The seven storey residential tower is located in an aggressive coastal area and was experiencing corrosion of reinforcement within the concrete structure at various locations including, but not limited to:
- Two (2) basement structural load bearing columns at the rear of the structure nearest the driveway – serious corrosion with the possibility of crushing failure
- Other basement perimeter columns that were suffering significant spalling
- Spalling to side wall balcony parapets
- Slab edge spalling to the podium slab edge
The two (2) columns were at risk of ‘crashing failure’ and required structural propping as they appeared to be no longer adequate to support the high rise structure. The client reported that the owners of the unit above these columns had removed structural walls within the unit without structural approval. This could not be inspected at the time, however, we believed it was unlikely that structural alterations within this unit has adversely effected load paths to the ‘at risk basement column’. The wall removal might adversely affect structural capacities elsewhere so we investigated this scenario as well.
The Body Corporate intended to carry out a repaint in the near future. We advised that the spalling should be arrested prior to this and this work should be carried out by a specialized repair contractor under the direction of an engineer prior to painting.
The scope of our initial consultancy was restricted to the engineering services as detailed below:
- We calculate the anticipated loads to the two (2) at risk columns and provided preliminary advice on the required propping and locations. This required closure of the two (2) affected garages. We also advised on ‘back propping’ locations within effected units.
- We directed a suitably qualified specialist remedial contractor to cut the driveway slab around the defective columns to find a suitable location to provide a base for the props, for example, headstock or footing, on completion we inspected the temporary propping arrangement for adequacy.
- We directed the Contractor to carry out trial ‘break out’ to assess the likely scope of the works, for example, concrete repairs, structural strengthening or column replacement.
We wrote a repair specification for the Contractor to follow. The repairs were staged, one half of the column(s) repaired and cured prior to repairing the other side(s). We carried out a number of inspections so the project could be progressively assessed.