Modern building steel structure engineering fireproof protection methods
A steel structure advantages.
A. Steel's light weight, although the ratio of the major steel, but because of its good mechanical properties, can withstand greater loads, so the size of a small section of steel structures, the same time span the same load, but the most weight of reinforced steel roof concrete roof trusses 1/4 or 1/3 of the weight of the steel structure is small, easy to transport.
B. Steel construction and ease of installation. Gang structure consists of specialized metal components plant components (beams, roof trusses, columns, etc.), in connection with the site welding or bolts (or high-strength bolts) up, construction and installation quick and easy, increase the speed of construction, has become the most to reduce the project cost The main factor, structural cost problem has been reduced to a secondary position. Moreover, steel bolted to facilitate the transformation of the demolition. Steel Works
C. steel manufacturing, installing high degree of mechanization. Steel has a certain segment of the technology-intensive nature of the material used in single steel and is finished, processing simple, high degree of mechanization, construction quick and easy to ensure quality, suitable for large batch production process from the factory components lifting to the scene, much higher than the level of industrialization in-situ reinforced concrete structure with the labor-intensive nature.
D. material uniformity, and mechanical calculations assume more consistent, more uniform steel internal organization, according to nearly isotropic body, but in a certain stress amplitude is almost perfectly elastic. Therefore, the actual results of the forces and building mechanical steel structure more in line with the calculation.
E. Steel flexibility in the layout, it is another important feature. In today's information age, for in-room flat, space and internal facilities requirements more stringent. The original layout and equipment, and soon may become less applicable or not applicable steel but can provide greater possibilities for re-layout of the plane, thus prolonging the life of the building.
Although there are so many advantages of steel, but there is a fatal flaw: not fire-resistant. Although steel is non-combustible material, but at high temperature fire, its mechanical properties such as yield strength, elastic modulus but it will decrease with increasing temperature, at around 550 ℃, lower margin is more evident, usually in about 15 minutes will lose the weight capacity and collapse. Steel building fire cases at home and abroad have proved less than 20 minutes after a fire burned the building collapse put, the final form ruins.
Two steel structure fire protection methods.
Due to the energy difference refractory steel, high temperature under fire soon collapse failure, fire resistance of only 15 minutes, if to take measures for protection of steel structures, so that when the fire temperature does not exceed the critical temperature, steel fire will be able to maintain the stability of the protective measures taken against steel, in principle, the major can be divided into two types: the closure method and counseling methods.
1. Closure Act
Closure law principle truncated or fire blocking heat flow generated transmission to the member, so that the member is within a predetermined time temperature does not exceed its critical temperature. Its approach is to set up a protective surface of the component materials, high temperature fires first pass these protective material, and then by a protective material to make components. Because the thermal conductivity of the material selected small, but has a larger heat capacity, they are able to block the heat flows nicely transmission components, which play a protective role. Closure Act is divided into spraying, encapsulation method, shielding method and water spray method. Steel Works
2. spraying
Spray with spray equipment to fire paint directly onto the surface of the component to form a protective layer. Fireproof coatings of different adhesives used in fire retardant paint can be divided into organic and inorganic fire retardant coating categories, according to the coating thickness into thin coating and thick coating type categories, thin coating of steel paint coating thickness is generally 2 ~ 7mm, there is a certain decorative effect, high temperature coating expands thickened, with fire-resistant thermal insulation, fire resistance of up to 0.5 to 1.5 hours, which is also called Gang structure expansion fireproof paint coating. Thick coating steel structure fire retardant coating thickness is 8 ~ 20mm, granular surface, less dense, low thermal conductivity, fire resistance of up to 0.5 to 3.0 hours, this coating also known as fireproof insulation coatings.
Affect the performance of the different elements of steel
(1) Carbon: the higher the carbon content, just the higher hardness, plasticity and toughness, but it worse.
(2) Manganese: can improve the strength of steel, can weaken and eliminate the adverse effects of sulfur, and can improve the hardenability of steel, high manganese content of high-alloy steel (high manganese) has good wear resistance and other physical properties.
(3) Sulfur: steel harmful debris, higher sulfur steel at high temperatures when the pressure processing, easy to rattle, often called hot brittleness.
(4) Phosphorus: make steel plasticity and toughness markedly decreased, particularly more severe at low temperatures, a phenomenon known as cold brittleness. In the high-quality steel, sulfur and phosphorus must be strictly controlled. But on the other hand, the high content of sulfur and phosphorus in the low carbon steel, so that it can be easily cut off, to improve the machinability of steel is advantageous.
(5) silicon: it can improve the hardness of the steel, but the plasticity and toughness decreases, electrical steel contains a certain amount of silicon, to improve the soft magnetic properties.
(6) Mo: You can clear progress steel hardenability and heat resistance, prevent temper brittleness, progress remanence and coercivity.
(7) Tungsten: Red steel can improve the hardness and heat resistance, and can improve the wear resistance of the steel.
(8) Chromium: can improve hardenability and wear resistance, to improve the corrosion resistance of steel and antioxidant effects.
(9) Titanium: to refine the grain structure of the steel, thereby enhancing the strength and toughness of steel. In stainless steel, titanium can eliminate or reduce the intergranular corrosion of steel.
(10) B: When the steel contains trace amounts (0.001-0.005%) boron steel hardenability can be multiplied progress.
(11) Nickel: steel can improve the strength and toughness, improve hardenability. High levels, it can significantly change some of the physical properties of the steel and alloy steel corrosion resistance progress.
(12) Aluminum: to refine the grain structure of the steel, mild steel aging repressor. Progress steel toughness at low temperatures, but also the progress of steel oxidation resistance, wear resistance and fatigue progress steel strength.
(13) V: can refine the grain structure of steel, the strength of the progress of steel, toughness and wear resistance. When it is melting into the austenite at high temperature, increase steel hardenability; on the contrary, when it exists in carbide morphology, it will reduce its hardenability.
(14) Copper: its prominent role is to improve the common low-alloy steel resistance to atmospheric corrosion, especially when the more obvious and phosphorus used in conjunction.
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