Method for prestressing tension of box girder cluster

Abstract

The present invention discloses a method for prestressing tensioning of a box girder cluster, including a box girder and a jack, and it comprises the following steps: arranging a plurality of prestressed tendon ducts in the box girder, determining the tensioning rounds according to the ratio of the number of prestressed tendon ducts to the number of jacks; evenly distributing the prestressed tendon ducts according to the tensioning rounds, and arranging the prestressed tendon ducts in sequence according to the tensioning rounds; calculating the compression amount generated by the prestressed tensioning for each round on the box girder concrete, and determining the over-tension amount of the prestress according to the concrete compression amounts of each round to carry out controlled forming. It has the advantages of simple structure, excellent effect, reasonable design, etc.; therefore, it is a product with superior performance in both technology and economy.

Description

Technical Field

[0001] The present invention mainly relates to a method for prestressing tensioning of box girder clusters.

Background Art

[0002] The prestressing tensioning of precast concrete box girders is a routine project. The existing tensioning technology involves two jacks. They are symmetrically arranged left and right and tensioned step by step from the upper row to the lower row. The use of two jacks is mainly because the number of prestresses in conventional box girders is not large (not exceeding 30 strands), and at the same time, the precision requirements for prestressing tensioning of conventional box girders are not high (the precision requirement is only ±5.0%). Therefore, the conventional method can meet the specification requirements.

[0003] However, with only two jacks in operation, the number of jacks is too small, and the jacks need to be continuously installed and transferred, resulting in very low efficiency and low tensioning precision (because the tension of the later batches will compress the beam body, causing the prestress of the previous batches to relax and affecting the tensioning precision of the previous batches). When the number of prestresses in the concrete box girder reaches 90 strands (the number of prestresses in conventional box girders does not exceed 30 strands), and the precision requirement for prestressing tensioning of the box girder is ±1.0% (the precision requirement for conventional prestressing tensioning is ±5.0%), the existing technology is difficult to meet this design requirement.

Summary of the Invention

[0004] To at least solve one of the above existing problems, the method for prestressing tensioning of box girder clusters of the present invention adopts the following technical solutions:

[0005] A method for prestressing tensioning of box girder clusters, including box girders and jacks, and it comprises the following steps:

[0006] (1) Set a number of prestress duct holes in the box girder, and determine the tensioning rounds according to the ratio of the number of prestress duct holes to the number of jacks;

[0007] (2) Evenly distribute the prestress duct holes according to the tensioning rounds, and the prestress duct holes are arranged in sequence according to the tensioning rounds;

[0008] (3) Calculate the compression amount of the box girder concrete generated by each round of prestressing tensioning. The calculation method is: the concrete compression amount generated by this round of tensioning = (the tension of this round of tensioning × the length of the box girder) ÷ (the cross-sectional area of the box girder × the elastic modulus of the concrete);

[0009] (4) Determine the over-tension amount of the prestress according to the concrete compression amounts of each round. The calculation method is:

[0010] The over-tension amount of the prestress in the Nth round = (the concrete compression amount generated by the (N + 1)th round of tensioning + the concrete compression amount generated by the (N + 2)th round of tensioning) ÷ the length of the box girder × the elastic modulus of the prestress tendon.

[0011] Preferably, the number of prestressed tendon ducts is 90, and the number of jacks is 32.

[0012] Preferably, the box girder includes a left arc ring and a right arc ring, which are axisymmetric. A first partition beam and a second partition beam are provided between the left and right arc rings, and the first partition beam and the second partition beam are arranged at intervals. The prestressed tendon ducts are arranged in the left arc ring, the right arc ring, the first partition beam and the second partition beam.

[0013] The beneficial effects of the present invention compared with the background technology:

[0014] Due to the excessive number of tensioning rounds in the prior art, it is no longer possible to accurately calculate the over-tension of each round, so the tensioning accuracy is very low. However, the few-round tensioning of the present invention can achieve high-precision over-tension calculation, thus achieving high-precision tensioning.

