1, project overview
A city interchange project adopts a three-story semi-circular ramp overpass, which consists of Zhonghuan Road (called the main line) and three ramps across the subway line, namely SW in the north and ne and WN in the south. The main line is located on the third floor of the overpass, with a length of 204m and a continuous steel bridge. There are four bridge openings, the largest of which is 80m long and 40m wide, the steel box girder is 4m high and the steel bridge is 35m high. There are 52 main copper bridges, weighing 4494t, and 34 tunnel steel bridge paddles, weighing 2450t t.
After repeated analysis and research by experts, the scientific and reasonable installation technology of "longitudinal sectioning, transverse sectioning, temporary pier supporting, double-machine lifting, sectional installation, embedded in the middle (across the elevated section) and extended on both sides", as well as the installation technology of "steel box girder embedded between ramp bridge holes" and carbon dioxide gas shielded welding technology were finally determined. The successful application of these technologies in engineering is not only the progress and development of bridge construction technology.
2. Key technologies and construction difficulties
2. 1 Subparagraph and resource allocation
Sectional hoisting, optimization of transportation machinery and transportation route. As we all know, there is no precedent at home and abroad for such a long bridge with wide deck and integral installation of steel box girder. It is the only way to divide the whole into parts and install them in sections. The scientific rationality of segmentation not only involves hoisting, transportation machinery and transportation roads, but also has great influence on economic benefits. On the premise of investigating the rational allocation of resources and the demand time, place and quantity of social hoisting machinery and transportation institutions, the economic benefits are considered to the maximum extent, and the subsection optimization scheme is determined.
2.2 linear control
According to the design requirements, the steel beam is made according to the pre-camber of quadratic parabola to ensure the pre-camber of the jig before the steel beam falls off the whole jig. According to on-site working conditions, after design review, except P26-27 bridge hole, the other three bridge holes are provided with temporary supports in the middle, and the steel box girder is lifted by hydraulic jacking device to ensure the pre-camber value. Because the installation conditions are different from the original design and manufacture, after analysis and discussion, it is decided to adjust the time limit increment of the other three bridge holes to two-thirds free state, and at the same time control the transverse slope according to the design requirements to ensure the alignment of the whole bridge.
2.3 Design and setting of temporary piers and safety risks
The main line P26-27 has a span of 80m, a deck width of 40m and a height of 35m. The stability of the temporary pier is very high, and the safety risk is great. At the same time, its setting has a great influence on the ground road traffic. It is necessary not only to ensure smooth roads, but also to limit the location and occupied area, to ensure the stability of piers, and to be foolproof. In addition, temporary piers and longitudinal beams are also tools for installation and adjustment. Through field investigation and establishing mathematical model, the temporary pier is designed, which overcomes the difficulty of installing the best of both worlds and the smooth road, and also meets the needs of assembly and adjustment.
2.4 Double-engine lifting, ferry steering and hook changing technology for crossing the elevated road longitudinal beam P26- 1
The heaviest longitudinal beam across the viaduct P26- 1 across the existing viaduct. The length of the bridge hole is 80m and the erection height is 32m. Because the segmented box girder P26 crossing the viaduct cannot be transported or parked on the viaduct, it has to turn 90. Only by considering the safety, reliability and economy of hoisting, after repeated research and planning, a brand-new installation technology of single-machine hoisting, steering and temporary shelving on one side of the existing viaduct is innovated, which is satisfied by the crane on the other side, and the main machine is hooked, hoisted by two machines, swung by two machines and landed, and good practical results are achieved.
Two cranes, CKE2500 and LR 1400, are used for hoisting. LR 1400 crane is responsible for unloading and hoisting to the temporary wharf for shelving. When LR 1400 does not loosen the hook, CKE2500 crane lifts one end of the longitudinal beam, and then LR 1400 crane loosens the hook. At this time, two-thirds of the weight end of the longitudinal beam is temporarily put on hold.
2.5 the transformation of three-dimensional space structure diagram
The steel bridges in the center line are all three-dimensional structures with complex shapes. In order to achieve the purpose of accuracy, intuition and convenience, the spatial structure transformation software of steel bridge is developed by ourselves in the detailed drawing transformation work. The actual results show that the overall dimensions, spatial angles and other aspects meet the design requirements, and provide model data for blanking and assembly process.
3, steel bridge installation technology and technology
3. 1 process
Technological process: axis elevation measurement → supporting steel frame foundation pouring → supporting steel frame erection → hoisting → assembly → welding → inspection → overall inspection application.
3.2 pier and beam installation technology
Pier beam is the benchmark of longitudinal beam installation, and its positioning, longitudinal beam installation and external linear shape of the whole bridge have great influence. Through field investigation, the following measures are determined:
(1) Before lifting the pier beam, check the elevation of the corresponding civil concrete column, the elevation of the bottom bearing of the steel box girder bridge and the relevant dimensions (design size and actual size) of the basin bearing. On the pier bridge deck, mark the axis and road centerline.
(2) Align the vertical and horizontal center lines according to the pier beam positioning requirements with the center lines marked on the pier beam, and keep the pier beam vertical.
