Bridge construction technology

1. Construction of Bridge Substructure

(1) Construction of Integral Piers

① Stone Piers

Lightweight scaffolding includes fixed lightweight scaffolding suitable for piers under 6m and simple mobile scaffolding suitable for piers under 25m; suspended scaffolding can be used for higher piers.

② Concrete Piers

Based on construction experience, fixed formwork is used when the pier height is less than 30m; sliding formwork is commonly used when the height is greater than or equal to 30m. The concrete of piers has its own characteristics, which should be carefully considered during construction. These characteristics are as follows: Pier concrete, especially solid piers, is large-volume concrete; slag cement and pozzolanic cement should be preferred. When using ordinary cement, the strength grade should not be too high.

When the pier cross-section is less than or equal to 100㎡, concrete should be poured continuously to ensure the integrity of the concrete; when the pier cross-section area is greater than 100㎡, appropriate segmented pouring is allowed.

③ Prefabricated piers are suitable for bridges spanning valleys, gentle streams without drifting debris, and riverbanks, especially in areas with frequent construction interference, narrow construction sites, and difficulties in water and sand supply.

④ Driven piles: Common construction methods include hammer driving, water jetting, vibratory driving, static pressure driving, and underwater driving.

2. Construction of Bridge Superstructure

The construction of the bridge superstructure mainly refers to the construction of its load-bearing structure. Common construction methods for bridge load-bearing structures include cast-in-place scaffolding, prefabrication and installation, cantilever construction, rotation construction, jacking construction, moving formwork per-span construction, lateral movement construction, and lifting and floating construction.

(1) Cast-in-place scaffolding.

Cast-in-place construction eliminates the need for prefabrication sites and large lifting and transportation equipment. The main reinforcement of the beam can be uninterrupted, resulting in good overall bridge integrity. The disadvantages are: long construction period, difficulty in controlling construction quality; significant stress loss due to concrete shrinkage and creep in prestressed concrete beams; high consumption of supports and formwork during construction, resulting in high construction costs; and the impact of support erection on flood control and navigation, with potential threats from floods and drifting debris during construction.

(2) Precast Installation Method.

The main characteristics of precast installation construction are as follows:

① Because it is factory-produced, the components are of high quality, which helps ensure the quality and dimensional accuracy of the components and allows for the use of mechanized construction as much as possible.

② The upper and lower structures can be operated in parallel, thus shortening the on-site construction period.

③ It can effectively utilize labor, thereby reducing project costs.

④ Due to the fast construction speed, it is suitable for emergency construction projects.

⑤ After prefabrication, the components need to be stored for a period of time, so they have a certain age before installation, which can reduce deformation caused by concrete shrinkage and creep.

(3) Cantilever Construction Method. The main characteristics of cantilever construction are as follows:

① Cantilever construction is suitable for bridges where the structural stress in the operational state is similar to that in the construction stage, such as prestressed concrete T-shaped rigid frame bridges, variable cross-section continuous beam bridges, and cable-stayed bridges.

② Cantilever casting is simple, has good structural integrity, and allows for continuous adjustment of the position during construction. It is often used on bridges with spans greater than 100m. The cantilever assembly method has a fast construction speed, allowing parallel operation of the upper and lower structures of the bridge. However, it requires high construction precision and can be used on large bridges with spans less than 100m.

③ Cantilever construction requires little or no support, and construction does not affect navigation or traffic under the bridge.

(4) Rotation construction method.

In rotation construction, the static combination remains unchanged. Its support positions are the rotating supports and rotation axes during construction. After the bridge is completed, the support conditions are changed according to the design requirements. The main characteristics of bridge rotation construction are as follows:

① Construction does not interrupt navigation, does not affect traffic under the bridge, and can be carried out on roads that are already in traffic.

② Fewer construction equipment, simpler devices, easier to manufacture and master.

③ Reduces high-altitude work, simplifies construction procedures, and speeds up construction. After the main structure is closed in the early stages, it facilitates subsequent construction.

(5) Incremental launching method

The characteristics of incremental launching method construction are as follows:

① Incremental launching can use simple equipment to build long bridges, with low construction costs, stable construction without noise, and can be used in deep water, valleys, and high piers, as well as on curved and sloping bridges with the same curvature.

② The main beam is prefabricated in segments, allowing for continuous operation and good structural integrity; since large lifting equipment is not required, the length of the construction segment can generally be 10-20m.

③ Incremental launching construction requires a higher amount of steel. ④ The incremental launching method is directly used on beams with uniform cross-sections.

(6) Moving formwork span-by-span construction method

Span-by-span construction is a construction method for medium-span prestressed concrete continuous beams. It uses a set of equipment to construct span by span from one end of the bridge to the other side.

The main characteristics of using moving formwork span-by-span construction are as follows:

① The moving formwork method does not require ground supports, does not affect navigation or traffic under the bridge, and is safe and reliable.

② It provides a good construction environment, ensuring construction quality. A set of formwork can be reused multiple times, which has the advantages of prefabrication.

③ It has a high degree of mechanization and automation, saving labor, reducing labor intensity, and allowing parallel operation of the upper and lower structures, thus shortening the construction period.

③ It has a high degree of mechanization and automation, saving labor, reducing labor intensity, and allowing parallel operation of the upper and lower structures, thus shortening the construction period.