An effective prestress inversion method based on prestressed steel tendon cut-off stress release

Abstract

The application discloses an effective prestress inversion method based on prestressed steel beam stress release, combines with an existing prestressed concrete beam bridge staged demolition scheme, determines a target prestressed beam, a cutting position and a plurality of monitoring sections, collects the top and bottom plate normal stress changes of each monitoring section before and after the target beam cutting, inversely calculates the prestress release amount in combination with the section geometric parameters, constructs a prestress release amount-distance curve, extrapolates the effective prestress before the target beam cutting according to a linear change section, determines the stress recovery length after the cutting by the intersection of the linear change section and a platform section, and determines the prestress recovery coefficient according to the platform section release amount. The application can utilize the stress release response generated by the prestressed beam cutting in the demolition process, inverses the effective prestress of the existing prestressed beam, the stress recovery length after the cutting and the prestress change rule within the stress recovery length after the cutting, and provides a basis for the existing prestressed concrete beam bridge structure state evaluation and demolition construction safety analysis.

Description

Technical Field

[0001] This invention belongs to the technical field of bridge health detection and structural condition assessment, and relates to a method for identifying effective prestress in existing prestressed concrete bridges, specifically a method for inverting effective prestress based on the release of prestressed steel strand cut-off stress. Background Technology

[0002] For prestressed concrete bridges, the effective prestress level of the prestressing tendons directly affects the crack resistance, stiffness, load-bearing capacity, and long-term deformation development of the beam, making it a crucial parameter for evaluating the service performance of bridge structures. However, during long-term operation, the prestress loss and its dispersion in existing prestressed concrete bridges can influence the assessment of their structural condition. Therefore, accurately identifying the actual effective prestress of the prestressing tendons in existing bridges is of great significance for assessing bridge load-bearing capacity, designing reinforcement, conducting safety analysis for demolition construction, and determining the remaining service life of the bridge.

[0003] Existing effective methods for prestress detection and assessment mainly include standard loss calculation, empirical reduction assessment, structural response inversion, finite element model correction, and methods such as anchor unloading or reverse tension detection, vibration frequency identification, and magnetoelastic or electromagnetic detection. For bonded prestressed tendons, local removal to expose the tendons, and stress release through slotting or drilling can also be used. While these methods can be used for prestress state assessment under certain conditions, they generally suffer from strong parameter dependence, limited applicability under specific field conditions, and significant uncertainty in results. Among these, detection methods for local damage or release of prestressed tendons are typically difficult to implement, costly, and may disturb existing structures, making them unsuitable for widespread application as routine detection methods.

[0004] In fact, for bonded prestressed tendons, when the tendon is cut at a certain location, prestress release occurs near the cut-off point, forming a stress transfer and recovery process within a certain range along the tendon direction. By arranging multiple monitoring sections near the cut-off point and measuring the changes in normal stress in the top and bottom slabs of the beam before and after tendon cut-off, the prestress release at different distances can be calculated, thus establishing a curve of prestress release as a function of distance. This curve can reflect information such as the effective prestress before tendon cut-off, the stress recovery length after cut-off, and the degree of prestress recovery beyond the stress recovery length after cut-off.

[0005] Therefore, in the phased demolition of existing prestressed concrete beam bridges, it is necessary to propose an effective prestress inversion method based on the stress release response of prestressed tendons after truncation. Through multi-section stress monitoring and release curve analysis, the effective prestress of existing prestressed tendons and the stress recovery length after truncation can be identified, providing a basis for performance evaluation and demolition safety analysis of existing prestressed concrete bridges. Summary of the Invention

[0006] To address the aforementioned issues, this invention discloses an effective prestress inversion method based on stress release during prestressed tendon truncation. This method is designed for the phased demolition of existing prestressed concrete beam bridges. First, it identifies the beam segments to be demolished, the construction sequence, and the prestressed tendon processing procedures according to the demolition plan. Then, it determines the target prestressed tendon at the specific demolition stage where the tendons need to be truncated. Subsequently, using the stress release response generated by the truncation of the target prestressed tendon, it inverts the effective prestress before truncation, the stress recovery length after truncation, and the prestress recovery coefficient beyond the stress recovery length after truncation, providing a basis for the effective prestress assessment of existing prestressed concrete structures.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] An effective prestress inversion method based on prestress release of prestressed steel strand cutoff stress includes the following steps:

