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Port authorities across Africa are spending heavily on modernisation: new berths, deeper channels, taller cranes and the covered sheds that sit between the quayside and the yard. On paper, adding a steel roof to an existing wharf sounds like the easy part. The ground is already there, the trucks already run, the operating crew already knows the job. In practice, a retrofit shed is often harder to design and erect than a brand-new one on a greenfield site. Three things make the difference.
On a greenfield site, the steel supplier gets a clean plot and the civil contractor puts in foundations where the design says. On an operating wharf, the deck already has a lifetime of services under it: cable trenches, drainage pipes, fire mains, bollard foundations, water lines. A new column position that looks fine on a drawing may land on a cable duct that nobody has drawn for thirty years. Before any hole is drilled, the existing services have to be located, surveyed and marked — and the column grid adjusted around them. That step alone can move the whole bay layout by half a metre.
A new terminal can be fenced off, cranes brought in at will and steel lifted whenever the weather is clear. A working port cannot stop. Vessels keep coming, trucks keep queueing, and the erection crew has to work around the operating schedule. Long components may have to be delivered at night. Cranes may only be allowed on the quay during a narrow window between ship calls. Welding and hot work may be permitted only after a fire watch is posted. None of this changes the design of the steel itself, but it changes the order in which pieces go up, and it adds temporary bracing and protection that a greenfield shed does not need.
When a new shed is designed, the foundations, the column base plates and the roof all come from one designer, and they agree. On a retrofit, the existing structure may be twenty or thirty years old. The anchor bolts do not line up with the new base plates. The old edge beam sits at a slightly different level than the new roof expects. The concrete in the deck may not be strong enough for the loads the new columns put on it. Each of these is fixable, but each fix is a site decision, not a shop drawing. That is why retrofit steel packages always carry a higher contingency than new builds.
Before asking for a price on a port shed upgrade, collect three things. A measured survey of the deck and the existing structure, not the original as-built drawings, because the as-builts lie. A services drawings showing the buried cables and pipes, or a commitment to locate them on site. And a statement of the operating hours during which erection is not allowed. With those three in hand, the supplier can design the columns around the constraints and price the temporary works. Without them, every quote assumes a clean greenfield site, and the bills that follow are not comparable.
Q: Can we reuse the existing columns and just put a new roof on top?
A: Rarely without a formal structural assessment. On most operating wharves older than twenty years, the existing columns were sized for a lighter roof, and their residual capacity is unknown. Anchor bolt misalignment can be solved with transition plates, but the real risk is the column’s internal integrity. Budget for new foundations at the correct positions unless a third-party survey proves the old columns can safely carry the new loads.
Q: Does a port retrofit shed need different corrosion protection than a new inland shed?
A: Yes. A wharf deck is a salt-laden, high-humidity environment. The coating system should be specified for coastal exposure, and any field welds on site need to be touched up with a matching system before the shed goes into service. This is true whether the shed is new or retrofitted; the retrofit just makes the touch-up work harder because the deck is live.
Upgrading a port shed is not a new build with less site work. It is a steel package designed around buried services, live operations and an old structure that does not match the drawings. The earlier the measured survey and the services record reach the steel supplier, the fewer surprises land on the deck during erection.
LF-BJMB designs and fabricates steel roof and framing for port, warehouse and industrial buildings, including retrofit packages on existing wharves. We work from the measured survey and the operating constraints, not just the original drawings.
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