Method for calculating longitudinal pre-deviator of continuous box girder support of high-speed railway

Abstract

The invention discloses a method for calculating the longitudinal pre-deviation of a continuous box girder support of a high-speed railway, which is characterized in that the offset of the support is mainly influenced by two factors, one factor is set as 1, namely the offset of each fulcrum caused by elastic deformation and shrinkage creep of a box girder; 2 is the offset caused by the temperature difference of the box girder system; the pre-bias of the corresponding support can be obtained by a formula =-(1 + 2), and a negative sign represents that the pre-bias of the support is arranged in the reverse direction of a numerical value obtained through calculation and is used for compensating deformation displacement of concrete caused by elastic deformation, shrinkage creep and temperature change. A calculation process and a key parameter value standard are defined, it is ensured that a support pre-deviation calculation result is accurate and reliable, the support installation quality is guaranteed, the later adjustment cost is reduced, the construction safety risk is reduced, and technical support is provided for high-speed railway continuous box girder engineering construction.

Description

Technical Field

[0001] This invention relates to the field of high-speed railway bridge construction technology, and in particular to a method for calculating the longitudinal pre-deviation of supports for continuous box girders in high-speed railways. Background Technology

[0002] With the rapid development of high-speed railway construction, continuous box girder structures are widely used in intercity high-speed railway projects due to their strong spanning capacity. As a key connecting component between the upper and lower structures of a bridge, the accurate calculation of the pre-deflection of the bearings is crucial for ensuring installation quality. Currently, traditional pre-deflection calculations lack detailed explanations in design reference documents or specifications, relying heavily on estimations based on the experience of construction personnel or making rough calculations by simply considering some influencing factors, without forming a systematic and precise calculation framework.

[0003] The limitations of traditional calculation methods for the longitudinal pre-eccentricity of continuous box girder supports in high-speed railways are as follows: 1. Traditional calculations lack unified standards and precise algorithms, easily leading to numerical deviations and inaccurate support installation positions. This necessitates later jacking up the girder to replace supports or adjust the pre-eccentricity, resulting in a massive workload and severely impacting construction progress. 2. The calculation process fails to fully consider the combined effects of key factors such as elastic deformation, shrinkage, creep, and system temperature differences, or misjudges the vector characteristics of these factors, causing the support stress state to fail to meet design requirements and even affecting the safety of railway operation. 3. Traditional calculations lack clear standards for determining key parameters such as closure temperature and support model and location, easily leading to errors in pre-eccentricity calculation due to improper parameter values, increasing construction quality risks. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for calculating the longitudinal pre-deviation of supports for continuous box girders in high-speed railways, ensuring the accuracy and reliability of the pre-deviation calculation results and guaranteeing the quality of support installation.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] The calculation method for the longitudinal pre-eccentricity of the support of the continuous box girder in this high-speed railway is as follows:

[0007] The support offset is mainly affected by two types of factors. The first is denoted as △1, which is the offset at each support point caused by the elastic deformation and shrinkage creep of the box girder; the second is denoted as △2, which is the offset caused by the temperature difference of the box girder system.

[0008] The pre-deflection at the corresponding support can be obtained by the formula △ = - (△1 + △2). The negative sign indicates that the pre-deflection of the support is set in the opposite direction according to the calculated value, which is used to compensate for the deformation and displacement of concrete caused by elastic deformation, shrinkage and creep, and temperature changes.

[0009] Further:

[0010] The offset caused by the temperature difference of the box girder system; when the closure temperature is greater than the design temperature, the offset direction is away from the fixed support; when the closure temperature is less than the design temperature, the offset direction is towards the fixed support.

[0011] The elastic deformation of the box girder and the offset at each support point caused by shrinkage and creep are all directed towards the fixed support.

[0012] The calculation method steps are as follows: determine the support model and location - clarify the closure temperature parameters - calculate the key offset - obtain the final value of the pre-offset.

