Structures of External Prestressed Cable Bridge

1. The external prestressing system adopts non bonded steel strands and an anti-corrosion structure in the anchorage zone, which is safe and reliable, with good anti-corrosion and anti fatigue performance. Special devices are designed in the system to effectively reduce the harm caused by cable vibration.

2. The construction of the external prestressing system is simple, easy to detect and maintain, and the cables can be replaced if necessary.

3. The steering device has a reasonable structural setting, which can evenly transmit loads and achieve cable adjustment and replacement functions.

The application of external prestressed structural system is very extensive, which can be used for new structures such as prestressed concrete bridges, special structures, and building engineering structures, as well as for the reconstruction, reinforcement, and maintenance of existing concrete structures. It can also be used for temporary prestressed concrete structures or construction of temporary steel cables.

Ⅰ. Cables of External Prestressed Bridge： 

They are divided into two types: split wire cables and finished cables. Generally, steel strands are used as the base material for cable bodies, and there are bonded and non bonded two types, which are various surface treatment methods for steel strands, including glossy, galvanized, and epoxy.

Split type cable body: The free end of the cable body belongs to the groutless type, which can be disassembled, adjusted, and replaced one by one, and the working condition of the cable body at the free 

end can be detected at any time. The cable body steel strand adopts non bonded steel strand, and its anti-corrosion mainly relies on the steel strand protective layer (galvanized or epoxy layer), grease or paraffin, and a single outer HDPE sheath.

Cross section of segmented cables:

Finished rope body: 

Five Types: S-type, A1 type, A2 type, B1 type, B2 type.

Selection criteria for cable body:

1. The criteria for selecting external prestressed cable bodies can be divided into three categories based on environmental conditions and their relationship with the structure；

2. Moderate: The structural components are usually in a dry state;

3. Medium: The structural components are usually in a humid environment;

4. Serious: The structural components are in a long-term humid or alternating wet dry environment;

5. Corrosive: The components of the structure are in a severely corrosive and harsh environment.

HDPE Casing Tube：

HDPE Casing Tube must consider its strength, durability, water tightness, workability, and processing performance to protect the pipeline from deformation when used or filled with anti-corrosion materials. It must also have a certain strength against external impacts and not undergo chemical reactions with grouting materials under any environmental conditions. The wall thickness of the cable sleeve that needs to be filled with filling material should not be less than D/17 (D is the diameter of the cable sleeve); The wall thickness of the cable sleeve that does not require filling material should not be less than D/32 and should not be less than 5mm.

Ⅱ. External Prestressing System Anchoring System：

The anchoring system of external prestressed cables generally includes protective covers, loose prevention devices, specialized anchors for external cables, anchor plates, and embedded pipes.

External prestressed cables are located outside the concrete structure and may only bond with the structure at the anchorage and turning blocks. They are a separate component relative to the overall structure.

Technical parameters of type A and type TA external cable anchors       （unit: mm）

Note: When the sealing cavity of this type of external prestressed anchor is filled with non-curing anti-corrosive materials such as grease and wax, the cable replacement function can be realized.

Technical parameter table of TS tape and TT type external cable anchor         （unit:mm）

Note: When the sealing cavity of this type of external prestressed anchor is filled with non-curing anti-corrosive materials such as grease and wax, the cable replacement function can be realized.

Technical parameter table of TSK type external cable anchor      （unit:mm）

Note: This type of external prestressed anchor is adjustable and replaceable, that is, the cable force can be adjusted during the operation of the bridge, and the whole cable can be replaced.

Ⅲ. External Prestressing System Vibration Reduction Device:

Due to various factors such as vehicle traffic, vibrations may occur between the structure and the cable body. If the natural frequency of the cable body is close to the vibration frequency of the entire structure, resonance may occur, posing a safety hazard to the entire structure. It is necessary to install vibration reduction devices at appropriate distances to shorten the vibration interval of the free section of the cable body and provide appropriate vibration reduction to the cable body.

Vibration reduction devices (dampers) are divided into two types: Finished Cable Dampers and Split-wire Dampers.

Ⅳ. External Prestressing System Anti-corrosion System:

The anti-corrosion system of the external prestressing system can be treated with materials such as cement slurry, special grease, paraffin wax, epoxy mortar, polyurethane foam material, and PU2509T modified polyurethane resin.

The anti-corrosion of steel strands is achieved through surface treatment, galvanizing, epoxy spraying, and epoxy filling; The external suspension system is used for anti-corrosion, with specialized cement mortar, grease, and polyurethane filling for anti-corrosion effect.

Ⅴ. External Prestressing System Deviating Device:

The divating device in externally prestressed concrete structures is the only key and special component of externally prestressed cables that is connected to concrete within the span, in addition to anchoring structures.

The external prestressing deviating device is mainly divided into:

1. Integral deviator: divided into A-type and D-type deviating devices, consisting of two steel pipes or a single steel pipe bent into a certain arc. The function of the two tubular steel pipes is to provide the required external cable turning angle and curvature for design, while the function of the inner steel pipe is to guide and isolate the cable body from direct contact with the outside, effectively protecting the anti-corrosion layer of the cable body.

2. Individual Strand Deviator: It mainly composed of guide tube, baffle, and partition. Composed of ZH mortar, it can be replaced with a single cable.

 The individual strand deviator includes B-type steel pipe welded individual strand deviator, C-type box type individual strand deviator, E-type round tube individual strand deviator, and F-type (double) multi tube individual strand deviator.

The steel pipe welding type individual strand deviator is made up of multiple steel pipes welded together, with a small cross-sectional size, which can be suitable for compact structures. It can ensure that the positions of each steel strand in the cable body are parallel, so that the steel strand is evenly stressed and can be replaced with a single cable.

Box type individual strand deviator is a new type of steering gear, consisting of an outer steel box, inner split tube, support plate, and filling material. The inner dividing tube is made of plastic pipe, which can ensure that the positions of each steel strand inside the cable body are parallel, so that the steel strand is evenly stressed and can be replaced with a single strand. Choose different types of deviator based on different designs.

Type A deviator specification table       Unit: mm

Type B deviator specification table     Unit: mm

Type C deviator specification table      Unit: mm

Working Principle：

The bending radius of the external cable steering gear is better in terms of the stress state of the steel strand. However, if the bending radius is set too large, the size of the bending component will increase, thereby increasing the weight of the bridge. Therefore, while ensuring safety, the bending of the steering gear can be made smaller. The smooth transition at the outlet of the steering gear can eliminate the additional stress caused by installation and construction errors, while reducing the wear of HDPE sleeves.

Packaging：

1) All the products are packed with seaworthy packing.
2) Customer's special requirement for packing can be satisfied.
3) Air freight, sea freight and truck freight are all available.