Cable system of high tower cable stayed bridge
- 产品详情
Cable system of high tower cable stayed bridge
In foreign countries, from the German leschel built the world's first cable-stayed bridge with a span of 32 meters in 1784, to desinger and German contractor Demag company to build the world's first modern cable-stayed bridge stromsonde bridge in Sweden in 1953, and now all kinds of cable-stayed bridges emerge at the historic moment and develop rapidly. In fact, the development of cable-stayed bridge has a long history.
In China, the development history of cable-stayed bridge is much later than that of foreign countries, but the development of cable-stayed bridge in China is quite rapid. Up to now, 27 cable-stayed bridges with a span of more than 400 meters have been built in China, of which 25 are in the world's top 50 cable-stayed bridges. From the previous cable-stayed bridge construction needs to learn from foreign countries, after several generations of bridge builders' efforts, to now we have independently designed and built Yangpu Bridge, Nanpu Bridge, Sutong Bridge, etc. The independent innovation of cable-stayed bridge construction has been realized. It makes our country gradually become a powerful bridge building country.
In the continuous development process of cable-stayed bridge, the problems that need to be paid attention to and improved are: wind resistant design, seismic design, service life (mainly anti-corrosion and fatigue), and improving the strength of structural materials to reduce self weight.
Stay cables are developed from prestressing technology, they use the same base material and similar principle. The difference is that the prestressed tendons are tensioned by jacks and the stay cables are passively stressed by the weight and load of the structure.
Parallel steel strand cables and parallel steel wire cables have been widely used as the main load-bearing components of cable-stayed bridges. The parallel steel strand cable is a new product developed in 1980s. It mainly adopts the diameter of 15.2mm epoxy coated steel strand or galvanized steel strand as the stress base material, uses the mechanical way of clamping the steel strand with clips, pours mortar, grease or oily wax in the anchor barrel to prevent corrosion, and the cable body adopts multi-layer protection, which has good anchoring performance, anti fatigue performance, good replaceability and maintenance With the advantages of convenient protection, low cost and excellent anti-corrosion performance, the bridge maintenance cost is reduced and the service life of the bridge is improved.
Compared with the common girder bridge, the high tower cable-stayed bridge has a larger span capacity, and is widely used in crossing rivers, valleys, oceans and other occasions, and is the main bridge type of long-span bridges. The stay cable of high tower is mainly composed of cable tower, main beam and stay cable. Because of its large span and high tower, there is often no cable saddle. One end of the cable is anchored at the beam end and the other end is directly anchored on the bridge tower. The cable tension on both sides is symmetrical with the bridge tower as the center line.
There are three main types of cables used in high tower cable-stayed bridge according to the cable body structure: parallel steel strand cable, cold casting heading anchor steel wire cable and extrusion anchoring steel strand cable.
● parallel steel strand cable system
The parallel steel strand cable mainly adopts the diameter of 15.2mm epoxy coated steel strand or galvanized steel strand as the stress base material. The steel strand is clamped with clips and the mortar, grease or oily wax are poured into the anchor barrel. The multi-layer protection has good anchoring performance, fatigue resistance, good replaceability, convenient maintenance, low cost and excellent anticorrosion performance, so as to reduce the maintenance cost of the bridge The service life of the bridge is improved.
In the parallel steel strand cable system, the dynamic load stress amplitude of 250Mpa is the most widely used. Its main performance characteristics are: when the maximum cable force is 0.45 σ B, the dynamic load stress amplitude is 250 MPa, it can withstand 2 million fatigue stress cycles, and the breaking area of the cable is less than or equal to 2% of the total cable area. Therefore, it has excellent fatigue resistance.
The qsm250 cable system mainly includes the following basic contents:
Anchorage section: a tension end anchorage section, e fixed end anchorage section
Transition section: B, D
Free section: C
● monitoring system
（1） Anchoring device of anchorage section
（2） Transition device of transition section
The transition section is composed of shock absorber, cable hoop and waterproof device
1. Shock absorber: the shock absorber is made of damping rubber and installed at the outlet of cable duct to fix the cable with the structure.
