Construction method of Chinese prestressed concrete bridge

China's prestressed concrete bridges are generally prefabricated or prefabricated, and the composite beams are sometimes partially prefabricated and partially cast. The prefabrication field is usually located at the bridge head. For example, the prefabricated yard built in Shanghai in 1969 uses prestressed anchors to prefabricate the medium and small span prestressed plates and beams. When the transportation between the construction site and the prefabrication plant is inconvenient, if the pre-tensioning method is used, the pedestal should be set at the bridge head. For example, the prefabrication work of the Yongding River hollow slab bridge in Beijing in 1966 is carried out by using the long-line pre-tension method at the bridge head.

The post-tensioned T-beam is usually produced on site and hoisted with different lifting equipment. The weight of the beam is the largest and the work of the girders is more complicated. The commonly used guide beam method is to pass the precast beam between two guide beams and to position the beam by lateral slip. Some bridges are hoisted with gantry cranes. For example, the Jilin Fusonghuajiang Bridge built in 1973 and the Hebei Xinyihe Bridge built in 1978 are all constructed by this method. Individual bridges are constructed using floating cranes or bridges.

Large-span T-shaped rigid frame bridges, cantilever beam bridges, continuous beam bridges, truss bridges or inclined bridges are generally constructed by cantilever construction, block precast suspension or segmented cantilever casting. The prefabricated hanging method was first used in the Yanhe T-shaped rigid frame bridge in Jiangsu in 1964. A special cantilever crane was designed, but it was applied only on the cantilever of one pier, and the cantilever crane on the other pier was assembled. Steel frame is assembled. The hoisting machine assembled with the steel frame is easy to manufacture and can also accomplish the task. Segmented cantilevering uses a hanging basket as the active scaffolding, supports the hanging basket on the completed beam section, and then vertical molds and concrete. In 1968, this method was first used on the Liuzhou Bridge and has since been improved. Whether the smashing method or the hanging method is completed, after the completion of a beam section construction procedure, the next beam section is moved until completion. For the simply supported systems such as cantilever beam and continuous beam, the temporary fixing measures of the support are required. Firstly, the cantilever assembly or cantilever casting method is used. The structural system is constantly changing during the construction. Finally, the fixed structure is completely dismantled and converted into the cantilever beam of the simply supported system. Or continuous beams.

The Yanhe Bridge hoisting is to first install the prefabricated block on the ship and then lift it from the ship; the asbestos Dadu River Bridge is assembled by cable, and the prefabricated block is lifted by the temporary cable with a span of 200m, and the block weight is 20-30t.

The medium-span continuous beam can be made into equal-height beams and constructed by the push-up method. In 1977, the Dongguan Bridge in Guangdong adopted the single-point push method. In 1981, the Hunan Minjiang Bridge adopted the multi-point push method. The push-up method is to pre-manufacture the beam at the bridge head, and push the edge while pushing, so it occupies a small area. In order to avoid the overhanging of the cantilever during the pushing process, the steel guide beam is installed on the front side of the first block to make it reach the fulcrum first. The push point of the single point push is concentrated on one pier, and the other points are provided with sliding devices. The multi-point push is to push the water jack on a number of piers for pushing. The Baotou Yellow River Bridge is constructed by multi-point pushing method with temporary piers in the middle.

The prefabricated T-beams of the same height are first mounted on the pier as simple supports, and then connected with prestressed steel bars at the adjacent two ends to resist the negative bending moment and form a continuous beam of several holes. This method is called a simple and continuous continuous construction method. For example, the Hebei Weihe Bridge, built in 1978, can function as a continuous beam under a part of dead load and live load.

Supporting the No. 4 Bridge in Mosul, Iraq, the 12-hole continuous beam is constructed by moving the sliding template of the moving bracket to the cast-in-span, which ensures the continuity of the concrete and the steel. Bridges with short bridge spans and short lengths have also been constructed by assembling a fixed continuous rack in the full length range for hanging.

The Sichuan Jinchuan Diagonal Bridge was successfully constructed by the horizontal swivel method in 1980. The structure weighed 1360 tons. Using the topographic conditions of the bridgehead, the beam was prefabricated on a simple support and then rotated across the river. The method is simple, and there are few construction equipment such as materials and anchors.

The shore part of the bridge is cast in a simple bracket, and sometimes it can be easily, materialized, reduced in equipment and cost.

Guangdong and Fujian provinces have floating crane equipment, and prefabricated beam sections can be installed by floating crane. In 1982, the continuous beam bridges of Rongqi and Xilu in Guangdong were constructed by large-scale prefabrication and floating crane installation. The lifting capacity is up to 500 t, which can eliminate many seaming processes. Due to the proximity of the bridges of several bridges, the use of centralized prefabrication saves a lot of equipment.

As mentioned above, there are many types of construction methods for prestressed concrete bridges in China. Especially after the success of the cantilever assembly experiment of Yanhe Bridge in 1965, methods such as overcasting, pushing, turning, bracket moving, and large floating cranes were successively produced. develop rapidly. The high pier and the pylon can be constructed by sliding mode. The box girder is constructed by the internal sliding mode method, and the construction speed is greatly accelerated. When determining the construction method, comprehensive consideration should be made based on climate, terrain, bridge span, bridge type, transportation and equipment conditions to determine economic and applicable construction methods.

The construction method of modern prestressed concrete road bridges must be considered before design. During the construction process, the system is continuously converted. For example, the Lanzhou Yellow River Bridge is continuous after the cantilever, and it is divided into two spans and four spans in succession. The Weihe Bridge is first supported simply and then continuously; when the Dongguan Bridge is pushed, before and after pushing, there is 24 structural state diagrams, each of which must be calculated separately.