Method for increasing the compressive stress reserve of the tower legs on the side spans of a spatial concrete main tower

Abstract

The application discloses a method for increasing the compression stress reserve of a tower limb on the side of a spatial concrete main tower, which comprises the following steps: when the main tower is constructed to the upper tower column, the bottom section of the upper tower column of the main tower is inclined and positioned, the inclination angle is alpha 0, the subsequent construction direction is pre-biased to the side of the midspan, the subsequent sections of the upper tower column are sequentially connected and constructed according to the inclined angle and direction, until the construction of the main tower is completed, at this time, the inclination value of the upper tower column to the side of the midspan is L0, alpha 0 and L0 are in a positive proportional relationship; before the bridge is completed, the upper tower column of the main tower is passively displaced to the side of the midspan by actively tensioning the cable on the side of the midspan, and the displacement value is L3. According to the application, the main tower is passively pre-biased to the side of the midspan from the original deflection to the side of the midspan, the unbalanced cable force of the cable on the side of the midspan is greater than that of the cable on the side of the midspan, the compression stress reserve of the bottom of the lower tower column on the side of the midspan is increased, the compression stress reserve is reduced when the vehicle live load is on the midspan, and the waste and cracking risk caused by the strengthening of the structure are reduced.

Description

Technical Field

[0001] This invention relates to a method for increasing the compressive stress reserve of the side span tower limbs of a spatial concrete main tower, belonging to the technical field of main tower stress adjustment in bridge engineering. Background Technology

[0002] The main tower of a cable-stayed bridge primarily bears the weight of the dead load from the main girder, stay cables, pavement, and live loads from vehicles. Common main tower structures are made of concrete. Concrete has a significant material property where compressive strength is far greater than tensile strength. Therefore, tensile stress in concrete structures generally needs to be strictly controlled to avoid exceeding the limits specified in codes and designs, which could lead to tensile cracking. The following symbols represent the forces acting on the stay cables: "Fside-Vertical": representing the vertical component of the force on the stay cables on the side span; "Fside-Horizontal": representing the horizontal component of the force on the stay cables on the side span; "Fcenter-Vertical": representing the vertical component of the force on the stay cables on the side span; "Fcenter-Horizontal": representing the horizontal component of the force on the stay cables on the side span. The basic principle of cable-stayed bridge design is "straight tower and level beam." "Straight tower" means that, under the theoretical design conditions (before completion and opening to traffic), the upper tower column of the main tower should be vertical, with no deviation in the plane, i.e., the upper tower column should not be tilted. This avoids additional internal forces caused by the vertical component of the stay cables deviating from the design state in the main tower's limbs. "Level beam" means that, under the theoretical design conditions (before completion and opening to traffic), the overall alignment of the main beam, supported by the vertical forces provided by the stay cables, is consistent with the design requirements, without any deviation. At this point, the horizontal components of the stay cables on both sides of the main tower are equal in magnitude and opposite in direction, i.e., ΔF = "Fside-Level" - "Fcenter-Level" = 0, canceling each other out and keeping the main tower vertical. Therefore, the optimal design state is to achieve both straight tower and level beam simultaneously.

[0003] After the bridge is completed and opened to traffic, the movement and random distribution of live loads such as vehicles will change the force on the main beam compared to when there are no vehicles. This will alter the equilibrium relationship where the horizontal components of the stay cables are equal in magnitude but opposite in direction, i.e., ΔF_horizontal = "F_side - horizontal" - "F_center - horizontal" ≠ 0. The main tower will then tilt towards the side where the horizontal component of the stay cables is larger. Figure 1As shown, when a vehicle drives to the middle span, it causes the middle span steel beam to deflect vertically (deformation towards the ground). At this time, "Fmiddle-level" > "Fside-level", causing the main tower to tilt towards the middle span, reducing the compressive stress reserve at the bottom of the lower tower column on the side span, and even causing tension. When a vehicle drives to the side span, it causes the side span steel beam to deflect vertically (deformation towards the ground). At this time, "Fmiddle-level" < "Fside-level", causing the main tower to tilt towards the side span, reducing the compressive stress reserve at the bottom of the lower tower column on the middle span. However, due to the support of auxiliary pier 5 on the side span side main beam, the vertical deflection of the side span steel beam is reduced. Therefore, under the same vehicle live load, the amount of main tower offset towards the side span is less than the amount of main tower offset towards the middle span when the vehicle is in the middle span. It can also be concluded that the loss of compressive stress reserve in the lower tower column on the middle span side is less than the loss of compressive stress reserve in the lower tower column on the side span side. Therefore, the key construction control condition is the sharp decrease in compressive stress at the bottom of the lower tower column on the side span caused by vehicles driving to the mid-span side, or even the transformation into tension stress, to prevent the concrete from cracking due to tension at this point. The traditional method is to increase the cross-sectional dimensions of the lower tower column during the design phase, thereby increasing the self-weight of the main tower and increasing the compressive stress reserve under the self-weight of the lower tower column, as well as increasing the bending and tensile resistance of the lower tower column.

