Railway multi-tower partial cable-stayed bridge high pile cap design and calculation method
By determining the characteristic parameters and selecting appropriate pile foundation types under the geological conditions of the deep reservoir area, combined with the revised load-bearing capacity and stable calculation model, the systematic design of the high pile bearing platform of the multi-tower cable-stayed bridge of the railway was achieved, and the solution was solved. The problem of large design workload reduces construction costs and improves design efficiency.
Patent Information
- Application Number
- CN202411223777.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-03
- Publication Date
- 2024-12-17
AI Technical Summary
The prior art lacks systematic methods and processes when designing high pile bearings of multi-tower cable-stayed bridges on railways, resulting in large design workloads, large manpower and material consumption, and it is difficult to accurately determine the design plan of the bearing.
By determining the characteristic parameters under geological conditions in deep reservoir areas, the pile foundation discrimination formula and the bridge span-pile diameter relationship formula are used to select the appropriate pile foundation type and diameter, and the single pile bearing capacity and pile group effect calculation formula are corrected, combining high The pile stability calculation model and economic decision coefficient are carried out, and iterative design is carried out to determine the base design plan.
It reduces the workload of high pile bearing design, saves construction costs, ensures the reliability and economicality of bearing design, and improves design efficiency.
Smart Images
Figure CN119150417A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of civil engineering, in particular to a design and calculation method of a high pile cap for a railway multi-tower partial cable-stayed bridge. Background Art
[0002] In recent years, with the rapid development of railways in my country, more and more deep-water reservoir bridges have been put into construction. In the selection of the substructure of deep-water bridges, high-pile cap foundations have been widely used in deep-water reservoir bridges due to their many advantages such as high bearing capacity, large rigidity, small settlement, and strong adaptability. Since the design of the high-pile cap scheme of conventional multi-tower partial cable-stayed bridges is generally based on engineering experience, the subjective experience of engineers has a great influence on the cap design. There is no specific process and method for design, and repeated calculations are required to verify the reliability of the structure, which is labor-intensive and consumes a lot of manpower and material resources. Therefore, it is particularly important to reasonably determine the high-pile cap design scheme based on the external conditions of the bridge. Summary of the invention
[0003] The purpose of the present invention is to provide a design and calculation method for a high pile pedestal of a multi-tower partial cable-stayed bridge on a railway based on the above-mentioned deficiencies in the prior art. The design scheme of the high pile pedestal is determined according to the geological conditions of the deep-water reservoir area, the elevation of the railway line, and the main structural parameters of the multi-tower partial cable-stayed bridge, which can reduce the workload of the high pile pedestal design and guide the design of the high pile pedestal in actual engineering.
[0004] The purpose of the present invention is achieved by the following technical solutions:
[0005] A design method for a high pile cap of a multi-tower partial cable-stayed bridge comprises the following steps:
[0006] Based on the geological conditions of the deep-water reservoir area, the values of multiple characteristic parameters are determined, and the pile foundation discriminant formula ▽=abc is proposed to determine the pile foundation type, and the pile foundation diameter d is proposed.
[0007] The specific steps to determine the pile foundation type are as follows:
[0008] a is the soil coefficient, a=0.5 for sandy soil, a=1 for other cases; b is the bearing layer burial depth coefficient, b=1 when the bearing layer burial depth is less than 60m, b=5 when the burial depth is greater than 60m and less than 80m, and b=10 when the burial depth is greater than 80m; c is the water quality corrosiveness coefficient, c=1 when the corrosiveness is strong, c=0.5 when the corrosiveness is weak. When ▽≤1, prestressed concrete pipe piles are selected; when 1<▽≤2.5, steel pipe piles are selected; when 2.5<▽, bored cast-in-place piles are selected.
[0009] The specific identification of pile foundation is shown in Table 1.
[0010] Table 1 Pile foundation type selection table
[0011]
[0012] According to the bridge span-pile diameter relationship formula d=βL+d0, the pile foundation diameter d is determined.
[0013] In the formula, L is the span of the bridge, β is the empirical coefficient, usually 0.005-0.01, and d0 is the initial pile diameter, usually 1-1.5m.
[0014] Considering the adverse effect of water in the reservoir area on the pile foundation, a revised single pile bearing capacity calculation formula is proposed based on the original single pile capacity calculation formula Substitute water depth, pile foundation type and pile foundation type coefficient into the calculation to determine the corrected single pile bearing capacity N.