Description of the Drawings

[0015] Figure 1 It is a schematic cross-sectional view of the box girder in the preferred embodiment provided by the present invention.

Detailed Embodiments

[0016] The embodiments of the present invention are described in detail below. The example embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0017] In the present invention, unless otherwise clearly defined and limited, the terms "assembled", "connected", and "joined" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can also be a mechanical connection; it can be directly connected, or connected through an intermediate medium, and it can be internally connected and communicated between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0018] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, the meaning of "several" is two or more, unless otherwise specifically defined.

[0019] The technical solutions and their beneficial effects of the present invention will be made clearer and more explicit by further describing the specific embodiments of the present invention in conjunction with the drawings of the specification. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0020] A preferred embodiment provided by the present invention: The prestress tensioning of precast concrete box girders is a conventional project. The existing tensioning technology involves putting two jacks into operation, symmetrically on the left and right, and gradually tensioning from the upper row to the lower row. Using two jacks is mainly because the number of prestresses in conventional box girders is not large (not exceeding 30 bundles), and at the same time, the precision requirement for prestress tensioning of conventional box girders is not high (the precision requirement is only ±5.0%). Therefore, the conventional method can meet the specification requirements.

[0021] However, when only two jacks are in operation, the number of jacks is too small. The jacks need to be continuously installed and transferred, resulting in very low efficiency and low tensioning precision (because the tension of the later batches will compress the beam body, leading to the relaxation of the prestress of the previous batches and affecting the tensioning precision of the previous batches).

[0022] In this embodiment, when the number of prestresses in the concrete box girder reaches 90 bundles (the number of prestresses in conventional box girders does not exceed 30 bundles), the precision requirement for prestress tensioning of the box girder is ±1.0% (the precision requirement for conventional prestress tensioning is ±5.0%), and it is difficult for the existing technology to meet this design requirement.

[0023] Therefore, for precast concrete box girders with a large number of prestresses, as Figure 1 shown, we propose a method for cluster prestress tensioning of box girders, which includes box girders and jacks, and it comprises the following steps:

[0024] (1) Set a number of prestress duct holes 1 in the box girder, and determine the tensioning rounds according to the ratio of the number of prestress duct holes to the number of jacks;

[0025] The number of prestress duct holes is 90 bundles, and the number of jacks is 32. The box girder includes a left arc ring 2 and a right arc ring 3, the left and right arc rings are axisymmetric, a first partition beam 4 and a second partition beam 5 are provided between the left arc ring 2 and the right arc ring 3, and the first partition beam and the second partition beam are arranged at intervals. The prestress duct holes are arranged in the left arc ring 1, right arc ring 2, first partition beam 3 and second partition beam 4.

[0026] (2) Evenly distribute the prestress duct holes according to the tensioning rounds, and the prestress duct holes are arranged in sequence according to the tensioning rounds; as Figure 1 shown, the first-round tensioning 11, the first-round tensioning 12, and the first-round tensioning 13 arranged in sequence.

[0027] (3) Calculate the compression amount of the box girder concrete generated by each-round prestress tensioning. The calculation method is: the concrete compression amount generated by this-round tensioning = (the tension of this-round tensioning × the box girder length) ÷ (the box girder cross-sectional area × the concrete elastic modulus);

[0028] (4) Determine the over-tension amount of the prestress according to the concrete compression amount of each round. The calculation method is:

[0029] Super - tensor of the N - th round of prestress=(Compression of concrete generated by the (N + 1)-th round of tensioning+Compression of concrete generated by the (N + 2)-th round of tensioning)÷Length of the box girder×Elastic modulus of the prestressing tendon

[0030] Further explanation: To solve the 90 prestressing tendon ducts of the box girder in this application and take into account the symmetry of the jack arrangement, 32 jacks are invested and evenly distributed around the box girder (i.e., on the same horizontal plane of the left arc ring, right arc ring, first diaphragm and second diaphragm).

