How Are High-Capacity Reinforced Concrete Silos Built?

A silo is not simply a large reinforced concrete tank for storing bulk materials. The weight and flow behavior of the stored product can generate very high lateral forces on the silo walls. The direction and distribution of these forces also change during filling and discharge.

For this reason, a silo project demands as much attention to product characteristics, discharge systems, wall design, reinforcement layout, and construction method as it does to storage capacity. For tall, large-diameter silos in particular, the reinforced concrete design and slipform application must be considered together.

A well-designed and properly built reinforced concrete silo delivers a long service life, low maintenance requirements, and high storage capacity. The consequences of a flawed application may extend well beyond the structure itself, directly affecting the production line and plant operations.

Loads on Silo Walls

The material inside a silo is not a liquid. Wall pressure therefore cannot be determined by a simple hydrostatic calculation based solely on fill height.

Cement, raw meal, clinker, fly ash, gypsum, grain, and coal all differ in bulk density, particle structure, moisture content, wall friction, and flow behavior. Filling pressure and discharge pressure are not necessarily equal.

In cases of eccentric discharge or irregular flow, one side of the silo may experience significantly higher forces than the other. Arching of the stored material followed by sudden movement can impose additional dynamic loads on the structure.

Silo design therefore considers not just "full" and "empty" conditions, but filling, discharge, various flow patterns, temperature, seismic, and wind effects together.

In multi-cell silos, loading scenarios where one adjacent cell is full while another is empty become particularly important. The internal partition walls separating the cells must safely carry these pressure differentials.

No Two Silos Are Alike

The first question that determines a silo's form is: what will be stored inside?

Raw meal silos are typically narrower and taller. Homogenization requirements, aeration systems, and internal bunker geometry become key drivers of the design.

Clinker silos, because they can reach very high capacities, are built with considerable diameters. When diameters reach 60–70 metres, wall forces, post-tensioning systems, large-span roofs, discharge galleries, and site logistics must all be resolved together.

In cement, fly ash, and gypsum silos, material flow, tightness, and dust control are primary concerns; in grain silos, moisture, ventilation, hygiene, and explosion safety become the dominant operating requirements.

Some facilities prefer multi-cell silos to a single large volume, allowing different products — or different batches of the same product — to be stored in separate compartments within a single structural shell.

Why Reinforced Concrete Excels at High Capacity?

There is no universal capacity threshold, but as capacity, diameter, and height increase, reinforced concrete silos become technically and economically the stronger choice. For some large-capacity facilities the required solution — in terms of structural system, fire safety, durability, and service life — is reinforced concrete.

The main advantages of reinforced concrete silos are:

• Forms a strong, rigid shell against high lateral pressures.
• Adaptable to large diameters and capacities.
• Resistant to fire and environmental exposure.
• Provides long service life with correct concrete, cover depth, and detailing.
• Low maintenance and life-cycle cost.
• Allows multi-cell or custom-geometry storage solutions.

To realise these advantages, crack control, reinforcement continuity, construction joints, and the necessary protective coatings of the reinforced concrete shell must all be correctly designed.

Reinforcement or Post-Tensioning for Lateral Pressure?

When a circular silo is filled, the lateral pressure of the stored material generates circumferential tensile forces in the silo wall. The structure, simply put, tends to expand under internal pressure.

In conventional reinforced concrete design these forces are resisted by dense horizontal reinforcement. As silo diameter and material pressure increase, so does the required reinforcement quantity. The reinforcement must not only be calculated correctly, but must also be placed in the right sequence and with correct lap details on the moving slipform platform.

For large-diameter, high-capacity silos, post-tensioning can be an effective solution. Post-tensioning tendons introduce circumferential pre-compression into the silo wall, counteracting the tensile effect of the stored material, improving crack control, and making the conventional reinforcement requirement more efficient.

Not every silo needs to be post-tensioned. The decision must be made based on diameter, wall forces, spans, crack limits, and an economic comparison.

Combining Post-Tensioning with Slipform

Post-tensioning is not a separate activity added to the structure after slipform is complete. A significant portion of the system is prepared together with the reinforced concrete shell as the slipform rises.