[0009] Step 1: Based on the phased demolition plan of the existing prestressed concrete beam bridge, clarify the sequence of beam segment cutting, component unloading and prestressed tendon treatment to be implemented in the current demolition phase; before entering the demolition process where the prestressed tendons need to be cut off, determine the target prestressed tendons to be cut off and the cutting position of the target prestressed tendons according to the prestressed tendon layout, demolition unit division and construction safety control requirements.

[0010] The target prestressed tendon is preferably a bonded prestressed tendon in an existing prestressed concrete structure, and the stress release response caused by its truncation should be identifiable separately from the monitoring responses of each monitoring section. In the same inversion process, one of the target prestressed tendons is used as the inversion object, and the inversion is performed based on the changes in normal stress at each monitoring section before and after its truncation.

[0011] Step 2: Using the cut-off position as a reference, arrange multiple monitoring sections along the direction of the target prestressed tendon, and arrange stress sensors or strain sensors on the top and bottom plates of each monitoring section.

[0012] The plurality of monitoring sections includes monitoring sections located within the expected stress recovery length after truncation, monitoring sections located outside the expected stress recovery length after truncation, and monitoring sections located near the boundary of the expected stress recovery length after truncation. Preferably, the number of monitoring sections is not less than five, wherein at least two monitoring sections are located within the expected stress recovery length after truncation, at least two monitoring sections are located outside the expected stress recovery length after truncation, and at least one monitoring section is located near the boundary of the expected stress recovery length after truncation.

[0013] The strain sensor collects strain data of the top and bottom plates at each monitoring section, and converts the strain data of the top and bottom plates into normal stress data of the top and bottom plates based on the elastic modulus of the materials.

[0014] Step 3: Collect the initial normal stress data of the top and bottom plates of each monitoring section before the target prestressed tendon is cut off, and collect the normal stress data of the top and bottom plates of each monitoring section after the target prestressed tendon is cut off.

[0015] Step 4: Based on the initial normal stress data of the top plate and bottom plate and the normal stress data after the top plate and bottom plate are cut off, determine the change in normal stress of the top plate and the change in normal stress of the bottom plate at each monitoring section.

[0016] For the m-th monitoring section, the changes in normal stress in the top plate and the bottom plate are respectively:

[0017] (1);

[0018] (2);

[0019] In the formula, Δσ t,m Let Δσ be the change in normal stress in the top plate at the m-th monitoring section. b,m Let σ be the change in normal stress of the base plate at the m-th monitoring section. t,m before and σ b,m before These are the initial normal stress data of the top and bottom plates at the m-th monitoring section before the target prestressed tendon is cut off, σ t,m after and σ b,m after These are the normal stress data for the top and bottom plates of the m-th monitoring section after the target prestressed tendon is cut off.

[0020] Step 5: Based on the changes in normal stress in the top plate and bottom plate, the cross-sectional geometric parameters, and the effective cross-sectional area of ​​the target prestressed tendon at each monitoring section, determine the prestress release amount corresponding to each monitoring section.

[0021] For the m-th monitoring section, the prestress release amount is:

[0022] (3);

[0023] In the formula, Δσ p,m I represents the prestress release amount corresponding to the m-th monitoring section. m Let e ​​be the moment of inertia of the m-th monitoring section. m h is the eccentricity of the target prestressed tendon relative to the centroid or neutral axis of the m-th monitoring section. m = y t,m +y b,m y t,mLet y be the distance from the centroid of the m-th monitoring section to its top edge. b,m Let A be the distance from the centroid of the m-th monitoring section to the bottom edge. ps This is the design value of the effective cross-sectional area of ​​the target prestressed tendon.

[0024] Step 6: Based on the distance from each monitoring section to the cut-off position and the prestress release amount corresponding to each monitoring section, construct the prestress release amount-distance curve.

[0025] Specifically, the distance x from the monitoring section to the cutoff position is used. m The x-axis represents the prestress release amount Δσ. p,m Plot the prestress release amount versus distance curve with the vertical axis as the ordinate.

