In order to confirm the location and size of the post tensioned tendons located with The Ground Penetrating Radar survey at 8501 5thAvenue, Brooklyn, the concrete slab was carefully jack-hammered in the marked locations. The exposed tendons confirmed that the GPR survey accurately located and indicated the size of the tendons.

Tendons are high-strength steel cables, coated with a protective coating, and encased in plastic duct sleeves. They are anchored at each end of the structure and are then embedded in a poured concrete slab. After the concrete slab is cured to a minimum of 75% of the 28-day design strength hydraulic jacks at each end of the slab tension the tendons to apply 33,000 pounds of force to the structure.

These tendons span the entire city block from 85th Street across to 86th Street. 

Views of steel tension tendons being exposed brought to you by Sasa Mikavica.