[0004] Traditional methods have the following shortcomings:

[0005] 1) Increasing the cross-sectional dimensions of the lower tower column can indeed reduce the tensile impact caused by the main tower's misalignment, but it will waste materials and increase the load transferred to the main pier foundation 6 and the underlying stratum, which may lead to adverse situations such as increased foundation settlement.

[0006] 2) In addition, the construction of large-scale concrete is prone to temperature shrinkage cracks caused by the heat of hydration of concrete, which leads to the deterioration of the main tower's performance.

[0007] 3) The stress mode of the structure, especially the difference in the reduction of compressive stress reserve of the lower tower columns on the side span and middle span caused by the distribution of live loads such as vehicle loads, was not analyzed, which made the reinforcement of the structure not very targeted, and often the lower tower columns on both the side span and middle span were reinforced. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method to increase the compressive stress reserve of the side span tower limbs of a spatial concrete main tower. This method involves pre-deflecting the upper tower column of the main tower towards the middle span during the main tower construction period, and then actively creating the condition of "F_side-flat" > "F_middle-flat" before the main tower opens to traffic. This causes the main tower to change from its original deflection towards the middle span to a passive pre-deflection towards the side span (caused by adjusting the cable force of the stay cables). At this time, F_side-vertical > F_middle-vertical, and the main tower shifts towards the side span. The unbalanced cable force of the side span stay cables compared to the middle span stay cables will increase the compressive stress reserve at the bottom of the lower tower column on the side span. This will help to resist the decrease in compressive stress reserve when the vehicle live load is in the middle span, thereby reducing the waste and cracking risk caused by structural reinforcement.

[0009] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0010] This invention provides a method for increasing the compressive stress reserve of the side span of a spatial concrete main tower, comprising:

[0011] When the main tower is constructed up to the upper tower column, the bottom section of the upper tower column is tilted and positioned at an angle of α0, so that its subsequent construction direction is pre-biased towards the middle span. The subsequent sections of the upper tower column are constructed in sequence according to this tilt angle and direction until the main tower is completed. At this time, the tilt of the upper tower column towards the middle span is L0, and α0 and L0 are directly proportional.

[0012] Before the bridge is completed, the cable stays on the side span are actively tensioned to cause the main tower column to undergo passive displacement towards the side span, with a displacement value of L3.

[0013] Furthermore, this also includes: before construction, based on the pre-established finite element simulation model of the bridge, calculating the stress values ​​σ0 before and after the live load on the side span lower tower column before and after loading. If the change Δσ = σ0 - σ1 is positive, it indicates that the main tower is still under compressive stress at this point; if Δσ is negative, it indicates that the main tower is under tensile stress at this point, and measures must be taken to increase the reserve of compressive stress.

[0014] Furthermore, α0 and L0 are obtained by calculation, and the calculation method is as follows:

[0015] A finite element simulation model of the bridge was established, and the offset of the main tower column towards the middle span after the live load was applied in the middle span was calculated to be L1.

[0016] In the finite element simulation model with only the main tower, by setting the offset from the top of the tower to the middle span side, the offset amount is L1, and the stress state σ2-side of the bottom of the lower tower column on the side span side is obtained. If σ2 is in tension at this time, the absolute value of L1 is reduced until σ2 is in compression. The corresponding offset amount is L2. The stress state of the bottom of the lower tower column on the middle span side will increase its compressive stress reserve σ2-middle due to the tilt of the main tower towards the middle span side.

[0017] σ2 is taken as the deviation L2 corresponding to the pressure state as the actual pre-deflection target L0 on site, and the angle α0 that the bottom section needs to tilt is calculated by back-calculating according to the size of the upper tower column.

[0018] Furthermore, the formula for calculating α0 is as follows: Tan(α0)=L2 / H; where H is the height of the upper tower column H.

