Title:
Punching Shear Strength of Post-Tensioned Concrete Flat Plates
Author(s):
N.J. Gardner
Publication:
Symposium Paper
Volume:
232
Issue:
Appears on pages(s):
193-208
Keywords:
continuous flat plates; prestressed; punching shear;structural design
DOI:
10.14359/14943
Date:
10/1/2005
Abstract:
Flat slabs are an economical structural system for medium height residentialand office buildings. Prestressed concrete flat slabs have the additional advantagesthat longer spans can be used and deflection problems are less significant. Punchingshear of reinforced or prestressed concrete flat slabs is an undesirable mode of failurein that it occurs without warning and can lead to progressive collapse of large areas ofslab or even complete structures. Modelling the punching shear strength ofprestressed concrete slabs is conceptually difficult as the tendons can be bonded orunbonded, the tendons can pass through the columns or not, the stress in the tendonsat punching failure is indeterminate, the tendons can be banded and the tendons canbe draped resulting in beneficial vertical components of the prestressing force.The paper describes the code provisions, ACI 318-05, BS 8110-97, CEB-FIP 1990 ModelCode (Comité Euro-International du Béton and Federation International de laPrecontrainte), CSA A23.3-04, DIN 1045-1:2001-07 and Eurocode 2-2003. In general, thecode provisions for punching shear of prestressed concrete flat slabs are extensions ofthe punching shear provisions for reinforced concrete flat slabs. Most codes requiresupplementary bonded reinforcement in negative moment regions which complicatesanalysis.The literature has been reviewed to locate experimental results of punching shear testsfor isolated prestressed concrete flat plates, continuous prestressed flat plate systemsand tests of flat plate column connections under shear and moment transfer. Recentresearch has indicated that the limitations on concrete strength in code equations andignoring the precompression close to the slab edge are too conservative.The simplifications of an effective slab depth not less than 80% of the slab depthpermitted by ACI 318 and CSA A23.3 in calculations of the punching shear capacity ofprestressed concrete flat slabs should be eliminated.