【 Weak current College 】 buildings in fire of collapse and response measures---Power By 【 China power house network 】

In recent years, as China's economic construction, building fire rate rise. This type of fire-induced deaths number shocking, and direct property damage is also skyrocketed. This type of fire not only to the fire-fighting and fire forces rescue work has brought about tremendous dangers, but also for firefighting agencies fire supervision proposed greater challenges. United States New York was "9.11" World Trade Center terrorist attacks and collapse, causing death 2797 people, loss 36 billion shocking tragedy; Qingdao jimo Zhengda food company plant fire caused the steel roof collapse, resulting in more than 20 employees, and for failure to timely evacuation was buried in the factory; Hunan Hengyang "11.3" fires caused by building collapse, causing 20 fire officers and soldiers died, a creation of the new China fire accident fire officers and soldiers of the sacrifice. Frequent fire collapse, as the new era of fire work presented a serious challenge. Actively study and discussion of various structures buildings in fire damage, characteristics and laws of the collapse, the strict architectural design fire safety audit and acceptance, develop practical fire-fighting and rescue operations, reduce such fire accident casualties and property damage are very important for relevance.
　　
First, fire several common structure of the general laws of the collapse of the building
　　
Building component materials, traditional building materials with brick, wood, cement, sand, and in recent years, with the iron and steel, plastics, and a large number of applications for new materials, structural steel, thin-shell structures, space frame structure structures forms in an increasing number of, physical and chemical properties of building elements are increasingly complex, combustion characteristics of damage or render the diversity and complexity. Different building elements and materials have their own combustion performance and fire resistance, in different fire conditions, would render different deformation and collapse forms, some local damage, there is partial of a collapsing full collapse, there are the rapid collapse of a whole building comprehensive.
　　
(A) brick (clay) wood-frame construction:
　　
Brick (clay) structural building construction's comparison of long, often found in the vast rural areas, their general wall general use clay brick masonry, the roof or Adobe using wood and other materials in the construction. Wood burning fire, its surface will be carbonized ablation, thus weakening the cross sectional area, resulting in a fall in the event of collapse carrying capacity. If the remaining cross section area is still able to bear the full weight of the original, the structure is not going to happen to collapse. The fire brigade arrived at the scene of fighting fires, wood members outside surface layer absorbs a large amount of moisture, to develop a good layer of protection, generally not prone to collapse. Thus wood frame buildings collapse of the roof, overall, and less local damage more.
　　
Brick fire resistance is good, can stand high temperatures, and built the walls, because the quality and masonry mortar fire performance difference, the fire resistance of brick wall than brick itself, but the fire resistance of ordinary brick walls are relatively high, such as 24-sided plastering non-bearing wall and ordinary clay brick entity of fire limit of 8 hours, General brick to fire bear hours is no problem, usually do not happen to collapse.
　　
Adobe walls fire-resistant and flame-retardant, but Adobe are water immersion will cause softening absorbs water, the water gun Jet powerful impact will lose their strength and the destruction of the collapse.
　　
(Ii) hybrid construction:
　　
Hybrid construction mainly wall clay brick, concrete block, stone and other building materials, masonry mortars, floor by floor or in-place concrete construction of the building. This class of buildings used for building materials for clay brick, concrete block, stone, concrete, and other non-burning material, the fire resistance of building elements are relatively high. As 24 common clay brick entities bearing walls of fire resistance 5.5 hours, i.e. in the standard fire test conditions, this type of wall in 5.5 hours without losing load capacity or failure. But the fire load of building a fire, the temperature may exceed 1000 ° C, masonry to fire surface and back fire surface temperature difference is very big, internal will produce much stress and carbonate, Portland under high temperature decomposition reaction occurs, and the masonry damage. Therefore, in the fire, mixed structure building building elements in its fire resistance in General not be destroyed, but in the high temperature for a long time, the building may be partial collapse, usually do not happen in large collapse.
　　
(3) reinforced concrete structures:
　　
Reinforced concrete structures are common in a number of workshops span, workshops, warehouses and high-rise buildings, including the frame, bent structure, shear wall, etc. This type of building structure of the main load bearing members to reinforced concrete member, clay brick, concrete block wall consisting of only up to the separated and functional role.
　　
Steel, cement, sand and other reinforced concrete building subjected to high temperature properties changes, strength as the temperature changes that are different, these artifacts in the fire will produce what kind of stress, this area is also no one detailed research. But concrete reinforced by temperature rise within the impact tensile strength decreases, carbonates and silicates under high temperature decomposition reaction occurs, and the destruction of the masonry, reinforced the protection layer thickness for beams, floors and other tensile resistance of reinforced concrete structures of influence is very big fire resistance. If the simple support of non-prestressed reinforced concrete beams, in protective layer thickness when its 1CM 1.2 hour fire resistance, in 4CM is 2.9 hours, therefore increasing tensile resistance of reinforced concrete structures of cover thickness can effectively improve the fire resistance of the component.
　　
Prestressed concrete structure in case of heat, causing loss of prestressing tendons, reducing structure carrying capacity. Prestressed concrete structure in fire resistance performance than reinforced concrete structure and must be upsetting the thickness of the reinforced protection can extend its resistanceThe fire, building and the safety of personnel and materials.
