Structural comparison

Steel hangar or concrete?

Section: Design & Engineering  •  Reading time: 9 min  •  By Samir Alsaade

Steel hangar with one clear span beside a concrete building whose columns split the span in three

The question is usually asked as "which is cheaper?", and that phrasing leads to a misleading answer. The two systems do not compete across the whole range; each has a band where it is the right choice both structurally and economically, and outside that band the other has no competitor. So let us fix the bands first, then talk about cost.

Note: The spans given here are common economical ranges, not absolute limits; special cases exceed them with special systems and a different cost. The final choice needs a study that accounts for loads, soil and building function.

1. Which one spans further without columns?

Steel, by a wide margin.

Cast-in-place reinforced concrete stops being economical for clear-span roofs beyond roughly 15 to 18 metres; the beam needs great depth and its own weight becomes a significant share of the load it carries. Prestressed concrete extends the range further, but it requires a plant and the transport of long, heavy elements — a logistical constraint before it is an engineering one.

Steel portal frames work efficiently from 12 m up to about 40 m, and steel trusses go beyond that. The reason is steel's much higher strength-to-weight ratio: a steel beam carries more and weighs less, so less of the structure is spent carrying itself.

From our projects: the widest span we have built is 40 m at the equestrian club hall — over a 132 m length with no intermediate column. There is no practical concrete solution at that span for a building of this function.

So if your project needs a span above 20 m, the question is settled before it starts.

2. How much do the two differ in build time?

The essential difference is not the speed of the work but where it happens.

Steel is fabricated in the shop while foundations are poured on site — the two tracks run in parallel. When the steel arrives, erection is assembly rather than fabrication, and nothing waits for a material to cure.

Cast-in-place concrete is sequential by nature: formwork, then reinforcement, then pour, then wait for strength, then strip, then the next element. Curing time cannot be compressed by adding labour, and weather affects pouring on top of that.

In practice, on a wide-span hall the difference is measured in months, not weeks. And if your opening date is part of the project's business case — a warehouse to be leased, a hall for a season — that difference is a financial line, not a scheduling one.

3. Which is actually cheaper?

There is no single answer, because the question is incomplete. Cost compares across four items, not one:

  • The structure itself: steel costs more per tonne, but you need far less mass.
  • Foundations: a steel frame is lighter by a wide margin, so foundations shrink — an item always forgotten in the comparison, and its effect grows as soil quality falls.
  • Time: months of delay are a cost, whether as financing interest or deferred revenue.
  • Later modification: adding an opening or an extension to a steel frame is a bounded operation; in concrete it is a heavy structural decision.

At short spans (under 12 m) concrete may genuinely be lower in total cost, particularly where labour is cheaper than material. As the span widens the balance tilts to steel, until there is no comparison left.

Any quotation that compares the two systems on price per square metre alone is hiding three items out of four.

4. Where does concrete genuinely win?

In four places, and stating them is fairness, not courtesy:

  • Thermal mass: concrete stores heat and softens temperature swings inside the building. A steel frame relies entirely on insulation to achieve that.
  • Fire resistance: concrete resists inherently, while steel loses much of its strength at high temperature and needs treatment or protection.
  • Long-term maintenance: no corrosion. A steel frame needs a sound protection system and periodic inspection — which we cover in protecting steel structures from corrosion.
  • Heavy static loads and vibration: concrete mass damps vibration, useful under heavy machinery.

Note that three of these four can be addressed in a steel frame through insulation, protection and maintenance — at a cost. A 40 m span in concrete cannot be addressed at all.

5. When is a hybrid the right answer?

When the requirements below differ from the requirements above.

The hybrid puts perimeter concrete columns under steel roof trusses: the columns get concrete's durability and its resistance to impact and moisture at ground level, while the roof gets steel's span and light weight.

From our projects: the equestrian club hall was built on exactly this system — perimeter concrete columns with steel lattice trusses at a 40 m span. The choice was not a compromise between two systems, but using each where it is stronger.

A hybrid also suits a building rising on existing concrete bases, or where the function demands a durable lower wall (bulk material stores, for instance).

6. How do you settle the choice for your project?

By ordering the questions like this — and the order is deliberate:

  1. What clear span do you need? Above 20 m: steel, discussion over. Under 12: compare seriously.
  2. Is the opening date constrained? If so, the schedule difference is a financial item.
  3. What is the building's thermal and fire duty? This sets the cost of treatments in the steel option.
  4. Will you extend or modify later? If yes, flexibility has real value.
  5. What is the soil like? Weak soil strongly favours the lighter structure.

You will find the first question settles most cases on its own. The rest settle the grey band between 12 and 20 m — and you can review our guide to spans and heights to fix the span you actually need before comparing anything.

  • Steel frame
  • Reinforced concrete
  • Clear span
  • Hybrid structure

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