Key Design Considerations for Large Fly Ash Steel Silos

 The design and safety of large steel silos have a crucial impact on industrial production, material storage, and enterprise operations. A scientifically sound design must not only meet the characteristics of materials such as density, flowability, and flammability, but also ensure that the silo maintains sufficient strength and stability under wind loads, earthquakes, temperature changes, and long-term use. Simultaneously, good ventilation, temperature control, corrosion prevention, and environmental protection facilities can effectively prevent safety hazards such as material mold, condensation, and explosions. Improper design may lead to serious accidents such as silo collapse, blockage, fires, and dust explosions, causing casualties and huge economic losses. Therefore, large steel silos must be comprehensively and meticulously designed from structure and process to safety monitoring systems to ensure storage safety, efficient operation, and sustainable development for the enterprise.

Large steel silos have large storage capacities, high heights, and complex structural designs. They are significantly affected by dynamic loads such as seismic and wind loads. Therefore, the safety and reliability of the structural design must be given full attention and guaranteed.

Meanwhile, considering the complex stress on the structure of large steel silos, this project, in the design process, based on theoretical calculations, used internationally renowned finite element analysis software such as STAAD to establish an overall model of the silo body and roof assembly, and conducted finite element analysis to accurately calculate the stress distribution characteristics and deformation features of the structure under load conditions such as dead load, storage load, live load, wind load, and seismic action, as well as load combinations, to ensure the safety and reliability of the structural design.

Silo Roof Structure Design

Taking a 63,000 m³ fly ash steel silo as an example, the silo is a large welded steel silo. The roof adopts an arched structure design with strong support and good drainage performance. The roof height is 8 meters, and the steel plate thickness is 5 mm. The entire roof structure adopts a truss structure, including truss beams, circumferential tie rods, cross bracing, and reinforcing flat steel. This design significantly enhances the safety and stability of the roof structure.

The silo wall is constructed by butt-welding steel plates of varying thicknesses. Depending on the thickness of the steel plates, the silo wall consists of 20 sections from bottom to top. The steel plate material is Q355B. The silo body uses channel steel for support. Vertical reinforcing ribs are installed inside the silo, and circumferential reinforcing ribs are installed outside the silo wall. The reinforcing ribs are fully welded to the silo wall. Both the circumferential and vertical reinforcing ribs are made of Q355B steel.

Structural Design Calculations

The structural design of the silo has fully considered the self-weight of the structure, the self-weight of the process equipment, the live load on the silo top, the storage load, wind load, seismic action, and other dead and live loads and their combinations during actual operation. The following loads are considered in the design: 

1) Dead load: self-weight of the steel structure 1) Self-weight of process equipment and supports
2) Live load: Roof live load 0.5kN/m2, ash accumulation load 1.0kN/m2, platform live load 6.0kN/m2, walkway live load 6.0kN/m2
3) Material storage load: Fly ash, process design density 0.8t/m3, structural calculation unit weight 8.5kN/m3
4) Dynamic load: Dynamic load of process equipment operation (applied as static load multiplied by the corresponding dynamic load coefficient)
5) Basic wind pressure: 0.54kN/m2 (50-year return period)
6) Basic snow pressure: 0.3kN/m2 (50-year return period)
7) Seismic action: Seismic fortification intensity VII (0.15g)

Material Storage Load

The material storage load was strictly considered based on the actual working and operating conditions of the equipment. The silo stores fly ash with a density of 0.8 tons/m³. A certain degree of redundancy was considered in the calculations, and the unit weight was set at 8.5 kN/m³.
Under the combined conditions of material storage load, live load, wind load, and seismic load, the maximum stress in the silo body (261 MPa) is less than the material’s design strength of 310 MPa, indicating that the silo structure is safe.

During the design process, this project fully considered the structural self-weight, storage load, live load (including ash load, roof live load, snow load), wind load, earthquake and other dynamic loads. Based on the specifications, the steel plate silo structure used in this project was accurately calculated using finite element methods to ensure structural safety. At the same time, weak points were reinforced, and the safety and reliability of the structure were fully guaranteed during the design process.