[0013] The determination of the bearing model and location: Select the bearing layout according to the peak ground acceleration Ag value in the engineering design parameters, clarify the installation pier number and line side of the fixed bearing and movable bearing in conjunction with the design specifications, determine the position of the pad stone and anchor bolt hole according to the bearing structure layout drawing, and confirm the unclear parts through the design liaison form;

[0014] Clearly define the closure temperature parameters: The design closure temperature should first adopt the value specified in the construction drawings or design briefing; if there is no specification, the annual average temperature of the project location should be used; the actual closure temperature should be the average daily minimum temperature of the month of construction closure, and the data should be obtained from the local meteorological website.

[0015] Calculate the key offsets: △1 The offset caused by elastic deformation and shrinkage creep of the box girder is listed in the design specifications, and the direction is towards the fixed support; △2 The offset caused by the temperature difference of the system is calculated according to the formula △2=α△t*l; α is the linear expansion coefficient of concrete, △t is the temperature difference between the design and the actual closure, and l is the beam length from the center of the support to the center of the fixed support. The offset direction is determined based on the temperature difference.

[0016] The final value of the pre-deflection is obtained: considering the vector characteristics of △1 and △2, the total pre-deflection is calculated by the formula △ = - (△1 + △2). Positive values ​​correspond to positive settings, and negative values ​​correspond to negative settings, so as to achieve accurate compensation for concrete deformation displacement.

[0017] The △1 refers to the elastic deformation of the continuous box girder concrete caused by stress and its own characteristics, as well as the deformation of the beam caused by shrinkage and creep. The deformation of the beam simultaneously affects the deformation of the support, which in turn causes the upper support plate to shift relative to the lower support plate. The direction of concrete shrinkage and creep generally does not change, and it is always a displacement towards the fixed support.

[0018] The beam length is affected by concrete shrinkage and creep or temperature changes, resulting in shrinkage or elongation. Since fixed supports are installed at the mid-span piers, displacement deformation is impossible. Therefore, the shrinkage or elongation of the beam is primarily reflected in the side span length, causing the beam joints in the side spans of the continuous beam to widen or narrow. To offset this deformation caused by the inherent properties of concrete and ensure that the beam joint width meets design requirements, compensation for the beam length needs to be made during the cast-in-place process of the straight section of the side span, based on the pre-deflection of the beam end supports.

[0019] The contraction or elongation of the beam concrete caused by temperature changes cycles repeatedly with the seasons throughout the year. During high-temperature periods, the beam expands due to heat, becoming longer and the gaps between beams narrower; during low-temperature periods, the beam contracts due to cold, becoming shorter and the gaps between beams widen. Δ1 is the primary value, with a larger value, while Δ2 is the secondary value, with a smaller value.

[0020] In the aforementioned calculation method, all external environmental conditions are assumed to be ideal. However, the actual on-site conditions may deviate slightly from the theoretical drawings. When compensating for the beam end length according to the value of △1, it is necessary to comprehensively consider the on-site measured data and combine them with the railway engineering acceptance conditions. By finding patterns in multiple lengthening data, the final beam joint width can be optimally controlled within the design value ±2cm error range.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] This invention provides a systematic, concise, and accurate theoretical numerical calculation method, which clarifies the calculation process and the standards for key parameter values, ensuring the accuracy and reliability of the pre-deflection calculation results of the supports, guaranteeing the quality of support installation, reducing subsequent adjustment costs, and lowering construction safety risks, thus providing technical support for the construction of continuous box girder projects for high-speed railways. Attached Figure Description

[0023] The following is a brief explanation of the contents of each of the accompanying drawings and the markings in the drawings:

[0024] Figure 1 and Figure 2 This is a schematic diagram of the support structure of the present invention.

[0025] Figure 3 This is a schematic diagram of the support arrangement of the present invention. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and through the description of the examples.

[0027] This invention provides a method for accurately calculating the theoretical value of the longitudinal pre-deflection of continuous box girder supports for high-speed railways. It is applicable to situations where the installation accuracy requirements of continuous box girder supports are high and control is difficult, and where there are no design reference documents or detailed specifications for calculating the pre-deflection of supports. It can accurately calculate the longitudinal pre-deflection of supports, providing a technical basis for support installation, maximizing the construction quality of continuous box girders, and reducing the amount of adjustment work in the later stages.