　　
Reinforced concrete structures are statically indeterminate structures, the role of the fire, the failure of a component may result in partial collapse, but the general collapse of large area will not occur.
　　
(4) steel-frame construction:
　　
Steel structure with stable performance, light weight and high strength, high-precision machining and Assembly of good performance, short construction period, etc., are currently widely used in hotels, restaurants, galleries and other civilian public buildings and factories, warehouses and industrial buildings. Steel has good heat resistance, heat resistance and not heat-resistant, with the temperature, the strength of steel will be gradually reduced. According to the test, when the steel structure component temperature reaches 350 ° c and 500 ° c, 600 ℃, the intensity decreased 1/3, 1/2, 2/3. Once you reach 500 ° c steel structural members rapidly softening occurs resulting in instantaneous collapse collapse. Unprotected layers of steel, steel, steel frame, steel components of the fire resistance of 0.25 hours or 15 minutes, that is in the fire, 15 minutes later at any time, with the steel structure could lose strength and collapse.
　　
Grid structure is steel structure buildings, is composed of many steel rod according to certain rules to connect through steel node of large space in the system. Due to the fire resistance of steel products, the difference in temperature of up to 500 ° c sharp reduction in load-bearing capacity of fire after a period of time, the steel component is softening warping, deformation, causing damage to the roof collapse. General steel structure and roof work space is relatively large, mutual coupling with a lot of support levers, so the grid structure of the general collapse is holistic, or better than most, but very few partial collapse.
　　
(5) thin-shell structure:
　　
Thin-shell structure suitable for large-area roof, the use of materials, characterized by span, thickness of small, light weight, its surrounding lives on both sides of the floor, Foundation or steel lever to support.
　　
The collapse of thin-shell structure is the whole, the shell itself is highly fire-resistant properties, its collapse was mainly due to the destruction of supporting conditions. As long as the support of conditions does not destroy, it is perfectly possible to avoid the collapse of a fire, should promptly cooling steel lever to prevent destruction of supporting conditions.
　　
Apart from the fire caused the collapse of the building interior and exterior of explosives-impact and damage is an important cause of the collapse of the building. In addition, the collapse of building superstructure on the impact of underlying structure, or floor materials absorb on the water, greatly increasing the load on the floor, causing the bearing structure cannot withstand huge loads and collapse.
　　
Second, the response to the collapse of building fire prevention measures
　　
Different reasons for the collapse of the building structure is different, the collapse of the situation is different, even if the same class structure will not be generalized. Fire departments should pay attention to building construction in front of the fire protection design audit work, the want to grasp the fire performance of building elements and fire resistance, in economic and reasonable basis to improve the building's fire resistance rating. The Fire Department should also learn about the different laws of the collapse of the structure construction, analysis and lessons learned, in fire-fighting and rescue is to take preventive measures, personal protection, vigilance to prevent personal injury accidents.
　　
(A) of the steel roof
　　
Steel structure for the roof of the building on fire, to prevent the fire burn directly to the roof, to use the flowering water gun or DC water gun, on roof surrounding roof panel walls and air for cooling of water to cool and protect the roof to prevent significant damage the structure as a whole, to prevent the collapse of the roof and wounding, this early in the fire is necessary and very effective. But even on very hot steel structure is immediately cooled to prevent roof collapse acceleration. In fire fighting, the combatants to fully rely on favorable terrain to occupy the House door and jetting water fire extinguishing.
　　
(2) reinforced concrete elements
　　
Concrete is fire-resistant. On fire, it is more secure and reliable. Reinforced concrete structural fire resistance time, generally more than the 1h. Prestressed reinforced concrete structure, is a new structure, capacity, materials, fire resistance. Fire, through its deformation of determining if there is a risk of collapse.
　　
(C) thin-shell structure roof
　　
Fire on the destruction of the thin-shell structure are often on the support of conditions, therefore its collapse are often large and even the whole. So when you first put out the fire is promptly cooling steel tie rod, avoid damage of conditions to prevent large thin-shell structure collapses.
　　
Note that when the shell structure of the roof is on fire, combatants on its roof in general do not; when you have landed on the roof Shell to put out the fire, the number of people on the roof is not excessive and that location to be dispersed, stay in the center of the shell is best, or symmetry in the Centre of side location.
　　
(4) wood frame
　　
Wood members special performances, will soon be burning. In the surface layer. Wood is burning speed and its density and moisture content which is directly linked to the size. Wood burning speed, with its density and moisture content of the reduction. According to the measured, wood inside burning velocity of theoretical average 0.6mm/min. Light and dry wood burning velocity of approximation is 0.8mm/min. The dense mass and wet wood burning velocity of approximation is 0.4mm/min. In the fire, we can use these statistics to estimate the combustion of wood members are.
　　
(5) walls and chimney
　　
Brick fire resistance is good, can stand high temperatures, and built the walls, because the quality and masonry mortar fire performance is poor, the brick wall of fire resistance thanBrick itself, but the General brick wall subjected to hours of burning is no problem. But when the fire broke out, brick wall or chimney collapsed there occur, mainly due to:
　　
(A) of the frame, frame fill wall is damaged;
　　
(Ii) because the floor collapse, or horizontal wall was destroyed, so that the longitudinal walls lost lateral support.
　　
(3) under the impact of external level.
　　
(4) the empty bucket walls, brick by brick deformation and damage, loss of bearing capacity.