Tensioning method and tensioning sequence of long-span simply supported T-beam

Abstract

The present invention discloses a tensioning method and tensioning sequence of a long-span simply supported T-beam, the method comprising: arranging prestressed steel bars in the middle beam of the T-beam, wherein some of the prestressed steel bars have horizontal lateral bending; establishing a tensioning simulation model according to the prestressed steel bars arranged in the middle beam, the model comprising a plurality of fixedly connected T-beams divided into units and nodes, adopting simply supported beam bridge constraint conditions at both ends of the T-beam, formulating a plurality of tensioning schemes, each tensioning scheme dividing the tensioning construction into a plurality of stages according to different tensioning sequences, performing simulation calculations in the tensioning simulation model, and determining the optimal tensioning scheme; tensioning the prestressed steel bars with the optimal tensioning scheme. The present invention determines the optimal tensioning scheme from tensioning schemes composed of different tensioning sequences, so that a tensioning scheme that can make the structural stress and anti-camber of the T-beam both beneficial to the structural safety and stability can be selected.

Description

Technical Field

[0001] The invention belongs to the technical field of bridge construction, and relates to a tensioning method and a tensioning sequence of a long-span simply supported T-beam. Background Art

[0002] In bridge construction, T-beam structure is a type of bridge superstructure. Usually, the superstructure adopts prefabricated T-beams. Several T-beams can be set along the width of the bridge, for example Figure 1 There are 5 T-beams in the middle, and adjacent T-beams 100 are connected by cross diaphragms. The lower structure adopts pile-column piers and cast-in-place pile foundation.

[0003] The main factors causing the lateral bending deformation of long-span precast T-beams include the position deviation of the prestressed steel bar channel, the tensioning sequence of the prestressed steel bars and the creep of concrete. Usually, the center beam structure is bilaterally symmetrical, while the side beams are asymmetrical. When designing the tensioning sequence of the prestressed steel bars, it is necessary to analyze the influence of the difference in the bilateral symmetry of the structure on the transverse mechanical properties and displacement of the T-beam. However, up to now, there is no effective method to guide the tensioning sequence of the T-beam to reduce the influence of the lateral bending deformation of the T-beam. Summary of the invention

[0004] This application analyzes the influence of the position deviation of the prestressed steel bar channel and the tensioning sequence of the prestressed steel bars on the transverse bending deformation of long-span thin-web T-beams, providing theoretical support for the later prefabrication of long-span T-beams.

[0005] A long-span simply supported T-beam tensioning method comprises the following steps:

[0006] In a middle beam of a plurality of T-shaped beams arranged along the width direction of the bridge, a plurality of prestressed steel bars are arranged along the length direction of the T-shaped beam, wherein one end of each prestressed steel bar is anchored on the center line of the web at one end of the middle beam, the other end of a portion of the prestressed steel bars is anchored on the center line of the web at the other end of the middle beam, and the other ends of the remaining prestressed steel bars have a horizontal side bend, at least one of the remaining prestressed steel bars is horizontally bent to one side and then anchored on the center line of the web at the other end of the middle beam, and at least one of the remaining prestressed steel bars is horizontally bent to the other side and then anchored on the center line of the web at the other end of the middle beam;

[0007] A tension simulation model is established according to the prestressed steel bars arranged in the middle beam. The model includes a plurality of fixedly connected T-beams divided into units and nodes. The two ends of the T-beam adopt the constraints of a simply supported beam bridge. One end constrains Dx, Dy, Dz, Rx and Rz, and releases Ry; the other end constrains Dy, Dz, Rx and Rz, and releases Ry and Dx, wherein Dx, Dy, Dz, Rx, Ry and Rz are the degrees of freedom in the x-axis, y-axis and z-axis directions of the Cartesian coordinate system, and the degrees of freedom of rotation around the x-axis, y-axis and z-axis, wherein Dx is the degree of freedom along the length direction of the bridge, Dy is the degree of freedom along the width direction of the bridge, and Dz is the degree of freedom in the vertical direction;

[0008] Formulate multiple tensioning schemes, each tensioning scheme divides the tensioning construction into multiple stages according to a different tensioning sequence, wherein at least one prestressed steel bar is tensioned in each stage, and the tensioning force is set as a percentage of the design tensioning force of the prestressed steel bar, and each tensioning scheme is simulated and calculated in a tensioning simulation model to determine the optimal tensioning scheme;

[0009] The prestressed steel bars are tensioned using the optimal tensioning scheme.

