The construction industry has experienced rapid development, leading to continuous changes in building structures. Among these, steel structures have gained widespread attention due to their high strength, lightweight, excellent seismic resistance, fast construction speed, low base cost, small structural footprint, and high level of industrialization. Although steel is not flammable, it conducts heat very easily. When the temperature reaches 540°C or higher, its mechanical properties drop rapidly. At 600°C, the strength of steel is almost completely lost. The fire resistance of unprotected steel is typically only 15–30 minutes. According to China’s building fire protection design specifications, the required fire resistance for columns, beams, slabs, and roof load-bearing members ranges from 0.5 to 3.0 hours.
On May 5, 1998, a fire at the Beijing Yuquanying Huandao Furniture City resulted in the collapse of 13,000 square meters of steel structure buildings due to inadequate fire protection, causing direct economic losses of 20.87 million yuan. Similarly, after the "911" incident, experts concluded that the planes did not directly bring down the buildings. Instead, the impact destroyed the fireproof coating on the steel structures, allowing the fires to expose the steel to intense heat. After over an hour, the structure softened, lost strength, and eventually collapsed. This highlights the critical need for proper fireproofing of steel structures to increase their fire endurance.
There are various fire prevention measures available for steel structures. Traditionally, cast concrete shells, refractory bricks, non-combustible materials like gypsum board, or water-cooled hollow pipes were used. However, modern approaches increasingly rely on spraying steel structure fireproof coatings. These coatings offer good fire resistance and thermal insulation, are not restricted by structural geometry, require no additional support, are easy to apply, and provide aesthetic benefits, making them widely used today. Nevertheless, issues such as improper selection, durability, and construction quality still pose challenges for fire safety supervision.
One major issue is the selection of fireproof coatings. According to GB14907-2002, steel structure fireproof coatings are classified into three types: ultra-thin (≤3mm), thin (3–7mm), and thick (7–45mm). Ultra-thin and thin coatings expand when exposed to fire, forming a carbonized layer that insulates the steel. Thick coatings, on the other hand, do not foam but rely on low thermal conductivity to delay temperature rise. While both types serve different purposes, improper use—such as selecting ultra-thin coatings for high-risk areas—can compromise long-term safety.
Another challenge is the lack of clear guidelines during the design and construction phases. Many designers simply specify the use of fireproof coatings without specifying the type, leading to misapplication. Additionally, environmental conditions and usage requirements are often overlooked, especially for outdoor or high-exposure areas. Using indoor-grade coatings outdoors can lead to degradation and reduced effectiveness.
To ensure proper application, it is crucial to select the right coating based on the structure's location and fire resistance needs. For example, intumescent coatings should not be used outdoors due to poor weather resistance and potential release of toxic gases. In high-risk environments like tunnels or industrial facilities, thick coatings are more suitable. Thin and ultra-thin coatings may be acceptable for lower fire resistance requirements, but they must be carefully selected and applied.
Durability is another key concern. Fireproof coatings are tested before use, but their long-term performance under real-world conditions remains uncertain. There is a lack of standardized evaluation methods for service life, and manufacturers rarely provide replacement schedules. Maintenance is also complex, especially for hidden structures, where repainting or reapplication can be difficult.
Construction quality plays a vital role in the effectiveness of fireproof coatings. Common issues include unqualified construction teams, improper surface preparation, and lack of quality control. Coating thickness, adhesion, and even visual appearance must be strictly monitored. Proper training, adherence to technical standards, and regular inspections are essential to ensure compliance.
Finally, acceptance and testing are critical steps. All fireproof coatings must be verified through independent testing institutions, following national standards such as GB14907 and CECS24. Comprehensive documentation, including test reports, construction records, and inspection data, must be provided to ensure compliance.
In conclusion, while fireproof coatings significantly enhance the fire resistance of steel structures, challenges remain in their selection, application, and maintenance. Addressing these issues requires careful planning, strict quality control, and ongoing research to improve performance and durability. Only then can the safety and reliability of steel structures be fully ensured.
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