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How to Solve Steel Silo Instability?
With the development of silo industry, people have developed spiral steel silo, which is widely used in our lives. However, precise calculation on the design of spiral steel silo is very crucial for the safety. The workers must pay attention to each detail for laying good foundation for silo construction. Next, we will introduce buckling analysis of spiral steel silo on the design.
Buckling analysis is mainly used to study the stability of the structure under certain load and to determine the critical load of structural instability. From the actual use document of domestic and foreign spiral steel silo, there have been a number of steel silo accidents due to their instability. Most of the accidents occurred in the unloading process, whose typical performances are silo body tilt after the local crowning and folding. Some are caused by wind load and other factors in the construction process. They have caused huge economic losses and casualties. Therefore, the stability problem of the steel silo has become more and more important, which is valued by domestic and foreign scholars all over the world.
The Analysis of Steel Silo Instability
In the structure, spiral steel silo mainly belongs to cylindrical shells under axial load. Its instability is characterized in crowning, tilting and collapse in the local part of the silo wall.
Main Reasons of The Tilt and Collapse of The Silo Are As Follows:
- Due to the eccentric loading and unloading, they bring uneven lateral horizontal pressure, or due to center loading, the rest of the material will form the horseshoe-shape block because of limits of free flow. And then, the circumferential pressure is not uniform, which is the lateral interference force. (Including wind load) Therefore, when the vertical force reaches the critical point, the silo will lose stability.
- The horizontal dynamic load side pressure increases as the unloading results in the increase of the vertical friction force of the material on the wall, that is, the vertical pressure on the wall of the silo is increased, and then the instability factors of the steel silo are intensified.
- The material forms the bridge on the unloading hole, and between the bridge and the unloading hole here will form local empty areas of unloading which will cause the formation of decompression area inside the silo. Meanwhile, at the bridging moment the area may still be in the state of material flow. This situation may bring about lateral horizontal pressure or other factors that result in lateral disturbance force. At the time, the silo wall pressure is suddenly increased, especially under the interactions of the bridging formation and collapse. This lateral horizontal pressure of the silo wall increases suddenly, which generally exacerbate the instability of the silo.
The Methods of Solving Instability of Steel Silo
- To fully calculate the load capacity of the steel silo when it is completely loaded, so as to design the bearing capacity of the foundation.
- To fully check the bearing capacity and soil density of construction site of the steel silo in order to get a reliable and practical foundation.
- To set up settlement observation area to make the above calculation and check work well. At the same time, get the difference between steel silo load and the bearing capacity of the foundation through the calculation.
- The level of the foundation settlement of steel silo must be equal to the height of the settlement area under the silo. Otherwise, the silo cannot be evenly sunk.
- After calculating the difference between the heavy load of steel silo and the bearing capacity of the foundation, according to the allowable value of the compression modulus of the foundation, through the increase of the soil density of the foundation soil, we can finish the bearing capacity of the steel silo that is needed.
- Spiral steel silo belongs to thin cylindrical shell under axial friction load and radial horizontal load. The instability of the silo can be attributed to the crowning in the some parts of the silo wall. That is to say, steel silo buckling may bring about a ripple in the height direction of the silo wall, similar to the sine curve, and then the ripples may be different in the number in the circumferential direction of steel silo wall. With the further development, this will cause the tilt and collapse of steel silo body, so it belongs to longitudinal instability.
- The instability of spiral steel silo is most likely to occur in the unloading process. In the process vertical pressure aroused by material friction in the silo wall will cause the structure damage of the steel silo, which is the most common form, namely buckling of cylindrical shells under axial compression. In the calculation of the critical load, considering the adverse effects of various factors and the good effects of the internal pressure, we should value the critical stress formula under the interaction of vertical stress and horizontal pressure on the silo wall. From the results of buckling analysis, due to its unique structure, its buckling form is a sinusoidal characteristic of deformation curve along the height direction. At the same time, around the silo wall the ripples are with different numbers. This situation is caused by the dynamic flow of stored material. Although it is rarely used to control the buckling analysis of the steel silo in the engineering design at present, we should strengthen the bending stiffness of the column and the thickness of the wall in order to prevent the buckling instability and failure of steel silo.
The detailed design at the early period can effectively protect the lifespan of the silo. The steel silo Flyer Company designed and manufactured creates quality with real strength to win customers. Please feel free to contact us for any information you want to know.
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