[0019] Furthermore, the finite element simulation model of the bridge includes a complete bridge model of the main tower, main beam, and stay cables.

[0020] Furthermore, L3 is calculated, and the calculation method is as follows:

[0021] 3-1: First, set the value of L3 to be the same as L2, with the direction tilting towards the side span. In the finite element simulation model of the bridge, the cable force of the stay cable on the side span forces the top of the upper tower column to undergo a displacement towards the side span. The displacement of the tower top is L2. The stress state σ3-side at the bottom of the lower tower column on the side span is obtained, and the stress state σ3-middle at the bottom of the lower tower column on the middle span is also obtained. Since the main tower shifts the force towards the side span, the compressive stress reserve of the lower tower column on the side span will increase, while the compressive stress reserve on the middle span will decrease. If σ3-middle is in tension, adjust the value of L3 until σ3-middle is in compression.

[0022] 3-2: Based on the calculation model in 3-1, apply a vehicle live load to the middle span side and calculate the stress state σ4-side at the bottom of the lower tower column on the side span side under the live load. If Δσ = σ3-side - σ4-side is positive, it means that the bottom of the lower tower column on the side span side is still under compression. If Δσ = σ3-side - σ4-side is negative, it means that the increase in the side span compressive stress reserve corresponding to the L3 pre-deflection is completely offset by the reverse action of the live load. At this time, the bottom of the lower tower column on the side span side is still under tension. Adjustment 3-3 is then performed.

[0023] 3-3: Adjust the side cable force of the side span, increase L3, and repeat the calculation from 3-2 to 3-3 until Δσ = σ3 - side - σ4 - side is a positive value. Take the value of L3 at this time as the final displacement value.

[0024] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0025] This invention provides a method for increasing the compressive stress reserve of the side span tower members of a spatial concrete main tower. First, during the main tower construction, the upper tower column is positioned, and an inclination angle α is set to pre-deflect the upper tower column in the opposite direction of subsequent passive deformation without stress. This increases the range of passive tilting of the main tower caused by later adjustments to the stay cable tension, thereby increasing the compressive stress reserve generated by passive deformation and making the structural stress more rational. This minimizes the increase in the main tower's cross-sectional dimensions, reducing material waste and the risk of temperature cracking. Furthermore, the design of the main tower structure can be optimized by adjusting the requirements of the construction process (using the method described in this invention). Attached Figure Description

[0026] Figure 1 This is a bridge span layout diagram provided in the background art of this invention;

[0027] Figure 2 This is a schematic diagram of the main tower and stay cables provided in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the pre-deflection of the upper tower column provided in an embodiment of the present invention.

[0029] In the diagram: 1. Main beam; 2. Stay cable; 3. Main tower; 4. Side pier; 5. Auxiliary pier; 6. Main pier foundation; 7. Upper tower column; 8. Middle tower column; 9. Main tower longitudinal and transverse beams; 10. Lower tower column. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0031] Example 1

[0032] This embodiment describes a method for increasing the compressive stress reserve of the side span of a spatial concrete main tower, including:

[0033] When the main tower 3 is being constructed up to the upper tower column 7, the bottom section of the upper tower column 7 of the main tower 3 is tilted and positioned at an angle of α0, so that its subsequent construction direction is pre-biased towards the middle span. The subsequent sections of the upper tower column 7 are constructed sequentially according to this tilt angle and direction until the main tower 3 is completed. At this time, the tilt of the upper tower column 7 towards the middle span is L0, and α0 and L0 are directly proportional.

[0034] Before the bridge is completed, the cable stays 2 on the side span are actively tensioned to cause the main tower 3 and the upper tower column 7 to undergo passive displacement towards the side span, with a displacement value of L3.

[0035] like Figure 2 , Figure 3As shown in the figure, the method for increasing the compressive stress reserve of the side span of the main concrete tower provided in this embodiment involves the following steps in its application process:

[0036] Step 1: Establish a finite element simulation model of the bridge and calculate the stress values ​​σ0 (before loading) and σ1 (after loading) of the lower tower column 10 on the side span before and after the live load (vehicle) is applied to the mid-span. If the change Δσ = σ0 - σ1 is positive (stress sign convention is "positive for compression, negative for tension"), it means that the main tower 3 is still under compressive stress, and the compressive stress reserve can be increased to increase the safety factor. If Δσ is negative, it means that the main tower 3 is under tensile stress, and measures must be taken to increase the compressive stress reserve to avoid adverse effects such as tensile cracking.

