume according to the "four-stage method"; Step 1.3, Use the elastic analysis method to determine the traffic volume growth rate, and conduct statistical analysis on the traffic volume in each characteristic year to obtain the composition of the traffic volume of the bridge crossing the river in each characteristic year.

3. The fatigue life evaluation method for the SMA+UHPC paving layer of the separated steel box girder cable-stayed bridge according to claim 1, wherein: The specific steps of the vehicle type classification in Step 2 are as follows: Step 2.1, Classify the composition ratio of vehicle types, vehicle types, and vehicle weights according to the composition of the traffic volume crossing the bridge in each characteristic year, and merge the statistical information of vehicles with the same number of axles to obtain the representative vehicle types; Step 2.2, Statistically analyze the occurrence frequency of each axle weight in the representative vehicle types to obtain the axle load frequency spectrum under full load; Step 2.3, Based on the axle load frequency spectrum, calculate the equivalent axle weight of each representative vehicle type according to the principle of equivalent fatigue damage; Step 2.4, Calculate the load data of each representative vehicle type according to the equivalent axle weight; Step 2.5, Conduct characteristic fitting on the load data of each representative vehicle type, and conduct fatigue contribution analysis of the vehicles, and screen out the representative vehicle type with the largest proportion of fatigue damage as the standard fatigue vehicle.

4. The fatigue life evaluation method for the SMA+UHPC pavement layer of the separated steel box girder cable-stayed bridge according to claim 1, characterized in that: The specific steps for determining the boundary conditions in Step 3 are as follows: Step 3.1, Use Midas finite element software to establish the full-bridge model of the cable-stayed bridge to be evaluated, and find the most unfavorable beam segment of the bridge deck pavement; Step 3.2, According to Saint-Venant's principle, extract the bending moment, axial force, and shear force of the most unfavorable beam segment of the bridge deck pavement as the boundary conditions, and use Solidworks software to establish a solid model; Step 3.3, Import the solid model into the finite element analysis software ABAQUS in the form of a component, and establish the local model of the most unfavorable beam segment of the corresponding bridge deck pavement.

5. The fatigue life evaluation method for the SMA+UHPC pavement layer of the separated steel box girder cable-stayed bridge according to claim 4, wherein: In the local model, shell elements are used for the top plate, web, bottom plate, U-rib, and diaphragm plate in the steel box girder of the cable-stayed bridge to be evaluated, and solid elements are used for the UHPC layer and SMA layer in the bridge deck pavement of the cable-stayed bridge to be evaluated.

6. The fatigue life evaluation method for the SMA+UHPC pavement layer of the separated steel box girder cable-stayed bridge according to claim 1, wherein: The specific steps of the stress analysis in Step 4 are as follows: Step 4.1, Apply the boundary conditions to the local model, add the loads borne by the local beam segment itself, and simulate the stress conditions of the local beam segment under the most unfavorable working conditions; Step 4.2: Using the vehicle axle load spectrum, apply different wheel loads in the form of uniformly distributed loads to the beam segment of the most unfavorable pavement layer according to the standard fatigue vehicle axle load, and simulate and analyze the stress and strain responses of the most unfavorable beam segment pavement layer to analyze the influence of different pavement layer parameters on the maximum transverse tensile stress, maximum longitudinal tensile stress and interlayer shear stress at the top of the asphalt layer; Step 4.3: Analyze the stress and strain responses of the steel bridge deck pavement layer considering the integral bridge effect, establish the correlation between axle load and tensile stress and tensile strain under different pavement layer parameters, and obtain the stress and strain spectrum of the bridge deck pavement layer considering the integral bridge effect.

7. The fatigue life evaluation method of the SMA+UHPC pavement layer of the separated steel box girder cable-stayed bridge according to claim 1, wherein: The specific steps of the fatigue performance calculation described in Step 5 are as follows: Step 5.1: Calculate the fatigue life of different axle loads according to the stress and strain spectrum of the bridge deck pavement layer under different parameters through the linear fatigue cumulative damage theory; Step 5.2: Linearly sum up the damages caused by each level of axle load to obtain the total damage degree of the bridge deck pavement layer.

8. The fatigue life evaluation method of the SMA+UHPC paving layer of the separated steel box girder cable-stayed bridge according to claim 7, characterized in that: The calculation formula for the total damage degree of the SMA layer in the bridge deck pavement layer is: where D is the fatigue damage degree of the SMA layer; n i is the number of applications of the i-level axle load; S i is the stress ratio; N is the number of lanes.

9. The fatigue life evaluation method of the SMA+UHPC pavement layer of the separated steel box girder cable-stayed bridge according to claim 7, characterized in that: The calculation formula for the total damage degree of the SMA layer in the bridge deck pavement layer is: where D is the fatigue damage degree of the SMA layer; n i is the number of applications of the i-level axle load; S i is the stress ratio; N is the number of lanes.

10. The fatigue life evaluation method of the SMA+UHPC paving layer of the separated steel box girder cable-stayed bridge according to claim 7, characterized in that: The calculation formula for the total damage degree of the UHPC layer in the bridge deck pavement layer is: Among them, D is the fatigue damage degree of the UHPC layer; n i is the number of times of the i-level axle load action; S i is the stress ratio; N is the number of lanes.

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