[0015] Where N is the characteristic value of the vertical bearing capacity of a single pile, U is the circumference of the pile section, ψ and λ are the coefficients of the pile foundation type, which are taken according to the specifications, and f i , R is the ultimate friction resistance of the soil around the pile and the ultimate bearing capacity of the soil in the bearing layer at the bottom of the pile, l i is the thickness of each soil layer that the pile passes through, A is the bearing area at the bottom of the pile, γ w is the density of water, h w For water depth.
[0016] Based on the design load of the upper part of the bridge structure, according to the pile foundation type and stress characteristics, and considering the pile group effect of the high pile foundation, a revised pile foundation quantity calculation formula is proposed based on the original calculation formula Substitute the cap vertical load F, single pile bearing capacity N and pile group effect correction factor into the calculation to determine the number of pile foundations n.
[0017] Among them, F is the vertical load borne by the foundation, μ is the empirical coefficient considering the moment effect, usually taking a value of 1.1-1.2, and ξ is the correction coefficient for the pile group effect.
[0018] The calculation method of the correction coefficient ξ of the pile group effect is:
[0019] Calculate n1 using the uncorrected pile foundation calculation formula, Considering the difference in bearing capacity between the center pile and the side pile, the correction factor is obtained n1 is the number of pile foundations before correction.
[0020] In view of the stability problem of high piles, a high pile stability calculation model is proposed to calculate the maximum free pile length of the pile foundation. The high pile instability calculation formula is: The maximum free pile length l can be obtained by the pile foundation stability calculation formula 0max .
[0021] Among them, P cr is the critical bearing capacity of pile foundation instability, k is the foundation constraint strength coefficient, is the pile-soil influence coefficient, usually 0.3-0.5, EI is the pile foundation stiffness, l0 is the free pile length, n0 is the number of pile foundations initially determined, l 0max is the maximum free pile length.
[0022] The method for determining the foundation constraint strength coefficient k is:
[0023] Since the foundation constraint is related to the pile foundation depth, and the greater the pile foundation depth, the less likely the pile foundation is to become unstable, the foundation constraint coefficient calculation formula is: h is the buried depth of pile foundation, l is the total length of pile foundation.
[0024] Since the pile length exceeds the maximum free pile length, the structure becomes unstable and damaged, the maximum cap bottom elevation can be obtained, and the cap should be higher than the riverbed surface to obtain the minimum cap bottom elevation. Therefore, the upper and lower limit constraint calculation formula is proposed: H min ≤H≤H max , H min =H0+h,H max = l 0max +H0+h, where H max is the maximum cap elevation, H min is the minimum foundation elevation, and H0 is the elevation of the pile foundation.
[0025] In order to determine the elevation of the pedestal, according to the upper and lower limit constraints of the pedestal design elevation, the calculation formula for the pedestal bottom surface design elevation is proposed: H b =H min +η(H max -H min ), substituting the constraint condition of the bottom elevation of the cap and the maximum free pile length, we can get The design elevation of the bottom surface of the pedestal can be obtained through the calculation formula.
[0026] Among them, H b is the bottom elevation of the pedestal, η is the economic decision coefficient, η∈(0,1).
[0027] The method for determining the economic decision coefficient η is:
[0028] As the elevation of the cap decreases, the amount of work in the water increases, which will significantly increase the cost of the project. At the same time, it can improve the stress of the pile foundation. The quadratic curve f(H) = AH 2 +BH+C is used for fitting. The engineering cost fluctuates little in the slow section of the curve. The slope is -1, which is the limit value. The economic decision coefficient
[0029] Among them, f(H) is the function of the change of project cost with the elevation of the foundation, and A, B, and C are the coefficients of the curve equation fitted according to the project budget data.
[0030] Based on the proposed cap design elevation and the number of pile foundations, a cap design scheme is proposed, and the diameter-elevation iteration method is used to obtain a reasonable cap design scheme.
[0031] The diameter-elevation iteration method verification includes the following steps:
[0032] The cap design plan is verified for shear failure, shear failure, bending and deformation. If it fails, the pile foundation diameter or the cap elevation is re-drafted according to the verification result to obtain a new cap design plan; if it passes, the final cap design plan is obtained.
