A cement terminal is a silo farm with a truck problem
A cement terminal receives cement in bulk, stores it in silos, and dispatches it into bulk tankers or bags. There is usually a small building for the bagging line, the office and the workshop, and a large amount of steelwork that is not a building at all.
That distinction matters at the start of a project, because the silos and the conveyors are usually designed by a different party to the one designing the building, and the interface between them is where the problems appear.
Silo loads are vertical and concentrated
A silo full of cement is a very large mass on a small footprint. The load reaches the ground through a ring of legs or a skirt, and it does not spread.
Two things follow. The foundation design is dominated by the silo rather than the building. And where silos are grouped, the settlement of one affects the connections to its neighbours through the conveyors and catwalks that join them.
Conveyor supports between silos are the detail that fails when settlement is not considered: the silo moves, the conveyor does not, and something has to give. Either the supports are designed to accommodate movement or the connections are detailed to allow it.
Dust escapes at every transfer point
Cement dust escapes where material falls, where it is loaded and where it is discharged. Those points are the silo top, the silo outlet, the transfer towers and the loading spout.
Cement dust is alkaline and it is abrasive. On a steel structure it settles, absorbs moisture and sets. A structure that is dusty and damp is a structure that is corroding, and the corrosion is hidden under a hard crust that looks like protection.
Access for cleaning is therefore part of the structural design, not an afterthought: walkways, ladders and platforms that let someone reach the surfaces that collect dust.
The truck queue decides the site plan
Bulk tankers arrive, queue, weigh, load and leave. The time each one spends on site and the number arriving per hour determine the length of the queue road, the number of loading bays and the position of the weighbridge.
Getting that wrong produces a terminal that works at design rate on paper and blocks the access road in practice. The calculation is not structural, but its output constrains the structural layout, and it is much easier to do before the silos are positioned.
The bagging building is the part that is a building
Bagging, palletising and bag storage need a real envelope: a floor that takes pallet loads, a roof that keeps the product dry, and enough height for the bagging machine and its silo.
Bag storage is also a fire load and a dust source, and the two are related: paper bags and cement dust in the same room is a combination worth separating from the loading area.
What I want before drawings
- The silo schedule with capacities, dimensions and support arrangements.
- Which party designs the silos, the conveyors and the building, and where the interfaces are.
- The throughput, the vehicle sizes and the expected arrival pattern.
- The dust extraction concept and who is responsible for it.
- Whether bagging is in scope, and the bag storage volume.
- The wind speed for the site in km/h from the applicable local code, not a round number.
Most cement terminal problems are interface problems rather than structural ones. Naming the interfaces at the start is the cheapest engineering in the project.
Written by Johnny Joe, who advises owners and project managers in Africa and South America on steel buildings. If this decision is live on a project, send the layout and the constraint that worries you and I will tell you what it changes.
Related: silo loads and differential settlement · the vehicle queue as a design input · traffic layout before the frame · how material crosses the site
