Advantages of the Post-Tensioned System
The fundamental action that gives the Post-tensioned method of Concreate Technology the advantage over other forms of concreate construction lies in the following:
- Floor cycles
- Materials Handling
- Deflection free slabs
- Reduced floor to floor height
- Column free space
- Column and footing design
These advantages result in more efficient use of construction materials, allowing lower building cost, and providing for innovative contemporary design incorporating the flexibility of large, open column free space.
Designers have the opportunity to impart forces internally to the concrete structure to counteract and balance loads sustained by the structure thereby enabling design optimization. Designers can utilize the advantage of the compressive strength of concrete while circumventing its inherent weakness in tension. Post-tensioned concrete combines and optimizes today’s very high strength concrete and steel to result in a practical and efficient structural system. A lighter more efficient structure can be achieved as slab thickness is reduced with Post-tensioned slab systems.
The selection of the most appropriate floor system for a building project should be based upon macroeconomic considerations as an important element of which the unit cost for each floor system is expressed in terms of cost per m². Speed of construction, together with material savings is improved with posttensioned slab systems.
Early transfer of prestress increases the rate of recovery and re-assembly of formwork by permitting early stripping and back propping. There is generally a corresponding reduction in the number of formwork sets required, which services the program.
An estimated saving in reinforcement materials handling for a post-tensioned design of 60%, in comparison with reinforced concrete, allows the crane to service other trades on the critical path.
Deflection Free Slabs
Post-tensioned concrete slabs may be designed as deflection free under a specific applied loading. Long term building maintenance costs are likely to be lower as long term deflection, including distortion and cracking of glazing and partitions, is minimized and exposed concrete structures may be rendered crack free by designing an appropriate level of prestress into the concrete slab.
Reduced Floor to Floor Height
The design of a multi-storey may allow for additional floors within a defined maximum building height by reducing the structural depth of the floor system.
Column Free Space
A longer span floor system may be designed as a post-tensioned floor at the same price as a given reinforcement concrete floor system. A reduction in the number of expansion joints could be a further saving.
Column and Footing Design
The reduced floor dead loads may be utilized in more economical design for the sizes of columns which may increase the floor net lettable area. Loads on columns are lower so foundation costs can be reduced.
Post-tensioned slabs may be designed as waterproof by providing sufficient residual prestress to overcome the tensile stress generated by differential shrinkage, column restraint, thermal loading and service load space, thereby obviating the need for a waterproof membrane.
Post-tensioned structures generally have less concrete and reinforcement and require less labour. The savings are all very important in these day of escalating costs and material shortages.