In the United States, multi-story light steel structures are mainly used in multi-story apartments and hotels. The earliest multi-story light steel residential building was designed in 1990. So far, the total area of ??multi-story light steel structures has grown to approximately 300,000 square meters. Judging from the development situation, the United States has successfully carried out the research and development and engineering application of multi-story light steel structure residential systems, and has many mature technologies that can be used as a reference for the development of multi-story light steel residential systems in my country.
The multi-story light steel structure residential technology in the United States is a comprehensive technology that integrates light steel structure, building energy saving and insulation, building fire protection, building sound insulation, new building materials, design and construction. , the social division of labor is clear, and manufacturers, constructors, and designers of various products work closely together. Under the promotion of the North American Metal Structure Association, it develops rapidly relying on the newly compiled light steel structure design standards and extensive publicity. It can be expected that the construction of light steel structures will be a major structural development direction for the construction of multi-story apartments and multi-story hotels in the United States.
The most critical issue in developing multi-story light steel structure residential technology is the performance of the structure itself. The floor structure must have an appropriate span and be as light as possible, and it is hoped to have a better floor plan. Stiffness, the wall structure not only bears vertical loads (self-weight and floor live loads) but also lateral loads (wind loads and horizontal earthquake effects). The characteristics of multi-story light steel structure residences in the United States are:
1. Lightweight floor system. The floor consists of C-shaped light steel joists and thin plates laid on the joists. The general span of joists is 3.6 meters to 4.8 meters, the joist height is 254 mm (the maximum span of joists can reach 11 meters), and the joist spacing is 600 mm. The patented joist product developed by the American company Dechuchi has large holes on the web, which is extremely convenient for the passage and arrangement of pipelines. There are three methods for flooring, namely: high-density wood fiber cement boards; full paving of profiled steel plates and then pouring 20 mm ceramsite lightweight aggregate concrete; full paving of oriented wood fiber boards or high-density laminated plywood. These lightweight floors can bear a load of 316 to 365 kilograms per square meter.
The weight of the floor structure system is only one-quarter to one-sixth of the traditional domestic concrete floor system, but the structural height of the floor will be 100 to 120 mm higher than ordinary concrete slabs.
2. Vertical wall structures generally use the inner transverse wall as the load-bearing wall of the structure. The wall columns are C-shaped light steel components. The wall thickness depends on the load, usually 0.84~2 mm. The spacing between wall columns is generally 400~600 mm. The lower end of the wall column is a bottom channel beam with a U-shaped opening facing upward. The upper end of the wall column is a top channel beam with a U-shaped opening facing downward. The joist is fixed to the side of the upper channel beam. . In order to improve the stability of wall columns, generally three light steel braces are provided within the height range of wall columns. This wall structure arrangement can effectively withstand and reliably transmit vertical loads, and is easy to arrange, but the wall structure cannot withstand horizontal loads.
In order to resist horizontal wind loads and earthquake effects, there are two methods of multi-story light steel structure residential systems in the United States, namely the use of light steel shear walls or the use of ordinary steel frame structures with cross bracing. Light steel shear walls are generally arranged in household walls. They use 0.5 mm galvanized thin steel plates to cover gypsum boards and then fix them on light steel wall columns to form a shear wall similar to a stress skin structure. Between each layer A special component connects the shear walls of the upper and lower floors to effectively transmit horizontal shear forces and tensile forces due to horizontal forces acting on the wall columns. In earthquake areas, in order to ensure structural safety, ordinary steel frames with cross supports are used as lateral force-resistant structures, forming a hybrid structural system in which light steel bears vertical loads and ordinary steel bears horizontal loads.
3. Building insulation and energy-saving technology
In the American light steel residential system, great emphasis is placed on insulation and energy-saving technology. For walls, in order to ensure the insulation effect, generally in addition to the wall In addition to filling glass fiber between the columns, a layer of insulation material is affixed to the outside of the wall, effectively blocking the thermal bridge from the wall columns to the exterior wall panels; glass fiber is filled in the joists between floors to reduce heat transfer through the floors; all interior The walls and walls are filled with fiberglass to reduce heat transfer between the walls.
4. Building fire protection technology
One of the most critical issues for light steel structures is the application of fire protection technology. Fireproof gypsum boards should be pasted on both sides of the wall and the ceiling of the floor. For ordinary fireproof walls and subdivision walls, use 25.4 mm thick (1 inch) gypsum boards to protect them to meet the 1-hour fire protection requirement. In addition, the glass fiber filled between the wall columns and the floor joists is good for fire protection and heat transfer. It also plays a positive protective role. These products have passed the testing and certification of the US UL certification laboratory. The fire resistance limit requirements of American houses are lower than those in China. This is related to the fact that American residential design places more emphasis on ensuring the time required for escape, rather than placing too much emphasis on the fire resistance limit requirements of the house itself.
5. Building sound insulation technology In light steel buildings, American research and development work has put a lot of effort into sound insulation. Glass wool is filled between the internal and external walls and floor joists, which effectively prevents the air from passing through. The audio part of the propagation, and for the impact sound propagated through solids, in the multi-story light steel residences in the United States, the following structural processing has been done: for the household wall, two walls are constructed with two walls with a gap in the middle; For the small keels used to fix the gypsum boards on the ceiling, an elastic structure with small slots is used to effectively reduce the transmission of solid sound between floors.
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