Structural Construction
The inspection and calculation of the slenderness ratio of steel structural members shall be conducted by measuring the member dimensions in accordance with applicable regulations; the slenderness ratio shall be calculated based on the actual measured dimensions.
Connections within the steel structure bracing system may be inspected in accordance with applicable regulations. The dimensions of bracing system components may be measured in accordance with applicable regulations; verification or assessment shall be conducted based on the design drawings or relevant design codes.
The width-to-thickness ratio of steel structural member cross-sections may be determined by measuring the relevant cross-sectional dimensions in accordance with applicable regulations and performing the necessary calculations; the assessment shall be conducted based on the design drawings and relevant codes.
Protective Coating
The quality of protective coatings for steel structures shall be inspected in accordance with the quality requirements specified in current relevant national product standards for such coatings.
The rust removal grade of the steel surface may be determined by visual comparison with the reference images specified in the current national standard *Rust Grades and Preparation Grades of Steel Substrates Before Application of Coatings and Related Products* (GB 8923).
The coating thickness for different types of coatings shall be inspected using the following respective methods:
1. Paint film thickness may be measured using a paint film thickness gauge. The number of components selected for random sampling shall not be less than the minimum sample size for "Category A" inspections as specified in the relevant standard tables, nor shall it be less than three components. For each selected component, measurements shall be taken at five distinct locations; the value recorded for each location shall be the average of the dry paint film thicknesses measured at three specific points spaced 50 mm apart.
2. For thin-film fire-retardant coatings, the thickness may be measured using a coating thickness gauge; the measurement procedure shall comply with the provisions of the *Technical Specification for Application of Fire Retardant Coatings for Steel Structures* (CECS 24).
3. For thick-film fire-retardant coatings, the thickness shall be measured using a probe and a steel ruler; the measurement procedure shall comply with the provisions of the *Technical Specification for Application of Fire Retardant Coatings for Steel Structures* (CECS 24). The measured coating thickness values and deviation values shall be assessed in accordance with the provisions of the *Code for Acceptance of Construction Quality of Steel Structures* (GB 50205). The visual quality of the coating system may be inspected and assessed-based on the specific coating materials used-in accordance with the provisions of the *Code for Acceptance of Construction Quality of Steel Structures* (GB 50205).
Steel Space Frames
The inspection of steel space frames may be categorized into items such as nodal bearing capacity, welds, dimensions and tolerances, member straightness, and frame deflection.
The inspection of the bearing capacity of welded spherical nodes and bolted spherical nodes in steel space frames shall be conducted in accordance with the requirements of *Standard for Quality Inspection and Evaluation of Space Frame Structures* (JGJ 78). For existing space frames utilizing bolted spherical nodes, specific nodes may be extracted from the structure to undergo ultimate bearing capacity testing. When extracting bolted spherical nodes, appropriate measures must be taken to ensure the structural safety of the remaining frame.
Welds within steel space frames may be inspected using ultrasonic flaw detection methods. The inspection procedures and evaluation criteria shall comply with the requirements of *Ultrasonic Flaw Detection and Quality Classification Method for Welds in Welded Spherical Node Steel Space Frames* (JG/T 3034.1) or *Ultrasonic Flaw Detection and Quality Classification Method for Welds in Bolted Spherical Node Steel Space Frames* (JG/T 3034.2).
The visual quality of welds in steel space frames shall be inspected in accordance with the requirements of *Code for Acceptance of Construction Quality of Steel Structures* (GB 50205).
The inspection of tolerances for welded spheres, bolted spheres, high-strength bolts, and structural members-including the specific inspection methods and permissible tolerance values-shall be carried out in accordance with the provisions of *Standard for Quality Inspection and Evaluation of Space Frame Structures* (JGJ 78).
The wall thickness of tubular members in steel space frames may be measured using an ultrasonic thickness gauge; any surface finishes or coatings must be removed prior to measurement.
The straightness (or lack thereof) of the axial lines of members within steel space frames may be inspected using the stretched-line method; the deviation from straightness shall not exceed one-thousandth (1/1000) of the member's length.
The deflection of steel space frames may be measured using a laser rangefinder or a leveling instrument. Within each half-span, there should be no fewer than three measurement points; specifically, one measurement point must be located at the mid-span, and the end measurement points shall be situated no further than 1 meter from the respective end supports.
Structural Performance: Real-Load Testing and Dynamic Testing
For large-scale and complex steel structure systems, in-situ, non-destructive real-load testing may be conducted to directly verify structural performance. Such real-load testing of structural performance shall be carried out in accordance with applicable standard specifications. The loading coefficients and acceptance criteria may be determined based on established regulations, or they may be appropriately adjusted to suit the specific circumstances of the project. When there are doubts regarding the load-bearing capacity of a structure or structural component, load tests may be conducted on the prototype or a full-scale model. Such tests should be entrusted to a specialized institution possessing adequate equipment capabilities. Prior to testing, a detailed test plan must be formulated, encompassing the test objectives, the selection or fabrication of test specimens, the loading apparatus, the layout of measurement points and instrumentation, the loading procedure, and the methodology for evaluating the test results. The test plan may be developed in accordance with relevant standards and must be approved by all concerned parties prior to the commencement of testing.
For large-scale, critical, or novel steel structural systems, it is advisable to conduct dynamic testing on the actual structure to determine dynamic parameters, such as the natural vibration period. Such structural dynamic testing should be conducted in compliance with relevant standard specifications.
The stress within steel structural members may be measured using resistance strain gauges or other effective methods, selected based on the specific field conditions.
