Some Problems about the Design of Ground Steel Silo
Ground Steel Silo is an important type of large steel silos. As we know, the column-supported steel silo is suitable for small and medium steel silos. The weight and large diameter of large steel silo is decisive for us to choose the ground type of steel silo. Judging from the seismic capacity, the column-supported silos are similar to the structure of chicken feet, so they cannot meet people’s needs. Therefore, when there are no special restrictions, especially for heavy load, high center of gravity overhead material storage, we should adopt ground steel silo.
With the continuous development of production demands and the requirements of saving the land, more and more tens of thousands of cubic meters of storage capacity of large steel silo are being put into use. Due to reasonable cylindrical structure and material consumption, large steel silos are highly valued.
However, a large number of large diameter steel silos have also brought us many engineering accidents in application. So some crucial problems must be paid attention to in the design of ground steel silo.
Structure of silo body
Large diameter steel silos adopt ground type in design mostly. The cylindrical silo is a typical thin-walled structure. Theoretically, when the ratio of the thickness and the minimum curvature radius (i.e. silo radius ratio) is less than or equal to 1/20, it can be considered as a thin-walled structure. The wall thickness ratio of large diameter steel silo is much smaller, even more so). So this structure perhaps brings us a series of problems we need to solve.
Problems of silo body
The core problem of steel silo in design is the stability. According to the geometric parameters of the cylindrical wall, it can be divided into short cylindrical wall, medium cylindrical wall and long cylindrical wall, which have different instability modes corresponding to the critical stress respectively. Steel silos belong to the long cylindrical wall. For large diameter Steel silos, most of them are not provided with the conical buckets that are directly connected with the silo walls. So there is no stability problem of ring beam. According to the stress state of steel silos, except that the wall parts at the places influenced by the wind pressure may be instable or collapsed, another two kinds of stresses may cause the instability of silo wall. The first is the instability arousing from the vertical stress (Including the friction between the material and the wall, the load of structures on the silo roof, wind load, seismic moment, etc.) over the critical stress. The vertical stress is generated by the horizontal overturning force. The second is the instability arousing from the shearing stress generated on the horizontal section plane of the wall. At present, the relevant specifications of silo adopt the method of unified reduction based on the theory formula after the comprehensive consideration of various unfavorable factors. At the same time, the factor of the improvement of loading capacity of ring tension stress to the wall.
Besides the above, the parameters of bulk materials in the aspects of humidity, compaction, size and others are fluctuated within certain constraints. So in design, we should calculate and take different parameter limits to enable the structure to be operated under the state impacted by the most adverse effects. Many factors can affect the pressure value of inner silo. Through the calculation, we can obtain the most valuable data. The result is that the pressure exceeds the storage pressure in the static state when the materials will flow, and with the increase of flowing rate, horizontal pressure also increases. But the specific reasons and distribution rules are still not clear. Thus the storage standard of China adopt the correction coefficient that is equal to static pressure of the materials multiplied by >1value of dynamic pressure. We don’t need to consider specific flowing pattern of the materials.
The eccentric loading problem
In the design of the steel silo for bulk storage, the loading process is a very crucial problem. The problem of eccentric loading and unloading can make the lateral pressure changed. The uneven horizontal circular material pressure will generate vertical and circular bending moment and cause the overall displacement of the silo and its changes of plane shape. In European and American nations, the eccentric loading and unloading problem is highly valued. They demand that the effect of asymmetric internal pressure must be carefully considered even in the case of symmetrical loading and unloading of the silo.
Many facts prove that most of the silo accidents are closely related with the eccentric loading and unloading operations. Therefore, we cannot ignore the importance of this problem.
The seismic problem
Another problem of steel silo is the earthquake. The bulk material also has certain rigidity. In fact, we can regard silo wall and storing materials as a composite combine structure consisting of two kinds of materials. The horizontal seismic impact will be distributed on the silo wall and silo bottom.
In addition to the above problems mentioned, the structures of silo roof, silo bottom and silo foundation have their own characteristics. In the design, we should fully consider various unfavorable factors.
The key problem of steel silo in design is the partial stability of the silo wall under the effects of vertical stress. We know that stable stress usually can control with the thickness of the wall. Because the rigidity of steel silo along the silo eaves is very small, so it is very sensitive to non-uniform load and we should pay more attention to it.
Ground steel silo is a kind of very good large building for storing materials. It needs relatively high industrial requirements, so the design is the most important job for us. FLYER Company has rich experience in design and construction of modern large spiral steel silo. We can effectively solve complex design problems you may meet. If you have any problems or requirements, please contact with us freely. We will provide you with relevant specified information. Expect to set up sincerely friendship with you!