[0010] Optionally, the prestressed steel bars are prestressed steel bars inserted into a corrugated pipe, and five prestressed steel bars N1, N2, N3, N4 and N5 passing through the corresponding corrugated pipes are anchored on the center line of the web at one end of the middle beam from top to bottom. Both ends of the N1, N2 and N3 prestressed steel bars are anchored on the center line of the web of the middle beam, N4 is horizontally bent to one side of the T-beam and anchored on the center line of the web at the other end of the middle beam, and N5 is horizontally bent to the other side of the T-beam and anchored on the center line of the web at the other end of the middle beam.

[0011] Optionally, at least 15 steel strands are arranged in each corrugated pipe of N1, N2, and N3, and at least 17 steel strands are arranged in each corrugated pipe of N4 and N5.

[0012] Optionally, the T-beam prestressed steel bars use low-relaxation high-strength prestressed steel strands.

[0013] Optionally, a prefabricated platform is used to support the T-beam, and the lower part of the prefabricated platform is supported by a pile-column pier.

[0014] Optionally, in the tension simulation model, the pressure of the T-beam on the precast platform is simulated by using a compressive elastic connection, and the effects of deadweight, prestressing, and concrete shrinkage and creep are taken into consideration.

[0015] Optionally, the tensioning simulation model selects the optimal solution based on minimizing the weighted sum of the absolute values ​​of the increase in the camber of the key control section in each adjacent tensioning stage, the absolute values ​​of the increase in the support reaction force in each adjacent tensioning stage, and the absolute values ​​of the increase in the stress in each adjacent tensioning stage.

[0016] Optionally, the critical control section refers to the cross section at the mid-span and the beam end, the stress refers to the stress at the upper edge of the top plate and the lower edge of the bottom plate of the critical control section, and the camber of the T-beam refers to the camber value at the mid-span.

[0017] Optionally, the sum of the absolute values ​​of the increase in the camber degree, the sum of the absolute values ​​of the increase in the support reaction force, and the sum of the absolute values ​​of the increase in the stress are weighted and summed according to a weight of 1:0.7:1.

[0018] The present invention also provides a tensioning sequence for a long-span simply supported T-beam, wherein a plurality of prestressed steel bars are arranged along the length direction of the T-beam in a middle beam of a plurality of T-beams arranged along the width direction of the bridge, wherein the plurality of prestressed steel bars include five prestressed steel bars N1, N2, N3, N4 and N5 anchored on the center line of the web at one end of the middle beam from top to bottom and passing through corresponding corrugated pipes, wherein both ends of the N1, N2 and N3 prestressed steel bars are anchored on the center line of the web at the middle beam, N4 is horizontally bent to one side of the T-beam and then anchored on the center line of the web at the other end of the middle beam, and N5 is horizontally bent to the other side of the T-beam and then anchored on the center line of the web at the other end of the middle beam, and then the tensioning operation is performed according to the tensioning sequence in the following table:

[0019]

[0020]

[0021] The present invention establishes a tensioning simulation model to simulate the tensioning process, and determines the optimal tensioning scheme from tensioning schemes consisting of different tensioning sequences, so as to analyze the stress influence of different tensioning sequences on the T-beam, and thus select a tensioning scheme that can make the structural stress and anti-arch degree of the T-beam beneficial to the structural safety and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of a T-beam;

[0023] Figure 2 It is the cross-sectional view of the beam end and mid-span of the T-beam;

[0024] Figure 3 It is a schematic diagram of the arrangement of prestressed steel bars in a longitudinal section of an embodiment of the present invention;

[0025] Figure 4 for Figure 3 Schematic diagram of cross sections at points Ⅰ and Ⅱ;

[0026] Figure 5 A schematic diagram of an edge beam in a tension simulation model of an embodiment of the present invention;

[0027] Figure 6-1is a comparison diagram of the end support reaction forces of the side beam and the middle beam of an embodiment of the present invention;

[0028] Figure 6-2 is a comparison diagram of the mid-span camber of the side beam and the middle beam of an embodiment of the present invention;

[0029] Figure 7 is a schematic diagram of the position of the stress point of the key control section of an embodiment of the present invention;

[0030] Figures 8-1 to 8-4 is a stress comparison diagram of four positions of the side beam and the middle beam of an embodiment of the present invention;

[0031] Figure 9-1 is a stress diagram of the side beam mid-span according to an embodiment of the present invention;

[0032] Figure 9-2 is a stress diagram of the middle beam in the middle span of an embodiment of the present invention;

