With the construction technology of crawler hydraulic inverting bridge formwork gradually being applied in the construction of bridges, the construction method of walking type pushing method has also paid attention to the field of bridge construction. Therefore, Xiao Bian expounds the characteristics of the crawler type push-pull construction technology in this paper, and focuses on the application of its construction technology in bridge engineering, and hopes to provide some reference for the peers.
First, the crawler hydraulic inverting bridge formwork push-push construction characteristics
1. Simple and flexible: The push-up method can use a simple device to build a long-span large-scale bridge. The construction cost is low, the construction is smooth and noise-free, the key is quick and flexible, which greatly saves labor cost and time. In addition, this method can be It is used on water depths, valleys and high bridge piers, and can also be used on curved and sloped bridges of the same curvature.
2. The main beam segment prefabrication: continuous operation, structural integrity.
3. Pushing method requirements: Segment beam construction is fixed in a site prefabrication, which is conducive to improving construction conditions and facilitating construction management. In addition, prefabricated stencils and equipment can be used multiple times, greatly shortening the prefabrication cycle of the segments.
4. The stress state of the segment beam changes greatly during the push-up construction, and one of the fracture risks is overcome when designing the beam section and the cable is laid, but it is easy to increase the amount of steel used and add cost. Therefore, measures such as adding temporary piers and setting front guide beams are taken during construction to reduce the internal force of the construction.
5. The push method should be used on the beam of equal section to save the amount of materials, reduce construction costs and difficulty.
Second, the two main ways of walking type push construction
1. Single point push construction
The so-called single-point push-push construction is to concentrate the thrusting device on the abutment or pier near the main beam prefabrication field, and set the sliding support on each fulcrum of the front pier. The slide supports a concrete block disposed on the pier, which is composed of a smooth stainless steel plate and a combined Teflon slider, wherein the slider is composed of a PTFE plate and a rubber block having a stiffened steel plate. When pushing, the combined PTFE sliding steel plate slides on the front and slides out in front. By continuously feeding the slider behind the chute, the beam body is advanced.
2. Multi-step step-type push construction
The so-called multi-point pushing construction is to install a pair of small tonnage horizontal jacks on each pier to distribute the concentrated top thrust to each pier. Considering the frictional resistance generated on the pier by the counter-balanced beam body transmitted to the abutment by the horizontal jack, the pier is subjected to a small horizontal force during the pushing process, so multiple points can be adopted on the flexible pier. Pushing construction. Due to the small tonnage of the equipment required for multi-point pushing, it is easy to obtain. Therefore, in recent years, the prestressed concrete continuous beam bridge constructed by the top pushing method in China has adopted the multi-point pushing method and multi-point pushing.
Third, the problem that needs attention when pushing construction
1. Determine the segment length and prefabricated field layout
The prefabricated field is the site for precast box girder and jacking transitions, including the casting platform and formwork for the main beam section, the processing site for steel and steel cables, the concrete mixing station, and the stacking of sand, stone, cement and transportation routes. If the embankment has been completed in advance, it is more reasonable to arrange the steel bar processing and material stacking. In addition, the jacking transition site needs to be arranged with a jack and a slip device, because after the main segment beam is prefabricated, the segment needs to be pushed forward, and the pouring platform is vacated to continue pouring the next segment, so before reaching the main span To set the transition hole, and determine the split hole and length by calculation; if there is a guide hole before the positive bridge, you can use the approach bridge as the push hole for the push.
2. Prefabrication of the section
The prefabrication of the segment determines the construction quality and construction speed of the bridge. The prefabrication work is generally fixed at one position for periodic production. The box girder template is composed of the bottom mold side mold and the inner mold. Generally, the top push method is used for construction. Section beam, template can be used for multiple turns. Therefore, it is advisable to use steel formwork to ensure the accuracy of prefabricated beam size. The prefabricated formwork structure is related to the construction method. One method is to install the section after the precasting of the precast yard. The stress ribs are pushed out to the prefabrication field; the other is to complete the casting of the bottom plate in the prefabrication field, and the prefabricated field is pushed out after the tensioning part of the prestressing tendon is pulled, and the construction of the web top of the box girder is completed on the transition hole; Or the bottom plate and the web are prefabricated for the first time, and the top plate portion is prefabricated for the second time.
3. The mastery of the walking type top thrust
The fulcrum reaction force at the top of the pier is the fundamental factor determining the magnitude of the thrust. The thrust of each jack is determined by the reaction force and friction of the top fulcrum of each pier. These parameters can be reflected in the form of the oil gauge. When adopting the push-up method of continuous push-up jacks, it should be calibrated according to the position of reasonable design. For large bridges, it is generally one pier, one station and two tops. All the pump stations are controlled by the main control station to ensure simultaneous operation and individual adjustment. . In addition, in order to ensure that the thrust can be properly seated, lateral guidance during construction must also be considered. The part of the prefabricated beam section that has just left the prefabrication field and the pier of the foremost end of the thrusting construction is the lateral guiding jack which mainly controls two positions in the jacking construction.
Therefore, it must be ensured that the guiding position of the front end of the beam is constantly changing position with the advancement of the pushing beam to prevent the position from being displaced. Also, the observation of the displacement must be taken care of in the step-by-step pushing process to prevent the offset from affecting the construction quality. The horizontal offset of the pier top and the midline offset of the beam body will affect the observation of the displacement. The method is to calculate the maximum deviation value according to the design allowable range, and then calculate the coordinate to observe the moving range of the beam body after the force is applied. When the maximum offset value is reached, stop immediately and re-adjust.