Post-Tensioned Civil Structures
Post-tensioning was originally developed for use in bridges, providing a cost-efficient method of construction. Skandinavisk Spændbeton has been post-tensioning bridges since 1947.
The main elements of a post-tensioned bridge are constructed in-situ, but post-tensioning is also used on bridges constructed using precast slabs, in order to provide the necessary cohesion and strength.
Post-tensioning is also used on silos where it acts as a band around the construction. Post-tensioned wind turbines can overcome the problems of height restrictions and logistics often associated with steel wind turbines.
The post-tensioning of beams can be used to achieve longer spans and a more stable construction.
Post-tensioned bridges are predominantly located over railways and roads. Typically they have spans greater than 25 metres and are used in applications which must accommodate heavy loads and which require enhanced crack resistance. The post-tensioning includes high strength steel with an 1860 Mpa stress.
The post-tensioning strands are fed into corrugated ducts and are then stressed. Grout is pumped into the ducts to protect the strands from corrosion.
Advantages of post-tensioning in Civil Structures
· Longer spans
· Reduction in construction height
· Reduced quantities of reinforcement
· Cost savings
· Crack resistance
In post-tensioned silos, the post-tensioning is usually rooted in the pillars to optimize the thickness of the construction. Both bonded and unbonded post-tensioning is used on silos.
Advantages of post-tensioned silos
· Less reinforcement
· Enhanced crack resistance
· Cost savings
The growth in the use of wind power has seen wind turbines continue to develop and increase in size. As a consequence concrete has become increasingly popular in the development of land-based wind turbines In-situ construction of the concrete towers helps to alleviate some of the logistical problems faced in the transportation of steel structures. The concrete also plays a significant role in minimizing noise.
The shafts are vertically post-tensioned to ensure compression and load transfer into the foundations. Using bonded post-tensioning, ducts are inserted during slip form construction Thereafter the strands are fed into the duct, stressed and grouted.