[0033] Figure 10-1 This is the comparison diagram of the end support reaction of the side beam under different tensioning schemes;

[0034] Figure 10-2 This is a comparison diagram of the mid-span camber of the side beam under different tensioning schemes;

[0035] Figures 10-3 to 10-6 : is a stress comparison diagram of four position points of the lower side beam under different tensioning schemes of an embodiment of the present invention;

[0036] Figure 11-1 This is the comparison diagram of the reaction force of the middle beam end support under different tensioning schemes;

[0037] Figure 11-2 This is a comparison diagram of the camber degree in the middle span of the middle beam under different tensioning schemes;

[0038] Figures 11-3 to 11-6 It is a stress comparison diagram of four positions of the middle beam under different tensioning schemes of an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The long-span simply supported T-beam tensioning method of this embodiment includes the following steps:

[0041] Step S1, arrange a plurality of prestressed steel bars along the length direction of the bridge in a middle beam of a plurality of T-beams arranged along the width direction of the bridge, wherein one end of each prestressed steel bar is arranged and anchored on the center line of the web at one end of the middle beam, the other end of a portion of the prestressed steel bars is arranged and anchored on the center line of the web at the other end of the middle beam, and the other end of another portion of the prestressed steel bars has a horizontal side bend, at least one of which is horizontally bent to the left and then anchored on the center line of the web at the other end of the middle beam, and at least one of which is horizontally bent to the right and then anchored on the center line of the web at the other end of the middle beam.

[0042] The lower end of the web in the middle of the span of the T-beam is horseshoe-shaped, and the web near the simple support point is thickened to at least the same width as the horseshoe. Figure 2 As shown in the figure, the horseshoe width is 62mm, which is thickened to 70mm at the beam end.

[0043] Prestressed steel bars can be made of steel strands inserted in corrugated pipes. T-beam prestressing uses low-relaxation high-strength prestressed steel strands. The diameter of a single steel strand is 15.2mm and the area of ​​the steel strand is 140mm. 2 , elastic modulus 1.95×105Mpa. For the five prestressed steel bars N1, N2, N3, N4, and N5, Figure 3 As shown in the figure, from top to bottom, a steel strand is anchored on the center line of the web at one end of the middle beam and passes through the corrugated pipe. At least 15 steel strands can be arranged in each corrugated pipe of N1, N2, and N3, and at least 17 steel strands can be arranged in each corrugated pipe of N4 and N5. It can be seen that the steel strand is bent and extended in the vertical direction. Figure 4 It can be seen that the N1, N2 and N3 prestressed steel bars have no horizontal bending, and both ends of them are arranged and anchored on the center line of the web of the middle beam; the N4 and N5 prestressed steel bars have horizontal bending, N4 is horizontally bent to the left side of the T-beam, and N5 is horizontally bent to the right side of the T-beam. They are arranged on both sides of the horseshoe shape of the center line of the T-beam in the mid-span, and their ends are anchored on the center line of the web at the other end of the middle beam.

[0044] Step S2, a tension simulation model is established according to the prestressed steel bars arranged in the middle beam (Midas civil software can be used), and a three-dimensional beam unit is used to simulate the T-beam. The model includes a plurality of fixedly connected T-beams divided into units and nodes, such as Figure 5As shown in the figure, a total of 110 units and 220 nodes are established for the whole beam. Prestressed steel bars are added to the three-dimensional beam unit according to the actual position of the prestressed steel bars. To simulate the boundary conditions, the two ends of the T-beam adopt the simply supported beam bridge constraint conditions. One end constrains Dx (along the length of the bridge), Dy (along the width of the bridge), Dz (vertical), Rx and Rz, and releases Ry; the other end constrains Dy, Dz, Rx and Rz, and releases Ry and Dx. To simulate the supporting effect of the precast platform on the beam body, the pressure of the T-beam on the precast platform is simulated by a compressive elastic connection (the elastic connection of the boundary conditions in the Midas civil software can be used to simulate it). Considering the influence of the self-weight of the structure, the prestressed effect, and the shrinkage and creep of concrete, the friction coefficient of the prestressed steel bar is taken as μ = 0.25, the channel deviation coefficient k = 0.0015, and the shrinkage and creep effect of concrete is calculated according to 15 "Bridge Code".

[0045] Step S3, formulate multiple tensioning schemes, each of which divides the tensioning construction into multiple stages in a certain tensioning sequence, wherein at least one prestressed steel bar is tensioned in each stage, and the tensioning force is set as a percentage of the design tensioning force of the prestressed steel bar. Each tensioning scheme is simulated and calculated in a tensioning simulation model to determine the optimal tensioning scheme.

