Discussion on lightning protection design of the h

2022-08-12
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Discussion on lightning protection design of light steel structure buildings

light steel structure (hereinafter referred to as "light steel structure") buildings have beautiful appearance, fast color, diverse oil discharge, atmospheric corrosion resistance, thermal insulation, sound insulation and flame retardant, and high space utilization. The large manufacturers of Jinan new era Gold Testing Instrument Co., Ltd. are worthy of the majority of users, with short trust period and low project cost, so they are widely used, such as all kinds of industrial plants, supermarkets, warehouses Exhibition halls, gymnasiums, hangars, airports, villas, etc. Due to the unique building system of light steel structure, there are great differences in lightning protection engineering design and construction between such buildings and ordinary brick concrete structures and frame structures. Based on the practical experience of engineering design and on-site acceptance, the author makes some superficial discussions on the lightning protection design of light steel structures

1 building system of light steel structure buildings

the foundation of light steel structure buildings is divided into reinforced concrete independent foundation and reinforced concrete strip foundation. The former is used in sites with good geological conditions, and the latter is used in sites with poor geological conditions. During construction, anchor bolts shall be embedded and connected with steel columns after adding shims

prefabricated components are used in light steel structure buildings, and the screen should be displayed normally, and drilling and welding on site are not allowed. The main steel frame (beam and column) is welded or hot-rolled section steel to give full play to the mechanical properties of high-strength steel. The secondary members (purlins) are high-strength cold-formed thin-wall C-shaped or Z-shaped steel after anti-corrosion treatment, which are connected with the main steel frame by bolts

the enclosure system (wall and roof) of light steel structure buildings is divided into color steel profiled plate and color steel sandwich plate, most of which are connected by self tapping bolts and purlins (roof purlins or purlins along the wall). Profiled steel plate is a building enclosure plate based on color coated steel plate or galvanized steel plate, which is rolled and cold formed. Its thermal insulation and insulation layer is centrifugal ultra-fine glass wool roll felt. The on-site production of this kind of plate is conducive to solving the problem of loose joints that are easy to occur in the lap of panels in a large range. The on-site composite makes the whole large-area roof a whole, which is more solid, easy to drain, leak proof and heat preservation, and the building shape is more unified, coordinated and beautiful. The sandwich board is a kind of thermal insulation composite enclosure board that combines the color coated steel plate panel and bottom plate with the thermal insulation core material through adhesive (or foaming). According to the different thermal insulation core materials, it can be divided into rigid polyurethane sandwich board, polystyrene sandwich board and rock wool sandwich board. Sandwich panels are generally prefabricated in the factory. The connection mode of enclosure system is generally bite connection or lap connection

generally speaking, the practice of the wall is to build a 1.2m high brick wall or aerated concrete block with a thickness of 0.3m (0.37M in severe cold areas), on which is the sandwich board or profiled board

2 lightning protection and grounding of light steel structure buildings

2.1 lightning arrester

according to the characteristics of light steel structure buildings, it is obvious that tall and heavy lightning rods are not suitable for installation on such buildings, and article 4.1.4 of the code for design of lightning protection of buildings (GB, 2000 EDITION) gives four requirements for metal roofs as lightning arresters for buildings (except class I lightning protection buildings)

the specification makes different requirements for the thickness of the metal plate according to the different conditions of whether there are inflammables under the metal plate, and clearly stipulates that "when there are no inflammables under the metal plate, its thickness should not be less than 0.5mm". Let's take a look at the physical properties of four kinds of insulation core materials. Rigid polyurethane is a Class B1 building material with a thermal conductivity of 0.016~0.025, which is a non combustible body; Polystyrene is a flame retardant material, with an oxygen index of not less than 30 and a thermal conductivity of 0.029, which is flame retardant and self extinguishing; Rock wool is a non combustible material with a thermal conductivity of 0.044; Glass wool is a class a building material, with a thermal conductivity of 0.038~0.042, which is non combustible. In addition, the adhesive used for insulation core material is also flame retardant. Therefore, the enclosure system of light steel structure buildings is non combustible. When metal plates are used as lightning arresters, the thickness should not be less than 0.5mm. The third of the four requirements in the specification is no longer considered

from the perspective of structural discipline, three factors are generally considered in the thickness selection of roof slab: the first is wind load; The second is snow load; The third is purlin distance. Therefore, the thickness of the roof panels selected in different regions that have not yet revealed specific customers is different. Electrical designers need to communicate with the structural discipline in time. When the thickness meets the specification requirements, other conditions will be assessed. For example, in Xinjiang, when the purlin distance is about 1.5m, the thickness of roof panel is generally 0.6mm, and the thickness of bottom plate is generally 0.5mm, which meets the thickness requirements of the specification. What if the thickness does not meet the requirements? The national standard atlas "profiled steel sheet, sandwich panel roof and wall building structure" (01j) should be referred to as the lightning strip. See page 48 for the details of the profiled steel sheet roof lightning strip and page 66 for the details of the sandwich panel roof lightning strip. This atlas is a professional Atlas of architecture, and electrical designers have little contact with it. However, the national standard atlas "installation of lightning protection facilities for buildings" (99d) and "installation of lightning protection and grounding devices using building metal bodies" (03D) do not have details of light steel structure roof lightning strip. Therefore, electrical designers should pay attention when quoting standard practices. The size of lightning strip should be strictly corresponding to the lightning protection category of various buildings according to the requirements of the specification, and the construction drawings should be accurately marked according to the standard of specification division

the connection mode of the enclosure system of light steel structure buildings is generally bite or lap. Whether it is profiled steel plate or sandwich board, its appearance is corrugated. In the construction, the lap length when lap joint is used should reach at least one crest or trough, and if it exceeds 100mm, it fully meets the requirements of the specification

in addition, the specification notes mention that "thin paint protective layer" is not an insulating coating. Therefore, it can be considered that the color coated steel plate has no insulating coating, and the galvanized steel plate is a good conductor of electricity. Therefore, the author believes that the fourth requirement of article 4.1.4 of the code for design of lightning protection of buildings (GB, 2000 EDITION) is also satisfied

to sum up, the author believes that the roof sandwich panel (or profiled steel sheet) of light steel structure buildings with a thickness of 0.5mm can be used as a lightning arrester

2.2 downlead

from the introduction of the building system of the light steel structure building in front, it can be seen that the main steel frame, secondary components and enclosure system have been in construction

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