We have been involved with the Middleborough Car Park in Colchester for over 32 years. It may qualify as our longest running project, having started as job no.5450, and now we are well into the 40,000’s!
The car park is a five-storey reinforced concrete structure built using the lift slab technique. That involves casting all of the floors at ground level, one above the other, jacking them up the full height precast concrete columns, then locking them into place with steel wedges. It was constructed during the summer of 1979.
Many car parks such as this have a history of early deterioration and structural defects due to both poor design and construction. A very significant factor is that car parks of this age were designed to normal building standards, although experience has now shown that they are subject to a much more severe exposure environment, particularly on the top deck, and also at the lower levels where cars bring in de-icing salts. This can often result in the early deterioration of the various structural elements and the associated cladding and barriers. In addition to shortcomings in the design and construction, low standards of maintenance and repair during the car park's operational life can also lead to deterioration and defects.
We first became involved in 1984, when we prepared some reports on the design and detailing of Royal London’s new head office, and we were also asked to look at the adjacent car park. We prepared check calculations which showed that the car park design was very economical, but we concluded that it was suitable for normal car park use. In 1997 a lift slab system car park at Pipers Row, Birmingham collapsed and the stability of all lift-slab system car parks was immediately questioned. We were asked to undertake a full inspection of the concrete structure, including a detailed investigation of the steel shearheads, which had been the cause of the failure in Birmingham. We concluded that the Middleborough car park had a more robust design, and was considered satisfactory, although regular inspections were recommended so that any significant deterioration could be detected before it was too late.
Over the years, we have carried out numerous rounds of inspections followed by concrete repairs, and work on other items such as the vehicle barriers, typically on about a 2 year cycle. The most recent repairs were completed in November 2016.