[0046] For example, in Table 1, Scheme 1 divides the tensioning stage into 10 stages. In the first stage, N1, N2, N3, N4, and N5 are all initially tensioned to 10% of the designed tensioning force. In the second stage, only N4 is tensioned to 30% of the designed tensioning force. In the third stage, only N5 is tensioned to 60%. In the fourth stage, N4 is tensioned to 70%. In the fifth stage, N5 is tensioned to 100%. In the sixth stage, N4 is tensioned to 100%. In the seventh stage, N3 is tensioned to 60%, N2 is tensioned to 60%, and N1 is tensioned to 60%. In the eighth stage, N3 is tensioned to 100%. In the ninth stage, N2 is tensioned to 100%. In the tenth stage, N1 is tensioned to 100%.

[0047] Multiple schemes can be set up and simulated using the tension simulation model to obtain bridge stress and deformation data.

[0048] Table 1

[0049]

[0050]

[0051] Among them, tensioning scheme 1: in the final tensioning stage, N4 and N5 are tensioned alternately first, and then N1, N2, and N3 are tensioned alternately.

[0052] Tensioning scheme 2: In the final tensioning stage, first tension N1, N2, and N3 alternately, and then tension N2 and N5 alternately.

[0053] Tensioning scheme three: In the final tensioning stage, first tension N2, N3, and N4 alternately, and then tension N1 and N5 alternately.

[0054] The tension simulation model selects the optimal solution based on the minimum weighted sum of the absolute value of the increase in the camber of each adjacent tension stage of the key control section, the absolute value of the increase in the support reaction force of each adjacent tension stage, and the absolute value of the increase in the stress of each adjacent tension stage. Specifically, the absolute value of the increase in the camber, the absolute value of the increase in the support reaction force, and the absolute value of the increase in stress between the first stage and the second stage are obtained, the absolute value of the increase in the camber, the absolute value of the increase in the support reaction force, and the absolute value of the increase in stress between the second stage and the third stage are obtained, and so on, the absolute value of the increase in the camber, the absolute value of the increase in the support reaction force, and the absolute value of the increase in stress between the ninth stage and the tenth stage are obtained, all the absolute values ​​of the increase in the camber are summed, all the absolute values ​​of the increase in the support reaction force are summed, and all the absolute values ​​of the increase in the stress are summed, and then the three summation results are weighted summed using weights. The sum of the absolute values ​​of the increase in camber, the sum of the absolute values ​​of the increase in support reaction, and the sum of the absolute values ​​of the increase in stress can be weighted and summed according to the weights of 1:0.7:1.

[0055] Step S4, tensioning the prestressed steel bars according to the optimal tensioning scheme.

[0056] The following is a specific example to illustrate the calculation and analysis of the tension simulation model.

[0057] The bridge used includes 6 T-beams, with a beam length of 55m, a beam height of 2.8m, a middle beam top plate width of 1.5m, and an inner side beam top plate width of 1.84m. The upper structure uses a prefabricated platform to support the T-beam, and the lower structure uses pile-column piers and cast-in-place pile foundations. The piers and prefabricated platforms are perpendicular to the bridge axis.

[0058] The stress and lateral deformation of the T-beam during the entire tensioning process are analyzed. From the bundle arrangement of the T-beam, it can be seen that the N1, N2 and N3 prestressed steel bars are arranged on the center line of the web of the T-beam. In theoretical calculation, no lateral bending will be caused during the tensioning process. The N4 and N5 prestressed steel bars are arranged on both sides of the center line of the web, and the step-by-step tensioning method is adopted. Especially in the final tensioning process, due to the asymmetric tensioning, the tensioning stress difference is relatively large, which will inevitably cause the beam body to produce a transverse bending moment and lateral deformation trend. The mid-span and beam ends are selected as the key control sections, and the beam end support reaction, mid-span anti-arch value and mid-span stress are used as indicators to compare and analyze the influence of the structural symmetry of the middle beam and side beam on the mechanical properties of the T-beam.