[0033] The advantages of the present invention are:
[0034] 1) The present invention can determine the number of pile foundations by determining the horizontal bearing capacity of a corrected single pile, thereby saving construction costs while meeting the requirements for the bearing capacity of the pile group;
[0035] 2) The present invention determines the free pile length through the pile foundation instability calculation model, thereby determining the design elevation constraint conditions of the high pile cap, taking economic indicators into consideration, and obtaining a reasonable high pile cap design elevation, which can reduce the design workload. BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Figure 1 It is a schematic diagram of the process of the present invention;
[0037] Figure 2 It is an intuitive illustration of each parameter of the present invention;
[0038] Figure 3 It is a schematic diagram of the method for determining the economic decision coefficient in the present invention;
[0039] Figure 4 It is a schematic diagram of a method for determining the design dimensions of a cap in the present invention;
[0040] Figure 5 It is a schematic diagram of the iterative method verification process in the present invention. DETAILED DESCRIPTION
[0041] The features of the present invention and other related features are further described in detail below through embodiments in conjunction with the accompanying drawings to facilitate understanding by those skilled in the art:
[0042] Example: Figures 1 to 5 As shown, this embodiment uses a railway bridge as an example to perform calculations to embody the design and calculation method of the present invention. The situation of the railway bridge is as follows:
[0043] A railway bridge is a double-track railway with a design speed of 350km / h and a track spacing of 5.0m. It adopts CRTS-Ⅰ type double-block ballastless track and a three-tower partial cable-stayed bridge with a span of 228m. The design load is ZK-live load. The bridge is located in the reservoir area. The water level in the reservoir area is stable all year round and the measured water level is 110.496m.
[0044] The soil layer is weakly weathered sandstone or weakly weathered quartz sandstone, the suitable bearing layer is buried at a depth of 10m and at an elevation of 72.5m. ⑥23 layers of sandstone: weakly weathered, R c =22.66MPa, σ0=600kPa, V-grade secondary rock. ⑥33-layer quartz sandstone: weakly weathered, R c =23.1MPa, σ0=800kPa, Grade V secondary hard rock.
[0045] Obtain the geological conditions of the deep-water reservoir area and the main structural parameters of the multi-tower cable-stayed bridge. If the soil layer is sandstone, then the soil coefficient a = 0.5, the appropriate bearing layer burial depth h = 10m < 60m, then the bearing layer burial depth coefficient b = 1, for the reservoir bridge, the water quality is weakly corrosive, then the water quality corrosiveness coefficient c = 0.5, the pile foundation buried layer elevation H0 = 72.5m, the reservoir water depth h w =27.996m, load transmitted from superstructure F=639158.4kN, bridge span L=228m.
[0046] Substitute the soil coefficient a, bearing layer depth coefficient b, and water corrosiveness coefficient c into the pile foundation discriminant formula ▽=a·b·c for calculation. After calculation, it can be obtained that ▽=0.5×1×0.5=0.25<1. According to the results, prestressed concrete pipe piles are selected.
[0047] According to the selected pile foundation type, the pile foundation diameter d is preliminarily determined according to the bridge span-pile diameter relationship d=βL+d0. By consulting some relevant information on cable-stayed bridges, it is known that a bridge with a span of 100m usually uses a 2m diameter pile foundation, and a bridge with a span of 350m uses a 3.5m diameter pile foundation. Taking β=0.006, d0=1.4, and substituting the bridge span L=228m into the calculation, d=0.006×228+1.4=2.768, the pile foundation diameter d=3m can be preliminarily determined.
[0048] According to the bearing layer conditions, pile foundation type and the initially proposed pile foundation diameter, and considering the strengthening effect of water in the reservoir area on the pile foundation, the single pile bearing capacity calculation formula is revised. Calculate the bearing capacity of a single pile foundation.
[0049] Perimeter U = πd = 3 × 3.14 = 9.42, pile bottom support area According to the pile foundation type, the values of ψ and λ are determined according to the "Code for Design of Foundations and Subgrades for Railway Bridges and Culverts". For prestressed concrete pipe piles, ψ=0, λ=0.3. Substituting them into the corrected single pile bearing capacity calculation formula, we can get
[0050]
[0051] According to the calculation formula of the number of pile foundations before correction Considering the magnitude of the moment, taking μ = 1.15, substituting the single pile bearing capacity N = 46913.1 kN, the number of pile foundations before correction is calculated. Substitute into the formula again Calculate and obtain the correction coefficient of pile group effect Finally, the revised pile foundation quantity calculation formula calculate, Round up to the number of pile foundations n0=18.
