Fire protection measures for steel structures balance fire protection duration and structural deadweight. The key lies in embracing a "protection-as-needed" approach, focusing on material selection, structural design, and process adaptation to ensure that fire protection duration requirements are met while avoiding excessive structural loads. Steel structures inherently have poor fire resistance and are prone to losing their bearing capacity at high temperatures, necessitating fire protection to slow the rate of temperature rise. However, the deadweight of protective measures directly impacts the structure's load-bearing efficiency, deflection control, and overall economic efficiency. Therefore, the key to achieving this balance is ensuring that every investment in fire protection is precisely aligned with the required duration without creating unnecessary deadweight.
The key to this balance lies in the matching of fire protection material density and performance, prioritizing the use of materials with low density and high fire resistance. The density of different fireproofing materials varies significantly. For example, traditional thick, heavy fireproof bricks have high density and a strong fireproofing effect, but they significantly increase the deadweight of the structure. They are more suitable for heavy steel structures that are less sensitive to deadweight and have extremely high fireproofing requirements, such as steel columns in steelworks. Lightweight fireproof coatings, such as ultra-thin intumescent coatings, have a density only a fraction of that of traditional materials. They expand at high temperatures to form a fire-resistant, insulating layer. While maintaining a 1-2 hour fireproofing effect, the coating thickness is much thinner than fireproof bricks, and the added deadweight is negligible. This makes them more suitable for large-span steel structures that are sensitive to deadweight, such as the steel beams of exhibition centers. By selecting materials based on the component's fire rating and deadweight tolerance, the waste of using heavy materials to minimize deadweight can be avoided from the outset, achieving a preliminary balance between deadweight and deadweight.
Precise design of the fireproofing layer thickness is key to reducing excess deadweight, and the minimum required thickness must be calculated based on the fireproofing effect requirements. Fire protection duration is determined by building codes based on the component's function. The corresponding fireproofing layer thickness is not "the thicker the better"—excessively increasing the thickness will lead to a sharp increase in deadweight without proportionally improving the duration (due to diminishing returns in thermal insulation effectiveness). During design, thermal conductivity simulations are used to calculate the temperature rise curves of the steel structure under different fireproofing layer thicknesses, identifying the minimum thickness that keeps the component's temperature rise within a safe range. For example, for a steel truss requiring a one-hour fireproofing period, if a lightweight fireproofing coating meets the insulation requirements at a certain thickness, the thickness can be increased. If a single material requires excessive thickness to meet the standard, a combination of a thin coating and a fireproof lining can be used instead. This synergistic insulation of the two materials reduces the overall thickness and deadweight, avoiding the unnecessary weight associated with relying solely on thicker materials for temperature control.
The use of composite protective structures can reduce overall deadweight through "functional complementarity" while simultaneously improving fire protection stability. Single fireproofing materials often require a compromise between thickness and performance, but composite structures can leverage the strengths of different materials. For example, a thin layer of intumescent fireproofing paint is first applied to the steel structure surface (to ensure initial insulation and adhesion at high temperatures), followed by a lightweight fire-resistant fiberboard covering (to enhance long-term insulation and slow paint aging). With this combination, the paint thickness only needs to meet basic adhesion and short-term fire protection, while the board's inherent lightweight properties provide long-term protection. The overall thickness is significantly less than that required for a single material to meet standards, reducing the weight by more than half compared to traditional, heavy-duty fireproofing. Furthermore, the composite structure offers greater fire resistance stability, preventing aging failure caused by localized damage in a single material. This eliminates the need to thicken a single material to compensate for deficiencies, further optimizing the weight.
Differentiating fireproofing measures based on the load-bearing characteristics of steel structure components can avoid the waste of weight caused by a "one-size-fits-all" approach. Different components have varying degrees of sensitivity to deadweight. The deflection of bending components (such as floor beams) is closely related to their deadweight. Increased deadweight leads to increased deflection, necessitating the use of the lightest fire protection measures (such as ultra-thin fire-retardant coatings). Axially compressive components (such as support columns) are more tolerant to deadweight and can employ slightly heavier but more stable fire-resistant materials (such as thick fire-retardant coatings). Stress-concentrated areas, such as truss joints, require fire-resistant performance while also avoiding localized excessive deadweight that could lead to unbalanced joint forces. This approach employs a "thick coating at the joints combined with a thin coating on the main structure" design, adding protection only to key areas while maintaining a lightweight structure. This achieves the goal of "no weight increase for key protection, and reduced weight for the main structure to ensure long-term performance."
Integrating fire protection with prefabricated steel structure components can reduce the weight of additional protective layers on-site. Traditionally, when applying thick fire-retardant coatings on-site, an extra 10%-20% is often applied to ensure quality (to avoid missing coatings and resulting in insufficient durability). This excess thickness increases the weight of the component. However, factory prefabrication allows for precise control of the fire-retardant coating thickness through automated spraying. Furthermore, the fire-retardant coating can be completed simultaneously with component surface pretreatment (such as rust removal and phosphating) during the component production phase, improving coating adhesion and avoiding the need to increase the coating thickness due to poor adhesion. Some prefabricated components also utilize an integrated "steel component + built-in lightweight fire-resistant core" structure (such as steel honeycomb panels with built-in refractory rock wool). This core material has a much lower density than traditional fire-resistant bricks, yet it enhances insulation by enclosing the cavity. The overall weight is lighter than a "steel component + external fire-retardant coating" approach, while also providing more stable fire-resistant durability.
The technological evolution of new lightweight fire-retardant materials offers greater potential for achieving a balance between improved durability and reduced weight. For example, nano-modified fire-retardant coatings optimize thermal insulation by adding nanoparticles. At the same thickness, they offer over 30% longer fire-retardant lifespan than traditional coatings. This means that to achieve the same lifespan, coating thickness can be reduced by 20%-25%, resulting in a corresponding reduction in weight. Lightweight, fire-resistant ceramic fiber tapes, which wrap steel components in a flexible structure, have a density only one-third that of fire-retardant coatings and can adapt to complex component shapes (such as bolted joints and elbows), eliminating the need for thicker coatings due to irregular shapes. These new materials achieve both lightweight and high lifespan by optimizing the inherent properties of the materials, rather than relying on increased thickness and weight to improve lifespan. This technically breaks the traditional limitation of a positive correlation between lifespan and weight, allowing for more flexible balanced design.
