How to prevent lightning in steel structure factories?
In recent years, due to the advantages of beautiful and elegant appearance, short construction period, and low engineering cost, light steel structure buildings have been widely used in various industrial factories, warehouses, sports venues, and other places. However, metal sheet roofs are prone to lightning strikes, which is different from the lightning protection design of ordinary brick and concrete structures and frame structures.
1. Lightning arrester
According to the light steel structure of buildings, using lightning rods is bulky and not in harmony with the overall appearance of the building. However, using a metal roof as a lightning arrester must meet the four requirements given in Article 4.1.4 of the Code for Design of Lightning Protection of Buildings.
In response to the regulatory requirement that "when there are no flammable materials under the metal plate, its thickness should not be less than 0.5mm". The enclosure structure (roof) of the main workshop building is made of hot-dip aluminum zinc coated steel plate, with a substrate thickness of 0.53mm (including aluminum zinc coating). A 75mm thick glass wool pad is added under the roof panel, wrapped in aluminum foil, and coated with φ 1.5 Non embroidered steel wire mesh layer support and upper edge of purlins. Glass fiber cotton belongs to A-grade building materials, with low thermal conductivity, flame retardant, non-toxic, and stable chemical properties, fully meeting the requirements of non flammable standards. According to civil engineering professionals, bite and overlap are used in the construction of the enclosure system connection method for light steel structures. The tower connection length must reach at least one peak or valley, and exceeding 100m is fully compliant with regulatory requirements.
In addition, as mentioned in Article 4.1.4, "the metal plate has no insulation coating". The hot-dip aluminum zinc steel plate used for the roof is a good conductor, and the thin paint protective layer applied on the surface is not considered an insulation coating according to the specifications, so it meets the requirements of the specifications.
In summary, in this project, the metal panel of the roof light steel structure can be used as a lightning arrester, which is not only aesthetically pleasing but also reduces the project cost, makes installation convenient, and does not affect the overall effect of the building.
To design a lightning protection system for metal sheet roofs, in addition to selecting a good lightning protection form and selecting a good lightning arrester, it is also necessary to do a good job in the down lead and grounding work.
2. Down conductor
For light steel structure buildings, there are many types of colored profiled panels, which are divided into single panel and composite panel. Composite panels are used in this workshop. During construction, we require coordination between the civil engineering and electrical specialties to ensure reliable connections between the roof metal compression plates, roof trusses, purlins, and steel columns. Therefore, steel columns are used as down conductors throughout the construction process. This is also stipulated in Article 4.2.3 of the Code for Design of Lightning Protection of Buildings, which states that metal structures such as fire ladders and steel columns in buildings should be used as down conductors.
3. Grounding device
At present, in design, we often use foundation steel bars as natural grounding bodies, connect them with 40X4 galvanized flat steel, and implement overall equipotential bonding. In this design, we did not strictly require the use of 40X4 galvanized flat steel, but instead relied on reliable welding between the strip foundation between the steel columns and the independent foundation of the steel columns to form an electrical pathway. For buildings with light steel structures, during the construction of independent foundations for steel columns, civil engineering should embed anchor bolts, so that when the steel columns are in place, the anchor bolts, nuts, and steel columns can be connected together. Please note that the anchor bolts and steel column foundation reinforcement are not connected underground! So, electrical designers need to require civil engineering professionals to indicate construction in the design specifications
