Multi-Storey Commercial Buildings


    (Reference is made to Cordell's Building Cost Guide under the chapter "Building Cost Indicators" which lists such group separately also)

Value engineering management processes maintain, that they have consistently proven that posttensioned concrete floor systems were the most cost-effective construction for these kind of buildings in Australia. Factors taken into account were not only the basic material costs but also the effects on the speed of construction, floor to floor heights, formwork, foundation loadings and room for services. There is always a cost premium for increased spans but this premium can be kept to a minimum by selecting post tensioned concrete. An additional benefit of post-tensioned concrete floors is the opportunity to cater for special heavy loads such as compactus units and/or industrial floor loads.

Two basic systems are commonly adopted:

A. Post-tensioned flat slab, with or without drop panels

As an example, Kneebone & Beretta Group can show you a flat slab adopted for a manufacturing floor for Autocal where a column lay-out of 7324 by 7750mm was adopted but a floor load of 10kPa had to be accommodated. For normal loadings, slab thicknesses of 1/44 of the larger column spacing can generally be accomodated with post-tensioned flat plate slabs with drop panels.

Example 3:  Manufacturing Premises, Mt Kuring-Gai

B. Post-tensioned wide band beams with post tensioned slab

For slabs over carparking areas the designer can now space the columns over 4 carparks or about I 1. 0 metres and across a driveway and generous set back giving about IL 6 metre spacing. Slab thickness of 210mm for normal loading and 250mm for compactus loads with 2400mm wide by 500mm thick beams can accommodate the above column layout.

The above column spacing also gives the designer great freedom in laying-out office areas and the columns are generally taken right through the whole building.

Example 4:  Office building, Lakemba

As a note of caution, designers should be careful when ending slab band beams right at the edge of outside columns. Congestion of column steel, prestressing anchors and anti-bursting reinforcement can often cause the engineer and builder great headaches. Even a small slab extension past the outside columns can greatly facilitate construction and thereby achieve better economies.

For general information about slab and wide beam thicknesses, see graphics attachment B:

Attachment B: Wide Beam Post-Tensional Slab

In any case, whenever a designer of a commercial building needs advice on the structural system for his building please contact Kneebone & Beretta Group on  This email address is being protected from spambots. You need JavaScript enabled to view it. and an engineer will get back for your assistance.