[0026] Step 7: Identify the linear variation segment and plateau segment in the prestress release amount-distance curve.

[0027] Specifically, the prestress release amounts corresponding to each monitoring section are sorted according to the distance from each monitoring section to the cutoff position; a linear function is fitted to several monitoring points close to the cutoff position, and when the fitting residual of the linear function is less than a preset residual threshold, the curve segment corresponding to the several monitoring points is determined as a linear change segment; when the rate of change of prestress release amounts between adjacent monitoring points far from the cutoff position is less than a preset rate of change threshold, the curve segment where the adjacent monitoring points are located is determined as a plateau segment.

[0028] Step 8: Based on the result of extrapolating the linear change segment to the cutoff position, determine the effective prestress before the target prestressed strand is cut off.

[0029] By fitting a linear function to the linear change segment, we obtain:

[0030] (4);

[0031] In the formula, x is the distance from the monitoring section to the cutoff position, and Δσ p denoted as , where 'a' is the slope of the fitted line and 'b' is the intercept of the fitted line.

[0032] Since the cutoff point corresponds to x = 0, the fitted line is extrapolated to the cutoff point, and the value of the fitted line at x = 0 is determined as the effective prestress σ before the target prestressed strand is cut off. peff :

[0033] (5);

[0034] Step 9: Based on the prestress release amount corresponding to the platform segment, determine the prestress recovery coefficient of the target prestressed strand outside the stress recovery length after truncation.

[0035] The average value of the multiple prestress release amounts corresponding to the platform segment is determined as the platform segment release amount C:

[0036] (6);

[0037] In the formula, Δσ̄ p,platform This represents the average prestress release amount of the platform section, i.e., the prestress release amount Δσ corresponding to each monitoring section of the platform section. p,m The arithmetic mean.

[0038] And based on the release amount of the platform segment and the effective prestress, the prestress recovery coefficient outside the stress recovery length after truncation is determined;

[0039] When the following conditions are met:

[0040] (7);

[0041] When it is determined that the prestress of the target prestressed strand is fully recovered beyond the stress recovery length after truncation, η = 1 is taken;

[0042] When the following conditions are met:

[0043] (8);

[0044] The prestress recovery coefficient is determined according to the following formula:

[0045] (9);

[0046] In the formula, C is the release amount of the platform segment, ε is the preset allowable error threshold, η is the prestress recovery coefficient outside the stress recovery length after truncation, and 0 < η ≤ 1.

[0047] Step 10: Based on the intersection of the linear change segment and the platform segment, determine the stress recovery length after the target prestressed strand is cut off.

[0048] The distance corresponding to the intersection point of the linear change segment and the release amount of the platform segment are determined, and the distance corresponding to the intersection point is used as the stress recovery length after the target prestressed strand is cut off. The stress recovery length after cutoff is:

[0049] (10);

[0050] In the formula, l tr Let be the stress recovery length after the target prestressed tendon is cut off, 'a' be the slope of the fitted straight line, 'b' be the intercept of the fitted straight line, and 'C' be the release amount of the plateau segment.

[0051] Furthermore, based on the effective prestress σ peffThe stress recovery length l after truncation tr And the prestress recovery coefficient η, determine the form of prestress variation along the distance direction after the target prestressed strand is cut off:

[0052] (11);

[0053] In the formula, σ p,after (x) represents the prestress at a distance x from the cutoff position after the target prestressed bundle is cut off.

[0054] The beneficial effects of this invention are as follows:

[0055] The present invention provides an effective prestress inversion method based on prestress release during prestressed tendon truncation. This method utilizes the stress release response generated by the truncation of a target prestressed tendon during the demolition of an existing prestressed concrete structure. It calculates the prestress release amount by analyzing the changes in normal stress in the top and bottom slabs of multiple monitoring sections. Based on the prestress release amount-distance curve, it identifies the effective prestress before truncation, the stress recovery length after truncation, and the prestress recovery coefficient beyond the stress recovery length after truncation. This method does not rely on pre-defined assumptions about prestress loss, tendon truncation, or bond transfer parameters in the finite element model. This improves the accuracy of evaluating the effective prestress and transfer characteristics of existing prestressed concrete structures, providing a basis for performance evaluation of existing bridges and safety analysis during demolition construction. Attached Figure Description

[0056] Figure 1 This is a basic flowchart of the effective prestress inversion method based on the stress release of prestressed steel strand truncation according to the present invention.