[0028] The specific method for accurately calculating the theoretical numerical value of the longitudinal pre-eccentricity of the support for continuous box girder in high-speed railway is explained below.

[0029] The bearing offset is mainly affected by two types of factors. The first is denoted as △1, which is the offset at each support point caused by the elastic deformation and shrinkage / creep of the box girder (the direction is towards the fixed support). The second is denoted as △2, which is the offset caused by the temperature difference of the box girder system (when the closure temperature is greater than the design temperature, the direction is away from the fixed support; when the closure temperature is less than the design temperature, the direction is towards the fixed support). Therefore, the pre-offset at the corresponding support can be obtained by the formula △ = -(△1 + △2). The negative sign indicates that the pre-offset of the support is set in the opposite direction of the calculated value to compensate for the deformation displacement of the concrete caused by elastic deformation, shrinkage / creep, and temperature changes, so that the support can autonomously "return" to its theoretical centerline position during normal operation. Among them, △1 is the primary value with a larger value, and △2 is the secondary value with a smaller value.

[0030] This calculation method establishes a complete and accurate calculation system by defining core parameters and standards, calculating key offsets step by step, and integrating vector characteristics to obtain the final result. The specific process is as follows:

[0031] Determine the bearing type and location: Select the bearing layout drawing based on the peak ground acceleration Ag value in the engineering design parameters, clarify the installation pier number and line side of the fixed bearing and movable bearing in conjunction with the design specifications, determine the location of the pad stone and anchor bolt hole based on the bearing structure layout drawing, and confirm the unclear parts through the design liaison form;

[0032] Clearly define the closure temperature parameters: The design closure temperature should first adopt the value specified in the construction drawings or design briefing; if there is no specification, the annual average temperature of the project location should be used; the actual closure temperature should be the average daily minimum temperature of the month of construction closure, and the data should be obtained from the local meteorological website.

[0033] Calculate the key offsets: △1 (offset caused by elastic deformation and shrinkage creep of the box girder) is listed from the design specifications, please refer to the table below for details, and the direction is towards the fixed support; △2 (offset caused by system temperature difference) is calculated according to the formula △2=α△t*l (α is the linear expansion coefficient of concrete, △t is the difference between the design and actual closure temperature, and l is the beam length from the support center to the fixed support center), and the offset direction is determined based on the temperature difference;

[0034]

[0035] The final value of the pre-deflection is obtained: considering the vector characteristics of △1 and △2, the total pre-deflection is calculated by the formula △ = - (△1 + △2). Positive values ​​correspond to positive settings, and negative values ​​correspond to negative settings, so as to achieve accurate compensation for concrete deformation displacement.

[0036] (a) Explanation of the calculation of the value of △1

[0037] △1 represents the offset at each support point caused by the elastic deformation and shrinkage creep of the box girder. The specific value is obtained from the main calculation results in the design description of the corresponding beam drawing.

[0038] △1 can be understood as the elastic deformation of the continuous box girder concrete caused by stress and its own characteristics, as well as the deformation of the beam caused by shrinkage and creep. The deformation of the beam affects the deformation of the support in sync, which in turn causes the upper support plate to have an offset relative to the lower support plate. The direction of concrete shrinkage and creep generally does not change, and is always a displacement towards the fixed support.

[0039] according to Figure 3 As shown in the table below, support 2 is a fixed / lateral support with △1=0; support 1 is a multi-directional / longitudinal support with △1 deformation direction being positive; supports 3 and 4 are multi-directional / longitudinal supports, both located on the same side as the fixed support, with △1 deformation direction being negative.

[0040]

[0041] (II) Explanation of the calculation of △2 value

[0042] △2 represents the offset caused by temperature difference in the box girder structure system, mainly due to the elongation or shortening of concrete as temperature changes. The calculation formula is △2 = α△t * l (mm), where α is the linear expansion coefficient of the continuous box girder concrete, generally α = 1.0 × 10⁻⁵ / ℃, △t is the difference between the design closure temperature and the actual closure temperature, and l is the beam length from the center of the support at the calculation location to the center of the fixed support. The farther away from the fixed support, the larger the value of △2, and vice versa.