2. Cable Hoop: gather the divergent steel strand into a compact whole.
3. Waterproof device: it is set at the outlet of cable body and cable conduit to prevent moisture from entering into the cable.
（3） Cable body of free section
Qsm250 cable body is generally composed of several protective steel strands in parallel. Each protective steel strand structure is epoxy coated steel strand (or galvanized steel strand) + anti-corrosion grease + PE sheath, and then covered with HDPE casing for overall protection.
main features
1. The steel strands are separated from each other and not in contact with other metals, so they have high fatigue resistance.
2. It is easy to install tension anchorage one by one.
3. Single cable can be replaced, convenient maintenance in later stage.
4. The cable length can be cut according to the construction site to avoid the prefabrication error, and the cutting length can be controlled flexibly.
5. It has multi-layer protection, which can avoid the influence on the anti-corrosion performance of the whole structure due to the defects of one protective layer.
6. The tensioning can be carried out in stages according to the design requirements, and the cable force can be adjusted for a long time through the threaded anchorage.
7. Each strand can be monitored at any time during the use of the structure.
8. The transportation is convenient and the cost is low, and the equipment required for the installation of steel strand is low.
■ structural parameters of anchorage
● tensioning end anchorage
● fixed end anchorage
Cold casting heading anchor wire and cable
Cold casting heading anchor steel cable is a kind of cable system, which is composed of hot extrusion HDPE high strength steel wire cable and cold casting heading anchor combined with internal and external dampers, waterproof cover, anchor head protection cover and other accessories.
The main contents of QSM cold casting heading anchor steel wire and cable are as follows:
● cable body ● anchoring device ● damping device ● anti-corrosion device ● monitoring system
Main technical performance indexes
① The static load performance meets the requirements of GB / T 14370-2015 anchorage, fixture and connector for prestressed tendons: the anchorage efficiency coefficient η a ≥ 95%, ξ APU ≥ 2%.
② The fatigue performance meets the requirements of GB / T 18365-2001 "technical conditions for hot extruded polyethylene high strength steel wire cables for cable stayed bridges". It can pass 2 million fatigue tests of 0.4 σ B stress upper limit and 0.28 σ B stress lower limit, and the total number of broken wires is less than 5%.
③ The HDPE performance of cable body meets the requirements of GB / T 18365-2001 "technical conditions for hot extruded polyethylene high strength steel wire cables for cable stayed bridges" and CT / t297-2016 "high density polyethylene sheath for bridge cables".
④ Properties of high strength steel wire: tensile strength ≥ 1670mpa, other properties shall not be lower than the requirements specified in GB / T 17101-2008 hot dip galvanized steel wire for bridge cables.
⑤ Elastic modulus of cable: e ≥ 1.9 × 105Mpa.
⑥ Waterproof performance: fully sealed waterproof structure.
⑦ The static stress release coefficient of HDPE is k > 0.3;
⑧ The maximum allowable rotation of spherical bearing: a = ± 4 °.
Design and selection suggestions
In order to ensure the safety of the structure, it is recommended that the safety factor of the cable be greater than 2.5 ~ 3. If the safety factor is too large, the cable body will not be stretched. In order to make the bridge cable beautiful, it is suggested that the actual use stress of the cable should not be less than 20% of the nominal breaking force of the cable body to ensure that the cable body does not bend.
The position of the shortest cable should be reasonably arranged in the structural design, and the free length of the shortest cable (excluding anchorage at both ends) should not be less than 2m.
In order to ensure the waterproof of the lower end, it is necessary to extend the lower cable conduit 100 ~ 150 mm out of the bridge deck structure.
Structure and parameters of cold casting heading anchorage
Cold cast heading anchor (cold cast anchor) is usually used as the anchor head of parallel steel wire cable. Its main structure includes anchor plate, nut, anchor cup, filling material, sealing device, etc.
The diameter of steel wire with diameter of φ 7 or steel wire of diameter of φ 5 should be used preferentially.
■ cable body
● extruded anchorage steel strand cables
The extruded anchorage steel strand cable includes fixed end and tension end. It has reliable anchorage, convenient cable tension and adjustment, compact anchor head structure, good fatigue and anti-corrosion performance. It is suitable for a variety of bridges. The product complies with the standard of JT / T 850-2013.