[0057] Figure 2 This is a schematic diagram of the target prestressed tendon cutoff location and the arrangement of multiple monitoring sections in this invention.

[0058] Figure 3 This is a schematic diagram of the sensor arrangement and cross-sectional geometric parameters of the top and bottom plates of the monitoring section in this invention.

[0059] Figure 4 This is a schematic diagram of the change in normal stress at the monitoring section before and after the target prestressed tendon is cut off in this invention.

[0060] Figure 5 This is a schematic diagram of the prestress release amount-distance curve and the identification of linear change segments and plateau segments in this invention.

[0061] Figure 6 This is a schematic diagram of the prestress variation along the distance direction after the target prestressed tendon is cut off in this invention. Detailed Implementation

[0062] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0063] like Figure 1 As shown, the present invention provides an effective prestress inversion method based on prestress release after prestressed steel strand truncation, which mainly includes the following steps: determining the target prestressed strand and truncation location, arranging multiple monitoring sections, collecting stress data on the top and bottom plates before and after truncation, calculating the change in normal stress, inverting the prestress release amount, constructing the prestress release amount-distance curve, identifying linear change segments and plateau segments, and inverting the effective prestress and the stress recovery length after truncation.

[0064] This embodiment uses an existing prestressed concrete continuous box girder bridge as an example. The main girder of the bridge is a single-cell prestressed concrete box girder, and the target prestressing tendon is a longitudinal prestressing tendon with a bonded structure located near the bottom slab of the box girder. This target prestressing tendon is constructed using the post-tensioning method and forms a bonded force transfer relationship with the beam concrete through grouting in the ducts. During the demolition construction, it is necessary to cut off the target prestressing tendon. To invert the effective prestress before the cutoff and the stress recovery length after the cutoff, the method described in this invention is used for monitoring and calculation.

[0065] Step 1: Determine the target prestressed tendons and cut-off locations in conjunction with the demolition process.

[0066] like Figure 2 As shown, firstly, based on the existing bridge demolition construction plan, the sequence of beam segment cutting, component unloading, and prestressed tendon treatment to be implemented in the current demolition phase is clarified. When the demolition process reaches the stage where prestressed tendons need to be cut off, the target prestressed tendon to be inverted and its cutting position are determined according to the existing bridge as-built drawings, prestressed tendon layout drawings, and construction safety control requirements. The target prestressed tendon is preferably a bonded prestressed tendon. In the same inversion process, only one target prestressed tendon is cut off so that the change in normal stress in the beam before and after cutting off is mainly attributed to the stress release of the target prestressed tendon.

[0067] In this embodiment, the target prestressed tendon is a longitudinal prestressed tendon near the bottom slab of the box girder. The cutoff position is set as the origin of the coordinate system, i.e., the cutoff position corresponds to x = 0. A distance coordinate axis is established along the direction of the target prestressed tendon, and the distance from the monitoring section to the cutoff position is recorded as x. m , where m is the monitoring section number.

[0068] Step 2: Arrange monitoring sections and sensors

[0069] like Figure 2 and Figure 3As shown, multiple monitoring sections are arranged along the direction of the target prestressed tendon, with the cut-off position as the reference. These monitoring sections should cover the area within the expected stress recovery length after cut-off, near the boundary of the expected stress recovery length after cut-off, and outside the expected stress recovery length after cut-off. The expected stress recovery length after cut-off is initially estimated using the calculation method for the prestressed tendon transfer length in current specifications, and appropriately adjusted based on the grouting and bonding conditions of the ducts.