[0043] Due to the inherent properties of concrete, the beam length will shrink or elongate due to concrete shrinkage and creep or temperature changes. Since fixed supports are installed at the mid-span piers, displacement deformation cannot occur. Therefore, the shrinkage or elongation of the beam is mainly reflected in the length of the side spans, causing the beam joints in the side spans of continuous beams to widen or narrow. To offset this deformation caused by the inherent properties of concrete and ensure that the beam joint width meets design requirements, it is necessary to compensate for the beam length according to the pre-deflection of the beam end supports during the cast-in-place process of the straight section of the side span.

[0044] Based on the foregoing, the pre-offset of the beam end supports consists of Δ1 (the offset at each support point caused by the shrinkage and creep of the box girder) and Δ2 (the offset caused by the temperature difference in the box girder system). The shrinkage or elongation of the beam concrete due to temperature changes cycles seasonally throughout the year. During high-temperature periods, the beam expands due to heat, becoming longer and the gaps between beams narrower; during low-temperature periods, the beam contracts due to cold, becoming shorter and the gaps between beams widen. Therefore, Δ2 is similar to "reversible deformation," with its deformation pattern and elongation / shortening influenced by temperature. Since the value of Δ2 is relatively small, it does not significantly affect the overall continuous beam. Therefore, this compensation need not be considered; only the changes in elastic deformation and the "irreversible deformation" Δ1 caused by shrinkage and creep of the box girder need to be considered.

[0045] Furthermore, since the calculations assume ideal external environmental conditions, actual on-site conditions inevitably deviate slightly from the theoretical drawings. When compensating for the beam end length based on the △1 value, it is necessary to comprehensively consider the actual measured data on-site, combined with railway engineering acceptance conditions, and to find patterns in multiple lengthening data to ensure that the final beam joint width is optimally controlled within the design value ±2cm error range.

[0046] For example:

[0047] 1. Design closure temperature tdesign > Actual closure temperature tactual:

[0048] When the design closure temperature tdesign > the actual closure temperature tactual, the Δ2 direction of support 1 is positive, while the Δ2 direction of supports 3 and 4 is negative, meaning that Δ2 moves towards the direction of the fixed support.

[0049] Support 1: △2 = α(t_design - t_actual) * b;

[0050] Support 2: △2=0;

[0051] Support 3: △2 = —α(t_design — t_actual) * c;

[0052] Support 4: △2 = —α(t_design — t_actual) * (b + c).

[0053] 2. Design closure temperature tdesign < Actual closure temperature tactual:

[0054] When the design closure temperature tdesign < the actual closure temperature tactual, the Δ2 direction of support 1 is negative, while the Δ2 directions of supports 3 and 4 are positive, meaning that Δ2 moves away from the fixed support.

[0055] Support 1: △2 = —α(tactual — tdesign) * b;

[0056] Support 2: △2=0;

[0057] Support 3: △2 = α(tactual - tdesign) * c;

[0058] Support 4: △2 = α(tactual - tdesign) * b + c).

[0059] 3. Calculation of △ values

[0060] Based on the above calculation and analysis process of △1 and △2, in the process of calculating the pre-offset, the values ​​of △1 and △2 are both given vector characteristics. When calculating the total offset, they can be directly added together. Therefore, the support pre-offset △ = - (△1 + △2). If the value of △ is positive, the direction of the support pre-offset is positive. If the value of △ is negative, the direction of the support pre-offset is negative.

[0061] It should be noted that since the value of △1 is much greater than that of △2, the direction of △ is opposite to that of △1, that is, both are directions away from the fixed support.

[0062] The following explanation uses the calculation of Δ for support 1 as an example:

[0063] (i) When tdesign > tactual, support 1 △ = — (△1 + △2) = — [△1 + α (tdesign - tactual) * b], (|△| > |△1|);

[0064] (ii) When t<design < t<actual, support 1△ = — (△1 + △2) = — [△1 - α (t<actual - t<design) * b], (|△| < |△1|).