[0059] First, analyze the influence of structural symmetry on the mechanical properties of the T-beam prestressed steel bar effect:

[0060] Figure 6-1The comparative analysis diagram of the reaction force of the beam end support under the tensioning sequence of the prestressed steel bars of two sections; Figure 6-2 The following is a comparative analysis of the effect of the tensioning sequence of the two sections of prestressed steel bars on the mid-span camber. Figure 6-1 , 6-2 It can be seen that before the prestressed tendons are tensioned, the deadweight of the T-beam is shared by the precast platform and the beam end support. As the prestressed tendons are tensioned, the beam body tends to arch upward, and the beam end support reaction gradually increases. In tensioning stage 6, when N4 is tensioned to 100%, the beam body is completely arched and separated from the precast platform, and the beam end support bears the deadweight of the beam body. Considering the difference in the shape of the side beam and the middle beam, the overall change law of the support reaction force and the degree of camber is similar. After the beam body is completely arched, the difference in the final support reaction force of the control section under the two working conditions of the side beam and the middle beam is small, and the maximum value differs by 5.55%. The degree of camber of the control section under the two working conditions is quite different. With the tensioning of the prestressed tendons, except for the difference of 79.97% in tensioning stage 6, the difference in the remaining construction stages is between 11% and 16%, and the maximum value differs by 15.67%.

[0061] Read the stress values ​​of key control sections, such as Figure 7 As shown in the figure, the top edge position 1 and position 2 of the top plate and the bottom edge position 3 and position 4 of the bottom plate are selected as the research objects. Figures 8-1 to 8-4 It can be seen that, considering the difference in the shape symmetry of the side beams and the middle beams, at the stress control points 1 and 2 of the mid-span control section, the side beams are smaller than the middle beams after the tensioning stage 4, and the maximum stress values ​​at position 1 differ by 43.31%, and the maximum stress values ​​at position 2 differ by 31.94%. At the stress control points 3 and 4 of the mid-span control section, the overall stress pattern shows that the side beams are smaller than the middle beams in the early stage, and the middle beams are smaller than the side beams in the later stage, and the maximum stress values ​​at position 3 differ by 37.97%, and the maximum stress values ​​at position 4 differ by 26.44%.

[0062] Then the influence of the tensioning sequence of prestressed tendons on the mechanics of the T-beam is analyzed:

[0063] Due to the difference in the symmetrical shapes of the middle beam and the side beam, two working conditions of the middle beam and the side beam are considered. The top edge position 1 and position 2 of the key control section and the bottom edge position 3 and position 4 of the bottom plate are taken as the research objects to analyze the influence of the tensioning sequence of the prestressed steel bars on the mechanical properties of the control points. The calculation results of each point are as follows: Figure 9-1 , 9-2 The stresses at each tensioning stage under the two working conditions of the middle beam and the side beam are shown in Table 2.

[0064] Depend on Figure 9-1 , 9-2It can be seen that because N1, N2 and N3 are arranged on the center line of the web, there is no flat bending, and theoretically no transverse bending moment will be generated. However, the N4 and N5 prestressed steel bars are arranged outside the center line of the web. During the prestressing process, the pressure applied to the main beam section by the tensioning is transversely asymmetric, and the beam body will inevitably produce a transverse bending moment, making the stress distribution on the left and right sides of the section asymmetric, and there is a certain stress difference. During the initial tensioning process, only 10% of the tension is controlled by the tensioning, and the bending effect is small. In the final tensioning stage, during the alternating tensioning of N4 and N5, the tensioning force reaches 30%, which is relatively large, and the transverse bending moment is relatively large. In the process of analyzing the influence of the prestressed steel bar tensioning sequence on the transverse bending moment of the middle beam, the stress state of the main beam is analyzed in two stages: N4 tensioning to 30% and N5 tensioning to 60%. In these two stages, the reserve compressive stress in the beam is relatively small, which is most likely to have an adverse internal force effect on the beam. In the subsequent tensioning process, as the reserve compressive stress of the beam increases, the stress difference of the prestressed steel bars in the N4 and N5 tensioning processes does not increase significantly, and the adverse stress state of the structure will be weakened accordingly. Finally, the cross-sectional stress state of the beam is analyzed after all the prestressing is completed.

[0065] Table 2

[0066]

[0067] Note: Compression is negative and tension is positive.

[0068] Table 2 lists the stress values ​​at the key cross-sections of the beam body during the main construction stages of Scheme 1. It can be seen from Table 2 that after the initial prestressing is completed, the stresses at stress points 1 and 2 on the same cross-section of the beam body are basically the same, and the stresses at stress points 3 and 4 are the same. Figure 9-1 , 9-2 From the cross-sectional stress distribution diagram, the beam is in a state of full-section compression, and the stresses on the left and right sides of the cross-section are in a symmetrical distribution state, indicating that after the initial tensioning is completed, the lateral effect of the beam caused by the prestressing can be ignored, and the unbalanced effects of N4 and N5 offset each other. However, at this time, the compressive stress reserve in the beam is relatively small, with the maximum value of the side beam being 0.49MPa and the maximum value of the middle beam being 0.72MPa.

