work progress
Wanzhou Second Yangtze River Bridge is located in the lower reaches of Wanzhou main city. The whole bridge is1148.86m long and 20.5m wide. As a suspension bridge, the main tower spans 1 span, 580m, with four lanes in both directions.
Wanzhou Second Yangtze River Bridge is a long-span suspension bridge with large scale, high technical requirements and many restrictive factors. Its design has obvious technical characteristics, with a total investment of 254.87 million yuan.
The project started in 2000 and was completed and opened to traffic in June 2003.
bridgework
Schema principle
According to the terrain, engineering geology and hydrological conditions, and considering the planning, navigation requirements and wiring conditions, the bridge span scheme is reasonably selected, and the scheme selection mainly follows the following principles:
1, which meets the planning requirements of navigation, interchange and wiring.
2. It is novel in structure, beautiful in appearance, economical and practical, and relatively simple in construction. It strives to be significantly different from the Yangtze River Bridge built in Wanzhou District and the "Wan Yi Railway Yangtze River Bridge" in structural form.
3. Reduce or avoid underwater foundation construction, speed up the construction progress and reduce the construction cost.
4. Optimize various design and construction schemes and control project investment and construction period.
In the feasibility study and preliminary design stage of the bridge, a comprehensive study and comparison were made on various bridge span structures. According to the engineering characteristics, the main bridge focuses on the design scheme of suspension bridge and cable-stayed bridge, and the approach bridge is mainly T-shaped simply supported beam with a span of 40 m. Reinforced concrete box arch bridge has been built in the main bridge of Yangtze River Bridge. In order to avoid the similarity of bridge types, this bridge is not compared with similar structures. At the same time, the arch bridge structure will also increase the possibility of ships hitting the arch ring. The topographical characteristics of this bridge are not suitable for the construction of arch bridges, and other bridge types are not suitable in terms of structural stress, spanning capacity and engineering investment. The investment of this bridge project is strictly controlled, and the investment of the main bridge accounts for a large proportion in the whole project. On the premise of ensuring safety, taking practical design and construction measures in combination with the technical characteristics of the bridge will play an important role in controlling the investment of the whole project.
Scheme of suspension bridge for main bridge
According to the topographic, geological and hydrological conditions, the suspension bridge scheme of the main bridge is compared with various span schemes. In order to control the project investment, they are all designed as single-span suspension bridges. The reasonable span selection range of each bridge location scheme is between 500 m and 720 m, and the influence of water storage level and anchorage setting position is the main control condition. For the recommended bridge location, 500 m and 580m span schemes are considered respectively. According to the technical characteristics of suspension bridge and the concrete conditions of the bridge, the rationality of the stiffening beam scheme of the main bridge plays a very important role in ensuring the advancement and rationality of the overall design scheme, which needs to be studied and compared. Considering the performance requirements, construction conditions, construction period, waterway management and other aspects, the stiffening beam adopts the steel structure scheme, and is designed according to the overall segmental manufacturing and site segmental erection connection scheme. Flat steel box girder, steel truss girder and space steel tube truss are adopted in the design.
(1) The flat steel box girder stiffening beam is widely used in the design of long-span suspension bridges at home and abroad, with mature technology, good structural integrity, small wind resistance, good aerodynamic stability and light overall weight of the superstructure, which is beneficial to the effective control of other related engineering quantities. However, the overall steel consumption of steel box girder is large, and the unit processing and manufacturing cost is high. Therefore, we should also attach great importance to the cracking, complex construction and high cost of the corresponding bridge deck pavement.
(2) Steel truss beam is also a commonly used stiffening beam structure for suspension bridges. When applied to the design of this bridge, the amount of structural steel is much lower than that of steel box girder, and the unit manufacturing cost is obviously lower. Although the overall weight of the superstructure is greater than that of the steel box girder scheme, the related workload increases, but the bridge is planned to adopt tunnel-type anchorage structure, and the proportion of anchorage in the total workload and investment is relatively limited, compared with the gravity-anchored suspension bridge. The steel truss beam scheme has good application conditions in this bridge, and it is also of great benefit to control the cracking of deck pavement, and the technical requirements of its pavement are far lower than those of the steel box beam scheme, so the construction is relatively simple and the cost is low.
(3) Space steel tube truss has good aerodynamic performance, and its structural steel consumption is obviously lower than that of steel box girder and steel truss girder. Considering the reasonable control of the main technical and economic indexes of this bridge and the development of bridge technology, this scheme is studied and compared as the main recommended scheme in design. Based on the application of other steel tube truss bridges, hollow steel balls are used to realize ideal articulation. The complicated numerical control cutting process of the spatial intersection of components is avoided, and the secondary stress of components is small, and the processing and manufacturing are simple. At the same time, structural treatment measures are taken to further improve the local stress situation of the joints. In order to strengthen the overall stiffness of the structure, it is planned to connect the bridge deck with the grid structure as a whole, participate in the overall stress and deformation requirements of the structure, and improve its performance index conditions.