[0065] The calculation principle for supports 3△ and 4△ is the same as above, and the length units should be kept consistent during the calculation.

[0066] like Figure 1 and Figure 2 As shown, it is a schematic diagram of the support structure layout; it is used to clarify the positional relationship and key dimensional parameters of the fixed support and the movable support, and to provide a basis for support positioning.

[0067] The table below shows the temperature data for the closure of the bridge. Taking Changzhou as an example, it displays the distribution of the average daily minimum temperature over the years, which is used to determine the actual closure temperature.

[0068] month 1 2 3 4 5 6 7 8 9 10 11 12 Average daily minimum temperature / ℃ 1 2 7 13 18 22 27 26 22 15 9 2

[0069] The table below shows the calculated values ​​of the longitudinal offset △1 for each support, clarifying the value and direction of △1 for each support under different beam types and load conditions;

[0070]

[0071] The table below shows the calculation ledger for the pre-deflection of the supports, recording key data such as the name of the continuous beam, pier number, △1, △2, and total pre-deflection, for easy traceability and verification;

[0072]

[0073] The applicant employed this precise calculation method to calculate the pre-offset of continuous box girder supports in the Jiangsu South Yangtze River Intercity Railway Station Front Section 5 project. This project comprises 33 continuous box girder sections with a total of 338 large-adjustment spherical steel supports, involving complex scenarios such as crossing highways, national and provincial trunk roads, and waterways. By accurately calculating the pre-offset using this method, the model and location of each support, closure temperature parameters, and offset values ​​were clearly defined. All supports were accurately installed, beam joint control was reasonable, and no quality or safety accidents occurred. This provided strong technical support for the smooth progress of the continuous box girder construction and verified the feasibility and accuracy of the calculation method.

[0074] The precise calculation method of this invention overcomes the shortcomings of traditional pre-bias calculation, such as lack of standardization, large errors, and chaotic parameter values, and has the following beneficial effects:

[0075] 1. The calculation results are accurate and reliable, and the standards for each key step and parameter are clearly defined, avoiding deviations caused by empirical estimation and ensuring that the support can autonomously "return" to the theoretical centerline position after installation.

[0076] 2. Reduce the workload of later adjustments, avoid problems such as support replacement and beam lifting caused by incorrect pre-deflection, reduce construction costs, and ensure construction progress.

[0077] 3. Comprehensively consider the influencing factors such as elastic deformation, shrinkage and creep, and system temperature difference, clarify the vector characteristics and calculation logic of each factor, so that the stress state of the support meets the design requirements and improves the safety and durability of the continuous box girder structure.

[0078] 4. The calculation process is simple and clear, and can be directly applied to various high-speed railway continuous box girder projects, which has broad promotion value and practical significance.

[0079] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the concept and technical solution of the present invention, or the direct application of the concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A method for calculating the longitudinal pre-eccentricity of supports for continuous box girders in high-speed railways, characterized in that: The calculation method is as follows: The support offset is mainly affected by two types of factors. The first is denoted as △1, which is the offset at each support point caused by the elastic deformation and shrinkage creep of the box girder; the second is denoted as △2, which is the offset caused by the temperature difference of the box girder system. The pre-deflection at the corresponding support can be obtained by the formula △ = - (△1 + △2). The negative sign indicates that the pre-deflection of the support is set in the opposite direction according to the calculated value, which is used to compensate for the deformation and displacement of concrete caused by elastic deformation, shrinkage and creep, and temperature changes.

2. The method for calculating the longitudinal pre-eccentricity of the support for a continuous box girder in high-speed railway as described in claim 1, characterized in that: The offset caused by the temperature difference of the box girder system; when the closure temperature is greater than the design temperature, the offset direction is away from the fixed support; when the closure temperature is less than the design temperature, the offset direction is towards the fixed support.

3. The method for calculating the longitudinal pre-eccentricity of the support for a continuous box girder in high-speed railway as described in claim 1, characterized in that: The elastic deformation of the box girder and the offset at each support point caused by shrinkage and creep are all directed towards the fixed support.