[0069] After N4 completed 30% of the prestressing, the stress on the left side of the upper edge of the mid-span section of the side beam (position point 1) was a compressive stress of 0.3Mpa, and the stress on the right side of the upper edge (position point 2) was -0.35Mpa, with a stress difference of 0.65MPa on the left and right sides; the stress on the left side of the upper edge of the mid-span section of the middle beam (position point 1) was a compressive stress of 0.52Mpa, and the stress on the right side of the upper edge (position point 2) was -0.2Mpa, with a stress difference of 0.72MPa on the left and right sides, indicating that this unbalanced tensioning has an adverse effect on the stress in the upper left corner of the section. The stress on the left side of the lower edge of the side beam (position point 3) is 0.34MPa, and the stress on the right side of the lower edge (position point 4) is 0.34MPa, and the stress on the left and right sides is the same; the stress on the left side of the lower edge of the side beam (position point 3) is -0.28MPa, and the stress on the right side of the lower edge (position point 4) is -0.06MPa, and the stress difference between the left and right sides is 0.34. The stress change on the left side of the lower edge before and after tensioning is not obvious, indicating that the superposition effect of the bending moment and axial force generated by N4 has little effect on the stress in the lower left corner of the section. During the tensioning stages 3 to 6, the entire cross-section of the beam is in a compressive stress state, but the calculation results also show that N4 must be tensioned in stages, and the stress difference between N4 and N5 needs to be controlled, otherwise it is easy to generate tensile stress in the beam body, affecting the structural safety performance.

[0070] After 60% of the N5 prestressed steel bars were tensioned, the stress on the left side of the upper edge of the side beam at the mid-span section was -1.7 MPa, the stress on the right side of the upper edge was -0.87 MPa, and the stress difference between the left and right sides was 2.57 MPa; the stress on the left side of the upper edge of the side beam at the mid-span section was -1.63 MPa, the stress on the right side of the upper edge was -0.7 MPa, and the stress difference between the left and right sides was 1.56 MPa, indicating that this unbalanced tensioning has an adverse effect on the stress in the upper right corner of the section. The stress on the left side of the lower edge of the side beam was -1.21 MPa, the stress on the right side of the lower edge was -1.46 MPa, and the stress difference between the left and right sides was 0.25 MPa; the stress on the left side of the lower edge of the middle beam was -1.26 MPa, the stress on the right side of the lower edge was -1.54 MPa, and the stress difference between the left and right sides was 0.28 MPa. During the tensioning process, the entire cross-section of the beam was in a compressive stress state, which also shows the necessity of graded and alternating tensioning of N4 and N5 to ensure the structural safety during the tensioning process.

[0071] As can be seen from Table 2, in the two construction stages after N4 completed 70% of the prestressing and N5 completed 100% of the prestressing, the compressive stress stored in the beam body kept changing, and the stress on the left and right sides of the section was different, which also showed that the beam body was subjected to uneven transverse compression in these two stages. This was caused by the stress difference between the N4 and N5 prestressed steel bars. At the stage when N4 completed 100%, the left and right sides of the beam body were evenly compressed, indicating that the lateral effect of the T-beam was basically offset by the joint action of N4 and N5.

[0072] Thereafter, during the tensioning of N1, N2 and N3, since these three prestressed steel bars are arranged on the center axis of the web, they will not cause lateral bending effect of the T-beam. This process will not be analyzed in detail. After the prestressing is completed, the stress at position 1 of the top edge of the mid-span section of the side beam is -2.91MPa, position 2 is 3.05MPa, the stress at position 3 of the bottom edge is -19.48MPa, and the stress at position 4 is -19.37MPa. There is a certain difference in stress between the left and right sides of the section. The stress at the top edge of the mid-span section of the middle beam is -2.33MPa, and the stress at the bottom edge is -21.71MPa. The stress on the left and right sides of the section is the same, which also shows that the beam body is basically not subject to lateral effect at this time. Figure 9-1 , 9-2 It can be seen that the stress distribution states on the left and right sides of the beam section are basically the same.

