Does The Steel Silo Have To Be Basic?
The vast majority of industrial steel silos need to be supported by a reliable infrastructure. The role of the foundation is not only to support the weight of the steel silo itself, but also to bear the weight of the materials stored inside and the equipment on the top of the silo, as well as to resist the horizontal forces such as wind loads and seismic effects. With different capacities, different silo types, and geological conditions on different sites, the corresponding basic plans are completely different. There is no unified fixed standard for the foundation of steel silos. Each project needs to be designed in accordance with actual conditions, and the plans of other projects cannot be directly copied.
Why Does The Steel Silo Need a Foundation?
The core role of the foundation is to safely transfer all the load of the steel silo to the foundation soil layer.If placed directly on ordinary ground, the bearing capacity of the soil layer is often not enough, and it is easy to sink or even collapse. In addition, the foundation must also ensure the overall stability of the entire silo.Especially steel silos with higher heights will be subjected to a lot of horizontal thrust in windy weather. Without basic anchoring and counterweight, it is easy to tilt or even capsize. Controlling uneven settlement is also the key role of the foundation.Once the foundation sinks more on one side and less on the other, the silo body will be skewed, which not only affects the discharge, but also causes the steel plate structure to produce additional internal force and shorten the service life. Supporting structures such as unloading equipment and conveying devices at the bottom of the silo also need a stable foundation as the installation benchmark.Without a flat and firm foundation, these equipment is difficult to install accurately, and it is easy to malfunction during operation. Therefore, it is impossible for an industrial steel silo with a slightly larger capacity to be simply placed directly on the ground. Even if the site looks very flat and strong, the basic design cannot be omitted.
What Loads Does The Steel Silo Foundation Need To Bear?
Many people think that the foundation only needs to support the weight of the silo body and grain. In fact, there are many types of loads to be considered in the actual design. The first is the weight of the empty silo, including the weight of the steel structure itself such as the steel silo wall, the top of the silo, the reinforcement ribs, and the internal funnel. Then there is the weight of the stored material, which is usually the source of the largest proportion of the load in the basic design.For example, in a silo of the same volume, the weight of cement and wheat is much different, and the foundation force is completely different. The weight of the top of the silo and the equipment on the silo cannot be ignored, such as the dust removal equipment, maintenance platform, guardrail, and conveyor head on the top of the silo, which add up to a lot of load. There are also conveying equipment and unloading devices for incoming and outgoing materials. Some of these equipment are installed on the foundation and some are connected to the silo body. Their weight and dynamic load during operation must also be included in the calculation. In addition to these vertical loads, horizontal loads such as wind loads and seismic effects must also be considered.The wind load in coastal areas and the seismic effects in high-earthquake areas often become the controlling factors of basic design. In addition, dynamic loads will be generated during the loading and unloading process, such as the impact of material falling and the friction changes of material flow during discharge, which will also produce additional forces on the foundation. Simply put, although the weight of the material is a big head, it is definitely not the only factor to be considered in the basic design.
What Are The Basic Types Commonly Used In Steel Silos?
At present, there are three main types of steel silo foundations commonly used in the industry, which correspond to different silo capacity and geological conditions.
Reinforced Concrete Ring Foundation
This is the most common basic form of circular steel silos. The foundation is only made directly below the silo wall, which is circular in shape, and the middle area is generally only made of thin cushions or left blank. The advantage of this kind of foundation is that it saves materials, costs relatively low, and construction is relatively simple.The load is evenly transmitted through the silo wall to the annular foundation beam, and then diffuses into the foundation. It is more suitable for sites with better geological conditions, such as sand and gravel soil layers, and projects with a small single silo capacity. Generally, small and medium-sized grain steel silos with less than 3,000 tons are more commonly used in this form.The cross-section size and reinforcement of the foundation should be calculated and determined based on the diameter of the silo, the total load and the soil bearing capacity.
Reinforced Concrete Raft Foundation
The foundation of the raft is a whole piece of reinforced concrete slab covering the entire bottom area of the silo, which is equivalent to pouring a solid cushion on the entire bottom of the silo. Compared with the annular foundation, its load distribution is more uniform and its anti-settling ability is stronger. It is suitable for some small steel silos, or silos with special bottom structure and overall support. This kind of foundation has certain requirements for the bearing capacity of the foundation. If the soil is too soft, the settlement of the raft foundation will be relatively large, and it needs to be used in conjunction with the foundation treatment.When designing, we should focus on verifying the bending resistance, shear resistance and overall sedimentation of the board.
Pile Foundation
If the site is soft soil or silt layer, the bearing capacity of the foundation is insufficient, or the project has particularly high requirements for settlement control, pile foundations will be used. The pile foundation transmits the load to the hard soil or rock formation with deeper underground and better bearing capacity through piles, which is equivalent to laying a deep root for the steel silo. Large and ultra-large steel silos, or silos built on weak foundations, basically use pile foundations.For example, some large steel silos of 80,000 tons will use PHC pipe piles, the pile length can reach 30 meters, and the upper bearing platform and ring beam can jointly bear the load through the pile. The cost of pile foundations is usually higher than the first two, but in sites with poor geological conditions, it is a necessary choice to ensure safety.