[0070] In this embodiment, the expected stress recovery length after truncation is approximately 2m to 3m. Therefore, nine monitoring sections (x1-x9) are arranged along the direction of the target prestressed tendon, with distances from the truncation position of 0.4m, 0.8m, 1.2m, 1.6m, 2.0m, 2.4m, 3.0m, 3.6m, and 4.2m, respectively. The monitoring sections within the range of 0.4m to 2.4m are mainly used to identify linear change segments, while the monitoring sections within the range of 3.0m to 4.2m are mainly used to identify plateau segments.

[0071] like Figure 3 As shown, strain sensors (T) are arranged on the top and bottom plates of each monitoring section. m and B m First, the strain changes of the top and bottom slabs are collected, and then converted into normal stress changes based on the elastic modulus of concrete. In this embodiment, strain sensors are used to collect data, and the elastic modulus of concrete is taken as E. c = 3.45×10 4 MPa.

[0072] Step 3: Collect normal stress data for the top and bottom plates before and after severance.

[0073] like Figure 4 As shown, the initial normal stress data of the top and bottom plates of each monitoring section were collected before the target prestressed tendon was cut off. For the m-th monitoring section, the initial normal stress of the top plate before cutting off is denoted as σ. t,m before The initial normal stress of the base plate before cutting is denoted as σ. b,m before .

[0074] After completing the data acquisition before truncation, the target prestressed tendon is truncated individually. After truncation and waiting for the local stress state of the beam to stabilize, the normal stress data of the top and bottom slabs at each monitoring section are then collected. For the m-th monitoring section, the normal stress of the top slab after truncation is denoted as σ. t,m after The normal stress of the base plate after severance is denoted as σ. b,m after .

[0075] Step 4: Calculate the change in normal stress in the top and bottom plates.

[0076] The change in normal stress of the top and bottom plates at the m-th monitoring section is calculated using formulas (1) and (2). It should be noted that the sign convention for tension and compression should be consistent during the calculation of the change in normal stress. For example, it can be agreed that tensile stress is positive and compressive stress is negative, or vice versa, as long as the consistency is maintained in the calculation of each monitoring section.

[0077] Step 5: Back-calculate the prestress release amount at each monitoring section.

[0078] like Figure 3 and Figure 4 As shown, since the target prestressed tendon has an eccentricity relative to the centroid or neutral axis of the monitoring section, its truncation and release will not only cause changes in the axial stress of the section, but also changes in the bending stress. Therefore, according to formula (3), the prestress release amount of the m-th monitoring section can be calculated using the difference in normal stress between the top and bottom plates, the geometric parameters of the section, and the effective cross-sectional area of ​​the target prestressed tendon.

[0079] In this embodiment, the moment of inertia of a certain monitoring section is taken as I. m = 2.80×10 12 mm 4 The eccentricity of the target prestressed tendon is taken as e. m = 1200mm, distance from centroid to apex is taken as y t,m = 1400mm, distance from centroid to bottom edge is taken as y b,m = 1600mm, then h m = 3000mm. The measured difference in normal stress between the top and bottom plates of the monitored section is 3.44MPa, and the effective cross-sectional area of ​​the target prestressed tendon is taken as A. ps = 2660mm 2 According to formula (3), the prestress release amount corresponding to this section is approximately 1005.6 MPa.

[0080] Step 6: Construct the prestress release amount-distance curve

[0081] like Figure 5 As shown, the distance x from each monitoring section to the cutoff position is used. m The x-axis represents the prestress release amount Δσ corresponding to each monitoring section. p,m Using the vertical axis as the ordinate, construct a prestress release amount-distance curve.

[0082] In this embodiment, the distances between each monitoring section and the prestress release amount calculated in reverse are shown in the table below.

[0083] Table 1 Prestress Release Amount at Each Monitoring Section

[0084] Monitoring section number <![CDATA[Distance x from truncation position m / m]]> <![CDATA[Prestress release amount Δσ p,m / MPa]]> 1 0.4 1005.6 2 0.8 811.3 3 1.2 612.8 4 1.6 418.0 5 2.0 221.4 6 2.4 24.8 7 3.0 24.1 8 3.6 23.3 9 4.2 24.4

[0085] As can be seen from the data in the table, the prestress release is greater at the monitoring section near the cut-off position. As the distance from the cut-off position increases, the prestress release gradually decreases. When the distance exceeds a certain range, the prestress release tends to stabilize, indicating that the stress release effect after the target prestressed tendon is cut off gradually enters the plateau section.

