How can the structure of the bridge not be damaged during the replacement of bridge supports? Since many bridges built in our country in the 1980s and 1990s (mainly hollow slabs and T-beams), inspections have now found that most The bridge's rubber bearings have become damaged and displaced after years of use. Therefore, rubber bearings must be replaced after being damaged in a certain number of years, and these bridges still bear important transportation tasks. In order to ensure the driving safety of the bridge and the smooth flow of traffic, the old bearings must be replaced under constant traffic. There is no way to replace the rubber bearing using an ordinary jack.
The use of air bag jacks in the bridge jacking process is a newly developed lifting equipment in recent years. The main configurations include: air bag cushions, high-pressure hoses, air pressure diverters, high-pressure air pumps, control systems, and electronic monitoring wait. The airbag jack is made of high-quality rubber steel wire material. The relevant technical indicators are: the maximum design stress is 1.6MPa and the maximum load is 40t. The geometric dimensions of the airbag are: 70cm long, 58cm wide and 3cm thick. Due to its small structural size, especially its ultra-thin thickness, it meets the requirement of small construction space that other jacks cannot meet. Therefore, the "ultra-low height airbag jack" can directly jack up the cover beam and is suitable for hollow slabs. Beam jacking and objects with small jacking clearance. The "ultra-low height airbag jack" not only meets the requirements for jacking directly on the cover beam and having a small jacking gap in terms of structural dimensions, but the stress analysis during jacking construction also fully meets the relevant requirements. In order to ensure the smooth progress of the engineering construction operations and to be aware of the situation, the stress and deformation of the hollow slab were analyzed and mechanical calculations were performed. The focus was on understanding the internal changes of the structure after stress.
The calculation model and parameters take a 30m-span hollow slab bridge as an example to mainly calculate the lateral force of the hollow slab, especially the lateral force of the bottom plate. The analysis and calculation are carried out according to the plane stress model, and the elements adopt 8-node isoparametric elements. The longitudinal force length is conservatively taken as the length of the airbag along the bridge, L - 70cm. For a 30m-span hollow slab bridge, the calculated load is: the self-weight of the beam is 43t, and the second-stage dead load is 9t. The calculation results are calculated through finite element. During the support replacement construction process, the maximum shear stress on the beam body is 1.03MPa. The maximum principal tensile stress of the beam is 5. -3.33MPa, which is greater than the allowable principal tensile stress [d:-] of c40 concrete - 2.34MPa under load combination II in the normal use stage; very close to the allowable principal tensile stress [铳] - 3.38MPa of c40 concrete in flexural components during the construction stage. However, considering that the range where large main tensile stress occurs is small, and the calculation adopts the relatively conservative assumption that only 70cm of the beam in the longitudinal bridge direction participates in the stress, the main tensile stress of the beam during the jacking process is basically within a safe range. . The maximum principal compressive stress S of the beam body. : ==2.73MPa, which is far less than the allowable principal compressive stress of c40 concrete in the normal use stage - 18.2MPa. Therefore, the main compressive stress of the beam body meets the specification requirements.
In order to solve this problem, our company has successfully developed a separate controllable jacking system based on many years of prestressed construction experience and the company's existing technical advantages. This system ensures uninterrupted lifting of the bridge. Under normal traffic operation, do not damage the bridge structure (and do not damage the continuous bridge deck system). Safely and quickly replace damaged supports when traffic is interrupted on one side for a period of time. The system can be divided into a hydraulic separated controllable fully automatic jacking system and a pneumatic separated controllable fully automatic jacking system.
The main steps for the construction process of "ultra-low height airbag jack" are: preparation, jacking test, overall jacking, support replacement, beam positioning, etc. The following is an introduction to a typical project construction. 3.1 Project Introduction A hollow plate girder bridge has 19 beams per span, the bridge deck is 20m wide, the bridge deck pavement is a continuous structure, and the hollow plate girder is a reinforced concrete prestressed structure. The single beam is 0.99m wide, 1.2m high and 30m long. The cross-section of the single-piece beam is a two-box structure. The top and bottom plates are both 20cm thick, the two outer webs are both 10cm thick, and the middle web is 8cm thick. The single-piece beam has a self-weight of 43t. Each beam is equipped with 2 plate-type rubber bearings at one end, and the bearing size is 14cm. ×14cm × 3cm, without support padding. It has been 9 years since the bridge was opened to traffic. The supports were seriously damaged due to excessive vehicle traffic for a long time. To ensure the safety of the bridge, the owner decided to replace the supports.
During the replacement process of bridge rubber bearings, it is necessary to conduct a comprehensive inspection of the bridge's foundation, piers, main beams, deck systems and ancillary projects one by one, and make records and take photos. The diseases existing on the foundation and piers should be treated first, and then the main beams should be treated. If the supports need to be replaced, it will be decided based on the specific conditions of the bridge deck system and ancillary projects whether to retain or completely remove the bridge deck system and ancillary projects; if they need to be retained, the longitudinal connections of each bridge hole must be released in advance and finally carried out. Bearing replacement construction. The traditional construction method requires a lifting bracket to be set up on the available expanded foundation or platform to carry out the operation, but the lifting point should be as close as possible to the original fulcrum. If there is no expanded foundation or cap that can be used, the temporary load-bearing foundation needs to be re-poured, and then the lifting bracket is set up to carry out the operation. This situation mostly occurs in bridge piers or solid pier structures where columns and piles are connected, and it is even more serious when encountering deep water foundations. difficulty.
Based on construction experience and actual conditions, if there is no disease in the pier structure, jacking can be carried out directly under the top surface of the cap beam and the flange plate of the hollow plate beam, but the height of the jack is required not to exceed 3cm. For this purpose, an "ultra-low height airbag jack" can be used. The preparation work is to set up an operating platform at the pier position. For waterless areas, the brackets are set up by using ordinary scaffolding steel pipes and fasteners. For the piers in the water, boats are used to erect the brackets. The strength and stability of the bracket should meet the requirements for operational safety. After the bracket is completed, conduct a comprehensive inspection of each pier support, and make records and numbers. Based on the inspection, determine the location, bridge span and number of replacement supports, and then formulate the best support replacement plan based on traffic conditions. The place where the jack is placed should be cleaned before operation to facilitate the stable placement of the jack and pad. At the same time, determine the backing plate used by the jack. The backing plate should be a steel plate (10mm thick) with a size of no less than 14cm × 14cm. Place it in front of the corresponding plate support and prepare a certain number of thin steel plates or wedge-shaped steel plates to facilitate the installation. During the lifting process of the plate girder, the super pad is wedged tightly. The airbag jack, air pipe, and gate should be subjected to load tests before use to check the effectiveness of each equipment. 3.4 The test can be carried out after the installation of the support frame, operating platform and jack.