(3) After the pier beam is positioned, the road centerline is calculated back to the pier beam, and the elevation of the main points of the bridge deck is measured: a, the road centerline points on both sides; B, four corners on both sides; C, such as the change of cross slope inflection point.
3.3 Installation technology of longitudinal beam
(1) The lifting and positioning of the longitudinal beam in the first section shall be subject to the road center line marked on the pier beam and the longitudinal beam respectively; In addition to aligning the webs, the hoisting positioning of other longitudinal beams should also be aligned with the reference diaphragms of adjacent longitudinal beams.
(2) In the assembly process of the longitudinal beam and the longitudinal beam, the deviation between the panel and the partition is adjusted in a local range by setting the code wheel and using the steel wedge; The large deviation is adjusted by setting jacks and brackets to ensure that the weld spacing and height difference after assembly are within the allowable range. For the large deviation of partition splicing, both sides of the partition are reinforced. Adjust the spacing of longitudinal joints, adjust two longitudinal joints by adopting blue bolts, jacks and other measures, and cut and adjust local deviation to ensure that the joint type of longitudinal joints is consistent with the baseline type.
(3) The hoisting of the longitudinal beam is basically carried out at night; Usually two pieces are loaded every night. In order to avoid the influence of ambient temperature, it is necessary to install the second longitudinal beam after the first longitudinal beam is positioned. When the longitudinal beam is installed, cut and adjusted, the construction environment temperature is close to the temperature when the first longitudinal beam is positioned, so as to avoid generating large internal stress.
(4) Strengthening the on-line measurement of steel beams; All longitudinal beams of each hole shall be erected and positioned, measured before and after jack-up and before and after the overall unloading of steel beams, and timely fed back to designers, so as to strengthen communication with designers, so that designers can master the dynamic situation of steel beam installation, so as to find problems and solve them in time.
4. Technical measures for installation and removal of temporary piers and temporary supports
(1)P26- 1 to 8-span viaduct overhead line's design and setting of temporary steel pier have passed the mathematical model verification, and the vertical load of left and right columns is 23 1.5 tons. The foundation area is 5×6m, and the ultimate bearing capacity is 300t >；; 23 1.5t, meeting the design requirements. The vertical load of the center column is 275.8 tons. The foundation area is 5×9m, and the ultimate bearing capacity is 450t >；; 275.8t, meet the design requirements. The foundation of temporary support has been established. Because there are all kinds of underground pipelines, measures must be taken to protect them. Therefore, a reinforced concrete foundation is set under each pier to protect underground pipelines and pavement. According to the preliminary engineering data, the characteristic value of pavement bearing capacity is 100kN/m2, and the strength check meets the design requirements, so the steel support is made. The foundation of temporary piers on both sides of viaduct shall be constructed according to the design drawings. On the basis of mastering the layout of underground pipelines in detail, it is considered that there is little or no influence on underground pipelines, and other supporting foundations are laid with ballast and compacted, and steel plates with a thickness of not less than 25mm are laid.
(2) 35 days before the installation of the steel pier, the steel pier foundation construction shall be carried out. For the foundation on the traffic road, the asphalt pavement should be roughened to a depth of about 200 mm before construction. If there is uneven ground under other supports, ballast should be laid and compacted to meet the bearing capacity requirements of 100KN/m2.
(3) Steel portal frames spanning both sides of the existing viaduct are assembled into 12m segments in the field, and erection and installation are carried out after the strength of concrete foundation meets the requirements; The steel support under the pier beam is made by the factory, with a cross section of 6m and 8m, and transported to the site for erection and installation. All steel supports (including portal beams) are connected by 10.9 high-strength bolts.
(4) The verticality of steel door posts shall be ensured, the bottom of steel frame shall be padded with foundation surface, and bolts shall be fastened and welded firmly. The steel support is placed on the paved thick steel plate, and small-angle piles are driven around the steel plate and welded. After the steel corbel is corrected vertically, its bottom is welded firmly with the steel plate, and the upper part of the steel corbel is bound with the adjacent concrete column.
(5) Set traffic warning reflective signs around the elevated steel portal foundation (60cm high) of the existing viaduct, and set traffic warning reflective signs on the steel column facing one end of the vehicle.
(6) After the installation of the steel box beam is completed, jack up the bottom of the steel beam with a screw jack at the top of the steel bracket (reserved position during installation), and cut the original stay bar at the same time to check whether it is still stressed. If it is stressed, continue to tighten 1000 kg until it is not stressed and the pillar (about 60cm) is cut off. Loosen the screw jack after cutting the strut. The box girder size with loose jack shall be recorded in the descending process.
(7) All upper sections of steel supports and crossbeams of portal frames shall be hoisted by cranes. Other supports are lowered directly by cranes.
5. Concluding remarks
The development and successful application of this technology has promoted the manufacture and installation of steel structure from building steel structure to municipal elevated bridge project, and achieved great social benefits. It has accumulated experience for the installation of similar projects, and also trained and trained a group of elites of large steel bridges.
The application of steel box girder construction technology of urban overpass above was collected and sorted by Zhong Da Consulting Company.
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