[0037] Step 2: When constructing the main tower 3 up to the upper tower column 7, tilt and position the bottom section of the upper tower column 7 at an angle of α0, pre-biasing its subsequent construction direction towards the mid-span. Subsequent sections of the upper tower column 7 are then constructed sequentially according to this tilt angle and direction until the main tower 3 is completed. At this point, the tilt of the upper tower column 7 towards the mid-span is L0. α0 and L0 are strictly matched and directly proportional (the proportional relationship is the relative relationship of the dimensions of the upper tower column 7, such as...). Figure 3 (As shown). α0 and L0 are obtained by calculation, and the calculation method is as follows:

[0038] 2-1: Establish a finite element simulation model of the bridge (including the main structure of the main tower 3, main beam 1, cable stay 2, etc.) and calculate the offset of the upper tower column 7 of the main tower 3 towards the middle span after the live load (vehicle) is applied in the middle span.

[0039] 2-2: In the finite element simulation model with only the main tower 3 (without main beam 1 and stay cables 2, only the main tower 3 structure), by setting the offset from the top of the tower to the middle span side, the stress state σ2-side at the bottom of the lower tower column 10 on the side span side is obtained. If σ2 is in tension at this time, the absolute value of L1 is reduced until σ2 is in compression, and the corresponding offset is L2. The stress state at the bottom of the lower tower column 10 on the middle span side increases its compressive stress reserve σ2-middle due to the inclination of the main tower 3 towards the middle span side.

[0040] 2-3: σ2 is the displacement L2 corresponding to the compressed state, which is taken as the actual pre-deflection target L0 on site, and is calculated according to the dimensions of the upper tower column 7 ( Figure 3 (As shown) The angle α0 required to tilt to reach the bottom section is calculated. Tan(α0) = L2 / H; (Height H of the upper tower column 7)

[0041] Step 3: Before the bridge is completed, the stay cables 2 on the side span are actively tensioned to induce a passive displacement of the upper tower column 7 of the main tower 3 towards the side span, with the displacement value being L3. L3 is calculated as follows:

[0042] 3-1: First, temporarily set L3 = L2 (inclined towards the side span). Within the model calculated in step 2-1 above, actively adjust (increase) the cable force of the stay cable 2 on the side span side to force the top of the upper tower 7 to undergo a displacement towards the side span side, with the tower top displacement being L2. This yields the stress state σ3-side at the bottom of the lower tower 10 on the side span side, and simultaneously the stress state σ3-middle at the bottom of the lower tower 10 on the middle span side. Due to the force shift of the main tower 3 towards the side span side, the compressive stress reserve of the lower tower 10 on the side span side will increase, while the compressive stress reserve on the middle span side will decrease, or even become tensile. If σ3-middle is in a tensile state, adjust the value of L3 (decrease) until σ3-middle is in a compressive state.

[0043] 3-2: Based on the calculation model in 3-1, apply a vehicle live load to the middle span side and calculate the stress state σ4-side at the bottom of the lower tower column 10 on the side span side under the live load. If Δσ = σ3-side - σ4-side is positive, it means that the bottom of the lower tower column 10 on the side span side is still under compression. If Δσ = σ3-side - σ4-side is negative, it means that the increase in the side span compressive stress reserve corresponding to the L3 pre-deflection is completely offset by the reverse action of the live load. At this time, the bottom of the lower tower column 10 on the side span side is still under tension, and adjustment 3-3 should be performed.

[0044] 3-3: Adjust the side cable force of the side span, increase L3, and repeat the calculation from 3-2 to 3-3 until Δσ=σ3-side-σ4-side is a positive value.

[0045] 3-4: On-site implementation shall be carried out according to the principle of adjusting the cable tension so that the main tower 3 upper column 7 is passively offset to the side span to meet the requirements of 3-3, L3.

