How to perform high-altitude bulk loading of space frame processing structures?

 1. When using small assembly units or members for direct assembly at high elevations, the sequence should ensure assembly accuracy and minimize cumulative errors. When using the cantilever method, the structure should first be assembled into a system capable of supporting its own weight, followed by gradual expansion. During the assembly process of space frame fabrication, the positions of reference axes, elevations, and deviations should be checked at all times, and corrections should be made promptly.

2. When erecting assembly scaffolding, the support points on the scaffolding should be located at the lower chord nodes. The scaffolding should be verified for its load-bearing capacity and stability, and load testing may be conducted as necessary to ensure safety and reliability. Measures should be taken under the scaffolding columns to prevent foundation settlement.

3. During the removal of the scaffolding, individual support points should be prevented from bearing concentrated loads. Based on the structural self-weight deflection values of each support point, the support points should be removed using a proportional reduction method by zone and stage, or an equal-step reduction method with each step not exceeding 10 mm.

Key points for installing steel structures

(1) Friction coefficient: where F is the force measured in the anti-slip test that causes the specimen to undergo initial slip, nf is the number of friction surfaces, and is the sum of the measured values of the high-strength bolt tightening preload corresponding to F.

(2) Torque coefficient: where d is the nominal diameter of the high-strength bolt (mm), M is the applied torque value (N·m), and P is the bolt preload. For 10.9-grade high-strength large hexagonal bolt connections, the average value of the torque coefficient K must be between 0.110 and 0.150. Its standard deviation should be less than or equal to 0.010.

(3) Initial tightening torque: To minimize the influence of steel plate deformation during bolt tightening, secondary tightening can be used to reduce the mutual influence between sequentially tightened bolts. The first tightening of high-strength bolts is the initial tightening, with the axial force preferably reaching 60% to 80% of the standard axial force.

(4) Final tightening torque: The torque used for the final tightening of high-strength bolts is the final tightening torque. Considering various losses of prestress, the final tightening torque is generally 5% to 10% greater than the torque value calculated theoretically based on the design prestress.

Causes of damage to steel structures and reinforcement measures

Steel structures can also sustain damage, and we must identify and address issues promptly. The Steel Structure Network outlines the primary factors contributing to steel structure damage:

1) Insufficient structural load-bearing capacity due to changes in load, prolonged service life, or revisions to standards and regulations;

2) Deformation, twisting, damage, or indentation of components caused by various accidents, leading to reduced cross-sectional area, warping of members, or cracking of connections;

3) Temperature differences causing deformation, cracking, and warping of components or connections;

4) Corrosion and electrochemical corrosion caused by chemical substances, leading to a reduction in the cross-sectional area of steel structure components;

5) Other factors, including design, production, and construction errors, as well as improper use and operation during the service period.

There are three main technical measures for reinforcing steel structures:

1) Section reinforcement method: Reinforce locally or along the entire length of the component with steel, connecting it into a whole so that it bears the load together.

2) Modifying the calculation diagram: Adding additional supports, adjusting the load distribution, reducing internal forces, applying forced displacement to the supports of statically indeterminate structures, and reducing stress peaks.

3) Prestressed cable method: Using high-strength cables to reinforce weak structural components or enhance the overall load-bearing capacity, stiffness, and stability of the structure.