[0052] Conduct field tests on the horizontal resistance of the soil layer to determine the pile-soil influence coefficient If the horizontal resistance is large, the value is large, the maximum value is 0.5, the minimum value is 0.3,
[0053] Due to the foundation constraint strength coefficient The total length of the pile foundation l is the solution value, so it cannot be solved directly, because the total length of the pile foundation is equal to the sum of the pile foundation burial depth and the free pile length, that is, l = h + l0, and when the total length of the pile foundation takes the maximum value, the critical load is smaller and safer, so l = h + l can be taken 0max Perform calculations.
[0054] According to the calculation formula of high pile instability, Derived the maximum free pile length calculation formula The foundation constraint strength coefficient Substituting into Let l 0max =x, that is, x 3 -202.5x-19968.4=0, solving the cubic equation can give the maximum free pile length l 0max =29.61m, and the maximum cap elevation H is calculated at the same time max =H0+h+l 0max =72.5+10+29.61=112.11m.
[0055] like Figure 3 As shown in the figure, the corresponding data of the foundation design elevation and the engineering cost are plotted into a graph, and a quadratic function is used for fitting to determine the function f(H) = AH 2+BH+C coefficients A = 2.25, B = -485.7, C = 26898, draw the function tangent when the slope is -1, and thus determine the curve transition section. The calculation formula The economic decision coefficient is calculated, in (η min ,1) that is, within the range of (0.961, 1), the value of the curve transition section is taken as η=0.98.
[0056] The maximum free pile length l 0max , Substitute the economic decision coefficient η into the calculation formula for the bottom elevation of the cap The design elevation H of the bottom surface of the pedestal is calculated b =111.5m.
[0057] like Figure 4 As shown in the figure, the design size of the cap is determined according to the calculated number of pile foundations n0 and the pile foundation spacing s required by the specification. The center distance of the pile tip is not less than 2 times the design pile diameter, the distance from the pile to the outer edge of the cap is not less than 0.3d, and not less than 0.5m. In this example, the center distance of the pile is not less than 6m, and the distance to the outer edge of the cap is not less than 0.9m. Taking s1=s3=2m, s2=6m, it can be obtained that the cap length is u=36m, the cap width is v=16m, and the cap thickness is taken according to the requirements of the specification, not less than 1.5m. Taking the cap thickness as 6.5m, the design elevation of the cap top surface is 118m, thus obtaining the cap design scheme.
[0058] like Figure 5 As shown in the figure, the proposed cap design scheme is checked for settlement, pile foundation bearing capacity, bending and deformation. If it fails, the pile foundation diameter d is re-drafted or the economic decision coefficient is re-selected to determine the new cap design elevation according to the verification result, and calculations are performed to obtain a new cap design scheme; if it passes, the final cap design scheme is obtained.
[0059] Although the above embodiments have described in detail the concepts and embodiments of the present invention with reference to the accompanying drawings, ordinary technicians in this field can recognize that various improvements and changes can still be made to the present invention without departing from the scope of the claims, so they are not described one by one here.
Claims
1. A design and calculation method for a high pile cap of a railway multi-tower partial cable-stayed bridge, characterized in that: The steps include: According to the geological conditions, the pile foundation type is determined according to the pile foundation discriminant formula, and the pile foundation diameter is formulated according to the bridge span-pile diameter relationship formula; Calculate the pile foundation bearing capacity according to the revised pile foundation bearing capacity calculation formula based on the pile diameter and geological conditions, and substitute the initially proposed diameter into the revised pile foundation quantity calculation formula to solve for the number of pile foundations; substitute the pile foundation diameter and the number of pile foundations into the high pile stability calculation formula to obtain the maximum free pile length, thereby obtaining the upper and lower limit constraints of the cap bottom elevation, and determine the cap design elevation according to the cap bottom design elevation calculation formula and the economic decision coefficient; The foundation design plan is obtained based on the number of pile foundations and the foundation design elevation.
2. The design and calculation method of the high pile cap of a railway multi-tower partial cable-stayed bridge according to claim 1 is characterized by: The cap design scheme is verified for shear failure, shear failure, bending and deformation. If it fails, the pile foundation diameter or the cap elevation is re-drafted according to the verification result to obtain a new cap design scheme; if it passes, the final cap design scheme is obtained.
