Construction of Long-Span Truss Structure ( Part 2)

The same weld should be welded continuously at one time, if it cannot be completed at one time, it should be preheated before welding. When welding, symmetrical welding is adopted, and the parts with large deformation are welded first, and the welding sequence cannot be concentrated, and welding is skipped at intervals between nodes. Each node is welded symmetrically, and the interlayer temperature is strictly controlled. Balance the heat to reduce deformation . For example, the three splicing points of the truss are welded from the middle to the two ends. First, the welding is applied to the chords at the same time, and then the rods and oblique rods are welded to minimize the structural welding deformation and post-weld residual stress.

The secondary welds and intersecting joint full-penetration welds required by the design shall be inspected by ultrasonic flaw detection. For those that do not meet the requirements, according to the position and depth of the defect, use grinding wheel grinding or carbon arc gouging to remove the defect. If there is a crack, Drill holes at both ends of the crack first, and remove the 50mm long base metal at both ends of the crack. The preheating temperature of welding repair is 25°-50°C higher than that of welding under the same conditions, and the reworked welding part should be completed at one time. For the same part, no more than 2 welding repairs are required. After rework, the flaw detection test should be carried out again to confirm that it is qualified.

（5）Bolt connection: flat washers should be placed under the bolt heads and nuts of permanent bolts, there should be no more than 2 washers under the nuts, and no less than one washer under the bolt heads; the bolt heads and nuts should be in close contact with the surface of the structural member and the washers. For the bolt connection on the inclined surface, the inclined gasket should be used to make it flat, so that the head bearing surface of the nut and the bolt is perpendicular to the screw rod, so as to avoid the screw receiving bending force when the bolt is tightened; the permanent bolt and anchor bolt should be in accordance with the construction drawings According to the design regulations in , use nuts or spring washers with loosening devices; the grade and material of the bolts used should meet the requirements of the construction drawings.

（6）Bolt ball joints: Bolt ball connections are composed of bolts, steel balls, screws (or pins), sleeves and cone heads (or sealing plates). It has the characteristics of strong node adaptability, high degree of standardization, and convenient installation and transportation. It is beneficial to the standardized design and industrialized production of the truss, improves the work efficiency, and can also be connected with multiple rods, the nodes are not eccentric, and the force is good. Its disadvantage is that the structure is complex and the amount of machining is large. It has been widely used in engineering.

5 hoisting components

5.1 Overall lifting: For large-span truss structures, due to their large components and heavy weight, the double-machine lifting method is usually considered during hoisting. During the construction process, both sides of the truss must be reinforced, otherwise it may be due to When turned into place, a lateral horizontal bending moment is generated, thereby causing lateral instability of the member. If the single-span mid-span hoisting method is used for construction, due to the application of the balance beam, multiple places in the truss are stressed vertically, thereby avoiding the tendency of horizontal stress in the truss, so many reinforcement measures can be omitted.

5.2 Overall lifting

Different from overall lifting, jacking is to place the lifting equipment directly under the support of the truss. The lifting equipment generally uses a large-tonnage jack. This hoisting method is usually suitable for four-point or six-point support trusses. During the lifting process, each column concentrates a large load, so for safety reasons, the rated load capacity of the construction needs to be multiplied by a reduction factor. Because it can install roof panels, purlins, suspended ceilings, ventilation, and electrical equipment in advance, it also reduces a lot of construction costs and has also been widely used.

6 Coating construction and seismic design:

6.1 Coating specifications: In order to implement and implement national safety production guidelines, policies and regulations, ensure the safety of architectural coating construction operations, and prevent construction accidents .

After completing the basic assembly of the structure, use a grinder to derust the damaged coating layer and welded joints on the steel pipe to st3 level, and then apply anti-rust paint. After the coating is finished, use a thickness gauge to check, and check visually and manually. The color and appearance (smooth surface, no obvious depressions, firm bonding, no loose powdering, and mastoids) must meet the requirements of the specification.

6.2 Anti-seismic design: Due to its light weight and good rigidity, the space frame structure suffers less earthquake damage than other types of structures. However, from the experience of other countries and regions, there are a few points that must be paid attention to:

(1) Special attention should be paid to the design and construction of the supporting part. Quite a few earthquakes are caused by the failure of supporting bolts or foundations .

(2) Maintain the shock resistance of the roof ceiling and suspended objects to avoid their collapse and affect the use of the entire truss structure.

Compared with the space frame, the truss has fewer rods, beautiful joints, and no large ball joints. Using the long-span space truss structure, various light and long-span structures can be built. In public civil buildings, especially In the construction of large-scale exhibitions and sports venues, it has the development prospect of extensive promotion and application.