Globally, the research on the spread of fire in high-rise buildings has a long history. In the past few decades, there have been good engineering practices on how to control the spread of fire. Many countries and regions have adopted standardized tests for the fire-proof sealing method of the interlayer joints of curtain walls. Relevant building and safety regulations began to make provisions for high-rise buildings with curtain walls to ensure the safety of life and property.
In order to better understand how the fire spreads in high-rise buildings with glass curtain walls, we need to imagine a scene like this: if a fire occurs on a certain floor, as the fire spreads, the indoor pressure on that floor will slowly increase, and the curtain wall The glass in the middle ruptures under the engulfing of the flame, so that more oxygen is added to the room, which encourages the fire to increase further and spread to the bottom of the board on the upper floor and the inner side of the curtain wall structure. Moreover, a certain flame may burst out of the broken window and begin to attack the outer side of the upper curtain wall structure. If there is a gap between the floor and the curtain wall structure, the flame will quickly rush from this interlayer seam to the upper floor. For this challenge, it is necessary to design and install an interlayer seam fire protection system reasonably, which can maintain stability throughout the fire It can also meet the requirements of receiving fire on both sides and avoiding the vertical spread of fire.
Because many building materials of curtain wall structure are not refractory materials, it further aggravated the spread of fire in high-rise buildings. Profiles such as glass or aluminum are usually integrated into modern curtain wall structures. Under normal circumstances, these materials are deliberately made lighter and thinner, thereby weakening their fire resistance. -Under normal circumstances, the glass will shatter in 5-15 minutes after exposure to fire, and the aluminum profile will melt when it reaches 660°C. Although materials that are considered to have better fire resistance are sometimes used, these materials often fail in actual fires, for example, stone partitions such as granite, marble, travertine, or gray sandstone or the filled partition itself It is a good refractory material and will not burn. However, in a fire, these panels will rupture after being heated, and even due to different degrees of extension in all directions, or the stone contains a certain amount of moisture, it will explode after heating. Does this mean that these materials cannot be used? This is definitely not the case.
The most feasible way is to improve the fire resistance of these components by adopting a simple system with high-temperature insulating materials, and at the same time, correctly install a fire-proof sealing system. This article discusses related issues and shares related engineering application experience.
(2) Introduction of fire-proof sealing system for interlayer seams
Fire-proof sealing system for interlayer seams, the term quickly became synonymous with preventing the spread of fire in high-rise buildings. The fire-proof sealing system of the interlayer seam includes fire-resistant floor slab components, external wall components and materials installed in the gap between the external wall and the floor slab. These materials avoid the formation of fire spreading channels between floors.
Some countries have adopted some test standards to evaluate the relative performance of the interlayer joint fire protection system. One of the standards is ASTM E2307-10, the American Standard for Fire Resistance of Interlayer Joints (ISMA), which uses a two-story medium-scale structural model to evaluate the performance of fire-proof sealing systems for interlayer joints in high-rise buildings. Fire-resistant aging, the front of the model is a glass curtain wall structure; the upper floor is the observation room, the lower floor is the laboratory (furnace), and the upper and lower floors are reinforced concrete floors. The fire protection system is installed in the horizontal gap between the floor slab and the curtain wall separation zone
After the test structure is installed, light the furnace in the laboratory. Five minutes later, another fire source outside the glass curtain wall was ignited to simulate the rising flames after the window was broken. That is to say, while the external components of the curtain wall structure are directly exposed to fire, the internal fire source has attacked the internal components of the curtain wall structure, the bottom of the floor and the related materials of the fire-proof sealing system of the interlayer seam. The termination of the test is based on the occurrence of the test failure phenomenon or the termination after the expected fire resistance aging is reached. Test failure refers to the phenomenon of flame passing through the fire-proof sealing system in the observation room. In addition, if there are any hot spots, it is also regarded as a test failure. By covering the interlayer seam fire protection system of the observation room with a piece of cotton mattress and keeping it for 30 seconds to observe whether there are cracks or holes in the fire protection sealing system. If the cotton mattress burns, the fire blocking system is also considered to be ineffective. If the blocking system cannot effectively reduce the heat from the overheated glass, the cotton mattress will burn prematurely.
During the test, the heat diffusion is analyzed by monitoring the temperature of the backfire surface. The fire-resistant aging and heat-resistant aging tested are based on the relevant procedures of ASTM E2307-10. Fire-resistant aging is the time for the fire blocking system to block the passage of flames; heat-resistant aging is the effect of heat transfer in the measurement system. Most curtain wall fire-proof sealing systems use aluminum profiles or anchors with good thermal conductivity, and their heat-resistant aging does not exceed 15 to 30 minutes, and the fire-resistant aging usually can reach 2 hours or more.
(3) The structure of the fire blocking system for the interlayer seam
2,1 mineral wool partition installation
The most common aluminum frame curtain wall structure with traditional (flammable materials, such as glass, aluminum or stone) partitions uses high temperature resistant mineral wool partitions. The mineral wool partition is made of slag wool or rock wool, which can withstand high temperatures up to 100 degrees. The vertical and horizontal members of the curtain wall frame around the partition are usually wrapped with mineral wool partitions (usually with a density of 96-128kg/m3). There are various ways to install mineral wool boards. Sometimes steel plates are used, but usually, the role of steel plates is only to beautify the shape of the partition; sometimes a series of horizontal steel members are installed on the partition between the vertical members; or through some steel clamps and steel nails. Fix the mineral wool board. In addition to fixing the mineral wool board with steel anchors and protective covers, usually steel bolts with large steel washers or cup-shaped welding nails can be used to fix the mineral wool board on angle steel, steel plate or channel steel at the overlap. The mineral wool partition of this curtain wall is a vital component. After the insulation layer on the exterior of the curtain wall is dropped, although the surrounding aluminum profiles and partitions will melt and fall due to heat, the mineral wool partitions can still maintain the integrity during the entire process of the fire-proof containment system.