[0086] Step 7: Identify linear change segments and plateau segments

[0087] like Figure 5 As shown, the prestress release-distance curve is segmented for identification. If several monitoring points near the cutoff position can be well fitted by a linear function, they are identified as linear variation segments; if adjacent monitoring points far from the cutoff position show small changes in release, they are identified as plateau segments.

[0088] Specifically, the prestress release amounts corresponding to each monitoring section are sorted according to the distance from each monitoring section to the cutoff position; a linear function is fitted to several monitoring points close to the cutoff position, and when the fitting residual of the linear function is less than a preset residual threshold, the curve segment corresponding to the several monitoring points is determined as a linear change segment; when the rate of change of prestress release amount between adjacent monitoring points far from the cutoff position is less than a preset rate of change threshold, the curve segment where the adjacent monitoring point is located is determined as a plateau segment.

[0089] In this embodiment, a preset change rate threshold of 5% can be used. According to the data in the table, the prestress release amounts at 3.0m, 3.6m, and 4.2m are 24.1MPa, 23.3MPa, and 24.4MPa, respectively, with relatively small variation ranges. Therefore, this section can be identified as a plateau section. The monitoring data within the range of 0.4m to 2.4m can be approximately fitted by a linear function, so this section can be identified as a linear change segment.

[0090] Step 8: Invert the effective prestress before the target prestressed tendon is cut off

[0091] The linear change segment is fitted with a linear function to obtain formula (4). Since the cutoff position corresponds to x = 0, when the fitted line is extrapolated to the cutoff position, the amount of prestress released at the cutoff position can be regarded as the effective prestress before the target prestressing strand is cut off, and is determined according to formula (5).

[0092] In this embodiment, a linear function is fitted to the monitoring data within the range of 0.4m to 2.4m to obtain an approximate relationship: Δσ p = −491.0x + 1203.0, and from this we obtain σ. peff = 1203.0MPa, that is, the effective prestress inversion value before the target prestressed tendon is cut off is 1203.0MPa.

[0093] Step 9: Determine the release amount and prestress recovery coefficient of the platform section.

[0094] Based on the prestress release amount corresponding to the platform segment, the prestress recovery coefficient of the target prestressed strand outside the stress recovery length after truncation is determined.

[0095] The average value of the multiple prestress release amounts corresponding to the platform segment is determined as the platform segment release amount, which is determined according to formula (6). In this embodiment, the prestress release amounts of three monitoring sections of 3.0m, 3.6m and 4.2m are taken as the platform segment data, then: C = (24.1+23.3+24.4) / 3 = 23.9MPa.

[0096] To determine whether the target prestressed tendon has fully recovered beyond the stress recovery length after truncation, a preset allowable error threshold ε is introduced, and calculations are performed according to formulas (7)-(9). In this embodiment, ε = 3% is taken, which satisfies formula (7), indicating that the prestress of the target prestressed tendon has fully recovered beyond the stress recovery length after truncation, and η = 1 is taken. If the release amount of the platform section is significantly large, for example, C = 90.2MPa, and the effective prestress is still 1203.0MPa, then the preset allowable error threshold is exceeded, satisfying formula (8), and η = 0.925 is calculated according to formula (9). This indicates that the target prestressed tendon has not fully recovered to the effective prestress level before truncation beyond the stress recovery length after truncation, and there may be bonding degradation, insufficient grouting, or insufficient re-anchoring.

[0097] Step 10: Determine the stress recovery length and the prestress change pattern after truncation.

[0098] like Figure 5 As shown, the intersection of the linear change segment and the platform segment corresponds to the position where the prestress release amount changes from a linear decrease to a stable platform. The distance from this position to the cut-off position can be used as the stress recovery length after the target prestressed strand is cut off. The stress recovery length after cut-off is determined according to formula (10).

[0099] In this embodiment, the fitting function for the linear variation segment is Δσ. p = −491.0x + 1203.0, substituting into formula (10), the stress recovery length l after truncation is calculated. tr = 2.40m, effective prestress value σ before cutoff peff = 1203.0MPa.