[0031] Determine the number of tensioning rounds according to the ratio of the total number of prestresses to the number of jacks. For example, in this application, the number of tensioning rounds is 90 / 32 = 2.8. When there is a decimal, take the advanced integer, that is, 3 rounds;

[0032] Calculate the compression of the box - girder concrete generated by each round of prestress tensioning. The calculation method is: Compression of concrete generated by this round of tensioning=(Tensile force of this round of tensioning×Length of the box girder)÷(Cross - sectional area of the box girder×Elastic modulus of concrete). All data are preset according to requirements. Here, only examples are given without limitation.

[0033] Determine the super - tensor of prestress according to the compression of concrete in each round. The calculation method is:

[0034] Super - tensor of the 1st round of prestress=(Compression of concrete generated by the 2nd round of tensioning+Compression of concrete generated by the 3rd round of tensioning)÷Length of the box girder×Elastic modulus of the prestressing tendon;

[0035] Super - tensor of the 2nd round of prestress=Compression of concrete generated by the 3rd round of tensioning÷Length of the box girder×Elastic modulus of the prestressing tendon;

[0036] Super - tensor of the 3rd round of prestress is zero. (When the number of tensioning rounds does not exist, ignore this value.)

[0037] In this application, a large number of jacks are invested to achieve high - efficiency tensioning of prestress, and the goal of high - precision control is achieved through the calculation of the super - tensor of prestress in each round. The number of jacks invested in this scheme is approximately equal to 1 / 3 of the total number of prestresses, and the method of high - precision control is achieved through super - tensor calculation.

[0038] This scheme has fewer tensioning rounds and high operation efficiency. Since the number of tensioning rounds in the prior art is too many and it is impossible to accurately calculate the super - tensor of each round, the tensioning accuracy is very low. However, the few - round tensioning of the present invention can achieve high - precision super - tensor calculation, thus achieving high - precision tensioning.

[0039] In the description of the specification, the description referring to terms such as "one embodiment", "preferably", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. The schematic expressions of the above terms in this specification do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0040] Through the description of the above structures and principles, those skilled in the art should understand that the present invention is not limited to the above specific embodiments, and the improvements and substitutions using the well-known technologies in the art on the basis of the present invention fall within the protection scope of the present invention, which should be defined by each claim.

Claims

1. A method for prestressing tension of box girder clusters, including box girders and jacks, characterized in that: It includes the following steps: (1) Several prestressed tendon ducts are arranged in the box girder, and the tensioning rounds are determined by the ratio of the number of prestressed tendon ducts to the jacks; (2) The prestressed tendon ducts are evenly distributed according to the tensioning rounds, and the prestressed tendon ducts are arranged in sequence according to the tensioning rounds; (3) Calculate the compression amount generated by the prestress tensioning of the box girder concrete in each round. The calculation method is: the concrete compression amount generated in this round of tensioning = (the tensile force in this round of tensioning × the length of the box girder) ÷ (the cross-sectional area of the box girder × the elastic modulus of the concrete); (4) Determine the over-tension amount of the prestress according to the concrete compression amount in each round. The calculation method is: The over-tension amount of the prestress in the Nth round = (the concrete compression amount generated in the (N + 1)th round of tensioning + the concrete compression amount generated in the (N + 2)th round of tensioning) ÷ the length of the box girder × the elastic modulus of the prestressed tendon.

2. The method for prestressing tension of box girder clusters according to claim 1, characterized in that: The number of prestressed tendon ducts is 90, and the number of jacks is 32.

3. The method for prestress tensioning of box girder clusters according to claim 2, characterized in that: The box girder includes a left arc ring and a right arc ring. The left and right arc rings are axisymmetric. A first partition beam and a second partition beam are provided between the left arc ring and the right arc ring, and the first partition beam and the second partition beam are arranged at intervals. The prestressed tendon ducts are arranged in the left arc ring, the right arc ring, the first partition beam and the second partition beam.

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