The QSM extrusion anchorage steel strand cable mainly includes the following basic contents:
● cable body ● anchoring device ● damping device ● anti-corrosion device ● monitoring system
Main features
1. The two ends of the steel strand are extruded and anchored, and the stress of each strand is isolated from each other, and the strand is difficult to fall off. Its static load is safe and reliable, and its fatigue performance is good.
After the two ends of the steel strand are squeezed into the anchorage sleeve, the holding force of the anchor head to the steel strand will not change again, and the retraction is very small during the tension, and the steel strand will not slip off under the condition of low stress or even negative stress. The bending angle of the steel strand entering into the anchor head is very small and almost free from bending stress. The whole bundle of isolated extrusion anchor of steel strand is mainly anchored by friction force, so its fatigue performance is very good.
2. The structure of anchor head is compact, which is conducive to the optimization and beauty of the overall structure.
In the case of the same stress level, the external dimension of the extrusion anchor head is much smaller than that of the cold cast anchor, hot cast anchor and clip anchor, which can reduce the size of the embedded pipe, and facilitate the connection of steel tie rod, fork lug and other structures, which brings great convenience for the installation and replacement of the bridge. Moreover, the steel strand (1860MPa) with higher strength than steel wire (1670mpa) is adopted. Under the same design stress, the total cross-sectional area and total weight of cable can be reduced a lot, which makes transportation more economical and convenient.
3. The anchor head adopts fully sealed structure with good anti-corrosion and protection performance.
After the anchor head is extruded, there is a sealing cover plate at the front end of the anchor head, and the PE part of the cable is sealed by the sealing cylinder and sealing device at the rear. Then, the elastic wrapping material is poured into the anchorage cavity for anti-corrosion, and the steel strand is completely and permanently isolated from the outside air and water vapor. After construction, the anchor head is coated with special anti-corrosion grease, which requires that the external surface is completely covered, and then the protective cover is installed. Because of the multi-layer protection, its permanent protection performance is quite reliable. Extrusion anchorage and its cable production, processing, assembly are completed in the factory, in the form of finished cable sent to the construction site, its quality is guaranteed.
Main technical performance indexes
1. The static load performance meets the requirements of GB / T 14370-2015 anchorage, fixture and connector for prestressed reinforcement: the anchorage efficiency coefficient η a ≥ 95%, ξ APU ≥ 2%.
2. The fatigue performance meets the requirements of pti-2003 regulations for design, testing and installation of stay cables. It can pass the fatigue test of 200 MPa and 0.45 σ B stress limit for 2 million times, and the broken wire rate is less than 2%.
3. Meet the requirements of DG / T j08-019-2005 "technical specification for application of cables for building structures": it can pass 2 million times of fatigue tests with stress amplitude of 250Mpa and upper limit of 0.45 σ B stress, and the broken wire rate is less than 2%.
4. The HDPE performance of cable body meets the requirements of CJ / T 3078-1998 "high density polyethylene plastics for building cables".
5. Performance of steel strand: tensile strength ≥ 1860MPa, other properties shall not be lower than the requirements specified in GB / T 5224-2014 steel strand for prestressed concrete.
6. Elastic modulus of cable: e ≥ 1.8 × 105Mpa.
7. Waterproof performance: fully sealed waterproof structure.
Design and selection suggestions
1. The free length of the shortest cable should not be less than 2m.
2. In order to ensure the safety of the structure, it is suggested that the safety factor of stay cables η ≥ 2.5 ~ 3.
3. In order to ensure the waterproof of the lower end, it is necessary to extend the lower cable conduit 100 ~ 150 mm out of the bridge deck structure.
4. Before sealing the anchor heads at both ends, apply anti-corrosion grease evenly on the outer surface.
5. Screw in position of nut: the installation position of nut is recommended to be in the middle of effective thread section of anchor head, and it is forbidden to screw in the part with internal thread.
■ parameters of cable anchorage for extruded anchorage steel strand
●QSM挤压索锚具(固定端)A型
■ cable body
Note: the steel strand in the finished cable can be smooth, galvanized, epoxy sprayed or epoxy filled.