Every warehouse enquiry we receive starts the same way: steel or concrete, and which one is cheaper. The honest answer is that price is the fourth question, not the first. Span, programme and supply chain decide it long before the bill of quantities does.
Start with the clear span
If the client needs an uninterrupted floor — forklift routes, racking aisles, a grain store that has to be swept end to end — the span drives everything.
Up to about 12m, a reinforced concrete frame with beams and columns is perfectly comfortable and often the cheaper answer. Between 12m and 30m, a steel portal frame wins on almost every measure: the rafters are doing the work in bending across the whole span, and you are not casting a beam deep enough to need a crane to prop it. Beyond 30m you are into lattice trusses or portal frames with haunches, and concrete stops being a serious contender.
Most of the light-industrial work we do in Kampala, Tororo and Juba sits in the 15–24m band. That is portal frame territory.
Programme
A steel frame is fabricated off site while the substructure is being built. Once the holding-down bolts are cast and cured, erection of a 20m x 60m frame takes a competent gang about a week. Cladding follows immediately.
A concrete frame is sequential and weather-dependent. Every column has to be formed, poured, cured and struck before the beams above it go in. On a Ugandan site through the March–May rains, a concrete frame that looks like ten weeks on paper is thirteen or fourteen in practice. If the client has a lease running or a harvest arriving, that difference is the whole decision.
Supply chain, which is where South Sudan differs
This is the part that gets underestimated. In Kampala, structural sections, purlins and profiled sheeting are readily available and there are several fabricators who can hold tolerance. In Juba, steel is largely imported, lead times are long, and the exchange-rate exposure on a fabrication contract is real.
Cement, sand, aggregate and reinforcement, by contrast, move through South Sudan continuously and can be bought in stages. On several Juba projects we have specified concrete not because it was structurally superior but because it was the material we could actually guarantee delivery of within the programme. A design that cannot be built on time is not a good design.
Foundations
Portal frames concentrate load and, critically, horizontal thrust at the base of each stanchion. That means either a substantial pad with a tie beam across the building, or a heavily reinforced pad resisting the moment on its own. On expansive clay this can quietly become the most expensive part of the job.
A concrete frame spreads load more evenly and pushes very little horizontally. On a poor site, that can flip the economics back towards concrete even at a 20m span.
Life cycle
Steel needs a coating regime and someone who honours it. In humid conditions, or anywhere near a fertiliser or chemical store, an untreated frame will show corrosion at the connections within five years. Budget for galvanising or a proper three-coat system and for inspection every few years.
Concrete is close to maintenance-free if it was poured with adequate cover and cured properly. If it was not — if the cover is 20mm where the drawing said 40mm — you get spalling and exposed reinforcement, and that repair is far more disruptive than repainting steel.
Where we land
For a Ugandan warehouse over 15m clear span with a tight programme and a reasonable site, we will normally recommend a steel portal frame. For a South Sudanese project where steel lead times are uncertain, or where the span is modest and the ground is difficult, reinforced concrete usually serves the client better.
What we will not do is quote one without having asked what goes inside the building, how quickly it is needed, and what the trial pits showed.
OK Estate Construction and Supply Limited designs and builds industrial and commercial structures in Uganda and South Sudan. Get in touch to discuss your requirement.