QSM external prestressed system
- 产品详情
External prestressing system
The external prestressing system is a kind of prestressed structural system formed by applying prestressing force to the prestressed tendons arranged outside the main body of the bearing structure.
The concept and method of external prestressing technology originated from France. In the 1950s, external prestressing technology was used in bridge construction. However, due to the technical limitations at that time, the protection and anti-corrosion problems of external cables could not be well solved, so many attempts failed to achieve success, which restricted the development of external prestressed structure in the following decades.
With the revival of cable-stayed bridges in the late 1960s, the protection of stay cables has been continuously solved and improved, and the related technologies have also been widely used to solve the anti-corrosion problems of external prestressed cables, which greatly promotes the development of externally prestressed bridges which are stagnant due to anti-corrosion problems.
In the 1970s, in the process of long-term practice of internal prestressing in European countries, it was found that the internal prestressed concrete bridge would cause the loss of prestress due to friction, and the pipe could not be completely compacted, resulting in the phenomenon of voids in the pipeline. In addition, due to the damage of the old bridge structure and the improvement of the load level, the bridge structure had to be reinforced Give. In this case, external prestressing has become the most important and active bridge reinforcement method. Through the experience gained from continuous reinforcement of bridges, people have realized many advantages of external prestressing. At the same time, the development and application of high-performance steel tendons bring convenience to the design and construction of externally prestressed bridges.
Since the 1950s, China has developed rapidly in the field of prestressed technology, especially after the reform and opening up, ushered in the golden age of bridge construction in China. Through the unremitting efforts of bridge builders, prestressed concrete bridges in China have been developed and matured. With the continuous increase of bridge construction and the continuous development of new technology in our country, we constantly have a higher technical level and rich practical experience, and the application of external prestressing technology has also attracted our attention.
Liuzhou qiaoxia cable products Co., Ltd. has been continuously researching and developing various related products in the field of external prestressing technology, and has made some achievements.
Technical characteristics of QSM external prestressed cable
1. The external cable adopts epoxy coating or galvanized steel strand with nominal tensile strength of 1860MPa and nominal diameter of 15.2mm.
2. The single wire sprayed steel strand meets the requirements of GB / T 25823-2010 single wire coated epoxy coated prestressed steel strand, and the filled epoxy coated steel strand meets the requirements of GB / T 21073-2007 epoxy coated seven wire prestressed steel strand and JT / T 737-2009 filled epoxy coated steel strand.
3. The external prestressing system meets the requirements of GB / T 30827-2014 technical conditions for external prestressing cables and JT / t853-2013 external prestressing tendons of unbonded steel strand; the performance of external cable anchorage meets the requirements of FIP acceptance and application suggestions of post tensioned prestressed system, materials and systems of external prestressing and national standard GB / T 14370-2015 anchorage, fixture and connector for prestressed reinforcement.
4. The external prestressed system is easy to detect and maintain, and the cable can be replaced if necessary.
5. Special protective components such as anchor protective cover, sealing device and sealing belt shall be adopted for the steel strand of anchorage section, and the steel strand, anchorage device and clip shall be fully protected by pouring and coating anti-corrosion filler.
6. Related supporting products of external beam include anchorage, steel beam, embedded steering gear, vibration reduction limiting device of external beam, etc.
●QSM体外预应力拉索体系基本构成
Schematic diagram of QSM external prestressed cable system
1 - protective cover 2 - working clip 3 - working anchor plate 4 - locking device 5 - anchor plate 6 - spiral reinforcement
7 - embedded pipe 8 - sealing device 9 - shock absorber 10 - external prestressing tendon 11 - HDPE casing 12 - embedded diverter
The QSM external prestressed cable system mainly includes the following basic contents:
External prestressed cable body
● anchoring device
Locking device
● steering device
Shock absorber
Anti corrosion device
● monitoring system
（1） External prestressed cable body
Qsm-s1 and qsm-s2 cables belong to grouting type and are mainly used for anti-corrosion through grouting. It is impossible to disassemble, adjust and replace the cable under the condition of water filled mud.
Qsm-s3 and qsm-s4 cables belong to the non grouting type, which can be disassembled, adjusted and replaced one by one, and the condition of the free section can be detected at any time. The anticorrosion of cable body mainly depends on the protective layer of steel strand, grease or paraffin and HDPE for single cable.
The qsm-s5, qsm-s6 and qsm-s7 cable bodies are non grouting type. The cable bodies are finished cables and can be disassembled, adjusted or replaced as a whole. The cable body has multi-layer anticorrosion.
