Cable system of Extradosed cable stayed bridge
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Cable system of Extradosed cable stayed bridge
Extradosed stayed bridge is a new type of bridge appeared in recent 20 years. Because of its superior structural performance and good economic index, it shows more and more great development potential. The Zhangzhou war readiness bridge built in 2001 is the first low pylon cable-stayed bridge in China.
In 1995, Yan Guomin, a famous bridge expert in China, defined it as "Partial Cable-stayed Bridge" for the first time. Its meaning is: in the structural performance, the stay cable only shares part of the load, and a considerable part of the load is borne by the bending and shear of the beam. "Partial Cable-stayed" is derived from the degree of cable-stayed. Later, some domestic articles defined this type of bridge as low pylon cable-stayed bridge according to its low tower height.
With the construction of more and more low pylon cable-stayed bridges in China, the scientific research, accumulated design, construction and management experience in the construction process of Extradosed stayed bridge have laid a good foundation for the further development of this type of bridge in China. In recent years, China's construction of low pylon cable-stayed bridge, the form is more rich, the structure is more novel.
Cable structure of qsmat low pylon cable stayed bridge
The cable saddle of qsmat low pylon cable-stayed bridge is designed by using the technology of wire dividing pipe, which can effectively improve the stress distribution in the tower, play the role of dispersing and evenly transmitting the load, and solve the problem that the traditional cable system can not adjust and replace the cable by single cable. It has the advantages of safety and reliability, clear stress, excellent anti-corrosion performance of cable body, excellent anti fatigue performance of cable anchorage, and convenient construction.
The cable system of qsmat Extradosed bridge is composed of cable anchorage, cable body, cable saddle, anti sliding anchorage device and monitoring system. It has the following technical features:
1. Fatigue resistance of cable anchorage: meet the requirements of FIP and pti2001. The results show that the fatigue resistance of the cable anchorage assembly reaches the upper limit of stress of 0.45 σ B, and the stress amplitude is 250 MPa. After 2 million cycle load tests, the broken wire rate is less than 2%;
2. Static load anchorage performance of cable anchorage: meet the requirements of GB / t14370-2015 anchorage, fixture and connector for prestressed reinforcement. The anchorage efficiency coefficient η a ≥ 0.95, ultimate elongation ξ APU ≥ 2%;
3. Cable saddle structure: adopt the structure of dividing pipe;
4. Anti slide anchor structure: the steel strand is evenly distributed in the anti slide anchorage device, and the anti sliding force is safe and reliable.
5. A variety of reliable waterproof and sealing measures are adopted to meet the requirements of long-term anti-corrosion protection of cables.
6. The length of the cable is cut according to the construction site, without prefabrication, which is convenient for construction.
Anchorage
The anchorage device is generally in the form of steel strand clip anchorage, one end or two ends are set with nuts for cable adjustment, and are equipped with auxiliary structures such as anti loosening device, sealing device and vibration damping device.
Cable body
The cable body of Extradosed cable bridge is mainly composed of several steel strands, which are sheathed with HDPE sheath. The steel strand mainly includes epoxy coated steel strand, galvanized steel strand, epoxy coated unbonded steel strand, etc. our company recommends the use of epoxy coated unbonded steel strand; HDPE sheath can choose smooth round pipe or spiral pipe resistant to wind and rain excitation.
Cable saddle
The cable saddle of wire bundle is used to make each strand evenly distributed, so that the stress is uniform, and it is convenient to replace the single strand in the later stage.
Anti-sliding devices
The steel strand of Extradosed bridge directly passes through the cable saddle embedded in the tower end, and both ends are anchored at the beam end. In order to prevent the cable force imbalance on both sides of the cable saddle, the cable anti sliding anchorage device must be installed near the cable saddle. The anti-sliding devices is set at the end of the cable saddle: one is to pour epoxy mortar and other wrapping materials into the anti slide anchor barrel, so as to achieve the anti sliding effect. The anti sliding force of this method is uniform and reliable, but it is unable to replace the single steel strand in the later stage; the other is to adopt the separate anchoring form which can replace the single cable, and anchor each steel strand by the anti slide key, and then fix it The locking device locks the steel strand bundle to achieve the anti sliding effect.
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. Hanging rope
The prepared steel strands can be hoisted in place one by one and connected with the anchorage respectively.
4. Tension adjustment
It adopts the method of equal tension: a force sensor is installed on the second strand to be tensioned, and the tensile force of other strands is compared with it until it is equal. After all the tensioning is completed, the first strand is tensioned, and finally the single hole tool anchor and force sensor are removed
When it is necessary to adjust the cable force of the whole steel strand, a large tonnage jack can be used to conduct integral tension through the screw nut at the tension end.
5. 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.
6. 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.