Tendon ducts, anchorage zones, anchor plates, cast-in items, and post-tensioning corbels can all be formed during the slipform operation. Tendon installation may be carried out while slipform continues, or after the shell is complete, depending on the system used.

Stressing is performed once the concrete has reached the required strength. Stressing forces and tendon elongations are measured and compared with project values, after which the necessary grouting and protection works are completed.

SİBA has extensive experience in the combined planning and execution of slipform and post-tensioning works. Success here depends less on knowing the two systems separately and more on being able to execute them together in the correct sequence and with the required precision.

Gaining Speed on Repetitive Silos

Silos built side by side or repeated within the same facility represent one of the strongest applications for slipform.

When sufficient slipform equipment, hydraulic gear, and experienced crews are allocated to the project, different silo groups can be raised concurrently or in close succession — without waiting for the same small system to be dismantled and relocated after each silo is finished.

Speed here should not be measured solely by the daily lift rate of the form. The total volume of forms that can work simultaneously, reinforcement preparation, concrete production capacity, crane plan, number of shifts, and standby equipment all determine overall project duration.

Baştaş Clinker Silo: A 67.8-Metre Diameter Reinforced Concrete Shell

SİBA's Baştaş clinker silo, constructed at the Vicat Baştaş Çimento plant in Ankara, has a storage capacity of 150,000 tonnes and a diameter of 67.8 metres.

The defining feature of the project is the silo's very large diameter. Raising a reinforced concrete shell approximately 68 metres in diameter by slipform demands high formwork capacity, uninterrupted concrete and reinforcement organisation, and precise level control.

This project stands as one of SİBA's key references demonstrating that slipform is an effective solution not only for tall structures, but also for large-diameter, high-capacity silos.

Norm Cement Baku: 14,500 m³ Six-Cell Multi-Compartment Silo

SİBA's Norm Cement Baku multi-cell silo project in Azerbaijan has a capacity of 14,500 m³ and six independent cells.

After the bunker level was completed, the internal cell partition walls and the outer silo walls were raised together in the same slipform operation, completing the broad reinforced concrete shell with six separate storage compartments in a single production cycle.

In such multi-cell structures, advancing interior and exterior walls simultaneously requires a high-volume slipform system, correct hydraulic load distribution, and continuous reinforcement organisation.

Execution Quality Directly Affects Plant Operations

Missing or incorrectly placed reinforcement, wrong lap lengths, insufficient cover, a defective concrete surface, or a mispositioned cast-in item in the silo shell can cause serious problems once the structure is in service.

Under high lateral pressure, cracks can widen, tightness can be compromised, and corrosion protection of the reinforcement can be weakened. Deformations affecting the discharge system or problems with bunker connections can also disrupt plant operations.

Carrying out major repairs on a large silo typically requires emptying the stored product and shutting down the associated production line. In such cases, the cost goes far beyond the structural repair bill and becomes a production loss for the plant.

The real value lies not in finding solutions after a problem has emerged, but in preventing it through correct design and execution from the outset.

For this reason, silo projects must be carried out by experienced teams who understand reinforced concrete design, material flow, slipform, reinforcement, and post-tensioning systems together.

Frequently Asked Questions

Why is a large quantity of reinforcement used in silo walls?

The lateral pressure of the stored material generates large circumferential tensile forces in circular silo walls. These forces are resisted by horizontal reinforcement, post-tensioning, or a combination of both.

Must every large silo be post-tensioned?

No. The post-tensioning decision is based on silo diameter, storage load, spans, crack control requirements, and economic comparison. It can offer significant advantages for large-diameter, high-capacity silos.

In what sizes can reinforced concrete silos be built?

Reinforced concrete silos can be built with diameters ranging from approximately 6–8 metres up to 80–100 metres, depending on the project. Heights can range from 15–20 metres up to 100 metres or even higher.

What products can be stored in reinforced concrete silos?

Reinforced concrete silos can be used to store cement, raw meal, clinker, fly ash, gypsum, grain, coal, fertiliser, and similar bulk materials. The silo geometry and internal systems are determined by the characteristics of the product to be stored.

Can the silo wall thickness be changed during slipform?

Yes. The form system can be reduced at a specified level, allowing a transition from a thicker lower section to the thinner main silo body within a few days.