2025-01-08    122

　　When steel structures require strengthening based on reliability assessments, professionals should undertake the strengthening design according to the assessment conclusions and the requirements put forward by the client, adhering to national standards and specifications. The scope of the strengthening design can encompass the entire structure, as well as partial structures, specific members, or components.

　　In steel structure strengthening design, it is crucial to closely integrate the design with the construction methodology. Effective measures should be taken to ensure reliable connections between the newly added sections, members, and components, and the original structure, enabling them to work together as a whole and avoiding adverse impacts on unstrengthened parts or members.

　　Generally, the primary methods for strengthening steel structures include load reduction, altering the calculation diagram, increasing the cross-section and connection strength of original structural members, and preventing crack propagation. When there is proven experience, other methods can also be employed for steel structure strengthening.

　　The method of altering the structural calculation diagram for strengthening involves changing the load distribution, force transmission paths, joint properties, and boundary conditions. Additional members and supports can be added, prestress can be applied, and spatial cooperative work can be considered. Specific strengthening techniques include:

　　1.For the overall structure:

　　⑴Adding supports to form a spatial structure and calculating accordingly.

　　⑵Adding supports to increase structural stiffness or adjusting the natural vibration frequency of the structure to enhance its bearing capacity and improve dynamic characteristics.

　　⑶Adding supports or auxiliary members to reduce the slenderness ratio of the structure, improving its stability.

　　⑷In framed structures, enhancing the stiffness of a specific column to bear most of the horizontal forces, reducing the load on other columns.

　　⑸In tower structures, installing tension rods or appropriately tensioned cables to enhance structural stiffness.

　　2.For flexural members:

　　⑴Altering load distribution, such as converting a concentrated load into multiple concentrated loads.

　　⑵Changing end support conditions, e.g., changing hinge connections to rigid connections.

　　⑶Adding intermediate supports or converting simply supported structures into continuous structures.

　　⑷Adjusting the support positions of continuous structures.

　　⑸Transforming the structure into a strut-type structure.

　　⑹Applying prestress and altering the internal forces within the cross-section for strengthening.

　　The method of increasing member cross-sections for strengthening is broadly applicable and relatively simple to construct. Under certain conditions, it can be performed under load. The primary technique is steel plate bonding. When using this method, the force-bearing conditions of the members and the inherent defects of the structure should be considered. The most effective cross-section connection form should be selected to achieve the desired strengthening effect, facilitating construction.

　　Repair and strengthening of cracks: When structures develop cracks with a tendency to propagate or brittle fracture due to repeated loading, material selection, design, manufacturing, or improper installation, they should be repaired. Before repair, the cause and severity of the cracks must be analyzed, and targeted measures should be taken to improve the actual performance of the structure or strengthen it. Components unsuitable for repair and strengthening should be removed and replaced.