What Factors Determine The Basic Design Of The Steel Silo?
Basic design is a typical targeted design work, and there are several core factors that will directly affect the final plan.
Steel Silo Capacity And Diameter
The larger the capacity and the larger the diameter of the steel silo, the greater the total load to be borne by the foundation, and the more concentrated the pressure on the foundation. For example, for a small silo of 100 tons and a large silo of 10,000 tons, the size, reinforcement, and form of the foundation may be very different.silos with large diameters are more sensitive to uneven settlement, and the stiffness requirements of the foundation are also higher.
Types Of Materials Stored
The bulk density of different materials is much different. For steel silos of the same capacity with different materials, the foundation force may be more than twice the difference. According to industry standard parameters, the bulk weight of wheat is generally 0.75t/m3, corn is about 0.73t/m3, soybeans are about 0.71t/m3, and rice is about 0.55t/m3; if it is cement, the density can reach about 1.6t/m3, and fly ash is about 0.8~1t/m3. Therefore, before designing the foundation, it is necessary to clarify what materials are stored, and it cannot be estimated based on food in general.If you want to exchange heavier materials in the later stage, you also need to calculate whether the foundation is sufficient a priori.
Site Soil Conditions
The geological conditions of the site are the key variables that determine the basic form and cost. It mainly depends on the soil carrying capacity, the level of groundwater, the distribution of soil layers, and the risk of sedimentation.For example, if the bearing capacity of hard plastic clay and sand and gravel layers is good, it is enough to make an ordinary circular foundation; if it is silt or miscellaneous filling soil, and the bearing capacity is poor, it may be necessary to make a pile foundation or first do foundation reinforcement. For sites with high groundwater levels, the erosion and buoyancy effects of groundwater on the foundation, as well as precipitation during construction, must also be considered.If there is a weak mezzanine underground, there may also be a risk of uneven settlement. It can be said that geological survey data is the core basis of basic design, and it is very irresponsible to do basic design without a geological survey report.
Local Wind Load And Seismic Conditions
The natural conditions in different regions are different, and the basic requirements are different. Coastal areas should consider a once-in-a-century strong typhoon. The overturning torque generated by the wind load is very large, and the foundation needs to have sufficient counterweight and anchoring to resist overturning. In high-earthquake areas, seismic effects must be verified, and the foundation and anchors must meet the seismic requirements to prevent horizontal shaking from causing the silo to become unstable. These must comply with local building codes and engineering standards, and cannot be a set of parameters that are common throughout the country.
Can Steel Silos Not Be Made Of Concrete Foundation?
This question cannot simply give an answer to whether it can or cannot. It depends on the situation. For large-scale commercial steel silos and fixed silos for industrial production, a formal reinforced concrete foundation is basically required, and professional structural calculations are required to comply with local engineering specifications. However, some small, temporary, or special steel silos may use other support methods.For example, a small mobile silo of tens of tons may use steel structure legs and pads and be placed on the hardened ground; some silos for temporary turnover may also use assembled basic modules. However, it should be noted that the absence of a traditional concrete foundation does not mean that there is no need for a support structure at all.Even for small silos, the force of the support point needs to be calculated to ensure that the ground’s bearing capacity is sufficient and no sedimentation or instability will occur. Whether an alternative solution can be used or not, it must be judged based on the structure, capacity, site conditions and local regulations of the silo, and cannot be simplified at will in order to save money.
How Deep Should The Foundation Of The Steel Silo Be?
People often ask how deep a silo foundation with a diameter of 10 meters should be. In fact, there is no unified depth suitable for all projects. There are many factors to be considered for the burial depth of the foundation: the distribution of soil carrying capacity, the depth of the permafrost, the height of the groundwater table, the total load of the silo, and the requirements of local building codes. For example, in cold areas in the north, the foundation should be buried below the permafrost layer to prevent frostbite from topping up the silo; where the water table is high, the foundation should be buried deep to consider anti-floating; if the topsoil is not good, it must be buried on the good soil layer below, or the pile foundation should be used to extend to the depths. Not only the depth, but also the width, thickness, and steel bar configuration of the foundation must be determined by engineering calculations.It is not recommended to simply set a basic size based on the diameter or capacity of the silo. In a word, the basic design must be designed independently for each project, and it is easy to go wrong by copying experience.
If the Foundation Is Not Done Well, What Will Be The Consequences?
