In the bridge jacking method, what are the requirements and precautions for the arrangement of prest

Answer]: c, d

The setting of the tension end of the tendon should meet the design requirements. When the design is not required, the following provisions should be met: curved prestressed tendons or linear prestressed tendons with a length greater than or equal to 25m next to the filial piety stove should be tensioned at both ends; Straight-line prestressed tendons with a length of less than 25m can be tensioned at one end.

Answer]: a, b

2021 textbook p261

This question examines the construction of the orange forest on the bridge of the round eggplant acre structure. The method of pushing construction can be divided into single-point pushing and multi-point pushing and pushing.

2) The construction points during the tensioning operation of the prestressed tendon by the pre-tensioning method.

1. In the process of tensioning, the movable beam should be kept parallel to the fixed beam from the beginning to the end, and the prestress value of the prestressed tendon should be spot-checked, and the absolute value of its deviation shall not exceed 5 of the total prestressed value of all the tendons of a component.

2. After the tensile tension is completed, the deviation from the design position shall not be greater than 5mm, and shall not be greater than 4 of the shortest side length of the component.

4. When tensioning, the number of broken wires of prestressed steel wires and steel strands in the same component shall not exceed 1, and the broken bars are not allowed for prestressed steel bars at the same time.

5. The beam must have sufficient stiffness, and the deflection after stress should not be greater than 2mm

6. The prestressed steel bar close to the center of gravity of the pedestal section should be tensioned first to prevent the pedestal from being subjected to excessive eccentric pressure.

7. When laying the prestressed tendons on the pedestal, measures should be taken to prevent the state from staining the prestressed tendons.

8. When tensioning the beam in batches, the jack should be arranged symmetrically to prevent the movable beam from tilting.

9 When tensioning, the tensioning direction is in a straight line with the prestressed steel.

10. When tightening the anchor plug, the force should not be too strong, in case the reinforcement of the sail force per mu is broken; When tightening the nut, care should be taken that the gauge reading is always kept at the control tension.

11. Protective measures should be set at both ends of the pedestal. When tensioning, a protective frame should be placed every 4 5m along the length of the pedestal. Staff are not allowed to stand at either end of the pedestal or enter the pedestal.

12. When the prestressed steel bar is stretched to the control tension force, it is advisable to stop for 2 3min and then tighten the clamp or nut, at this time, the operator should stand on the side.

Hello dear <>

The jacking method is a common scheme for erecting prefabricated segmental prestressed concrete continuous beam bridges. The main steps are as follows:1

Production and transportation of prefabricated segments: According to the design requirements, the required prefabricated segments are made in the deficit factory, and then transported to the construction site with equipment such as cranes or cranes. 2.

Construction of support: At the position of the bridge pier or bridge fiber platform, the support is built first for subsequent construction. The bracket needs to be able to withstand the weight of the prefabricated segments and the loads of personnel and equipment during construction.

3.Positioning of the segment: on the bracket, the positioning steel plate and bolts are installed first, and then the prefabricated segment is placed on the positioning steel plate according to the design requirements, and it is fixed with bolts.

4.Tensioning of the segments: After the segments are placed, the tensioning work begins.

First of all, at the anchorage points at both ends of the segment, the anchors and anchors are installed respectively. Then, through jacks and other equipment, the prestressed steel bundle is stretched to the specified prestress level, so that the concrete inside the segment begins to be subjected to pinned finger compressive stress, so as to form a prestressed concrete structure. 5.

Removal of supports: When all the prefabricated segments are completed, the supports and other auxiliary facilities can be removed to complete the erection of the entire bridge. It should be noted that a variety of factors need to be considered in erecting a prefabricated segmental prestressed concrete continuous beam bridge by jacking method, such as the tensile force of the prestressed steel bundle, the connection mode between the prefabricated segments, the strength of the concrete, and so on.

Therefore, in actual operation, it is necessary to carry out construction in strict accordance with the design requirements and relevant standards. <>

1) The jacking method can use simple equipment to build long and large bridges, the construction cost is low, the construction is stable and noiseless, and it can be used on deep water, valleys and high bridge piers, and can also be used on curved bridges and hidden slope bridges with the same curvature.

2) The main beam is prefabricated in sections, continuous operation, and the structure integrity is good; Because there is no need for large-scale lifting and excavation carrying equipment, the length of the construction section can be selected according to the conditions of the precast yard and the reasonable position of the section, and 10 20m can generally be used.

3) The beam section is fixed in the same site for prefabrication, which is convenient for construction management, improves construction conditions, and avoids high-altitude work. At the same time, the formwork and equipment can be used for many turnovers, and the cycle of beam section prefabrication under normal circumstances is 7 10d.

4) the stress state of the beam changes greatly during the jacking construction, and the difference between the construction stress state and the operating stress state is also more, so the requirements of construction and operation load should be met at the same time when the cross-section design and prestress bundle are arranged; During construction, temporary piers, guide beams and other measures can also be taken to reduce construction stress.

5) the jacking method should be used on the equal section beam, when the bridge span is too large, the selection of equal section beam causes the uneconomical material, also increases the construction difficulty, so the continuous beam of medium span is appropriate, the recommended jacking span is 40 45m, and the total length of the bridge is also 500 600m.

The shortcomings of adopting the jacking method construction are: generally adopt the continuous beam of equal height, the quantity of materials consumed by the structure will be increased, and the large beam height will increase the amount of approach road earthwork, and is not conducive to the appearance. In addition, the span of the continuous beam that is judged to be cut off by the jacking method is also limited to a certain extent.

Answer] :d test point is the knowledge of bridge engineering prestressed tendon cherry blossom tension. The tensioning of prestressed tendons is a sub-project with large technical content, in which the tensioning sequence of prestressed tendon bundles is crucial and should meet the design requirements.

CJJ2 stipulates that when the design is not required, it can be stretched in batches and stages symmetrically and evenly, and it is advisable to carry out tensioning operations in the middle first, then up, down or on both sides. Except for option D, none of the other options conform to the principle of "symmetrical, balanced" tension and are distractors.

Answer] The :d test point is the knowledge of tensile tendons for bridge engineering. The tensioning of bonded pre-stressed tendons is a sub-project with large technical content, in which the tensioning sequence of the prestressed tendon bundle is crucial and should meet the design requirements.

Urban Bridge Engineering Construction and Quality Acceptance Regulation Spine Early Slippage Fan "CJJ 2 stipulates: when the design is not required, it can be tensioned in batches, symmetrically and evenly in stages, and it is advisable to carry out tensioning operations in the middle, and then up, down or on both sides. Except for option D, none of the other options conform to the principle of "symmetrical, balanced" tension and are distractors.

Sui Shenliang answer]: b

After the assessment of this question, the type of prestressed tendon is the type of filial piety.