[0100] Furthermore, such as Figure 6 As shown, it can be based on the effective prestress σ peff Stress recovery length l after truncation tr The prestress recovery coefficient η is used to determine the prestress change pattern along the distance direction after the target prestressed strand is cut off, according to formula (11).

[0101] As demonstrated by the above embodiments, this invention can utilize the stress release response generated by the truncation of the target prestressed tendon during the demolition of existing prestressed concrete bridges. It can back-calculate the prestress release amount by monitoring the changes in normal stress in the top and bottom slabs of multiple monitoring sections, and, based on the prestress release amount-distance curve, invert the effective prestress before truncation, the stress recovery length after truncation, and the prestress recovery coefficient beyond the stress recovery length after truncation. This method does not rely on pre-defined assumptions about prestress loss, tendon truncation, or bond transfer parameters in the finite element model, thus improving the accuracy of evaluating the effective prestress and transfer characteristics of existing prestressed concrete structures.

[0102] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. An effective prestress inversion method based on prestress release of prestressed steel strand cutoff stress, characterized in that: Includes the following steps: Step 1: Based on the phased demolition plan of the existing prestressed concrete beam bridge, clarify the sequence of beam segment cutting, component unloading and prestressed tendon treatment to be implemented in the current demolition phase; before entering the demolition process where the prestressed tendons need to be cut off, determine the target prestressed tendons to be cut off and the cutting position of the target prestressed tendons according to the prestressed tendon layout, demolition unit division and construction safety control requirements. Step 2: Using the cut-off position as a reference, arrange multiple monitoring sections along the direction of the target prestressed tendon, and arrange stress sensors or strain sensors on the top and bottom plates of each monitoring section. Step 3: Collect the initial normal stress data of the top and bottom plates of each monitoring section before the target prestressed tendon is cut off, and collect the normal stress data of the top and bottom plates of each monitoring section after the target prestressed tendon is cut off; Step 4: Based on the initial normal stress data of the top plate and bottom plate and the normal stress data after the top plate and bottom plate are cut off, determine the change in normal stress of the top plate and the change in normal stress of the bottom plate at each monitoring section; Step 5: Based on the changes in normal stress in the top plate and bottom plate of each monitoring section, the cross-sectional geometric parameters, and the effective cross-sectional area of ​​the target prestressed tendon, determine the prestress release amount corresponding to each monitoring section; Step 6: Based on the distance from each monitoring section to the cut-off position and the prestress release amount corresponding to each monitoring section, construct a prestress release amount-distance curve; Step 7: Identify the linear variation segment and plateau segment in the prestress release amount-distance curve; Step 8: Based on the result of extrapolating the linear change segment to the cutoff position, determine the effective prestress before the target prestressed strand is cut off; Step 9: Based on the prestress release amount corresponding to the platform segment, determine the prestress recovery coefficient of the target prestressed strand outside the stress recovery length after truncation; Step 10: Based on the intersection of the linear change segment and the platform segment, determine the stress recovery length after the target prestressed strand is cut off.

2. The effective prestress inversion method based on prestressed steel strand cutoff stress release according to claim 1, characterized in that: The multiple monitoring sections mentioned in step 2 include monitoring sections located within the expected stress recovery length after truncation, monitoring sections located outside the expected stress recovery length after truncation, and monitoring sections located near the boundary of the expected stress recovery length after truncation. The number of monitoring sections is no less than five, of which at least two monitoring sections are located within the expected stress recovery length after truncation, at least two monitoring sections are located outside the expected stress recovery length after truncation, and at least one monitoring section is located near the boundary of the expected stress recovery length after truncation.

3. The effective prestress inversion method based on prestressed steel strand cutoff stress release according to claim 1, characterized in that: In step 4, for the m-th monitoring section, the changes in normal stress of the top plate and the bottom plate are respectively: （1）； （2）； In the formula, Δσ t,m Let Δσ be the change in normal stress in the top plate at the m-th monitoring section. b,m Let σ be the change in normal stress of the base plate at the m-th monitoring section. t,m before and σ b,m before These are the initial normal stress data of the top and bottom plates at the m-th monitoring section before the target prestressed tendon is cut off, σ t,m after and σ b,m after These are the normal stress data for the top and bottom plates of the m-th monitoring section after the target prestressed tendon is cut off.

