Reinforced-Concrete Strengthening

Reinforced-concrete strengthening is an intervention that changes a building’s identity. You enlarge column sections, add new shear walls and sometimes widen the foundation. Done properly it transforms the building’s seismic behaviour; done badly it can create a new irregularity and make matters worse.

That is why we always begin with a performance assessment and a strengthening design. The most common mistake we meet on site is shear walls added without a design, shifting the building’s centre of rigidity and creating a torsional irregularity.

The strengthening methods we use

The choice of method follows the shortfall the performance assessment reveals:

• Column jacketing — a reinforcement cage is built around the existing column and new concrete is cast. It is the method that adds most to axial and shear capacity.
• Added reinforced-concrete shear walls — give the building lateral stiffness and reduce storey drift. They must be carried down to the foundation.
• Foundation strengthening — foundation enlargement, conversion to a raft or mini piles, to carry the load of new shear walls and jacketed columns.
• Epoxy anchoring — new reinforcement doweled into existing concrete. Hole cleaning and embedment depth determine the performance directly.
• Steel collars and bracing — preferred in industrial buildings where a fast, reversible solution is needed.

Three details that decide whether jacketing works

Whether a jacket does its job depends less on its thickness than on three details:

• Bond — the existing column face must be roughened and the laitance removed. A jacket cast onto a smooth face does not act together with the column.
• Stirrup continuity — the jacket stirrups must pass through the floor slab and continue into the storey above; a jacket cut off between floors adds no ductility.
• Concrete quality and placement — if the concrete cannot flow into the narrow form, voids remain. A flowing, well-graded mix and correct vibration are essential.

How the process runs

On strengthening jobs the programme is set less by the construction than by the decision stage. We follow this order: building investigation and core sampling, performance assessment, strengthening design, approval, construction and final inspection. For apartment-block work that has to be presented to the owners, we also prepare the visuals and the cost breakdown that make the decision easier to take.

What the scope covers

• Column and beam jacketing
• Added reinforced-concrete shear walls
• Foundation enlargement and epoxy anchoring
• Hybrid steel and reinforced-concrete solutions