4. The method for calculating the longitudinal pre-eccentricity of the support for a continuous box girder in high-speed railway as described in claim 1, characterized in that: The calculation method steps are as follows: determine the support model and location - clarify the closure temperature parameters - calculate the key offset - obtain the final value of the pre-offset.

5. The method for calculating the longitudinal pre-eccentricity of the support for a continuous box girder in high-speed railway as described in claim 4, characterized in that: The determination of the bearing model and location: Select the bearing layout according to the peak ground acceleration Ag value in the engineering design parameters, clarify the installation pier number and line side of the fixed bearing and movable bearing in conjunction with the design specifications, determine the position of the pad stone and anchor bolt hole according to the bearing structure layout drawing, and confirm the unclear parts through the design liaison form; Clearly define the closure temperature parameters: The design closure temperature should first adopt the value specified in the construction drawings or design briefing; if there is no specification, the annual average temperature of the project location should be used; the actual closure temperature should be the average daily minimum temperature of the month of construction closure, and the data should be obtained from the local meteorological website. Calculate the key offsets: △1 The offsets caused by elastic deformation and shrinkage creep of the box girder are listed in the design specifications, and the directions are all close to the fixed supports; The offset caused by the temperature difference in the △2 system is calculated according to the formula △2=α△t*l; α is the linear expansion coefficient of concrete, △t is the temperature difference between the design and the actual closure, and l is the beam length from the center of the support to the center of the fixed support. The offset direction is determined based on the temperature difference. The final value of the pre-deflection is obtained: considering the vector characteristics of △1 and △2, the total pre-deflection is calculated by the formula △ = - (△1 + △2). Positive values ​​correspond to positive settings, and negative values ​​correspond to negative settings, so as to achieve accurate compensation for concrete deformation displacement.

6. The method for calculating the longitudinal pre-eccentricity of the support for a continuous box girder in high-speed railway as described in claim 5, characterized in that: The △1 refers to the elastic deformation of the continuous box girder concrete caused by stress and its own characteristics, as well as the deformation of the beam caused by shrinkage and creep. The deformation of the beam simultaneously affects the deformation of the support, which in turn causes the upper support plate to shift relative to the lower support plate. The direction of concrete shrinkage and creep generally does not change, and it is always a displacement towards the fixed support.

7. The method for calculating the longitudinal pre-eccentricity of the support for a continuous box girder in high-speed railway as described in claim 6, characterized in that: The beam length is affected by concrete shrinkage and creep or temperature changes, resulting in shrinkage or elongation. Since fixed supports are installed at the mid-span piers, displacement deformation is impossible. Therefore, the shrinkage or elongation of the beam is primarily reflected in the side span length, causing the beam joints in the side spans of the continuous beam to widen or narrow. To offset this deformation caused by the inherent properties of concrete and ensure that the beam joint width meets design requirements, compensation for the beam length needs to be made during the cast-in-place process of the straight section of the side span, based on the pre-deflection of the beam end supports.

8. The method for calculating the longitudinal pre-eccentricity of the support for a continuous box girder in high-speed railway as described in claim 7, characterized in that: The contraction or elongation of the beam concrete caused by temperature changes occurs cyclically with the changing seasons throughout the year. During high-temperature periods, the beam expands due to heat, becoming longer and the beam joints shrink. During periods of low temperature, the beam contracts upon cooling, causing the beam length to shorten and the beam joints to widen. △1 is the primary value, with a larger value, while △2 is the secondary value, with a smaller value.

9. The method for calculating the longitudinal pre-eccentricity of the support for a continuous box girder in high-speed railway as described in claim 8, characterized in that: In the aforementioned calculation method, all external environmental conditions are assumed to be ideal. However, the actual on-site conditions may deviate slightly from the theoretical drawings. When compensating for the beam end length according to the value of △1, it is necessary to comprehensively consider the on-site measured data and combine them with the railway engineering acceptance conditions. By finding patterns in multiple lengthening data, the final beam joint width can be optimally controlled within the design value ±2cm error range.

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