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2023.02.06

Fire protection design of large-span steel structure buildings

Space frame construction of unloading hall

1. The importance of fire protection design of large-span steel structure buildings

1.1 Properties of Steel Structure Buildings

From a physical point of view, the raw material steel in steel structure buildings has a certain heat resistance and is not flammable. In theory, it could have become an ideal fireproof material. Form, unless the fire temperature reaches 500 ℃ in a short period of time, it is possible to change the state of the steel. Obviously, an accidental fire under normal conditions cannot cause such a temperature in a short time, so the fire can be extinguished artificially. But this is only a theoretical basis, and the results of the practical application of steel structure buildings are not like this. Since most of the steel structure buildings in real life are large-frame structure buildings such as workshops, gymnasiums, and large warehouses, these buildings have larger internal space, more basic equipment and better ventilation, so when a fire occurs in a certain place, Good ventilation provides conditions for the spread of fire. In addition, due to a large number of internal facilities, it has a great impact on firefighters’ fire-fighting work. In practice, once a large-span steel structure building catches fire, it is difficult to put out a fire. Relevant designers should pay attention to it. This, especially steel structure building designers, must design corresponding fire protection measures.

1.2 The fire resistance of large-span steel structure buildings is poor

Steel is widely used in architecture. It is formed by extruding steel ingots and billets through external force interference. It has good seismic resistance, high-quality bending resistance, and a super rigidity component. In addition, some steels also have good flexibility, which solves the problem that materials cannot be bent in architectural design, and provides convenience for many aesthetic buildings. Therefore, steel has a prominent position in the construction industry and is favored by designers. However, steel structure buildings have a fatal weakness, that is, the fire resistance is very poor, and its mechanical properties, such as yield point, tensile strength, and elastic modulus, will drop sharply due to the increase of temperature. When the temperature of the steel structure reaches 350℃, 500℃, and 600℃, its strength is 1/3, 1/2, and 2/3 respectively. Not only that, in the high-temperature environment, the shape of the steel will change greatly, and the load-bearing capacity of the structure will drop sharply. In theory, the deformation temperature of the steel is about 300 ℃, but the internal temperature after the fire spreads is as high as 1000 ℃, so this kind of In the environment, steel has no fire resistance at all. In a short period of time, the overall steel structure will be deformed instantly, and buildings without structural frames will collapse instantly, causing casualties. At present, there are many cases of casualties caused by steel structure building fires in the world. In 2009, the appalling “9.11 Incident” occurred in New York. Four civil aviation planes were kidnapped by terrorists and crashed into the World Trade Building. The big fire, the internal steel structure of the World Trade Center was deformed instantly under the high temperature, and the world’s tallest building collapsed in just a moment. Due to the lack of fire protection design, many firefighters were buried forever under the ruins without preparation. Therefore, the fire performance of steel structure buildings is very poor, and designers must design fire protection measures in a targeted manner.

2. Problems existing in the fire protection design of large-span steel structure buildings

2.1 Lack of practical application of fire protection design

At present, there are many problems in the fire protection design of large-span steel structure buildings, one of which is that the fire protection design does not meet the actual requirements, and the designers have the ability to talk on paper but ignore the practical application of fire protection design. Some designers do not have a firm grasp of relevant fire protection knowledge and lack practical experience, resulting in the design of fire protection measures that cannot be applied to real life. For example, most high-rise buildings will be equipped with elevators, exhaust ducts, and other equipment that run through the entire floor. Some designers ignore fire separation measures during design or do not handle fire separation measures in place, resulting in equipment running through the floor when a fire occurs. The formation of a natural fire pit can help the fire to spread faster, which in turn can cause the fire to get out of control and even cause greater casualties.

2.2 Poor fire protection design

In the construction industry, some companies cut corners on raw materials, which sometimes seems to be a norm in the construction industry. The purpose of this behavior is only to save costs and seek benefits. In the process of material selection by many construction teams, the selected materials seriously do not meet the standards stipulated by the state. The inferior steel has extremely poor fire resistance and generally deforms at about 300 °C. This inferior steel constitutes great building safety. Hidden dangers have had a huge impact on the lives of residents. The state should strengthen supervision and severely punish the behavior of cutting corners in the construction.

performance of steel, and there is no national standard specification. Inexperienced construction departments will have great deviations when purchasing materials. Not only that, but today, with technological progress, more and more Many new materials continue to enter the market, and the difficulty of standard formulation is further strengthened. In addition, some new materials have some problems, which are not discovered in time. When architects apply them to steel structure buildings, some new hidden dangers are often generated. Data analysis shows that the fire resistance of some new steels may change when the fire temperature reaches 40°C. This is a very scary concept. Once a fire occurs, casualties are inevitable.