4. The effective prestress inversion method based on prestressed steel strand cutoff stress release according to claim 3, characterized in that: In step 5, the prestress release amount corresponding to the m-th monitoring section is: （3）； In the formula, Δσ p,m I represents the prestress release amount corresponding to the m-th monitoring section. m Let e ​​be the moment of inertia of the m-th monitoring section. m h is the eccentricity of the target prestressed tendon relative to the centroid or neutral axis of the m-th monitoring section. m = y t,m + y b,m y t,m Let y be the distance from the centroid of the m-th monitoring section to its top edge. b,m Let A be the distance from the centroid of the m-th monitoring section to the bottom edge. ps This is the design value of the effective cross-sectional area of ​​the target prestressed tendon.

5. The effective prestress inversion method based on prestressed steel strand cutoff stress release according to claim 4, characterized in that: Step 7 involves identifying the linear variation segment and plateau segment in the prestress release amount-distance curve, including: The prestress release amounts corresponding to each monitoring section are sorted according to the distance from each monitoring section to the cut-off position; A linear function is fitted to several monitoring points near the cutoff position. When the fitting residual of the linear function is less than a preset residual threshold, the curve segment corresponding to the several monitoring points is determined as a linear change segment. When the rate of change of prestress release between adjacent monitoring points far from the cut-off position is less than a preset rate of change threshold, the curve segment where the adjacent monitoring points are located is determined as a plateau segment.

6. The effective prestress inversion method based on prestressed tendon truncation stress release according to claim 5, characterized in that: In step 8, a linear function is fitted to the linear change segment to obtain: （4）； In the formula, x is the distance from the monitoring section to the cutoff position, and Δσ p denoted as , where 'a' is the slope of the fitted line and 'b' is the intercept of the fitted line. The fitted straight line is extrapolated to the cutoff position x = 0, and the value of the fitted straight line at x = 0 is determined as the effective prestress before the target prestressed strand is cut off: （5）； In the formula, σ peff The effective prestress before the target prestressed bundle is cut off.

7. The effective prestress inversion method based on prestressed tendon truncation stress release according to claim 6, characterized in that: In step 9, the average value of the multiple prestress release amounts corresponding to the platform segment is determined as the platform segment release amount C: （6）； In the formula, Δσ̄ p,platform This represents the average prestress release amount of the platform section, i.e., the prestress release amount Δσ corresponding to each monitoring section of the platform section. p,m The arithmetic mean; And based on the release amount of the platform segment and the effective prestress, the prestress recovery coefficient outside the stress recovery length after truncation is determined; When the following conditions are met: （7）； When determining that the prestressed tendon has sufficient prestress recovery beyond the stress recovery length after truncation, η = 1 is taken; where C is the release amount of the platform segment, and ε is the preset allowable error threshold. When the following conditions are met: （8）； The prestress recovery coefficient is determined according to the following formula: （9）； η is the prestress recovery coefficient beyond the stress recovery length after truncation, and 0 < η ≤ 1.

8. The effective prestress inversion method based on prestressed steel strand cutoff stress release according to claim 7, characterized in that: In step 10, the distance corresponding to the intersection of the linear change segment and the release amount of the platform segment is determined, and the distance corresponding to the intersection is used as the stress recovery length after the target prestressed strand is cut off. The stress recovery length after truncation is: （10）； In the formula, l tr Let be the stress recovery length after the target prestressed tendon is cut off, 'a' be the slope of the fitted straight line, 'b' be the intercept of the fitted straight line, and 'C' be the release amount of the plateau segment.

9. The effective prestress inversion method based on prestressed steel strand cutoff stress release according to claim 8, characterized in that: Based on effective prestress σ peff Stress recovery length l after truncation tr And the prestress recovery coefficient η, determine the form of prestress variation along the distance direction after the target prestressed tendon is cut off: （11）； In the formula, σ p,after (x) represents the prestress at a distance x from the cutoff position after the target prestressed strand is cut off.

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