In recent years, the application of space steel structural engineering has become increasingly widespread in the construction industry. Steel structural factory buildings are one of the primary factory forms chosen by many enterprises for production. Due to historical reasons, a large number of "three non-" steel industrial factory buildings—those without formal design, construction, or supervision—are in use, posing significant structural safety hazards. To ensure the structural safety of factory buildings, the structural safety assessment work has become particularly important in response to this phenomenon.

It is widely known that the main issues with steel structures are centered around the stability of the upper structure, the strength of the components, and the stability of the foundation. We approach these three points together, combining them with the order of the identification work to understand their importance in the safety assessment of steel structure factories from the surface to the profound. 1. Structural Stability: In accordance with the normal sequence of identification work, we first conduct a detailed survey of the overall structural layout and overview of the factory based on the drawings. We check if the structural form used in the building conforms to the design drawings and national specifications, if the force transmission path is clear, if the structural layout is reasonable, and if the support system is complete and meets the specification requirements for slenderness ratio. All these factors relate to the stability of the structure. Structural stability has always been a major issue with steel structures, and once instability occurs, it not only leads to significant economic losses but also easily causes severe personnel injuries. Therefore, it is crucial to understand the basic concepts of structural stability, as only then can we better identify and address issues of structural instability in the safety assessment of steel structure factories.

1. Structural Stability: In accordance with the normal sequence of identification work, we first conduct a detailed survey of the overall layout and overview of the factory building based on the drawings. We inspect whether the structural forms used in the buildings comply with the design drawings and national specifications, whether the force transmission routes are clear, whether the structural layout is reasonable, and whether the support system is complete and meets the specification requirements for slenderness ratio. All these factors are related to the structural stability. Structural stability has always been a major issue in steel structures. Once a steel structure instability incident occurs, it not only results in significant economic losses but also easily causes severe personnel injuries. Therefore, we must understand the basic concepts of structural stability, so that we can better identify and handle steel structure instability issues in the safety identification work of steel structure factories.

The stability of steel structures can be divided into two types: the overall stability of the structure and the inherent stability of the components. The overall stability in the longitudinal direction of the structure mainly relies on the support system, such as the inter-column supports of steel columns, the horizontal and vertical supports of steel trusses, and so on. The reliability of the support system in transmitting the horizontal loads (wind loads, seismic loads, crane loads in workshops, etc.) in the longitudinal direction is crucial. In the lateral direction, it depends on the stiffness of the structure itself (frame or bays), so the main consideration is whether the structure can reliably transmit lateral horizontal loads. The inherent stability of the components is mainly ensured by the stiffness of the component parts, ensuring that the components and their components (beams or plates) do not buckle under load and lose stability (this situation mainly occurs in compression or bending components). Therefore, the stability factors of the components mainly include the calculated length and cross-sectional characteristics of the components, including both in-plane and out-of-plane directions. Of course, the strength and stress magnitude of the material should also be included. It primarily identifies the unstable equilibrium state between external loads and the internal resistance of the structure, i.e., the state where deformation begins to increase sharply, and aims to avoid entering this state. Therefore, it is a deformation issue. For example, in an axially compressed column, due to instability, lateral deflection causes a significant increase in bending moment within the column, resulting in the failure load of the column being much lower than its axial compression strength. Clearly, the axial compression strength is not the main cause of column failure.

In structural stability inspections, focus is primarily on the following key aspects: ① The quality of high-strength bolt connections in factory components, verified by total station measurements for the bolt thread external leakage. ② The quality of welding connections in factory components, assessed by ultrasonic testing to determine the weld quality grade in compliance with standards. ③ The deflection deformation of factory components, measured by leveling instruments or stringing methods to determine the deformation amount.

2. Component Strength: After addressing the stability issues of the structure, the next concern is the strength of the components. We must adopt different modern testing technologies based on various structural forms to obtain the necessary structural functional parameter indicators. For instance, when the column is made of reinforced concrete, we use core drilling, rebound, and rebound plus core strength correction methods to test the concrete compressive strength; ultrasonic testing is used to detect internal defects in welds; and the Rockwell hardness test is employed to determine the steel grade of steel plates.

The issue of strength essentially refers to whether the large stresses caused by loads on structures or individual components exceed the ultimate strength of the construction materials under a state of stable equilibrium. Therefore, it is a matter of stress. The value of ultimate strength depends on the material's characteristics; for brittle materials like concrete, it can be taken as its high strength, while for steel, it is often its yield point. Low component strength can lead to insufficient structural bearing capacity, significantly affecting the normal use function and seismic resistance of the structure. In terms of component strength testing, the focus is mainly on the following aspects: 1. Factory concrete strength testing 2. Factory steel component raw material testing (mechanical and process properties) 3. Factory steel component connection high-strength bolt testing (torque coefficient, anti-slip coefficient) 4. Factory steel component dimensional deviation testing 5. Factory steel component appearance quality testing 6. Factory steel component material thickness testing 7. Factory steel component material coating thickness testing

3. Foundation Stability: After the upper structure assessment is completed, the stability of the foundation becomes a concern. Generally, a high-precision total station is used to measure and judge the tilt of the column frames and the corners of the building to assess structural deformation.沉降观测 may be conducted on the building as necessary to determine the stability of the foundation. The national codes and regulations referenced during the inspection include: "Reliability Assessment Standard for Industrial Buildings" (GB50144-2008), "Technical Standard for Building Structure Inspection" (GB/T50344-2004), "Construction Quality Acceptance Specification for Steel Structures" (GB50205-2001), "Technical Standard for Field Inspection of Steel Structures" (GB/T50621-2010), "Technical Specification for Concrete Strength Testing by Core Drilling Method" (CECS03:2007), "Technical Specification for Concrete Compressive Strength Testing by Rebound Method" (JGJ/T23-2011), "Technical Specification for High-Strength Bolt Connections in Steel Structures" (JGJ82-2011), "Code for Measurement of Building Deformation" (JGJ8-2007), and related design specifications, etc.

Basic stability issues essentially revolve around whether the foundation can meet the requirements for strength and deformation. Failure to do so can lead to general settlement and uneven settlement, with the upper structure exhibiting overturning and excessive plastic deformation, making it unsuitable for continued load-bearing, thereby affecting the normal function and seismic resistance of the structure.