3 Fire protection design measures for large-span steel structure buildings

3.1 Optimizing the fire protection design of buildings For the problem of poor fire resistance of large-span steel structure buildings, designers should optimize the fire protection design of buildings to ensure their safety of steel structure buildings.

Designers should understand the fire performance of different materials when carrying out fire protection design, select materials in strict accordance with national regulations, and set up fire protection equipment reasonably to ensure that the water outlet system of the entire building can continue to operate. Designers can start from the following aspects when optimizing building fire protection design:

(1) Start with electrical fire prevention. Generally speaking, electrical fire is a difficult problem to solve in fire protection. Due to the electrical connection of many household appliances, once a fire starts, a series of chain reactions will occur, resulting in a short-circuit fire in a short period of time. When the equipment explodes, many electrical appliances will become the source of the fire. Not only that, but due to the strong conductivity of water, this kind of fire cannot be extinguished by water. Therefore, the designer should optimize the internal structure of the electrical appliance and use special materials to transport the electrical pipelines. Provide enhanced protection to reduce the possibility of fire due to damage to electrical equipment.

(2) The architect should set up a refuge layer in the design. The partition of the refuge layer is composed of fireproof materials, which can isolate the internal space from the outside. Generally speaking, a high-rise fire will occur. It is impossible to break through the fire area and can only wait for rescue, and the spread of fire is often rapid. If there is no refuge layer, these residents are likely to be swallowed by the fire without waiting for rescue. Therefore, designers should formulate corresponding refuge layers and equip With certain firefighting equipment, in the event of an emergency of 100,000 fires, evacuation personnel can obtain a lifeline through these lifesaving equipment. Generally, a more reasonable refuge floor is designed on the 15th floor. This height is the result of rigorous data analysis. Firefighters below the 15th floor can directly carry out the rescue.

3.2 Strengthen electrical fire protection design

Investigations show that most building fires are caused by improper use of electrical equipment. Therefore, for large-span steel structure buildings, the most important consideration in fire protection design is to eliminate the potential safety hazards caused by electrical appliances and to reduce the risk of fire through electrical fire protection design. possibility. How to carry out electrical fire protection design is a very academic problem. Designers must have a solid physical foundation and practical life experience. For example, in elevator design, the power supply method should be different from that of general electrical equipment. The elevator should use a dual-circuit power supply, and at the same time, The live wire should also be equipped with capacitors. Once there is a short circuit on the circuit, the power supply will be cut off quickly, which will directly kill the hidden danger. Not only that, but architects should also do a good job in the design of smoke exhaust systems when designing houses. As we all know, the cause of many fire casualties is not caused by burning, but because the deceased inhaled a large amount of carbon monoxide generated by the fire. Therefore, the construction of the exhaust system is very important. In addition, each floor building should also install corresponding fire extinguishing equipment, such as fire hydrants, fire extinguishers, etc., so that the fire protection system of the steel structure building is relatively complete. In most residential buildings, electrical fire protection design should be done well. In addition to the existing fire protection system, the electrical safety factor of the steel structure workshop should be improved, so as to avoid the overload and aging of each circuit during long-term use, which may lead to a fire. So as to completely protect the electrical function of residential buildings. And standardize all kinds of electrical facilities in residential buildings to protect the safety of residents’ lives and property.

3.3 Use the water cooling method

The water cooling method is the most effective method in the fire protection measures of steel structure buildings, which mainly includes the water shower cooling method and the water filling cooling method. The so-called water spray cooling method is to install an automatic sprinkler system and sensor on the steel frame structure. When the indoor temperature reaches the sensor standard, the sprinkler will start to spray cooling water on the steel structure, thereby achieving the effect of extinguishing the fire and cooling the steel. , which can largely prevent the spread of fire and keep the mechanical structure of the steel frame unchanged. The water-filled cooling method is different from the water-spray cooling method. It uses the heat-absorbing capacity of water. By adding cooling water to the hollow steel member, it absorbs the heat of the external fire and delays the heating of the steel frame through continuous evaporation cycles. The speed ensures that the mechanical structure of the steel frame will not be changed. In theory, this is the most effective method for the fire protection of steel structures. However, due to the technical difficulty and the increased weight of the building, in order to prevent rust and prevent water from freezing, it is necessary to add rust inhibitors and antifreeze agents to the water, which is expensive, and only a few foreign applications are used.

Steel is one of the most widely used building materials in the world. Buildings based on it are firm, durable, and aesthetically pleasing, and are an important cornerstone for the development of architecture in the new era. However, steel will deform at high temperatures, the original mechanical structure will no longer exist at high temperatures, and steel structure buildings will collapse in a short time. Therefore, architects should pay attention to fire protection design when designing large-span steel structure buildings to ensure the personal safety of residents.