The foundation is the foundation of the steel silo. If the foundation goes wrong, the consequences are often serious and difficult to remedy. The most common is uneven settlement.If one side sinks more and the other sinks less, the silo will slowly tilt.According to the requirements of the specification, the inclination rate of the steel silo foundation should not exceed 0.002, and the average settlement amount should not exceed 200mm.Once the standard is exceeded, the first thing that affects the unloading system is the poor discharge, partial load, and serious damage to the equipment. Then there is the cracking of the concrete.If the foundation strength is not enough, the reinforcement is insufficient, or the settlement difference is too large, cracks will appear in the foundation beam or raft, the steel bars will rust, and the bearing capacity will be slowly lost. Anchors are also prone to problems.Uneven foundation settlement or too large horizontal load will cause the anchor to be pulled, shearing, loosening or breaking, and the connection between the silo body and the foundation will fail. No matter how serious it is, the structure of the silo body will be deformed, the steel plate wall will bulge, fold, and even the welds will crack.If you encounter extreme conditions such as high winds or full silos, safety accidents such as silo tilting or collapse may also occur. There have also been many such cases in the industry. Some fly ash silos eventually collapsed due to the failure of basic anchoring and excessive sedimentation, resulting in loss of personnel and property. Therefore, the quality of steel silos does not only depend on how thick the steel plate is and whether the galvanized layer is good or bad. The overall engineering design and basic construction quality also determine the service life and operating safety of the silo.
Who Is Responsible For The Basic Design Of The Steel Silo?
In a steel silo project, the basic design involves several participants, and the division of labor is different. Steel silo manufacturers usually provide basic parameters related to the equipment, such as the load data of the top surface of the foundation, the layout of the anchor bolts, the size of the base, and the installation requirements, to provide the basis for civil engineering design. The final civil foundation design is generally completed by qualified civil or structural engineers, who will combine the geological conditions of the site and local regulatory requirements to complete the basic calculations and construction drawing design. If the geology of the site is complex, geotechnical engineers are also required to intervene to do special tasks such as foundation treatment and pile foundation design. The on-site construction is completed by a local civil contractor, who is responsible for pouring concrete and embedded components according to the drawings. The project owner needs to coordinate all parties, provide accurate site information, and supervise the quality of construction. Simply put, the manufacturer is responsible for the equipment interface requirements, and the professional engineer is responsible for the basic structural design. Only by cooperating with the two can a qualified foundation be made.
Before The Basic Design, What Information Does The Steel Silo Manufacturer Need?
Many buyers will wonder, why do manufacturers always ask a bunch of questions about the site and materials before quoting?In fact, these are all the information necessary for basic design, and they can probably be organized into a list.：
- Determine the capacity of a single silo, the diameter and height of the silobody
- The type and bulk density of the materials stored in the silo
- The number and overall layout of the silo
- Determine the specific location of the project location
- Geological survey report of the construction site
- According to the local wind load and snow load parameters
- Meet the requirements of seismic fortification
- Determine the form, weight and layout of the inlet and outlet equipment
- The more complete the storage configuration required by the manufacturer, such as whether there are functions such as thermal insulation and fumigation, the more accurate the plan and quotation given by the manufacturer.If the information is incomplete, either the quotation deviation is large, or the plan has security risks.
What Factors Affect The Cost Of Steel Silo Foundation?
When many people consult the price of steel silos, it is easy to ignore the basic part of the investment.In fact, the basic cost fluctuates greatly, and there is no fixed unit price. It is mainly affected by these factors: the first is the capacity and diameter of the silo.The larger the capacity, the greater the foundation force, the more concrete and steel bars are used, and the higher the cost.According to the current industry situation, for small silos of 100 to 300 tons, the foundation is about 80,000 to 150,000 yuan; for medium-sized silos of 2,000 to 3,000 tons, the foundation is about 280,000 to 380,000 yuan; for large silos of 10,000 tons, the foundation is usually more than 500,000 yuan, and it will be higher if the geology is poor. Then there is the number of silos.If multiple silos are built side by side, the foundation can share part of the area, and the unit cost will be lower. The geological conditions of the site are the key variables that affect the cost.For the same silo, built on hard soil and built on soft silt, the basic cost may be more than double.Soft soil sites require piling and foundation treatment, and the cost will rise significantly. The form of foundation also affects the price. The ring foundation is the cheapest, followed by the raft foundation, and the pile foundation is the most expensive. In addition, the material prices of concrete and steel bars, local labor costs, site leveling and earthwork excavation costs, and construction conditions will all affect the final foundation cost. Here is a reminder that the equipment quotation of the steel silo is not the same as the total investment of the complete project.Infrastructure, civil construction, and supporting equipment usually need to be evaluated separately. You can’t just look at the bare price of the silo to make a budget.Generally speaking, basic projects will account for about 15% to 25% of the total investment in the entire steel silo project, and the proportion of sites with poor geology will be higher.
Summary
The vast majority of industrial steel silos require a professionally designed infrastructure, but there is no common basic solution suitable for all projects. The basic plan needs to consider the structure of the steel silo, the characteristics of the stored materials, the size of the capacity, the geological conditions of the site, as well as the local natural environment and engineering specifications at the same time. It is a comprehensive engineering design. For the purchaser, when choosing a steel silo supplier, it should not only be based on the thickness of the steel plate, the quality of galvanized steel and the price of the equipment, but also on whether the supplier can provide complete engineering and technical information, and whether it can cooperate with civil engineering design and on-site construction. After all, a solid foundation is as important as a high-quality steel silo for a steel silo that can be used safely for 20 or 30 years.