Another component that must be installed is the horizontal clamping groove. It is placed between the vertical frames, fixed to the side angle steel, the vertical frame, or is spot welded or seam welded to the steel back plate. The location of the clamping groove is directly collinear with the location where the fire containment system will be installed, so it should be installed at half the thickness of the floor. Tightening grooves can be constructed with channel steel, steel vertical bars or two angle steels joined to form a’T’. The clamping groove is installed when installing other mineral wool support grooves (angle steel or backing board) and installed behind the insulation layer of the curtain wall. Its main function is to ensure that the fire-proof sealing system (the mineral wool) is in a compressed state when exposed to fire.
Fire blocking of 2,2 horizontal seams
After introducing the installation of the mineral wool partition of the curtain wall structure and the related supporting system, it is necessary to introduce how to plug the horizontal interlayer seams. The correct way to plug the horizontal seam is to insert a light-weight (usually 64kg/m3) mineral wool sliver in the seam. Cut the mineral wool board into a certain width of mineral wool slivers, and put several mineral wool slivers together, which is about 25% to 33% wider than the interlayer seam, so that a compression rate of 20% to 25% can be obtained. When installing, the mineral wool strip should be kept flat, usually the surface of the mineral wool is flat with the floor. Under normal circumstances, mineral wool only needs to be squeezed tightly and no additional supporting members are required. After installing the mineral wool, make a layer of fireproof sealing layer or apply fireproof sealing glue on the surface of the mineral wool. These products are usually latex substrates, most of which can be painted or sprayed with a spray machine. This layer of fireproof sealing layer is very important.On the one hand, it can glue the various components (several mineral wool strips, the frame of the curtain wall and the edge of the floor) together to form a system; on the other hand, it is A sealing layer that can not only ensure the integrity of the mineral wool, but also isolate the high-temperature flue gas; sometimes, the silicone base material can also be used for waterproofing.
For some designs, the last step in the interlayer seam fireproof sealing system is the protection or wrapping of the curtain wall mullions. This is a very small part of the curtain wall insulation layer made of the same mineral wool. By wrapping the mullions on the upper and lower floors with mineral wool boards, the thermal insulation performance can be improved, and the thermal insulation layers of the curtain wall can be connected to form a continuous fire separation belt.
Four) Prevent the spread of smoke
At the fire scene, smoke is a fatal factor. The correct fire-proof sealing system for interlayer seams can help reduce the spread of smoke. Usually, the insulation layer of the curtain wall structure is provided with aluminum foil at the separation zone. In addition, the fireproof sealing layer or fireproof sealing glue is used as a continuous component to block the spread of smoke in the void. Many related laboratories have established air tightness laboratories for testing fire-proof sealing layer or fire-proof sealing glue. The best fire containment system can achieve a release rate of less than 1 liter per second per unit length.
When a fire occurs, the pressure in the fire area gradually increases, and smoke and combustion byproducts lighter than air begin to accumulate on the ceiling. If the pressure continues to increase, which smoke and combustion by-products will be squeezed into some unplugged holes. In addition, in high-rise buildings, due to the pressure difference caused by the temperature difference between indoor and outdoor, the airflow movement forms a chimney effect. The chimney effect is considered to be the main reason for the vertical movement of smoke. The higher the height of the building, the more obvious the chimney effect. Using some products with better airtightness can help cope with the vertical spread of smoke
(5) Engineering case
On February 9, 2009, a fire broke out in the commercial and residential building at 510 Madison Avenue in the United States during the reconstruction process (see Figure 1Ol, the fire was effectively controlled on the fire floor (2nd floor X, see Figure 11), the building adopted the United States ST丨Special Technology Co., Ltd. provides a fire blocking system. What is worth thinking about is that a fire broke out in the North Power Distribution Building of the CCTV building just completed in China on the same day, but the fire spread so severely that almost the entire building was overfire.
(6) Conclusion
The fire prevention plan introduced in this article is mainly to limit the spread of fire, smoke and combustion by-products in the interlayer seams. Due to the vertical construction of the curtain wall structure itself, the gap between the relevant links of a relatively large curtain wall structure and the floor slab naturally exists, and sometimes it may be for the installation of water pipes or the leveling of independent partition walls. The floor slab can effectively ensure that the function of the fire compartment can be extended to the outer wall of the building through the fire-proof sealing system of the interlayer seam. The modern fire blocking system aims to design a safe and simple interlayer seam fire protection system, while meeting other needs. Of course, some regions, such as China, have not established a complete interlayer seam sealing system testing program, but the relevant engineering guidelines provided by qualified engineers can be used to enable the people in the region to adopt more suitable The fire-proof sealing system of the interlayer seam can construct safer buildings for production and life. Typical fire-proof sealing products usually (before they are sold) need to be tested tens of thousands of times under different working conditions according to relevant regulations, and the relevant performance test reports confirm that they can be used in various specific situations. Using these products, in the case of no increase in construction costs, in addition to playing the role of fire and flame retardant, but also can achieve the effects of heat preservation, energy saving, moisture prevention, fog prevention and sound insulation.