[0073] Analysis of the influence of different prestressing schemes on the mechanical properties of T-beams

[0074] Depend on Figure 10-1 It can be seen that the end support reaction forces of the beams in the final tensioning stage under the three different tensioning sequences are relatively small. Compared with the design tensioning scheme, Scheme 2 has a maximum difference of 44.87% in tensioning stage 6 and 1.41% in the final tensioning stage. Scheme 3 has a maximum difference of 14.62% in tensioning stage 3 and 2.84% in the final tensioning stage. The support reaction force curves of Schemes 1 and 3 are relatively close, while the support reaction force curves of Scheme 2 fluctuate greatly compared with Schemes 1 and 3, and a sudden change occurs in tensioning stage 5.

[0075] Depend on Figure 10-2 It can be seen that the mid-span camber of the side beam in the final tensioning stage under the three different tensioning sequences is quite different. After the beam is fully arched, compared with the design tensioning scheme, the maximum difference of scheme 2 in tensioning stage 7 is 44.87%, and the final tensioning stage is 36.04%. The maximum difference of scheme 3 in tensioning stage 3 is 25.27%, and the final tensioning stage is 9.39%.

[0076] Depend on Figures 10-3 to 10-6 It can be seen that under the three different tensioning sequences, the mid-span stress of the side beam in the final tensioning stage is under compression except for the initial tensioning stage, and the overall rules are similar.

[0077] Compared with the design tensioning scheme, the stress difference of tensioning scheme 2 is larger at position 2 of the mid-span top plate, that is, at the end of the long arm of the top plate. During the tensioning process, the maximum difference of 44.75% occurs when the prestressed steel bar N4 is tensioned to 100%. After all the tensioning is completed, the difference is 34.36%. Due to the symmetry of the bottom plate structure, the difference between position 3 and position 4 is similar. When N5 is tensioned to 100%, there is a maximum difference of 91.67%, and the final tensioning stage is 27.84%.

[0078] Compared with the design tensioning scheme, tensioning scheme 3 has a greater stress difference at the long arm end of the mid-span top plate. During the tensioning process, the maximum difference of 78.01% occurred when the prestressed steel bar N5 was tensioned to 100%, and the difference was 16.72% after all tensioning was completed. The bottom plate stress had a maximum difference of 189.47% when N5 was tensioned to 60%, and 7.7% in the final tensioning stage.

[0079] Depend on Figure 11-1 It can be seen that the end support reaction forces of the beams in the final tensioning stage of the middle beam under the three different tensioning sequences are slightly different. Compared with the design tensioning scheme, the maximum difference of scheme 2 is 49.14% in tensioning stage 6 and 1.09% in the final tensioning stage. The maximum difference of scheme 3 is 13.99% in tensioning stage 3 and 6.37% in the final tensioning stage.

[0080] Depend on Figure 11-2 It can be seen that the mid-span camber of the middle beam in the final tensioning stage under the three different tensioning sequences is quite different. After the beam is fully arched, compared with the design tensioning scheme, the maximum difference of scheme 2 at tensioning stage 7 is 66.48%, and the final tensioning stage is 33.01%. The maximum difference of scheme 3 at tensioning stage 3 is 168.07%, and the final tensioning stage is 15.48%.

[0081] Depend on Figures 11-3 to 11-6 It can be seen that compared with the design tensioning scheme, the mid-span top plate stress of tensioning scheme 2 has a maximum difference of 115.71% when N5 is tensioned to 60%, and the difference is 49.36% after all prestressed tendons are tensioned. The bottom plate stress has a maximum difference of 82.1% when N5 is tensioned to 60%, and 50.21% in the tensioning completion stage.

[0082] Compared with the design tensioning scheme, the mid-span top plate stress of tensioning scheme 3 has a maximum difference of 61.35% when N5 is tensioned to 60%, and the difference is 71.96% after all prestressed tendons are tensioned. The bottom plate stress has a maximum difference of 137.98% when N5 is tensioned to 60%, and 10.72% at the tensioning completion stage.

[0083] Different tensioning sequences have a greater impact on the tensioning process of the end support reaction force of the T-beam, but a smaller impact on the final tensioning process. Different tensioning sequences have a greater impact on the tensioning process and final tensioning results of the mid-span camber of the T-beam. Pre-tensioning N1, N2, and N3 will reduce the camber of the T-beam. Different tensioning sequences have a greater impact on the stress of the T-beam tensioning process and the final tensioning stage. From the overall stress change curve, the tensioning sequence has a greater impact on the upper edge of the T-beam, that is, the three prestressed beams N1, N2, and N3 have a greater impact on the stress of the upper edge of the T-beam.

[0084] From a comprehensive comparison, the T-beam structural stress and camber of Scheme 1 are more conducive to structural safety and stability.

[0085] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations shall fall within the protection scope of the claims of the present invention.

