Accidents involving steel structures in construction projects can be classified into several types based on the form of damage: steel structure instability, brittle fracture of steel structures, failure of steel structure bearing capacity and stiffness, fatigue failure of steel structures, and corrosion failure of steel structures.
- The instability of steel structures mainly occurs in axial compression, compression bending, and bending members. It can be divided into two categories: loss of local stability and loss of overall stability. The main reasons that affect the local stability of structural components are:
① Unreasonable reinforcement rib construction measures for local stress areas. When there are no supporting reinforcement ribs in the local stress areas of the component, such as supports and large concentrated load points, the external force is directly transmitted to the thinner web plate, resulting in local instability. If there is no transverse partition set at both ends of the component transportation unit and in the middle of the longer element, it is difficult to ensure the geometric shape of the cross-section remains unchanged and it is easy to lose local stability
② Improper selection of lifting point position during hoisting can cause significant local compressive stress on the component, leading to local instability. Therefore, during the construction of steel structures, the construction plan should provide detailed instructions on the correct lifting methods and lifting point positions.
③ When the local stability of the component does not meet the requirements, such as the width to thickness ratio of the flange and the height to thickness ratio of the web plate of the I-shaped and groove shaped sections of the component being greater than the limit value, local instability is prone to occur; Special attention should be paid in the design of composite section components.
- The main reasons that affect the overall stability of structural components are:
① Components have various initial defects, and in the stability analysis of components, the impact of various initial defects on their ultimate bearing capacity is relatively significant.
② The temporary support system for construction is insufficient. During the installation process of the structure, some temporary support systems need to be set up to ensure the overall stability of the structure or components, as the structure has not fully formed the required load-bearing whole or its overall stiffness is weak.
③ Changes in the stress conditions of steel structures, such as overloading, node failure, temperature changes, uneven settlement of foundations, unexpected impact loads, and changes in calculation diagrams during structural reinforcement, can cause an increase in stress in compression members or transform tension members into compression members, resulting in overall instability of the members.
④ The main parameter affecting the overall stability of the component that does not meet the requirements is the aspect ratio. Attention should be paid to the possible differences in the calculation length between the two main axis directions of the load surface, as well as the differences between the actual support situation at both ends of the component and the calculation support.