Qsm-s8 and qsm-s9 cables are non grouting type. The cable body is finished cable and the base material is high strength steel wire.
Selection of cable body -- the selection of QSM external prestressed cable should be considered according to the use environment, maintenance, cost and other aspects.
It is recommended to use epoxy coated steel strand with multi-layer protection. Under the general anti-corrosion requirements, smooth steel strand cable body can also be used. In addition, the cable body type can also be selected according to the construction conditions: if it has better threading conditions, the finished cable is recommended; if the reinforcement space is narrow, the single wrapped HDPE split wire cable can be selected.
（2） Anchoring device
In the external prestressing system, anchorage not only bears tension, but also bears other potential forces in the life cycle of the structure. The external prestressed cable is located on the outside of the concrete structure, and it may bond with the structure only at the anchorage and the turning block. Under the action of active load, the strain amplitude of prestressed tendon is a very important parameter in the design of prestressed anchorage system. Therefore, the reliability and safety requirements of external prestressed anchorage are more stringent than that of internal prestressed anchorage. QSM provides two different types of external prestressed anchorage to meet different engineering requirements.
● QSM.TW . type a external prestressed anchorage
● QSM.TW.TSK Type external prestressed anchorage
（3） Locking device
In the process of using the bridge, vibration will inevitably occur. The clip and anchor plate are easy to loose and slip, especially when the tension is small. Therefore, the external prestressed anchorage must be equipped with anti loosening device.
For the external prestressed anchorage, the main measures are as follows:
1. The structure of the clip itself has a certain anti loosening ability in the design.
2. At the later stage of clip installation, additional anti loosing device is installed.
The external prestressed anchorage designed and produced by our company adopts the above two anti loosing measures at the same time to ensure the safety of the bridge.
（4） Steering gear
The larger the bending radius of the external cable diverter is from the stress state of the steel strand, the better. However, if the bending radius is set too large, the component size of the bending part will be larger, which will increase the weight of the bridge. Therefore, under the condition of ensuring safety, the bending radius of the steering gear can be smaller. The smooth transition of steering gear outlet can eliminate the additional stress caused by installation and construction errors, and reduce the wear of HDPE casing.
Due to the additional bending stress, the fatigue strength of the bent external prestressed cable decreases. Therefore, in the design process, it is necessary to check the stress value of the steel strand with the bending stress value. It is difficult to calculate the bending stress value of the tensile steel strand. However, assuming that there is no friction between the steel wires, the bending stress value can be calculated according to the following formula:
The stress loss caused by friction between prestressed reinforcement and duct wall consists of two parts: one is the friction loss caused by the vertical extrusion force on the curved section; the other is the friction loss caused by the position deviation and unevenness of the pipeline.
μ - friction coefficient between prestressed reinforcement and pipe wall
K-the influence coefficient of the local deviation of the pipeline per meter on the friction
The external prestressed steel cable is arranged outside the concrete structure, and its wire shape is composed of the curve section at the turning position or anchoring position and the straight line section between them. For the straight section, the linear and external dimensions of the steel cable pipeline are not affected by the construction factors, so the influence of the friction caused by the unevenness of the pipeline is not great, and the prestress loss of this part can be ignored; for the curve section, because the length of the pipe here is short, the friction loss caused by the deviation and unevenness of the pipeline along the length of the curved section can also be ignored.
The external cable steering device is another important link besides the external cable anchorage. In the steering device, the prestressed tendons will bear large bending and offset forces, and friction will occur between the tendons or between the tendons and the steering device during tensioning and working. When local stress is generated, the surface of prestressed tendons will be damaged, thus reducing the anti-corrosion effect of the tendons.
Therefore, according to different forms of prestressed cable body, our company designs and provides various types of steering devices, such as single pipe integral steering gear, double pipe integral steering gear, steel pipe component wire type steering gear, box type split wire steering gear, etc.
The single pipe integral steering gear is composed of steel pipe bent into a certain radian.
The double tube integral steering gear is composed of two steel pipes bent into a certain arc.
The function of the lined steel pipe is to isolate the cable body from the external steel pipe and guide, so as to prevent the cable body from losing its anti-corrosion function due to excessive friction caused by direct contact with the outside.
The steel pipe component wire type steering gear is composed of a number of steel pipes bent into a certain arc.
Its section size is small, and it can be used in the situation of compact structure. It can ensure that the position of each steel strand in the cable body is parallel, so that the stress of steel strand is uniform, and single cable can be replaced.
The box type wire dividing type steering gear is composed of an outer steel box, an inner dividing pipe, a supporting plate and a filler.
