In recent years, the application of space steel structure engineering has become increasingly widespread in the construction industry. Steel structure factory buildings are one of the primary choices for many enterprises when selecting factory forms for production. Due to historical reasons, there are numerous industrial steel structure factories that lack formal design, construction, and supervision, posing significant structural safety risks. Ensuring the structural safety of the factory buildings is crucial, making structural safety assessment work particularly important in addressing this issue.

It's widely known that the main issues with steel structures focus on the stability of the upper structure, the strength of the components, and the stability of the foundation. We'll delve into these three points together, understanding their significant roles in the safety assessment of steel structure factories by combining them with the sequence of the identification work, from superficial to deep.1Structural 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 check if the structural forms used in the buildings comply with the design drawings and national codes and regulations, if the force transmission routes are clear, if the structural layout is reasonable, and if the support system is complete and its slenderness ratio meets the code requirements, as all these relate to the structural stability. Structural stability has always been a major issue with steel structures. Once an instability accident occurs in steel structures, it not only leads to significant economic losses but also easily causes severe personal injuries. Therefore, we must understand the basic concepts of structural stability, only then can we better identify and handle steel structure instability issues in the safety identification work of steel structure factories.

1Structural 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 check whether the structural forms used in the building comply with the design drawings and national specifications, whether the force transmission routes are clear, whether the structural layout is reasonable, and whether the supporting system is complete and meets the specification requirements for slenderness ratio, as all these are related to the structural stability. Structural stability has always been a major issue with steel structures; once an instability accident 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, only then can we better identify and address steel structure instability issues in the safety identification work of steel structure factories.

The stability of steel structures can be categorized into two types: the overall stability of the structure and the inherent stability of the components. Overall stability along the structure's length primarily relies on the support system, such as the inter-column supports of steel columns, the horizontal and vertical supports of steel trusses, etc. The reliability of the support system in transferring horizontal loads (wind, seismic, crane loads, etc.) along the structure's length is crucial. Lateral stability depends on the rigidity of the structure itself (frame or bay) to ensure reliable transfer of lateral horizontal loads. The inherent stability of the components is mainly guaranteed by the rigidity of their constituent parts, ensuring they do not buckle under load and lose stability (this primarily occurs in compressed or bending components). Therefore, the factors affecting the inherent stability of components are mainly the component's calculated length and cross-sectional characteristics, including in-plane and out-of-plane directions, and of course, the material strength and stress magnitude. It mainly identifies the unstable equilibrium state between external loads and the internal resistance of the structure.,The state where deformation begins to increase sharply,Therefore, efforts are made to avoid entering such a state.,It's a deformation issue. Such as, an axis-compressed column.,Due to instability,Lateral deflection significantly increases the bending moment within the column.,Therefore, the destructive load of the column can be significantly lower than its axial compressive strength. Clearly.,Axial compressive strength is not the primary cause of column failure.

In the aspect of structural stability testing, the focus is primarily on the following key points:① The quality of high-tensile bolt connections for factory components is ensured through the use of total station equipment to check the exposed threads of bolts in the connection areas. ② The welding connection quality of factory components is determined by the ultrasonic flaw detection method to assess whether the weld quality grade meets the standard requirements. ③ The deflection deformation of factory components is measured using a level instrument or string line method to determine the deformation amount.

2Component 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 for steel plates.

The issue of strength essentially refers to whether the large stresses induced by the loads on the structure or individual components in a state of stable equilibrium exceed the ultimate strength of the construction material.,Therefore,This is a stress issue. The value of the ultimate strength depends on the material's characteristics.,For concrete and other brittle materials,Can be chosen for its high strength,Steel yield points are commonly taken. 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 following key aspects are mainly focused on: 1. Factory concrete strength testing 2. Factory steel component raw material testing (mechanical and process properties) 3. Factory steel component high-strength bolt testing (torque coefficient, anti-slip coefficient) 4. Factory steel component size deviation testing 5. Factory steel component appearance quality testing 6. Factory steel component material thickness testing 7. Factory steel component material coating thickness testing

3Basic Stability: After the structural assessment of the upper part is completed, the stability of the foundation becomes the issue. 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; if necessary, settlement observations of the building are conducted to determine the stability of the foundation. The national codes and regulations referred to during the inspection include: "Reliability Assessment Standard for Industrial Buildings."GB50144-2008"Building Structure Inspection and Testing Standards"GB/T50344-2004"Specification for Quality Acceptance of Steel Structure Construction"GB50205-2001"Standard for On-Site Inspection Technology of Steel Structures"GB/T50621-2010"Technical Code for Concrete Strength Testing by Core Method"CECS03：2007"Rebound Method for Testing Concrete Compressive Strength Technical Specification"JGJ/T23-2011"Code for Technical Specifications of High-Strength Bolted 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 overall 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 functionality and seismic resistance of the structure.