Local welding problem of bolt ball joint space frame (Part 1)

一、A bolt ball joint space frame

Bolt-ball joint space frame is a good structural form, which has the special force characteristics of space structure. Its components are completely manufactured in the factory, the quality is guaranteed, and the transportation and installation are convenient. Is unmatched by any other structure.

Since the early 1980s, this new structural system has been rapidly popularized in China, and has been widely used in various fields of industrial and civil buildings. More than 20 years, our country has developed into a big country of space frame in the world, no matter in the number of completed engineering projects and the total area covered by space frame engineering, created the most in the world.

With the development of computer technology, a large number of space frame structure calculation and aided design software have emerged, which greatly promotes the development of space frame structure production and construction industry in our country. However, in the design and construction process, it is often encountered that the rod “fight”, the roof slope support installation position is not correct, and the process requires the arrangement of air pipes, catwalks, light racks and so on.

Most software development, has not taken into account these details. For a long time, it is customary to adopt on-site welding to solve these problems. However, many people “talk about welding color change”, think that the welding of any part of the screw ball joint space frame is never allowed, and then talk about the local welding of the bolt ball joint space frame.

二、The appearance of large size bolt ball

1、 The size of the bolt ball diameter specification is related to the size of the internal force of the rod. Such as the promotion of bolt ball joint space frame in the early stage, the space frame is more flat, the plane size is more rectangular, the span is 18~30m, the maximum M30 of high-strength bolts, the steel pipe to the middle 114mm, and the ball diameter of 120mm is enough. With the development of national construction, the span and plane size of buildings are constantly increasing. National industry standard JG10-1999 “bolt ball joint space frame”, the bolt is expanded to M60, bolt ball to 260mm; In the national standard GB/ T16999-1997 “High strength bolts for steel space frame bolt ball joints”, the bolts are expanded to M64X4. M68, M80~M125 are used in the high-strength bolts in the actual engineering in China. Of course, this needs to take the corresponding heat treatment process, and some use the advanced alloy steel for aviation.

Due to the increase of internal force, it is normal for the diameter of the bolt ball to increase.But the size of the bolt ball diameter depends not only on the size of the internal force, some are due to the structure, the ball is not only because the rod is large and the bolt is large. The depth of the bolt hole of the high-strength bolt into the ball is >1.1 times the outer diameter of the bolt, and the bolts shall not touch in the ball body; The hexagonal sleeve, sealing plate, cone head and pipe end between the rod members shall not touch each other outside the ball; The bearing surface of the ball hole end face should be large enough. These factors determine the size of the bolt ball diameter.

With the progress of science and technology and the development of construction industry, owners and architects pursue novel and beautiful shapes of buildings. Various architectural shapes require structural design to complete, which makes the form of grid structure more and more complex. Planar, curved, parabolic… . A variety of irregular shapes and shapes, colorful, shiny debut! Some projects appeared in the extra-large ball, such as 400mm, a ball is 263kg! However, it is not because of the large force, but because of the distribution of nodes and the arrangement of bars in the design and modeling, the Angle between adjacent bars on the node is too small, and the large ball is automatically generated by the software. The appearance of the big ball, neither economic nor aesthetic, is a major defect!

3、Due to the needs of construction and use functions, some engineering grids should be equipped with maintenance lanes, some need to arrange air conditioning and fire pipes, and some need to be hung centrally… . Although the added load is considered in the design, the reservation holes of the nodes cannot be generated automatically by the software. A small number of projects will be the horse way, pipe, light bridge and other use in the space frame on the bottom chord, which is not allowed. All loads can only be added to the node, because the rod only bear tension, pressure, it is not bending members, this use and construction personnel must be sober! 

三、The choice of treatment plan

1、Start with the design. In the design and modeling of space frame, it should be considered to avoid the appearance of nodes with too small angle between members. The bearing ball of the upper string support, the abdominal rod will not touch the beam or the pillar, these can not be ignored, otherwise there will be big trouble when installing. After the preliminary design, check whether there is a large size bolt ball. Under the condition of ensuring the safety of the structure and not affecting the use function, adjust the coordinate position of the node and its nearby related nodes until the large ball is adjusted.

2、Some process holes, such as catwalk, air conditioning and fire pipes, large audio and light bridge layout, generally in the lower string space frame two rows of lower string balls, set up support, two volleyball support on the use of steel cross arm, upper ladder and railing.

If Party A or the design institute provides the process diagram, the bolt ball at the corresponding position shall be added with the process top hole during the secondary design, so as to avoid the presence of on-site welding.

Schematic diagram of adding ball handle or welding joint plate

Structure diagram of ball handle