The main cable adopts prefabricated galvanized parallel steel strands, which are horizontally arranged outside the sidewalks on both sides. The center distance between two cables is determined according to the structural requirements. In order to ensure the reasonable spacing control requirements between anchors, the main cable is set with a certain outward horizontal deflection angle. Through the comprehensive comparison of stress, deformation and material consumption of structures with different rise-span ratios, it is determined that the rise-span ratio is110.5, and the main cable is adopted. Technical and economic comparison is made between two schemes of prefabricated galvanized parallel steel wire bundles and steel wire ropes, and the prefabricated galvanized parallel steel wire bundles are determined, and the suspender spacing is reasonably determined according to the stiffening beam scheme and structural characteristics. Generally, 7 ~ 13m is adopted, and the safety factor of suspenders is k ≥ 3.0. Hot-cast anchorage is used for anchorage connection of large cables and suspenders. The cable clamp, cable saddle and connecting sleeve are all made of cast steel, in which the cable clamp is two-piece and connected with high-strength bolts during installation. In order to control the transportation and hoisting weight, the cable saddle is divided into two halves and then assembled at the top of the tower. According to the requirements of stress and deformation control, vertical tension and compression bearings and horizontal wind-resistant bearings are respectively arranged at the end of the main bridge.
The bridge tower adopts reinforced concrete portal frame structure, and the tower height of each scheme is about130 ~170 m. According to geological conditions, the foundation adopts bored pile foundation. In order to effectively control the project investment and consider the topographic and geological conditions, this bridge adopts tunnel anchorage, but the influence of groundwater and water storage must be considered. In order to prevent rock cracks and joint surfaces from softening due to seepage, strict waterproof measures should be taken accordingly. Relatively speaking, for the same bridge site, the use of large span can effectively improve the stability conditions of anchorage, but the corresponding upper engineering quantity and investment will be greatly increased.
Scheme of main bridge cable-stayed bridge
Various span combinations of cable-stayed bridge schemes of the main bridge are comprehensively compared at each bridge position. According to the topographical and geological conditions, except Yuanjiadeng Bridge site, all of them are cable-stayed bridges with three towers and four spans, and the reasonable selection range of main spans is between 380 m and 500 m. The bridge adopts spatial double cable planes and fan-shaped dense cable systems, and the cable spacing on the bridge deck is generally about 8 m. The stay cables are parallel steel wire bundles composed of galvanized steel wires, protected by PE materials and anchored by cold cast piers. The stiffening beam adopts prestressed concrete structure and spatial floating system. The section forms of side girder and double box girder are compared comprehensively. According to different spans, the height of the beam is 2.5 ~ 3.5 m, and a detailed comparative analysis is made on whether to set up side span auxiliary piers. The bridge tower is a gem-shaped reinforced concrete structure, and the upper part of the main tower beam is in an "A" shape. The tower height of different schemes is between 2 10 m ~ 230 m, and the building height is very high. The foundation adopts bored pile foundation.
Approach bridge design
According to the topography, geology and construction height of the bridge, in order to facilitate the design and construction, and control the project investment and construction period, prestressed concrete T-shaped simply supported beams are generally used in the approach bridge in each bridge span arrangement scheme, and the span is considered as 25m ~ 40m. The approach bridge pier is a double-column pier, and the abutment is generally designed as a U-shaped abutment or ribbed slab abutment. When the abutment is too high, special research is needed, and the foundation is bored pile foundation. In addition, for the scheme that the main bridge is a single-span suspension bridge, the length of the approach bridge is longer and the construction height of the bridge is very high. Combined with the terrain characteristics and geological stability conditions, the corresponding long-span continuous structure schemes are also comprehensively studied and compared in the design, which provides a scientific basis for scheme decision.
Precast components are mainly used for the carriageway slabs and sidewalk slabs of the main bridge and approach bridge to speed up the construction progress and facilitate the construction quality control; According to local engineering practice, in order to prevent pavement cracking, steel fiber concrete is used for bridge deck pavement, and sawing is needed after pavement construction; In order to ensure the beautiful appearance and control the project investment reasonably, the sidewalk railings and lampposts are all made of steel structures, and the materials are made of composite steel pipes. The surface layer is made of stainless steel, and the inner layer is made of ordinary steel to meet the relevant stiffness requirements. The special requirements of landscape lighting are considered in the investment. According to the requirements of the navigation demonstration conclusion, consider the specific requirements of beacon light setting, harbour superintendency administration and waterway management; Limited by mountainous terrain and other conditions, the connection conditions are very difficult and there are many restrictive factors. In the design, the schemes of grade crossing and interchange are compared comprehensively.
technology standard
1. Road type: urban expressway.
2. Driving speed: 60 km/h
3. Design load: automobile-level 20 or above; Check the load: trailer-120
4. Bridge deck width: 15m+2 × 3m+ (bridge structure width)
5. Longitudinal slope and transverse slope of bridge deck: the longitudinal slope is ≤ 3%, and the transverse slope is 2% of the outward two-way transverse slope.
6. Navigable water level: Calculate the backwater of the bridge site according to the normal water level of the Three Gorges Reservoir.
7. Navigation standard: Class I channel, with a clear height of 24m and a clear width of 300m.
8. Earthquake intensity: ⅵ degree. Considering that this bridge is a special key bridge, it is fortified at VII degree.
9. The Beijing coordinate system and the Yellow Sea height system are adopted in this project.
Important significance
This bridge is a suspension bridge with a super bridge tower. The project started in 2000 and was completed and opened to traffic in June 2003. Wanzhou is the largest immigrant city in the Three Gorges reservoir area. The completion and opening of the Second Yangtze River Bridge in Wanzhou is not only beneficial to the development of Wanzhou city, but also beneficial to the production and life of immigrants in the Three Gorges reservoir area.
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