3. The design and calculation method of the high pile cap of a railway multi-tower partial cable-stayed bridge according to claim 1 is characterized by: The pile foundation discriminant is: ▽=abc; Wherein, a is the soil coefficient, a=0.5 for sandy soil, and a=1 for other cases; b is the bearing layer burial depth coefficient, when the bearing layer burial depth is less than 60m, b=1, when the burial depth is greater than 60m and less than 80m, b=5, when the burial depth is greater than 80m, b=10; c is the water quality corrosiveness coefficient, when the corrosiveness is strong, c=1, when the corrosiveness is weak, c＝0.5； When ▽≤1, prestressed concrete pipe piles should be selected; when 1<▽≤2.5, steel pipe piles should be selected; when 2.5<▽, bored cast-in-place piles should be selected.
4. The design and calculation method of the high pile cap of a railway multi-tower partial cable-stayed bridge according to claim 1 is characterized by: The calculation formula of the bridge span-pile diameter relationship is: d = βL + d0; Where, d is the diameter of the pile foundation; L is the span of the bridge; β is the empirical coefficient, usually 0.005-0.01; d0 is the initial pile diameter, usually 1-1.5m.
5. The design and calculation method of the high pile cap for a railway multi-tower partial cable-stayed bridge according to claim 1 is characterized by: Considering the adverse effect of water in the reservoir area on the pile foundation, a revised single pile bearing capacity calculation formula is proposed based on the original single pile capacity calculation formula Substitute the water depth, pile foundation type and pile foundation type coefficient into the calculation to determine the corrected single pile bearing capacity N. cr is the critical bearing capacity of pile foundation instability, k is the foundation constraint strength coefficient, is the pile-soil influence coefficient, usually 0.3-0.5, EI is the pile foundation stiffness, l0 is the free pile length, n0 is the number of pile foundations initially determined, l 0max is the maximum free pile length.
6. The design and calculation method for high pile cap of railway multi-tower partial cable-stayed bridge according to claim 1 is characterized by: Based on the design load of the upper part of the bridge structure, according to the pile foundation type and stress characteristics, and considering the pile group effect of the high pile foundation, a revised pile foundation quantity calculation formula is proposed based on the original calculation formula Substitute the cap vertical load F, single pile bearing capacity N and pile group effect correction factor into the calculation to determine the number of pile foundations n; Where F is the vertical load borne by the cap, μ is the empirical coefficient considering the moment effect, which is usually taken as 1.1-1.2, and ξ is the correction coefficient for the pile group effect.
7. The design and calculation method of the high pile cap for a railway multi-tower partial cable-stayed bridge according to claim 1 is characterized by: In view of the stability problem of high piles, a high pile stability calculation model is proposed to calculate the maximum free pile length of the pile foundation. The high pile instability calculation formula is: The maximum free pile length l can be obtained by the pile foundation stability calculation formula 0max ; Where P cr is the critical bearing capacity of pile foundation instability, k is the foundation constraint strength coefficient, is the pile-soil influence coefficient, usually 0.3-0.5, EI is the pile foundation stiffness, l0 is the free pile length, n0 is the number of pile foundations initially determined, l 0max is the maximum free pile length.
8. The design and calculation method for high pile cap of railway multi-tower partial cable-stayed bridge according to claim 1 is characterized by: The method for determining the upper and lower limit constraints of the bottom elevation of the cap is: Since the pile length exceeds the maximum free pile length, the structure becomes unstable and damaged, the maximum cap bottom elevation can be obtained, and the cap should be higher than the riverbed surface to obtain the minimum cap bottom elevation. Therefore, the upper and lower limit constraint calculation formula is proposed: H min ≤H≤H max , H min =H0+h,H max = l 0max +H0+h, where H max is the maximum cap elevation, H min is the minimum foundation elevation, and H0 is the elevation of the pile foundation.
9. The design and calculation method of the high pile cap of a railway multi-tower partial cable-stayed bridge according to claim 1 is characterized by: The calculation formula for the design elevation of the bottom surface of the pedestal is: H b =H min +η(H max -H min ); Substituting the constraint condition of the bottom elevation of the cap and the maximum free pile length, we can get The design elevation of the bottom surface of the pedestal can be obtained through the calculation formula.
10. The design and calculation method of the high pile cap of a railway multi-tower partial cable-stayed bridge according to claim 1 is characterized by: The economic decision coefficient is