The Characteristics And Seismic Design Of Steel Silo

At the beginning of the last century, people began to use steel silos for grain storage. At that time, riveting technology was usually used to rivet 6-12 mm steel plates into steel silos. However, with the development of welding technology, it gradually replaced riveting technology and became the main building method of steel silos. In 1968, the German Lipp used SM special equipment to build the spiral double-layer steel silo (called Lipp silo). The steel plate of Lipp silo body is only 3mm-4mm, but it has considerable ring tension strength and can withstand great radial pressure. At the same time, this kind of silo has the advantages of saving material, high strength and no leakage.
Nowadays, according to incomplete statistics, steel silos are occupying 92% of the total silo numbers in rice processing plants, flour mills, vegetable oil factories, food factories, wineries and other enterprises. Because they meet the needs of short storage time, high mechanization and high efficiency, they are favored by all kinds of enterprises. In this paper, after introducing the characteristics of the steel silo, we will make a further discussion on the seismic structure and seismic design of the steel silo.

The Structure of Steel Silo

The structure of steel silo can be divided into six basic parts as follow: the building above silo roof, silo roof, silo wall, silo bottom, supporting structure and the silo foundation. Usually, steel silos with diameter less than 10 m should adopt the overhead supporting structure and a conical bottom, which is beneficial to mechanized operation, while steel silos with diameter more than 12 m are suitable to adopt floor-type flat bottom and underground discharge chute. The foundation will bear most of the material’s weight.

Characteristics of Steel Silos

Compared with concrete silos and other types of silos, steel silos have the following characteristics:
 
Light Weight and Low Cost
The weight of the steel silo is approximately 1/4 to 1/6 of that of a reinforced concrete silo with the same volume, so its building saves a lot of cement, sand and other building materials, the cost is lower than that of the reinforced concrete silo. In addition, because of its light weight, the cost of infrastructure and foundation treatment is also greatly reduced. If the construction is in poor geological conditions, the cost of reinforced concrete silos foundation treatment may account for more than 50% of the total project investment. Overall, the total investment of steel silos is 20%-50% less than that of reinforced concrete silos.
 
Short Construction Period
Reinforced concrete silos are constructed by means of on-site steel binding and concrete pouring, the construction period is relatively long. While the materials used to build the steel silo are prefabricated in the factory and built on site by special equipment with the characteristic of simple operation and fast speed. Because there is no wet work in the installation process, the steel silo’s construction period is short. A steel silo of 6000t only takes about 15 days to install, which is 1/3 ~ 1/4 of the reinforced concrete silo of the same volume.
 
Low Construction Height and Large Occupation Area
The height of steel silos is limited to a certain extent, generally not exceeding their diameter. For silos with the same capacity, the height of reinforced concrete silos is not so limited and the area occupied is relatively small.
 
Short Service Life
Reinforced concrete silos generally have a service life of more than 50 years with very low maintenance costs. The service life of the steel silo is only about 20 years, and the maintenance cost increases year by year. However, if the material with strong anticorrosive property is used, the service life of the steel silo can be extended.
 
High Maintenance Cost
The maintenance cost of steel silos is higher because its surface is easy to rust, and it needs to be painted every 2-3 years. While the reinforced concrete silos have no need to be maintained after completion.
 
Poor Leakage-proof and Moisture-proof Performance
Because of its material characteristics, the reinforced concrete silo has good air tightness, good moisture-proof and rain-proof effect. It is less affected by the change of external temperature difference and is suitable for long-term storage of materials. The steel silo has a thin wall and is greatly influenced by the outside temperature. With the increase in its service life, the airtightness will become worse and worse. Therefore, it is only suitable for material short-term storage.

The Seismic Design of Steel Silo

Compared with other silos, steel silo has the characteristic of high-quality, high strength and strong earthquake resistance. However, in large earthquakes, if the silo is not strong enough and designed properly, there is a high probability that it will collapse. So a reasonable seismic structure is an essential part of the seismic design of the steel silo.
When steel column is used to support steel silo, as the wall of the silo is thin and the connection with the steel column is only structural, the reliable transmission of force cannot be guaranteed, so it is unfavorable to earthquake resistance. Therefore, in the construction process, the section and spacing of steel pillars should be determined by calculation, and we need to adopt batten plates to connect the pillars to the wall as far as possible. In addition, the spacing between batten plates should not be greater than 1.0m. However, the section of the steel column is generally small. Considering the overall stability of the supporting structure of steel silo, the supporting steel column should be supported by column bracing, and not less than two under each silo. This is an effective measure to ensure the overall stability of the structure.
Above contents are the things we talked about the characteristics and seismic design of steel silos. Hope this article will bring you some useful information.