PUNCHING SHEAR-STRENGTH OF CONTINUOUS POSTTENSIONED CONCRETE FLAT PLATES

This paper describes a rest to failure of a two bay by two bay continu ous, unbonded post-tensioned flat plate designed in accordance with th e provisions of ACI 318-95, except that no supplementary bonded reinfo rcing steel was provided. The prestressing tendons,were distributed un iformly in one direction and banded irt span/3 column strips in the ot her direction. In both directions the average prestress on the concret e was 3.5 MPa. The dimensions of each bay were 2.7 nl by 2.7 m, the sl ab thickness was 89 mm, and the mean concrete cylinder strength was 44 MPa. The load was applied monotonically until punching shear occurred at an edge column on the side parallel to the banded tendons. The fai led column was shored and the slab reloaded until punching shear occur red at the interior column. Finally both the edge column and the inter ior column were shored and the slab loaded until a corner column faile d. All the punching shear failures were violent and without,warning. T he literature was reviewed to locate experimental results of punching shear rests for isolated prestressed concrete flat plates, continuous prestressed for plate systems, and tests of flat plate column connecti ons under shear and moment transfer: The measured punching strength ca pacities were compared to those calculated using the provisions of ACI 318-95 BS 8110-85 and a proposed method.