Pretensioning is a specific prestressing method used primarily in precast concrete plants. High-strength steel strands are stretched tightly between heavy anchor abutments, and then concrete is poured into forms around the tensioned cables. Once the concrete cures and bonds directly to the steel, the cables are cut from the abutments. The cables try to shrink back to their original length, transferring massive compressive force into the concrete.
They pretension the double-T beams at the factory, so they arrive on site with a slight upward camber.
Do not mix it up with
- Post-tension: Pretensioning happens before the pour and relies on the concrete bonding to the cables. Post-tensioning happens after the pour using cables inside unbonded ducts.
Related terms
Prestress
To introduce internal compression into concrete before it is subjected to structural loads.
Post-tension
To apply tension to steel cables inside concrete after the concrete has hardened.
Tendon
The steel strand assembly in post-tensioned concrete that is pulled tight to precompress the member.
PT
Post-tensioning: reinforcing concrete with steel tendons that are stretched tight after the concrete hardens.