Key Technology of Welding Construction of Large Span Hangar Space Frame

 Due to its special use function, the hangar has extremely high requirements on space and force. The current design scheme mostly adopts the welded ball space frame with a large span, good force, and low self-weight. Ground assembly and overall lifting are the most commonly used lifting methods for large-span welded ball space frames. Therefore, controlling the quality of the ground scattered welding and the welding quality of high-altitude supplementary rods is the key to ensuring the safety of the construction space frame structure.

1 Project overview

1.1 General overview of the project

Air China Base Project No. 101 Maintenance Hangar Project is located in Chengdu Tianfu International Airport. The building covers an area of 20,562 square meters, with a total construction area of 28,447 square meters and a total building height of 37.65 meters. A330 series aircraft are parked side by side, which can guarantee the warehousing maintenance of A350-900 and take into account the warehousing of A350-1000

1.2 Overview of the space frame structure The roof space frame of the hangar hall is composed of a 3-layer welded ball structure, which is a diagonally placed quadrangular pyramid unit, with a height of 6m, 1872 welded balls, a maximum diameter of 800 mm, 7125 rods, and a maximum wall thickness. 40mm, the total steel consumption is about 2 000 t, and the whole space frame is fixed on the top supports of 25 concrete space frame columns through embedded parts. Since the span of the hangar reaches 146m, the gate area is designed as a steel pipe truss structure system with prestressing. The height of this part of the space frame is 13m, and there is a height difference of 3.5m above and below the space frame in the hangar hall. The facade form is shown in Figure 1

1.3 Overview of space frame installation process

The space frame will be installed in the way of "in-situ assembly and overall lifting", that is after the overall assembly and welding of the hangar hall and the large la-J2 area space frame are completed on the ground, 17 TLJ-600 The lifting system is composed of the TLJ-2000 hydraulic lifter lifts it to the support point as a whole. Since the lower part of the space frame in the truss area of the hangar gate is 3.5 m lower than the space frame in the hangar hall, it is necessary to lift the hangar to the position of the support point. After the hall area is assembled, it is first lifted to a height of 3.5m, and the second assembly with the gate truss area is completed before the overall lifting.

2 Analysis of the difficult points in the quality control of space frame welding

1) The plane size of the hangar space frame is 146 m × 90 m, which belongs to the large-span roof steel space frame system, with a large number of ball joints, chords, webs, and other components, and a large amount of assembly and welding works.

2) Since the gate area of the space frame is a steel pipe truss system, there is a height difference of 3.5 m with the hangar hall, so it is necessary to connect with the gate truss area in the air under the stress state after the first lift of the hangar hall area, which is easy to occur. Welding stress concentration, space frame deformation, etc.

3) The overall lifting quality of the space frame is close to 2000 t, which is prone to quality problems such as overall downward deflection, rod deformation, or weld cracking.

3 The control points of the space frame assembly and welding stage Considering the characteristics of the space frame welding deformation, the entire space frame is divided into 9 parallel sections, namely the hangar hall A to H area and the gate truss area J. The width of a single section is 18 m. Specifically as shown in Figure 2. The two areas of the hangar hall and the gate truss are separately welded by random welding. The final assembly forms 2 separate areas. Among them, the areas A-G of the hangar hall start from the two sections A and B in the middle, and are welded parallel to both sides by two teams, which is not only conducive to the precision control of each area but also conducive to the release of welding stress.

According to the assembly sequence of the space frame, determine the welding sequence of "from the inside out, first down and then up, free shrinkage, error adjustment, single-pole double-welding, double-pole single-welding". Arrange a double number of welders to perform symmetrical welding on any plane (space), to avoid deformation of components caused by welding stress to the greatest extent, the bottom welding of the entire node should be welded first, then the filling welding of the entire node should be welded, and finally, the welding should be applied. The cover welding of the nodes makes the stress of each layer have a free release process.

Specifically, starting from the middle of the structure, arrange double-numbered welders to perform bottom welding to the symmetrical rods at both ends, and then arrange double-numbered welders to weld horizontal web rods to both ends from the middle of the structure as the starting point. After the bottom welding is completed, the above sequence is repeated to fill and weld the structure. After the filling is completed, the above sequence is repeated to cover the structure. At the same time, during the welding process, referring to the node deviation of adjacent small splicing units, appropriate compensation is made according to the law of welding shrinkage to reduce the deviation value and avoid error accumulation.

The welding sequence is to weld the lower chord weld first, then the upper chord weld, and finally the web and lower chord ball weld. To ensure the welding quality of the space frame, the project department optimized the inspection to 100% of all welds based on the original design of 100% inspection of the first-level welds and 10% of the second-class welds.