As a specialized industrial grain storage structure, steel silos require comprehensive design consideration of four main load factors: permanent loads, variable loads, temperature effects, and seismic effects, to ensure the structure's safety and durability under complex operating conditions.
Permanent loads are the fundamental loads that steel silos bear over the long term, primarily including the structure's self-weight, the weight of fixed equipment, and the self-weight of the internal suspension system. The structure's self-weight encompasses the weight of the steel silo walls, roof, supporting components, and connecting nodes, and its value must be accurately calculated based on the design dimensions. The weight of fixed equipment, such as ventilation equipment and grain condition monitoring devices, must be added item by item from the equipment list. The weight of the internal suspension system, such as cables used to monitor grain temperature and humidity, must be considered, along with the additional tensile force generated by friction with the grain. These loads remain largely constant throughout the structure's service life and are the primary fundamental conditions that must be met during design.
Variable loads are a key challenge in steel silo design, as their magnitude varies significantly with time and operating conditions. The grain storage load is the core variable load, and its effect is closely related to the type of grain, bulk density, and loading height. Different grains exhibit significant differences in physical properties. For example, rice has a smaller internal friction angle, making it prone to forming flow zones; while wheat has a higher bulk density, resulting in greater lateral pressure on the silo walls. The design must employ the most unfavorable grain parameters for structural stability, considering the combined effects of changes in grain loading height on the horizontal pressure on the silo walls, the vertical pressure at the bottom, and the vertical friction force on the walls. Furthermore, live loads on the silo roof (such as those from maintenance personnel and equipment operation), snow loads, wind loads, and loads from movable equipment must also be included in the design. For instance, wind loads have different effects on independent silos and silo clusters, requiring adjustments to the wind load shape coefficient based on the silo cluster layout.
Temperature effects are caused by changes in ambient temperature. The thermal expansion and contraction characteristics of steel lead to temperature stress in the silo structure. In areas with large diurnal or seasonal temperature differences, temperature stress can cause silo wall deformation, loosening of connections, and even cracking. The design must utilize structural measures such as expansion joints and flexible connections to release temperature stress, for example, by installing sliding supports between the silo walls and the foundation to allow for free expansion and contraction of the silo structure. Meanwhile, the impact of temperature on the mechanical properties of steel must be considered. The yield strength of steel decreases at high temperatures, necessitating an appropriate increase in structural redundancy.
Seismic action, though an accidental load, has a significant impact on steel silos. During an earthquake, the inertial effect of the stored material superimposed on the structural dynamic response can lead to silo overturning, connection failure, or foundation anchorage failure. The design must calculate horizontal and vertical seismic forces based on seismic intensity and site conditions. For areas with high seismic fortification intensity, vertical seismic action calculations must be performed on the connection between the silo's lower hopper and the silo wall, and seismic structural measures such as reinforced supports and the addition of dampers must be implemented. For example, the vertical seismic action coefficient can be taken as 0.1 in an 8-degree fortification zone, but needs to be increased to 0.2 in a 9-degree fortification zone.
Load combination is a core aspect of steel silo design. The most unfavorable load combination must be selected and verified based on the structural usage stage (empty, full, eccentrically loaded) and the probability of simultaneous load action. For example, when the silo is full, the grain load, wind load, and seismic action must be considered simultaneously; when the silo is empty, the combined effect of wind load and temperature action needs to be carefully calculated. Through scientific and reasonable load combinations, sufficient load-bearing capacity and stability can be ensured even under extreme conditions.
The design of steel silos requires a systematic consideration of four major load factors. Through precise calculations, reasonable combinations, and structural optimization, the safety and durability of the structure under complex working conditions can be ensured.