Claims

1. A long-span simply supported T-beam tensioning method, characterized in that: The following steps are involved: In a middle beam of a plurality of T-shaped beams arranged along the width direction of the bridge, a plurality of prestressed steel bars are arranged along the length direction of the T-shaped beam, wherein one end of each prestressed steel bar is anchored on the center line of the web at one end of the middle beam, the other end of a portion of the prestressed steel bars is anchored on the center line of the web at the other end of the middle beam, and the other ends of the remaining prestressed steel bars have a horizontal side bend, at least one of the remaining prestressed steel bars is horizontally bent to one side and then anchored on the center line of the web at the other end of the middle beam, and at least one of the remaining prestressed steel bars is horizontally bent to the other side and then anchored on the center line of the web at the other end of the middle beam; A tension simulation model is established according to the prestressed steel bars arranged in the middle beam. The model includes a plurality of fixedly connected T-beams divided into units and nodes. The two ends of the T-beam adopt the constraints of a simply supported beam bridge. One end constrains Dx, Dy, Dz, Rx and Rz, and releases Ry; the other end constrains Dy, Dz, Rx and Rz, and releases Ry and Dx, wherein Dx, Dy, Dz, Rx, Ry and Rz are the degrees of freedom in the x-axis, y-axis and z-axis directions of the Cartesian coordinate system, and the degrees of freedom of rotation around the x-axis, y-axis and z-axis, wherein Dx is the degree of freedom along the length direction of the bridge, Dy is the degree of freedom along the width direction of the bridge, and Dz is the degree of freedom in the vertical direction; Formulate multiple tensioning schemes, each tensioning scheme divides the tensioning construction into multiple stages according to a different tensioning sequence, wherein at least one prestressed steel bar is tensioned in each stage, and the tensioning force is set as a percentage of the design tensioning force of the prestressed steel bar, and each tensioning scheme is simulated and calculated in a tensioning simulation model to determine the optimal tensioning scheme; The prestressed steel bars are tensioned with the optimal tensioning scheme. The tension simulation model selects the optimal solution based on the minimum weighted sum of the absolute value of the increase in the camber of each adjacent tensioning stage of the key control section, the absolute value of the increase in the support reaction force of each adjacent tensioning stage, and the absolute value of the increase in the stress of each adjacent tensioning stage. The critical control section refers to the cross section at the mid-span and the beam end, the stress refers to the stress at the upper edge of the top plate and the lower edge of the bottom plate of the critical control section, and the camber of the T-beam refers to the camber value at the mid-span.

2. The long-span simply supported T-beam tensioning method according to claim 1, characterized in that: The prestressed steel bars are prestressed steel bars inserted in corrugated pipes. From top to bottom, five prestressed steel bars N1, N2, N3, N4 and N5 passing through the corresponding corrugated pipes are anchored on the center line of the web at one end of the middle beam. Both ends of the N1, N2 and N3 prestressed steel bars are anchored on the center line of the web of the middle beam. N4 is horizontally bent to one side of the T-beam and anchored on the center line of the web at the other end of the middle beam. N5 is horizontally bent to the other side of the T-beam and anchored on the center line of the web at the other end of the middle beam.

3. The long-span simply supported T-beam tensioning method according to claim 2, characterized in that: At least 15 steel strands are arranged in each corrugated pipe of N1, N2 and N3, and at least 17 steel strands are arranged in each corrugated pipe of N4 and N5.

4. The long-span simply supported T-beam tensioning method according to claim 1, characterized in that: The prestressed steel bars are low-relaxation high-strength prestressed steel strands.

5. The long-span simply supported T-beam tensioning method according to claim 1, characterized in that: A prefabricated platform is used to support the T-beam, and the lower part of the prefabricated platform is supported by a pile-column type pier.

6. The long-span simply supported T-beam tensioning method according to claim 5, characterized in that: In the tension simulation model, the pressure of the T-beam on the precast platform is simulated by using a compressive elastic connection, and the effects of deadweight, prestressing, and concrete shrinkage and creep are considered.

7. The long-span simply supported T-beam tensioning method according to claim 1, characterized in that: The sum of the absolute values ​​of the increase in camber, the sum of the absolute values ​​of the increase in support reaction, and the sum of the absolute values ​​of the increase in stress are weighted according to the weight of 1:0.7:

1.

8. The long-span simply supported T-beam tensioning method according to claim 2, characterized in that: The optimal tensioning scheme is to perform the tensioning operation according to the tensioning sequence in the following table:

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