The inner dividing pipe is made of plastic pipe, which can ensure that the position of each steel strand in the cable body is parallel, so that the stress of steel strand is uniform, and single cable can be replaced.
（5） Damping device
The bridge structure and cable body will vibrate during the service period. When the natural vibration frequency of the cable body is close to the vibration frequency of the whole structure, resonance may occur, which will bring about safety risks. In order to make the vibration frequency of the cable body different from that of the whole structure, the vibration damping device must be installed at an appropriate position to shorten the vibration range of the free section of the cable body, and provide appropriate vibration reduction for the cable body, so as to avoid harmful vibration of the cable body.
（6） Anticorrosion system
The anticorrosion of steel strand can be treated by surface treatment, including galvanizing, epoxy spraying, epoxy filling, etc. The anticorrosion of external cable system is mainly filled with special cement slurry, epoxy mortar, grease, polyurethane and oily wax.
Construction technology
1. Installation of embedded parts
The installation position of embedded parts shall be determined according to the design requirements, and the installation error shall be within the design range.
2. Cable cutting
The steel strand can be cut according to the length at the construction site. The cutting length must be accurately calculated, and the adjustment range required for the reserved tension should be calculated.
3. Threading
The prepared steel strands can be hoisted in place one by one and connected with the anchorage respectively.
4. Single cable pre tightening
The steel strand shall be tensioned and pre tightened one by one, so that the stress of each strand is uniform.
5. Tensioning
Tension construction shall be carried out as required.
Cable tension construction: under normal circumstances, the external cable body is long. When the cable is tensioned to the design force, the cable body has a large extension. The maximum stroke of the piston for ordinary tension jack is usually 200 mm, so the jack needs to travel back and forth several times during the tension construction.
Ordinary tensioning
Generally, there is a supporting foot between the jack and the working anchor plate for tension
。
Suspension tensioning
An adjustable limit plate is arranged at the front end of the jack, and the limiting plate is adjusted before stretching. During the tensioning process, the work clip does not bite the steel strand and is always in a "suspension" state. After tensioning in place, adjust the limit plate, compress the working clip, return oil to the jack and anchor.
For epoxy coated steel strand, in order to ensure the clamping effect, the suspension tension method must be used to tension the cable body.
Jacking tension
The top pressure tensioning method is reformed on the structure of the suspension tensioning method. A jack jack is installed at the front of the jack, the top jack jack is connected with the top pressure limit plate, the limit plate is adjusted before stretching, the working clip does not bite the steel strand during the stretching process, after the tension is put in place, the top pressure limit plate is tightly clamped to the work clip, and the jack returns oil and anchors, thereby ensuring the anchoring. It is reliable and has little prestress loss.
Tension rod tension
Tension rod tension method is mainly used for the tension of anchor head in the form of thread, or when the overall adjustment of cable force after tension.
Single tension
The single tension method adopts the equal tension method: install the force sensor on the first steel strand to be tensioned, and compare the tension of other steel strands with this until it is equal. Finally, remove the single hole tool anchor and force measuring sensor.
6. Install the shock absorber
A shock absorber is installed at the exit of the cable embedded pipe to fix the cable body with the structure to reduce the adverse effect of vibration on the stay cable.
7. Protective treatment
Install waterproof cover at the exit of cable embedded pipe. Cut off the redundant steel strand at the anchor head, install the anchor head protective cover, pour anti-corrosion grease into the protective cover, and seal all seals.
Construction precautions
1. According to the type and specific situation of the cable, prepare the required relevant accessories and auxiliary construction equipment (such as tensioning machines and tools).
During lifting, the cable must be stable to avoid accident.
3. The anchor plate should be vertical to the extension direction of the cable when it is installed, and shall not be inclined.
4. Clean up the construction site, and clean up the support duct and surrounding.
5. The anchor head shall be kept clean and free from corrosion, and the anchorage shall not be damaged by bumping and knocking, and the surface shall not be attached with other substances affecting the tension construction and anchoring.
6. Enough installation and tensioning space shall be ensured, and the cable body shall not be damaged during installation.
7. The cutting length must be accurately calculated, and the adjustment range required for the reserved tension should be calculated to avoid the cable being too long or too short to meet the requirements or cause waste.
8. The surface of free section cable body shall not be damaged. If there is any damage, it must be repaired in time.
9. Before sealing the anchor, according to the structure and design requirements, use the grinding wheel cutter to cut off the redundant steel strand. Do not use flame cutting method such as oxygen cutting.
10. After tensioning, the anchor head shall be kept clean, coated or filled with anti-corrosion grease, and anti-corrosion protection work shall be done well.