[0046] This embodiment fully utilizes the mechanical characteristic that the imbalance of cable forces on both sides of the main tower 3 (F-side-flat ≠ F-middle-flat) will cause the main tower 3 to passively tilt under stress. Once the main tower 3 passively tilts under stress, the compressive stress reserve of the tilted tower leg will increase. In order to amplify the magnitude L3 of the main tower 3's tilt under stress, the upper tower column 7 is positioned during the construction of the main tower 3. By setting an inclination angle α, the upper tower column 7 of the main tower 3 is pre-deflected without stress in the opposite direction of the later passive deformation. This increases the range of passive tilt of the main tower 3 caused by the adjustment of the cable forces of the cable 2, thereby increasing the compressive stress reserve generated by the passive deformation and making the structural stress more reasonable. This minimizes the increase in the cross-sectional size of the main tower 3, reducing material waste and the risk of temperature cracks. In addition, the design of the main tower 3 structure can be optimized by the requirements of the construction process (the method described in this invention).

[0047] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for increasing the compressive stress reserve of the side span of a spatial concrete main tower, characterized in that, include: When the main tower is constructed up to the upper tower column, the bottom section of the upper tower column is tilted and positioned at an angle of α0, so that its subsequent construction direction is pre-biased towards the middle span. The subsequent sections of the upper tower column are constructed in sequence according to this tilt angle and direction until the main tower is completed. At this time, the tilt of the upper tower column towards the middle span is L0, and α0 and L0 are directly proportional. Before the bridge is completed, the cable stays on the side span are actively tensioned to cause the main tower column to undergo passive displacement towards the side span, with a displacement value of L3. α0 and L0 are obtained by calculation, and the calculation method is as follows: A finite element simulation model of the bridge was established, and the offset of the main tower column towards the middle span after the live load was applied in the middle span was calculated to be L1. In the finite element simulation model with only the main tower, by setting the offset from the top of the tower to the middle span side, the offset amount is L1, and the stress state σ2-side of the bottom of the lower tower column on the side span side is obtained. If σ2 is in tension at this time, the absolute value of L1 is reduced until σ2 is in compression. The corresponding offset amount is L2. The stress state of the bottom of the lower tower column on the middle span side will increase its compressive stress reserve σ2-middle due to the tilt of the main tower towards the middle span side. σ2 is the offset L2 corresponding to the pressure state, which is taken as the actual pre-offset target L0 on site, and the angle α0 that the bottom section needs to tilt is calculated by back-calculating according to the size of the upper tower column. L3 is calculated as follows: 3-1: First, set the value of L3 to be the same as L2, with the direction tilting towards the side span. In the finite element simulation model of the bridge, the cable force of the stay cable on the side span forces the top of the upper tower column to undergo a displacement towards the side span. The displacement of the tower top is L2. The stress state σ3-side at the bottom of the lower tower column on the side span is obtained, and the stress state σ3-middle at the bottom of the lower tower column on the middle span is also obtained. Since the main tower shifts the force towards the side span, the compressive stress reserve of the lower tower column on the side span will increase, while the compressive stress reserve on the middle span will decrease. If σ3-middle is in tension, adjust the value of L3 until σ3-middle is in compression. 3-2: Based on the calculation model in 3-1, apply a vehicle live load to the middle span side and calculate the stress state σ4-side at the bottom of the lower tower column on the side span side under the live load. If Δσ=σ3-side-σ4-side is positive, it means that the bottom of the lower tower column on the side span side is still under compression. If Δσ=σ3-side-σ4-side is negative, it means that the increase in the side span compressive stress reserve corresponding to the L3 pre-deflection is completely offset by the reverse action of the live load. At this time, the bottom of the lower tower column on the side span side is still under tension. Adjustment 3-3 is then performed. 3-3: Adjust the side cable force of the side span, increase L3, and repeat the calculation from 3-2 to 3-3 until Δσ = σ3 - side - σ4 - side is a positive value. Take the value of L3 at this time as the final displacement value.

2. The method for increasing the compressive stress reserve of the side span of the main concrete tower according to claim 1, characterized in that, Also includes: Before construction, based on the pre-established finite element simulation model of the bridge, the stress values ​​σ0 before loading and σ1 after loading of the side span lower tower column under live load were calculated. If the change Δσ = σ0 - σ1 is positive, it means that the main tower is still under compressive stress at this point; if Δσ is negative, it means that the main tower is under tensile stress at this point, and measures must be taken to increase the reserve of compressive stress.

3. The method for increasing the compressive stress reserve of the side span of the main concrete tower according to claim 1, characterized in that, The formula for calculating α0 is as follows: Tan(α0) = L2 / H; where H is the height of the upper tower column.

4. The method for increasing the compressive stress reserve of the side span of the main concrete tower according to claim 1, characterized in that, The finite element simulation model of the bridge includes the main tower, main beam, and cable-stayed bridge model.

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