COMMERCIAL / RESIDENTIAL

This project involved providing parking and file storage for Old Mutual required the construction of a platform 54 m wide by 340 m long platform (about 3 rugby fields placed end to end) over operational railway lines without interrupting the trains.

To accommodate the trains, reinforced concrete strip footings and support columns were cast in place between the railway lines. The columns included corbels which would support precast, prestressed beams, which in turn carry the precast panels which make up the deck. The structure was tied together with an in situ structural topping.

Further prestressing was applied to achieve continuity and provide adequate strength to support 2 additional floors of file storage, or 3 additional floors of parking. The file storage building was completed during phase 1, but the parking was only added ten years later, when the 3 parking levels which the deck had been designed to carry were constructed.

A post-tensioned flat slab system was used for the additional parking. The structure was optimised by varying the slab depths. The slab depth is greatest over the column zones with shallower sections at midspan and the cantilever ends. The upper parking slab was designed to be waterproof, without applying of a waterproofing membrane. To achieve this, a higher level of post-tensioning was used.

To provide access ramps to the parking added in the second phase, precast pre-stressed beams supporting precast deck panels were added at the end of the building.